DUPL'CATE "'HX0b020290 RKGSl Es? CoIumMa ®nttier^itp mtl)e€itpof3lmlork ^cfjool of l^ental anb 0xal burger? LIBRARY OF Dr. carl F. W. BODECKER 1846-1912 The gift of Dr. Henry and Dr. Charles Bodecker 1929 Digitized by tine Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/americantextbookOOessi LIST OF CONTillBUTOilS. BURCHARD, HENRY H., M.D., D. D.S. ; ESSIG, CHARLES J., M. D., D.D.S.; EVANS, W. W., D. D.S.; GODDARD, C. L., A.M., D. D. S."; MOLYNEAUX, GRANT, D. D.S.; OTTOLENGUI, RODRIGUES, M.D.S.; TEES, AMBLER, Jr., D.D.S. ; THOMPSON, ALTON HOWARD, D.D.S. /^ / ^ /^ t>^^i^ ^— (_^^^ — y >-— CX with about four times its weight of pure lead, L ^^W^ ^J^yf ^^^ *^®^ placed on the cupel and the oxi- l|||fe---._f_ --TiijiBf dizing flame of the blowpipe directed on it. ||1||| . --^c-i; ^ iilfijiJB The oxidizing process soon begins, and in lllffe: ■ '-^UirnKK ^^o^* thirty minutes all the lead will be llllllir ■''iSSl,\i\i^^^B _ converted into litharge, which is fusible and l|#'i • ^''' I'lllii^^ is readily absorbed into the porous substance ^^~------^_.:jWii^^ of the cupel, carrying with it all the oxidiz- The cupel. able metals that may be present. At this point the button, having parted with every trace of the latter, assumes an exceedingly bright appearance, technically called the "brightening of the button," thus offering a certain means of ascertaining when the process of cupellation is complete. Cupellation under the oxidizing flame of the blowpipe for quantitative discrimina- tion requires careful management, particularly when the silver has parted with the base metals and approaches a state of purity ; for it is at this stage of the operation that the well-known property of melted silver, of absorbing oxygen from the atmosphere and then parting with it as it approaches the point of solidification, may be observed. The giving off of the absorbed oxygen is what causes " sputtering," by which minute globules of the metal are thrown off and lost, thus rendering the assay inaccurate. Besides the method of obtaining silver above described, the metal may be obtained by converting sulphide into chloride, the latter being easily reduced to metallic silver by the wet method. The sulphide is also sometimes converted into sulphate, when the silver may be reduced from the solution by precipitation. Another method of separating silver from its ores consists in roasting the latter with common salt to convert the silver into chloride, which is dissolved out of the mass by means of a strong solution of chloride of sodium ; the silver is then recovered in the metallic state by precipitating with copper. Hyposulphite of soda has also been employed to dissolve ^ Cupels may be obtained at the chemists' furnishing-shops ready for use. SILVER. 117 out the chloride of silver, the resulting solution, being precipitated by sulphide of sodium, yielding sulphide of silver, which requires roasting to drive off the sulphur and liberate the metallic silver. Compounds of Silver. — There are three compounds of silver with oxygen : the suboxide, AgO ; the oxide, AgP ; and the peroxide, which is thought to have the formula of Ag.p.^- The oxide is the only one having any practical importance. Being the base contained in the salts of silver, it is obtained by adding caustic potassa or baryta-water to a solution of nitrate of silver. Silver nitrate (AgNOg) is prepared by dissolving silver in nitric acid by the aid of gentle heat, after which it is evaporated to dryness or until it crystallizes. These crystals are colorless, transparent, and soluble in an equal weight of cold and in half the quantity of boiling water. They are also soluble in alcohol. Nitrate of silver is fusible, and when poured into cylindrical moulds forms the lunar caustic employed by surgeons. At high temperatures (red heat) it is decomposed, yielding pure metallic silver. Silver sulphate (AgaSO^) is prepared by boiling metallic silver in sulphuric acid. Silver sulphide is remarkable for being so soft and malleable that medals may be struck from it. It may be formed as a black precipitate by the action of hydrogen sulphide (H2S) upon a solution of silver nitrate, or it may be formed by heating silver with sulphur in a covered crucible. It is the affinity existing between these two elements which renders the combination of silver and vulcanizable rubbers impractica- ble. Silver sulphide is not soluble in dilute sulphuric or hydrochloric acid, but is readily dissolved by nitric acid. Metallic silver also dis- solves sulphide of silver when melted with it. Silver chloride (AgCl) is the form into which silver is commonly converted in separating it from other metals or from its ores. It is a white, curdy precipitate, and may be obtained from a solution of the nitrate by the addition of sodium chloride or hydrochloric acid. When freshly prepared it is perfectly white, but soon darkens, and eventually becomes quite black by exposure to solar light, parting with a portion of its chlorine and becoming a subchloride (AggCl). Silver chloride may also be formed by suspending a silver leaf in a glass vessel containing chlorine gas, and when thus prepared it is not blackened by exposure to light. Argentic chloride is fusible at 500° F. A much higher heat converts it into vapor, but does not decompose it. It is soluble in ammonia. Discrimination. — The chlorides and hydrochloric acid precipitate white argentic chloride, and so delicate is the test that when 1 part of silver is dissolved in 200,000 times its weight of water it may be readily detected by the opalescence which is imparted to the fluid by the pre- cipitant. This precipitate is always changed to a violet-black by expos- ure to light, but the presence of mercury ^ will prevent discoloration. It is insoluble in nitric acid, but is readily soluble in ammonia, and may be fused to a horny mass without decomposition. Sulphuretted hydrogen added to a solution containing silver throws down a black precipitate of silver sulphide, which is not soluble in dilute ^ Mercurous chloride. 118 METALS AND ALLOYS. acids, alkalies, or potassic cyanide. Sulphuric acid at a temperature of 212° F. will, however, dissolve it, with separation of the sulphur. Ammonia or potassa, when employed as a precipitant, throws down a brown oxide, insoluble in the latter, but soluble in the former, and if freely exposed to air this solution will deposit fulminating silver. The blowpipe is frequently used in the discrimination of silver com- pounds, which when heated on charcoal with sodic carbonate yield a bright bead of metallic silver, often accompanied by a red-colored deposit on the charcoal. Quantitatively, the estimation of silver may be accomplished either by the usual humid process or by assaying. The first consists in pre- cipitating the metal as chloride, which is to be separated and weighed. The precipitation is effected as follows : The silver solution is acidulated by nitric acid ; hydrochloric acid or sodic chloride, slightly in excess, is then added, but, as silver chloride is to a certain extent soluble in either of these, an undue excess must be avoided. The chloride must now be carefully and repeatedly washed and filtered in a thoroughly dry filter, previously weighed. After the solution has passed through the filter the latter with its contents is dried and weighed, and the weight, minus the weight of the filter, will be the quantity of silver chloride present. The dry method or assaying process consists in forming an alloy of the silver with lead, and is especially applicable to ores and the sweepings of the dentist's laboratory. The specimen to be treated is heated with from twelve to thirty times its weight of pure granulated lead in a bone- ash cupel, which is placed in a muffle so arranged that a current of atmospheric air may pass freely over the vessel and oxidize the lead. This oxide of lead, being quite fusible, combines with any base metal present and oxidizes it, uniting subsequently with the oxide as a fusible slag, while the gold or silver will be held by the unoxidized portion of the lead. In the treatment of specimens of alloys, such as plate or coin, a quantity of the specimen is accurately weighed and mixed with from four to five times its weight of pure granulated lead. It is then placed in the cupel and exposed to heat, as above described, until all the lead is oxidized or converted into litharge, when the remaining button assumes the brilliant appearance of surface before alluded to, which denotes that the base metals or oxidizable constituents have been oxidized and taken up by the lead oxide. This button is then to be weighed by means of a delicate assay-balance, and the loss of weight shows the proportion of alloy that wa's present. Pure Silver. — Pure silver, which is reckoned as 1000 fine, may be obtained from standard or other grades of silver by dissolving them in nitric acid slightly diluted with water, the solution being much facilitated by exposure to gentle heat. If gold be associated with the alloy, it will be found at the bottom of the vessel, in which case it will be necessary to use a siphon to remove the argentic nitrate solution. The silver is now to be precipitated in the form of chloride by the addition of an excess of common salt. When all has subsided the liquid is carefully poured off and the chloride thoroughly washed to remove all traces of acid. The chloride is then placed in water acidulated with hydrochloric acid (an ounce of chloride requiring 6 to 8 ounces of water), and pieces of clean wrought iron put in it, when a copious evolution of hydrogen follows. SILVER. 119 which, uniting with the chlorine of the argentic chloride, liberates metallic silver. The latter should not be disturbed until the last particle of it is thus reduced, when it will be found to be a spongy mass. The undis- solved iron should now be carefully removed, the ferrous and ferric chloride carefully decanted, and the silver washed in hot water contain- ing about one-tenth its bulk of hydrochloric acid. This is repeated several times, and finally the silver is again thoroughly washed with pure hot water. The silver, after drying, is then ready for melting, and if care has been observed in the process it will be found to be of a fineness of 999.7 parts in 1000, the 0.3 of impurity present being due to traces of iron. The chlorides may be acidulated with sulphuric acid, and reduced with zinc instead of iron. Another method of precipitating silver in the metallic form consists in placing a sheet of copper in a solution of argentic nitrate. The metal is thrown down in a crystalline form. Silver thus obtained is never free from traces of copper. Pure silver can only be obtained from samples of a lower grade by fusing the pure chloride with sodic carbonate. The reaction is shown in the equation : 2AgCl + Na^COg =: Ag^ + 2NaCl + O + CO.. Owing to the copious evolution of carbonic-acid gas which takes place during the decomposition, some of the silver may be thrown from the crucible, and loss may occur by the absorption by the crucible of some of the fused chloride. To avoid this the sides of the vessel should be coated with a hot saturated solution of borax. A composition of 100 parts of argentic chloride, 70.4 of calcic carbonate (chalk), and 4.2 of charcoal has been recommended as a means of obtaining pure silver. This mixture is heated to dull redness for thirty minutes, and is then raised to full redness ; carbonic acid and carbonic oxide are given ofP; the calcic chloride is converted into calcic oxychloride, underneath which, in the bottom of the crucible, will be found the button of pure silver. Alloys of Silver. — In consequence of its softness, silver in the pure state is liable to considerable loss by attrition. For all useful purposes, however, the requisite amount of hardness may be conferred upon it by the addition of a small proportion of copper. Thus, silver for coinage and manufacturing purposes usually contains in 1000 parts from 900 to 925 of silver and from 75 to 100 of copper. The term "standard silver" refers to the metal thus alloyed with copper, that of the United States coinage being — silver 900 parts, copper 100. . Previous to the introduction of vulcanized rubber as a base for arti- ficial dentures standard silver was much employed in the United States for temporary dentures when cheapness was an important consideration. In England a much more durable alloy is used, in which the alloying metal is platinum, in the proportion of from 3 to 10 grains of the latter to each pennyweight of silver. The advantages possessed by this alloy over ordinary standard silver may be summed up as follows : It resists wear better, and not even a suspicion can be reasonably entertained of any ill effects occurring, either locally or to the general system, from its presence in the mouth. It permits of the employment of a higher grade 120 METALS AND ALLOYS. of solder, and it is a much more rigid alloy than ordinary standard or coin silver. Hence it makes a stronger artificial denture, which is less likely to have its adaptation impaired by bending. But, while silver is improved in some respects when platinum is the sole alloying component, it must not be supposed that its affinity for sulphur is thus materially lessened, or that its tendency to blacken when brought into contact with that element or its compounds is obviated. Indeed, it may be stated that platinum added to silver in such small quantities does not wholly protect the latter from the action of its ordinary solvents. Such an alloy of silver, for instance, would not only be readily dissolved by nitric acid, but the platinum also, though unaffected ordinarily by that menstruum, would readily yield to it when combined with silver. This alloy of silver, which is known in England as " dental alloy," often contains from 25 to 30 per cent, of platinum. To separate the latter metal from the silver the alloy is dissolved in nitric acid, which on the addition of heat will dissolve all of the silver with about 10 per cent, of the platinum. On introducing a bar of copper into this solution the silver and platinum are quickly precipitated in a metallic state. This precipitate is again placed in nitric acid, which redissolves the silver, leaving the platinum untouched, which, however, may be dissolved, with the other 15 or 20 per cent, of the platinum left at first, in aqua regia. Precipitating by an excess of ammonium chloride, evaporating to dryness, and igniting yields pure platinum. The silver may be recovered in the usual way by precipitation in the form of a chloride, which may be easily reduced to a metallic state by treating with a plate of zinc in acidulated water. It is a somewhat common belief that the putting together of silver and platinum in the formation of an alloy of this kind, owing to the infusibility of platinum and the wide diiference in the fusing-points of the two, is a matter of great difficulty. It should be borne in mind, however, that between the metals more or less affinity exists, especially at high temperatures ; hence it is only necessary to introduce the plati- num, rolled into thin ribbons, into the crucible containing the silver in a state of complete fusion, and the platinum will be observed to quickly fuse and mix with the other metal. It is sometimes thought advisable to add larger proportions of platinum than the quantity here given. This may be done by adding the platinum until the alloy becomes infusible ; and this result will be attained as soon as sufficient platinum is added to raise the fusing-point of the alloy above the capacity of the ordinary melting apparatus. Von Echart's alloy, employed to some extent in France as a base for artificial dentures, is composed of the following proportions : silver, 3.53; platinum, 2.40; and copper, 11.71. It is very elastic (which property it does not lose by annealing) and can be highly polished. Silver Solders. — When the plate to be united consists of pure silver alloyed with platinum, the solder may be formed of the standard metal (coin), with the addition of from one-tenth to one-sixth its weight of zinc according to the proportion of platinum contained in the alloy. Silver solders are, however, generally composed of silver, copper, and zinc, or silver and brass, in variable proportions, of which the following are examples i PLATINUM. 121 No. 1} Silver 66 parts. Copper 30 " Zinc 10 " No. ^? Silver 6 dwt. Copper 2 " Brass 1 " No. 3. Silver 5^ dwt. Brass wire 40 gr. In putting together the constituents of silver solders the affinity for oxygen manifested by zinc, brass, and copper when exposed to high temperatures should be remembered, and in order to guard against loss the mode of procedure should be as follows : The silver, placed in a clean crucible, with a sufficient quantity of borax to cover it, should be thoroughly fused, and, without permitting it to cool in the least, the zinc, brass, or copper, as the case may be, should be quickly added. Before pouring it should be shaken or agitated to ensure admixture. When cool it may be removed from the ingot-mould and rolled into plate of, say, No. 27 of the standard gauge. The surface of standard silver may be whitened by being heated and immersed in dilute sulphuric acid. It is in this way that frosted silver is produced. The acid, dissolving the oxide of silver from the surface, leaves a quite pure superficial film. Silver may be deposited upon the surface of another metal by con- necting the article to be silvered with the negative (zinc) pole of the galvanic battery, and then immersing it in a solution made by dissolving cyanide of silver in a solution of cyanide of potassium. The current decomposes the argentic cyanide, and the metal is deposited upon the object connected with the negative pole. During this decomposition the cyanogen liberated at the positive (copper or platinum) pole acts upon a silver plate with which this pole is connected, the quantity of silver dis- solved at this pole being precisely equal to that deposited at the opposite pole : the silvering solution is always maintained at the same strength. Platinum. Atomic weight, 197.6. Symbol, Pt. Platinum is found in nature in flattened grains of varying sizes, more or less alloyed with palladium, rhodium, ruthenium, davyum, and iridium.^ It occurs in Brazil, Peru, Australia, and California. Russia, however, furnishes the largest supply of platinum, from the Ural Moun- tains. It was discovered in 1736 by Anton Ulloa at Choco, in South America, but in consequence of its infusibility and unworkable nature no use was made of it, and its presence in mining products was considered ^ Kichardson's Treatise on Mechanical Dentistry. '^ Ibid. ^ A group of rare metals only found in platinum ores, and known as the " platinum metals." 122 METALS AND ALLOYS. :i detriment. Dr. Wollaston devised the first practical process of work- ing it, and in 1859, Deville and Debray published improved methods of fusing large quantities of platinum. Wollaston's method, which consists of a series of chemical and mechanical processes of a rather complicated nature, may be thus de- scribed : The ore is first heated with nitric acid to dissolve any copper, lead, iron, or silver. It is then washed and heated wdth hydrochloric acid to remove any magnetic iron ore that may be present ; after which the ore is to be treated with nitro-hydrochloric acid diluted with an equal bulk of water to prevent the iridium generally present from being dissolved. The proportions of acids are 150 parts of hydrochloric to 40 parts of nitric. Three or four days' digestion, aided by gentle heat, is necessary to complete solution. The suspended matter, generally con- sisting of iridium, is allowed to subside, when the solution may be siphoned off. Ammonic chloride ^ is next added as a precipitant, and throws down the yellow crystalline ammonio-platinic chloride, which is readily de- composable by heat, yielding platinum in a finely-divided state. The liquid from which the precipitate is obtained will still be found to contain about 11 parts of platinum, together with all the associated metals. These are all thrown down by means of a plate of zinc and washed carefully, and again dissolved in nitro-hydrochloric acid. A small quantity of strong hydrochloric acid is added to avoid precipita- tion of lead or palladium, when precipitation of the remaining platinum may be again effected by ammonic chloride. This precipitate will re- quire careful washing in cold water to remove iridium, which during the process forms a double salt with the ammonic chloride. The next stage in the operation consists in separating the metal from the ammonia salt by ignition, and, as it is important to the success of the subsequent working that the precipitate shall remain in a finely- divided state, too high a degree of heat must be avoided, as otherwise cohesion of the particles will take place. Ignition is generally accom- plished by the following means : The precipitate is heated in a graphite crucible until nothing remains but the finely-divided platinum. This is powdered, should it be found somewhat lumpy, in a wooden mortar with a wooden pestle, sifted through a fine lawn sieve, and mixed with water to the consistence of a stiff paste. This is placed in a brass mould with a slightly tapering cylindrical cavity about 7 inches in length, provided with a loosely-fitting steel stopper which enters to the depth of a quarter of an inch. The mould is first oiled and set up in a vessel of water. The platinum mud is then introduced, and as it settles into the water air is displaced, and the platinum is thus made to fill every part of the mould. The water is allow^ed to drain, and its removal may be aided by pressure. Ultimately, however, the mould is placed in a press worked by a powerful lever, by which the mass sustains an enor- mous pressure, after which the plug and the column of platinum are removed by gently tapping the mould. It is then heated in a charcoal fire in order to thoroughly dry it and to burn off any adherent oil. The next step, which depends upon the quality of welding possessed by platinum, consists in heating the porous cylinder in a blast-furnace to ' About 40 parts. PLATINUM. 123 white heat, when it is removed, set upright on an anvil, and hammered on the ends in order to weld the particles ; after which it is coated with a mixture of borax and carbonate of potash, and again heated for the purpose of removing traces of iron, which is dissolved by the mixture, the latter being removed by immersion in dilute sulphuric acid. The bar of platinum is now ready for use and may be rolled or ham- mered. It may readily be surmised that so imperfect a means of obtaining a solid bar of metal as the latter part of the operation just described can- not always be relied upon for the production of a uniform and solid specimen ; and, indeed, platinum prepared in this way, though of great purity, is liable to blister upon its surface, this being probably due to minute globules of air encased in the body of the ingot during the forg- ing ; which globules during the conversion of the ingot into plate by means of rollers are elongated and spread out in the form of blisters. The dry metallurgic operations of Deville and Debray consist in heating in a reverberatory furnace about 2 hundredweight of platinum ore with an equal weight of galena (sulphide of lead). When the ore is sufficiently heated (to bright redness) portions of the galena are added and mixed with the ore by constant stirring. An equal quantity of litharge is next added in order to supply oxygen to the sulphur of the lead ore, which passes off as sulphurous anhydride, reducing all of the lead Avhich combines ^vith the platinum. After remaining in a state of fusion for a short time the upper portion is ladled off, and Avill be found to consist of an alloy of lead, platinum, and smaller portions of palla- dium and silver, the latter being introduced from the galena, which always contains more or less silver. The heavier metals of the platinum group, from their greater density, subside to the bottom. Cupellation is now resorted to in order to separate the platinum from the lead. This consists of two distinct operations. The first is performed at the ordinary furnace temperature, and is continued until by loss of lead the fusing-point of the remaining alloy rises to such an extent that a state of fusion can no longer be maintained. The second and final operation is performed in an apparatus which serves the purpose of both furnace and cupel. It is formed of blocks of thoroughly-burned lime. In form it may be described as a sort of basin or concavity with a sim- ilar piece for a cover. The low^er part is intended for the reception of the metal : through the centre of the upper portion or cover pass the tubes for the oxyhydrogen jet, while the lower portion is provided with a lip or spout for pouring the melted metal. The tubes which pass through the top for the transmission of the two gases are generally formed of copper, with platinum tips. The outer and lower tube carries hydrogen, while the inner and upper one carries a jet of oxygen into the middle of the flame. The tubes are furnished with stopcocks, so that the supply may be regulated. When the object is merely to fuse some scraps of platinum, the lime furnace is first put together, the hydrogen jet is lighted, oxygen is then turned on, and the interior of the apparatus soon becomes heated. The platinum is then introduced in pieces through a small hole at the side, and quickly fuses after entering the furnace. When used as a cupel the lime absorbs the impurities, and the plat- inum is kept in a state of fusion until all the lead is oxidized, when the 124 METALS AND ALLOYS. metal may be poured from the lime cupel into an ingot-mould formed of coke or plates of lime. Some difficulty may be experienced at the moment of pouring in consequence' of the dazzling white surface of the molten lead. From seven to eight pounds may be melted in this way in from forty to sixty minutes. Although such metals as palladium, osmium, gold, silver, and lead are volatilized at the intense heat used, it has been found that platinum obtained by the Deville-Debray method is not as pure as that obtained by Wollaston's plan. Properties, — Platinum is somewhat whiter than iron. It is exceed- ingly infusible, requiring the flame of the compound blowpipe (oxyhy- drogen) to render it fluid. In both the hot and cold states it is exceed- FiG. 105. Oxyhydrogen blowpipe ingly malleable and ductile,' It is the heaviest substance in nature, its specific gravity being 21,5, and it is exceeded in tenacity only by iron and copper. No single acid attacks it, and it is unaffected by air or moisture at any temperature. It is therefore of great value in the con- struction of chemical vessels. At bright- red heat platinum welds quite readily, and injured vessels may be repaired in this way. In the finely-divided state, as obtained by Wollaston's process, it may be made into vessels by pressing the pul- verulent metal into suitable moulds, heating and hammering to complete, the welding of the particles. ' WoUaston, in endeavoring to substitute platinum for the spider's web usually em- ployed in micrometei's, made platinum wire finer than had hitherto been obtained. This was accomplished by forming a coating of silver upon a platinum wire and then passing it through the drawplate, after which he dissolved the silver, leaving the platinum the 3 00^ of an inch in diameter, a mile of which, notwithstanding the high specific gravity of the metal, would only weigh a single grain. PLATINUM. 125 Platinum possesses the remarkable property of inducing chemical com- bination between oxygen and other gases. Even in the compact condition it possesses this quality, as demonstrated by the familiar experiment of suspending a coil of platinum wire in the flame of a spirit-lamp, and suddenly extinguishing the flame as soon as the metal becomes entirely heated, when, by inducing the combination of the vapor of the spirit with oxygen, the wire will continue to glow. An instantaneous light appa- ratus has been made in which a jet of hydrogen is thrown upon a ball of spongy platinum : the latter induces combination between the oxygen condensed between its pores and the spirit- vapor, and ignition takes place. Platinum-black, in which the metal exists in an exceedingly fine state of division, possesses this power of promoting combination of oxygen with other gases to the highest degree. In this form it is capable of absorbing eight hundred times its volume of oxygen. No combination, however, takes place between the two, the gas being merely condensed within the pores of the metal ready for combination with other bodies ; hence if a jet of hydrogen be thrown upon a small lump of this powder, ignition ensues. During the operation of melting, platinum absorbs oxygen and gives it off in cooling, " sputtering " as silver does under like conditions. The proper solvent for platinum is nitro-hydrochloric acid, the chlorine evolved being the active agent. Alloyed with silver, however, platinum will be dissolved in nitric acid, and when platinum is found in gold as an alloy it may be separated by quartation with silver. Alloys. — Equal weights of platinum and gold afford a malleable alloy : the brilliancy of appearance characteristic of gold is, however, much lessened by the admixture. The two metals, combined in the pro- portions of 1 part of platinum to 9.5 of gold, form an alloy of the same density as platinum. An excess of platinum with gold yields an alloy which is infusible at ordinary furnace-heat. The tenacity of gold is very greatly increased by admixture of plati- num, while at the same time it is rendered more elastic. Platinum and silver may be combined in all proportions, constituting alloys of greater hardness than either of their constituents, while the color is between the color of silver and that of platinum. Hot sul- phuric acid will dissolve the silver from an alloy of this kind, and when 1 part of platinum is alloyed with 10 parts of silver both metals may be dissolved by nitric acid. Platinum and mercury do not amalgamate readily, and combination can only be effected by rubbing finely-divided platinum, such as is reduced from the ammonio-chloride, in a heated mortar with mercury moistened with water acidulated with acetic acid. By this means an unctuous amalgam is obtained which has been employed in platinizing metallic objects in a manner similar to that known as fire-gilding. The use of platinum as a constituent in alloys for dental amalgams has been almost entirely abandoned. The author found, as the result of a large number of experiments, that it rendered the alloy very brittle, and, while its presence seemed to retard amalgamation, it increased the capacity of the alloy for mercury. Iridium confers upon platinum great hardness and tenacity ; indeed, 126 METALS AND ALLOYS. the alloy resulting from this combination is so rigid that it is with the greatest difficulty it can be swaged into plates. It is, nevertheless, an alloy of great value to the mechanical dentist, as it aifords a means of obtaining great strength in artificial dentures of the " continuous-gum " class, and it has been used in the author's laboratory since 1870 in con- nection with vulcanized rubber, the plate being constructed of iridio- platinum, with the teeth, single or in sections, attached by means of rubber. The swaging requires the use of the zinc counter-die, and when the ridge is very prominent it is best not to attempt to carry the plate entirely over it, rather allowing the rubber to take its place. An arti- ficial denture constructed in this way has no superior in point of strength and durability. Nothing but pure gold should be used as a solder in uniting two pieces of platinum or iridio-platinura. Indeed, so feeble is the union between the latter and an ordinary gold solder that two pieces united by its agency may be readily torn apart with the pliers. The addition of iridium is also of value in the construction of platinum vessels for experimental laboratory use, as the metal is thereby rendered more resistant to high temperatures and less susceptible to the action of chemicals. Platinum combines with tin in all proportions, and the resulting alloy is hard, brittle, and more or less fusible. Between the platinoid metals and tin, at the moment of fusing together, phenomena very suggestive of true chemical union have been observed, and if tin and platinum foils be rolled together and heated under the blowpipe, combination takes place explosively. It is in consequence of this affinity that two such metals, one of which is infusible at ordinary furnace temperature, while the other is readily fusible at a low degree of heat, may with the greatest facility be melted together to form an alloy.' Oxides. — Platinum unites with oxygen to form two compounds — the monoxide or platinous oxide (PtO) and the dioxide or platinic oxide (Pt02). The first is obtained as a black powder by digesting the dichlo- ride with caustic potash. The second (PtOj) may be prepared by adding barium nitrate to a solution of platinic sulphate. Barium sulphate and platinic nitrate are thus formed, and from the latter caustic soda pre- cipitates one-half of the platinum as platinic hydrate, a bulky brown powder which, when gently heated, becomes black and anhydrous. It is also formed when platinic chloride is boiled with an excess of caustic soda and acetic acid added. It combines with bases and dissolves in acids. Platinic oxide with ammonia forms an explosive compound which detonates violently at about 400° F. Both oxides of platinum are reduced to the metallic state by heating to redness. Platinic chloride (PtCl4) is the most useful salt of the metal, and is the one from which all the platinum compounds are obtained. It may be prepared by dissolving scraps of platinum in a mixture of 4 measures of hydrochloric acid with 1 of nitric acid, 100 grains of platinum requiring the presence of 2 ounces of hydrochloric acid. After com- plete solution the liquid is evaporated at a gentle heat to a syrupy con- sistence, redissolved in hydrochloric acid, and again evaporated to expel excess of nitric acid. The syrup-like fluid solidifies on cooling to a ^ See cliapter on " Alloys." IRON. 127 red-brown mass which is deliquescent and readily dissolves in water or alcohol. Spongy platinum is prepared by heating the yellow crystalline pre- cipitate obtained by the addition of amnionic chloride. Platinous chloride (PtCy may be formed by heating platinic chloride to a point somewhat above 450° F. A very high temperature reduces it to the metallic state. Sulphides. — The compounds PtS and PtS^ are produced by the action of hydrogen sulphide, or the hydrosulphide of an alkali metal, on the dichloride and tetrachloride of platinum respectively. They are both black, insoluble substances. Discrimination of Platinum Salts. — 1st. A blackish-brown pre- cipitate, insoluble in nitric or hydrochloric acid singly, will be thrown down by the addition of hydrogen sulphide (H2S). 2d. Ammonia or potash throws down a yellow crystalline precipitate. 3d. A brown hydrated platinic oxide is precipitated from the salts of platinum by the addition of soda, and it should be remembered that the precipitate is soluble in an excess of the soda. 4th. A deep-brown color is imj)arted to solutions of platinum salts by the addition of stannous chloride, but no precipitate is obtained. Quantitatively, platinum may be separated from other metals with which it is likely to be associated by precipitating with ammonium chlo- ride. This is added to the platinum solution, followed by a little alcohol. The precipitate is collected, washed with alcohol, and dried, when it is ready for weighing. Every 100 parts will contain 44.28 of platinum. Iron. Atomic weight, 56. Symbol, Fe (Ferrum). Iron is present in nearly all forms of rock, clay, sand, and earth. It is the most widely diifused of the natural coloring ingredients, and its presence may be readily distinguished by the color which it imparts. It is found in varying proportions in plants and the bodies of animals, the blood of the latter containing about 0.5 per cent, of iron associated with its coloring matter. Iron seems to have been known very early in the world's history, and at a remote period instruments of agriculture and war were manu- factured of it.^ Its chief ores are oxides, carbonate, and sulphides. Metallic iron^ is met with in nature in the meteorites or metallic masses of unknown origin which occasionally fall to the earth.'^ The carbonate and oxides are the ores from which iron is chiefly obtained. Their re- duction — that of the oxide especially — is exceedingly simple, and con- sists in merely heating them in contact with carbonaceous compounds, by which means the metal is liberated. Properties. — Pure iron is nearly white in color, extremely soft and ^ Arcbseologists distinguish a Bronze Age in preliistoric times intermediate between those of Stone and Iron. ^ Metallic iron, though of exceedingly rare occurrence, has been found at Canaan in Connecticut, forming a vein about 2 inches thick in mica slate. ^ Isolated masses of soft iron sometimes of large dimensions, have been found upon the surface of the earth in South America; they are supposed to have had a similar ■origin. 128 METALS AND ALLOYS. , tough, and has a specific gravity of 7.8. Iron may be regarded as possessing a greater number of vahiable qualities than any other metal ; hence it occupies the highest place in the useful arts. Although pos- sessing nearly twice as much strength as the strongest of the other metals, it is yet one of the lightest, and is therefore peculiarly fitted for use in the constru(;tion of bridges, ships, etc. It is rendered so ductile by heating that it may be rolled into very thin .sheets or drawn into the finest wire, and yet at ordinary temperatures it is the least yielding of the metals in common use, and may always be relied upon to afford a rigid support. An iron wire one-tenth of an inch in diameter is capa- ble of sustaining 705 pounds. It is very difficult of fusion, and before becoming liquid passes through a soft or pasty condition. Pieces of iron pressed or hammered while in this state cohere or weld together. The fusing-point of iron has been estimated at 2900° F. It is sol- uble in nitric, dilute sulphuric, and hydrochloric acids, but is not much affected by strong sulphuric acid. Chlorine, iodine, and bromide attack it readily. Under certain circumstances it is not acted upon by strong nitric acid. If a piece of platinum wire be kept in contact with it, it will remain in this acid for many weeks without being acted upon. Its crystalline form is supposed to be a cube. When rolled into bars or drawn into wire it possesses a fibrous texture, upon the perfection of which much of its strength and value depends. It is the most tenacious of all the metals. At red heat iron decomposes water, evolving hydro- gen, and is changed into the black oxide. It is a strongly magnetic metal, but loses this quality when heated to redness. Iron does not oxidize in dry air at ordinary temperatures, and it may be immersed in water from which the air has been carefully excluded without change. Contact with a more electro-positive metal will also, prevent oxidation. Thus, fine steel instruments are sometimes packed for exportation by wrapping in thin sheet zinc. For a description of the compounds of iron and the reagents employed in its discrimination the student is referred to Fownes's Elementary Chemistry. The value of iron does not depend alone upon its physical properties, for it enters into a large number of compounds which are of great use in the arts, and its chemical relation to carbon is such that the addition of a small quantity of that element converts it into steel, harder and more elastic than iron, while a larger quantity of carbon produces cast iron, which is so fusible that many useful articles may be made of it by casting. Steel. — Herodotus states that among the most precious gifts pre- sented by the Indian monarch Porus to Alexander the Great was a pound of steel, the value of which at that time has been estimated at about two hundred dollars. At a later period the manufacture of steel in its application to warlike implements was carried to a great state of perfection in India and in the south of Europe. Steel differs from iron in possessing the property of becoming very hard and brittle if, when heated to bright redness, it is suddenly cooled by being plunged into water. Steel is simply iron chemically combined with the precise amount of carbon which will produce the condition referred to, together with additional toughness. It does not, however, become decidedly steel-like until the carbon amounts to 0.3 per cent. IRON. 129 The hardest steel contains about 1.2 per cent, of carbon, and when that proportion is exceeded it begins to assume the properties of cast iron. There are several processes by which steel may be produced. Bars of iron imbedded in charcoal powder in a suitable crucible or chest made of some substance capable of resisting the fire are, after several hours' exposure to heat, converted into steel, the iron taking up the requisite amount of carbon. The product of this operation is called " blistered steel," and is far from uniform either in composition or texture, as por- tions of the bars thus produced will be found to contain more carbon than others, and the interior to be more or less porous. For the pur- pose of improving its quality the bars are cut into short lengths, made up into bundles, heated to the welding-point, and placed under a power- ful tilt-hammer, which consolidates each bundle into one mass. This is called " shear steel." Fusing and casting steel is another process for the treatment of the blistered form, by which is produced the best and most homogeneous variety. It consists in fusing about 30 pounds of broken fragments of blistered steel in a plumbago crucible, the surface being protected from oxidation by glass melted upon it. When perfectly fluid the steel is cast into ingots, and when it is desirable to form a very large ingot several crucibles are simultaneously emptied into the same mould. Cast steel is superior in density and hardness to shear steel, and is the form best adapted to the manufacture of fine cutting instruments. It is, however, somewhat brittle at red heat, and much care and skill is required in forging it. The addition to it while fused of 1 part of a mixture of charcoal and oxide of manganese affords a fine-grained steel, which may be cast into a bar of wrought iron in the ingot-mould, in order that the tenacity of the iron may be an offset to the brittleness of the steel when forged together, while it affords an economical compound in the manu- facture of cutting implements, the iron forming the back and the steel the edge of the instrument. Bessemer ' steel is produced by forcing atmospheric air into melted cast iron. The carbon, which is oxidized more readily than the iron, escapes in the form of carbon monoxide, combustion of which takes place on coming in contact with atmospheric air, and sufficient heat is thus generated to keep the temperature above the melting-point of steel during the operation. The current of air is stopped as soon as the decar- buration has progressed far enough, when a quantity of white pig iron containing manganese is added to the fluid metal for the purpose of assisting the separation of gas from the melted metal. It is then ready for casting. Some New Iron Alloys. — The combinations of iron with aluminum, chromium, copper, manganese, nickel, silicon, and tungsten constitute a class of alloys which are essentially new and are termed steels, and are usually designated with a prefix of the name of the particular element present, as nickel steel, chrome steel, etc. Aluminum Steel. — The addition of aluminum slightly increases the tensile strength, and proportionately the elastic limit, in rolled and cast steel when the amount added is not greater than 1 per cent. ^ For other methods of producing steel see Percey's, Phillips', or Makins' works on metallurgy 130 METALS AND ALLOYS. Chrome Steel. — Chromium increases the hardness, tensile strength, and elastic limit of iron, but lessens its weldability. Ferro-chrome is made by heating the mixed oxides of iron and chromium in brasqued crucibles, adding powdered charcoal and fluxes. Chrome steel is then produced from ferro-chrome by melting it with wrought iron or steel in graphite crucibles. It has been stated that the presence of chromium in steel renders it more susceptible to oxidation by exposure to air and moisture than ordinary steel. It w^as thought that chrome steel would admirably fill certain special requirements where great hardness and toughness is needed, as the manufacture of dental instruments, pro- jectiles, cuirasses, etc., but there are other steel alloys coming into use which are so much better that it is probably only a question of time when it will be superseded. Copper Steel. — M. Henry Schneider of Creusot, France, obtained patents for the manufacture of alloys of iron and copper and steel and copper. These alloys can be made in crucible, cupola, or open-hearth furnace. The furnace is charged with copper scraps and cast iron mixed between layers of coke, or, if a cupreous coke be employed, then the cast iron is laid in alternate layers with it, and a layer of anthracite is laid over the whole. The alloy thus formed contains generally from 5 to 20 per cent, of copper, according to the purpose for which it is to be em- ployed, and it is remarkable for its great strength, tenacity, and malle- ability — properties which may still further be developed by chilling or tempering. Nickel Steel. — United States patents 415,657 and 415,655, NovAnber 19, 1889, were granted M. Henry Schneider of Creusot, France, for the manufacture of alloys of cast iron and nickel and steel and nickel, respectively. The alloy of cast iron and nickel contains from 5 to 30 per cent, of nickel, and is remarkable for its great elasticity and strength — properties which admit of further development by the usual chilling or tempering. The alloy of steel and nickel usually contains about 5 per cent, of nickel, and is especially suitable for use in the construction of ordnance, armor-plate, gun-barrels, and projectiles. Some specimens of nickel steel recently produced by Carnegie, Phipps & Co. for the U. S. Navy Department, containing -^^ per cent, of nickel, showed, when tested, the following results : Elastic limit, 59,000 and 60,000 pounds per square inch ; ultimate tensile strength, 100,000 and 102,000 pounds per square inch. It is stated that the presence of manganese in nickel steel is most important, as it appears that without the aid of manganese in proper proportions the best results could not be obtained. Nickel steel is said to be less liable to corrode in salt water than ordinary steel, which, it may be proper to observe in this connection, is more readily acted upon by sea-water than are the more impure grades of iron. The success of the nickel-steel armor-plate at the recent test by the U. S. Navy Department, in which the nickel-steel plates alone withstood the eight-inch chrome-steel projectiles without cracking, has had a most important influence upon the manufacture of that alloy. Manganese Steel. — The maximum of strength, toughness, and hardness is probably reached in this alloy when about 15 per cent, of IRON. 131 manganese is added to steel. The chief obstacle to the commercial pro- duction of manganese steel is its extreme hardness. The working of some of the grades of this material by the ordinary methods is almost impossible. Manganese steel is usually made by adding ferro-manganese to molten Bessemer or open-hearth steel. The extreme point of brittleness in this alloy occurs in specimens containing from 4 to 5 per cent, of manganese. Extremes of atmosphere, heat or cold, do not appear to aifect the prop- erties of manganese steel. When a piece of it, heated sufficiently to be seen red hot in a dark room, is plunged into cold water, it becomes soft enough to be easily filed. Hardness is then restored by reheating to a bright red and cooling in air. Hardening and Tempering. — Hardening of ordinary carbon steel is effected by subjecting the object to extremes of temperature. The com- mon practice is to first coat the surface of the metal with some carbon- aceous substance, such as soap, to prevent scaling and oxidation of the surface. Ferrocyanide of potassium has also been used for surface- hardening. This salt contains cyanogen (CgNg), a gas consisting of 12 parts by weight of carbon and 14 of nitrogen. This is decomposed at the high temperature which is employed, and supplies carbon to the sur- face of the metal. This salt is, however, better suited to the process known as case-hardening, while in retempering dental instruments soap answers every requirement. The metal is next heated to the point of full redness, and then sud- denly plunged into cold water, oil, tallow, or mercury, or, in the case of small objects, is merely placed on a large piece of cold metal. It is thus rendered very hard, while at the same time it increases slightly in volume. If hardened steel be heated to redness and allowed to cool slowly, it is again converted into soft steel, but it may be proportionately reduced by heating to a temperature short of redness, the proper point of which may be ascertained by noting certain colors which appear on the ground or brightened surface of a steel instrument when held over a flame. This discoloration is due to the formation of a thin film of oxide, and as the temperature rises the film becomes thicker and darker and the instrument softer. It is therefore necessary to plunge the instrument into a cold menstruum the instant the color indicating the desired degree of hard- ness is reached. The following table indicates the tempering heats of various instruments : Temperature. Color. Use. 430° to 450° F. 470° F. 490° F. 510° F. 520° F. 530° to 570° F. Light yellow. Medium yellow. Brown-yellow. Brown-purple. Purple. Blue. Enamel chisels. Excavators. Pluggers. Saws, etc. Wood-cutting tools. When elasticity is desired. In "' letting down " or tempering dental instruments the flame of a spirit lamp may be employed, the instrument being placed in it : the flame should strike, however, some distance from the cutting end, and when the proper color reaches the end it should be thrust into water. Another 132 METALS AND ALLOYS very convenient means of effecting the same result consists in heating an iron bar to redness at one end, and then fixing it in a vise. The object to be tempered is placed in contact with this until the desired tint appears. Steel when fractured shows a fine silky appearance of the broken sur- face. Overheating, however, deprives it of carbon, when the fractured surface presents a coarse granular condition, showing that it is unfit for use for fine cutting instruments. Case-hardening consists in conferring the hardness of steel upon the external surface of iron objects which are to be subjected to considerable wear, such as gunlocks, etc., and is accomplished by heating them in some substance rich in carbon (such as bone-dust, cyanide of potassium, etc.), and afterward chilling in water. The body of the piece so treated retains the toughness of iron. Malleable iron is produced by a process the reverse of that employed in case-hardening. It consists in heating the object, usually made of cast iron (when great softness and tenacity are required), for some hours in contact with oxide of iron or manganese, by which its carbon and silicon are removed. A steel instrument may be readily distinguished from iron by placing a drop of nitric acid upon it, a dark stain being produced upon steel by the action of the carbon. Lead. Atomic weight, 207. Symbol, Pb (Plumbum). The reduction of lead is effected in a reverberatory furnace in which the broken lead ore (galena) is roasted at a dull-red heat, by which means the sulphide becomes oxidized and converted into sulphate. At this stage of the operation the contents of the furnace are thoroughly mixed and the temperature raised, which causes the sulphide and sul- phate to react upon each other, producing sulphurous oxide and metallic lead. Lead is the softest metal in common use, and may be said to be the least tenacious. In fusibility it also surpasses all other metals com- monly employed in the metallic state except tin, the fusing-point of lead being 617° F. = 325° C. It is quite malleable and ductile, and will admit of being rolled into thin sheets or foil, in which form it was at one time much used in filling teeth. Its chief use in the dental labora- tory consists in the formation of counter-dies. Alloys. — Lead unites with tin in all proportions, the resulting alloys being more tenacious and fusible than either constituent. By the addi- tion of bismuth the fusing-point is reduced below the boiling-point of water. Lead amalgamates readily with mercury, condensation accompanying the union. The noble metals are all rendered brittle and unworkable by the presence of lead. There are some properties peculiar to alloys of lead and silver Avhich are turned to advantage in the separation of silver from lead when it occurs as a native alloy. Lead combined with a con- siderable quantity of silver will remain fluid at a lower temperature than COPPER. 133 other specimens containing a smaller percentage, thus affording an opportunity for the poorer lead to crystallize, when it is ladled out.^ The smallest proportion of lead in gold will greatly impair the ductility of the latter. Makins states that "■ Hatchett found that yw2^ of lead destroyed the coining qualities of gold." Gold reduced to standard fineness by lead is light-yellow in color and quite brittle. The contents of the dentists' gold-drawer are always liable to contamination by small pieces of lead, the latter being much used in the form of thin sheets in the making of patterns by which the gold or silver plate is cut. As the working qualities of the precious metals are seriously impaired by its presence, means should be instituted to ensure its complete re- moval. This may be accomplished by cupellation, or by melting the gold or silver in a crucible and adding nitrate of potassium when the point of complete fusion has been reached. Lead and platinum, like tin and platinu«i, appear to possess con- siderable affinity for each other, and an alloy of the two can be formed at a comparatively low temperature. An alloy of lead and platinum is very hard and brittle. With palla- dium also lead forms a very hard and brittle alloy. The most valuable alloys of lead are those which it forms with tin, antimony, and bismuth, constituting solders, pewter, type-metal, etc. Soft solders usually consist of lead and tin in various proportions. Bismuth and sometimes cadmium are added when a more fusible solder is required. Metallic tin is used alone in some cases, as in the soldering of fine utensils of tin-plate. Lead is also soldered to lead by simply melting the edges by means of a blowpipe flame. This is called autog- enous soldering. Soft solders are termed common, medium, or best according to the amount of tin entering into their composition. Fine or best solder is largely used for uniting objects composed of britannia metal, tin-plate, brass, etc. An alloy of 1 part of tin to 2 parts of lead is the common solder used by plumbers. The composition of the different kinds of soft solder is given in the following table •? Tin. 1 . 1 . 1 . 1 . 1 . Lead. . 10 Tin. 2 3 4 5 Lead. . 1 . 1 . 1 . 1 . 1 For the discrimination of lead the student is referred to Fownes's or other standard works on chemistry. Copper. Atomic weight, 63.4. Symbol, Cu (Cuprum). Copper is a metal with which mankind has been acquainted from the most remote periods, and probably the first metallic compound employed was copper alloyed with tin (bronze), of which many relics in the form ^ See chapter on "Silver." ^ Mixed Metals, Hiorns. 134 METALS AND ALLOYS. of arms, ornaments, and domestic implements, evidently belonging to an early period in prehistoric times, are still to be found.^ It is probable, however, that the production of the pure metal is an operation of a more recent date. Copper ores are found in many parts of America and Europe. In some parts of the United States the native metal is found in immense masses many hundred pounds in weight, sometimes slightly intermixed with silver. Nothing is certainly known of the origin of these, but they are supposed to have been formed from the cupric sulphide, which by exposure to air and moisture was converted into sulphate, and then, by electro-chemical agency, reduced to the metallic state. There are several ores which yield copper. The one most commonly employed, however, is copper pyrites, a combination of sulphide of copper and iron. The blue and green carbonates, known respectively as azurite and malachite, are beautiful minerals extensively used in Russia and Bohemia in the manufacture of ornamental objects. They contain upward of 50 per cent, of copper. The process of obtaining copper from an ore, such as copper pyrites, may be thus briefly described : The ore is heated in a reverberatory furnace for the purpose of converting the iron sulphides into oxide. The copper, which remains unadulterated, is then heated with a siliceous sand, which combines with the iron oxide to form a slag and separates from the heavier (copper) compounds. By repeating this process the iron is finally gotten rid of, when the copper sulphide begins to decompose in the flame-furnace, parting with its sulphur and absorbing oxygen. The resulting oxide is, however, reduced by the aid of carbonaceous matter and a high degree of heat. Properties. — Pure copper may be obtained by decomposing a solution of pure sulphate of copper in the galvanic current. If the negative wire be attached to a copper plate immersed in the solution, the pure metal will be deposited on it, and may be readily stripped off. The chief value of copper in the useful arts is due to its great malleability, in which quality it is only exceeded by gold and silver. It fuses at about 2000° F. It expands in solidifying, and absorbs oxygen very much in the same manner as does silver under similar conditions. In tenacity copper ranks next to iron, as a copper wire of one-tenth of an inch in diameter will support about 385 pounds. Its power of con- ducting electricity is nearly equal to that of silver, while in the trans- mission of heat it is surpassed only by silver and gold. It is readily soluble in nitric acid, but in sulphuric acid only with the assistance of heat. Hydrochloric acid attacks it slowly, and in vacuo is inactive. The specific gravity of copper is 8.93. For the compounds of copper with the non-metallic elements the student is directed to Fownes's, Bloxam's, and other works on chemistry. Amalg-ams. — Copper does not readily unite with mercury without the assistance of heat. There is, however, an amalgam of pure copper and mercury extensively used in Europe under the name of Sullivan's amalgam. Its preparation is as follows : Pure copper in a finely-divided state is obtained by boiling a concentrated solution of cupric sulphate ' The epoch marked by the use of bronze is known as archaeological chronology as the Bronze Age. COPPER. 135 with distilled zinc until the blue color of the salt disappears, when the zinc should be removed. The copper, which will be found in a pul- verulent mass at the bottom of the vessel, should be washed with dilute sulphuric acid, subsequently in hot distilled water, and dried. It is then moistened with a solution of nitrate of mercury, by which means the copper becomes completely coated with mercury. The mercury is then added to it to the extent of twice the weight of copper (3 of copper to 6 of mercury). It is then rolled into small, lozenge-shaped pieces, which become quite hard, and are supplied to the profession in bottles con- taining an ounce or more. This amalgam possesses the property of softening with heat and again hardening, and when employed as a filling material one of the lozenge-shaped pieces is placed in a small iron spoon made and sold for the purpose, and heated over the flame of a spirit- lamp until small globules of mercury are driven to the surface, when it is placed in a small glass or porcelain mortar and rubbed into a smooth paste. Some recommend washing with a weak solution of sulphuric acid or soap and water, and lastly with clean water alone to remove the last traces of either acid or soap, and finally squeezing through chamois leather to exclude surplus of mercury, when it is ready to be introduced into the cavity. It requires several hours to harden. Mr. Fletcher says of this amalgam that " it is an absolutely permanent filling, as the copper salts permeate and perfectly preserve the tooth." It is said to be quite insoluble in the mouth. It, however, becomes intensely black, and imparts a most objectionable stain to the teeth. According to Watts' Chemical Dictionary, the specific gravity of pure copper amalgams is the same after hardening as before ; " hence the presence of copper in amalgam alloys lessens their contractibility." It is said ^ that the tendency of copper amalgam to discolor may be lessened by careful attention to its j)reparation. The older way of pre- paring it was by precipitating copper from a solution of cupric sulphate, with mercury at the bottom of the vessel that contained it, by stirring the fluid with a bar of zinc ; but a better way, and one now employed, is to substitute a clean iron bar for the zinc, and leave it from twelve to twenty-four hours in a jar containing the solution. The iron bar becomes covered with a dull-red flocculent precipitate of copper. When a suf- ficient quantity of the precipitate is formed it is collected into another jar, and well washed with a stream of cold water until it becomes quite clean. It is then ground in a mortar until it begins to amalgamate, the amalgamation being hastened by hot water slightly acidulated with sul- phuric acid, which will also remove traces of iron. It should next be washed in liquor ammonia to neutralize traces of acid, and must then be thoroughly triturated in a mortar until thorough amalgamation has been effected. The amalgam should be rolled into small pellets and allowed to set for twenty-four hours before using. The expectations of valuable therapeutic qualities in copper amal- gams have not been realized. Dr. C D. Cook and W. St. G. Elliott of London found by experiment that copper amalgams shrunk more than simple alloys of tin and silver, and the opinion seems to be gaining ground among those who have recently somewhat eagerly adopted it as a filling material that it is a very uncertain agent, and that, " whatever ^ Mr. E. P. Collett, British Journal of Dental Science, April 15, 1890. 136 METALS AND ALLOYS. antiseptic influence it has, it does not prevent decay from beginning and progressing directly in contact with it." ^ Alloys. — Copper unites readily with all other metals, and many of the resulting alloys are of great value in the industrial arts — of even more value than the pure metal. It is added to silver for the purpose of conferring sufficient hardness upon the latter to enable it, in the form of coin or plate, to withstand the attrition to which such articles are exposed. The formation of a perfectly uniform alloy of silver and copper is a process attended with some uncertainty, owing to a tendency on the part of the copper to separate and pass oiF toward the edges as the ingot solidifies. Thus, in silver coins one portion of the piece will frequently be found to contain more copper than another. The decimal proportions of copper and silver in standard silver (coin) of several different nationalities are as follows : Of the United States silver 900, copper 100 " France " 900, " 100 " England ■•.... " 925, " 75 " Indian rupees '■ 947, " 53 " Germany — Prussian thalers " 811, " 189 " " Prussian silver groschen " 283, " 717 The properties conferred upon gold by the addition of copper are similar to those imparted to silver. These have already been alluded to on page — . The decimal proportions in the gold coins of the United States, France, and Holland are — gold 900, copper 100 ; while English coins are composed of 916.6 of gold and 83.3 of copper. In coin-gold malleability is not greatly interfered with. Gold may, however, be rendered brittle by large proportions of copper or when the latter is impure. Copper and platinum form an alloy, when the proportions are equal, of nearly the same specific gravity and color as gold. Copper also unites with palladium to form a light, brassy alloy. By admixture with lead or bismuth copper is rendered quite brittle. The principal alloys in which it forms a leading ingredient are brass, bronze, and German silver. The alloys manufactured under the name of German silver or nickel silver consist usually of nickel, copper, and zinc. In some cases a little cobalt is present, and from 1-3 per cent, of lead is sometimes added when the alloy is to be used for cast work. The formulas for the com- position of German silver are very numerous, but probably the best quality of the alloy is made of the following proportions : Copper 46 Nickel 34 Zinc 20 " The German method of mixing the different metals in the forma- tion of nickel silver, as given by Hiorns,^ is as follows : The zinc and nickel to be used for a certain quantity of copper are divided into 1 Dr. Howe in discussions of J. Allen Osmun's paper entitled "Some Observations on the Use of Copper Amalgams," read before the New York Odontological Society, pub- lished in the International Dental Journal for July, 1892. ^ Mixed Metals, p. 224. COPPER. 137 three equal portions. On the bottom of a graphite crucible, capable of holding 22 pounds of the alloy, is placed a layer of copper, and upon this a layer of zinc and nickel ; upon this another layer of copper is placed, and so on until all the copper is in the crucible. One-third each of zinc and nickel is retained for future addition. The contents of the crucible are then covered with charcoal powder, and the metals melted in an ordinary casting furnace. When the contents are supposed to be liquefied an iron rod is inserted, and if the whole is thoroughly fused, it is then vigorously stirred. The remaining zinc and nickel are then added in portions at a time, and the whole well stirred after each addi- tion, a brisk fire being maintained to prevent chilling of the alloy by the freshly-added metals. After the introduction of the last portion an additional piece of zinc is thrown into the crucible to compensate for loss of zinc by volatilization. If the alloy is intended for rolling, it should be kept liquid for some time longer before casting, keeping the surface well covered with charcoal." Aluminum bronze is formed of pure copper alloyed with from 2.5 to 10 per cent, of aluminum. It is quite malleable, and has a fine, rich golden color. Phosphor bronze is copper combined with from 3 to 15 per cent, of tin and from \ to 2^ per cent, of phosphorus. Other metals, such as silver, nickel, cobalt, antimony, and bismuth, frequently enter into the composition of bronzes. Copper in small quantities (from 5 to 7 per cent.) is said by Mr. Fletcher to confer upon amalgams the quick-setting property obtained by the addition of platinum. It is, however, considered inferior to platinum as a constituent in dental alloys ; but in the absence of plati- num amalgams are improved by the addition of a small proportion of copper. It is stated^ that an alloy of tin 10, silver 8, gold 1, copper 1 has been extensively used (in England probably) under the names of gold amalgam and platinum amalgam. Hydrogen sulphide (HgS) and ammonium sulphide, when added to a copper solution, aiFord a brownish-black cupric sulphide. Caustic potash throws down a pale-blue precipitate of cupric hydrate, which changes to a blackish-brown anhydrous oxide on boiling. Am- monia also gives a blue precipitate, soluble in excess, affording a deep purplish-blue solution. Potassium ferrocyanide gives a red-brown precipitate of cupric ferro- cyanide. It may also be detected in very weak solutions by placing a drop on a slip of clean platinum-foil. A point of zinc is then dipped in so as to touch the foil, and instantly a spot of reduced copper appears. A green line is imparted to the oxidizing flame of the blowpipe when a copper salt is heated in it. It also communicates a green tint to borax when heated with it. There are several methods which may be advantageously employed for the estimation of copper. The operations of the dentist, however, are chiefly confined to the examination of amalgam alloys. The alloy should first be acted upon by nitric acid ; silver, if present, may then be recovered in the form of chloride ; after which the copper may be pre- cipitated from the remaining solution either as oxide, sulphide, or in the ^ Fletcher. 138 METALS AND ALLOYS. metallic state. When attempting the estimation of an alloy a qualitative examination should first be made, and if the solution to be examined is found to contain no other metal whose oxide is thrown down by caustic potassa, an excess of that agent is to be added. In the resulting precipitate, when boiled, washed, dried, and weighed, every 100 parts may be estimated as containing 79.85 per cent, of metallic copper. When hydrogen sulphide or ammonium sulphide is employed as the reagent, the resulting cupric sulphide is usually oxidized by nitric acid, and again precipitated by potassa, so as to estimate as oxide. The estimation as metallic copper is accomplished as follows : Place in the solution contained in a platinum dish a piece of zinc, adding also a little hydrochloric acid. The electrolyzing action instantly commences, and continues until the solution is colorless and the zinc completely dis- solved. The finely-divided metallic copper will be found at the bottom of the vessel. This is to be well washed, dried, and weighed. Zinc. Atomic weight, 65.2. Symbol, Zn. The ancients were undoubtedly acquainted with an ore (probably cadmia"^) which they employed with copper to form brass. Many objects of ancient manufacture, analyzed at different times, have been found to contain zinc.^ The extraction of the metal itself, however, is probably a modern discovery. Metallic zinc is never met with in nature. The principal ores are the red oxide, the sulphide of zinc (blende), and the native carbonate (calamine). The latter is the most valuable of the zinc ores, and is pre- ferred for the extraction of the metal. It is first roasted to expel water and carbonic acid, then mixed with fragments of coke or charcoal, and distilled at a full red heat in an earthen retort. Carbon monoxide escapes, while the reduced metal volatilizes and is condensed by suitable means. Properties. — Zinc is a brittle, crystalline metal, with a density vary- ing from 6.8 to 7.2. Until about the commencement of the present century the valuable property possessed by this metal, of becoming quite malleable between 248° and 302° F., was not known ; hence prior to that discovery it was but little used in the industrial arts. Between these degrees of heat it may be rolled or hammered without the least danger of fracture. Sheet zinc of commerce is manufactured by this means, and it retains its malleability when cold. Zinc fuses at 773° F. (below red heat). At a bright-red heat it boils and volatilizes^ and if heated in air combustion takes place, during which it unites with the atmospheric oxygen with brilliant incandescence. At 410° F. zinc is so brittle that it may be powdered in a mortar. Alloys. — With mercury, zinc forms an exceedingly brittle amalgam. The two combine in the cold state, but union is greatly facilitated by heating. Zinc is occasionally employed as a constituent in dental alloys. An amalgam has been suggested, the proportions of which are "ap- ^ An ore used by the ancients containing cadmium and zinc '^ Phillips made a number of analyses of such objects, all of which showed the presence of zinc. ZING. 139 proximately " given as — tin^ 50 odd ; silver, 30 ; gold, 5 to 7 ; zinc, 2 to 4 ; and recent experiments with it have proved so satisfactory that it has to a certain extent taken the place of platinum in dental amalgams. Added to silver in the proportion of 2 of zinc to 1 of silver, a nearly white malleable alloy results. The color of gold is heightened by the addition of zinc, while its malleability is greatly impaired. Makins state that gold rendered stand- ard by zinc is a greenish-yellow, brittle alloy, with a specific gravity above the mean. Combination between zinc and platinum or palladium may be effected at a comparatively low temperature, and it is accompanied by evolution of light and heat. It is stated that an alloy of 1 6 parts of copper, 7 of platinum, and 1 of zinc closely resembles 16-carat gold, is quite malle- able, does not tarnish in air, and is capable of resisting cold nitric acid. Zinc and lead mix with each other to a very limited extent. If equal parts of the two metals are melted together and allowed to cool, they will be found to have separated into two layers, the upper, and con- sequently the lighter, one, zinc, retaining 1.2 per cent, of the lead, while the lower layer consists of lead alloyed with 1.6 per cent, of zinc. The necessity of carefully keeping these two metals separate in all moulding operations in the dental laboratory will readily be appreciated, as a failure to observe precaution in this direction will be followed by vex- atious consequences. If by accident lead becomes mixed with the zinc . used for dies, the lead, by its greater specific gravity, will settle to the bottom and fill up the deeper portions of the sand matrix representing the alveolar ridge, the most prominent part of the die. This may not be discovered until an attempt to swage is made, when the die will be found to be totally unfit for the purpose. In such cases the mixed metal should be discarded and new zinc substituted. Zinc and tin unite in all proportions without diflficulty. Alloys of zinc and tin are frequently employed in casting dies for swaging plates. Richardson ^ gives a formula for an alloy consisting of zinc 4 parts, tin 1 part, which, he states, fuses at a lower temperature, contracts less in cooling, and has less surface hardness than zinc. Fletcher, however, states that all alloys of zinc and tin are superior to zinc alone for dies. The impression from the sand he believes to be much finer, and the shrinkage in cooling greatly reduced. Zinc 2, tin 1, is given as the best proportion.^ Makins states that zinc and tin, when combined in equal proportions, form a white, hard alloy, not very malleable or ductile^ which is capable of being worked as readily as brass. Zinc and copper unite in various proportions to form many different grades of brass, kno\vn respectively as pinchbeck, Manheim gold, similor, Bath metal, Prince Rupert's metal, Muntz's sterro, Gedge's and Aich's metals. German silver and Chinese alloys known as pakfong and tutenag are also alloys of zinc and copper, with the addition of nickel. Dies and Counter-dies. — Zinc is the metal most commonly employed in the formation of dies for swaging plates, and is superior to any of its alloys.^ Another important application of zinc is in the formation of ' Mechanical Dentvitry. ^ Practical Dental Metallurgy, p. 69. * The author has not found the alloys of zinc and tin to be, in any respect, superior to zinc alone for dies. 140 METALS AND ALLOYS. counter-dies. The die is placed in the iron ring when a Bailey flask is employed, or invested in the moulding sand and then surrounded by a suitable iron ring in the old-fashioned way. The zinc is then heated and poured in upon the zinc die just at the moment of complete fusion. Should the metal be accidentally allowed to remain on the fire too long, and thus reach a higher temperature than is necessary, it should not be poured until it begins to solidify at the edges. The belief seems to be pretty general that melted zinc cannot be poured upon a zinc die without causing cohesion ; ^ but if the necessary precaution regarding the proper temperature at which the metal is poured is observed, it is im- possible for union to take place, and when cool the die and counter-die will separate quite as readily as though the latter was of lead. It fre- quently occurs that the zinc die and lead counter-die are totally inad- equate to bring a plate (particularly if the latter is of platinum-gold or iridium-platinum) into perfect adaptation to all parts of a model, espe- cially where the palatal arch is very deep and the rugse are prominent. The zinc counter-die is also of especial service in partial cases where a number of teeth remain. These are cut off from the plaster model previous to moulding within one-sixteenth of an inch of the margin of the gum, so that a sufficiently distinct impress may be made in the plate to serve as a guide in filing the latter to fit around the natural teeth. Where the swaging is likely to be attended with difficulty, at least three sets of dies and counter-dies should be made. The most imperfect of these should be furnished with a lead counter-die, and used as a pre- liminary die upon which to start the plate. The next in quality may be used with the zinc counter-die, and the nearest perfect of the three, with a lead counter, reserved as a finishing die. When the plate, by means of the horn or wooden mallet and some preliminary swaging with a light hammer, has been made to assume somewhat the form of the die, and has been carefully carried past the stage when pleating or wrinkling of the plate is likely to occur, it should be trimmed to the proper dimen- sions, annealed, and placed between the die and zinc counter-die, and at first gently tapped with a hammer until the die passes well into the counter-die, when one or two sharp blows with a heavy hammer, either upon the die or its counter, will carry the plate into perfect adaptation to all parts of the former. Some slight compression, however, of the prominent points of the die is likely to occur in the use of the zinc counter, so that it will be necessary to anneal and give the plate two or three sharp blows between the finishing die and its lead counter-die ; after which it will be found to perfectly fit the mouth without any attempt to compensate for contraction of the zinc.^ It will be seen that the zinc counter-die is not intended to supersede, but is merely used as an adjunct to, the lead counter, and there is probably no better means of carrying the plate to the deep parts of the model and of obtaining a sharp, well-defined impress of the rugse and prominent parts of the model. ^ If the melted metal be poured, at a temperature of 800° F., upon a die having a temperature of 70° F., the fused zinc by contact with the iron ring and by radiation will lose heat enough to cause its temperature to fall far below the fusing-point, and it will probably not impart to the die more than 400° F. ^ The subject of shrinkage of zinc when used for dies in forming metallic plates has been fully referred to on pp. 77 and 78. ALUMINUM. 141 Compounds of Zinc. — The oxide and the chloride are the com- pounds of this metal most frequently employed by dentists. The first forms the chief ingredient in the plastic filling materials known as oxy- chlorides and oxyphosphates. Zinc oxide is a white powder, the product of the combustion of the metal. It turns yellow on heating, but resumes its pure white color on cooling. Chloride of zinc, prepared by acting upon the metal with hydro- chloric acid or by heating metallic zinc in chlorine, is a fusible deliques- cent substance quite soluble in water and alcohol. Oxychloride of zinc, the well-known filling material, consists of a powder and a fluid. The first is prepared by various formulae. One in common use is as follows : Grind together, in a mortar, borax 2 grains, fine silex 1 grain, oxide of zinc 30 grains. When thoroughly mixed these are placed together in a small crucible and heated to bright red- ness. This is called the frit, and when cool requires grinding to again reduce it to a pulverulent state. It is then thoroughly mixed with three times its weight of calcined oxide of zinc. The fluid usually employed with the powder consists of chloride of zinc diluted with water in the following proportions : Deliquesced chloride of zinc, 1 ounce ; water, 5 or 6 drachms. The oxyphosphate powders are similar mixtures.' The fluid, however, is prepared by dissolving in pure water some glacial phosphoric acid, and then evaporating until the solution attains the con- sistence of glycerin. The presence of zinc in solution is distinguished by the following reactions : a white precipitate soluble in excess of the alkali is obtained by the addition of caustic potash, soda, or ammonia, and zinc is distin- guished from all other metals by ammonium sulphide, which precipitates white sulphide of zinc, insoluble in caustic alkalies. Aluminum. Atomic weight, 27.4. Symbol, Al. Occurrence. — Aluminum is never found in the metallic state. Of all the metals, the sources of alumina are the most numerous and abun- dant. Its chief combinations are with silicon and other bases. These substances, undergoing atmospheric changes, form clays and soils, which under the influence of heat and moisture become fruitful. It would seem that its presence is not necessary to the maintenance of animal or vegetable life, since no traces of it have been found in either. Some of the compounds of aluminum are quite unattractive, but there are a number possessing great hardness and extraordinary beauty. The fol- lowing, with their formulae, are a few examples of the latter : Ruby^ AlA- Sapphire AI2O3. Garnet (CaMgFeMn)3Al2Si30,2. Cyanite AljSiOs. ^ Oxide of zinc 200 parts, silex 8, borax 4, ground glass 5, levigated under water to ensure complete admixture, then dried by evaporation, calcined at a white heat, and pul- verized, have been found to be equal in durability and working qualities to any of the numerous oxyphosphates now in the market. ■'' Corundum, the ruby, and the sapphire have the same chemical formula, Al^Oj. 142 METALS AND ALLOYS. As early as 1760, Guyton de Morveau called the substance obtained by calcining alum alumina. Lavoisier, sixteen years later, suggested the existence of metallic bases of the earths and alkalies, and alumina was thought to be an oxide of a metal which was called aluminium ; and thus it was named long before it was isolated. In 1807, Sir Humphrey Davy tried to decompose alumina by means of an electric current, and again to reduce the metal by vapor of potas- sium, in both of which experiments he failed. In 1827, Wohler isolated the metal by decomposing aluminium chloride by potassium. The metal first isolated by Wohler was a gray powder, taking under the burnisher the appearance of a highly polished metal. Later, in 1845, Wohler obtained the metal in small malleable globules by making a vapor of aluminum pass over potassium placed in platinum vessels, and from these specimens he was able to determine the properties of the metal with some degree of accuracy. The credit of the reduction of aluminum in a state of purity and the determination of its true properties belong to H. St. Clair Deville, who in 1854 brought it from the rank of a mere laboratory curiosity to that of the useful metals. In 1854 the emperor Napoleon III., in the hope that aluminum might be used in the construction of armor and helmets for the French cuirassiers, authorized experiments on a large scale to be carried on at his own expense. In 1855 the emperor put the necessary funds at the disposal of Deville, whose experiments were continued for four months, the result being that in August of the same year aluminum was placed on the market in Paris at 300 francs a kilo. The first article known to have been made of aluminum was a baby- rattle for the infant prince imperial, for which purpose it was well fitted on account of its sonorousness ; but application of the metal to the manufacture of cuirasses and helmets was decided to be impracticable, and the idea was abandoned. Reduction of Aluminum. — A mixture of the double chloride of aluminum and sodium or the double fluoride of aluminum and sodium (cryolite) is heated to redness with the metal sodium, when energetic chemical action takes place, during which chloride of sodium is formed and the metal aluminum separated. Aluminum may be separated by electrolysis. The electric current from a ten-cell-battery, provided with carbon poles, is passed through the fused salt. The metal appears at the negative pole in large glob- ules. In 1882 the cost of aluminum was materially lessened by inventions of Webster of Birmingham, England. This inventor's method of pro- ducing the rtietal consisted in reducing sodium compounds in cast-iron pots from a fused bath of caustic soda. By this means the yield of sodium is much greater than by the method of Deville, while the tem- perature required in the operation is considerably less. In 1859, Mr. Charles M. Hall of Ohio obtained letters-patent for an electrolytic method which is superior to any that preceded it. The prin- cipal feature of this process is the electric decomposition of alumina suspended or dissolved in a fused bath of the salts of aluminum, the current reducing the alumina without affecting its solvent. Mr. Hall ALUMINUM. 143 has succeeded in producing the metal aluminum as an article of com- merce at $2 per pound. Aluminum is nearly the color of new zinc. It is very malleable and ductile, and admits of rolling into thin sheets or it may be drawn into fine wire. It is highly sonorous, and has the power of conducting heat and electricity in about the same degree as silver. It is only two and a half times heavier than water (four times lighter than silver). Its specific gravity is 2.46, and it melts at a red heat. Aluminum does not oxidize in air, and is not attacked by sulphur •compounds. It is not attacked by strong nitric acid, and is insoluble in dilute sulphuric acid, but it may be readily dissolved in either dilute or strong hydrochloric acid, which is its true solvent. The metal is easily dissolved in solutions of caustic potash or soda. As the result of the invention of tlie electrical furnace of the Messrs. Cowles of Cleveland, Ohio, aluminum bronze is made directly from corundum (Al^Og). Twenty-five pounds of the crushed ore is mixed with about 50 pounds of copper and 12 pounds of a mixture of charcoal and electric-light carbon, and placed in a rectangular box of firebrick lined with limed charcoal to prevent loss of heat by radiation and to protect the firebrick from disintegration. The charge is surrounded on all sides by a layer of charcoal to prevent the alloy from being contam- inated with calcium from reduction of the lime present. The cast-iron slab forming the cover of the furnace is then securely luted on, and the current from a powerful dynamo-electric machine is passed into the fur- nace by means of two large electric-light carbons which pass through the ends of the furnace and into its contents. It requires about five hours of exposure to the intense heat afforded by the electric current to reduce the aluminum from its ore. When the furnace has cooled suf- ficiently the product of the reduction will be found to consist of about 50 pounds of a copper alloy containing from 15 to 35 per cent, of alu- minum, which may be brought to the usual 10 per cent, standard of aluminum bronze by remelting it with the proper proportion of copper. The reaction which takes place in the process, which is aided by the intense heat of the electric current, is probably as follows : The carbon unites with the oxygen from the corundum, forming carbon monoxide ; a small percentage of the aluminum remains free, mixed in small par- ticles with the charcoal, while the greater portion unites with the copper to form the alloy. Nearly all the oxide is reduced and the charcoal is changed to graphite. Some of the aluminum unites with carbon to form the carbide of aluminum. The fusing-point of 10 per cent, aluminum bronze is somewhat below that of pure gold. Aluminum may be melted in an ordinary clay crucible. No flux need be used. Borax is not only useless, but is actually hurtful, as aluminum readily attacks the glasses. Biederman ^ recommends dipping the scraps which are to be melted together in benzine before putting in the crucible. Should any of them be contaminated with solder, it may be removed by immersing in nitric acid, which does not act upon the aluminum. Annealing. — Aluminum may be softened by heating to redness and ■chilling suddenly by dropping into water. Richards recommends rub- ' Aluminum : its Properties, Metallurgy, and Alloys, Richards. 144 METALS AND ALLOYS. bing the piece to be annealed with tallow and then heating until the fat is carbonized, when at the moment the last trace of black disappears from the metal it may be dropped into water. Alloys. — Aluminum forms alloys with nearly all the metals. That with copper ^ is the most important, and presents a closer resemblance to gold than, perhaps, any other alloy. It is used for articles of jewelry, for mountings of astronomical instruments, and for making balance- beams. German dentists are now using aluminum bronze as a base for arti- ficial dentures. Professor Sauer, in a paper on the application of this alloy to dental purposes, says "that in the proportion of Cu 900 to Al 100 it oxidizes but superficially in the mouth, and is as strong and resistant to attrition as 1 8-carat gold ; it may be swaged as easily as 20- carat gold, but it must be annealed frequently, and it is necessary to carry the heating almost to whiteness, for if the bronze be merely heated until it assumes a dark-red color it remains as hard as before." He also gives the point of fusion of the alloy as above that of 1 8-carat gold, so that 14- or 1 8-carat gold solder alloyed with copper may be used upon it without difficulty. Although the alloy is highly recom- mended by many German dentists, the author does not hesitate to express the opinion that it will not find favor in this country. The following solders are well adapted to aluminum bronze : 1. Hard Solder for 10 -per cent. Aluminum Bronze. Gold 88.88 per cent. Silver 4.68 " Copper , 6.44 " 100.00 per cent. 2. Medium Hard Solder for 10 per cent. Aluminum Bronze. Gold 55.00 per cent. Silver . , 27.00 " Copper 18.00 " 100.00 per cent. S. Soft Solder for Aluminum Bronze. Copper, 70 per cent. \ -p i ^ oa ^ Tin 30 " j ^^^^^ 14.30 per cent. Gold 14.30 Silver 57.10 " Copper 14. 30 100.00 per cent. Aluminum with tin and zinc forms a brittle alloy, and with silver it yields a hard though workable compound. Aluminum amalgamates with mercury by the assistance of heat, and at the boiling-jDoint of mercury the solution is very rapid. Aluminum may be made to unite with mercury by the intervention of a solution of caustic potash or soda If the surface of the metal be well cleaned or moistened with the alkaline solution, it is immediately melted by the mercury ; but the affinity of the aluminum for oxygen is greatly increased by the state of fine division, so that the amalgam when ' Aluminum bronze — alloy of copper with 5 per cent, of aluminum. ALUMINUM. 145 exposed to the air soon becomes covered with a white excrescence, which Watts found to be pure alumina. Aluminum is employed in the manufacture of very small weights, such as the milligramme of the metric system — a use to which, in consequence of its exceedingly low specific gravity, it is particularly well adapted. Its lightness, strength, and resistance to oxygen and the sulphur com- pounds are proj)erties which would seem to point to this metal as a suit- able substance as a base for artificial teeth. The readiness, however, with which it is attacked by alkaline solutions renders it unfit for use in the construction of a permanent artificial denture. Aluminum, notwithstanding its extreme lightness, may be cast with great exactness. The late Dr. J. B. Bean, who patented a process for casting aluminum, succeeded in producing castings of exquisite fineness. Indeed, it may be stated that Bean succeeded in overcoming all the physical difficulties encountered in the effi:)rt to render aluminum avail- able in prosthetic dentistry, but its susceptibility to the action of alkaline solutions finally compelled him to abandon it. Dr. C. C. Carroll of Meadville, Pa., has devised a means of casting alu- minum which, while much simpler than the method of Dr. Bean, aifords results equally good. The metal is melted in a plumbago crucible (see p. 476) having the form of a thick- walled cylinder closed at one end, which serves as a bottom. A channel is formed within the wall of the crucible, one orifice of which terminates within at the side close to the bottom. Starting from the orifice, the channel rises in the crucible wall near the top, making a sharp return upon itself, and descends in a parallel course after the manner of a siphon, and makes its exit at the base and near the side of the crucible. Here it terminates in an iron nipple that fits into a corresponding socket in the gateway of the moulding-flask. A cylindrical plug of soapstone which fits the open mouth of the crucible is provided with a central tube of brass, to the free end of which is con- nected by a short length of rubber tubing a large rubber bulb. When the metal has been brought to a state of fusion the crucible is connected by means of the iron nipple at its base with the gateway of the flask, which has been previously heated to redness, and the soapstone plug is inserted in the mouth of the crucible. Compression of the air at this point by means of the rubber bulb forces the fluid metal out of the crucible through the syphon-like channel into the mould, filling the most minute lines and aifording an exceedingly fine casting. Carroll makes the somewhat extraordinary statement that he has found a means of controlling the contraction of the metal, together with its tendency to disintegrate from exposure to the fluids ^ of the mouth, by the admixture of other metals. Richards, in his valuable work on aluminum, states that to overcome the difficulties of contraction and corrosion by the fluids of the mouth Dr. Carroll adds " a little copper, which, he says, decreases the contraction, while the addition of some platinum and gold renders it unalterable in the mouth." Aluminum may be cast upon plain teeth with comparative safety, provided the metal is prevented from overlapping the necks of the teeth. But when gum-teeth are employed, either single or in sections, their fracture is almost certain to follow the contraction incident to the cooling ^ Demonstration before dental class University of Pennsylvania. 10 146 METALS AND ALLOYS. of the metal. Specimens of Dr. Carroll's work have fully jDroved this, and it was the one difficulty which finally defeated Dr. Bean's eiforts by compelling him to cast his plate separate from the teeth ; for, if it had been practicable to cast the metal directly upon block-teeth without danger of fracture, the denture would have lasted for at least six or eight years ; but the necessity of attaching the teeth to the plate by another metal so hastened disintegration that a few months only were necessary to render the piece useless. There are two methods which have been employed in the construc- tion of artificial dentures of this metal. The one most frequently re- sorted to consists in merely swaging a plate in the ordinary way. A number of countersunk holes are then made along the part covering the top of the alveolar ridge as a means of fastening the teeth, which are attached with rubber or celluloid. Sets of teeth made in this way have been known to do good service for eight or nine years, but they showed unmistakable evidence of the action of the oral fluid. In the second method the plate is cast, but disintegration in this case progresses with much greater rapidity. As the plate is cast separate from the teeth, and the latter are afterward attached by means of tin or an alloy of tin and aluminum, it is probable that the galvanic action incident to the pres- ence of the two metals greatly hastens dissolution of the plate. For some time the difficulty of soldering aluminum prevented the metal from being applied to useful purposes. The solder recommended for general use in the manufacture of articles of ornamentation is com- posed of copper, 4 parts ; aluminum, 6 parts ; zinc, 90 parts. The use of this requires some skill and experience. At the moment of fusion small aluminum tools are used, the friction of which is necessary to induce adhesion. Borax cannot be employed as a flux, as it is liable to attack the metal and prevent union. Another method of uniting two pieces of aluminum with ordinary solder, in conjunction with silver chloride as a flux, has recently been recommended by F. J. Page and H. A. Anderson of Waterbury, Conn. The finely powdered fused silver chloride is spread along the lines of junction, and the solder is melted with a blowpipe or other device. The union thus obtained is said to be perfectly strong and reliable.^ The following alloys are also used as solders in unalloyed aluminum articles of jewelry : I. II. III. IV. Zinc 80 85 88 92 Aluminum 20 15 12 8 In soldering with these alloys a mixture is used as a flux consisting of 3 parts copaiba balsam, 1 part Venetian turpentine, and a few drops of lemon-juice. The soldering-iron is dipped into the mixture. Mr. Wm. Frismuth of Philadelphia recommends the following solders for aluminum, with vaselin as the flux : Soft Solder. Pure Block Tin from 99 to 90 parts. Bismuth " 1 " 10 " ^ Chemical News, iv. 81. , ALUMINUM. 147 Hard Solder. Pure Block Tin from 98 to 90 parts. Bismuth " 1 " 5 " Aluminum " 1 " 5 '' Schlo-sser ^ recommends two solders containing aluminum as espe- cially suitable for dental- laboratory use .* Platinum-aluminum Solder. Gold 30 parts. Platinum 1 " Silver 20 " Aluminum 100 " Gold-aluminum Solder. Gold 50 parts. Silver 10 " Copper 10 " Aluminum 20 " O. M. Thowless has patented the following solder for aluminum and method of applying it ; Tin 55 parts. Zinc 23 " Silver 5 " Aluminum 2 " The silver and aluminum are first melted together ; the tin and zinc are then added in the order named. The surfaces to be soldered are im- mersed in dilute caustic alkali or a cyanide solution, and then washed and dried. They are next heated over a spirit lamp, coated with the solder, and clamped together ; small pieces of the solder being placed at the points of union, the whole is then heated to the melting-point. No flux is used. The only oxide of this metal is alumina (AljOg). It is prepared by mixing a solution of alum with excess of ammonia. The resulting pre- cipitate (aluminum hydrate) is of a bulky, gelatinous character, and requires to be calcined at a high temperature ; after which it may be described as a perfectly white powder, soluble in caustic potassa or soda, and not readily acted upon by acids. Corundum and emery are nearly pure alumina. The ruby and sapphire are also transparent varieties of alumina in a crystalline state, their brilliant colors being due to oxide of chromium. The only knoAvn sources of corundum until 1869 were a few rivers in India, where it occurred in crystals having the form of the double six-sided cone. Its cost at that time was from twelve to twenty-five cents a pound. Since that date, however, it has been discovered in inexhaustible quantities in Georgia, North Carolina, and Pennsylvania. At present it can be bought at the mines at $10 per ton. (For the discrimination of the salts of aluminum see any of the recent works on chemistry.) ^ Richards. 148 METALS AND ALLOYS. Tin. Atomic weight, 118. Symbol, Sn (Stannum). The metal tin has been known for probably three thousand years. It is found in all parts of the world, chiefly as oxide. In reducing the ore it is first powdered and roasted to free it of sulphur and arsenic. It is then exposed to a high temperature with charcoal, and the metal is thus liberated. Pure tin is white in color and is perfectly soft and malleable. It has a density of 7.3, and its fusing-point is 458.6° F. (237° C). It is but slightly acted upon by air, but when heated much above its melting- point it oxidizes freely, and is converted into a yellowish-white powder — the well-known polishing putty. The action of nitric acid upon tin is to convert it into a white hydrated dioxide. It is dissolved by hydro- chloric acid, assisted by heat, and forms stannous chloride. Nitro- hydrochloric acid acts upon tin with much energy, converting it into stannic chloride. Alloys. — Tin is readily dissolved in mercury. With silver it forms a malleable alloy, which is considerably harder than tin. The late Dr. Bean used tin alloyed with a small percentage of silver for lower den- tures, which he cast directly upon the teeth after the ordinary cheoplastic method. Alloys of tin and silver, in which the former is slightly in excess,. are much used as amalgam alloys. Tin 10, silver 8, gold 1, is also fre- quently employed in filling teeth ; and tin 10, silver 8, gold 1, copper 1, has, according to Fletcher, been largely used as " gold-and-platinum "^ amalgam. It is stated that from 5 to 7 per cent, of copper has the property of replacing platinum in amalgams, conferring the quick- setting quality claimed for platinum.^ Dr. G. F. Reese has formed an alloy for a base for artificial dentures composed of 20 parts of tin, 1 of gold, and 2 of silver.^ This is cast directly upon the teeth, the process being similar to the cheoplastic method. The alloys which have been used in the cheoplastic process are chiefly composed of tin, silver, bismuth, and, in some instances, cadmium and antimony. According to Makins, gold and tin form a malleable alloy,^ and gold reduced to standard by pure tin retains its malleability.* Tin and platinum in equal proportions aiford a hard and quite brittle alloy, fusible at a comparatively low temperature. When it is remem- bered that the fusing-points of these metals almost represent extremes of temperature, it would seem that their union must be attended with dif- ficulty, but, as has already been stated,^ it is probable that some affinity exists between the two, as platinum is readily dissolved by and with the' fused tin. ' F. Fletcher. ^ Alloys and Amalgams chemically Considered, J. Morgan Howe, M. D. ^ A precipitated alloy of gold and tin, having the form of a black powder, may be formed by acting upon a concentrated solution of trichloride of gold with stannous chloride. * The author has found that the color and the general working qualities of gold are- greatly impaired by admixture with small quantities of tin. * See chapter on " Alloys." TIN. 149 With palladium, tin is said to form a brittle alloy. With lead, tin forms the chief part in the alloys used for soft solder- ing, and in the compounds known as pewter and britannia metal. Tin solders are composed of 2 parts of tin to 1 of lead, pewter consists of 4 parts of tin to 1 of lead, while britannia metal is formed by the addition of small quantities of antimony and copper. Alloys of tin and lead are harder and tougher than either metal singly, and they are more fusible than the mean of their constituents. The addition of bismuth to such an alloy lowers the melting-point to a remarkable degree, and the fusing-point is still further reduced by the addition of cadmium. Thus, an alloy composed of 15 parts of bismuth, 8 of lead, 4 of tin, and 3 of cadmium fuses at 145° F. ( = 63° C). Dr. C. M. Richmond uses a fusible alloy in crown- and bridge-work which he states is as hard as zinc, and can be melted at 150° F,, and poured into a plaster impression without generating steam. The formula of this alloy is as follows : Tin 20 parts by weight. Lead 19 " Cadmium 13 " " Bismuth 48 " " The following fusible-metal alloys are also suitable for the purpose ; Tin. Lead. Bismuth. Melting-point of alloy, Fahr. 1 2 2 236° 5 3 3 202° 3 5 8 197° Dr. George W. Mellott of Ithaca, N. Y., to whom is due the credit of having introduced the use of fusible metal and the compound called " moldine " into bridge- work, uses an alloy of — Tin : 5 Lead 3 Bismuth 8 Moldine, of which Mellott forms his matrix for casting, is a com- pound of potter's clay and glycerin. The alloy known as " Wood's metal," occasionally employed by den- tists in replacing teeth on vulcanite plates, is composed of 7 j)arts of bismuth, 6 of lead, and 1 of cadmium, and fuses at 180° F. (= 82° C.) — a temperature much below the boiling-point of water. In replacing a broken tooth by means of Wood's metal the usual dovetail is cut in the rubber plate with a fine saw, the tooth is fitted to its place, and the fus- ible alloy is packed in with a spatula heated in a spirit-lamp. Lead 75, tin 5, and antimony 20 parts is the composition of the best quality of type-metal. With copper, tin affords a number of very useful alloys. Bell metal is formed of 78 parts of copper to 2 of tin. Gun metal is formed of 90 per cent, of copper to 10 per cent, of tin. Speculum metal is formed of 6 parts of copper, 3 of tin, and 1 of arsenic. Babbitt metal, named after Isaac Babbitt of Boston, Mass., is an alloy consisting of 9 parts of tin, 10 parts of copper, used for journal- 150 METALS AND ALLOYS. boxes {vide patent 1839). Many modifications have since been made in this alloy, but the term is still applied to any white alloy employed in the construction of bearings, to distinguish it from the '' bronzes " and " brasses." Mr. Fletcher recommends an alloy of copper 4 pounds, Banca tin 96 pounds, regulus antimony 8 pounds. This alloy is said to be nearly as hard as zinc, while its shrinkage is much less. These qualities, together with the low temperature at which it fuses, entitle it to a place in the dental laboratory for the preparation of dies and counter-dies. Dr. L. P. Haskell recommends the formula tin 72.72, copper 9.09, antimony 18.18. Bronze is an alloy of copper and tin, and sometimes zinc. It is affected by changes of temperature in a manner precisely the reverse of that in which steel is affected, becoming soft and malleable when quickly cooled, and hard and brittle when allowed to cool slowly. The art of making bronze was practised before any knowledge of the working of iron existed, and it was used at a very early period in the manufacture of weapons. Commercial tin is liable to contain minute quantities of lead, iron, copper, arsenic, antimony, bismuth, etc. Pure tin may be precipitated in crystals by the feeble galvanic current excited by immersing a plate of tin in a strong solution of stannous chloride. Water is carefully poured on, so as not to disturb the layer of tin solution. The pure metal will be deposited on the bar of tin at the point of junction of the water and the metallic solution. Perfectly pure tin may also be obtained by dissolving commercial tin in hydrochloric acid, by which it is converted into stannous chloride. After filtering, this solution is evaporated to a small bulk and treated with nitric acid, which instantly converts the stannous chloride into stannous oxide. This is thoroughly washed and dried, and exposed to red heat in a crucible with charcoal. A button of pure tin will be found at the bottom of the crucible. Pure tin in the form of foil is frequently used in filling teeth, for which purpose it doubtless ranks next to gold. The foil is also em- ployed in connection with non-cohesive gold in filling approximal sur- faces of cavities in bicuspids and molars. Two sheets of foil, one of gold and the other of tin, are placed together and made into mats or cylinders. These are carefully packed against the cervical margins of the cavity. The frequent failure of ordinary gold fillings at this point has led some practitioners to entertain the theory that between the tooth-substance and the gold there is galvanic action, to which the lime salts of the tooth yield, and that by the combination of two metals, whether tin and gold or amalgam and gold, the galvanic action is con- fined to the metals, the tooth-substance being thus protected. The appearance of a filling formed of tin and gold would seem to confirm this theory, as it soon becomes dark in color, and presents a surface resembling amalgam, but it effectually protects the margins from decay.- Tin, having but slight affinity for sulphur, is largely used in the ^ Prof. James Truman, Report of Proceedings of Odontological Society of Pennsylvania, November, 1881. TIN. 151 formation of models in the construction of vulcanite dentures, and tin- foil forms the best coating for plaster casts in the vulcanizing process. The manufacturers of miscellaneous rubber articles do not use plaster in forming the matrix in which the rubber is packed before vulcanizing, having long since discovered that contact with plaster lessens the toughness and elasticity of the indurated rubber : they there- fore form every matrix of sheet tin, which is placed in a suitable iron box and covered tightly with dry powdered soapstone (steatite). Dr. J. S. Campbell, wdio introduced the vulcanizer known as the '' New Mode Heater," described a means whereby all parts of the matrix contained in the flask in constructing rubber dentures could be covered by sheet tin, so that after vulcanizing and the removal of the sheet tin or foil the surface of the rubber would be found to be smooth and highly polished, and, if the " waxing up " had been carefully done, little or no Bling and scraping were needed. The method demonstrated by Dr. Campbell possessed precision and saved labor, and it is to be regretted that it was not generally adopted by mechanical dentists, who have not improved to any extent upon the slovenly methods employed in 1858, when indurated rubber was first employed in dental practice. When tin-foil is used as a coating for plaster casts in rubber work, the foil may be removed with the finger-nail if the surface of the plaster model was smooth and hard, and this condition of the plaster surface can be obtained by using nothing as a coating for the plaster impression but sandarac varnish, and carefully avoiding the use of oil or solutions of soap as a means of separating the impression from the model. If, how- ever, in consequence of the roughened surface of the plaster cast the tin-foil adheres so tenaciously that it cannot be removed except by means of a solvent, hydrochloric acid is the only one that will accom- plish that end without injury to the rubber. Both nitric and nitro- hydrochloric acids should be avoided, as they attack indurated rubber with more or less energy. Lower vulcanite dentures may be loaded with tin to give them addi- tional weight, and by lessening the quantity of rubber prevent the occurrence of porosity during the process of vulcanizing. Solvents. — Tin is readily dissolved by either of the three mineral acids. Sulphuric acid converts it into stannic sulphate. Tin dissolved in hydrochloric acid forms stannous chloride. By the action of dilute nitric acid tin is not dissolved, but is converted into stannic oxide, which settles to the bottom of the vessel as a white powder. This, when ren- dered anhydrous by heating to redness, affords the well-known polishing- powder called " polishing putty.'' Chlorides. — There are two chlorides of tin — stannous chloride or protochloride of tin (SnCla), and stannic chloride or bichloride of tin (SnCl4). Stannous chloride is prepared by dissolving tin in hydro- chloric acid, the action being assisted by gentle heat. Stannic chloride is obtained by dissolving tin in nitro-hydrochloric acid (aqua regia). These two compounds of tin are employed in the preparation of purple of Cassius, in which process stannous chloride is added to a mixture of stannic chloride and trichloride of gold (see page 109). (For other compounds of tin see works on chemistry.) Discrimination. — Tin is detected before the blowpipe by fusing the 152 METALS AND ALLOYS. compound under examination on charcoal with sodium carbonate, when a bead of the metal is obtained. From a tin solution caustic potash and soda precipitate a white hydrate, soluble in excess. Ammonia affords a similar precipitate, not soluble in excess. Hydrogen sulphide and ammonium sulphide throw down a dark-brown precipitate of mono- sulphide. Trichloride of gold added to a dilute solution of stannous chloride causes a purple precipitate (purple of Cassius). CHAPTER III. PRINCIPLES OF METAL WORK. Sheet-metal Work in Detail; the Manufacture of Taps, Screws, Nuts, Threaded Wires, Bands, Regulating Ap- pliances, ETC, — Special Tools and Appliances Required. By C. L. Goddard, A. M., D. D. S. Plate or Sheet Metal. As the refining, alloying, and working of metals and forming an ingot have been described in other parts of this work, the present chapter will begin at that point. The Ingot. — After an ingot of metal has been moulded it should be forged for three purposes — to test its malleability, to reduce its thick- ness, and to bevel one edge slightly. Sheet-metal or Plate. — Although an ingot may be reduced to plate by hammering, it is a slow and laborious process. It is better to use a rolling-mill, such as is shown on page 37. The mill should be provided with long handles, and both ends of the rolls should be adjustable by means of one screw. A geared mill is much easier to work than one without gearing. After annealing, the bevelled edge of the ingot should be introduced between the rollers, which should be adjusted so as to only slightly com- press it as the handles are turned. For rolling a large, thick ingot two persons are required, one for each handle. The rolls should be brought nearer together, the ingot passed through again, and the process repeated, with occasional annealing, till it is reduced to plate of the desired thick- ness. If plate is desired wider than the ingot, it should be rolled till the desired width is obtained, then annealed, reversed, and rolled cross- ways till reduced to the desired thickness. If, in rolling, the plate curves, showing that one edge is thinner than the other, screw the rollers nearer together on the thicker side of the plate and roll again, repeat- ing the process till the plate is reduced evenly. If this precaution is neglected and the plate merely reversed and rolled again, it will be rolled thinner on the edges than in the middle, and will crumple. For bands for regulating appliances plate is best rolled from round wire. This gives a long, narrow ribbon, the edges of which are less liable to tear than the edges of cut plate. The thickness of metal plate and also the size of wire are measured with a plate or wire gauge (page 38). There are several of these, but 153 154 PRINCIPLES OF METAL WORK. the one used most by dentists is the American standard wire gauge, called generally the Brown & Sharp (or B. & S.) gauge. All numbers of plate and wire in this chapter refer to this gauge, and are generally marked B. & S., as band ribbon No. 32 to 36 B. & S. gauge, or wire No. 16 or 18 B. & S. gauge, etc. Matebials for Regulating Appliances. Quite a variety of materials are needed for regulating appliances, for bands, caps, screws, nuts, springs, clasps, plates, hoods, etc. Materials for such use should not be deleterious to the teeth in any respect, and should be inconspicuous. Some should be soft and pliable, others hard and rigid, others elastic. They should not corrode nor tarnish in the mouth. It is not always possible to obtain all the desirable qual- ities in one material, hence it is sometimes necessary to sacrifice one quality for another that is more important. Some metals or alloys that corrode or tarnish readily in the mouth have qualities of such import- ance that less important ones must be ignored. Utility must not be sac- rificed to appearance. For bands the most suitable metals are platinum, combined platinum and gold, and German silver. Platinum is best, because it does not cor- rode and may be soldered with pure gold without a flux. It is soft and pliable, and may be easily bent around a tooth and burnished accurately to fit the contour. To some patients the color is objectionable, hence for the anterior teeth the writer prefers a combination of platinum and gold made for crown-work, platinum coated with gold on one side. This has all the advantages of platinum in strength, and all the advantages of gold in appearance. It may be soldered with 20-carat solder. Coin gold or 22-carat is also good for bands, but must be used thicker than platinum to obtain the requisite strength. German silver was introduced for regulating appliances by Dr. E. H. Angle. It is strong, elastic when rolled without annealing, yet very soft and pliable when annealed. It may be soldered with gold or silver solder. It has the disadvantage of discoloring easily, though the more highly it is polished the less it discolors. It may be protected by electro- plating with gold or nickel, but, unless the plating is quite thick, dis- coloration will still take place. Vulcanite is used as in prosthetic work for making plates for attachment of ligatures, rubber bands, springs, etc. It has been replaced to a very great extent by appliances attached directly to the teeth. Tubes. — For use on posterior teeth or on the lingual surface of ante- rior teeth nothing is superior to German silver. For use on the anterior teeth tubes may be made of coin or 22-carat gold, about No. 30. Bars may be made of German silver or clasp gold according to the position in the mouth, and soldered with gold or silver solder. Wire may be made of clasp gold or German silver. Both of these materials are made elastic by drawing through the draw-plate, but an- nealing lessens the elasticity of the former and entirely removes it from the latter. The former retains its color well in the mouth, while the latter discolors very easily. TOOLS AND APPLIANCES NEEDED. 155 Piano wire is more useful than any other for springs for moving teeth. It is polished steel, and possesses more elasticity than any other wire that can be used in the mouth, yet is pliable enough to be readily bent without breaking. In some mouths it oxidizes so rapidly as to materially reduce its strength in a few days, while in others it will merely discolor slightly, but still retain its strength. It cannot be hard soldered without drawing the temper so much as to ruin its elasticity, but may be attached to other metals with soft solder with- out injury. It is best to use tubes as a means of attachment, so that a new piece may readily be substituted whenever oxidation has reduced its strength or elasticity. (See Fig. 179.) Nos. 20 and 24 B. & S. G. are the most use- ful sizes : the former is large enough for coiled springs for spreading the arch (see Figs. 158 and 160), while the latter is suitable for springs where less force is needed. Piano-wire manufacturers use a different gauge, No. 15 piano-wire gauge corresponding to No. 20 B. & S. Nuts may be made of German silver, clasp gold, iridio-platinum, or nickel. The relative hardness and durability increase in the order named. Clasp gold retains its color better than either of the others. Screws may be made of German silver, clasp gold, or steel. Their strength varies in the order given. Clasp gold retains its color best. German silver retains its hardness, and will wear much longer if not annealed after drawing and screw-cutting. Although it is softened in the process of soldering, it still retains sufficient rigidity for most purposes. Steel oxidizes so readily in the mouth that its use for screws has been practically abandoned. Nickel-plating does not entirely remove the objection, as steel will oxidize under the nickel-plating and peel it off. Swaged caps may be made of German silver, platinum, or gold, the thickness varying from No. 30 to 36. Tools and Appliances Needed. It is unnecessary to describe Fig. 106. the operation of soldering to any one who has reached this point in his professional education, but a few useful appliances and tools may be enumerated. A soldering pad or block is very easily made of plaster and fibrous asbestos, such as is used for investing. By mixing it thick it may be moulded like putty in any form desired. A brass or sheet-iron base may be made by cutting out a round piece, slitting the edges, and turn- ing them up. Such a block is soft enough to stick pins in to hold parts together in soldering. Soldering block. 156 PRINCIPLES OF METAL WORK. Fig. 106 shows a much more convenient form. A base of plaster is made in the form of a hemisphere by making a mould from any kind of smooth ball. In use this is set in a ring of some kind or in the mould reduced to smaller dimensions. The block can thus be tilted at any angle, and both hands are left free for work. Fig. 107 shows a very useful soldering block with clamps for holding pieces in soldering. A chemist's filter stand is of great conyenience in a dental laboratory. Fig. 107 shows how one ring may be used for holding the soldering block at any convenient height. The blowpipe Fig. 107. may rest in another ready for use. A ring may be used to support an invested case while heating before soldering. An adjustable arm or clamp may be used to hold the blowpi])e at any angle, so that both hands are left free. The following tools are also needed : Plate shears ; plate punch ; flat-nose pliers ; wire-cutters ; round-nose pliers ; clasp-benders ; nip- pers ; spring pliers, large and small ; small anvil ; riveting hammer ; Bunsen burner ; blowpipe ; soldering clamps ; pin vice ; jeweller's .saw : calipers ; soldering copper ; vulcanizer ; flat file • half-round file ; draw- TOOLS AND APPLIANCES NEEDED. 157 plate, round; draw-plate, square; screw-plate (Figs. 110 and 111); plate-gauge (p. 38) ; draw-tongs. Drawing "Wire. — As it is not always possible to obtain wire of a desired size, every dentist should know how to draw it. Draw-plates are made of hardened steel and contain a series of holes finely graded from large to small (Fig. 108). The change in size of holes from one to another should not be too abrupt. AVire may be drawn from a larger size or from an ingot moulded for the purpose. Ingot-moulds are furnished that will pro- duce a long round or square ingot. The mould should be oiled and warmed before pouring the metal in it, so as to make a perfect ingot. After cooling the ingot should be reduced in size by forging. The square ingot is most easily reduced by holding it on a smooth anvil and hammering the sides alternately. Some care and practice is necessary, as the ingot cannot be well drawn out unless its square shape is pre- served. It should be annealed frequently. Having thus reduced the ingot to a size that will enter the largest hole in the draw-plate, hammer the corners slightly to make the square an octagon. Large and strong draw-tongs are needed, and those should be selected which have short jaws and long handles, not less than eight or ten inches in length, so that they can be grasped with both hands. The end of the ingot or large wire must be pointed, so that it can enter the next smaller hole in the draw-plate, and project at least a quarter of an inch, so that it can be readily seized by the draw-tongs. Fasten the draw-plate in a vise and apply oil or beeswax in each hole. Seize the projecting end of the wire or ingot, and with a quick motion draw it through the hole. Repeat the action with successive holes, Fig. 108. annealing frequently, till the wire is reduced to the desired size. The action of drawing hardens the wire and gives it elasticity. If it is desired to retain this elasticity, it should be annealed as little as possible during the process, and not at all afterward. If it is desired to solder 158 PRINCIPLES OF METAL WORK. such a spring of German silver to another appliance, soft solder should be used, as the heat necessary for hard solder will destroy the elasticity. Tubing- or Tubes. — Tubing is made by means of a draw-plate like wire. Having made a ribbon of the width and thickness desired, cut one end tapering, curl it slightly, and draw it through the largest hole in the draw-plate. The diameter of this hole should not be much less than the width of the ribbon. The edges will be curled slightly, and the operation should be repeated with successive holes till the edges of the tube are in contact (Fig. 108). The tube may then be still further reduced in size, the same as wire, unless the plate selected was so thin that the edges slide over each other instead of making a butt joint. For making a tube to fit any desired size of wire or screw the width of the strip should be a little more than three times the diameter of the wire or screw : No. 30 B. & S. G. plate is thick enough for tubes for most of regulating appliances. If a thread is to be cut in the tube, heavier plate should be used. Taps and Dies. — For cutting large screws taps are used which are in sections, so that the thread may be cut slightly at first, and then Fig. 109. deeper by screwing the sections nearer together (Fig. 109). In cutting threads in a nut a tapering tap is first used, next another with parallel Fig. 110. 7 G 5 4 Cut screw plate. sides, but smaller than the screw which is to fit ; then a tap is used of the full size. Fig. 111. Jam screw plate. This is necessary in steel and other hard metals or alloys, but with the softer ones the threads for both nuts and taps may be cut full size at first. TOOLS AND APPLIANCES NEEDED. 159 Sectional dies are seldom made small enough for dentists and jewel- lers' use, but screw-plates are provided with holes of different sizes, resembling draw-plates, except that the holes are screw cut. These are known as cut plates or jam plates according as they actually cut a V- shaped spiral groove or produce it by pressing into the surface. (See Figs. 110 and 111.) The most efficient tap for dentists' use is a compound instrument combining a drill and a tap. It is readily made from an old excavator, one with a long handle preferred (Fig. 112). First draw the temper; Fig. 112. Combined drill and tap. then, by rotating the instrument in the left hand while the end rests in a notch in the file-block of the bench, file it round for a distance of about five-eighths of an inch from the end. For one-fourth of an inch or more from the end the size should be such that the instrument wilt fit loosely the first tap-hole above the one selected in the screw-plate. For a space of one-fourth of an inch above that the instrument should be of a size to enter snugly the second hole above, and be slightly indented by the threads as it is screwed in the first hole above. Flatten the lower one-fourth of an inch and shape the end as usual for a spear-pointed drill. Cut the desired thread in the second ■one-fourth of an inch of the instrument. To do this well, fasten the screw-plate in a vise, and, holding the instrument at right angles, screw it slowly into the tap desired. Oil the instrument and turn it back and forth, gradually advancing it as the thread is cut. The die-plate is so hard and the annealed steel is so soft that the tap should be made with- out special difficulty. To temper the tap heat it to a cherry red to a •distance of three-quarters of an inch from the end and plunge it in ice- water ; this makes it extremely hard and brittle. To draw the temper and make the instrument tough as well as hard, first brighten one side, then heat the end in the Bunsen or alcohol flame till the drill portion is reduced to a straw color, the tap to the slightest blue obtainable, and the shank above the tap to a spring-blue color. The drill point should be properly shaped by grinding. (See Fig. 112, showing bevelled cutting edges.) Grind the tap triangular or square. Cutting Threads on "Wire. — Select a wire which will fit loosely the second hole of the screw-plate above the size desired, or draw wire for the purpose. In the bench vise place two blocks of hard wood, and grasp the wire so as to leave about a quarter of an inch exposed (Fig. 114). File the end slightly pointed, put on a drop of oil, apply the screw-plate so that the point of the wire will enter the countersunk side ; press slightly and revolve the plate in the direction indicated by the thread about one turn ; revolve it back about half a turn, then forward again. By this time the thread will have caught sufficiently to hold without downward pressure. Work the plate forward and backward, advancing a little each time till the plate has run down to the wooden blocks. Un- screw the vise, raise the wire a little, and proceed as before. By thus 'exposing only a slight portion of the wire at a time a less amount of it is 160 PRINCIPLES OF METAL WORK. subjected to strain, and it is less likely to bend or break. The softer the wire the more readily will the thread be cut, and the harder it is the more Fig. 113. Cutting threads on wire. care must be taken to advance the die-plate only a little at each turn, keeping the wire well lubricated. It is well to make a screw several inches long, from which pieces may be cut off as needed. Taper the cut end slightly, as the thread is liable to injury from the ^^^- l^^- shears or niiiDers ^^^mmm^^ma A square end may be filed on the screw to fit a watch-key, or, if a larger head is needed, screw on ^ ^taaiaiiHiiSB} a square nut and solder it (Fig. 114, A). Cuttlna: tliread on wire : If a round head is needed, solder a piece of ^oCd-hetdTcrew!"''' ' ^' tubing on the screw at any position desired, and drill holes through it at right angles for the insertion of a pointed in- strument for turning it (Fig. 114, B). In most appliances the screw is stationary and the nut turned. Nuts. — The following is Dr. C. S. Case's description of his method of making nuts: "The nuts are made of JIG. 115. five-cent nickels, which are found to be of r^: - —3^^-7-7 T^^ a (^ proper quality and the thickness to be easily Cases guide in making nuts. cut and withstand cvery desired force, while they suffer no oxidation in the mouth that retards them from readily gliding upon the screw. Saw the nickel in halves, and mark it into squares a little larger than the required size of TOOLS AND APPLIANCES NEEDED. 161 Fig. 116. the nut. These are again cross-marked or punched in the centre for a guide to the drill. At the other end of the tap (or on an excavator handle) I make a screw the length of the nut with an abrupt shoulder, and square the shank the required size of the nut. (See Fig. 115.) This when tempered quite hard will be found a valuable and almost indis- pensable adjunct to the finishing of these exceedingly small nuts." Screw the roughly-shaped nut against this shoulder and file to the size and shape. Dr. Matteson's method of making nuts •} " In regard to making these nuts for irregularity cases, I have found cutting them out of solid nickel and German silver plate, to be drilled, tapped, and squared, a very tedious process. The process may be greatly simplified by first drawing tubes Square tubing for nuts. Qf platinized silvcr (1 part platinum and 2 parts silver), soldering the joint with 20-carat gold, then drawing through a ' square-hole ' draw-plate, in- serting piano wire in the tube, thus making a square tube with a round hole, then sawing oif enough for a nut" (Fig- 116). German silver may be used instead of platinized silver, but is not as hard. It is not necessary to insert piano wire in the square tube in drawing. Even if the opening is reduced very small, all that is needed is enough to guide the point of the drill in enlarging it. To make the nut, saw off a short piece of the square tube, and hold it in the vise. With the drill and tap shown in Fig. 112 enlarge the hole in the centre and cut the thread. In doing the latter work the tap from left to right, advancing a little each time till the thread is cut through the length of the nut. It is as easy to make a long nut as a short one, and the greater the number of threads in a nut the better will it hold and the longer will it last. Keys for fitting the square ends of screws may be made by selecting Fig. 117. Keys and wrenches. a watch-key or small clock-key (Fig. 117, A) to fit, cutting oif the handle, and fastening it to a socket handle with shellac (Fig. 117, B), To do this fill the socket with powdered shellac, heat the key enough to ^ Review, vol. iv., 1892, p. 566. 11 162 PRINCIPLES OF METAL WORK. soften or melt the shellac, and press it to place. The key may be fas- tened with soft solder as folloAVS : First brighten the inside of the socket and outside of the key ; apply to each dilute chloride of zinc (tinner's "acid ") ; melt small pieces of solder in the socket till nearly full ; heat the key and press into place. Pure tin may be used for soft solder in these cases. A right-angled key may be made by filing a slot in the end of a handle, squaring the key-shank, and fastening with either hard or soft solder (Fig. 117, C). A wrench may be made by filing a slot in the end of a flattened instrument and bending to any desired angle (Fig. 116, D and E). Apparatus Employed. Plates. — For making a simple vulcanite plate to fit against the lingual surfaces of the teeth an impression should be taken in plaster, though modelling compound will do in some cases. By making a large vacuum chamber many of these simple plates can be retained by atmo- spheric pressure. Although plates have been superseded in a great degree, they are not only useful in a number of cases, but in some cases are better than anything else. Advantages. — Plates by their contact with a greater number of teeth, and also with the palatine portion of the alveolar ridge, distribute their anchorage more than any other appliance ; they are easily constructed. Disadvantages. — On account of impaction of food under a plate it is more uncleanly than any other form of regulating appliance, hence necessitates very frequent visits to the dentist. In many cases, however, plates may be so constructed as to be advantageously removed by the patient for cleansing. Fig. 118 shows the simplest form of a plate for moving a tooth lingually. Fig. 119 shows a similar one Fig. 119. for moving all the incisors lin- gually. / r V r^- A tooth may be moved labially Fig. 118. by means of rubber, compressed wood, or tape between the edge of the plate and the tooth. The edge of the plate should be made thick, and a box or dovetailed space may be cut in it, with inserted cone bars to retain the rubber or wood (Fig. 120). This is one of the oldest appliances on record. By boring two small holes through the plate near the edge a lump of APPARATUS EMPLOYED. 163 rubber may be tied to the edge with floss silk (Fig. 121). At a second visit a thicker piece or two thicknesses of the same may be tied in place. A better plan is to enlarge the plate at that point with gutta- percha (Fig. 122). Cut a dovetailed box in the edge with an inverted cone bur, warm a lump of gutta-percha, press it in the box, put the plate in the mouth, and press it in place. The gutta-percha will mould itself against the tooth that has moved, and thus enlarge the plate just that much. A Fig. 120. Fig. 121. Plate with box {A); B, rubber or compressed wood in box. Rubber tied on a plate. piece of soft rubber may now be ligated in position as before. At the next visit of the patient the gutta-percha may be softened and pressed again against the tooth, thus enlarging the plate a second time. When the tooth has reached the desired position, it can be retained by the enlarged plate, but a better retainer is shown in Fig. 123. Such plates may be advantageously ligated to deciduous molars or bicuspids. Two holes should be drilled through the plate from the Fig. 123. Author's retainer, band, and round wire. Fig. 124. Plate with gutta-percha extension. Ligatures for securing or holding plate. lingual surface, and should emerge at the cervico-palatme edge. The holes should not be more than one-eighth of an inch apart. Pass the ligature through the holes as shown in Fig. 124, and tie firmly around the neck of the tooth. The plate can be advantageously used with the labial bow, as shown in Fig. 125. 164 PRINCIPLES OF METAL WORK. The Coffin split plate is shown in Fig. 126. Plates are advantageously used for anchoring piano- wire springs, either simple or coiled, for moving Fig. 125. teeth in all directions (Figs. 126 and 127). The end of such spring should be flattened or bent at right angles for about one-eighth of an inch, and imbedded in the wax base-plate, with the projecting portion resting against the tooth to be moved. This projecting end will be securely held in plaster while the wax is re- moved and rubber vulcanized.. Bands. — The origin of the closed band for regulating ap- pliances is lost in obscurity. It was doubtless invented in- Coffin split plates. Plate and wire springs for self-protru- sion—Jackson's method. dependently by several different men. The writer distinctly remembers such a closed band with a hook attached having been used in rotating teeth in Grand Rapids, Mich., in 1863. The cementing of a band on a tooth has developed a new era in regu- lating appliances. In the early days of orthodontia one of the most per- APPARATUS EMPLOYED. 165 plexing problems was the attachment- of appliances to the teeth. Liga- tures and clasps were used, but were unsatisfactory, especially with partially erupted teeth. Sometimes pits were drilled in teeth for the ends of appliances to rest in, and sometimes these pits were deepened so that a screw could be inserted or a pin cemented in. The invention of the closed band cemented on a tooth renders these previous methods unnecessary. The ribbons for bands should be rolled from wire No. 13 to 16, B. & S. gauge, and so thin that they can be easily bent around a tooth, and as wide as the tooth will admit. For bicuspids and molars the thick- ness should not be more than No. 36, B. & S. G., while for incisors the bands may be used still thinner. After rolling the ribbon should be annealed and polished. The simplest method of making bands is thus described by Prof. Angle : " The surface of the tooth to be banded is carefully cleaned by means of a pledget of cotton ^ moistened in alcohol or ether. A loop of band material is then slipped over the tooth. The ends should be grasped close to the tooth with a pair of closely- fitting fiat-nosed pliers and the band drawn tightly around the ^ ^, band fitted ;£, ready for soldering. tooth, a strong burnisher being applied at the same time to make it con- form still further with the shape of the tooth. Remove the band, which now presents the appearance shown in Fig. 128. Place a small bit of solder and borax at the junction between the ends, and carry the band in contact with the flame of the soldering lamp. After it is soldered clip the ends off, and the band is now ready for any attachment which may be made." This description applies equally to bands of German silver, platinum, or platinum faced with gold. The rubber dam should be applied before cementing a band on a tooth. In soldering such a band the projecting ends may be held in the pliers, but a simpler method is the following : Cut off one end at a six- teenth of an inch from the p ,nQ junction, and the other a little longer (Fig. 128, A). ^^^ ^ — Bend the longer end over . ^ j, ^ \.f the shorter, and pinch them '^ ^Sb' tightly together (Fig. 128, B). With light spring pliers * \ grasp the band on the oppo- Stea,i^ and borax on the junction and hold in a soldering flame site side, lay a bit of solder | i ( J K on thft innntion. '^\ ( I ^—or Matteson Cap. — ^This is V a swaged cap fitting wholly or partially over the cutting Making Matteson caps. edges or grinding surface of a tooth, and extending nearly or quite to the gums or even under their free margin. Such a cap will adhere to a short or conical tooth much better than a band (Fig. 129, A). Take an 166 PRINCIPLES OF METAL WORK. Fig. 130. miRtmmM"riimiiin^|wft impression with Mellott's moldine, and make a die and counter-die of his metal. If a harder die is necessary, take an impression with Teague's impression compound or other similar material, dry it, and fill with zinc or Babbitt metal. Make a counter-die of lead or lead and tin. In most cases a cap may be swaged from a single flat piece of metal, but it is better in some cases to cut and shape a piece partially before swaging. For a short cuspid cut a circular piece of plate having a radius equal to the longest side of the tooth ; cut a slit from periphery to centre or cut out a V-shaped piece (Fig. 129, E). Bend the piece into a hollow cone (Fig. 129, C) ; place it in the counter-die and swage. For a molar it is best sometimes to shape the plate like a Maltese cross (Fig. 129, D), with the centre piece as large as the occlusal surface and each arm slightly wider than the side of the tooth. After swaging the seams should be soldered with a high-grade solder. In some cases it is ad- vantageous to make a single cap or chain of caps for several teeth, as for bicuspids and molars (Fig. 129, E and F). Clamp Bands. — Fig. 130, a, shows Dr. J. N. Farrar's clamp band, which was illustrated in the Cosmos, Jan., 1876, and used for drawing the cuspid back. Since that time Dr. Farrar has applied the band for many other purposes and for the attachment of other appliances, to a sin- gle tooth in some cases, but more often to two or more (Fig. 130, 6, c, d, e). It is constructed of 18-carat gold or platinum ribbon made by roll- ing out wire to a thickness of No. 30 B. & S. G. or less. To one end of the band is soldered a square nut and to the other a "smooth bone" nut. A headed screw passing through the latter engages with the former, and is tightened around the teeth by means of a wrench. The head of the screw is made square or round. If the lat- ter, it must be perforated so as to be turned by a pin wrench (Fig. 131). To prevent the band sliding against the gums, lugs or ear-pieces are soldered on it at appropriate places and bent over the occlusal or against the inclined surfaces of the teeth. To these bands are soldered wire hooks or staples for attachment of other appliances, such as "push jacks," "pull jacks," levers, rubber bands, springs, etc. The nuts on these clamp bands are single, double, or triple, as illustrated in Fig. 131. Fig. 132 shows two bands adjusted with two screws work- ing in a double nut. Angle's Adjustable Clamp Band. — From No. 36 band ribbon, as wide as the length of the crown will allow, cut a piece long enough to nearly surround a tooth. To one end solder a short screw, and to tlie other a short tube just large enough to pass easily over the screw. By means of a nut on the end of the screw the band may be tightened around (Fig. 133). The band should then be burnished to fit ac- The edge should be slightly bent over the occlusal surface to P Farrar's clamp band. Fig. 131. Single, double, and triple nuts (Far- rar). the tooth curately. APPARATUS EMPLOYED. 167 Use of double nut (Farrar). prevent the band sliding against the gum. To this clamp band may be soldered other attachments. Bands and caps should be soldered with as high grade Fig. 132. of solder as they will allow, so that attachments may be soldered to them with a lower-grade solder without danger of unsoldering the first seam. This, however, is not al- ways necessary ; with the skilful use of the blowpipe solder- ing may be accomplished on one side of the band without heating the other side to so high a temperature. Platinum should be soldered first with pure gold, then appliances may be attached with any grade of solder they will admit. With pure gold or gold-faced platinum, solder as high as 22 carats may be used first, and lower grades afterward. With 22-carat, or coin gold, use 20-carat solder first. With German silver use silver plate or coin silver for the first soldering, and for the second use silver solder. Soft solder may be used for attaching piano wire or springs of any kind which will lose their temper in a high temperature. Hooks. — The simplest way to make a hook is to form it where the band is lapped. When the band is bent around the tooth and drawn tight with the pliers, any point of junction may be selected that will be most suitable for a hook, yig. 133. whether on the labial or lingual surface (Fig. 134, a). The projecting ends may be bent at an acute angle with the band instead of a right angle, and after soldering the hook may be filed nar- rower than the band and the edges rounded (Fig. Biscupid. 134, b). If a hook is needed on both sides, make the first one by doubling the rib Fig. 134. Molar. Making hooks on bands. bon, as in Fig. 134, c, and soldering the junction, then bending it around the tooth as usual, and making the other hook wherever desired (Fig. 134, d). A bar or lug may be made by doubling the band for a longer distance (Fig. 134). Such a bar should be thick enough Fig. 135. to file round or half- round, as the purpose in most / / cases is to rest on an adjoining tooth as a retainer. rr\f J I A round wire resting on a tooth touches it at one / / point only, and can be kept clean easily, but a flat ^ bar will retain fluids in eontact with a tooth the whole width of the bar (Fig. 135). 168 PRINCIPLES OF METAL WORK. Soldering- a "Wire to a Band. — A wire is easily soldered to any part of a band as follows : Melt a small piece of solder on the band wherever the attachment is desired. Hold in the fingers or pliers a piece of wire three or four inches long, and rest the other on the band where the solder was fused (Fig. 136, a). The band may rest on a soldering block or be held in the soldering pliers. Direct the blowpipe flame on both wire and band. The wire, being smaller than the band, will be heated more quickly, and be ready to attract the solder as soon as it is melted. The surplus wire can then be cut off. The end of the wire may be stuck in a cork or piece of soft wood if the heat is communicated to the fingers, or a short piece of wire may be held in the long-handled spring pliers. Fig. 136. Fig. 137. ^-"0 © Soldering wire to bands. Farrar's bands, hooks, and staples. A wire can be thus attached to a band at any angle.. A wire hook may be made by soldering the wire at right angles to the band, cutting off the surplus, and then bending the remaining portion in the shape desired (Fig. 136, b-d). A staple may be made by bending the loose end over on the band and soldering with a lower grade of solder. Dr. Farrar's method of attaching a staple or a lever is to punch a hole in the band and insert one arm of the staple or one end of the lever to hold it in place for soldering Figs. 136, 137). To Solder a Tube to a Band. — Proceed as if it were a piece of wire and cut off the surplus. To prevent a tube opening after it is attached care must be taken to place the seam next to the band before soldering, during which process the edges become soldered also. If the seam is Fig. 138. Fig. 139. Soldering a tube to a band (Angle). Soldering regulating appliances (Farrar). slightly flattened with a file, it is more easily kept in place while solder- ing. A short piece of tubing may be attached by holding it with a small steel instrument, as shown in Figs. 138 and 139, or by holding in place with a spring clamp (Fig. 140). APPARATUS EMPLOYED. 169 Another method of attaching a bar, wire, or tube is to pres.s the edges of the band slightly into the soldering block of plaster and asbestos, and then tilt the block to an angle of about 30°, so that the tube, wire, or bar when placed in position will rest against the desired surface and be re- tained by gravity. Apply borax and solder to the point of contact, and direct the blowpipe flame so that the parts will be heated evenly and the solder flow to both at once. The operation is simplified if a bit of solder is first fused on the band. Pins or pieces of piano wire may be stuck in the soldering block to hold the parts in contact. Two bands or a series of bands may be attached at their contiguous surfaces by placing them on the teeth in the position desired, then taking an impression with modelling compound. The bands should be removed Fig. 140. Fig. 141. Soldering a tube to a band. from the teeth and placed in the impression, which should be filled with equal parts of plaster and sand, marble dust, chalk, or other suitable material. Teague's impression compound is well adapted to the purpose. When the cast is removed from the impression the bands will be found in the exact position in which they are to be soldered to each other. This may be done by melting a small piece of solder at each point of contact. Where special rigidity is needed a stiff wire may be soldered on the labial or lingual surfaces so as to unite all the bands. A socket for retaining the end of a spring or screw may be made by soldering a short tube to the band vertically or at whatever angle may be best suited to the case. A hole may be punched or drilled in a band where it is lapped or the band may be thickened at any point for the same purpose. A slot may be made in the band in the same manner to retain the flattened end of a screw and prevent its turning (Fig. 141). Partly-made Appliances. — To facilitate work when a patient is in the chair many partly-made appliances should be kept on hand, as follows : Band material or ribbdn in coils, No. 31 to No. 36, from l to ^ of an inch wide, of German silver, platinum, etc. (Fig. 143, a). 170 PRINCIPLES OF METAL WORK. Wire. — German silver, clasp gold, and piano wire Nos. 13 to 24, also iron or copper binding wire, silver suture wire, and fine platinum wire. Partly-made bands, with tube or wire bar Fig. 142. attached (Fig. 143, B and c). By placing such a partly-made band on a tooth with tube in the position desired it may be drawn tightly with pliers and finished as in Fig. 143, D. The partly-made band c may be finished as a retainer, e or F, or the bar may be cut short enough to serve only as a hook for attachment in rotating G. The outer half of the tube may be filed or ground away to serve as a Fig. 143. Partly-made appliances. notch in which to rest a wire or bow, h. Either the upper or lower portion may be filed away so as to leave a hook, i. Adjustable bands (Fig. 142), either plain or with tube attached, j and K. Screw loire (Fig. 144, a) should be kept on hand a few inches in length. Not more than two sizes will be needed in many cases. Nos. 16 and 19 B. & S. G. are convenient sizes. Fig. 144. Screws and tubes. Bound tubing (Fig. 144, b) of German silver for back teeth and of gold for anterior teeth should be of several sizes, to use with screws or plain wires. Some tubing should be very small for fine piano wire. No. 24 B. & S. G. Flat Tubing (Fig. 144, c). — This is seldom needed except in short lengths, and may be made by bending a piece of the thicker band ribbon over flat-nosed pliers or a flat spatula with parallel sides, or by flattening a round tube. It is useful as a socket for a loop in the end of a piano wire, D, to keep it from turning out of position, or for a sliding bar. Square tubing (Fig. 116) for nuts (p. 161) of one or two sizes. Nuts, both long and short (Fig. 144, f), to fit each size of screw. FORCES APPLIED. 171 Rubber tubing, from ^6 **^ T i^ich, g (Fig. 161) ; Floss silk, previously washed ; Twisted silk and linen thread ; Tape for wedging ; Compressed wood ; Jack-screws, partly made, with long sheath, which may be quickly shortened to suit any case in hand (pp. 171 and 172) ; Talbot springs (p. 174) ; Matteson springs (p. 174). Forces Applied. Forces. — For applying intermittent force the screw is more useful than any other appliance. It is used for pushing and pulling. A pushing screw is generally known as a jack-screw, and a pulling screw as a " drag-screw." The Angle jack-screw is the simplest and easiest to make. Having de- cided on the length needed, cut off a piece of screw wire a little shorter and fit it with a nut. Flatten one end by hammering, so as to spread it out wide. In some cases it is desirable to file a notch in the flattened end. Select or make a piece of tubing of such a size that the screw wire will pass in it easily without binding. Flatten one end of the tube or solder in it a short piece of wire and file it to a point. Insert the screw in the tube, and the jack-screw is complete (Fig. 145). In use one end is in- serted in a socket or hole in a band attached to a tooth, and the other in a slot in a similar band. Sometimes it is best to solder either the tube or the screw to a band or some other appliance. This jack-screw may be of any length, from i Angle's jack-screw. Fia. 146. (See Figs. 154, 155). inch to 2 or 3 inches. Angle's drag or traetion screw is simply a wire bent into a hook at one end and screw cut at the other, with a nut attached, No. 17 or 18 B. & S. G. In use one end is hooked into a tube attached to a band and the other passed through a tube on another band. Turning the nut will draw the teeth toward each other. (See Fig. 146.) Angle's drag-screw. Farrar's Push- and Pull-jacks. — Figs. 147-153 show various push- and pull-jacks as made by Dr. Farrar. Fig. 147 shows a fish-tailed — -^s Fig. 147. Fig. 148. A rnriim saim^^"- B jack. A fish-tailed screw engages in one end of a screw tube. A fish- tailed wire enters loosely in the other. The tube is turned by inserting a pointed instrument in the hole drilled for that purpose. Fig. 148 shows a spjndle-end jack-screw similarly constructed, except that the fish-tailed piece is soldered in one end of the tube. 172 PRINCIPLES OF METAL WORK. Fig. 149 shows what Dr. Farrar calls a nut-jack, used in construction of his clamp bands : the eye is made by soldering a short piece of tubing on the screw and turning it spherical in a lathe. The end beyond the eye is filed square to fit a key. Fig. 150 shows Farrar's simplest form of screw-jack, consisting of a Fig. 149. Fig. 150. Fig. 151. -=cs: _|GS5ssO];:>> "1imair°T^:=- fish-tailed tube in which the screw moves loosely. On one end of the screw is an eye and fish-tail. A nut provided with eyes for turning fits on the screw and rests on the end of the tube. Fig. 151 shows a series of spindle-end jacks constructed like those in Fig. 148, except that both tube and screw end in spindle points. One Fig. 152. i^ objection to these jacks is that two instruments are necessary in working them, one for holding and one for turning. Fig. 154. Fig. 152 shows a "cylindrical swivel screw-jack." To one end of a threaded tube is soldered a hook, and to the end of the screw is FORCES APPLIED. 173 attached a swivel ending in a hook. By turning the screw by means of a pointed instrument in the eye the hooks are drawn toward each other. Fig. 153 shows a "barrel-turning draw-jack." A piece of plate is bent twice at right angles, A, and through the middle third is inserted a wire hook, aS*. It is then soldered to the extremity of the threaded barrel or tube, B. The hooked screw engages in this tube, which is turned by inserting a wrench in the square opening at A. To prevent wabbling while being operated the hooks are bent so that the draught will be in a direct line with the screw. Application of the Jack-screw. — The Angle jack-screw is varied easily in length by changing the length of the tube. It can be applied in many different ways, among which are the following : Fig. 154 shows the use of a very long jack-screw, moving an incisor forward (Fig. Fig. 155. 155), spreading the arch. The application of Farrar's screw-jack is shown in Figs. 156 and 157. Fig. 156. Fig. 157. Application of fish-tail and spindle- jack (Farrar). Jacks and clamp bands (Farrar). The Talbot spring is made as follows : Drive a piece of piano wire in the bench or hold it in the vise, and around this wind another piece of piano wire by holding each end Avith pliers. Make two or more turns ; then bend the wire at right angles along the coil to a point 174 PRINCIPLES OF METAL WORK. opposite the beginning, then again at right angles in the same plane as the other end (Fig. 158). This latter is not necessary unless there are Fig. 158. Fig. 159. Talbot spring. several coils. Piano wire No. 15, equal to No. 20 B. & S. G., is stiff enough for most cases. Occasionally a spring of smaller or of larger wire will be needed, but not often. German-silver or clasp-gold wire may be used for such a spring, but the elasticity is not so great. The Matteson spring differs from the Talbot spring in having two coils instead of one (Fig. 159). The Coffin spring, used in a split plate for spreading the arch, consists of a piano wire No. 20 B. & S. G. bent with clasp- benders into the general shape of the letter W, as shown in Fig. 160. The ends are flattened or bent at right angles for retention in the vulcanite. Fig. 160. Fig. 161. Matteson spring CofBn spring. f[| Rubber tubing for bands. For rubber bands use French tubing, from \ inch in diameter to ^ or less, cutting them wider or narrower according to the amount of force needed. Bands \ inch in diameter are the most useful (Fig. 161). Bands made from large tubing are often so thick as to take up too much room and spread teeth apart. Bands may be made from rubber dam by cutting with two sizes of punches, or by first cutting a hole with a punch and trimming around it with scissors. Compressed wood is useful for spreading teeth apart or for moving a tooth in any direction in connection with a plate or other appliance. Select a fine-grained wood and compress it laterally in a vise or with large pliers. The wood of floss-silk spools is good for the purpose. Tupelo-wood is highly recommended, being already compressed as sold by dealers. Any dry wood will swell when wet, and compressed wood will swell much more. FORCES APPLIED. 175 The swelling of pellets of cotton or of cotton tape folded in two or more thicknesses will spread teeth apart or move a tooth from some fixed position. Rubber strips or wedges of differ- ent thicknesses may be used for the Fig. 165. same purposes. To move one or more teeth by means of compressed Fig. 162. Twisted ligatures of silk, linen, or wire. Fig. 163. Twisting wire (Case). Fig. 164. Angle's instrument for compressing and elongating wire. wood, cotton, tape, or strip of rubber the material may be confined between the teeth or between the edge of a plate and a tooth. A box or mortise cut in the thickened edge of a plate will hold such material more securely. Silk or linen ligatures are very useful for moving teeth slowly. If a ligature of floss silk be tied tightly around two teeth not in contact, or 176 PRINCIPLES OF METAL WORK. from a tooth to some fixed point on a plate or other appliance, the tooth or teeth will be moved slightly by compression of the peridental mem- brane, and held thus till absorption takes place. By frequently renewing such ligatures teeth may be moved some dis- tance. A twisted ligature of silk or linen is more efficacious, because it tightens when wet on account of the swelling of the fibres, and thus continues to act for some time after being put in position. The longer such a twisted ligature is, the more force it will have. Its greatest effect is shown in Fig. 162, where, after being looped around one hook, the two strands are twisted around each other in an opposite direction to the natural twist of the thread, before being tied to another hook or tooth. Twisted wire ligatu7'es are very efficacious. By looping a copper wire over two pins or hooks the parallel wires may be twisted around each other, once or twice a day, by inserting an excavator or pointed instrument between them, or a square nut may be first put on one wire and the twisting done with a wrench, as devised and used by Dr. C. S. Case (Fig. 163). Pinched Wire. — A new method of applying force has been introduced by Prof. Angle — the elongation of a straight wire by compressing it in one or more places from day to day by means of round-nose pliers made especially for the purpose (Fig. 165). German-silver wire No. 18 is a suitable size. Application of Hooks, Tubes, etc. — The chief use of a hook on a band is for rotation by attaching a rubber band or twisted ligature to Fig. 166. Fig. 167. Plate and band for rotating. the hook and extending it to a plate (Fig. 166), or to a hook on another tooth (Fig. 167), or to a labial or lingual bow (Fig. 174). Fig. 168. Fig. 169. In some cases it is necessary to make two hooks on one band, and extend a rubber band from each to some firm point of attachment, as in Fig. 172. FORCES APPLIED. 177 Double rotation may be accomplished by means of two hooks and two bands. Figs. 168 and 1,69 show double rotation in opposite Fig. 170. Fig. 171. directions, and Figs, 170 and 171 in the same direction. Fig. 172 shows the use of hooks for attachment of rubber bands for drawing in a prominent incisor. It will be noticed that the anchor bands have each a round bar soldered to the buccal surface to increase the anchorage. Fig. 172. Fig. 173 shows how the author, following the suggestion of Dr. Angle, elongated non-occluding bicuspids and molars and brought them into occlusion by means of rubber bands ligated to the lower Fig. 173. Author's plan of occluding bicuspids and molars. and extended to hook bands on the upper teeth. One or two extra bands were ligated on each tooth to be used in case of breakage of the first. 12 178 PRINCIPLES OF METAL WORK. Special. Appliances. Tubes. — The attachment of a tube to a band serves so many uses as to have almost revolutionized the practice of orthodontia. Figs. 174 and 175 show its use for retaining the end of the labial and lingual bows. Fig. 175. Fig. 174. Labial and lingual bows. Angle's drag-sorew. Fig. 176 shows its use with the drag-screw. Fig. 178 shows its use in making up an appliance for spreading the arch. Fig. 176. Fig. 178. Lugs on angles. Fig. 177. Appliance for double rotation. Tube and piano wire for rotation (Angle). Fig. 179. Tube and piano wire for rotation (Angle). Fig. 177 shows its use for double rotation. In this appliance (Angle's) care must be taken to make the tubes short and solder them SPECIAL APPLIANCES. 179 to the labio-buccal line angle of the band. A piece of No. 24 B. & S. G. piano wire inserted in the tubes will rotate the teeth. The author has found it necessary in some cases to solder lugs on the disto-lingual sur- faces of the bands to touch upon the lateral incisors and prevent the teeth from being rotated out of the arch. Figs. 179 shows the use of the tube as a socket to insert a lever of piano wire for rotation. Fig. 180 shows the use of the tube for holding a retaining Avire for a tooth which has been moved into the line of the arch either labially or lingually. Provision for such reten- tion may be made by attach- ing such a tube before the Fig. 181. tooth is moved (Fig. 182), so that when the tooth is in place a wire can be inserted for retention. Dr. Angle Fig. 180. Ketainer (Talbot Providing in advance for retention. secured this wire by drilling a small hole through one side of the tube and the retaining wire and inserting a small pin. The author has found it a good plan to cement the wire in the tube. A short tube soldered vertically to a band serves as a socket for the end of a jack-screw or spring. A hole drilled or punched in a tube or a slot serves the purpose in many cases. Another use of tubes or bands is to serve as hooks for attachment of rubber bands in retracting cuspids or bicuspids, as shown in Fig. 182. Fig. 182. Author's, modification of diiilford & aiiplianie When the desired retraction has been accomplished the tubes serve to hold the ends of a labial bow, from which rubber bands may be extended for propulsion or rotation (Fig. 183). 180 PRINCIPLES OF METAL WORK. A tube soldered to one or more bands serves as a socket for holding Fig. 183. Further use of same tubes for holding bow. one end of piano wire (Fig. 184), while the other is utilized for moving teeth in different directions (Figs. 184, 185). Fig. 184. Tube band and spring appliance (Matteson). Fig 185. Author's appliance, close bite. A flat tube for the insertion of the looped end of a spring will hold it more firmly for pressing on the buccal or labial surfaces of teeth (Fig. 186). SPECIAL APPLIANCES. 181 Appliances for Extruded Teeth. — An appliance for pushing an extruded tooth into its socket is readily constructed as follows : Fit Fig. 186. Fig. 187. Flat tube for piano-wire spring. Appliance for reducing extrusion. wide bands to the two adjacent teeth, and solder a tube to the lingual and labial surfaces of each band (Fig. 187). When these bands are firmlv cemented on the teeth, connect the labial tubes and also the lingual tubes with stiff wires, preferably cemented in the tubes. From the labial wire or bar extend a rubber band or a twisted ligature over the cutting edge or occlusal surface of the extruded tooth, and attach it to the lingual bar. If the extruded tooth is of such shape that the rubber band will not stay in place, cement a swaged cap on the occlusal surfiice and make a notch in it. The construction of this appliance is simplified as follows : Instead of tubes, solder on the labial and lingual surfaces of one band stiff wires long enough to reach to the next tooth beyond the one extruded. To make the other band, first double the band material, then about Jg of an inch from the doubled end bend each part at right angles and solder the parts in contact. Finish the band, cutting off the projecting ends about ylg of an inch from the band. A notch is to be made in the upper side of each projection, and where the band is cemented to the tooth these notches form hooks in which to rest the ends of the wires extending from the other band (Fig. 188, d). The rubber band is more easily attached to these bars than to the ones previously described, because it can be slipped over the end of Fig. 188. Fig. 189. Details of appliance for reducing extrusion. Author's appliance for reducing extrusion. each wire where it rests in the hook. When the extruded tooth has been pushed up in its socket, it may be retained by substituting a small plat- inum or silver wire for the rubber band or ligature, but a better plan is to make three bands for the three teeth, solder them together where they are in contact, and cement them to the three teeth. 182 PRINCIPLES OF METAL WORK. Appliances for Forcible Eruption. — For this operation an appliance is needed which is just the reverse of the other : for drawing down an Fig. 190. Author's appliance for elongating broken tooth. incisor either partially erupted or broken, swage caps for the contiguous teeth, and connect them by a wire extending from the cutting edge of one to the cutting edge of the other (Figs. 190 and 191). Fig. 191. Author's appliance for forcible eruption. On the tooth to be elongated cement a band made as in Fig. 190, or one to which hooks have been soldered on both labial and lingual sur- faces. From the labial hook extend a slender rubber band or twisted ligature over the connecting wire and secure it to the lingual hook. The movement must be slow to avoid rupturing the pulp at the apical foramen. The bar forms a limit bevond which the tooth cannot be drawn. The Fig. 192. Fig. 193. Forcible eruption (Angle). tooth may be retained Iby substituting a platinum or silver wire for the rubber band, but better by three bands. SPECIAL APPLIANCES. 183 Fig. 192 shows Prof. Angle's appliance for elongation or forcible eruption. Its construction is very simple, consisting of a tube soldered to a band on any convenient tooth. From the tube a stiff wire extends across the space, and is hooked over the cutting edge of the next con- venient tooth. From this bar a rubber band is extended to a pin anchored in the tardy tooth or to a hook soldered to a cap cemented on the tooth. Fig. 193 shows a similar appliance in which lower teeth are used for anchorage. Fig. 194 shows a case treated under the author's directions in the infirmary of the College of Dentistry of the University of California, Fig. 194. Fig. 195. by a senior student. The occlusion was brought about in three or four weeks, Fig. 195. During the performance of mastication the patient unhooked the rubber bands, so as not to produce too severe a strain on the alternating teeth. Application of the Drag-screw. — Angle's drag-screw is one of the most simple and effective appliances. It consists of a stiff wire screw Fig. 196. Angle's drag-screw. cut at one end and bent into a hook at the other. Fig. 196, a, shows the appliance; Fig. 196, h, shows its use for retracting a cuspid. Double anchorage is secured by soldering a long tube to a molar and a bicuspid band. By this means the two teeth are so firmly yoked together that tipping is prevented, and the teeth, if moved at all, must be dragged bodily through the process. The attachment to the cuspid varies according to the movement re- quired. If the attachment is made as in Fig. 198, right side, the tooth will be rotated as well as drawn backward. If the hook is attached as in Fig. 197 or Fig. 198, left side, the tooth will be drawn backward without rotatina:. 184 PRINCIPLES OF METAL WORK. Fig. 199 shows the author's use of the drag-screw for reducing a prominent cuspid and at the same time making room, on the principle Fig. 197. of drawing two wedges toward each other. The cuspid forms one wedge and the lingual bar another. The drag-screw, hooked in the cuspid band and drawn through the bar by the nut, forces the two wedges together. Fig. 200 shows another use of the drae:-screw. Fig. 199. Author's appliance for making room and drawing cuspid in. Fig. 200. Drawing cuspid in (Angle). SPECIAL APPLIANCES. 185 The Jackson Crib. — The crib devised by Dr. V. H. Jackson of New York is essentially a pecnliar clasp which clings readily to a molar or bicuspid, and to which springs, screws, etc. may be attached. Its construction is as follows : First, a piece of German silver plate, No. 30, is fitted to the lingual or buccal surface of a molar or bicuspid. It should be made concave with contouring pliers or by striking a rounded instrument while it rests upon a piece of lead, or against it, so that it will fit snugly against the rounded surface of the tooth, especially at the cervical margin. This is best accomplished by exaggerating the concavity a little, so the piece will touch the tooth only at its edges. (See A, Fig. 201.) Fig. 201. The Jackson crib and base wire. The clasp portion is made of piano wire No. 20 B. & S. G., or of hard drawn German silver wire nnannealed, slightly larger, by first bending it at right angles (Fig. 202), leaving the width between parallel sides equal to the antero-posterior width of the tooth to be clasped. The part that is to clasp the neck of the tooth is then so bent with clasp-benders that it will be perfectly adapted to the curve of the cervex (Fig. 203). Both arms of the wire are then bent at nearly a right angle at a proper distance to cause them to pass over the grinding surface of the tooth or the points of contact with the adjacent tooth, and again bent in the same manner to extend toward the neck of the tooth on the lingual side (Fig. 204). The ends are next bent toward each other near the gum-line Fig. 202. Fig. 203 Fig. 204. O^ over the piece of metal ])reviously described, as seen at A in Fig. 201, and tacked with soft solder. The crib thus made clasps the tooth at the cervico-l)uccal and cervico-lingual portions, and is prevented from sliding up too far by the wires passing over the occlusal surface. If a spring is to be atta(!he' ■ il 20 " " " " il 16 li ¥'8 While the study of the foregoing classification of shapes and sizes would be a great help to manufacturers of artificial teeth, it must not be supposed that even the most intimate knowledge of it or of any other system will reduce the selection and assembling of the porcelain substitutes and their adjustment to the mouths of patients to an ordinary mechanical operation. From this system of Dr. Hall there are doubt- less almost unlimited deviations, and it was clearly his aim in making the classification and measurements to place within the reach of manu- facturers a practical plan which might take the place of the haphazard methods heretofore pursued in that "branch of industry. Beyond a cer- tain point the interests of the manufacturers and the wants of the den- tist are neither identical nor reciprocal. The latter often needs teeth imitating irregularities of position, color, etc. designed for special cases, the production of which the manufacturer is not prepared to attempt, as 228 MOULDING AND CARVING PORCELAIN TEETH. it would compel him to depart from the routine work of his factory — a course which he would find unremunerative ; hence the dentist must depend much upon his own artistic taste and skill in making such changes in the shapes and positions of the teeth obtained from the manufacturers as the case in hand demands. This can be better done with single plain teeth than with either sectional-block or single gum teeth. It is to be regretted that more attention has not been given to imitating in sectional-block teeth the changes characteristic of age, such as the recession of the gums, which begins in many cases in early middle life and progresses until a large part of the dentine above the crown is uncovered ; the loss of that uniformity of color which con- tributes so much to the beauty of the teeth in youth ; and the changes which take place at the cutting edges of teeth as years advance. The absence of these details is largely the cause of the gradual discon- tinuance of the use of sectional blocks. Really artistic teeth in blocks or sections should cost no more to produce, after the designs and moulds are made, than do the inartistic and conventional sets which we find in such abundance at the manufacturer's. Unusual shapes of teeth are sometimes demanded for special cases, when the prosthetic dentist must depend upon his own resources for their production. We occasionally need exaggerated examples of teeth of the third class referred to on p. 227, described as flat-faced, wherein the flatness goes so far as to nearly constitute a concavity of the face of the tooth. When this is the case it will be found impossible to secure such teeth from the dental depots, and the dentist must depend upon the corundum wheel, with which he may make such changes as are required. This may be done by using a wheel of the finest grit, after which the ground surface of the porcelain may be polished with a small wheel made of Arkansas stone, followed by a small wooden wheel armed with oxide of tin mixed with water. This may be done with the teeth of any of the manufacturers, but it is especially successful when teeth of Eng- lish make are used, they being formed of porcelain of such closeness of texture that they may be ground and polished without any material change in the surface. On the other hand, it is sometimes necessary to make additions to teeth in order to bring their forms to correspond with unusual shapes of remaining natural organs. An instance of this occurred recently in the author's practice, in which he found it impossible to match the shapes of some very peculiar lower incisors. These teeth had from early child- hood projected so far beyond the upper incisors as to be practically use- less in the incision of food ; as a consequence, the corrugations which are seen in the incisor teeth of children were still present, although the patient was nearly fifty years of age. The natural teeth had become so loosened that their loss was a question of a short time ; they were broad at the cutting edges and unusually round on their faces. This promi- nence made them a noticeable feature of the patient's face, and after the first attempt to substitute porcelain teeth it was seen that any departure from the form and size of the natural organs greatly changed the ex- pression of the mouth. The difficulty was finally overcome by selecting the exact color from the enamels furnished with the " Downey furnace," described on p. 260. The faces of the teeth were built upon with this SHAPES AND SIZES OF TEETH. 229 material, which fuses at a much lower degree of heat than do the bodies and enamels of ordinary porcelain teeth. They were then burned separately in the Downey furnace of the pattern recommended for crown- work, the corrugations having previously been cut in them with a corundum wheel. The result was so successful that it established the value of the Downey furnace as a most useful accessory of the author's laboratory. The relative positions of teeth in the present state of tooth manu- facture belongs almost exclusively to the dentist himself. In the as- sembling of fourteen teeth in the construction of an upper artificial denture he should bear in mind that teeth are lost through two principal causes — namely, the ravages of decay and premature loosening (pyorrhoea alveolaris). In the first case, decay usually begins early in life, and generally before the teeth are finally lost some have become devitalized — a condition necessarily accompanied by change in color. This is an important feature in the general eifect of an artistically arranged den- ture, and the almost total neglect on the part of both manufacturer and dentist to imitate it is one of the prominent causes for the glaring un- naturalness of their products. Teeth of the frailest class, which have been constantly filled and refilled up to middle age, will generally be found to have lost much of the appearance of regularity which they may have had in early youth. These defects should to a certain extent be imitated. To be natural in appearance teeth must be inconspicuous, in the sense that they must not attract unusual notice. What then could be more startling to the friends and relatives of a patient, whose teeth had always required constant attention on the part of the dentist, than for him to suddenly appear with a denture of pearly whiteness, painfully regular, and in all respects better suited to the age of sixteen or eighteen than to late middle life ? Fig. 263. In the arrangement of teeth serious errors are constantly made by the dentist. The work is usually considered well done if a perfectly sym- metrical arch has been obtained, whereas in life we rarely find a fault- lessly regular arch. Referring again to the classifications of shapes and sizes which have been considered, we not unfrequently find in the third class the flat-faced, angular teeth of that type standing perpendicularly or nearly so, and at their distal approximate sides either quite straight (Fig. 263) or turned slightly outward (Fig. 264). In the first class of round-faced teeth with broad necks the positions of the centrals are nearly perpendicular, with perhaps a slight inclination toward the centre line. 230 MOULDING AND CARVING PORCELAIN TEETH. In the second class the teeth will be found to stand with a slight in- clination toward the centre line, from which the incisors are the starting- point of a symmetrical curve (Fig. 265). Fig. 264. In the arrangement of teeth with reference to the inclination of the front teeth backward or forward, corresponding to the conformation of the face, three somewhat hypothetical divisions of physiognomies are made. The first class is a type of the Anglo-Saxons or their Anglo- American descendants : these are described as having oval cranial con- tour, with forehead slightly sloping, maxillary bones equal in length, the position of the teeth perpendicular or nearly so, to which is due the firm expression of the mouth supposed to be observed in the facial expression of the unmixed native population of the United States. The second class is not confined to any particular nationality, and is distinguished by poor development of the lower jaw, resulting in a re- treating chin. The faces of individuals of this type have a weak ex- pression, and may be found Fig. 265. amongst any nation or class of people. Its direct effect upon the teeth is to cause the upper incisors to incline back- ward to meet the lower teeth. Upper teeth carved or arranged to suit articulations of this class should incline somewhat back of the perpendicular, while the lower teeth should incline forward, so that they may pass just inside of the superior incisors and cuspids. The third type, which is found chiefly amongst a certain class of Celtic origin, is marked by upper and lower jaws of great prominence, causing the teeth to protrude at a sharp angle at the cutting edges. In this facial type both jaws incline forward at an angle of from 70° to 80° ; the upper lip is long and without graceful curves. The facial types above considered refer to individuals with full den- tures, and will serve in a general way to illustrate the inclinations which may be found necessary to the maintenance of the natural expression of the patient's face. There is another point of importance in the manufacture and arrange- ment of artificial teeth which deserves notice before the details of their production are considered. This is the fact that in nearly all normal natural dentures the teeth are in contact and each tooth supports its neighbor. Teeth that stand alone and are without lateral support are CARVING BLOCK TEETH. 231 liable to become loosened by the strain of mastication. It is evident that this provision of nature is for the purpose of preventing too much force from being thrown upon the socket of any one tooth, yet all the sectional-block teeth that are made have permanent separations between them. Natural teeth with separations, when such a condition in the positions of teeth does occasionally occur, impart a peculiar expression to the mouth and face, and porcelain teeth so arranged are at once recog- nized as artificial. Spaces should never be made between artificial teeth unless it be done to imitate a similar peculiarity previously existing in the natural denture. Carving Block Teeth. The early workers in this art seem to have striven for entirely dif- ferent results. The object of one worker was to compound bodies and enamels which would maintain their form during the vitrefying process, regardless of color, translucency, and texture ; that of another, the secur- ing of all these qualities at the expense of stability during burning. Fig. 266 shows a set of teeth carved by Joseph E. Mcllhenny about 1835 ; Fig. 267 represents a block carved by Prof. Wildman some years later. The first has maintained the form and position of the teeth while fusing, but the amount of clay used to secure these qualities has imparted to the teeth the opaque and cloudy appearance sometimes seen in devitalized Fig. 266. Showing faces of front teeth, carved by J. E. Mcllhenny. teeth. In the block carved by Prof. Wildman the teeth have graceful lines, and in color, translucency, and life-like texture have not been ex- celled up to this time ; but the great spaces between the teeth due to shrinkage of tlie body gives them a most unnatural appear- ance. The carved teeth of fifty years ago were generally arranged with holes through ^, ^^ „ ^„r... , '=' „ . *' . T-» j^i i? j_i • Block carved by Prof. Wildman, bhow- them lOr riveting. l^otn OI the SpeCl- ing spaces caused by shrinkage of mens of the work of Wildman and Mc- '^"'^^' Ilhenny were so constructed, as shown in Fig. 268. This was done to avoid the danger of fracture during " heating up " preparatory to soldering. As improvements were made in the composition of bodies and enamels the quality necessary to enable them to withstand high temperatures was secured without loss of life-like color and texture. Carving block teeth is a delicate art, requiring skill, experience, and artistic taste. The simplest natural objects need skill and training in their imitation. The beginner need not expect to faithfully reproduce 232 MOULDING AND CARVING PORCELAIN TEETH. Showing arrangement for uniting blocks to plates : teeth made by Mcllhennj'. the forms of natural teeth in porcelain without first having studied the shapes of many different types of those organs, when, if he possesses artistic ability, more or less success may attend his efforts. Hand-carved blocks have not Fig. 268. reached a very high standard as reproductions of the natural or- gans, and are inferior from an artistic standpoint to the sectional- block teeth of the best manu- facturers of the present time. The works of the few carvers who have given their attention to this branch of tooth-making are exceedingly conventional, and vary only in size : hence carved block teeth have become nearly obsolete. In carved work the liability to warp- age and " sprawling " of the teeth is greater than in moulded work, and chance has much to do with the final result. Where teeth are to be carved for special cases it is necessary to first finish the plate, and then obtain the wax articulation, care being taken to get the exact height and fulness required by the case. The correct centre line is then to be marked. The plate, with the trimmed wax, is placed on the plaster model : in the sides of the model concave retaining-points are cut to assist in retaining the outside walls of plaster, the formation of which is the next step in the operation. The model is then varnished, allowed to dry thoroughly, and then oiled. The })laster is mixed rather thick and built upon the model with a steel spatula until it entirely covers model and wax ar- ticulation to the thickness of half an inch : it should extend above the edge of the wax to a little more than one-eighth of the proposed length of the block, to allow for shrinknge in burning. The walls are usually made in three sections, the two side walls being made first, and the front wall next, each wall being made somewhat longer than the required length of the block, to compensate for shrink- age. A vent-groove must be cut at and below the edge of the gum to receive the excess of body (Fig. 270). The surface of the walls against which the plastic body is to be moulded must be lined with tin-foil, made to adhere to the plaster by means of shellac varnish. The inside wall is made by building a '^^UIL.-^ CARVING BLOCK TEETH. 233 mass of plaster upon the plate and against the inside of the articulating wax. This should also be lined with tin-foil. Fig. 269 shows the cast with the articulating wax, the inside wall (A), and outside walls (D E F) in position. Fig. 270 shows all the pieces separately — the inside wall by A ; the articulating wax by B ; the model by C ; the inside walls hy D E F ; the vent-grooves by the dark line in the three latter. Fig. 270. Mixing- and Moulding- the Body. — The dry body is mixed with perfectly clear water, to which has been added gum tragacanth, 8 grains to the pound of body. Freslily mixed body is too friable for either moulding or handling. It, however, acquires plasticity and toughness by age, and is greatly improved by being kept wet for several weeks before using. The composition is mixed in a suitable porcelain or glass vessel to the consistency of cream, and poured into a porcelain bowl and allowed to 234 MOULDING AND CARVING PORCELAIN TEETH. settle. When the water on top is quite clear it is drained off by tipping the bowl, care being taken to prevent any of the composition from flow- ing out with it. To prevent any of the coarser parts of the body from settling to the bottom, it must be mixed again very thoroughly by means of an ivory or bone spatula : this must be done with the utmost care, to prevent air-bubbles from being confined in the body, as such an accident Fig. 271. B c Carving instruments. might be the cause of complete failure of one of the blocks ; for if the smallest portion of air becomes enclosed in the block and escapes detec- tion, it may expand enormously during the burning process and distort CARVING BLOCK TEETH. 235 the block beyond remedy. The jarring cau.sed by gently pounding the bowl on the table will often induce disengagement of air-bubbles and force them to the top. The body is next to be freed of its surplus moisture by gentle heat, which also further assists in the expulsion of air. When it acquires the consistency of fresh putty pieces can be cut off as required for moulding. The remainder must be kept tightly covered, and sufficient water occasionally added to keep the mass plastic. The inside wall, A, is now placed in position, and, together with the outside wall, E, and that portion of the plate to be covered by the block, given a thin coat of olive oil. A piece of body somewhat larger than is required in the formation of the block is cut from the mass and worked with the fingers to a convenient shape on a slab of plate glass or porce- lain tile : by a sliding motion it is then lifted from the slab and placed on the model, and with the fingers worked against the inside wall in the space upon the ridge previously occupied by the articulating wax, B. The outside wall is now quickly applied with sufficient firmness to bring it quite close to the model ; the vent-groove shown by the dark line on the walls in Fig. 270 will prevent any resistance being met with in the surplus body, which otherwise might be forced between the wall and model. The walls are held in position until the body is dry enough for their safe removal. The drying is done by applying heat to the outside of the walls with the flame of a spirit-lamp : the walls are then removed, and the Fig. 272. moulded block lifted with great care from the model and placed under a bell-glass until needed. Tools Used in Carving Blocks. — These are few in number and simple in character. Figs. 271 and 272 represent the carving tools : D, a small penknife blade set in a han- dle of cedar or poplar wood on account of its lightness, is the carving knife and performs the greater part of the work ; A, string bow formed by stretching a piece of fine cotton thread across the bend of a piece of whale- bone about 7 inches in length ; B, pro- portional dividers, shown half size in the illustration ; C, enamel tool ; E, bone spatula ; F, spoon scraper ; G, drill, made by flattening and tempering a piece of steel wire ; H, excavators for cavities ; I, pin-tweezers. The cuts give actual sizes of all the instru- ments except the dividers. All bodies contract in burning, the amount of contraction depending to some extent upon their composition and the amount of compression they receive before burning : thus, carved blocks will contract about one- F Carving instruments. 236 MOULDING AND CARVING PORCELAIN TEETH. sixth of their entire bulk, and moulded blocks somewhat less. Hall gives one-eighth as the allowance generally made for shrinkage and loss in grinding to fit the plate after burning, but he refers to the body alone, and does not include in the " one-eighth " given the addi- tional shrinkage of the point enamel added after the shrinkage allow- ance is made in the carving previous to biscuiting. If the shrinkage were to be measured by instruments of precision, it would probably be found to be about one-sixth. The allowance for shrinkage is arranged with the proportional divi- ders set to one-eighth increase, the short points being used to measure the articulating wax from gum edge to articulating edge. The respective distances are marked on the cast as shown on G, Fig. 270. The block is carefully placed on the plate and suppprted by the inside wall ; the proper height with shrinkage allowance is then scribed on it with the adjusted dividers, one point resting in the horizontal line, while the other touches the block. By drawing it gently along the top of the block a distinct mark is made, indicating the point to which it is to be cut down. This cutting down is done by removing the block and lightly grasping it between the thumb and index finger of the left hand, with the middle finger curved under it in a manner to form a cushion or support for it. The knife is then brought into use, and all material above the line made by the dividers cut away. So fragile is the un- burned body that the slightest excess of pressure may crush the block : a gentle yet firm handling of the unburned material will, however, come to many workmen with practice, but there are undoubtedly some who never can acquire the ability to go through the different stages of carving an entire upper and lower denture without an accident, for the blocks must be taken up and put down many times before they are ready for the final burning. Fig. 273. Method of holding block when carving the labial side. The widths of teeth are next to be marked off on the block. This is done by first marking the centre line, and then indicating on each side of it, by a shallow incision in the body, the desired size of the centrals : CARVING BLOCK TEETH.. 237 if the latter be medium in width, the laterals should be two sizes nar- rower, cuspids one size narrower, than the centrals. In arranging for shrinkage a good plan is to select either a natural or porcelain tooth of the desired size, which, for the sake of example, may be assumed as 16 forty-eighths of an inch wide. The width in carving must be in- creased 'to allow for shrinkage, so that after burning the carved teeth will be exactly the size of the sample. To accomplish this the sample tooth is measured by the small points of the dividers ; the large points will indicate the increase. In the first carving no attempt is made to obtain precision of form or full relief, as shown in Fig. 273. The teeth are but superficially laid out, and purposely left flatter than would be desirable when finished. The first step is to cut an inverted A-shaped space at the centre line to represent the space between the central teeth : this is repeated between centrals and laterals and laterals and cuspids. The edges are slightly rounded, and by a circular cut of the knife-point the necks of the teeth are formed, while at the same time the correct lengths are given them. During this preliminary work the block is held gum upward : it is now to be reversed and the points of the gum between the teeth are carved down, and both ends of the blocks cut square for jointing to the side blocks. The inside is then trimmed to the proper thickness, and the sulci or depressions peculiar to the palatal surfaces of incisors and canines are formed with the instrument F, shown in Fig. 272. Separa- tions are made with the bow-saw A (Fig. 271). The block is then ready for the platinum pins. If the blocks are to be soldered, a level surface is left from the point at which the palatal surfaces of the teeth end to the portion intended to rest upon the plate. Into this level surface holes are drilled for the reception of the pins. These holes are made by rotat- ing a small drill, as shown in G (Fig. 272), between the thumb and index finger. The drill, made of a piece of No. 20 steel wire with the end flattened to the width of No. 13 of the standard gauge, will form a hole large enough for the reception of the head of the pin. Two-thirds of the pin should be imbedded in the block. The pins are put in position by means of the tweezers shown in Fig. 272, and a thin mixture of body and water floated around them by means of a small camel's-hair pencil, care being taken that the mixture is carried quite down to the heads of the pins without enclosure of air. If the blocks are designed for mounting on rubber base, a recess must be made for the pins, as shown in Fig. 275. If the blocks are very fragile, the holes may be drilled and the pins put in after they are biscuit-burned. Biscuiting. — Biscuit-burning is the partial vitrefying of the blocks by which they are hardened sufficiently to admit of handling without danger of breaking, and, what is even of greater importance, their form is to a certain extent permanently fixed, so that they will not become plastic or semifluid when the wet enamels are laid on them. The blocks are placed on a fire-clay slab called a " slide," and thoroughly dried by gentle heat before they are put in the muffle and exposed to a bright-red heat. The burning must be carried beyond the point where the body can no longer be softened by water, and yet not be too hard to cut. It should remain porous enough to absorb the water from the enamels as 238 MOULDING AND CARVING PORCELAIN TEETH. they are laid on, otherwise enamelling will be found impossible or nearly so. The slightest glazing of the surface must be avoided. About the hardness of a piece of cuttle-fish bone is the proper condi- tion. The biscuited blocks may be cooled in the air without danger of cracking. Enamelling-. — Enamels should be kept in small glass jars provided with tight stoppers to exclude the dust. Each enamel must be carefully kept from accidental admixture with others, and the jars should be labelled with the number, color, and other explanatory remarks written plainly thereon. A small piece of body, with some of the enamel fused on it, may be tied to the jar ; this affords absolute accuracy in the deter- mination of the color, when burned, of the contents of each jar. More failures occur in enamelling than in any other part of block- carving. Great care is constantly required to see that the enamel is laid on of the proper thickness, that it is uniform in quantity, that it does not unite with the body, and that point and base enamels are so applied that a perfect blending of the two colors may result. The coat of enamel on the teeth and gums should be at least ^4^^ ^^ ^^ mah thick ; the development of the translucency of the spar and brilliancy of the colors demands at least that quantity. The body, having clay in its composition, is opaque, and would show through a thinner layer of enamel and impart to the teeth a flat and lifeless appearance. In mixing enamels 15 grains of gum arable to each ounce of enamel is used, to prevent the coloring materials from settling when mixed with water, to make the enamel work smoothly, and to enable it to be handled when dry without rubbing off. In addition to the point and base (neck) enamels alluded to in the description of the manufacture of these materials, there is a class of enamels used for staining teeth in imitation of the dark spots on the cutting edges of much-worn incisors and cuspids of middle-aged and elderly patients, and for reproducing in the porcelain teeth the discolor- ation incident to devitalization of the natural organs, etc. These are usually the darkest shades of brown and olive. Enamels are mixed with clean water until the mixture presents a cream-like appearance. They are then applied with camePs-hair pen- cils of different sizes. The first layer is placed on the necks of the teeth, extending to near the cutting edge, tapering in quantity as it approaches the point. In applying the enamel the block is held gum upward, care being taken that the enamel adheres to the body, and, if any creases occur, to wet them down by touching them with a wet camel's-hair brush, and that all ridges be smoothed or trimmed down with the small carving knife. When the point enamel is applied the block should be reversed, so as to be held with the teeth upward. The brush is partly filled with the point enamel, and applied lightly to the cutting edges of the teeth to the thickness of about a^th of an inch, and carefully worked down with a full brush in the direction of the neck of each tooth. All the neck enamel previously laid on must be quite covered, but the point enamel should be applied very sparingly as it approaches the margin of the gum, full thickness being given at the cutting edge only. Some experience is required in laying on the point enamel to avoid CARVING BLOCK TEETH. 239 wiping off the neck enamel at the same time. It is desirable that the latter should show through the thin layer of the former and be toned and blended by it. To prevent mixing of the two enamels, and the consequent injury to the effect of each, the brush full of enamel should be drawn lightly over the teeth in a manner to allow the enamel to be drawn from off the point of the brush upon the block. The edges may be made even by touching them with a wet camel's-hair brush. It is essential that the enamel be carried well between the teeth. After completing the enamelling, the carving and shaping is begun by separating the teeth from each other with the string bow. The con- tour is now carefully formed, the separations at the necks being made by cutting inverted A-shaped spaces between them. The block is again reversed with the cutting edges down, and the necks given distinctness by well-directed sweeps of the knife to form the semicircular lines between the necks and the gum. The faces of the teeth are then given the character of the type which they are designed to imitate. It must be remembered that the tendency of the vitrefying process is to flatten down prominences and to round off corners ; therefore all the features and outlines of the teeth should be somewhat exaggerated, so that the finished block may retain the requisite degree of individu- ality. Forming the contour of the teeth from the neck to the point is the most important part of the operation of carving, and the style of teeth needed for the case in hand will depend upon the amount of prominence given the enamelled block. With a definite model in mind the carver must take into consideration and anticipate all the changes incident to the burning process. Some well-thought-out systematic plan for carving teeth, and one that will include the general characteristics of the natural teeth, will be found of great convenience, so that close imitations may be obtained. A small, well-selected collection of natural teeth should be made, such as will serve the purpose to show the wide ranges of sizes and shapes existing in the natural organs. Gum Enamel. — This enamel requires in mixing at least 20 grains of gum arable to the ounce of enamel to prevent it from settling to the bot- tom of the cup on account of its greater coarseness. It is first applied to the festoons between the teeth with the point of the carving knife ; the rest is easily put on with the brush, care being taken to carry it close to the necks of the teeth, but not to allow it to overlap the necks. It is not necessary to lay the gum enamel on very smoothly ; the result will be better if left rough and somewhat uneven : fusing at a lower tempera- ture than the point enamels, it will take care of itself in burning, and a moderate degree of unevenness of surface tends to produce a natural effect in the finished block. The gumming process in carved work is, as a rule, poorly done. It is not always recognized that the surface of the natural gums have cha- racteristic irregularities and variations in degrees of shade and color. The ridges around the necks of the teeth should be carefully imitated. The shade of the gum is a little deeper between the teeth than immedi- ately over the roots : this should not be overlooked. The palatal surfaces of the teeth and inner surfaces of the blocks 240 MOULDING AND CARVING PORCELAIN TEETH. should be given a thin layer of point enamel to serve as a glazing to the rough surface of the body, after which the blocks are ready for burning, and should be allowed to dry perfectly for that purpose. (Figs. 274 and 275 show a finished front block.) Fig. 274. Fig. 275. Labial side ol flnislnd block. Lingual side of finished block. If the teeth are long, and it is desirable to maintain close contact between centrals, difficulty may be encountered in preventing " spread- FiG. 276. Fig. 27'J ing" while burning. This may be prevented by tying the teeth together with a loop of body placed across the separations from one tooth to another. It is done by mixing some body with water, so that it can be ap- plied with a small brush. After the teeth are burned the loop of body can be ground away with the corundum wheel. Fig. 276, A, shows the spreading as it often occurs during the burning of a block not so reinforced ; Fig. 276, B, shows the manner of arranging the body to prevent spreading ; Fig. 276, C, shows block from same mould in which no change has occurred in consequence of the reinforcement of body on inside. White, opaque spots are frequently seen on natural teeth : these may be imitated with an enamel of the following proportions : An example ot "sprawling Opaque E'namel Kaolin, Feldspar, ■k oz. Mix well. Before burning small depressions are cut in the soft enamel and filled evenly with the opaque enamel. Staining Teeth. — To closely imitate certain peculiarities of the natural organs it is sometimes desirable to stain their cutting edges to represent the dark-brown dentine often noticed betM^een the outer and inner plates of enamel in the much-worn teeth of middle-aged men who CARVING BLOCK TEETH. 241 have used tobacco ; or, again, to occasionally darken a tooth in imitation of the color of teeth in which the pulps have died. The following for- mulae may be used Avhere properly indicated : Dark-greeniiih Stain : Platinum sponge, Titanium oxide, Feldspar, Enamel tlux, Dark-yellow Slain : Titanium oxide. Gum frit, Enamel flux, Black Stain : Iron scale, Feldspar, 5gr. 10 " 10 " 2 " 20 gr. 4 " 2 " 10 gr. 5 dwt. These stains, like the otlier enamel frits, vary in depth according to the state of fine division attained ; they should be kept in small glass jars, with fused trials fastened outside for reference. Cavities for filling may be cut with excavators in the biscuited teeth. As a rule, cavities for filling in artificial teeth are objectionable. Occasion- ally, however, a patient loses a tooth which has been conspicuously filled with gold for a number of years : in such instances its replacement by an ordinary tooth might constitute so noticeable a change as to war- rant the attempt to imitate the filled natural tooth. Other methods have been devised to produce block teeth for special cases with less expenditure of time, and to avoid the liability to accident so common in the plan just described. In the various processes sug- gested the tendency has been to adopt some plan of moulding instead of carving, and to make the work more a mechanical procedure than one which requires a high degree of artistic talent. Fig. 278. Biscuited teeth. In one process biscuited plain teeth were placed in position while the body was soft (Fig. 278 gives front and side views of the forms of bis- cuited teeth designed for this purpose), but this plan has been abandoned on account of the frequent failure of the partly burned teeth to unite with the soft body, which was often only apparent after the teeth were burned. Another process consists in making movable matrices of different sizes and styles to correspond to the classes of teeth described in this chapter, the object being to do the enamelling and moulding of the entire block in one operation. These matrices are made of very thin sheet ifi 242 MOULDING AND CARVING PORCELAIN TEETH. brass, about No. 32, stamped over hard brass or steel dies : the die must necessarily be an accurate copy of the teeth desired, with Fig. 279. Enamel cups. allowance for shrinkage and other changes incident to burning. These cups are arranged on the wax articulator precisely in the position required in the finished Fig. 280. block. Walls of plaster are then made in the manner described on page 232. When hard enough the walls are removed, bringing with them the brass enamel cups, as shown in Fig. 279. The gum surfaces of the walls are then lined with tin-foil ; the enamel cups are to be made fast, should any become detached from the wall, by means of hot wax or resin and wax cement. The cups and walls are then oiled, the enamel is placed in the cups, point enamel first, and then the base. The body is applied the same as in ordinary carved work (Fig. 280). The heat of a small spirit lamp is applied until the body is dry (enough and the wax or cement sufficiently softened to admit of the removal of the wall. The cups will be found adhering to the block : these must be removed without injury to the moulded teeth. Dr. W. R. Hall, to whom is due the credit of devising this method, found the dif- ficulties of making the dies and forming the cups very great, the very large munber of the latter needed for a working set, over a thousand being required, complicating instead of simplifying the production of block teeth. On the other hand, the method possesses the advantages Brass cups in position for moulding. CARVING BLOCK TEETH. 243 over carved work of affording more perfect and finished teeth, greater facility in their duplication, less liability to accidents, superior density, and uniformity of distribution of the enamels. Brass Moulds for Porcelain Teeth. — Mould-making is generally thought to require peculiar talents and a high degree of mechanical skill. It certainly does demand artistic talent, but the mechanical part of it is not particularly difficult. It includes the carving of the plaster blocks, making the plaster pattern of the mould, casting it in hard brass or bronze, and the " cutting " or finishing of the mould. The plaster blocks constitute the design, and are a complete set of block teeth carved in plaster, with allowance made for shrinkage and other changes which take place in the vitrefying process. This part of the work must be done by an artist and one who has knowledge of the several classes of human teeth. These designs should always be made from natural teeth, but the custom amongst manufacturers is to use plaster face-blanks, made from plain teeth moulds, somewhat larger than is needed for the set to be made, to allow for carving to the proper size and shape. The blanks are arranged on a rim of wax similar to articulating wax ; the gums are formed of paraffin or the pink combina- tion of paraffin and wax ; broad spaces are left between the centrals ; the cuspid and first bicuspids and the second bicuspids and first molars, as sectional blocks for an entire upper denture, are divided into six pieces. Each block must be provided with a slight excess of material at the joint, to afford sufficient latitude in fitting them together. A wall of plaster about one-fourth of an inch in thickness is run on the outside of the model, so as to include the entire set of blanks : when hard enough it is trimmed so as not to exceed in height the cutting edges of the tooth blanks, varnished, and oiled ; an inside wall is then made of plaster of Fig. 281. the same height as the outside one. The inside wall is removed when hard in one piece ; the outside one is cut into six pieces with a thin saw- blade, the cut being made between the centrals, the cuspids and bicus- pids, and the bicuspids and molars at the spaces shown in Fig. 281. The sections thus made arc then separated from the model. Both the outside and inside walls are trimmed, varnished, and laid aside to dry. The removal of the blanks from the model is next in order, and both walls are given a coating of shellac varnish. Fig. 282 shows the walls made for a lower set of plaster blocks. The walls are now to be placed on the model and secured in position with twine or wire : they are then oiled, and plaster mixed to the consist- ence of cream is first painted over the surface, as representing the Tooth-blanks arranged on cast. 244 MOULDING AND CARVING PORCELAIN TEETH. teeth, with a camel's-hair brush, when the residue is run in between the inside and outside walls and allowed to set thoroughly before removal. If the plaster has been carried into all depressions and inter- stices between the walls, a continuous set of plaster blocks will be the result. These are separated into six sections by means of a thin saw- FiG. 282. View of the walls and cast, separated. blade, as shown in Fig. 282, the six front teeth in two sections of three each, the first and second bicuspids of each side in two other sections ; the molars are divided in the same way. These plaster blocks now require trimming on the inside, the carving of the masticating surfaces of the bicuspids and molars in imitation of the natural organs, and the cutting of a recess for the pins, as seen in Fig. 283. The ends of the blocks, or those parts technically called the joints, must be trimmed so that they will taper sufficiently to ensure their safe de- livery from the plaster mould, as shown by the pin sides of the plaster blocks in Fig. 283. If not properly bevelled at all points, so that no undue retention will occur, it may be necessary to remove the pattern CARVING BLOCK TEETH. 245 blocks piecemeal. The plan of such a mould would then be found to be defective, and, as may readily be surmised, it vyould not be possible to Fig. 283. Plaster blocks, finished. obtain a brass mould from a pattern in which so serious a fault existed. After these details have received careful attention and the blocks have been trimmed and carved to the satisfaction of the workman, they should receive at least two coats of shellac or sandarac varnish. The Plaster Mould. — The preparation of the plaster mould is the second part of the process of mould-making, the first part being the modelling of the designs in the form of plaster blocks. These designs are really the foundation of the whole system, and require in their pro- duction artistic talent and knowledge of the forms of the different types of human teeth. With the exception of the cutting or finishing of the brass mould, the rest of the process is purely mechanical, but the carving Fig. 284. Foundation plate. of the models and the finishing of the face sides of the brass moulds should be done by the same hands. The mechanic to whom this part 246 MOULDING AND CARVING PORCELAIN TEETH. of the work is usually entrusted is liable to cut out many of the lines and depressions observed in the natural teeth and imitated in the plaster models. By referring to Figs. 288 and 289 it will be seen that the finished mould consists of five pieces — the face side, the pin side, two end- or crown-pieces, and a key-piece. These pieces have all to be made in plaster to serve as patterns from which to cast facsimiles in brass. The plaster blocks are arranged on a foundation plate. This plate can be made of brass or zinc, as shown in Fig. 284, 6^ inches long, 3 inches wide, and J of an inch thick, with oblong recesses to receive the blocks — those for the front blocks 1 inch long and J an inch wide ; those for the bicuspids, f of an inch long and J an inch wide ; and those for the molars, ^ of an inch long and ^ an inch wide. The black lines on the plate are used as guides to measure from in placing the blocks; the round holes at the ends are to receive the pins seen on the frames in Fig. 285. The plaster blocks are placed on the foundation plate faces upward, wdth the cutting edges opposite to each other, as seen in Fig. 286, and are then secured in position with beeswax, clay, or putty, which also marks the correct line of division between the two halves of the mould. This is a very important detail of mould-making ; upon its correct man- agement depend the successful application of the enamels and the safe delivery of the moulded porcelain blocks. This line of division should extend along the middle of the cutting edges of the incisors and canines and the gum edge, but should include but little of that portion of the block called the joint. By referring to Fig. 207 the reader will see that the face side of the mould gives merely the distinct outline of the entire face of the block, and that the bulk of the block is represented in the pin side ; yet the edges of the face side of the blocks should be sufiiciently Fig. 285. Brass frame. well defined to assist in holding the enamels in position when the mould is pressed together. The front blocks are secured to the plate two six- CARVING BLOCK TEETH. 247 teenths of an inch from its centre line ; the bicnspitl blocks, three- sixteenths of an inch from the line ; the molar blocks, four-sixteenths from the line. The side blocks are arranged farther apart at the end near the molars than at the other, to allow for a tapering key, as shown by C in Fig. 289. If all spaces between the block and the foun- dation plate have been stopped with clay or putty, the ])late with arranged blocks is ready for the frame. The frame is in two sections made of polished brass, one section made to articulate with the other by means of pins and corresponding holes, as seen in Fig, 285. The inside tapers so that the plaster mould when hard may deliver without difficulty. Tliese frames measure 4f inches in length and 2f inches in width, each section being f of an inch high with a thickness of ^ of an inch. The part with pins is well oiled on its inside and placed on the plate. The plaster blocks having been oiled, the plaster is mixed by dropping it into water and allowing it to settle without stir- ring, so as to exclude air ; the excess of water is then poured off; the blocks carefully coated with thin plaster by means of a small camel's-hair pencil ; the rest of the plaster is then poured in and levelled off even with the top of the frame with a spatula. When the plaster becomes hard the plate is removed and the face side of the pattern is secured. The blocks are then carefully taken from the face side of the plaster mould, and, if any of the edges are broken, they must be repaired with wax or plaster and made smooth. After the removal of the blocks the mould must be varnished with shellac or sandarac and allowed to dry thoroughly, when the blocks are replaced. The space between the bicuspid and molar blocks is filled by a piece of wax, as seen in Fig. 286, to form the depression intended for the end-pieces and key in the Fig. 286. Pin side of plaster mould, witVi plaster blucks and wax in position. pin side of the mould. The whole fixture is then thoroughly saturated in clean water, the surfaces coated lightly with oil, and the other section of the brass frame placed in ])osition and filled with plaster mixed and applied in the manner previously described : this forms the pin side of the mould. The two sections are easily separated when the plaster has hardened sufficiently by introducing a knife-blade between them and carefully prying apart. The plaster blocks will usually be found in the pin side of the mould, because the greater portion of the block is embraced in that part of it, and consequently offers more surface for 248 MOULDING AND CARVING PORCELAIN TEETH. retention than does the face side. The brass frames are next to be removed from each part of the plaster mould by tapping the former gently with a small wooden mallet. The blocks are then to be removed from the pin side of the mould : this must be done with the greatest care by inserting a sharp excavator or knife-point under the block and gently prying it out. If any part of the mould is broken and carried away with either of the blocks, the piece may be fastened back to its proper place with thick shellac varnish, or, if lost, the defect may be repaired with beeswax. The crowns or masticating surfaces of the bicuspids and molars are formed by end-pieces held in place by a wedge-shaped piece of brass, as shown by A, B, and C, Fig. 289. The wax seen in Fig. 286 must be taken away from between the side blocks, and the blocks removed and carefully cleaned ; the space formed by this piece of wax must be trimmed so as to increase its width about three-sixteenths of an inch, its floor made perfectly flat and its sides perpendicular, and arranged to taper toward the end nearest the front blocks, where it should be slightly narrower than at the molar end of the space. This space at its floor and sides must be level and true, or the crown-pieces and key A, B, C (Fig. 290) will not fit well in the finished mould : the surface of the Fig. '2^1 Face side of plaster mould, with temporary key. recess is then varnished. A temporary key of brass is placed midway in this space and secured with wax, as shown in Fig. 287, and allowed to extend a quarter of an inch beyond the end of the mould. The plaster mould is then oiled and put in w^ater to drive out the air ; the side blocks are oiled and put in place ; the face side of the mould is oiled and put in position, and the two sides tied together. Plaster, mixed thin, is then run into the spaces on each side of the temporary key extending beyond the mould to the end of the key. After the plaster is hard the temporary key is carefully drawn out by means of pliers, when the crown-pieces may be easily removed. All the parts of the plaster mould are now to be thoroughly dried by gentle heat ; grooves are then cut around each block in both sides of the mould to allow for the escape of the excess of body and enamel usual in moulding teeth. All parts of the plaster mould must be made as smooth and perfect as possible, as its condition, whether good or bad, is duplicated in the brass castings, where it is much more difficult to correct imperfections or faults CARVING BLOCK TEETH. 249 than in the plaster. When entirely finished and thoroughly dried all the parts of the plaster mould are to be varnished with shellac and Fig. 288. Face side of brass mould. allowed to dry thoroughly, when they are ready to be sent to the foundry to be cast in hard brass. Fig. 289. Pm side of brass mould Fig. 288 shows the face side of the finished brass mould. Fig. 289 shows the pin side, A and B the crown-piece, C the key. Retaining Fig. 290. Crown-piece. pins of brass are put in to prevent movement of the crown-piece during moulding : the heads of these are seen in Fig. 289 between the molar and bicuspid blocks. 250 MOULDING AND CARVING PORCELAIN TEETH. Cutting- and Finishing Brass Moulds. — Undoubtedly, moulded teeth afford opportunities for better results in the imitation of the natural organs than does carving, but the original designs, as well as the cutting and finishing of the moulds, must be executed by a higher class of workmen than have as yet been entrusted with that exceedingly artistic work. Much of the work of the mould-maker is apparently done rather from habit than through any clear insight into the actual requirements of his task. The horizontal depressions on the faces of the central and lateral incisors are usually too stiff and distinctly defined, while their lines are straight and unnatural. These, however, are de- fects of execution rather than of the system of mould-production, and will doubtless eventually be remedied. The tools required in mould-finishing are comprised in the following list: Two or three flat files, 10 or 12 inches long, bastard and smooth- cut, for finishing the outside of the mould ; small files, flat and half- round, for the inside ; a half-dozen gravers, such as are used by wood- engravers, flat and round-edged, of the different sizes shown in Fig. 291 ; a bench-vise with jaws about 3 inches wide ; an upright breast- FiG. 291. Gravers, of Stub's steel. drill, with three sizes of Morse drills for adjusting the guiding pins ; taps and dies for the same ; two pairs of steel dividers ; a pair of steel callipers ; a steel square, 4 inches long, for truing up the mould ; a hack saw, for sawing off the pins ; a steel clamp, to hold the two sides of the mould together when drilling the holes ; a 30-pound anvil ; a 4-pound hammer ; a taper reamer for the guiding pin-holes. An unskilful workman can do much harm to the brass mould in the cutting and finishing. The graver should not be used to change the contour or lines of the teeth : any good founder can reproduce all the parts of the plaster mould in brass in so nearly a perfect condition that the gravers will be needed only to finish the surface of the mould, but not to change it. Brass or bronze, like other hard metals, when cast will shrink somewhat, and thus the brass casting becomes smaller than the plaster model of which it is a facsimile : in finishing the sur- face of the depressed teeth and gums in the brass mould the workman will necessarily enlarge to some extent the reversed representation of the blocks to the original size of the plaster models, and the work should be done with such precision that the latter can be placed in the brass mould and fit as though they had been moulded in it. CARVING BLOCK TEETH. 251 A hard bronze, containing about 15 per cent, of tin, is better adapted for moulds than is ordinary brass, as it affords a sharper casting and the requisite degree of hardness to prevent the moukl from yielding when exposed to heavy pressure. When the castings are received from the foundry it will be seen that the edges along the line of division of the blocks on the face and pin sides of the mould do not touch when these two parts are placed together : this is due to the unequal contraction of the metal, and must be corrected by filing down the high parts, so that all edges will meet and the two halves of the mould fit together without rocking. After fitting together the two sides of the mould, trial blocks of plaster should be made, to ascertain if the outlines of the blocks meet properly. The trial blocks, made by pressing plaster between the two halves of the mould, will indicate any defect in adjustment. If, how- ever, it is found that the outline edges are quite together, and that the relation of one half to the other is correct, the guide pins are to be put in, in order that the relation of the parts be permanently fixed. This is done by firmly holding the two parts of the mould in a steel clamp, and then drilling the holes for the pins entirely through each side with a three-sixteenths of an inch drill. One of the guide pins is placed in the face side of the mould opposite the right central, the other in the pin side opposite the left molar. They must be permanently screwed, one in each side of the mould, as shown in Figs. 288 and 289. After the holes are drilled, the one in the face side opposite the central and the one in the pin side opposite the left molar must be screw-tapped to receive the screw end of the guide pins ; the other end of the pins must taper slightly near its extremely so as to freely enter the hole opposite to it ; but the pins must fit close enough to prevent lateral movement when the two parts of the mould are quite together. These pins should be made of steel wire not less than three-sixteentlis of an inch in thickness. The outside of the mould is then to be squared and finished : this may be done either in a lathe or by filing guided by the try-square and cal- lipers, for it is very important that the mould when the two parts are together should be uniform in thickness and perfectly level, as there is danger if these conditions are not secured of its being sprung out of shape by the press in moulding teeth. The next step toward the completion of the mould is the fitting of the end-pieces in the space between the back blocks : the floor of the space must be filed perfectly flat and level, and the side made perpendic- ular ; the crown-pieces where they are in contact with the key are made smooth and true ; the taper key, C (Fig. 290), is made to fit between them and holds the crown-pieces securely against the perpendicular walls of the space alluded to above during the operation of moulding teeth. This key is made longer than the crown-pieces, so that it can be driven between them with a wooden mallet to facilitate its removal. To prevent the crown-pieces from sliding back while the mould is under pressure, two brass-headed pins are riveted in the pin side of the mould between the bicuspid and molar block, as shown in Fig. 289, the pin being partly in the mould and partly in the crown-pieces. The cutting and smoothing of the gums and faces of the teeth in tlie castings is not, as is generally believed, a very difficult mechanical ope- 252 MOULDING AND CARVING PORCELAIN TEETH. ration ; it does, however, require artistic skill and judgment. The fine lines of the plaster pattern are made less distinct by the casting of the metal. The gravers are to be employed to restore the definiteness of outline and contour, and great care must be taken in doing this to avoid change or obliteration of the characteristic features of the original pat- tern. The gravers should be of the best quality of steel tempered to a straw color ; they must be kept ground to a long bevel and a keen edge, the latter being made by means of an Arkansas stone : the gouge-shaped graver is used at first to cut a clean and smooth surface on the part of the mould reprCvSenting the faces of the front teeth. A plaster set of teeth should then be made, Avhich, on comparison with the original pat- terns, will indicate that further cutting is needed to bring the mould to correspond exactly Math them. The pin side of the mould will require trimming with the flat or chisel-shaped graver to give it a smooth sur- face, and to bring the size to that of the original pattern, which should fit perfectly into the brass mould as though it had been moulded there ; and this is a good test for the accuracy of the brass casting. During the cutting repeated trials should be made with plaster to see if the edges come properly together with no overlapping ; and as the cut- ting proceeds it will be necessary for the workman to frequently see the reverse aspect of the teeth : this he does witli black try-wax, which is made by mixing beeswax and lampblack with a few drops of turpentine. Small pieces of this wax are held in the hand while cutting, the warmth of the hand being sufficient to soften it : in this way the mould-maker is able to take impressions of the concavities of the teeth as the work proceeds. Care is required in carving the original patterns to form the margins aronnd the necks of the teeth, so that they are sharp and sufficiently well defined to keep the gum enamel from mixing with the crown enamel when the mould is pressed. The mould-trimmer must be cautioned against obliterating this line of deinarkation between crowns and gum. The finishing of the pin side of the mould is a purely mechanical operation, and is done with square-edged gravers of several different sizes. In finishing corners and levelling straight edges a small variety of square-edged punches can be used to advantage. When the mould is complete in respect to size and form of the teeth, another set of plaster blocks should be made in it, for the purpose of determining whether the blocks leave the mould readily when slightly tapped M'itli a wooden mallet. If the blocks are difficult to remove, it will be evident that retaining points exist which retard their delivery : these are easily discovered by the abrasion they make upon the plaster, and such points should be bevelled sufficiently to allow the blocks to drop from the mould without injury wlien gently tapped by the mallet on its sides or ends. Finally, small holes are to be drilled in the pin side of moidd for the platinum pins ; these holes are drilled perpendicularly to the face of the mould and parallel witli each other, five for each front block, four for the bicuspid blocks, and three for the molar blocks. The mould is now to be thoroughly cleansed of all particles of brass, and is ready for use. Moulding and Burning Block Teeth. — The first step in moulding is to oil tlie brass mould and put the platinum pins in tlie small holes drilled for their reception in the ])in side of the moulds. The point CARVING BLOCK TEETH. 253 enamel is then put in the face side of the mould, and arranged with a small spatula to the full thickness at the point and tapered down sparingly toward the neck. A thin coat of point enamel is placed on the lingual side of the front teeth and on the masticating surfaces of the bicuspids and molars. The mould is then laid aside to dry before placing the gum enamel in place. Some makers of teeth use but one enamel : instead of applying a yellow neck enamel, they allow the body to show at the neck of the tooth ; this is probably done to save time and labor, but it does not afford the best results as to translucency and natural appearance. The gum enamel is mixed with water and made just stiff enough to stay where it is placed by the enamel spatula, and is then spread evenly over the gum surface of the mould, the thickness being ascertained by touching the point of the spatula to the mould at every eighth of an inch. The placing of the enamel requires more experience than does any other part of the moulding process. The gum enamel must be placed close to the necks of the teeth, but must not be allowed to im- pinge upon the crowns : when complete it is allowed to dry partially. The body is applied in small pieces slightly in excess of the quantity needed for each block. These are taken up with a small spatula, formed into balls, and laid on the pins in the pin side of the mould. The two sides of the mould are then placed quickly together, put under the press, and the lever applied to force the two parts of the mould together. The mould is then taken from the press, put in an iron clamp, and screwed firmly together : it is then heated on a stove until the mould becomes hissing hot, when it is taken off and allowed to cool sufficiently to handle. The clamp is then removed, the mould opened, and the block made to drop out by striking the mould with a wooden mallet. If the heating has been carried to the proper point, the blocks will be found hard enough through the agency of the starch — which, it will be remembered, is an ingredient in the formulas for bodies for moulded teeth — to admit of trimming : this is done with small files and separating saws. After trimming, the blocks are laid aside in complete sets for burning. Moulds for Special Cases. — Moulds of blocks for special cases can be made by any dentist who is willing to give his time and labor in the production of highly artistic imitations of the natural organs Fig. 293 shows models made by the author for such a special case. The patient, a lady of thirty-two, had lost all the superior teeth in consequence of extensive exostosis of the roots. The incisors and cuspids had been preserved by the patient, and served as valuable guides in the prepara- tion of the brass mould. The bite was an exceedingly short one, as shown by Fig. 292, yet considerable fulness was required to restore the natural expression of the lip. A gold plate was made to the model, the roots of the natural teeth were cut off, and the crowns fitted to the gold plate just as ordinary plain teeth would be. Calculating the total shrinkage as one-sixth the bulk of the teeth, allowance was made by spaces left between the natural teeth (Fig. 293). The gums were formed of wax and modelled to imitate the irregularities of nature as closely as possible ; plaster walls were then made in the manner described on page 243, These walls, which served as impressions of the natural teeth, were removed when the plaster had become sufficiently hard, and given two 254 MOULDING AND CARVING PORCELAIN TEETH. coats of shellac varnish and then oiled. The plate was thoroughly- cleaned of adhering wax, the walls were replaced, and plaster was run in between inside and outside walls, as described on page 243. By this means plaster facsimiles of the natural teeth, which had been temporarily set upon the plate, were obtained. The spaces which had been left were then filled up with plaster mixed with water and applied with a camel's- hair brush until the width and length of each tooth were increased one- sixth, and the outline and contour of the natural teeth closely imitated : Fig. 292. Fig. 293. this, of course, required careful modelling with the natural teeth for guides. To save time, two blocks of four teeth each were made, includ- ing the central and lateral incisors, the cuspids and the first bicuspids, the second bicuspids and molars, ^vere selected from ordinary stock teeth. Fig. 293 shows the arrangement of teeth with the spaces ; the dotted line indicates the additions made to the width and length to compensate for shrinkage. Fig. 294 shows the block enlarged and modelled to imitate Fig. 294. Fro. 295. the natural teeth and gums. A plaster mould was made from the two plaster blocks of four teeth each ; this was reproduced in hard brass, the trimming and adjusting of which was carefully done, so that no change would be made in the outline or contour of the faces of the teeth. The mould with sample of shade was then sent to a manufacturer to have several pairs of blocks made. Fig. 295 illustrates the block after burn- ing : comparison with Fig. 294 will show the difference in size between the unburned and burned blocks. All-porcelain Dentures. Under this heading are included full and partial dentures made entirely of porcelain in one continuous piece. The most favorable cases for this form of denture are those in which the natural gums are very much absorbed, resulting in a very flat palatine arch. In such cases there is generally room for sufficient body to afford reasonable strength. The following is the method given by Dr. Wm. E. Hall in carving full upper sets : ALL-PORCELAIN DENTURES. 255 Two casts are taken from a plaster impression of the edentulous upper jaw. A thin lead plate is then made to fit one of the casts by burnishing it down in every part. A piece of softened beeswax is then put on the ridge, and the articulation procured in the usual way : extra care must be taken to trim the wax to the exact fulness and height required. The cast and wax articulating model must then be enlarged to compensate for the contraction of the porcelain in burning : this con- traction amounts, practically, to one-ninth of its bulk. To make this enlargement the cast and articulation are divided with a thin saw into four sections. The first line of division is at the centre along the mesial line to the back of the cast ; the second, across the cast just back of where the cuspid teeth are located. The wax articulation can be cut freely with a piece of fine wire. Previous to this division the bottom of the cast must be made smooth and level : this is most easily done by pouring mixed plaster on a piece of window-glass and setting the cast on it, letting it remain until the plaster sets hard, then trimming the edges. After the cast has been divided the sections are again placed on the piece of glass in such a manner as to leave between each of them a space of about a quarter of an inch : if in irregular cases more accuracy is desired, the proportional dividers should be used. The space must then be filled with freshly-mixed plaster, the sections being held in posi- tion by small pieces of wax. When the plaster becomes firm a new lead plate is cut, and by burnishing is made to fit accurately. The sections of the wax articulating model are placed on the enlarged cast, and the interspaces are filled with melted wax, thus making the model conform to the size of the enlarged cast. An outside wall must then be made for moulding the body : this is done by bending a piece of tin round the front and sides of the cast (with the wax articulating model on it) to get the correct curve. The tin is then removed one-fourth of an inch from the cast in front and at the sides, and is sustained in this position until freshly-mixed plaster is poured into the space between the cast and tin. When this wall is trimmed it should reach one-fourth of an inch above the artic- ulating wax, after the removal of which the wall should be lined with tin-foil. Both the cast and the wall are then freed from all small pieces of wax or plaster and perfectly cleansed for moulding. The body is prepared as directed in the section on block-carving, and is moulded on the lead plate made to fit the enlarged cast : the lead plate is used to facilitate the removal of the moulded set from the cast. The lead plate and inside of the wall should be oiled, and a piece of the body large enough for the purpose laid on the lead plate before the wall is put in place, and gently worked over the edge of the gum with the fore finger until it reaches the proper limit of the plate line. The Avail is then put in place, and held firmly while the body is packed up against it as high as the top of the wall : the rest of the body is then pressed down to the surface of the lead plate, extending back as far as it is proposed to carry the plate. The body is then allowed to dry suf- ficiently to carve into shape. The wall is removed and the moulded set examined : if the body has split in drying, it can be repaired by work- ing water into the fissure with a small carving knife. The moulded 256 MOVLDINO AND CARVING PORCELAIN TEETH. piece should then be carved out roughly on the cast in the manner directed in the section on block-carving. When roughly carved and reduced to nearly the proper thickness, the piece must be thoroughly dried and biscuit-baked in the furnace : all errors in the carving are then corrected. When the piece has been enamelled and the final carving and gumming completed, the set is dried, and is then ready for the muffle. The burning of such large pieces of porcelain is more difficult than the burning of ordinary blocks : it is not admissible to draw the slide to the mouth of the muffle and return it again if not quite fully glazed, as this might crack the set. To determine the proper degree of glazing, small pieces of body with enamel on them are placed close to the set on the side near the mouth of the muffle : these may be pulled out with a hooked iron rod and examined. When removed from the furnace to the cooling muffle, the set should not be allowed to remain in the open air a moment longer than is necessary to carry it thither. The muffle must be immediately closed with a hot stopper from the furnace. The extra precaution is sometimes taken of covering the muffle with hot ashes to retard the cooling process. The requisite care in adjusting the set on the slide for burning must not be omitted : the sagging of the palatine arch is of frequent occur- rence if it is not properly supported. If the whole weight of the piece should rest on two or three points of the gum, it might result in serious warping. To provide against sucli a result, clay supports are moulded, upon which the piece of carved work rests and is sustained during the burning process. The formula for the composition of the support is — Kaolin or white clay, 1 part ; Pulverized quartz, 2 parts. Mix with sufflcient water to form a mass plastic enough to mould in small pieces to the under side of the carved set. Four small pieces made into balls are required — three in the groove directly under the teeth, the fourth under the palatine portion of the set. These balls are placed on a piece of glass in position for the teeth to be pressed firmly down on them, and are left undisturbed until the supports are dry enough to be safely removed. They are then to be surfaced with powdered quartz, and dried to be ready for use. When the teeth are removed from the cooling muffle the set will require more or less grinding to fit the original cast, which, as will be remembered, was left unenlarged. This is accomplished with corundum wheels and points. To facilitate the grinding the prominent parts of the cast are coated with a mixture of rouge and oil, which will spot the under side of the set and show the exact place to be ground oif to make the case fit solidly on the cast. Very small corundum wheels and points are needed for grinding the more inaccessible places and for making small depressions for the rugse, etc. : these wheels and points should be mounted on long thin mandrels, and be held either in the hand-piece of a dental engine or in a chuck attached to the grinding lathe. ALL-PORCELAIN DENTURES. 257 With these appliances the successful result will depend upon the skill and judgment of the operator. Burning-, — In manufacturing on a large scale the blocks are arranged in complete sets on a fire-clay slide covered with coarse quartz. These slides are 6| inches in width by 9|^ inches in length : they have raised edges to retain the quartz which serves as a bed for the blocks ; they hold from twelve to fifteen sets according to the size of the blocks. The furnaces used by the large manufacturers, having a capacity of three or four hundred sets per day for one furnace, are built of ordinary red brick held together with iron bars, the inside being made of fire- brick. These furnaces are square, with a heating oven directly over the fire, the muffle being placed lower down : the furnace is connected with the smokestack by flues at the top. The muffles are constructed of the best prepared fire-clay, 27 inches long, 8 inches wide, 5f inches high, and 1^ inches thick. The muffle must be thoroughly swabbed with clay mixed thin with water, to fill up all cracks or defects through which the gases from the fuel might enter the muffle. Such accidents are of fre- quent occurrence in burning, and are always ruinous to the teeth, the gas generally imparting to them a ghastly blue appearance. As it is necessary to cool the blocks very gradually after burning to prevent cracking, they are placed in cooling muffles or ovens made of flat pieces of fire-brick about 12 inches square. These are built in tiers of ten in each row : each oven is provided with a loose fire-brick stopper. Large furnaces of this description require a charge of nearly half a ton each of the best grade of anthracite coal. The slide containing the teeth is placed in the heating muffle at the top of the furnace before burning : this preliminary heating prepares them for the higher temper- ature of the muffle, into which they are lifted on a flat iron shovel ; the door is then closed. The length of time required for burning the blocks on each slide varies according to the heat of the muffle : about fifteen minutes is allowed each slide, and the draft is regulated by dampers arranged on the top of the smokestack, operated from the inside of the furnace-room. When the teeth glaze in less than fifteen minutes, the damper should be closed enough to diminish the draft. A too rapid heat tends to burn out or vaporize the colors of the enamels. The proper glazing of the teeth is ascertained by placing them under a gas-jet, and when the final burning is satisfactorily accomplished they are put in the cooling muffle, protected from the air by a door or stopper, and left un- disturbed until quite cold. Furnaces, Muffles, Slides. — These are made of burnt clay pounded into a coarse powder and mixed with fresh clay in proper proportions to form a plastic mass for moulding. This combination of burnt and un- burned clay is made to lessen the shrinkage which occurs in all clays when exposed to high temperatures. After being kiln-burned the muffles will always be found to be somewhat porous, and, unless the pores are filled up with kaolin mixed with water and well rubbed in with a sponge inside and outside, gases from the fuel will get through and discolor the teeth. The muffle of the furnace should receive a thorough swabbing with fire-clay or kaolin after every heating. 17 258 MOULDING AND CARVING PORCELAIN TEETH. The furnace generally used in burning carved block work is shown in Fig. 296. It is oval in shape : the muffle, occupying the shortest diameter, leaves sufficient room inside for the fuel. The height from the top, exclusive of the pipe extension to the bottom, is 32 inches. The fur- nace is in three sections, the muffle being fixed in the middle piece, which is 15 inches high; the dome, or top piece, is 8 inches high ; the ash-pit, or lower piece, holding the iron bars which serve as a grate, is 9 inches high. The width or largest diameter of the mid- dle pieces is 18 inches. The other sections correspond in width with the middle piece. The muffle is 3| inches, inside measurement. This part of the furnace requires constant care and at- tention, as frequent exposure to very high temperatures causes sagging and partial collapse of the sides, by which its width may be diminished : for this reason the slide should not measure more than 2| inches in width. This is sufficient to hold eight carved blocks without danger of contact with each other. The door of the muffle is at- tached to the sheet-iron jacket of the furnace by a hinge, and when closed is securely held by a thumb-latch. All the parts of the furnace are bound or covered with sheet iron, as seen in the illustration. One charge of coke will burn but one slide of carved blocks. If the coke is well packed, the burning heat will last for half an hour. The combustion of coke is very rapid, and no time is to be lost in taking advantage of the proper degree of heat for burning while it lasts. The fire is made with small pieces of kindling-wood laid upon the iron bars under the muffle : these are lighted, and sufficient coke, not of too large size, is shovelled in until even with the top of muffle : the stopper is then placed in the dome section of the furnace, and when the coke is ignited and the lower part of the muffle is slightly red hot, the draft is removed. All the ashes of the kindling-wood are carefully raked out ; fresh coke is added and carefully packed under the muffle and quite up to the stopper, until there is no room for more fuel ; the stopper is then placed in and luted up with clay. Anthracite coal is used in the same way : the burning temperature can be maintained by it for a much greater length of time, but the long-continued heat which it affords is objectionable, and is more or less destructive to the muffle. Two or three slides can be burned at one heating with hard coal. When ready for burning the blocks are placed on a bed of coarse quartz of the size of scouring sand. The blocks are stood nearly upright on the gum edges, and the coarse quartz is banked up under them in a manner to thoroughly support them, so that they will not warp or twist IMPROVEMENTS IN FURNACES. 259 while partially fused. The quartz must not be allowed to touch the outside or enamelled part of the block. The blocks must be thoroughly dried before they go into the hot muffle. The slide is then gradually placed in the mnflfle by means of a pair of tongs, and, a narrow muffle- shovel held by the left hand under it to guard against breaking, it is lifted carefully to the middle of the slide without jarring. The door is left open until all vegetable matter is burned off, when it is closed, and not again opened for about ten minutes. If the temperature has reached the burning-point, the blocks Avill appear slightly glazed and the enamel somewhat colored : the door should then be closed for three or four minutes, the slide drawn to the mouth of the muffle and quickly exam- ined to ascertain whether the blocks are thoroughly glazed : if not, they are to be returned, the door closed, and examined again in two or three minutes, when, if properly glazed, they are to be immediately placed in the cooling muffle and left until quite cold. The cooling muffle is intended to protect the blocks while hot from contact with the cool air : an ordinary muffle is used for this purpose, and is closed with the red-hot stopper of the fuel-hole in the dome. Improvements in Furnaces. The first important modification on the old-fashioned furnace shown in Fig. 296 was made by Dr. Ambler Tees in 1880. His improvement consists in the great reduction of size of the apparatus, and in the quick- ness with which it can be made to do its work. It was intended prin- cipally for use in the continuous-gum process, but may be employed in burning blocks, single teeth, porcelain crowns and inlays, etc. The Fig. 298. The Verrier gas furnace. The bi-muffle gas furnace of Dr. C. H. Land. dimensions of the furnace are— ISJ inches high, 12 inches wide, and 8 inches deep, with walls 1 inch thick, being divided into three sections, which so reduces its weight that very little eifort is required in handling 260 MOULDING AND CARVING PORCELAIN TEETH. it. Scarcely more than half a peck of coke is necessary for each burn- ing, and when the draft is good the body of a continuous-gum denture can be fused in about thirty-five minutes after the fire is lighted : at other times, when the draft is not particularly strong, the burning can be accomplished in about fifty minutes. An illustration of this furnace, with directions for its charging and management, will be found on page 457 (chapter on the Continuous-gum Process). Within the past few years much attention has been given to the con- struction of furnaces which can be operated successfully without the use of solid fuels : this has been accomplished in the use of gas in combina- tion with the air-blast. Dr. C. H. Land of Detroit, Michigan, has invented four diiferent forms and several styles of gas furnaces for the fusing of porcelains and melting of metals, which are said to be much more economical, cleaner, and have made the fusing of porcelain safer and more certain in results than is possible with coal or coke. The successful application of these later devices gave promise of greater economy of time in firing, freedom from dirt, smoke, and pro- longed heat after the work was done — the greatest objections to the old- fashioned solid-fuel furnaces. The liability to the vexatious accident of " gasing," however, still remained ; but in later improvements this objection has, it is believed, been entirely overcome. In the bi-muffle gas furnace of Dr. Land it is claimed that high-grade porcelain can be fused in from six to fifteen minutes : it has been found very useful in changing the forms or color of plain teeth, in porcelain crown- and bridge-work, in adding any style of platinum pins or loops to suit special cases, making sections of block work, changing plain teeth into gum teeth, and making porcelain inlays, etc. The Verrier gas furnace is an invention of Dr. A. B. Verrier of Wey- mouth, England (Fig. 297). It is operated by coal gas or benzoline vapor in conjunction with the blast from the foot-bellows. Its dimen- sions are 6 cubic inches, and it is so small that it may be placed upon a bracket in the workroom. The inventor claims that within ten minutes from the time of starting the fire sufficient heat will be obtained to fuse the body and gum enamel. The Do-wnie Furnace. — This furnace is designed for baking crowns, porcelain inlays, sections, etc., and is undoubtedly an improvement on any gas furnace which has preceded it. The muffle is made of platinum, thus entirely obviating the danger of "gasing" which is so liable to happen in the porous fire-clay muffle. It does its work so quickly that porcelain inlays can be fused in about one minute and crowns in from two to three minutes from the time the furnace is lighted. The size of the muffle is ^ of an inch wide by f of an inch high. The openings at the sides of the entrance to the muffle are temporary ovens in which to set the work to gradually cool after baking. The operator can easily see the work while baking, and readily distinguish when the fusing of the porcelain is complete. With it broken teeth may be repaired, and crowns and porcelain teeth may be built to any shape desired. A small platinum tray takes the place of a slide : the crown inlay or tooth is placed upon it and carried into the muffle (Fig. 299). To Make the Downie Croicn. — Take a strip of platinum of sufficient width for the band. Cut the band a thirty-second of an inch longer than IMPROVEMENTS IN FURNACES. 261 Fig. 299. the circumference of the root ; level both ends before lapping them and solder with pure gold. Fit the band to the root, letting it extend slightly under the free margin of the gum and down beyond the surface of the root about as much as it ex- tends above. Remove the band and clip out V-shaped cuts all around. When the band is re- placed in position the points are to be bent down upon and over the root. The band ^vill then appear as in Fig. 300, a. Select a plate tooth, take a square iridio-platinum wire of sufficient size for the post, taper one end, and tiatten the other with a hammer a little wider than the space between the pins of the tooth ; file a notch in each side, and, ])laci ng it between the plat- inum pins, bend them over as in Fig. 300, 6, and solder with pure gold. If the bite is close, grind the pins down to give room. After fitting the tooth to position by bending the post, if necessary, or grinding the base of the tooth, put a napkin in the mouth, dry the root and adjacent parts, and, Avarming a small pellet of sticky wax, place it on the end of the root and force the post through it and the tooth to its proper relation to the root. Press the wax up against the back of the tooth and ascertain whether the articulation is correct. Fig. 300, c, shows the tooth set on the root with wax backing. Carefully remove it by loosening the band with a hoe-shaped excavator. Remove the wax from around the post where it has Fig. 300. Downie's porcelain crown furnace. been forced into the canal. Mix silex and plaster in the proportion of 2 parts of plaster to 3 parts of silex, and fill the band with the invest- ment, building u}) slightly around the post : after the investment sets boil out the wax. 262 MOULDING AND CARVING PORCELAIN TEETH. Fig. 300, d, shows the tooth with the investment in the band and the wax removed. The porcelain body is now built on until the tooth cor- responds in shape to the natural teeth, when it is put in the furnace and fused. More body is then added and the band covered so as to con- ceal it : the crown is then fused a second time, when it may be considered as finished, as seen in Fig. 300, e. In baking the crown is placed on the platinum tray, as shown in Fig. 300, /, putting the post through the hole in the back end of the tray, face up. This prevents the tooth being fused fast to the tray. Ordinary teeth for vulcanite work answer well in making this crown. When they are used the post should be soldered between the pins with pure gold. In the case of bicuspids and molars, especially where the bite is short, it is often better to build them up entirely with the body and not use any tooth or facing. The author has frequently secured satisfactory results in the case of bicuspids and molars by making a cap of platinum and then enamelling it with a body which corresponds in color with the natural teeth. The Downie Furnace for Bridge-work. — This is of larger size and greater capacity than the preceding, and is designed especially for bridge- work, gum sections, etc. It has a platinum muffle 1-| inches wide and 1 inch high. Crowns and bridges can be fused in this furnace in from two to four minutes from the time the furnace is lighted, although, for the greater safety of the teeth, it is better to light the gas and allow it to burn for a few minutes without the blast. The opening of the muffle is not closed while the crown or bridge is being enamelled, and tlie work may be watched constantly until the proper point of glazing is reached. The temperature falls the instant the gas is extinguished : the crown or bridge may therefore be left in the muffle until it is entirely cold. Porcelain bridge-work has many advantages, amongst which may be mentioned cleanliness and the complete concealment of the metal frame- work. Wherever a cap or ferule is visible, it is only necessary to extend the porcelain coating to it and it appears as a continuation of the tooth. The Downie Furnace for Continuous-guni "Work. — This is a similar furnace, made large enough to receive a full upper or lower den- ture. Like the two preceding ones, the muffle is formed of platinum, and all liability to cracking of the muffle and the consequent gasing of the work, so frequent where fire-clay muffles are used, is entirely done away with. After a short preliminary heating without the blast to pre- vent fracture of any of the teeth, the case may fused in about twenty minutes from the time the furnace is lighted, the front of the muffle being open, so that the proper degree of fusion is easily seen the instant it is reached. Tempering ovens are arranged on each side of the opening into the muffle, and the hearth is provided with two slides, so that the case can be brought out on to the hearth and put into the tempering oven by simply shoving the slide to one side by the small porcelain knob seen at the bottom of the hearth. The fuel used with the Downie furnace is either ordinary illuminating gas or gas generated from gasoline, the latter being quite as effec- tive as coal gas, and much cheaper. An apparatus has been designed IMPROVEMENTS IN FURNACES. 263 for use with the Downie furnace, which it is claimed generates gas at a cost of about ten cents per one thousand feet. This gives dentists prac- tising in small towns the same advantage as those in cities, as it will operate either of the fnrnaces above described equally as well as coal gas. Fig. 301 illustrates the foot-bellows used for supplying the air-blast : it is made in three sizes to correspond with the capacity of each furnace. These bellows liave improved rubber treadle feet to keep them from shifting when in use, and nets made of strong flax cord. Their dimeusions are as follows : Small, 8^ by 9^ inches. Medium, 10 by 11 L « Large, 12 by 13 " Fig. 301. Foot-bellows for the Downie furnaces. Fro. 302. Dr. John H. Mayer describes a preparatory muffle and annealing ovens to be used with an oil furnace for continuous-gum and other porcelain work. The preparatory muffle (Fig. 302) is placed in the elbow of the furnace-pipe, and so arranged as to utilize the escaping heat as it passes upward from the furnace. The heat distributed around the muffle reaches a temperature of about 1800° F. This preparatory muffle is large enough to receive five cases, which can be placed in it before the oil is ignited, and grad- ually heated up, and when the lower muffle has attained the necessary baking heat the cases may one by one be transferred to it, and when satis- factorily fused placed in the asbestos- lined ovens (Fig. 302). The improvement claimed for this furnace is that in ordinary single-muffle furnaces but one case at a time can receive attention, while by the prepara- ^'^^"''^ °^' '^™'''' tory-muffle arrangement five cases may be fused in rapid succession. 264 MOULDING AND CARVING PORCELAIN TEETH. Electric Heat in Prosthetic Dentistry. Dr. Levitt E. Custer has constructed a small electric oven for fusing porcelain, the heating principle of which is a coil of iridio-platinum wire imbedded in a refractory mixture just deep enough to be supported while highly heated, and yet to radiate its heat directly into the oven-cavity. This latter furnace consists of an upper and lower section somewhat the shape of the flasks used in rubber work, with an inner cavity large enough to contain an upper or lower denture of the maximum size, and with such arrangement of the wire that all parts receive the same degree of heat. (See chapter on Continuous-gum Work.) The upper half is hinged to the lower. The electric connection is automatically made by closing the sections of the furnace. There are two openings through which the fusing process may be watched. These are placed at such positions that rays of light entering one will be reflected out by the plate through the other. This overcomes the intense glare of the heat, and at the same time brings the plate clearly into \'\e\\, making it possible for the operator to accurately determine the degree of fusion. There are many possible advantages offered by the use of electricity in fusing porcelain. It gives rise to no products of combustion, and it is therefore impossible to produce with it the condition knoAvn as "gasing,'' and it has been observed that porcelain fused by it not only possesses unusual clearness, but appears to be more dense. The accuracy with which electric heat can be regulated by means of the rheostat, the clean- liness, simplicity, and freedom from noise and odor, are advantages over the older methods of burning porcelain work. Electricity is so easily controlled that it is not improbable that an automatic appliance will soon be invented to regulate the heat according to the fusibility of the porcelain treated. The best current with which to operate tlie Custer furnace is the Edison, but the 52-volt alternating current, while somewhat slower, serves the purpose very well. The procedure in the practical use of the oven is exceedingly simple. The case is placed on the tray in the loAver section, and the upper is then closed down. The lever of the rheostat is placed on the first button, and heat for drying out the case is quickly obtained. When the operator is satisfied that there is no more moisture present he raises the heat by pushing the lever to the right. (See chapter on Continuous-gum Work.) If he allows two minutes to each button, it will require from twenty to twenty-five minutes to reach the fusing-point. If it is a crown or bridge, less time may be consumed in raising the heat without danger to the case, and it may be fused in from ten to fifteen minutes by throwing the lever over more rapidly. When the desired temperature has been obtained and the fusing of the porcelain is complete, the lever of the rheostat is throAvn l)ack and the current cut off*. At that instant the heat begins to go down, so that neither oA'er-fusing nor loss of brilliancy in the gum color can occur. To Fuse Platinum. — Disconnect the rheOvStat and attach an arc-light carbon to one wire and a carbon-battery plate to the other. Place the platinum upon the carbon plate and touch the platinum with the pencil. Upon raising the pencil an arc will be formed upon the platinum, Avhich PIN LESS GUM AND PLAIN TEETH. 265 will then be melted. If there is any noise in the arc, reverse the connec- tions of the wires to the plate and pencil. There can be scarcely a doubt that electricity will be made to meet all the requirements of the prosthetic dentist in the fusing of porcelain as w^ell as in the melting of metals, and the electric oven of Dr. Custer may even now be truly said to be in advance of any of the older means of obtaining high temperatures. English Tube Teeth, These are of the class of single plain teeth. They are made with a platinum tube burned in the porcelain, extending entirely through the centre of the tooth, corresponding to its long axis. In form these teeth are excellent imitations of the natural organs. The texture of the material of which they are made resembles very closely that of the natural teeth. The sliape of an English tooth may be altered by grind- ing with the corundum wheel, and the ground surface may be completely restored to the original condition by polishing. On account of the close- ness of texture and greater strength of the porcelain of which English teeth are made many expert bridge-workers prefer them to those of American make. (For full details in the setting of tube teeth, with their a]>plication to crowns and bridges, the reader is referred to the chapter on English Tube Teeth.) PiNLESs Gum and Plain Teeth. Owing to the increased demand and consequent advance in the price of jilatinum incident to its uses in electric lighting, manufacturers have endeavored to dispense with })ins in all classes of teeth designed for rubber work. The illustrations rejirescnt a new form of pinless teeth. In these the holes are so constructed that the rubber vulcanizes well in the teeth and unites them firmly to the plate, and it is claimed that they hold equally as well as, if not better than, ^\n teeth. Fig. 303. Single Plain Teeth with Countersunk Pin. — The countersunk tooth crowns were introduced by the S. S. White Dental Manufacturing 266 MOULDING AND CARVING PORCELAIN TEETH. Co. in 1885. It has beeu said of them that, properly mounted, they ibrm dentures which fairly rival continuous-gum work in naturalness of appearan(;e, witiiout the oljjectionablc weiglit of the latter. Their close conformity in contour to the natural organs makes them much more acceptable to the tongue than teetli backed in the ordinary manner, renders articulation easier and more distinct, and prevents disclcjsure of artificiality when the mouth is opened. In addition, it is claimed that these crowns allow of greater facility of adaptation to the maxillary ridge, and that the tlenture is in no degree inferior in strength to any that have yet been made on a plastic base. These crowns may be used with either vulcanite, celluloid, or fusible- metal base. For a vulcanite base the case should be flashed in the usual way, but in packing each countersink should be carefully filled with small pieces of rubber to ensure the rubber being thoroughly forced into the counter- sink and around the pins. AVhen the base is to be of celluloid, the countersinks must be first filled with small pieces of celluloid moistened with spirits of camphor, and the case Avell heated before bringing the two parts of the flask together. For a fusible-metal base every precaution should be taken to expel the air from the countersinks, such as jarring the flask or tapping it with a mallet. It would probably l)e safer to use in pouring a conduit which Avould give the pressure of a column of the melted alloy : this would afford a sharper casting and be nearly certain to fill all the countersinks as well as all other deep places in the matrix. Great improvement has been made in the variety of sizes and forms of porcelain teeth designed for use in the continuous-gum process. Generally, these teeth are supplied with but one long platinum pin, by which the teeth are soldered to the backing strip. While the single pin is probably sufficient for strength, it is often found to be inadequate as a means of holding the teeth securely in position while the denture is PINLESS GUM AND PLAIN TEETH. 267 being burned. To prevent lateral movement of the teeth, and to main- tain their correct relation to each other, Dr. C. H. Land has recom- mended the arrangement of two lateral pins to each tooth, as shown in Figs. 305 and 306. Fig. 305. Fig. 306. The cut (Fig. 307) shows the approximal, labial, and lingual faces of a superior continuous-gum central, the side view giving the position and length of pin and the inclination of the labial face. Fig. 308 shows the half of a set of six front teeth for continuous-gum work. In burning single plain teeth it has been observed that exceedingly small specimens vitrefy more quickly and are more liable to change of Fig. 307. Fig. 308. form from over-burning than the larger ones. To avoid accidents of this nature it has been recommended that the small be separated from the larger teeth, and that each lot be placed upon the slide and burned separately. Fig. 309. Fig. 310. Fig. 311. Figs. 309-314, show some of the unusual forms of moulded sec- tional rubber blocks, in which considerable improvement has been 268 MOULDING AND CARVING PORCELAIN TEETH. made within a few years. These are made in a variety of sizes and degrees of curve. Fig. 312. Fig. 313. Fig. 314. Tinting and Staining Porcelain Teeth. Changes may be made in the color or shades of teeth, or devitalized and discolored teeth may be imitated, by the system demonstrated by Dr. George Cunningham at the Columbian Dental Congress, which consisted in the application of a set of paste colors or the stains pre- pared and furnished by Poulson of Dresden or Ash Sons of London.* The colors usually employed in china painting will answer very well for the purpose, and a small selection, consisting of sepia, ivory black, rose pompadour (gum color), ivory yellow, brown yellow, celestial blue, and relief white will be sufficient with which to form almost any shade required in the imitations of the usual discolorations of the teeth as met with in the natural organs. The implements required for the mixing and application of the tints are a plain glass slab, on which to mix the colors in small quantities ; a small palette knife ; a small, short-bristled brush for stippling or spread- ing the color, such as can readily be formed by cutting off the bristles of a camel' s-hair or sable brush, so that the remainder is short, stubby, and square at its end ; alcohol, with which to clean the teeth ; brushes ; oil of cloves, oil of lavender, or turpentine to thin the paints to proper consistence. The grays, yellows, and browns are the tints most frequently required in imitating the discolorations of the natural teeth. Ivory black is of course not to be used by itself, but it is indispensable as a means of deepening the color of the grays and browns. In the use and application of pigments for the purpose of staining porcelain teeth the operator should study the colors of the natural organs as met with in the mouths of patients, and he should acquire experience in noting the effect of admixture of the pigments when applied to porcelain teeth. This is essential, as the colors when devel- oped by exposure to high temperatures are not always of the degree and shade expected. A few experiments, which can easily be made upon odd teeth by means of the Downie or Custer furnace, will enable the operator to apply the colors with some degree of certainty. ^ From paper on " Artistic Staining of Artificial Teeth " in Ohio Dental Journal, by Dr. George H. Wilson of Cleveland, Ohio. TINTING AND STAINING PORCELAIN TEETH. 269 The occasions requiring tinting or staining are not numerous, and the system should be applied with taste and judgment. These occasions are found in cases where it is necessary to imitate the discoloration of a devitalized tooth ; to deepen the color of the cuspids ; to imitate the dis- coloration of the dentine left bare by the recession of the gums ; to darken the dentine between the plates of enamel on the cutting edges of the teeth of elderly subjects ; to imitate the opaque or white spots in the enamel of incisors or cuspids, or the yellow spots occasionally seen on the surfaces of the incisors. In applying the stains the tooth should be thoroughly cleaned with alcohol, dried, and held by the pins with a pair of pliers : the color is mixed with oil of cloves or lavender and applied with a cameFs-hair pencil, the quantity or thickness being governed by the depth of shade required. The color is fixed by subjecting the teeth to a temperature of about 2000° F. The firing may be satisfactorily accomplished in either of the furnaces above named, or, as described by Dr. George H. Wilson, " by shaping a piece of No. 36 platinum plate so as to cover and enclose the teeth, except on one side, which is left open as a peep-hole. This miniature oven or furnace containing the teeth is placed over the Bunsen burner for about five minutes, when the flame from the blowpipe is placed against the outside of the clay slab, upon which it is held, and gradually bringing it over upon the top of the platinum," two minutes' work of the blowpipe being sufficient to vitrefy and fix the colors. '' Atrophy and worn conditions are imitated by grinding and then stain- ing." Gum colors are formed by the use of the rose pompadour, the depth of the shade being secured by varying the amount of the relief white. CHAPTER V. THE PREPARATION OF THE MOUTH; CHOICE OF MATERIAL AND TYPE OF DENTURE. By H. H. Burchard, M. D., D. D. S. When it is considered that artificial dentures are designed to restore the partially lost function of mastication, together with the appearance possessed by the mouth when the natural teeth were in position, it is evident that we have several important matters for consideration — the furnishing of a surface which shall afford the necessary support to the denture, the replacement of the organs of mastication, and the restora- tion of the facial expression. The natural gums themselves, Avhen in a normal condition, form dense, fibrous, elastic, and insensitive pads which may, without discomfort to the individual, be subjected to considerable pressure. If the gums become hypersemic or inflamed, their sensitivity is increased ; there is an inter- cellular infiltration of fluids into the submucosa ; the epithelial covering- becomes sodden ; the structures furnish a yielding instead of a firm base for the support of a plate. It is obvious, therefore, that where a morbid condition exists its cause is to be sought out and remedied. Morbid Conditions of the G-ums. — The general condition of hyper- semia of the mouth will be found frequently associated with more or less inflammation of the pharynx and certain forms of gastric disorders, notably irritative dyspepsia. This oral condition will be commonly noted in spirit-drinkers and confirmed smokers. The first step toward its cure is to remove these exciting causes : the use of spirits is to be interdicted and the smoking lessened if not discontinued. It is not infrequently found that the dyspepsia itself is traceable to the loss of the masticatory apparatus, the patient bolting food or pre- senting to the stomach masses much larger than can be perfectly digested. While in actual practice few of these conditions receive consideration at the hands of the prosthetist, it is undoubtedly advisable that they should be corrected in order to bring the oral structures to a normal condition. In the condition due to non-mastication of food the gastric symptoms and oral disorders arising from tliem are usually relieved through the use, for a period, of soft foods and the internal administration of — I^i. Bismuth, subnit., gr. x ; Acid, carbolic, gr. f ; Sodii bicarb., gr. x. M. et ft. pulv. (i). Sig. To be taken two hours after meals. 270 RETENTION OR EXTRACTION OF NATURAL TEETH. 271 The intestinal functions are to be regulated through the administration of mild saline aperients. Where the symptoms are those of chronic gas- tric catarrh and of fermentation of food-masses, discomfort during diges- tion, burning eructations, and occasional sharp pains which last during the slow digestion, the silver salts are efficacious. To allay the pain a sedative is indicated, but, as many of these cases are attended by con- stipation, opium is contraindicated and belladonna or hyoscyamus substituted. I^. Argenti oxidi, gr, v ; Ext. hyoscyami, gr. v. M. et ft. pil. No. X. Sig. One pill three times a day before meals (Bartholow). The mouth is to be washed periodically with some mild astringent antiseptic, such as borine, listerine. If there are marked symptoms of stomatitis, probably the most effective mouth-lavage is a solution of potassic chlorate, gr. xv-sj. Starchy and fatty articles of food are to be omitted from the dietary for the time being, as they undergo fermentative changes in the stomach. The local maniifestations are to receive appropriate treatment. Stomatitis itself may be due to a variety of causes ; any cause, in fact, which lessens the general bodily tone may determine it. When it ap- pears as small ulcers, these are touched with pure carbolic acid, and then usually take care of themselves. Their recurrence may be usually pre- vented through the internal administration of I^. Acid, hydroch. dil., gtt. V. — S. Immediately after meals, well diluted. If the ulceration is dif- fused, a spray of hydrogen peroxide, followed by one of a solution of potassium chlorate, will be found efficacious. Mercurial stomatitis may be cured by tlie same local applications. In short, the several causes of stomatitis are to be sought out and removed. Gingivitis or ulitis, characterized by a boggy condition of the gums, may arise from a variety of causes : those specifically demanding the aid of the dental practitioner are due to the presence of salivary calculi about the natural teeth, to extension of chronic inflammatory processes from the roots of necrosed or partially necrosed teeth, or, again, to any stage of the process known as pyorrhoea alveolaris, including under this head all of those inflammatory degenerations which lead to the gradual exfoliation of the teeth. Scurvy is a malady so rare as to scarcely require mention in this con- nection. Retention or Extraction of Natural Teeth. — When a case presents for an artificial denture, if the mouth be edentulous and the condition of the gums normal, the preliminary steps in the construction of a denture may be taken. If, as commonly found, there are present natural teeth or roots, it is to be determined, first, which of these shall be retained and which extracted. It is to be remembered that, although the gen- eral removal of isolated teeth may render more simple and easy the adaptation of an artificial denture, the latter is of decidedly less value to the patient than are natural teeth. Dr. Black ' has found that the force a patient could exert upon artificial dentures was from one-tenth to one- 1 Cosmos, 1895. 272 THE PREPARATION OF THE MOUTH, ETC. fourth that exerted by the natural teeth, the force of the former not being sufficient to crush many of the usual articles of diet. There will be seen in this a cause of the dyspepsia common among those wearing artificial dentures. Whether to retain or extract roots or teeth will depend, first, upon the possibility of readily bringing such teeth to a condition of health. A general rule is that those containing vital pulps are to be retained. Teeth or roots in which there is evident necrosis of the pericementum are immediately removed, as they are an incurable source of inflamma- tion in the gum-tissues. Roots which are the seat of pericemental in- flammation are to receive appropriate treatment ; if they do not respond, they are deemed a detriment and are extracted. If retained, they should perform service, and are to receive artificial crowns. If they are not sufficiently strong to furnish a base for an artificial crown, they are, as a rule, unfit for retention. It is not absolutely essential that un- crowned roots should be extracted, but their presence is generally a hin- drance rather than an aid. Teeth of which the crowns have been lost, if brought to a condition of health, by receiving artificial crowns may be made to furnish acceptable clasp teeth. The gums about vital teeth must be brought to a condition of health. The most common source of inflammation, deposits of calculi upon the gums and beneath the margins, must be thoroughly removed, and the gums receive such treatment as shall render them firm and resistant, the operator painting them occasionally with dilute tr. iodine, the patient to employ an astringent and antiseptic wash until a normal condition obtains. One of the most satisfactory of formulae for this purpose will be found in a wash of — I^. Zinc, chlorid., gr. v-x ; Aquse, sj. — M. Sig. Its use continued for a week. Should the tumefaction of the gum-tissue be but slight, a mildly astrin- gent wash suffices : Sir ^. Ext. hamamelis virg., ij; Aquse, §vj Jsed ad libitum. -M. The gradual and progressive loss of teeth, due to the process called pyorrhoea alveolaris, leaves the poorest of bases for an artificial denture. The gradual loss of the alveolar process which accompanies, or rather causes, the loss of the teeth leaves the condition known as the flat, flabby arch. The resorption is confined to the bony tissues, leaving the en- gorged soft tissues without a corresponding diminution of volume. It is needless to emphasize the extreme importance of checking and holding in check this malady, the bUe noir of dentistry. In examining the palatal vault it is to be noted whether its configu- ration is such as to militate against the employment of a chamber plate. Are there protuberances or tuberosities of bone occupying a portion of the vault to be covered by the vacuum chamber ? In that event it is SURGICAL COMPLICATIONS. 273 doubly desirable that clasp support be obtained, and so increased signif- icance attaches to the retention of such roots as may be properly crowned or such teeth as may serve for clasp attachment. The question frequently arises whether or not to extract isolated teeth which are healthy, but which render more difficult the adaptation of an artificial denture. The writer advises against it as a general rule. Such teeth are valuable in that they stay the bite. In occluding they limit the amount of displacing stress brought to bear upon the artificial den- ture, and thus increase its actual capability of service. Such teeth are lost sooner or later, and yet they may remain for many years. It is especially desirable that the cuspid teeth be retained. They main- tain a contour at the canine eminences which the artificial denture does not always fully restore when once lost. Even the roots themselves should, when possible, be retained, and crowned when practicable. It is better, as a general rule, to retain all healthy teeth and roots : the skill of the operator is to make his work conform to conditions rather than alter conditions to suit his convenience. A solitary tooth remaining in the upper arch necessitates a break in the general plate outline detrimental for the following reason : The gum upon which the plate rests at the site of the natural tooth undergoes absorption, and hence a space develops between plate and gum which permits the ingress of air to the palatal surface of the plate and destroys atmospheric adhesion. Isolated molars, if perfectly firm, are to be per- mitted to remain ; even more, in many cases they are to be carefully pre- served. If there be one on either side, a double advantage is obtained : if the future denture is to be mounted upon a vulcanite plate, the latter, embracing these natural teeth, has an additional source of support ; if mounted upon metallic plates, these teeth furnish means of clasp attach- ment. In the lower jaw teeth which stand in a column of two or more than two should nearly always be retained. Isolated teeth are to be retained when they can possibly be made to serve as clasp teeth. Lower den- tures, depending almost entirely upon weight to keep them in position, need clasp support whenever admissible. Even a solitary bicuspid should usually be retained, and if one on either side can be retained the patient is immeasurably the gainer. A solitary inferior incisor is to be extracted : the writer also advises the extraction of a superior lateral incisor when the latter is the only tooth remaining. It will not remain long enough to be of any actual service, while a central may last much longer ; but even a central inci- sor, except under unusual circumstances, when it is the solitary tooth of an arch, had better be extracted. Surgical Gomplications. — The length of time to elapse between the extraction of teeth and the insertion of artificial teeth varies with the existing conditions. After the forcible removal of a firmly implanted tooth there is more or less inflammatory swelling of the soft tissues. A plate or tooth adapted to such a place during the height of the swell- ing would have its relation to the gum altered as soon as the swelling has disappeared. It is the general rule, therefore, to await the subsidence of the inflammatory swelling before taking an impression. Should it be that it is imperative to insert the artificial teeth immediately 18 274 THE PREPARATION OF THE MOUTH, ETC. upon the extraction of the natural organs, due allowance is to be made for the inevitable swelling and subsequent shrinkage. Succeeding the latter wall be a resorption of the alveolar process, which varies widely its extent according to the individual and the local conditions. In very rare instances the following condition may be found : At some point a cicatricial adhesion has occurred between the mucosa of the cheek and that of the alveolar wall. This may be a cord-like attach- ment which marks the site of the fistulous opening of a previous abscess ; the point of the attachment may be at any part of the alveolar wall. Unless it should be at the level with the top of the alveolar arch, it will not disturb the stability of an artificial denture and calls for no inter- ference. Should its attachment be at or beyond the height of the ridge, operative measures are indicated, as the movements of the cheek trans- mitted through the cord would displace a fixture. Wounds of this part of the mouth, whether incised or from injuries by caustics, may in healing cause extensive attachment of the cheek to the alveolar wall, and render the wearing of a plate difficult if not impossible. The surgical principle involved in correcting the condition is a separation of the attachment and preventing adhesion of the cut surfaces until perfect cicatrization has occurred. An impression of the mouth is taken and a model made. (See Chap- ters VIII. and IX.) At the site of the adhesion represented on the model the latter is cut away to the usual plate depth, leaving the model more prominent than anatomically correct, so that there shall be no pressure by a plate upon the alveolar wall. A plate of vulcanite is constructed upon the model, its edges rounded, smoothed, and the entire piece highly polished. When this is finished the mouth is thoroughly sterilized and painted with a 10 per cent, solution of cocaine ; the cheek is drawn away from the alveolar wall, making the tissues tense, and a sharp bistoury is used to divide the attachment, the cut to be made in the middle of the attaching tissue. A styptic applied or a spray of hydrogen peroxide usually checks the hemorrhage. The cut surfaces are dried by means of lint, both are painted with a solution of styptic collodion, and as soon as this has dried the plate is inserted. The anti- septic varnish called steresol is an admirable covering for these as for any wounds about the mouth. The patient is directed to wash the mouth several times a day with an antiseptic such as borine, listerine, borolyptol, etc., and the case, if the person be healthy, should rapidly proceed to cure. Should the granulating surfaces become unhealthy- looking, they are to be washed or painted with a solution of silver nitrate, gr. iv-gj. The plate is worn until healing is complete, usually in about two weeks, when an impression for a denture may be taken. Choice of Base. — In the mouths of patients who have worn arti- ficial dentures it will be found not infrequently that the tissues under- lying the plates are in a condition of hyperemia or even marked con- gestion. While this condition is more common under plates of vulcanite than under those made of metal, it is occasionally found under the latter class of plates. It is most usual under vulcanite plates which are im- properly finished on the palatal surface, the roughness of the latter acting as an irritant to the soft tissues. In the degree that plates of this base are highly finished there is a lessening of what is called rubber USE OF CLASPS. 275 sore mouth. Lack of cleanliness upon the part of a patient is a prolific source of the hypersemia. Deposits of food-debris, being permitted to remain upon the plate, undergo fermentative and putrefactive de- composition, the products of which act as irritants. Aside from vascular injection of the soft parts due to these palpable sources of irritation, instances are seen where the wearing of a vulcanite plate, no matter how carefully finished or cleansed, is attended by hypersemia of the underlying tissues. In lieu of a better explanation this condition is ascribed to lack of conductivity of the base. This view becomes more plausible when it is seen that a plate constructed of a good conductor (of metal) may be worn without causing the effects noted under plates of vulcanite. Vacuum chambers which are too deep and which have too sharp edges are a source of irritation. Therefore, where an artificial denture upon a vulcanite base is presented for examination, complaint being made by the patient of soreness of the parts enclosed by it an examina- tion is made to note the position of the irritated areas. If due to the cutting of the air-chamber, the edges of the latter must be smoothed and the chamber partially obliterated by placing a thin layer of paraffin and wax in it. Should the plate be rough itself or contain foreign sub- stances, it is washed with a strong antiseptic. The writer lays the plates in a 10 per cent, solution of sodium peroxide ; they are then rinsed in a 5 per cent, solution of sulphuric acid, scrubbed, and their palatal surface brushed with pumice and stiff brushes. Where and when a choice of base is admissible gold is as much king in prosthetic as it is in operative dentistry. A general rule for its em- ployment, based upon the cases or classes of cases in which it is found to serve best, would be as follows : It is the only material in present use which meets all the indications for a proper base for all partial dentures. In full cases gold or continuous gum is the choice. It may be given as a principle that the tissues of the mouth prefer the contact of a metal surface to that of one of the vegetable bases ; so that in all cases where, by the experience of the patient, the weight of a perfectly fitted denture is not urged against gold or continuous gum, these latter are to be pre- ferred. In lower cases, where weight is an advantage, this feature doubly recommends the metallic base. Vulcanite serves best in mouths having firm gum-tissues, a high vault, and where the bulk of the piece is unusually great, and in which the plate adhesion has been demonstrated to be weak. Flat mouths, with flabby tissues, bear metal better than they do vulcanite. Continuous-gum dentures serve best in what woidd be termed vaults of the average depth, moderately high alveolar walls, and where a greater bulk of material is required to restore lost form than can be had with gold plates. When accurately adapted, continuous-gum dentures serve admirably as full lower cases. Use of Clasps. — The question of the use of clasps is determined by necessity. They are, as a general rule, attached to all partial lower den- tures where practicable. When an option is admissible, they are not attached to the class or varieties of teeth which are seen to be susceptible to dental caries. If sufficient stability can be secured without their use, they are not employed. This, however, necessitates that a plate shall be large enough to serve as a stable base, one which is unnecessarily large 276 THE PREPARATION OF THE MOUTH, ETC. for carrying one or two teeth, so that small plates supporting very few teeth are frequently mounted upon small plates, and have their attach- ment through the medium of clasps. Type of Denture. — Where the configuration of the vault is of such form that a median vacuum chamber is inadmissible, owing to the pres- ence of tuberosities which cover the median line of the vault, what is known as a horseshoe chamber is tested : if this prove insufficient, two distinct lateral chambers, occupying respectively areas upon the right and left lateral aspects of the plates, may used. It is in such cases that natural teeth should be preserved to serve as clasp attachments should attempts to secure adhesion by means of the chambers prove unavailing. For the same reason roots are retained which may serve as the bases for artificial crowns, to which clasps may be fitted. Cast or swaged aluminum dentures serve best in those shapes of vault and alveolar walls in which vulcanite renders good service, and in mouths apparently irritated by the presence of a vulcanite plate may be advantageously substituted for the latter base. In regard to the choice between bridge-work and partial plates, if the conditions present permit the ready placement of a properly designed bridge, with a probability of its permanent usefulness, it is selected ; otherwise the indication for a plate denture prevails. The direct indica- tions for a bridge are a loss of teeth between others which have sound and firmly fixed roots, and preferably those which require no mutilation to fit them to serve as abutments ; little or no loss of gum-contour at the sites of the absent teeth ; an articulation of a type which shall permit the placing of perfectly protected porcelain facings, which shall meet all requirements as to restoration of appearance ; the spaces beneath the body of the bridge to be accessible to tooth-brushes. The introduction of removable bridge-work has eliminated many of the objections urged against this class of fixture. In addition, what are known as detach- able plate-bridges remove other objections to the general class of bridge- work ; but the judgment of the conservative operator still finds many cases in which partial plate dentures are the rational indication and bridge-work clearly contraindicated. CHAPTER VI. TAKING IMPRESSIONS OF THE MOUTH. By H. H. Burchard, M. D., D. D. S. Taking an impression of the mouth is an operation of such apparent simplicity as to seem to require but brief description, and yet it is one which is as rarely done well as any operation in the practice of dentistry. It is absolutely necessary for the proper adaptation of an artificial denture that this, the primary step in its construction, be accomplished with an accuracy which shall eliminate any faults of the denture traceable to an inaccurate impression. The operation consists in securing a perfect imprint of the jaw in some soft substance which by its hardening will retain the impression made in it. The impression material is conveyed to position and confined by means of an appropriately-shaped tray. Materials Employed. — There are two classes of impression material in general use : first, those which are softened by heat and harden in cooling ; second, those made into a paste with water, the paste hardening through crystallization. The first class includes beeswax and prepara- tions made of it, such as wax and paraffin, wax and gutta-percha ; next modelling compound, a mixture of gum copal, stearin, and French chalk ;^ lastly, gutta-percha. The second class includes plaster of Paris and the various mixtures made with it as a basis. Plaster of Paris when in a condition of paste is perfectly adaptable to any surface, no matter how irregular the latter may be, and causes no displacement of parts or alteration of their positions. When set it possesses such rigidity that its withdrawal from undercuts is impossible without fracture of the mass or yielding of the parts enclosed by it. In setting the mass expands about one five-hundredth of its volume. It is said not to expand when sodium chloride or potassium sulphate is added to the paste. (For the chemical and physical properties of plaster, its preparation and treatment, see Chapter I. page 22.) Beestoax. — The special advantages of wax are that it is easily manip- ulated, is inelastic, and contracts but slightly in cooling. The disadvan- tages are — the pressure required to adapt it forces all the soft parts out of normal position, and renders the taking of a perfect impression of some mouths with it impossible ; the tendency to distortion of its form ^ Dr. J. W. White, "Taking Impressions of the Mouth." 277 278 TAKING IMPRESSIONS OF THE MOUTH. in withdrawing is also a serious objection to its use. It does not give as accurate an impression as plaster, but still is preferred by some ope- rators. When wax is used, either a pure specimen should be obtained or one which has been judiciously combined with a foreign substance for a spe- cific purpose. Commercial adulterations with tallow, resin, vegetable wax, etc. injure it, making it difficult to manage. White wax has an advantage over the yellow in that it does not draw out of shape so readily, and there is consequently less liability to have the impression distorted than with yellow wax. It takes a sharper impression than the yellow variety, but it is more difficult to bring to the required plasticity, and more force is required to obtain a correct impression unless the wax is made hot. In summer-time the additional hardness is in its favor. Scrap wax of either variety should never be used without remelt- ing, as it is difficult, if not impossible, to get it into a homogeneous mass. Paraffin is frequently added to wax, >and imparts to it the property of becoming plastic at a lower temperature. A small proportion improves it, especially for use in cold weather, but if in excess it causes the wax to separate into layers which are not easily reunited. It take a sharper impression than wax alone, with less liability of drawing out of form, the addition of the paraffin in proper quantity causing the composition to be harder when cold than the wax alone. A combination of wax and gutta- percha is used and highly prized by some, on account of its toughness. The objection to it is that it is sticky. It may adhere to the plaster in making a model unless previously varnished. The other plastic materials will be described together with methods of manipulation. Impression Trays. — Impression trays are receptacles designed to carry impression material into position in the mouth, to retain it while there, and to hold the form of the impression during and after its removal from the mouth. Properly shaped, a tray should represent in form the particular jaw of which an impression is to be taken, to be only sufficiently larger than the jaw to have the volume of the impression material great enough to hold together in a common mass. For the majority of cases, and with any of the materials employed in impression-taking, this would require a cup to be about one-quarter inch or less larger in all respects than the parts it is to embrace. The well-equipped laboratory should be provided with an extensive set of trays as furnished by the manufiicturer to meet the needs of the majority of cases. Figs. 315 and 316 show the class of trays designed for the taking of full upper impressions. Three sizes will usually be found to meet general requirements. Cups especially designed for use with plaster are illustrated in Fig. 316. These cups, made of britannia metal, may be filed, cut, or bent to conform to irregularities of arch outline or palatal vault, so that the tray shall be uniformly one-quarter inch larger than the parts it is to enclose. IMPRESSION TRAYS. 279 Figs. 317 and 318 illustrate the trays designed for the taking of full lower impressions. These frequently require alteration of form by bend- FiG. 315. Fig. 316. Fig. 317. ing and cutting. It is necessary that lower trays should have their edges and outlines conform to those of the jaw, for assurance that the im- pression material shall be properly carried into position. 280 TAKING IMPRESSIONS OF THE MOUTH. For partial upper dentures the form of tray shown in Fig, 319 will be found generally applicable. To ensure a closer adaptation of the Fig. 318. tray to the vault and alveolar wall an adjustable tray (Fig. 320) is em- ployed when indicated. Fig. 319. For a common class of partial lower impressions a tray of the general form of Fig. 321 is employed, the edges of which shall extend at all points deeper than the plate line. Where the remaining natural teeth are scattered, trays of the forms Figs. 322 and 324 are usually employed— Fig. 322 where the crowns of IMPRESSION TRAYS. 281 the teeth are short ; Fig. 324 when they are long. The adjustable tray, Kg. 322, may be adapted to different arch outlines. Fig. 320. Fig. 321. The impression trays as they are received from the manufacturer, while adapted for tlie taking of impressions of the majority of cases, are 282 TAKING IMPRESSIONS OF THE MOUTH. frequently found to require alteration of their forms or outlines to adapt them to odd cases. The requirements of a proper cup, that its outline shall embrace more Fig. 323. Fig. 324. of the jaw than is to be covered by the plate, and to be at all points about a quarter of an inch larger than the jaw, show that many cups in their IMPRESSION TRAYS. 283 original forms are not correctly applicable. It may be that a close cor- respondence between the tray and alveolar arches is not to be had in the original form of the tray, or, again, some portions of the edge of the tray may impinge upon the frsena or upon the mucous membrane reflected from the cheek or lips. In adapting trays to full dentures the former are to be bent by means of pliers when it is necessary to alter their outlines to conform with those of the alveolar arch. Any edges of the tray which may impinge upon the soft tissues are dressed down by means of shears and flies until a proper adaptation is secured. Heavy plate-nippers are employed to cut out the tray about the site of a frsenum. The cut edges should be rounded and smoothed before the impression is taken. The necessary changes to a tray for a full denture are best or most accurately made by forming a plaster model in a wax impression, then by means of pliers, flies, shears, nippers, and the horn mallet bring an approximate tray into the correct position of about one-fourth of an inch larger at all points and parts than the model. Fig. 325. Special Trays. — It is occasionally found — more frequently in such partial lower cases as is illustrated by Fig. 325 — that none of the ready- made trays can be altered sufficiently to form a correct tray. It may be necessary to make a special tray. A large wax impression is taken and Fig. 326. a plaster cast poured. The cast is warmed, and covered completely, at the portions to be embraced by the cup, by a layer of wax at least one- 284 TAKING IMPRESSIONS OF THE MOUTH. quarter of an inch thick. The wax is made thicker about the necks of the teeth — about half an inch thick or more ; small spaces between neighbor- ing teeth are to be filled flush with the general surface of the wax. A heavy zinc die and counter-die are made, as described in Chapter X., and a piece of sheet brass No. 22 is swaged to cover as much of the die as should be embraced in the impression cup. A long strip of the same metal doubled on itself serves as a handle ; this may be attached by means of a soft solder. The principle embodied in the following method is one of wide appli- cation — viz. that the plaster covering the vault and arch should be of uniform thickness, and to ensure that it shall be carried into position in such a layer it is necessary that the cup should be properly adapted to that end. Dr. J. B. Bean's Method of Preparing Trays and Taking Impressions. — A wax impression of the arch and vault are taken, and a plaster model made : over all of the surface to be embraced by the future plate, and for about half an inch beyond it at all points, a layer of wax having a uniform thickness of about one-eighth of an inch or more is placed. Dies and counter-dies are formed, between which a stout brass plate is swaged. The tray is thrown into nitrous acid, washed in soap and water, and dried in sawdust, which develops a surface resembling frosted gold. The tray is heated and two coats of thick shellac varnish are applied (the tray is lacquered). While the shellac is soft a ball of cotton is pressed into the interior of the tray, and when the lacquer has hardened the cotton is drawn away, leaving small tufts which have been caught and retained by the shellac. The impression is taken in plaster : the small volume of the latter lessens any tendency to nausea, and its even distribution equalizes any possible changes in the plates consequent upon its expansion. Moreover, there is an increased accuracy, due to the plaster being carried with certainty into all parts. After the plaster cast has been poured, the tray is heated until the shellac is softened, when the tray is removed and the model separated from the impression. Selecting Material for Impressions. — Plaster of Paris is justly re- garded as the impression material par excellence. It is extremely exceptional in the making of an artificial denture that its construction is not preferable upon a basis of an exact reproduction of the mouth in a plaster model. Plaster is the only impression material which possesses the properties which give assurance of accuracy. It is inserted without the exertion of any force which could cause the displacement of movable parts, may be insinuated into minute spaces or irregularities, and after setting its form is unalterable. The practised operator secures with this material impressions of any jaw, no matter what the anatomical pecu- liarities may be. Impressions may be taken with it of partial cases in which no two of the remaining teeth are parallel^ (Fig- 327). A general rule more applicable than any other is that "just in the degree that an impression is difficult to take, owing to irregularities of form or in the positions of the teeth, it is imperative that it should be taken in plaster." The exceptions to this rule are so rare as to scarcely require mention. ^ See Cosmos, Nov., 1895, "Old Dentures." IMPRESSION TRAYS. 285 Of the several materials made plastic by heat, modelling compound is usually regarded as having the widest field of usefulness. When soft it is sufficiently plastic to receive imprints of fine lines, and yet it in- evitably displaces to a greater or less degree the soft tissues against which it is pressed. If the natural teeth are in irregular positions, Fig. 327. portions of an impression are bent from their true form when the impression is withdrawn from the mouth. The material being in some degree elastic, this deformity tends to partially correct itself. It may be mentioned that the most common use of this material is for securing impressions from which to form orthodontic appliances. Pure beeswax becomes softer than modelling compound and at a lower temperature. When soft it is inelastic : although receiving the imprints of fine lines, it exhibits no tendency to adjust itself to undercuts, as does the compound. Additions of paraffin or gutta-percha to a basis of wax render it firmer. All preparations of wax are distorted permanently, to some degree, in being withdrawn from undercuts. Gutta-percha, a substance once employed to some extent, has fallen into general disuse as an impression material, being replaced by modelling compound, the latter possessing more virtues and fewer disadvantages than gutta-percha. The last-mentioned material requires a compara- tively great amount of heat to soften it : during the operation of im- pression-taking it is driven into irregular spaces, from which it is diffi- cult to withdraw it when the material is cold. Impressions in Heat-softened Materials. — Impressions in any of these materials are taken after one common principle : A properly adapted tray is selected or when necessary is fitted : the material itself is placed in lukewarm water, the temperature being raised gradually until the mass is of uniform softness. The tray is heated sufficiently to cause the material to adhere to it, when the impression material is moulded in the tray until of almost uniforni thickness, except at its highest part, where it is left thickest to ensure perfect contact with the height of the vault. The patient is seated in a dental chair placed at its lowest position, the operator standing behind. The tray is held in the right hand, two fingers 286 TAKING IMPBESSIONS OF THE MOUTH. under its body, the thumb on the handle. The right side of the impres- sion tray is to have its middle engage and draw away the lips at their angle ; the fingers of the left hand draw away the left angle of the lip when the handle of the tray is swung into the median line ; by a steady movement the impression material is now pressed into position : the fingers of the left hand are swept around the alveolar wall, so that the cheek shall not interfere with the perfect placement of the impression tray, which is now firmly held in place by two fingers pressed against the bottom of the sides of the tray. The patient is directed to contract the cheeks and lip against the impression material. When the latter is cold it is to be withdrawn, the fingers of the right hand holding the tray as during its introduction, the fingers of the left hand lifting the cheeks and lips away. The impression is plunged immediately into cold water to chill and fix it. In taking the impressions of lower cases the operator usually stands in front of the patient. The same directions apply in the taking of these as in upper impressions. As soon as the material is pressed into position the patient is directed to protrude the tongue, so that the adja- cent portion of impression will be pressed into position. Plaster Impressions. — For the taking of any plaster impressions a properly adapted tray is essential. It is necessary that its outlines should be larger and greater in depth than the future denture. Between the tray and the arch and vault should be a space of about one-quarter of an inch — rarely less, except at the posterior border of upper impressions, as very thin layers of plaster are liable to fracture in pieces too small for accurate replacement. With a greater distance between the tray and the parts of which an impression is to be taken there is danger that the plaster will not be properly carried into position. For full upper cases trays having a raised heel (Fig. 316) are em- ployed, or a layer of wax is built across the heel so that the plaster cannot escape posteriorly. Each fresh purchase of plaster should be tested, so that the length of time required for setting may be determined. Impression plaster should set more rapidly than that used for casts, but should permit thorough mixing and placing before it begins to harden. Arranging Patient to Take Impression. — The patient should be seated, and instructions given as to position and the reasons therefor; the patient inclining the body slightly forward, and in readiness when the plaster is introduced to allow the head to be thrown still more forward, the object being to determine any excess of plaster to the front of the mouth and prevent it from falling into the fauces. Too many directions and an ostentatious preparation will, however, cause failure with timid patients, by inducing undue nervous irritability from a magnified fear of the ope- ration. When about to take a plaster impression a towel or large napkin should be spread in the front of the patient's dress to receive any excess of plaster which may be dislodged. The patient may be directed to dry the mouth with a soft napkin if there is an excess of saliva, but this is rarely if ever necessary in taking impressions of the upper jaw, and some mouths are naturally so dry that the difficulty is rather to prevent the plaster from adhering too firmly to IMPRESSION TEAYS. 287 the tissues. In such cases it is not well to absorb what little moisture there may be. Some operators always direct the mouth to be rinsed with warm water, which, it is claimed, by removing the mucus facilitates a more even flow of the plaster, diminishes its liability to an undue adhe- rence to the membranes, and produces a smoother and more delicate im- pression. Some always brush the parts over with glycerol if the mucous membrane appears abnormally dry. Before introducing the tray some operators instruct the patient to breathe through the nostrils, considering that the liability of fragments of plaster being drawn into the pharynx is much increased when the patient breathes through the mouth. The late Dr. Joseph Richardson took, however, an opposite view, arguing that in the act of breathing through the nose the velum palati is depressed to cut off the passage of air through the mouth, and is thus brought more immediately in contact with any portion of plaster that may be protruding from the heel of the tray ; that the stimulus of contact produces involuntary contraction, and that thus fragments of hard plaster may be drawn back into the fauces, producing the very evils which nose- breathing is thought to avoid ; and that if patients are instructed at all in this respect, they should be advised to breathe through the mouth. ^ About a gill of water is placed in a rubber plaster-bowl (Figs. 328- 330) and a pinch of salt added. These bowls of soft vulcanized rub- Fio. 328. Fig. 330. Fig. 329. Rubber bowls for mixing plaster. ber cannot be broken ; their sides can be pressed together to form a lip or spout for pouring thin-mixed plaster ; and any unused plaster of the mixing which sets in them can be thoroughly crushed and readily removed by squeezing the sides of the bowls together. Their superi- ority has made for them a place in almost every dental laboratory. Plaster is slowly sifted into the water until it is at the surface of the ^ J. W. White : Taking Impression of Mouth. 288 TAKING IMPRESSIONS OF THE MOUTH. Fig. 331. latter, when it is stirred with the spatula until a thin paste is made. A quantity of the batter is carried into the tray and distributed by means of the spatula until it is something more than a quarter of an inch in depth. The tray is carried into the mouth as described : its posterior edge is first brought into position, and then by a gradual elevation of the handle of the tray the plaster is carried into all depressions ; the cheeks and lips, lifted away, are allowed to fall back against the plaster which has pressed over the edges of the tray, carrying it into close contact with the alveolar walls. The impression is now held immovably in position until by test of the plaster re- maining in the bowl it is seen that the impression is hard. The lips and cheeks are lifted from the impression ; the handle of the tray is elevated to detach the heel of the impression, which is now withdrawn. Should the case present an unusual depth of palatal vault, air may be enclosed between the soft plaster and the mucous membrane and produce flaws in the impression. It is advisable in such cases to fill the tray with plaster ; then a portion of the batter is taken on the end of the spatula-blade and carried into the height of the vault, smearing the plaster into the deepest recesses : the plaster in the tray is immediately carried into position, joining the plaster of the tray with that in the vault. It is occasionally found that patients have what are called " irritable throats," the presence of any substance in contact with the soft palate causing any degree of protest from a slight gagging to marked retching or even vomiting. It is necessary, in such cases, to temporarily benumb the parts to enable the operator to secure an impression. The usual means of securing this end is through the employ- ment of a gargle of camphor-water (not spirits of cam- phor). This suffices in many cases : the more irritable ones are directed to employ a gargle of potassium bro- mide, gr. XX, water an ounce.^ Should these means not suffice, the patient is given a gargle of glycerin and water ; after a thorough lavage with this the soft palate and pharynx are sprayed with a 1 per cent, solution of cocaine hydrochlorate in an atomizer. In five minutes an impression may be taken without fur- ther difficulty. In taking lower impressions the batter is made slightly thicker than for upper cases. The tray is carried into position, and before pressing it home a tremulous move- ment is made to introduce the plaster into undercuts ; then it is pressed into position and firmly held upon both sides. The patient is directed to protrude the tongue to carry the plaster well against the alveolar wall anteriorly. Lower impressions are permitted to remain longer in position than those ^ Oral Surgery, Garretson. Spatula or palette-knife. IMPRESSION TRAYS 289 for upper dentures, for, being bathed in saliva, they set more slowly. In taking plaster impressions tlie handle of the impression tray should always be in the median line, and the body of the impression should be held immovably in position supported upon both sides. Any pieces of impression which may break from it during its re- moval are carefully preserved and fitted into their proper positions. The plaster when fully set breaks with a clearly defined fracture line, furnish- ing a guide for the accurate replacement of fragments or sections. Cases are occasionally met with where the patient complains of the instability of a denture now worn : an examination shows an apparently accurate adaptation of the plate to the vault and the teeth in proper oc- clusion. Removing the artificial denture and passing the finger over the area of the vault and arch, it will be observed that the tissues do not offer uniform resistance to pressure ; certain areas are hard, others soft or spongy, so that a plate closely adapted to the mouth at rest would exert uneven pressure upon its bed. Many operators prefer for such cases beeswax or modelling compound as an impression material, which by pressing away the soft parts should cause a plate made upon such models to have a uniform bearing. Unfortunately, this one feature of these materials rarely compensates for their lack of accurate adaptation to the parts and the danger of change of form in them. The offices and advantages of wax or compound and plaster are com- bined in the following method : An impression is taken either in wax or compound ; then by testing the density of the tissues the hard areas are determined and the impression is carved away at these parts. The prepared impression then serves as an impression tray in which an im- pression in plaster is taken. The greatest pressure is evidently exerted by those portions of the improvised tray which have not been cut away, those beneath the soft areas. Dr. B. H. Catching^ describes a method of quickly making special impression trays, for which the operator's ingenuity Avill devise many ap- plications : A piece of base-plate wax is moulded to fit approximately the parts to be enclosed by the tray. This when removed from the mouth — or model if it be formed upon a model — is chilled and a wax handle formed. A plaster matrix is made of the tray in an exterior and interior section. The walls of the matrix should be thin. After separating the halves of the matrix the wax tray is removed, the matrix bound together, and the space formerly occupied by the wax is filled with molten fusible metal. If the tray is to be made of an alloy having a higher melting-point, the matrix is to be formed in sand and plaster mixture and well dried before the metal is poured. Impressions for Partial Dentures. — The necessity for a properly adapted tray is redoubled in the taking of impressions for partial den- tures. One of the square-edged trays illustrated is selected whose arch is a quarter of an inch larger than that of the teeth. Closely fitting trays frequently cause the plaster about the natural teeth to break into such small fragments that accurate replacement of them is impracticable. Across the heel of the cup a dam of wax is built, so that the plaster will be well enclosed and none or but little of it shall escape posteriorly. Any ^ Comp. of Pract. Dent., 1895. 19 290 TAKING IMPEESSIONS OF THE MOUTH. further lack of adaptation is to be corrected by building wax about the borders of the tray or cutting away from the latter parts which may interfere with its proper placement. The tray is filled with plaster — an examination of the comparative sizes of the tray and mouth will indicate the quantity of plaster required — and it is carried into position in the man- ner previously described. When the plaster and tray are in position they should be held by the fingers of both hands to ensure against rocking. When the plaster has set the cheeks and lip are raised from the impres- sion, and the latter is loosened by depressing its heel. It is usual, and in many cases inevitable, that there is a greater or less amount of fracture of partial impressions. The body of the impres- sion, that in the tray, is set aside, and all broken pieces are lifted away with a pair of tweezers and ranged around the tray. An examination is made of the spaces about and between the teeth and any fragments found are detached and preserved. As soon as the impression is dry enough, in about fifteen minutes, each fractured surface is brushed free of any adherent particles (the brush should be very soft). The greater masses are now adjusted to one another, and the shapes of the spaces between parts of them noted ; the pieces which fit such spaces are selected from the smaller fragments and set in position until the surfaces of the impression are complete. The pieces should be so adjusted to one another as to make the lines of junction almost indistinguishable. Fig. 332. Weirich's new flexible-rim impression trays. Melted adhesive wax is applied to each joint upon the exterior of the impression to hold the pieces in their positions. Small pieces which it is impossible to thus attach without applying wax to the inner surface IMPRESSION TRAYS. 291 of the impression may be made to adhere by treating the surfaces to be joined with thin mucilage (Fig. 332). The impression tray of Dr. Weirich is designed for the taking of im- pressions of the forms which suifer fracture of their outer walls in with- drawing them from the mouth. The soft plaster exudes through the perforations of the flexible rubber rims when the tray is carried into position in the mouth, \yhen hardened the plaster is thus held firmly against the flexible wall. As the impression is withdrawn from its posi- tion it fractures above the sites of undercuts : the flexible rim yields, and yet holds the broken sections firmly, and when removed from the mouth the elastic rim carries these sections back exactly into position. The operation of taking partial lower impressions is essentially the same. The tray is to be one-fourth of an inch larger than the arch at all points, and the edges of the tray are to extend beyond the plate outlines. The most common classes of cases, those in which the anterior natural teeth are in situ, are taken in the variety of tray made for them. (See Fig. 321.) Where the natural teeth are present at irregular intervals, trays having square edges, such as figured, are employed ; if the teeth are very long, trays such as are shown in Fig. 334 are applicable. It is usual that these impressions suffer extensive fracture in their remoyal. A tray filled with plaster is inserted, and before pressing it fully into position is jarred, so that the plaster will be brought into perfect contact with all portions of the dental arch. It is then pressed into place, and held until it has set hard. Cases in which the natural teeth are in an unbroken line usually fracture less than those in which the teeth are scattered. The pieces, large and small, are collected and each is accu- rately fastened into position. Should the spaces between the teeth present marked undercuts, or should any of the natural teeth be loose, it is advisable to remove the impression in sections in such a manner as to produce no strain upon loose teeth and to preserve the shapes of undercuts. This applies equally to partial upper cases in which similar conditions are present. A square-edged cup is selected and its inner surface oiled. The posi- tions of the natural teeth are noted — which of them are loose and inclined. The tray and plaster are carried into position as before, and when the impression is hard the tray is withdrawn, leaving the impression in the mouth. With a sharp knife-blade groove the impression along a line which will pass through the middle of the articulating face of each tooth. When the groove extends to the crowns of the teeth, transverse cuts are made from the outer wall of the impression into the buccal or labial surfaces of the teeth : these grooves mark the impression into inner and outer sections and into two or more sections anteriorly. The tip of a finger is introduced beneath the edge of a posterior section, and it is detached ; the remaining outer sections are removed in the same manner. A finger introduced between the natural teeth exerts pressure upon the inner section of the impression, and it is pushed upon until loosened and detached. The writer has never met with a case, no matter how irregular, of which a plaster impression could not be secured by a careful following of this method. 292 TAKING IMPRESSIONS OF THE MOUTH. The several pieces are adjusted to one anotlier, and cemented together and to the tray. It has been recommended in taking impressions for this class of cases that a wax impression be first taken, which is then carved out to serve as a tray in securing an impression in plaster. This method is applica- ble when there is but slight danger of fracture of the plaster in remov- ing the impressions from the mouth, but when the irregularity of the parts embraced by the impression is marked enough to cause fracturing of the impression, many of the fragments of the latter will be found too small and too thin for accurate replacement. Moreover, the heat engendered by the setting of the plaster softens the wax matrix and fre- quently renders the accurate replacement of fragments impossible. For this reason it is better to secure the primary impression in modelling compound, cutting it away until it is of the proper size and form. In cases which have remaining one or two unusually long natural teeth it is advisable to cut large openings in the tray which shall permit the ready placing of the tray in position (Fig. 333, A ; 334, J.). Without these apertures a tray rides on the natural teeth, so that it is difficult to prevent movement of the impression while it is setting. The setting of a thick mass of plaster about isolated teeth, which are frequently at an acute Fig. 333. angle with the plane of the mouth, and which are broader upon their masticating surfaces than at their necks, renders it most difficult to remove the impression. About the openings cylinders at least twice as wide as the IMPRESSION TRAYS. 293 teeth are attached (Fig. 333, B ; Fig. 334, B) : these may be made of the heavy pattern tin of the laboratory or of sheet wax : wax is melted about their bases to hold them to the tray. The tray, filled with plaster, is carried into position. The body of the tray should be well adapted to the Fig. 334. alveolar arch, so that the body of the impression is quite thin. When the plaster is hard the cylinders are stripped from the plaster. A groove is made along the length of the plaster projection until the knife-blade is felt to touch the enclosed tooth. Introducing a broad dull blade in the groove, the cylinders are split in two sections, making sharp fracture surfaces. The tray and body of the impression are now withdrawn, and the plastic cylin- ders adjusted and cemented to it. It is occasionally necessary, as has been stated, to alter the original forms of trays to make them conform to irregularities of the parts embraced by the impression. While slight alterations by cutting, filing, or bending may serve to adapt the tray in many cases, there are others in which it may be necessary to so trim a tray that it is out of all resemblance to its original form. At the site or sites of a column or columns of natural teeth it may be necessary to remove entirely those portions of the tray which interfere with the pas- sage of the tray to within one-eighth of an inch of the vault. Instances and illustrations of this necessity and the modus operandi of making the changes are appended. Fig. 335 shows the tray in process of being cut by means of plate-nippers, the most expeditious means of making the 294 TAKING IMPRESSIONS OF THE MOUTH. changes without that distortion of the general edge outline of the tray which accompanies trimming by shears. Fig. 336 illustrates a tray for a partial lower case cut out for the passage of the anterior teeth, the lingual wall of the tray being divided to accommodate an unusual confirmation of the lingual aspect of the alveolar wall. Fig. 337 shows a tray pre- pared for taking an impression for a partial upper case. Fig. 335. Fig. 336. Fig. 337. The trays, altered so that they will pass readily into position, have softened sheet wax moulded about the openings, forming chambers slightly deeper than the lengths of the teeth and about twice as broad. Their edges are cemented to the tray about one-eighth of an inch beyond the bor- ders of the openings in the trays, so that the plaster of the impression will be caught by the under surface of the tray at these points and serve to with- draw the impression in the tray. Cases are occasionally seen in which the plaster exhibits an undesirable tendency to cling to the surfaces of the teeth. To overcome this it is the usual practice to coat each natural tooth with olive oil before taking the impression. A ball of cotton is dipped in the oil, and then passed over the surfaces of the teeth. As in these cases the plaster tends to adhere to the mucous membrane also, the oiled cotton is to be passed over all portions of the mouth to be embraced by the impression. Dr. L. C. Ingersoll^ advises mixing in the plaster batter about one-third of its volume of pulverized pumice. In rare instances the natural teeth may converge toward one another, so ' J. W. White : Taking Impression of the Mouth. IMPRESSION TRAYS. 295 that their walls, together with the palatal vault, form more than a hemi- sphere seen in section or semicircle (Fig. 338). It is evident that in snch a case it would be impossible to withdraw en masse the body Fig. 338. of an enclosed impression without displacement of these teeth. It is necessary that this portion of the impression shall be removed in halves. To render this division as easy as it should be, a wedge- shaped piece of modelling compound is placed along the median line of the tray, and deep enough for its sharp edge to be in contact with the palatal vault. The impression tray is heated and roughened along its line of attach- ment to secure it firmly to the compound, which is chilled and the .sides of the wedge made smooth and flat, then oiled, as is also the interior of the tray. The tray is filled with plaster and placed in the mouth : when hard the tray is removed and the outer portion of the impression detached. If the wedge of compound has not come away with the impression tray, a hook instrument is inserted in its posterior wall, and by this means it is detached. The right and left segments of the impression may now be removed without difficulty. Occasionally it may be required of the dental operator to take an impression of an arch in which one, or it may be several, of the teeth are loose, and it is designed to retain them until a fixture is ready to be inserted, so that the patient may be spared the annoyance, humili- ating to morbidly sensitive persons, of exhibiting vacant spaces in the dental arch. The greater number of these cases are those suffering from some phase of pyorrhoea alveolaris. The teeth are recognized by the operator as being past hope of retention, and the patient protests against their forcible extraction, preferring to await the inevitable exfoliation. In such cases a tray is adapted : its inner surface is oiled, and the tray is withdrawn from the impression, which is then removed in sections to avoid stress upon the loose teeth. Unusual care must be exercised in these cases, as the danger of extracting the loose teeth in withdrawing the impression is not remote. Particular care must be observed to secure an accurate impression of the gums and gingival margins. If the case be one for which a new plate is to be made, the plaster teeth are cut from the model, and the plaster cut away, representing accurately the appearance and form of the gums when the loose teeth shall have been lost. This trimming, while following with exactitude the gum outline which will be left at the site of each lost tooth, should be of sufficient depth to ensure the close adaptation of the future plate to the natural gum. In taking impressions for cases requiring palatal restoration either of hard or soft palate, or of both, it is required that an accurate impression be secured of all of the edges of the opening representing the anatom- ical deficiency. An examination of the anatomical parts will exhibit the 296 TAKING IMPRESSIONS OF THE MOUTH. palatal structures as a partition-wall between the nasal and oral cavities : it is evident, therefore, that care must be exercised and means adopted which shall prevent the entrance into and the retention of the impression material in the second, the nasal chamber, an impression of which for present purposes is not required. An effective method for securing the desired impression is that devised by the late Prof. Geo. T. Barker, and employed by him almost exclusively. A piece of soft sponge is trimmed to approximate the form of the break, and make slightly larger than it ; the sponge is to be softened in warm water. The sponge is then saturated with a batter of impression plaster, placed and held carefully in position until the plaster has hardened. The sponge is then carried backward to separate it from the parts and permit its removal. Its under (the lingual) surface is trimmed smooth, varnished, and oiled, and replaced in its position. The case is now one to which the ordinary methods of impression- taking apply, except that the extent of surface is greater. An extension of tin or of wax is cemented to the heel of an appropriate impression tray, this extension to be long enough to carry the plaster to the poste- rior pharyngeal wall. The tray is tilled with plaster, carried into posi- tion, and held until the material has hardened. The impression is with- drawn, separating it from the sponge section, which is next detached and set in its proper position in the body of the impression. In taking impressions of cases of fractured maxillse, for which inter- dental splints are to be made, no attempt at the full reduction of the dis- placement is attempted. Plaster of Paris is the impression material to be employed, as its proper manipulation in these cases is attended by the exhibition of less force than with any other material. A large impression tray is selected, its surfaces are freely oiled, a plaster batter is placed in it, and the tray is carried into position. When the plaster has hardened the oiled tray is detached, separating readily. The impression is next re- moved in sections, which are adjusted to the tray, cemented together, varnished, and a plaster cast poured. The further steps of these opera- tions will be described under the head of " Interdental Splints " in the chapter on " Dentures upon the Vulcanized Caoutchouc Base." ^ Impressions into which molten metal is to be poured are taken in a mixture of plaster and marble dust, pumice, or whiting, the mixture requiring a greater length of time for setting than does plaster alone. The impression is placed in an oven and carefully and thoroughly dried : it is now set in a bed of moulding sand, which is built up around it to any depth it is desired to have the metallic model. The metal, usually tin, to serve as a base upon which a vulcanite plate is formed is poured in the impression and sand walls. Impressions taken in this mixture are by some operators made to serve as soldering investments for bridge- pieces. Models of what are known as the fusible alloys may be poured in plaster impressions as soon as the latter are removed from the mouth : such models are never to be subjected to a temperature above 150° F. 1 C. J. Essig. CHAPTER YII. MAKING OF MODELS AND THEIR PREPARATION. By H. H. Buechaed, M. D., D. D. S. Impeessions of modelling compound receive no treatment prelim- inary to pouring the plaster cast, except that they are dipped in water and the surplus of the latter shaken out, leaving a moist surface over which the plaster batter will flow freely. When the cast is hard the modelling compound separates readily from its surface when the impres- sion is softened by heat. Wax impressions receive a coating of thin sandarac varnish prior to forming the cast ; then, if the wax is not made too hot, it will separate from the plaster without adhesion to its surface. Without the interposition of the layer of varnish the wax exhibits a tendency to cling to the cast. All of the pieces broken from a plaster impression in its removal from the mouth are to be carefully preserved and fitted to their proper positions. This detail frequently requires the exercise of much patience, but when it is considered that any defects existing in the impression are reproduced in the model, and that the success of a finished piece depends primarily upon the accuracy of the model, it becomes evident that time spent in carefully putting together a broken impression is ultimately time saved. Each piece is fastened into position and the impression attached to the tray by means of adhesive wax. At the completion of this operation it should be noted that the impression is in accurate contact with the cup, that the lines of fracture are but hair lines, and that all edges are closely adapted to those of the tray. Any minute imperfections may be rem- edied by placing small pieces of softened wax in them, and by means of a spatula making it flush with the surface of the impression. Separating Media. — It is necessary to coat the surface of the impres- sion with some medium which shall prevent the adhesion of the plaster of the cast to the impression, and yet be of such tenuity as not to oblit- ■erate any of the fine lines of the latter. A wash of soapsuds is employed in some laboratories as a separating medium. An ounce of Castile soap is placed in a pint of water, which is then heated until the soap dissolves. This solution is painted over the surface of the impression while the latter is still damp, and as soon as the impression is glazed the cast may be poured. Thin solutions of collodion painted over the surface of the impres- sion will glaze its surface and prevent the adhesion of soft plaster. The method most commonly and acceptably employed is by double 297 298 MAKING OF MODELS AND THEIR PREPARATION varnishing the impression. After the latter has set for about half an hour, long enough for it to harden perfectly and yet not dry out, a large camel's-hair pencil is dipped in shellac varnish and a thin coating applied to all the surfaces of the impression : this speedily soaks into the substance of the plaster. Every part of the impression is to be colored a light brown. This coating should not be thick enough to glaze the surfaf^e, as it is the coloring, not the separating medium proper. When the shellac is dry a uniform coating of sandarac varnish is applied : this should give a glaze to the surface of the plaster, and yet should not be thick enough to obliterate any fine lines. It is the prac- tice in some laboratories to apply a third coat, one of oil. This is quite unnecessary ; moreover, should there be the slightest excess of the oil that portion of the plaster in contact with it is made soft, and this may injure the model. Several varnishes have been suggested one coat of which shall serve the double office of coloring the impression to some depth and glazing its surface. These varnishes must not be thick enough to obliterate any of the fine lines of the impression. Should the case be one in which there are isolated, long, or irregular teeth whose plaster forms are liable to fracture in separating the model from the impression, or which it may be desirable to subsequently remove from the model, long toilet pins are thrust into each tooth impression : when more than one tooth requires support, see that the pins are as nearly parallel as practicable. With lower impressions it is a general practice to cut a piece of sheet wax to fit between the inferior edges of the impression, so that a flat surface is made representing the floor of the mouth. The prepared impressions now represent matrices in which a model is to be cast which shall be an exact reproduction of the jaw in plaster. This cast is to be so made that it exhibits no blemishes on its faces or defects in its substance ; not a line or depression is to be seen on its sur- face which is not there in consequence of its presence in the impression. The immediately succeeding operation, although apparently of great simplicity, is a procedure in which few become expert and a less number masters : it is that of forming the model making the plaster cast. There are four primary requisites for its proper performance : The first, the preparation of the impression, securing a uniform and dry glaze on its surface, without destroying any of its fine details. Second, the proper variety of plaster : this, when set, should be much harder than the impression, should mix readily with water without the formation of lumps, should set slowly, and when poured upon a smooth surface should glaze. When hard it should have no suggestion of pastiness about it, cutting as a crystalline body, and not, as inferior plasters do, as a semi- glutinous mass. The best plaster is that known as the coarse Eastern ^ variety. Its particles appear much coarser than those of ordinary plaster, and are more distinct ; it appears drier ; it does not set perfectly for several hours, but after some days acquires a brick-like hardness. Italian image-makers employ it for making casts. Many of these casts, when examined, are seen to have a perfectly smooth surface, and yet have been made of the coarse plaster. This is explained by the statement ^ Made in Nova Scotia and Maine. POURING THE CAST. 299 that the coarse particles are surrounded by a powdery plaster, which, when the mass is poured, fills the spaces between the coarser particles. The next, the tliird requisite, is that the plaster shall be properly mixed with water, combined with it to form a paste which shall be perfectly smooth and semifluid. The last requisite is that this paste shall be per- fectly applied to every portion of the surface of the impression. Aside from a rough surface of a model caused by improper preparation of the impression or faulty mixing of the plaster for the model, the most common cause of blemishes or flaws will be found in air-bubbles entangled in the soft plaster and leaving spaces upon the model unfilled by plaster. Pouring the Cast. — Plaster flows poorly over dry surfaces, so the sur- face of the impression is wet and the surplus water shaken out. Should the impression have become unusually dry, it is immersed until air-bubbles cease to rise from it ; this will render separation from the model easier. As a preliminary step Dr. Essig advises making a thin, smooth batter of plaster, which by means of a camel's-hair pencil is painted into the deepest portions of the impression and into its fine lines. If the case is one for which a metal plate is to be made, the model is to be thicker and broader than if the plate is to be of vulcanite. Casts for vulcanite are made never less than three-quarters of an inch thick at the thinnest parts ; those for metal at least two inches thick. Assuming that the model is to be for a metal plate, about half a pint of water is placed in a plaster-bowl, without salt or any substance to hasten the setting of the plaster or which would cause deterioration of a model. Into the water plaster is slowly sifted, so that in the passage through the water each particle is wet : the sifting is continued until the surface of the plaster is level with that of the water ; the mixture is now thor^ oughly stirred with a spatula until a perfectly smooth paste is made which shall flow freely and yet not be too watery. The impression is held in the left hand, its distal angle elevated ; the ball of the hand is resting upon the edge of the plaster table. A portion of the plaster is taken upon the end of the spatula and placed at the elevated heel of the impression ; now, by a continuous jarring of the hand upon the edge of the table the plaster is made to flow forward, driving all air from the deepest portions of the impression. More plaster is added and jarred into place, and more and more added as the plaster ceases to flow until the impression of the teeth and that of the alveolar walls is filled. The tray is now placed in a horizontal position, additions of plaster made and jarred into place until the impression is more than full. The plaster in the bowl, now beginning to thicken, is taken in larger quan- tities, laid upon the cast, and thoroughly spatulated : the additions are made until the mass of plaster represents an inverted pyramid, the distance from the edge of the tray to the base of the pyramid being about two inches. The spatula is passed around its walls, smoothing them as shown by Fig. 339, and the mass is inverted upon a piece of glass and permitted to set thoroughly. The method of pouring the cast is the same irrespective of the im- pression material. If this be of wax or modelling compound, the base of the cast is set on a M^arm stove-plate or upon anything which shall now gradually raise the heat of the cast and impression to something 300 MAKING OF MODELS AND THEIR PREPARATION. less than 200° F. . When the impression is made as soft as when pre- pared for the mouth, a finger is caught under a lateral border, and the Fig. 339. softened material is drawn entirely away from the walls of the model. The heel of the impression is next loosened ; then by steady traction the body of the impression is withdrawn. The wax, if a wax impression, should be softened, not melted, as in the latter case the surface of the plaster becomes infiltrated with the wax. If small portions of modelling compound adhere to the face of the cast, the softened impression which has been removed is pressed against them ; they adhere to it and are removed. With due care two casts may be secured from one modelling-com- pound impression. One cast is poured, and when hard is set in cold water to below the edge of the impression. The water is slowly raised to the softening heat of the compound, when the latter parts readily from the wet cast, being withdrawn by steady traction in the direction of the axes of the teeth. Of course the soaked model is unfit for laboratory use ; however, it may serve for comparison after the working model is destroyed. The impression is immediately chilled and a second cast poured. Separating Plaster Impressions. — In separating a plaster impression from the cast it is quite possible by undue haste or carelessness to irre- trievably damage the latter. The practised laboratory workman removes an impression from a cast without even slight mutilation of the parts or surfaces of the latter, no matter what irregularity may be present, such as long, irregular teeth or undercuts. As in putting together broken im- pressions, infinite care and patience are necessary. The sides of the cup are first freed of plaster, so that none of its edges interfere with the removal of the tray. The tray is tapped lightly from side to side and across its bottom until it is seen to loosen from the im- pression. Should the latter be for a full denture, the plaster overlying the alveolar ridge is scraped away until approach to the cast is shown by entrance to the layer of plaster which has been colored by the shellac varnish. It has been recommended to color the water into which the plaster for MARKING THE PLATE OUTLINE. 301 the impression has been sifted with aniline red, to furnish a guide in separating the cast from the impression.' This, however, does not pro- vide the danger-signal that shellac varnish does. The latter, by coloring the impression to a limited depth, indicates when the knife is approaching the cast : in the former case the cast may be inadvertently marred by the abrupt passage from the red to the white plaster. When the yellow appears as a continuous line, the upper edge of the impression is freed from overlying portions of the cast : a small knife- blade, introduced under the edges, removes the outer wall of the impression in pieces, separating it from the body of the impression at the yellow line. A blade introduced beneath its posterior edge dislodges the body of the impression en masse. If a full lower impression, the cast is cut away until all of the borders of the impression are free, when it is removed after the same manner. In separating casts for partial cases the first object is the perfect free- ing of the plaster teeth from the impression plaster. The highest (most prominent) parts of the impression are scraped away until the varnish overlying the tips of the teeth is exposed. Beginning at the masticating surfaces, the impression is chipped away piecemeal from the plaster teeth until they are entirely free, and for more than a quarter of an inch about the base of each tooth the cast is clear of impression. The alveolar por- tions are removed in sections ; the body of the impression may usually be detached in one piece. At the completion of the separating process the cast should show no knife-marks. Trimming the llodel. — If the model is one over which a plate is to be made of one of the vegetable bases, it is cut down until less than one inch thick, and the surplus plaster beyond the lines of the mouth is cut away, leaving a model which may be set in a vulcanizing flask without requiring further trimming. If to be reproduced in metal — that is, if a plate is to be made of one of the malleable metals — and dies are to be cast, the walls of the model are given a slope at all its sides, so that the broadest part is its base. The thickness of the model is not reduced at all. Any small and evident defects about the necks of plaster teeth or between them are to be corrected by means of a pointed blade, carefully trimming out the portions which represent the imperfections. Marking the Plate Outline. — Upon the surface of the model the out- lines desired in the finished plate are marked. It is first determined what may be the extreme limit of its posterior border. This must be anterior to a line affected by the movements of the muscles of the soft palate. The anterior limit of movement of these muscles varies with the individual : in one it may be posterior to the junction of the maxillary with the palate bones ; in another it may be forward of a line joining the condyles of the alveolar arch. In flat mouths the line will, as a rule, be found comparatively far back ; in high arches it is frequently found for- ward. The limit-line is noted by having the patient make the sound ah! with the mouth wide open, and noting the line at which the muscular movements of the palate cease. The line will be usually found at about the line of the condyles ; the posterior edge of the plate is therefore curved forward from such a line. 1 Dr. C. W. Spalding. 302 MAKING OF MODELS AND THEIR PREPARATION. Fig. 340. The alveolar edge of the plate is now to be marked. It should extend as far as possible up the buccal and lingual aspects of the alveolar wall, without impinging upon those soft parts affected by the movements of the cheeks or lips. Beginning at the fraenum of the upper lip, the plate line is marked clear of this from the middle point. The plate lines now ascend in a curve to about the positions of the first bicuspids. The line now curves downward to escape the anterior edge of the buccinator muscle, and ascends again, enclosing the condyles and joining the line marking the posterior limit of the plate. In the mouth of one patient these lines may be nearly half an inch above the alveolar borders at their highest points ; in another, less than one-fourth of an inch. The outline follows that of the mucous membrane reflected from the lips and cheeks upon the alveolar wall, and must be made to accord with it. Should the labial portion of the alveolar process be unusually prominent and high, so that no increase of fulness is permissible, the natural gum not having lost its normal contour, the plate is not carried over the labial wall : its anterior edge is drawn along a line which is that of the necks of the incisor teeth. The usual outline for a full upper plate is shown in Fig. 340. In marking outlines for a full lower plate, it is to escape, to be made clear of, the mucous mem- brane reflected from the cheeks, lips, and floor of the mouth, and to be cut well out at the insertion of the frsenum of the tongue. The muscular parts of these regions carry the overlying tissues to higher points than indicated by the model, so that full allowance must be made in marking the plate outline. This is particularly notable in the movements of the frsenum of the tongue. In marking the outlines of a partial lower plate, they are drawn to Tepresent the plate resting upon about one-half the lingual aspects of the natural teeth when these stand in columns ; when there are isolated teeth, these are generally utilized for clasping and the plate is carried around their edges. The same rules are observed as to free- dom from impingement upon the soft parts. When an iso- lated tooth stands perpendic- ular to the alveolar arch, the buccal line of the plate is A' V_ ..liisasi^ y made continuous, an opening being made in the plate for the passage of the tooth. A common result attending the wearing of lower plates accurately fitting a model is a tendency to bury their buccal edges into the soft tissues. The precaution is taken to raise this portion of the plate from Position, relative size, and shape of vacuum- cavity for broad palatal arch. VACUUM CHAMBERS. 303 the mouth, so that this tendency becomes impotent. A layer of wax is built over the outline of this portion of the plate edge about one-eighth of an inch deejD, immediately over the line, and shading to a feather edge where the wax comes in contact with the alveolar wall. Raised from this edge, the pressure of the plate is greatest at the height of the ridge at B, Fig. 341. This precaution is always taken for partial lower plates. Where the crest of the ridge is represented by a sharp edge, it is usual to place over it a layer of wax about one-sixteenth of an inch in thick- ness, the same precaution to be taken in raising the plate edge. This throws the greatest pressure of the plate upon the alveolar walls. If not raised at the crest, a plate will bear too hard upon the underlying soft tissues and cause distress. Any areas of the arch or vault enclosed in the plate outline which represent hard nodular parts are to receive a coating of wax, so that when the soft tissues yield to the pressure of the plate, the latter will bear uniformly upon all parts of its base. In lower cases these nodular areas are most commonly or nearly always found at some part of the lingual aspect of the alveolar arch. At about the site of the first bicuspid is the usual situation. In upper cases they are almost invariably found occupying the median line of the vault, in a position which w^ould underlie the posterior portion of the plate. They commonly mark the junction of the palatal processes of the superior maxillary and palate bones. It has been advised in such cases to scrape from the impression itself, before pouring the cast, a layer of plaster just thick enough to represent the yielding of the soft tissues. This method, although satis- factory in many cases, alters the model and does not give full assurance of accuracy, so that the method to be preferred is to make a perfect model and reverse the procedure : build wax over the prominences to a depth equalling the scraping of the first method. These protuberances may extend so far forward as to demand change in the configuration of the plate outline ; this will be discussed later. Vacuum Chambers. — These are concavities made in the palatal aspect of the plate which, when the plate is in position in the mouth, have the air partially exhausted from them, and the atmospheric pres- sure upon the lingual surface of the plate causes the latter to adhere to the surface of the vault.^ There is a lack of harmony of opinion as to the utility of this device, many maintaining that its office is either but temporary or that it is unnecessary. A majority of prosthetists have, however, an abiding faith in its permanent utility. It is important that these depressions be properly shaped and correctly placed. The follow- ing description will illustrate the means of determining their positions : The slight movement usual with a plate during mastication tends to separate it from the mucous membrane and permit the access of air to its under surface. The line of least movement, as the movement is lateral, a rocking from side to side, is along the median line of the vault ; and as the con- cavity of the hard palate is usually of an irregular vault form, the point of least movement is near its apex. If the movement does not extend to an edge of the chamber, the stability of the plate is not materially ^ Dental Cosmos, vol. xxxvii. 304 MAKING OF MODELS AND THEIR PREPARATION. affected, but when one of these edges loses its contact, air enters the chamber and adhesion is destroyed. The more closely the edges of the chamber approximate this line the less tendency to disturbance there is, so that comparatively narrow chambers are to be preferred ; but the depression should be of sufficient size to not materially lessen the effects of partial vacuum. Naturally, the chamber should be in the area of greatest stability, that of least movement. This area will be found around and about the centre of gravity, and in shape resembling the outlines of the dental arch. The dental arch represents, approximately, a parabola in outline. This encloses a trapezoid, the centres of the cuspids marking the extremities of the short, the centres of the third molars those of the long, parallel side. Straight lines, joining these points, complete the figure. The centre of gravity of a trapezoid is found by suspending it first by one obtuse angle, and next by one of the acute angles ; vertical lines dropped from the points of suspension will, in intersecting, mark the centre of gravity. Thus, on the diagram (Fig. 342, A, B, C, D), suspend it first from the angle A, D, C, and drop a vertical, D, F. Suspend from the angle B, A, D, and drop a vertical. A, E. Their intersection at the point G is the centre of gravity, which is posterior to the intersection of the diagonals. Fig. 342. A, B, C, D, trapezoid of the superior dental arch gravity lines, their intersect G, centre of gravity of figure ; A, G, E; D, G, F, ons marking G (Burchard). About the centre of gravity the vacuum chamber should be placed, its outline following that of the arch, on a smaller scale. In the vast majority of cases the centre of gravity thus determined will be found at about the height of the vault. The ends or apex and angles of the chamber should be about equi- distant from the centre of gravity — as a rule, the apex of the chamber as far in front of the intersection of the diagonals as the centre of gravity is behind that point. To apply these facts practically as a guide to finding the correct position of a chamber, draw first on the plaster model the median line VACUUM CHAMBERS. 305 of the vault. From the centres of the cuspidati to the centres of the third molars draw diagonal lines, the diagonals of the trapezoid. When all the teeth are absent, draw from the positions formerly occupied by the cuspidati to the centres of the condyle the two diagonals (Fig. 343). Fig. 343. To find the centre of gravity, draw from tlie centres of both condyles lines to the junction of the first and second bicuspids of the opposite sides other lines, which intersect at a point of the median line G ; this point will be the centre of gravity of the trapezoid and of the palatal vault. The intersection of the diagonals will mark the focus of the small parabolic area to be covered by the chamber-piece. Draw this parabola, its apex, about as far in front of the point of intersection of the diagonals as the centre of gravity is behind the latter point, the angle of the parabola the same distance from the centre of gravity as the apex. Should there be a lack of harmony, of bilateral symmetry of the right or left side of the arch outlines, make the outline of the chamber in correspondence. Fig. 343 represents a model, having the outline of an old chamber too far front ; the correct position is marked behind it, also the lines which have determined its position. It may be remarked, parentheti- cally, that an increased stability was secured by correcting the position of the chamber in this case. To form the chamber-piece, fold a small strip of paper, and lay the line of fold along the median line of the arch, and on the surface of the paper draw one-half the outline of the chamber area. While folded the paper is cut along this line, unfolded, and is now the pattern for the chamber-piece. If of metal, mark the shape of the paper on the metal and cut out, and fix in position by means of a pin at the apex and at each angle. If of wax, cut from a sheet of gutta-percha and wax base-plate (which is usually too thin by half for chambers). Make this cut firmly and sharply. Soften the wax slightly, flow over the height of the vault a little melted adhesive wax, and press the wax chamber into position, the outlines of wax and ])encil-marks corresponding. A warmed spatula is used to smooth the edges of the chamber, which should be sharp, dis- 20 306 MAKING OF MODELS AND THEIR PREPARATION. Fig. 344. tiuct, and a slight slope given to the walls. Chambers which have not sharp outlines do not afford firm adhesion. I have followed this little plan for at least ten years, and in that time applied it to thousands of cases, and believe with better results than had haphazard placing of a chamber been practised. Plates .should by all means be made without chambers if without it they still fulfil all the requirements for a good piece ; but experience has taught that this result is the exception, and not the rule. The foregoing description applies to the average vault : peculiarities in the configuration of the latter may demand modification of the form or of the position of the chamber. Nodular areas which underlie that portion of a correct plate line, which the posterior portion of the plate and the posterior edge of the chamber would embrace, demand change of principle. Where these protuber- ances are exactly in this position a satisfactory adhesion is occasionally had by first covering the nodular areas with wax, then adapting the wax chamber model, making its posterior portion very shallow (Fig. 3-14). Should the protuberance extend well into that portion of the plate area covered by the vacuum chamber, it is usually neces.sary to carry the ])osterior edge of the chamber ward of the anterior edge of elevation, giving the heel of chamber a concave form (Fig. 345). Should the elevation lie entirely in an area which would normally be embraced by the chamber, a thin wax chamber model is cut and adapted to cover it, its edges bearing upon the soft tissues around the base of the elevation. In some instances the disturbing element may occupy so much of the for- the the Fig. 345. Fig. 346. height of the vault that a median chamber is inadmissible. A weak adhesion is secured by means of what are known as lateral chambers (Fig. 346). These are made small, oval, and comparatively deep, the VACUUM CHAMBERS. 307 Fig. 347 edges nearest to the height of the vault to impinge upon the soft tissues at the base of the hard elevation. What are known as horseshoe chambers are applicable where the hard area does not extend too far forward. Dr. U. B. Kirk noted in his practice a case in which adhesion could be secured only by the form of chamber shown by the dark shading in Fig. 347. In all of these odd chamber forms the walls of the wax pieces should be trimmed at such an inclination that no undercuts are formed ; each chamber wall should be almost paralled with the axis of the model, and each should be sharp and distinct. The junc- tion of the chamber-piece with the face of the model should be sharply outlined. If after trial in matrix-mak- ing (Chapter VIII.) it is found the sand drags about the wax chamber-piece, the latter must be trimmed to overcome the dif- ficulty : the angle of its walls with its free surface must be made more obtuse. The model is now ready for the succeeding stages of preparation. Recalling now that from this model a matrix of moulding sand is to be made — a mould which shall be a reverse to every line of the plaster model — it is evident that the latter must be prepared so that it may be withdrawn from its bed without breakage or distortion of the sand. Bodies of shapes ranging from those of cones to those of cylinders may be withdrawn and leave a true matrix ; but anything resembling a re- versed cone would necessarily break or disfigure the sand matrix by its withdrawal. First, the model must be given a coating of sandarac varnish, glazing it faintly, so that the moulding sand will not adhere to it. Next, any depressions present at parts not to be covered by the plate are built out to the pyramid faces by means of wax ; as, for instance, at the labial aspects of the inferior anterior teeth in partial lower cases. Teeth which are much inclined from the vertical or which have such shapes as would complicate the moulding operation are to be removed. At about one-sixteenth of an inch above the surface of the model a saw- cut half through tlie plaster tooth is made ; light force will now break the attachment of the tooth, and it is slipped from its pin support. The sharp line of fracture furnishes a guide in replacing the tooth after the dies are made. It is occasionally designed, particularly for plates having all or part of the artificial gum formed of vulcanite, to form the alveolar edge of the plate into a rim. This form of rim is always employed with continuous- gum dentures. The method of preparing the model for this variety of dentures will be described in Chapter XIII, on Continuous-gum Work. 308 MAKING OF MODELS AND THEIR PREPARATION. The edge of the rim, marking the height of the plate, must be at a line which shall ensure against reducing the plate after it is finished. At about one-sixteenth of an inch beneath the usual plate outlines a wall of wax is applied to the alveolar border of the model : the angle which this wax forms with the alveolar wall should not be more than a right angle, and if possible it should be acute. The ledge of wax is made perfectly smooth and clear cut: it should be something more than one-eighth of an inch broad. Its outer wall is to merge into the general walls of the model. Fig. 348. Cast of upper jaw, ready for moulding The model for the \ acuum-chamber is in position. The experience of many skilled prosthetists has demonstrated an ad- vantage to be gained through a judicious alteration of the face of a model. Vaults which exhibit defined areas of differing density are subjected to uneven pressure by a plate which is perfectly adapted to an accurate model. It is recommended that a careful topographical examination be made of the vault, and those portions found to be soft are to have the cor- responding areas of the model scraped away as much as they will yield to the pressure of the plate. The portions to be trimmed are commonly in the height of the vault at both sides of the median line : between the apex of the vault and the beginning of its walls at their posterior portions will be found in most mouths areas softer than the other aspects of the vault. This method is particularly applicable for mouths where it is designed to construct a plate without a vacuum chamber. CHAPTER VIIT. DIES, COUNTER-DIES, AND MOULDING. By H. H. Burchard, M. D., D. D. S. A DIE is the duplication of a model in metal made to facilitate the formation of some resistant substance into a plate which shall be per- fectly adapted to the surface of the model. A counter-die is the female die, formed by pouring over the surface of the die a defined block of a metal or alloy more fusible than the die. The operation of moulding consists in forming in sand or any suitable medium a matrix which shall represent accurately a reverse impression of the plaster model : the die is formed by filling the matrix with molten metal. The purpose of the latter operation and the implements produced by it is the securing of two metallic blocks of sufficient rigidity to permit the forming between them of a sheet of metal of a size, sliape, and variety suitable to serve as a supporting base to an artificial denture — a lamina which shall be perfectly adapted to the surfaces of the alveolar ridge and palatal vault. Moulding Sand. — Three varieties of sand are used in the dental laboratory for making matrices. The first and oldest is the finest grade of iron-founder's black sand ; the second, the brass-moulder's brown sand ; and third, marble dust. The last is used perhaps more frequently tlian either of the others : it is no better than the second variety — indeed, the writer believes the brass-moulder's sand gives the best matrices. A sand for this purpose should be fine-grained enough to give a smooth surface to metals poured over it, and yet possess sufficient poros- ity when packed in a moulding ring to permit the escape of steam formed when molten metal is poured in a moist matrix, and should form a mass of sufficient coherence to maintain a given form and to permit the with- drawal of a prepared model from it without fracture. Marble dust has the two advantages of being more cleanly and retaining moisture longer. Preparing the Sand. — Upon the preparation of the moulding sand will depend much of the success of die-making. The sand should be moistened uniformly and sufficiently to give a sharp line of fracture when a mass made by squeezing in the hand is broken, and yet be in such a condition that it will readily pass through the meshes of a fine flour-sieve. To attain or produce this condition care and deliberation are necessary. Twenty minutes is none too short a time in which to properly prepare three quarts of sand. 309 310 DIES, COVNTEB-DIES, AND MOULDING. About a gallon of the sand is placed at one end of the sand-tray and gradually drawn toward the operator by means of the sand-crusher, pul- verizing any lumps which may be present. It is now sifted, and hard lumps, fragments of zinc, lead, or other foreign materials thus separated are cast aside. The sand is spread over the floor of the sand-tray in an even layer, and sprinkled with about half a pint of water ; it is then stirred and tossed with a broad wooden spatula, and then thoroughly rubbed with the sand-crusher for fifteen minutes or more, then sifted. The sieved sand should be tested by compressing a quantity in the hand ; it should break with a sharp line of fracture. There is an indescribable feel to properly prepared moulding sand with which the experienced moulder becomes familiar. It has been recommended to substitute oil for water in the preparation of moulding sand, as the sand so prepared is always ready for use. This single advantage does not compensate for the dirty working of the material tempered by that medium. Its odor when heated by the molten metals is also objectionable. Metals Used for Dies and Counter-dies. — The prepared model is to be reproduced in some metal which possesses the following character- istics : It should be hard enough to withstand the force of swaging with- out marked bruising of its surface ; it should be tough and not brittle, so that it will not break ; the degree of contraction should be low — that is, the mass should shrink but little upon solidifying ; finally, it should be readily fusible in the common heating appliances of the laboratory, and when molten should possess a quick fluidity which shall permit of its flowing freely into small spaces. Of all the available metals, zinc alone possesses these several features, and is therefore in general use for the making of dental dies. The alloys of zinc do not answer as well for this purpose.^ The alloy known as Babbitt metal is frequently used for die-making. It has a lower index of contraction than zinc, is more fusible, and is more brittle. Plates made upon dies of this alloy fit the plaster model as they fit the die. In lower plates, particularly those for partial lower dentures, or clasp plates for the upper jaw, this is a desirable feature. Prof. C. J. Essig^ regards the contraction of zinc as being a strong feature of recom- mendation for use in making dies for full upper dentures, for " it Avill be noticed that a plate fitted to a zinc die is found to be in close contact with the plaster model throughout the alveolar walls, but at the pos- terior edge it is short of contact ; thus the greatest pressure is upon the ridge, and the danger of resorption of the tissues of the vault is avoided. With the greatest pressure along the ridge absorption occurs, but in the parts underlying those in which resorption is merely a physiological process. HoM^ever, plates perfectly fitting to zinc dies when placed in the mouth are found to have accurate adaptation ; the expansion of the plaster compensates sufficiently for the contraction of the zinc, and again the yielding of the soft tissues brings the plate in contact throughout its area. The zinc of commerce contains a variable amount of impurities : samples derived from the ores of several localities show an inconstancy ^ Essig's Metallurgy. ^ See Chapter II. PROCESS FOR STAMPING PLATES BY HYDRAULIC PRESS. 311 of physical properties when formed into dies. The variety known as Bertha zinc appears to be about the toughest and most homogeneous. There are many formulas published of alloys to which are given the general title of Babbitt metal. The formula best adapted for dental purposes is that of Dr. L. P. Haskell : containing the ratio of tin that it does, it is comparatively expensive, but the cheaper specimens are not serviceable as dies. The alloy known as Babbitt metal is composed of tin, 72.72 ; copper, 9.09 ; antimony, 18.18. The alloy is largely a mechanical mixture. In melting it is seen that a portion becomes fluid, in which are suspended the crystals of the more refractory metals. In solidifying the base of a die is seen to exhibit distinct evidence of the differences of points of crystallization, one portion crystallizing, while others are still fluid. For small dies the bismuth or cadmium alloys, known as fusible metals, are occasionally used : they are very brittle, entirely too frangible to withstand any but light blows. Compounds known as Spence's metal have been in very limited use for the making of dies. They are sulphides of metals, dissolved by heating in an excess of sulphur. The mixture and the method of using are described by Dr. E. H. Bog Lie : "Description of Process for Stamping- Plates by Hydraulic Press.^ — Within a few years a material called Spence metal has been devised. This substance is really sulphur and iron. It melts at about the boiling- point of water, and in process of cooling a stage is reached, just before solidification takes place, at which the mass becomes exceedingly fluid. At this stage it can be poured into an impression of plaster or even Stent's composition. " This circumstance has caused Spence metal to be used in the hy- draulic press for the purpose of stamping dental plates, as a steady pres- sure of almost any power may be had by this means. It is also possible to make the dies and stamp a plate within two hours from the time of taking the impression. A description of a case in hand will perhaps best serve my purpose. In the present instance an impression was taken with Stent's material, and all the rest of the work was done by my friend and assistant, Mr. Fred. Collett. The impression was chilled with cold water, and sculptor's clay was built up around the margins to the height of half an inch. A paper could have been wrapped around equally well. The impression then was coated with a solution of soap and water. Into this impression, thus prepared, Spence metal, just before the point of solidification, was poured. This Spence metal was chilled immediately on touching the Stent's composition, so that all contraction took place from the top of the centre downward. " The small die thus made was then provided with three legs made of pins heated and pressed into the metal. These pins held it at just the required height, so that the die, being placed in the middle of the iron ring in which the pressure was to be given, stood at the height required for an additional quantity of Spence metal to be poured into the con- cavity and around this little die up to the required level. This die, * Read at the semi-annual meeting of the Massachusetts Dental Society, Boston, June 6, 1889, International Dental Journal, July, 1889. 312 DIES, COUNTER-DIES, AND MOULDING. being quite cold, is covered with whiting, and a counter-die of Wood's fusible alloy ^ is poured over it. This fusible alloy melts at a still lower temperature than Spence metal, and it is poured over the male die by using the heavy iron ring in which the counter-die must remain during the swaging process. This first set of dies being completed, dupli- cates are made, if required, by taking the impression of the male die and repeating the process of casting the dies as often as may be required. " The Spence metal is exceedingly brittle, so nothing but steady pres- sure nnist be permitted. If it should be found necessary to use succes- sive force, others must be made of some other material. In the present instance a Babbitt's-metal die with a tin counter-die was made upon which to break up the plate. '' The flat plate may be placed between the dies with a bit of giove-kid or rubber dam between the plate and the counter-die, and the flask con- taining it placed directly in the press. The screw at the top of the press being turned down to give such pressure as is possible from above, the second screw connected with the plunger at the side is then gradually turned inward by means of the large driving-wheel. The manometer is watched, as indicating the amount of pressure that is being given ; four hundred pounds to the square centimetre is generally enough, though I have as an experiment run it up to twelve hundred. " During the swaging process the plate should be frequently annealed. When finally down, close to the duplicate dies, it receives its last trimming, its last annealing, and is then put upon the original die that was made directly from the impression. When taken from the press after this final pressure, the fit is more perfect than any struck swages can make it. " For suction-plates it is generally necessary to scrape the centre of the plaster impression and not to put in an air-chamber, the fit of the hydraulic-press plates seeming to be as good as the impressions from which they are made." The material and method have not been adopted ; but such a com- pound would serve well for the making of very small dies to which much force is not to be applied. For general use zinc is to be employed for the dies for full upper plates and for the primary dies of all ; Babbitt metal is most useful for making the finishing dies of all partial cases and for full lower plates, and also the finishing dies for the full upper plates occasionally made without vacuum chambers. Metals for Counter-Die^. — The metals in use for making counter-dies are lead, an alloy of lead and tin, and zinc. When molten these metals may be poured upon a zinc die without fusing the face of the latter, provided, of course, their temperature be not too high. Lead, because of its softness, is used as a counter to the first die, and it may be for the second or third die also ; but the lead- and-tin alloy, being harder, is to be preferred for the final swaging. Zinc is used as a counter-die for those cases presenting very deep and ^ Composed of 15 parts of bismuth, 8 of lead, 4 of tin, and 3 of cadmium. This forms a silvery-white, gi-annlar allov, which becomes soft at 135° F. (= 57° C), and fuses at about 145° F. (= 63° C). MOULDINO FLASKS. 313 irregular rugce ; also for swaging platinous gold. The leacl-and-tin alloy is employed as a counter for dies of Babbitt metal. Type metal may be employed for the same purpose. Moulding" Flasks. — The moulding flasks of the dental laboratory have the forms of rings which have been flattened upon one side, corre- sponding with the general outline of the plaster model. They are made of several sizes, telescoping one over another. The largest sizes are used for enclosing the matrix, the smaller to deepen the matrix cavity and thus give increased thickness and strength to the die. A set known as the Bailey flasks is in general use (Figs. 349-351). Fig. 349. Fig. 350. Fig. 351. Bailey's flasks. Dr. Uriah B. Kirk, an expert prosthetist, many years ago introduced as moulding rings sections of heavy five-inch stovepipe, having riveted joints. These sections answer admirably, as there is less danger of pack- ing too tightly the large mass of sand contained in them than were the mass smaller. The writer has for several years used them with greater satisfaction. They are made about five inches deep. A sectional cylinder, known as the Hawes flask (Figs. 352-354), is commonly employed for moulding cases presenting marked alveolar undercuts. Moulding". — The prepared sand is placed to one side of the sand-tray ; the model is set upon the zinc floor, and a large moulding ring is placed around it, using a size which shall clear the model on all sides at least half an inch. A pint or more of the sand is placed in a flour sieve and sifted over the face of the model, adding more and more until the ring is about half full ; then, using the tips of the fingers, the sand is pressed on and about the model until it is packed firmly ; more sand is added until the Fig. 353. Fig. 354. ring is more than full : it is pressed down firmly ; then, using a broad sharp spatula or table knife, the sand is trimmed level with the top of the flask. 314 DIES, COUNTER-DIES, AND MOULDING. The ring is now inverted and placed upon the floor of the sand-tray ; an old excavator having a tapering point is gently driven into the centre of the base of the model, and serves as a handle by which to withdraw the model from its sand bed. Using the handle of the smoothing knife as a percussing tool, the model is lightly tapped on all sides until it begins to loosen ; then, grasping the projecting handle, a gentle traction is exerted upon the model, continuing the tapping, and the model is withdrawn. Another method of detachment is by holding the base of the model over a bed of sand made to receive it; it is tapped until it falls from the matrix. Another is to loosen the model by tapping upon alternate sides, then inverting over the sand bed and permitting the model to drop out. The first method described is to be preferred, as there is less danger of disturbing the matrix. The mould is now examined : if it exhibits a coarse, porous surface, if any portions have broken away, which may be noted by ragged sur- faces to any part of the matrix, it is to be rejected, and the moulding operation repeated until at least two good moulds are obtained. If the case be one in which teeth are remaining, see that the outlines of each tooth be distinct, and also the lines between the teeth. Any teeth standing in such positions as to cause dragging of the sand in withdraw- ing the model from the matrix are to be removed before the moulding. There are cases in which, despite repeated attempts, good moulds are not secured. One class of these cases is formed of those having an overhanging alveolar ridge, particularly at its anterior portion. If the undercut be not too marked, the front of the walls may be raised, bring the axis of this portion of the ridge nearer to a vertical line. An in- FiG. 355. clined bed of sand is made, the front of the model resting upon its highest portion, the heel of the model upon the floor of the sand-tray : it is enclosed by a moulding ring, the sand packed as described, the ring inverted, the base of the metal freed from sand, and it is then detached by holding it over a sand bed and tapping : by this means moulds of undercut cases may usually be secured. If the mould be accurate, the CORE-MO ULDING. 315 sand in the ring is trimmed to a flat surface, A, B. The matrix and ring are then set on an inclined bed of sand, so that the line C, D is almost or quite horizontal. The undercut may be so marked that this expedient does not suffice, the sand breaking away at the part of the mould corresponding to the undercut. The device known as the Hawes flask is now in order. The model if too thick should be trimmed away at its base until the surface of the alveolar ridge is level with the jointed section. This section, with the pins fastening it, is placed in position about the model, and sand packed about the latter. The surface of the sand is made level, and powdered charcoal or talc dusted over it to prevent the sand of the superimposed section from adhering to it. The second section is placed in position and filled with sand, well packed and its surfaces trimmed flat. The second section is removed and placed upon a flat surface. The pin holding the sectional cylinder together is removed, and the cylinder is then carefully opened sufficiently to permit removal of the model. The cylinder is closed, the pin placed in its opening, and the second cylinder set in position over the first. Much care is required to secure accurate moulds with this device, and it may be the dernier- ressort of the moulder will be necessary — the operation known as core- moulding. Core-moulding. — At the site of the undercut the varnished surface of the model is oiled. A batter of 2 parts marble dust, pumice, or beach sand and 1 part plaster is used to extend the wall of the model to the shape of a larger pyramid. When this has set it is carefully Fig. 356. detached from the model, its external wall, upper and lower surfaces smoothed by means of sand-paper, then thoroughly dried over a stove : if used wet, bubbling of metal in contact with it will ensue. When it is cold it is placed in position on the model, and its outer surface and top are varnished. When the varnish has hardened, a mould is made which must be perfect, the outlines of the core being plainly marked. The core is removed from the model and placed in its position in the matrix, and its edges luted to the latter by wetting the sand along the line of junction. The matrix is dried before pouring metal into it. Occasionally it is necessary to use cores for limited undercuts at the lingual aspect of lower cases. They are to be used in all cases where it is impossible to secure an excellent matrix without them. Usually a matrix accurate enough for the starting die may be made by the ordi- 316 DIES, COUNTEB-DTES, AND MOULDING. nary method, tlie core used for the matrix of the finishing dies. Imperfect dies are to be trimmed as described later. A smoother surface may be given the matrix and die by " sooting " the surface of the former, holding it over the flame of a candle. Making- Dies. — The ladles in which die and counter-die metals are melted should be plainly marked, to avoid mixing the latter. About three pounds of fine zinc ingots are placed in a ladle and melted in any of the laboratory furnaces. Where gas is not obtainable excellent gasoline melting furnaces may be used (see pages 25 and 26). The zinc is to be entirely molten before pouring ; if used before it is perfectly fluid, or rather while an unmelted core remains in it, bubbling is almost certain to occur. If raised to too high a temperature, the zinc produces brittle dies. If old dies, and not zinc ingots, have been used, a quantity of scrap wax is thrown upon the molten metal, and it is well stirred, disen- tangling the oxides, which then float upon the surface and are skimmed ofl" before the zinc is poured. When perfectly fluid the zinc is poured into the matrix, holding the mouth of the ladle quite close to the ring. The matrix is poured nearly full ; a smaller-sized moulding ring is set around the matrix and resting upon the sand : this is poured full or nearly full to give increased weight and strength to the die. In about five minutes the die and enclosing parts are freed from sand. The die is now examined for any imperfec- tions : these when found are remedied by trimming with a sharp chisel. The zinc when hot may be cut as readily as half-set amalgam ; if per- mitted to cool, trimming is difficult. The second die is examined, and the better one of the two is reserved for a finishing die. If the case be one for a partial denture, the zinc teeth of the starting die are cut off" by means of a small cold chisel to within one-sixteenth of an inch of the surface of the model, leaving a sharp edge to the stumps, so as to mark the plate in swaging. If for a partial lower, the teeth on the first die are cut off" to just above the plate line, and at an acute angle. As a rule, the teeth should remain on the finishing die. If the dies are of Babbitt metal, the metal must be perfectly fluid before pouring : when the matrix is full a second ring is placed over it, and about a half inch of the molten metal poured in this, and the die is permitted to partially set before further addition is made. As stated before, this alloy is in great part a mixture, not a chemical compound, of the several metals, so that the most fusible constituents remain fluid for some time after the more refractory metal or alloy has set : if too much be poured, the fluid portions ooze from beneath the upper ring. Dies of this metal should be made very thick, as the alloy is much more brittle than zinc. They should remain undisturbed until it is seen from the surface that solidification is complete. They are to receive any necessary trimming while hot, and to be perfectly chilled and dried before pouring the counter-die. Counter-dies. — The cooled dies are freed from sand, and, if they have been chilled by placing in cold water, wiped perfectly dry. Serious acci- dents have occurred through pouring molten lead upon wet dies. The steam confined between the two metals expands with explosive force and drives out and scatters about the molten lead. COUNTER-DIES. 317 Enough sand is placed in a large moulding ring, which has been in- verted, to bring the plate line of the die a little higher than the edges of the ring ; sand is packed about the die level with the edge of the ring. Around and over the die is placed another moulding ring. Babbitt-metal dies and those which are to have zinc counters made over them are to have their surfaces blackened over an oil or gas flame, to prevent adhesion of the counter-die metals. Counter-die metals are to be poured as soon as fluid. The tempera- ture of molten lead is to be tested by thrusting into it a wisp of paper : if it merely browns the paper, it is at the proper temperature ; if it carbonizes or ignites it, it is too hot. The lead-and-tin alloy, the counter-die metal used with Babbitt-metal dies, is to be poured while a small portion of it is still unmelted. Zinc for counter-dies is poured while a portion is still unmolten. When fluid the metal is poured in a small stream, but rapidly, until the ring is full. In pouring counters for Babbitt-metal dies or in making zinc counter- dies do not permit the molten metal to fall from a height upon one point of the die ; it tends to fuse that spot of the latter. When the counter-die has set the mass is freed of sand and chilled in cold water. The die and counter are separated by drawing blows delivered upon the base of the die. The counter-dies are then set upon an avil, the dies adjusted to them, and they are driven together by blows of a swaging hammer. In cases Die and counter-die. which present an unusually high vault and ridge it is advisable to use partial counter-dies to form the vault portion of the plate before any attempt is made to form that portion covering the ridge and outer alveolar wall. The writer has for ten years used a graded set of these partial counters for this purpose. For the largest the die is imbedded in sand to the level of the sum- 318 DIES, COUNTER-DIES, AND MOULDING. mit of the ridge, and a counter-die poured as described. When this has been separated two or more pyramidal masses of lead, covering the height of the vault and about two inches high, are poured, almost drop by drop. These extend about half an inch beyond the borders of the vacuum chamber. The several dies and counter-dies are marked at their heels to designate the dies and counter-dies which belong together. They are brushed clean before using them.^ The methods described are those commonly practised, and which have survived the test of time. Other methods for making dies have been ad- vocated, but they are more the nature of curiosities at this day than applied methods. One of these processes is die-making by dipping. The plaster model has its chamber-piece made of plaster, and is left unvarnished. A sheet-iron basin some four or five inches in diameter, smaller at the base than across its uncovered top, is filled with molten zinc ; in this the face of the unvarnished model is thrust to above the plate outlines. When the metal has set the plaster is removed, the model being destroyed in removal. Around the depression representing the counter-die a mould- ing ring is placed, and the die is made of a metal more fusible than the counter-die. The counter-die may be smoked, and the die made of zinc also. Occasionally dies have been made of the bismuth alloys called fusible metals. The sides of the impression being enclosed with a putty wall of the proper height, the molten metal is poured directly into the plaster impression. Dr. B. W. Franklin^ devised the means of securing counter-dies when this alloy is used for tlie die. A sheet-lead plate is burnished and pressed to fit the die ; this is filled with moulding sand and set upon a bed of the latter ; around it a moulding ring is set, and a counter-die made of tin or a low-flowing alloy. The die is reinforced by the addition of a brass head. A flattened pyramid of the latter metal, having a tinned base of three inches or more, is heated until the solder or tin is fused ; upon this surface the base of the die is set ; when the surfaces are united cold water is poured over die and counter. These methods are rarely practised, as moulding in sand is preferable for obvious reasons. 1 A similar method has been described bv Dr. I. N. Broomell, Internat. Dent. Joum., 1890. ^ Eichardson' s Mechanical Dentistry, 3d ed. CHAPTER IX. SWAGED METALLIC PLATES. By H. H. Burchard, M. T>., D. D. S. The sheet metals employed as bases of support for artificial teeth are gold, silver, platinum, and aluminum. For a brief period sheet palladium was applied for the purpose. A chance overstocking of the market brought the commercial value of the metal to a price making it economically available for dental use. This, however, was but a curiosity in the history of dentistry. The present pi-ice of the metal places it beyond the list of those available for plates. Palladium possesses almost the infusibility and insolubility of platinum, and has the additional properties of greater rigidity and a less specific gravity to recommend it. Platinum is rarely or never used as a base-plate for soldered den- tures ; it is too soft and inelastic : its infusibility fits it for employment when covered by substances fusing at high temperatures, as where faced with porcelain continuous-gum work. The alloy of platinum and iridium, known as iridio-platinura, is oc- casionally employed in the making of plates, the addition of iridium producing a very rigid alloy. Under exceptional conditions plates may be made of the alloy of gold and platinum, called platinous or clasp gold ; this, however, is rare : the alloy is, as a rule, only employed for clasps and to form supplementary pieces for strengthening the weak areas in plates made of more pliable alloys. It is employed when either rigidity, elasticity, or both, are re- quired. Aluminum is occasionally employed as a base-plate, the denture proper being mounted in vulcanite. Its lightness and comparatively easy work- ing properties recommend it, its greatest deficiency being the impractica- bility of neatly and eifectively soldering it. (See chapter on Aluminum, page 146.) The metals commonly employed are gold and silver, the latter used but seldom since the introduction of vulcanite. Sheet gold for making plates is usually 18 carats fine ; it should never be of less fineness, and if finer than 20 carats does not possess sufficient rigidity. Silver plate is the 900-fine alloy known as coin silver. Pure silv^er is too soft. An alloy of silver and platinum is to be preferred to the coin silver ; it is more rigid, and may be made more so by increasing the percentage of platinum in the alloy ; it is less liable to tarnish, and has .S19 320 SWAGED METALLIC PLATES. a much better surface. It is much less rigid than platinous gold. (See Alloys of Silver, page 120.) When the employment of a metal plate is an imperative indication, economical reasons alone prompt the use of silver. Gold is of all metals best adapted for the purpose ; by varying the fineness of the alloy and its components any desired quality of plate may be obtained. Indications for the Use of Metal Plates. — Metal plates possess certain advantages over those of vulcanite, celluloid, or even continuous gums, which are utilized when and where indicated. They are stronger, thinner, smoother, and have a greater conductivity than any of the veg- etable bases. Mouths in which it has been shown that plates constructed of vul- canite exercise an undesirable influence, owing mainly to the non-conduc- tivity keeping the underlying structures at a constant temperature, a metal plate, preferably gold, should be substituted. Metal plates are an imperative indication when the distance between the natural gums and occluding teeth is very slight, or when these latter in occlusion touch the gum of the antagonizing arch. The attachment of the teeth for such cases must necessarily be by means of solder, and a very thin plate is alone admissible ; so that vulcanite, the stronger of the vegetable bases, is inadmissible. Peculiarities of the Plate Metals. — In manipulating gold it must be frequently annealed, raising it to a dull red heat and plunging it into cold water. Under manipulation it soon becomes very elastic and obdu- rate, and must be reannealed as soon as this condition is re-established. 20-carat gold, while not as rigid or elastic as 18-carat, is not so ho- mogeneous an alloy : although it is softer, it has a greater tendency to crack under manipulation, and much care must be exercised in working it over tuberosities and into undercuts. Gold may be stretched — that is, it exhibits its malleability under the operation of swaging — but, as this thins the ])late, it is better to so manipulate the latter that it maintains a uniform thickness. It is to be pressed into position, not turned into it, as is done under the operation of spinning or raising sheet metal. Particles of base metal must be kept from its surface : a particle of lead will form with the gold underlying it a brittle alloy, melting at a low temperature, so that when the plate is heated a hole is burned through the plate at that point. Heavy sheets of gold, as indeed of any metal, work more smoothly and exhibit fewer wrinkles than thin sheets, but their adaptation is not so close. The latter require much care to work smoothly, the former much force, and generally a zinc counter-die to produce accurate adapta- tion to the die. Platinum is annealed at a very high temperature, and then becomes very pliable, and offers a surface to which the base metals attach them- selves closely ; and as some of these latter form very fusible alloys, pen- etrating the substance of the platinum as soon as heated red, care must be exercised that the surface of the platinum be kept free from such contamination. Silver is annealed at a temperature a little below red heat : its surface oxidizes quickly above that point, and it fuses with startling suddenness. This metal almost invariably suffers more or less change of form in heat- FORMING THE PATTERN. 321 ing. Although requiring less frequent annealing than gold, it is more liable to crack unexpectedly. Aluminum behaves under the swaging hammer after the manner of sheet zinc. If annealed at too high a temperature, it becomes brittle and cracks readily ; annealed and manipulated deliberately at a low tempera- ture, it is tough and fibrous. More pressure than percussion is required to adapt it — the reverse of the platinoid alloys, which require hard blows to adapt them. Palladium is at present never used, but should it ever become cheap enough for dental application, it is to be worked like gold. Forming- the Pattern. — The first step in the making of the plate is the important detail of forming the pattern. Due regard for economy suggests that the pattern be no larger than the plate itself — than is abso- lutely necessary. Gold plate in the condition of scrap has its commercial value diminished 25 per cent. The pattern should be formed upon the die, to avoid the bruising of the plaster model. A sheet of pattern foil about four inches square, and stout enough to require some force in manipulating it, is laid upon the die, and by the fingers is pressed into the deeper portions of the die : when adaptation is as close as can be made by such means the rubber tip of a lead pencil is used to secure a closer adaptation ; this is succeeded by the pressure of small smooth points made of old tooth-brush handles until the pattern metal fits the die. It is marked by a sharp steel point along the plate outline, and a penknife blade applied to cut off tlie surplus metal. Pat- terns for partial plates should be cut out carefully at the necks of the teeth. The chamber-piece should also be represented in a pattern, extending on all sides about one-eighth of an inch from the base of the chamber. Occasionally, in cases having an unusual distance from condyle to con- dyle, those in which experience demonstrates that lateral bending is a danger, the chamber-piece may be extended at the angles, forming but- tresses to the plates (see Fig. 358). Ficx. 358. Fig. 359. The pattern is removed from the die and carefully flattened between the fingers. It is then laid upon a sheet of cardboard, and an outline about one-eighth of an inch larger than the tin pattern is marked. Adepts in the laboratory require less margin, novices usually more. 21 322 SWAGED METALLIC PLATES. At places representing the necks of teeth the plate should always be cut with a rounded, never an angular, outline. Patterns for lower plates require additional care : the adaptation of the tin along the lingual aspect must be very accurate. It is a matter of some difficulty to accurately straighten or flatten these patterns, and it is of the utmost importance that no distortion occur in the operation. The true outline being repre- sented by the solid lines (Fig. 359), it will readily be seen that if the pattern were bent to the outlines of the dotted line, a plate cut by such a pattern could not be adapted to the die with accuracy. A greater surplus is allowed with partial lower plates, to compensate for the greater danger of the displacement of the laminae in swaging. For upper plates the patterns are duplicated in plates of No. 26 of the B. and S. gauge. The cap piece is to be of No. 28, or, under excep- tional circumstances, No. 27 ; that is, where an increased rigidity of the plate is demanded. Lower plates are usually made of two laminae of No. 29. In partial lower cases, across the space occupied by natural teeth, and to about one-half an inch beyond on both Fig. 360. ^ sides, a piece of platinous gold No. 27 is fitted as described be- low : without this supplementary piece these plates bend too easily (Fig. 360). Plates for upper dentures which are to be retained by means of clasps are preferably made of two laminae of No. 30 plate : their horseshoe form is an ele- ment of weakness, and a single lamina of plate when sufficiently rigid is too thick to be accurately adapted : however, through the Partial lower plate, withj^einforcing piece in posi- ^^^ ^f ^ ^^ ^^^ COUUter-dic a plate of No. 24 gauge may be well adapted ; and this is the thickness to be employed when the operator prefers a single plate. The same care is exercised in flattening these patterns as for partial lower plates. The results due to distortion of the pattern are not so great as with the lower plates, but are none the less annoying, and it may be serious. Forming the Plates. — The poorer die is cleansed, assuming that the plate is one for a full upper denture, by brushing off any particles of sand or metal. The plate is laid upon a block of charcoal, and the broad flame of the blowpipe directed against it until it is a dull red : it is then plunged into water. The coating of oxide formed by this heating is per- mitted to remain, as it serves to prevent, in some measure, the intimate contact of the surface of the gold with the base metal of the die and counter-die. The tin pattern is laid upon the annealed plate, and its out- line marked with a sharp point. The points of the pattern representing the anterior and posterior of the middle line of the vault are marked on the plate, which is then bent by the fingers along a line having these FORMING THE PLATES. 323 points as extremities. It is then placed upon the die, its posterior edge carefully placed in position, and by means of blows delivered with the horn mallet the posterior part of the plate is driven into position : from this work forward, first along the median line, driving the plate into con- tact with the die at the deepest portions of the latter. As soon as the metal plate develops an increased elasticity, remove from the die, brush Fig. 361. Horn swaging mallet. it free of any adherent particles of metal, and reanneal it ; then place on the die, and continue the malleting until a rough adaptation of the plate to the vault is .secured. If the partial counter-dies have been made, the first of these is placed over the plate and struck three or four times with the heavy swaging hammer. Brush and reanneal the plate ; then, using the next counter-die, swage again. Now, while the palatal portion of the plate is held in position by the partial counter-die, the broad end of the horn mallet (Fig. 361) is employed to roughly form the alveolar por- tion of the plate. The outer edge of the plate at this stage having a greater length than the plate outline marked along the model, it is evident that to adapt one to the other at least a portion of the surplus length must be cut out, or the plate must be so manipulated as to contract it along this line, or else the amount of surplus length will be represented by wrinkles in the plate. Some operators prefer removing from the portion of the plate at the frsenum labialis a V-shaped section something less than enough to fully compensate for the increased length of the plate line. The writer prefers a method of manipulation which does not involve cutting the plate. It is difficult and somewhat tedious to prevent wrinkling by this method, but through the exercise of care, plates may be adapted to even marked alveolar under-cuts without wrinlding. The plate is cut something larger than usual along this portion of its outline. When it has been adapted to the stage, and through the means described it is well annealed and placed in the counter-die, the die is 324 SWAGED METALLIC PLATES. set in it, and one or two light blows are delivered with the swaging ham- mer on the die. The plate is again annealed ; any wrinkles which have formed are removed by blows of the horn mallet ; set in the counter-die, and again swaged lightly. Repeat the annealing, malleting, and swaging until all the wrinkles along the plate edge are but small irregularities and nowhere extend to the final plate outline. It is then annealed and swaged, using now heavy blows on the die, and turning the latter with the left hand, so that the blows are delivered above successive portions of the plate. The edge of the plate is now trimmed to near its true line. Forming" the Cap. — The cap piece is annealed and placed in position in the die, and fixed there by light malleting. The first of the partial counter-die is placed over it and swaged. The gold is annealed and swaged by the best counter-die. A pair of dividers, measuring the nar- rowest portion of the ledge of the cap, is passed around the chamber- piece, marking a ledge of uniform width ; it is then trimmed along this outline, and finally its edge is given a long bevel from its upper surface. Plate and cap are again annealed ; the latter set in the second or finishing counter-die, and swaged. Removing the cap, the plate itself is placed in the counter-die, and it is again swaged. Cutting Out the Chamber. — Midway between the lines representing the top and base of the vacuum chamber the plate is pierced by a plate punch. In this opening the blade of a plate saw, set to draw, not push cut, is placed, and then securely fastened in its frame. Rubbing the saw-blade with wax to make it cut more smoothly, the chamber is sawn out along a line a trifle above the base-line. The plate is now swaged, and then placed on the plaster model. The chamber outline is filed out, using a small smooth-cut half-round file for the purpose, until the line of junction between the base of the wax chamber and the model is just visible . The cap piece and plate are again annealed, the former placed in position in the counter-die, and over it the plate, the die set over them, and then by several hard blows the swaging is completed. By means of sharp shears, using only their tips, the plate is trimmed to almost the outline marked on the model, and then a smooth file is used to complete the shaping ; next an annealing, and then final swaging. Testing the Adaptation. — The plate and cap are boiled in a 1:10 sulphuric-acid solution, washed, dried, and the plate tried on the model. The adaptation is tested by noting that the plate is in contact with the model throughout its upper edge, and that the edge of the chamber is in contact with the model. If zinc dies have been used, the posterior edge of the plate will be about one-sixteenth of an inch short of contact with the vault. If a Babbitt-metal finishing die have been used, this portion of the plate should be in contact with the vault. The uniformity of the contact is tested by pressure applied along the height of the ridge. Pressure at any point should not cause movement of the plate on the model. Next apply alternating pressure on the sides ; if the adaptation be correct, there should be no rocking. Should the plate rock, the point upon which it appears to ride is noted. The cause of the fault, as a rule, will be found in the die, usually due to some prominence being bruised during the swaging, or it may be an inaccuracy due to imperfect mould- ATTACHING THE CHAMBER-PIECE. 325 Fig. 362. ing. The plate is annealed : a thickness of pattern tin is placed over the faulty spot of the die, and the counter-die scraped out at the corre- sponding place. The plate is set in position on the die and swaged, then placed on the model, and. again tested. Should it be impossible to secure freedom from rock by this means, it is advisable to made a new die and counter-die, exercising the utmost care in moulding. Attaching- the Chamber-piece. — When the plate fits the model cor- rectly the chamber-piece is set upon the former, and it is noted whether it is in perfect contact with the plate. The contact surfaces are cleansed by boiling in the sulphuric-acid solution, and then by scraping until they are bright. Borax is applied to the prepared surface, and the cap is clamped to the plate by means of two clamps made of No. 16 iron wire, shown in Fig. 362 — one applied to either side of the chamber-piece flange, the other arms pressing the palatal surface of the plate. A small square of 18-carat solder is placed at the forward extremity of the chamber-piece, and the plate set upon a bed made of pieces of charcoal so distributed as to furnish a support to the entire plate. The broad flame of a blow- pipe is rapidly passed around, beneath, and over the plate until the latter is heated to a cherry red, when a fine flame is directed against the plate near the solder until the latter begins to fuse, when the flame is thrown on the flange of the chamber-piece and the molten solder drawn beneath it. When the piece is cool, note whether the contact of the cap piece and the plate is perfect; if there be any separation — and separation of the surfaces is not unusual — the plate is reswaged. With the clamps in position four squares of solder are placed along the sides of the cap and one at its posterior edge, the plate heated, and the solder melted as the first piece ; the fine flame is then passed rapidly around the chamber-piece until the solder flows freely, and upon examination is seen to fill the joint line at the palatal aspect of the plate. If the operation have been carefully done, the plate will have suflered no change of form, but should this latter have occurred reswaging is necessary. The plate is boiled in the acid solution, washed, and dried. The edges are smoothed and rounded with No. emery-paper, and its surfaces brightened with brush wheels and powdered pumice. It is now ready for trial in the mouth. Swaging- Rimmed Plates. — If the plate is to have its upper edge turned over to form a rim, the model has been prepared and dies made as described in Chapter X. Additional care is necessary in manipulating the metal over the ridge in such plates. The annealing and light swaging are to be more frequent. After a moderately good adaptation is had, the plate is placed on the die, and by means of a brass chaser having a sharp wedge-shaped end about a quarter of an inch broad, the angle of the rim is clearly outlined, driving 326 SWAGED METALLIC PLATES. the plate along this line into the angle by rapidly-delivered blows of a small, light hammer. When swaging on the finishing die the plate is covered by a sheet of the cloth in which dental rubbers are enclosed. The cloth is wetted and laid over the plate, then covered by the counter-die and swaged. With- out this adjunct it is frequently difficult to withdraw the plate from the counter-die without bending it. The same device is useful in swaging all plates which cling obstinately to the counter-die. The plate edge is trimmed to the correct outline and smoothed. Plates Without the Cut-out Chamber. — Plates are seldom made without the cut-out chamber unless designed as a basis for continuous- gum work or made of aluminum, for which there is no suitable solder. It is a difficult but necessary task to so adapt the edges of the vacuum chamber that they shall fit perfectly to prevent the access of air to the chamber space. The plate is annealed frequently, and for the final swaging a zinc counter-die is advisable to drive the edge of the chamber into position. If this does not produce a sharp and distinct outline, a small brass chaser, driven by rapidly repeated blows of a small hammer, is employed to define the chamber edge. This is succeeded by a swaging with the zinc counter-die. Be careful that the edge of the chaser does not perforate the plate, and at the completion of the swaging examine the plate at the chamber edge for minute openings : should there be any, they are to be covered by a small piece of thin plate attached by means of solder. In the making of swaged plates of aluminum select plate of about No. 24 gauge. In being reduced to plate from the ingot this metal ap- pears to acquire its maximum toughness at this thickness ; that is, as far as the swaging operation is concerned. Anneal the metal at as low a heat as possible — considerably below red heat. The finished plate is tougher if, instead of plunging it into cold water after heating, it be allowed to cool gradually. Covering its surface with oil and burning the latter off anneals the plate, and at a safe temperature, but a dirty discoloration difficult to remove remains. Over the face of the die spread a layer of tissue-paper and press the counter-die down upon it. Over the tissue-paper then set the annealed plate and press into the deeper portions of the vault. In working this metal it is preferable to have a series of partial counter-dies. The smallest of these is covered by a wet sheet of rubber muslin, and the plate is lightly swaged. It is reannealed and placed on the die, covered by the next sized counter-die, and again swaged. It is advisable to always have interposed between the plate surfaces and those of the die and counter-die enclosing it two layers — one of paper next to the die, another of muslin next to the counter-die — to prevent con- tamination of its surface by the base metals. The entire process of swaging should be gentle and gradual. The metal is very pliable and readily adapted ; but, any sudden force tends to fracture it. An- nealed at too high a temperature, it develops an increased liability to fracture. In giving the final finish to this metal use dry brushes ; the wet polishing powders form upon its surface a black and tenacious scum. Partial Plates. — Plates for partial dentures are of three varieties : first, those for the lower jaw ; second, the tM^o types used for the upper jaw, those retained by means of a vacuum chamber ; and, third, those held in position by means of clasps attached to the natural teeth. PARTIAL PLATES. 327 The first and last of these require special description by themselves. Partial upper plates, having vacuum chambers, are made after the same principle as any upper plate. The dies are made and prepared as de- scribed in the foregoing chapter. The tin pattern is to be made so that it represents Fig. 363. an accurate copy of the future plate. When flattened a duplicate is made of 18-carat gold plate of No. 26 gauge, and made about one-sixteenth of an inch or more larger, and giving a rounded outline to the portions about the necks of the teeth (Fig. 363). When the plate has been annealed the tin pattern is laid on it and its outlines plainly marked. These lines serve as a guide in swaging, by keeping them oppo- site to and against the respective teeth. The median line is noted as with the full j51ate ; the gold, well annealed, is laid upon the die, from which the teeth have been cut, and malleted until the median line is represented in its proper position in the plate. The malleting is continued, alternating from side to side, until the gold becomes elastic ; it is then reannealed and the malleting resumed. Before any attempt at swaging proper is made the plate should be sufficiently., adapted by the mallet to secure it against slipping from position. When this degree of t? a adaptation is had, the plate is an- ^^' nealed and set in proper position in the counter-die, the die placed over it, and a few very light blows are struck. The die and counter are separated for assurance that the plate is in position. If it is not, or the plate is found to have moved, it is reannealed and further malleted, and again placed in the counter-die. When it is certain that it will not slip several heavy blows are struck with the swaging hammer, driving the plate well into posi- tion. It is removed from the die and boiled in pickle, then rean- nealed. A sharp point is passed around the plate, marking it plainly about one-sixteenth of an inch beyond the final line of the plate. By means of sharp- pointed shears, cutting with their points alone, by plate-nippers (Fig. 364), removing small portions at a time, and finally by half-round plate files, the plate is dressed out to the lines marked, Plate nippers, three sizes. 328 SWAGED METALLIC PLATES. and no more. It is again placed in the counter-die and swaged heavily. If the case be one having very deep and angular rugse or a very deep vault, it is occasionally necessary to employ a zinc counter-die to drive the metal into the deepest parts. The chamber is cut out as before described, the cap piece swaged, and next the plate and cap are swaged together, and the amount of trimming necessary to bring the edges of the plate to the outline marked on the model is noted. The surplus metal is to be removed by means of small half-round plate files of the finer cuts. The pieces are annealed and transferred to the finishing die, and swaged separately at first, and then together. After boiling in the sulphuric-acid solution, the plate is tried on the model. All of its edges should be in contact with the model, and correspond with the pencilled outline. It should respond to the same test as for any plate — immobility when any part is pressed upon. The chamber-piece is soldered in as described. Strengthening- Pieces. — If the case be one having an unusual dis- tance between its posterior extremities, and which exhibits an undue weakness laterally, it is advisable to furnish additional support across these parts of the plate. The pattern for the chamber-piece has its basal angles continued to the posterior angles of the plate (see Fig. 358), and the pattern, uniformly enlarged, is duplicated in gold. Additional care is necessary in the first swaging of this piece that it should not alter position. It is fitted, trimmed, and bevelled as any chamber-piece, and then soldered in position. Should the case exhibit breaks in its continuity which permit its ready bending, additional supports are required. Around isolated teeth crescents of plate No. 27 gauge about a quarter of an inch broad are swaged. The writer usually places these pieces upon the palatal surface of the plate, filing them to a feather edge before attaching them. Occasionally it is necessary, with plates bearing alone the posterior teeth, to place across the anterior weak segment, opposite the natural teeth, a stiffening piece. This is to be made of No. 29 plate ; it is annealed, roughly swaged, and cut to a uniform width of about three-eighths of an inch or less. The plate and piece are cleansed and the posterior edge of the latter bevelled. A cream of borax is applied to the surfaces to be united, a minute piece of solder placed at a point of the anterior edge ; then, heating first the body of the plate under the blowpipe, the solder is fused, and serves to hold the pieces in correct position. Transferred to the die, the two are well swaged. The extremities of the piece are held against the plate by means of two small clamps, two small squares of solder placed at the anterior edge, and the plate is heated until the solder flows between plate and teeth, filling the space perfectly ; more solder is added if necessary, but never use an excess. The plate is now trimmed about the necks of the teeth, bevelling from the lingual side. A neat finish is given about natural teeth and an effective strength- ening piece furnished by partially encircling them with a piece of No. 16 gold wire which has been fitted and then flattened ; this is attached to the plate by means of the minimum of solder. At the sites of missing teeth the rounded tongues of plate upon which the artificial teeth are to rest are cut away, so that when the artificial LOWER PLATES. 329 teeth are adjusted they shall hide the plate perfectly, and yet the tongues furnish adequate basal support. The edges of these tongues are to be given a long bevel. The other edges of the plate are to be rounded and smoothed. Lower Plates. — Plates for lower dentures are preferably made of two laminae of metal, using for the purpose No. 29. If made of a single piece, No. 24 gauge is to be employed. Much care is required in making and flattening the patterns for these plates, as any carelessness in these operations might alter the width or distance across the plate extremities, thus making accurate adaptation of the plate most difficult or impos- sible. The plates are annealed : one is taken and pressed to the summit of the die by means of the fingers ; the malleting is then begun at the mid- dle of the labial aspect, continuing the malleting along the labial and buccal portions until there is a rough adaptation of this portion. Next mallet the lingual aspect until it assumes an approximately correct form, annealing as soon or as often as the piece develops elasticity. When malleted sufficiently to maintain its position on the die, it is transferred to the counter-die and swaged lightly ; when assured that it will not slip from position in the counter-die, it is aimealed and swaged well. The process is to be repeated with plate No. 2. Both plates are now annealed and swaged together. One of the pieces is trimmed to almost the plate outline marked on the model, the other remaining untrimmed, forming a ledge between the plates which Fig. 365. Fig. 366. serves to hold the pieces of solder which are to unite the two. The plates are again annealed, and are separately swaged on the Babbitt- metal finishing die, and next swaged together, the untrimmed plate next to the die. 330 SWAGED METALLIC PLATES. This latter piece is boiled in the sulphuric-acid solution and placed on the model. It should rest firmly upon the latter, exhibiting no movement when pressure is made upon any point of the plate. Should the alveolar ridge be unusually high, it is a useful expedient to roughly shape the plate along the groove by means of a tooth-brush handle used as a chaser, driving the middle line of the plate into a concave form, a grooved block of hard wood forming the piece into which the plate is driven. Plate-benders occasionally serve a useful purpose to the same end (Fig. 365). When the larger plate fits the model perfectly, and the second plate is so closely adapted to the first that their point of union is almost imper- ceptible, they are in a condition to be soldered together. Both are boiled in the acid solution, and the surfaces to be united are well brushed and brightened by means of a coarse brush-wheel and pumice ; they are washed, dried, and a coating of borax given the brightened surfaces. At the middle line, and on either side near the posterior extremities, wrap- pings of fine binding wire are placed, holding the plates firmly together (Fig. 366). Along the lingual border of the ledge squares of solder of the same fineness as the plates are placed, forming a continuous line of the pieces : no solder is placed on the labial and buccal portions of the ledge. The solder is to be drawn through from the lingual side, so as to furnish assurance of perfect union of the plates throughout. The plate is laid on a bed made of small pieces of charcoal, and a blowpipe flame passed above it, not on it, until efflorescence of the borax ceases, when the broad flame is applied to the plate until it is heated to a uniform red, when the fine flame is directed against the solder pieces, fusing them one by one. As soon as the pieces have melted, a larger flame is thrown upon the labial and buccal aspects of the plate until these portions are at a higher temperature than the lingual ledge, the heat carried then forward until the entire mass of solder is seen to flow like water and appear at the labial and buccal portions of the joint, uniting the plates perfectly. When cold the binding wires are removed and the plate boiled in the acid solution. The ledge of the lower plate is trimmed away, using for this purpose the points of a very sharp pair of curved shears (Fig. 367). The trimming is completed by means of Fig. 367. S. S. W. curved plate-shears. files, and when the plate outline corresponds with the pencil line on the model, its edges are rounded and smoothed with fine emery-paper. Partial Lo^wer Plates. — The most difficult class of plates to fit accu- rately and correctly are those for partial lower dentures. The operator's ingenuity and manipulative ability are taxed to provide in such cases acceptable substitutes for the lost organs : however, when these dentures are well made and adjusted they are among the most satisfactory of prosthetic appliances. PARTIAL LOWER PLATES. 331 Except under very unusual circumstances, it is unwise to insert a lower piece, when no teeth but the second and third molars have been lost, the increased masticating surface thus provided rarely compensates for the inconvenience caused by the presence of a large plate. Viewed as to the laboratory operation required in making the plates, the cases may be divided into two classes : First, those in which Fig. 368. Partial lower plate, Class 1. the natural teeth present are in one unbroken column ; second, those in which the natural teeth are in broken column. A typical case of the first class is most common of all, requiring a partial lower denture, six, eight, or ten of the anterior teeth remaining (Fig. 368). Fig. 369. Partial lower plate, Class The second is represented by cases having the cuspids and bicuspids of both sides remaining; the incisors and molars are to be replaced (Fig. 369). 332 SWAGED METALLIC PLATES. The first requisite to success with this class of dentures is an accurate impression, always to be taken in plaster. In the degree that impression is difficult to secure by the use of plaster, the more imperative is the in- dication for the employment of that material. The plaster model should have strengthening and guiding pins in all of its teeth ; the base should be broad and be given sloping walls. Greater stability is secured by making these plates as large as possible compatible with the comfort of the wearer. The plate outline is marked at its lingual borders as deep as possible, with- out any impingement upon the tissues movable by the movements of the tongue, and to rest upon about one-half the lingual walls of the natural teeth. The labial and buccal edges are carried to a depth which shall aiFord a generous support to the artificial teeth, and be clear of impingement upon the soft tissue re- flected from the cheek and lip. To neutralize the tendency of these plates to bury the external border in the soft tissues their edge is to be elevated from one-sixteenth of an inch to one-eighth of an inch by placing a layer of wax of this thickness over that portion of the model. (See Chapter VIII.) The dies and counter-dies are made as described in Chapter VIII. The finishing die is to be made of Babbitt metal, and is to be very heavy. From the inferior die the zinc teeth are cut a trifle above the plate outline, and the angle between the lingual wall and tops of the teeth made acute, so that by bending the plate over the edges it is prevented from slipping during the operation of swaging. The teeth to be clasped are cut almost level with their necks. The plate, to assure accurate adaptation and to increase its rigidity, should be made of two laminae, of No. 29 gauge. The completed piece should have sufficient rigidity to resist bending even when severely tried, so that an additional layer of material is necessary across the weak spaces, the lingual portions of the plate, which are back of the natural teeth. To ensure the required rigidity this supplementary piece is to be made of platinous gold of No. 27 gauge. A greater stiffness and better aesthetic effect are given if this piece be placed between, and not over, the two plates. Much of the accuracy of the fit of the plate will depend upon the care with which the patterns are made. Heavy pattern material is used for this purpose, and adapted to the Babbitt-metal die so that it is an accurate representation of the future plate. Much care is necessary in flattening it, and the proper pattern is cut with greater surplus than usual with other classes of plates. The pattern for the supplementary piece extends across all breaks in the plate continuity for about three-eighths of an inch beyond on both sides. It should be wide enough to extend from the necks of the natural teeth to the extreme lower edge of the plate. Making- the Plate. — The pieces are well annealed, and one is taken and bent roughly with the fingers. It is malleted into approximate adaptation at the middle of its lingual portion. Next the buccal sides MAKING THE PLATE. 333 are malleted, and as soon as the plate becomes obdurate or exhibits a tendency to wrinkling it is reannealed and again malleted, the upper edge of the plate being bent over the cut surface of the zinc teeth. When it is approximately fitted by this means, and not before, the plate is placed in the counter-die, the die set over it, and tapped gently until it begins to settle into position. The die and counter are separated, and if the plate maintains its position, the die is replaced over it and a few moderately heavy blows struck with the swaging hammer. Piece No. 2 is annealed and similarly manipulated. Both pieces are now boiled in the acid solution to remove the particles of base metal always adherent, and again annealed. Each in turn is placed between die and counter-die and swaged well. Usually it will be found that one piece has a greater surplus at its lingual border than the other, and it is set aside. The other plate is trimmed by means of sharp shears, plate- nippers, and files until it is within a trifling distance of the plate outlines marked on the model. The supplementary piece of platinous gold is annealed at a high heat, and malleted to the die, reannealed and remalleted. It is next placed in position in the counter-die and swaged, again annealed, and again swaged. The extreme elasticity of this alloy necessitates that it should be annealed more frequently than ordinary plate. It is then trimmed to its proper size, and all of its edges except the inferior border bevelled. All of the pieces are annealed ; the trimmed plate is set in the counter-die : within it is placed the stiifening strip, and over both the untrimmed plate, the die placed in position, and the three pieces swaged together. Kemoved from the counter-die, they are boiled in the acid and again annealed. The untrimmed plate is placed in the finishing counter-die and swaged. It is partially trimmed at its upper border, so that it may be placed in position on the plaster model, which it should fit with the utmost accuracy. If it do not, it should be reannealed and reswaged. Any points of the plate interfering with its placement on the model are to be trimmed away. Plate No. 2 is next placed in the finishing counter, and over it the strip of platinous gold ; over both, the larger plate. The die is set in this, and by several heavy blows the swaging is completed. If there be any unusual difficulty in removing the pieces from the counter-die, the pieces bending in removal, they are to be reannealed and placed in position on the die and covered by a strip of the cloth enclosing dental rubber, which has been made perfectly pliable by soaking in water. The counter- die is set over this, and the swaging repeated. Upon separating die and counter, traction upon the cloth will withdraw the plates from the counter- die. The pieces are boiled in acid, and the surfaces to be united are cleansed perfectly by means of brushes and pumice, and well washed and dried. The strengthening piece is first united to the larger plate, that next to the model. A thin mixture of borax is applied to the surfaces of plate and piece which are to be united, and they are bound together by means of binding wire holding the extremities and middle of the sup- plementary piece. A small square of solder is placed at one edge, and the plate and piece are heated uniformly until the solder flows between them. If the platinous gold piece do not change form and separate at any edge from the plate, three more squares of solder are placed one at 334 SWAOED METALLIC PLATES. the top, tlie others at the side joints, and are flowed between the pieces, uniting them perfectly. Boiled in acid, washed, and dried, the plate is now placed on the model ; if it have undergone any change of form during the soldering, it is reswaged. If not, the surfaces of the two plates are now painted with a cream of borax, and hrmly held together by means of three or four wrappings of binding wire. No borax should be present on the external portions of the plate. Along the ledge of the untrimraed plate, beneath the lower edge of the trimmed plate, a line of solder is placed, made of squares of about an eighth of an inch size. The plates are warmed until efflorescence of the borax ceases, and then a blowpipe flame is directed beneath the plate until both sections are heated to a bright red, when the solder will melt and flow freely between the plates and appear at the opposite edges. More solder is added at the same place if required, and it is melted and drawn between the plates until by its filling of all the joints it gives assurance that the plates are united throughout. It usually requires about a pennyweight of solder to perfectly unite the three pieces. Remove the binding wires and boil the plate in acid. The lower plate is now trimmed to the outline of the previously dressed plates ; the upper edges resting upon the natural teeth are bevelled lingually, the other edges rounded and smoothed. Bending the plate between the fingers is now a matter of difficulty. It is placed upon the model and should fit it perfectly. As a rule, these plates are held in position in the mouth by means of clasps encircling two or more of the natural teeth. These will be de- scribed later in the cliapter. Clasp Plates for Upper Dentures. — Occasionally it is necessary that partial plates for the upper jaw be retained by means of clasps, instead of the vacuum chamber. These plates are usually given a horseshoe form, but it may be that smaller devices are at times applicable. The first indication for the employment of this type of plate is such a configuration or peculiarity of the palatal vault that the vacuum cham- ber is inapplicable. Another class of cases are those in which the patient objects strenu- ously to the presence of a plate of the size necessary when a vacuum chamber is used. In rare instances the projecting chamber is a continued hindrance in enunciation, and the difficulty is remediable through the use of a small unprojecting plate. Another class is found in cases in which artificial dentures mounted upon plates having vacuum chambers are displaced by the forces of mastication. Other cases in which one or more teeth are to be replaced may be retained by a small plate held by clasps, where the chamber plate to be used would necessitate the wearing of a large piece. Typical cases of the first class mentioned are found in those mouths presenting a large bony tuberosity occupying the height of the vault, one or more of the natural teeth absent, and deplacement is demanded. The presence of a plate of the size required when a chamber is present may be productive of a continued nausea. Singers, actors, and orators CLASP PLATES FOR UPPER DENTURES. 335 occasionally demand a fixture which shall be firmly held, and which shall not alter the form of the palatal vault. Fig. 371. Fig. 372. Partial upper denture supported by remaining teetii. Badly -arranged clasp plate. Fig. 373. A typical case of the last class is one for the replacement of the incisors, the denture being displaced at every attempt at biting. The plates are always more firmly held if the clasps are placed on both sides, so that the most usual form of these plates is that of a horseshoe (Fig. 371). This figure illustrates a typical clasp plate and the indication for this form of denture. Figs. 372 and 373 illustrate the form of device obviating the necessity for the employment of an extensive plate. It is determined, as described later, the several positions and forms of the clasps, the bases of which, as a rule, mark the pos- terior length of the plate. The latter is usually made to enclose an area of the vault extending rarely less, and as a rule more, than one-half of an inch from the necks of the teeth. The outline of the plate is marked on the model. To ensure accurate adaptation and sufficient rigidity the plate is made of two laminae of No. 30 plate. One of these is in swaging left larger than the other, so as to form a ledge upon which to place the solder used in uniting them. While soldering the plates are held together by means of the clamps used when attaching chamber-pieces, but when possible binding wire is to be preferred : the form of the plate, however, does not, as a rule, permit of this means of holding the plates together. After soldering the plate should be trimmed to fit closely about the necks of the natural teeth, but never to rest upon the teeth themselves. All Supplemental clasp to relieve strain on molar tooth. 336 SWAGED METALLIC PLATES. edges are next bevelled and smoothed : the posterior edge of the plate should be filed to a thin yet smooth edge, so that it shall not be readily perceptible to the tip of the tongue. Cases present at intervals in which there is a loss of the bicuspids and two molars of one side, the solitary molar standing as a projection from a rounded tuberosity, and occupying the centre of the latter. The plate Fig. 374. form is given this outline (Fig. 374), the plate covering the tuberosity and perforated at the side of the molar. The tooth reproduced in the die is removed from one and permitted to remain on the other. The stump left by its removal is filed, giving it a square edge, so that it shall mark the outline in swaging. The section is sawn out, beginning in a perforation made with a plate-punch. After swaging on the finishing die the perforation is filed away to ex- pose the neck-line of the tooth. In making plates for the class of cases described in Chapter VIII. those having loose teeth in the arch which are to be removed, and have a restoration by either artificial teeth or the crowns of the natural teeth themselves fitted to the plate, a plate support must be formed for the bases of the latter. The impression taken and model made and prepared as described in Chapter VIIL, the plate outline is marked along a line representing the labial or buccal line of the natural teeth. Dies are made and a plate swaged as for an ordinary case : if teeth are to be attached by means of soldered stay backings, the making of the plate and the mounting of the teeth do not differ from those operations for ordinary cases. Should it be designed to mount the crowns of the natural teeth upon the plate, sup- ports must be provided for them. Obviously, the only means by which this may be done is by attaching posts to the plate, over which the crowns are to be cemented. In the depressions which have been carved to represent the gum outlines which will exist as a consequence of the extraction of the teeth, marks are made to indicate the sites of the pulp-chambers of the teeth. The plate is to be made so that the base of the crown will rest upon it. This plate extension is to be perforated over each mark, and in the direction of the axes of the teeth when these latter shall be properly adapted. The openings are to be countersunk at their under surfaces. In each open- ing a platinous gold wire No. 16 is to be placed, tapered sufficiently to enter the opening, and be rigidly held in position by the plate. The countersunk sides of the openings and the protruding tips of the posts are touched with the borax mixture; a small square of 18-carat CLASPS. 337 solder laid beside each post. The plate is heated from its upper sides : when at a uniform red heat a fine flame is directed against the plate at the base of each post, fusing and drawing through the solder. The introduction of bridge-work has lessened to a great extent the employment of dentures mounted upon clasp plates. The substitution, although a wise procedure in many cases, in others is just as clearly con- traindicated. It is undoubtedly true that the unilateral loss of teeth, leaving a space at the ends of which are teeth eminently suitable as abutments for the support of a bridge, finds the best prosthetic appliance in a bridge. In point of fact, bridge- work has even among conservative operators re- placed most of the unilateral devices, but occa- sionally the use of plates for such cases is still found imperative. The introduction of the clasp of Dr. Bonwill (Fig. 375) gives an additional application of these small plates. Clasps. — Clasps are metallic bands partially encircling the crowns of natural teeth, and serving as a means for the retention of artificial den- tures. The employment of the device is prompted by necessity, and not by choice. With upper plates they are employed where the vacuum chamber is found to be insufficient to retain a denture in position, where the configuration of the vault renders the chamber inapplicable, or where the positions of the replaced teeth render the covering of the vault with a large plate unwarrantable. They are attached to partial lower dentures to prevent displacement by the movements of the tongue, cheeks, and lips, and by the forces to which these pieces are subjected during masti- cation. The great advantage of the employment of clamps is an increased stability of the piece ; the disadvantage is, if worn long enough they eventually cause the loss of the crown of the tooth clasped, through chemical solution, not mechanical abrasion. The food-deposits beneath and about the clasp are the seat of lactic fermentation, so that a gradual solution of the crown by lactic acid occurs if the clasps are not kept in an aseptic condition. Not infrequently, the teeth are so mechanically strained by the force of mastication transmitted through the clasps that the retentive appa- ratus of the teeth succumbs and the teeth are dislodged. The latter is a more serious consideration than the loss of a crown : an artificial substi- tute for the latter may be provided, and serve for clasping ; but loosened teeth are the b^te noir of dentistry. This danger is lessened by accuracy of adaptation of the plate, and by having the clasps of sufficient elasticity to yield to stress and diminish the strain on the teeth. Clasps properly adapted serve but to stay a plate, not to support it : the support should be derived from uniform pressure upon the soft tis- sues ; the clasps are an adjunct preventing displacement. The violation of this principle is responsible for many of the ills attributed to the wearing of clasps. In selecting teeth to be clasped, where a selection is possible, they should be chosen with a regard to their form, the position and condition of the tissues of the teeth, and the surrounding parts. It is desirable that the clasps should not be exposed by the move- 22 338 SWAGED METALLIC PLATES. ments of the lips, so that teeth posterior to the first bicuspid are prefer- ably selected. To secure the best adaptation the walls of the teeth should be nearly parallel. Conical teeth, the base of the cone being at the necks of the teeth, are of improper form. A reversed relation, teeth much smaller at the necks than at their masticating surfaces, are also of disad- vantageous form. Freedom from caries, firm fixation in their sockets, and no exposure of the cementum are desiderata, and where and when it is possible to secure these features they are to be regarded as essentials. In the event of the absence of a latitude of choice certain precautions are to be observed. Carious cavities are to be perfectly filled and per- fectly finished and the teeth to undergo periodical examination. Should there be any recession of the gum, exposing the cementum of the tooth, the clasp must embrace none but enamel surfaces. Exposure of cemen- tum indicates loss of a portion of the retentive apparatus of the tooth, a relative lengthening of the crown, and hence an increased leverage upon the socket of the tooth ; stress is lessened by making the clasp of thinner metal. Clasping loose teeth always results in their loss, and is justifiable only under extremely rare circumstances, and then the clasp should be very light and elastic. Clasps should be so adapted to the teeth upon which they are worn that there shall be no projections acting as sources of irritation to the tongue or cheeks. All of the edges should have a rounded bevel and be made perfectly smooth. The length of a clasp is of two parts as to function — one, serving as the part of attachment to the plate ; the other consists of one or two free ends which admit of form change, grasping the tooth and holding by the elasticity of the metal. These free ends should have perfect elasticity, in so far as the prop- erty is present in the platinous gold alloy ; they should permit sufficient yielding to allow the wing of the clasp to be carried over a tuberosity, and return to their original forms as soon as the stress is removed. The perfect elasticity is due in great part to the form of the clasps. The strain upon the metal itself is at its narrowest part, so that if this part be at the point or slightly beyond the point Fig. 376. Fig. 377. of the attachment to the plate, the elasticity is mark- edly lessened and there is danger of breakage (Fig. 376). The maximum of elasticity is secured by having the greatest thickness of the metal at the angle, and diminishing its thickness toward the free extremity of the clasp (Fig. 377). When a choice offers as to the passing a clasp with its body across the distal or mesial wall of a Fig- 376 clasp weaken- tooth, it is usual to place it ou the distal wall as the er edge. better position to resist displacement of the denture, ^'shS'd^^^'^ properly ^i^^^y^ provided the distal wall be not too short and inclined from the back. The free ends of a clasp when possible are to be at the buccal aspect of the tooth. Greater stability is afforded by having a clasp embrace as much of CLASPS. 339 Fig. 378. Fig. 379. the enamel surface of a tooth as possible. Each individual case is a rule for itself as to the manner of placement of clasps. The operator by an examination of the teeth of the model and of a careful scrutiny of the natural organs determines the teeth which shall afford the best bases for clasps and secure the greatest stability to an artificial denture. Fre- quently it is necessary to modify the form and size of a plate according to necessities arising out of the enforced selection of clasp teeth. The outlines of the future clasp are plainly marked on the plaster teeth by mean of a blue pencil. If the cemen- tum of the tooth be exposed, the clasp is not to pass beyond the enamel border. At the side of the attachment to the plate it is made the section of a cylinder extending from just below the grinding surface of the tooth to the plate at its neck (Fig. 378). This form is frequently necessary with the clasps of partial lower dentures. For extremely short crowns the clasp is made of half-round platinous gold wire. A pattern of the clasp is to be made of heavy pattern tin closely adapted to the plaster tooth and trimmed to correspond exactly with the pencil-marks. The ex- ternal free ends of the clasps are plainly marked so as to distinguish each when flattened. They are flattened between the fingers. As a rule, the thickness of the metal should be greater with increase in the length of the free ends. Clasps are rarely made lighter than No. 26 gauge, and never heavier than No. 22. Wide clasps having comparatively short free ends, and which are subjected to light stress, are made of No. 26 ; those having long and narrow free ends are made of the heavier numbers. The average thickness is No. 25. The patterns are reproduced in the clasp metal, the edges of the latter being filed to conform perfectly with those of the tin pattern. Three pairs of pliers are usually sufficient to shape the various forms of clasps — a pair of four inch round-nose pliers to bend the clasp at its angles ; a pair of four inch flat- nose pliers, having sloping beaks — these to adapt the flat aspects of the clasp ; a pair of four inch round-nose pliers, bent to a curve of about one inch radius (Fig. 379) — these are used to make the clasp con- form to rounded surfaces of the clasp tooth. Some operators prefer a special pair of pliers for this purpose — what are known as clasp-benders: the skilful mechanic usually finds them needless. Curved pliers. 340 SWAGED METALLIC PIRATES. The metal is well annealed. Usually the bending is begun in the middle of the clasp, unless one extremity of the latter should be between two teeth, when that extremity is adapted first. Work from the middle toward either end, changing the pliers when necessary to make the clasp conform to the surface of the plaster tooth. When the clasp tooth has been accurately reproduced on the die, the clasp may be first bent to this and the fitting completed on the plaster tooth. It is a wise precaution to give the plaster teeth a coat of thin sandarac varnish before bending the clasps to them to prevent any abrasions of the surface of the plaster. When the clasp has been made to conform perfectly with the surface enclosed by the pencil-marks made on the plaster tooth, its edges are given a rounded bevel ; they are smoothed with emery-cloth and buifed with pumice or a felt cone. The extremity or extremities which are not to be attached to the plate are bent away from the plaster tooth, so that the clasps may be readily withdrawn. It is desirable that the axes of the clasp teeth be nearly or quite parallel. Should this not be the case, the cervix of one clasp must stand off from the neck of the tooth, so that the lingual walls of the several clasps are parallel. Violation of this precaution may render it impossible to withdraw the fixture from the model, when the clasps are cemented to the plate, without disturbing the mutual relations, or make it equally impossible to place the fixture in the position in the mouth when the clasps are attached to the plate with solder. The plate is placed on the model, and one clasp set over its tooth : any points of the plate interfering with the placement of the clasp in its true position are to be filed away until the clasp is properly adjusted, and its junction with the plate is represented by a line. The plate is cut away in the same manner to permit the adjustment of the other clasp or clasps. It is advisable to now attach the clasps very lightly to the plate, so that they are held by but one point, permitting the making of any changes in the form of the clasp which may be found necessary when the fixture is placed in the mouth. Occasionally the soft tissues of the mouth yield so much to the pressure of the plate that the same relations are not present between the pieces in the mouth as they were on the model ; and if the attachment of the clasps to the plate be too extensive, there is no latitude for making the necessary changes in the pieces. The clasps are fastened to the plate by means of adhesive wax made very hot : short sections of wire to extend at an angle from the top of the clasp to the plate are heated and laid in the cement. These pre- vent fracture of the latter in removal of the fixture from the model. When the cement is hard, the plate with the clasps attached is care- fully lifted from the model, so that the cement attaching the clasps is not broken. About a couple of tablespoonsful of beach sand are placed in a plaster-bowl and just covered with water ; plaster is dusted into this and stirred, making a thick batter, with which the plate and clasps are filled from the palatal side and nearly covered upon the lingual portion. When the investment is hard the cement is picked away, and a sharp- pointed scraper passed along the joints between clasps and plate to furnish a fresh surface for soldering. As but a small attachment is to be made at this time, all of the joint except one-eighth of an inch of its length is filled with a paste of whiting. PARTIAL CLASPS. 341 The point of soldering is made usually at the mesio-palatal angle. Borax is applied to this portion of the joint and a minute piece of plate laid over it. Two very small pieces of solder are covered with borax, and one laid on the plate, the other on the clasp above the joint. The mass is heated on a furnace, and then on a charcoal bed under the blowpipe until it is a uniform red, when a fine blowpipe flame directed on the plate just beyond the joint causes the solder to flow and attach the clasps to the plate. When cold the plate is boiled in acid and buffed, and is ready for trial in the mouth. When the tissues of the arch and vault are softer than usual, their yielding alters the relations of the clasp and plate. When this softness is found to exist, it is advisable to test the adaptation of the pieces, both plate and clasp, before attaching the latter by means of solder. The plate, with the clasps cemented in position, is placed in the mouth ; the plate is pressed into position, the clasps are pressed into apposition with the natural teeth. A small piece of sponge saturated with ice-water is then laid upon the wax until it is perfectly hard, when plate and clasps are removed, placed in an investment, and soldered. Partial Clasps. — Any support which embraces less than two-thirds of the periphery of a crown may be fitly termed a partial clasp. Such appliances are designed mainly as braces. They are employed upon the palatal surfaces of bicuspids where no space exists through which a clasp may be carried, and where a plate, as for one tooth, may fre- quently be retained by bracing. Occasionally it is necessary to make the space between the teeth by means of a file, subsequently smoothing and polishing the cut surface of the tooth. Such mutilation is to be regarded as an unmixed evil and never to be practised unless absolutely necessary. Placed upon bicuspids, these devices are usually made in pairs for the first and second bicuspids. The ends are to be made thin, so as to extend as far as possible between the teeth, the bodies of the pieces covering the palatal ^^®- ^^0. Fig. 381. surfaces of the teeth (Fig. 381). When the bicuspids and molars of the lower jaw are all lost, and the lingual wall of the cuspids sloping so that a large clasp covering it would prevent the plate from settling into position, a half clasp is applied, grasping the cervical half of the labial face (Fig. 380). The same device is applicable to the superior cuspids. The exposed ends of such clasps may be made to resemble gold fillings by filing the edges thin and soldering to them a layer of pure gold. A piece of the latter metal of No. 31 gauge is annealed and burnished over the clasp, the sur- faces covered with borax, and united by means of 20-carat solder. With small saddle plates, or partial lower plates which exhibit an undue tendency to bury themselves in and irritate the soft tissues, an inverted L made of half-inch round wire is soldered to the clasps, resting upon the grinding surfaces of the teeth. This device is particularly useful for partial lower dentures, when the third molars are remaining (Fig. 369), it being necessary to dress the plate away to permit placing 342 SWAGED METALLIC PLATES. it in position, so that its posterior extremity is driven into the gum at every attempt at mastication. In such cases the L is frequently used without a clasp. Dr. Bonwill has recently furnished a solution to a class of cases which heretofore has baffled the skill of the prosthetist. These are partial cases in which the axes of the natural teeth have been at such angles to one another as to make the adjustment of plate and clasps by ordinary means impossible. Such a case is illustrated in Fig. 385. The lingual cavity had the form of a frustum of a cone, the base of a cone the floor of the mouth, the top of the frustum the cutting edges of the teeth. The device necessary for this case would have been ineffective without the peculiar clasp support introduced by Dr. Bonwill. When trimmed, it was found that the ordinary partial lower plate could not be adjusted to such a model, the distance between the edges of the teeth and their bases being so marked that it would be impossible to insert a plate in any other way than from without inward, thus vir- tually necessitating the plate support proper to be at the labial and buccal aspects of the ridge. The plaster teeth were sawn half through, then broken off, leaving a sharp line of fracture, and all of them preserved. Dies were then made ; a brass plate swaged of sufficient size to sup- port the teeth. Openings were made in the plate corresponding with the bases of the incisor and bicuspid. The plaster teeth were now cemented to place on the model. The trial plate of brass was tried to the model, and cut away at all points interfering with its placement upon the ridge, and at the com- pletion of this process had acquired the irregular form represented in Fig. 282 ; a saddle resting upon the alveolar ridge, and having two apertures much enlarged to permit passage over the isolated teeth at its extremities, dressed away to allow passing over the overhanging edges of left inferior second bicuspid and right inferior second molar. The plate was reproduced in gold, using two laminae of No. 29. This, when placed in the mouth, was found to have a lateral movement upon pressure, due to its lack of contact with the natural teeth. Fig. 382. Fig. 383. Fig. 384. Ordinary clasps for such a case are out of the question, so on the molar and bicuspid partial clasps were made of the pattern suggested by Dr. Bonwill, having in the middle of each an inverted L resting upon the masticating surfaces of the teeth, and protecting against the extremities of the plate burying in the gum. The Ls were made of half-round platinous gold, the lower end extending to the plate and soldered to it, this extension serving as an elastic supporting-bar (Fig. 383). PARTIAL CLASPS. 343 The clasp upon the left bicuspid (Fig. 383) was arranged somewhat differently from the molar clasp in that its attachment to the L support was at almost its lingual extremity. This was done to increase the spring-like action of the clasp and enable it to pass easily to position without interfering with the perfection of its grip upon the tooth when the denture was finally in place. Prior to attaching these clasps both apertures in the plate were sur- rounded by a heavy triangular gold wire, to prevent irritation by a thin edge at these places. Plain teeth were fitted to the plate, backed and soldered, and along the external wall of the plate an artificial gum was made of the mixed rubber known as Walker's granular gum. Fig. 385, A, represents the finished piece, and Fig. 385, B, the same in position upon the model. The bars which attach plate and clasp are placed at the plate edge opposite to the overhanging wall of the tooth, so that the elasticity of the bar, while permitting the placing of the clasp over the overhanging wall, draws it close to the latter when the denture is in position. It was found necessary in the case illustrated to attach both clasps by posts placed at the disto-buccal angles of the plate. Dr. Bonwill applies the device with small saddle plates carrying one or two teeth when the clasp teeth are much inclined, and its application is eminently satisfactory. A class of partial lower cases will be met with in which the dentures made for them have a tendency to slip from position backward. Clasps applied to the natural teeth but insufficiently overcome this tendency. 344 SWAGED METALLIC PLATES. Prof. C. J. Essig has devised an adjunct to the plate which effectually overcomes this difficulty. In swaging the plate the anterior end of the buccal portion is carried farther forward than usual. A die and counter- die are made of the labial wall of the model, and two strips of metal are Fig. 386. swaged, one of No. 28 plate, the other of No 27 platinous gold, and made to fit this wall above the necks of the teeth. The pieces are soldered together, and their extremities are joined to the lengthened plate, the Fig. 387. pieces invested and soldered. A modification of this idea, and suggested by it, is the device shown in Fig. 287. It is designed to lessen the strain upon the natural teeth due to the force of mastication acting at an unusual angle. It subserves its purpose perfectly. Swaging- with Shot. — An apparatus and method have been devised by Dr. Parker of Grand Rapids, Mich., through which the adaptation of aplate to a model may be secured with a greater degree of accuracy than attainable by swaging between dies and counter-dies. The apparatus con- sists of a heavy cast-iron cylinder having a thick bottom. The chamber of the cylinder is about four inches in diameter, large enough to freely admit the base of a large plaster model. The cylinder A is bored for the reception of a heavy plunger having a concave face, B ; the plunger is turned to fit the cylinder. The plate is approximately adapted to the plaster model by means of dies and counter-dies. Fine bird shot is placed in the cylinder until it is filled to about an inch or more above ELECTRO-DEPOSIT PLATES. 345 the alveolar edge of the model. The plunger is placed in position and its cylindrical head struck several times with a heavy hammer. The Fig. 388. pressure of the shot, evenly distributed over the entire plate area, drives the plate into accurate apposition with the plaster model. The plaster model itself is made to serve as a die. The plate is adapted by means of dies and counter-dies as closely as possible, when it is annealed, placed on the plaster model, and the swaging accomplished. The shape of the plunger is such that the shot about the labial and buccal walls of the plate is first compressed, supporting the model laterally ; the suc- ceeding pressure is upon the palatal portion of the plate, forcing it into accurate apposition with the model. The model, supported equally on all sides, is not fractured. Electro-deposit Plates. — This variety of plate was designed to com- bine the advantages of a metallic plate with the accuracy of adaptation of those constructed of the vegetable bases. Its method of making is thus described by Dr. C. S. Stockton : A plaster model is obtained, upon which reliefs, chamber, and rim outlining ridge are built of plaster. The model is boiled for a few minutes in wax or paraffin. The surface to be embraced by the plate is coated with plumbago. The model is immersed in a silver solution and connected with the battery as in any silver-plating operation : it is permitted to remain in the solution for four or five days, when it is withdrawn. The deposited silver is removed from the model, trimmed to the correct plate outlines, and polished. The surface to be covered by the vulcanite at- tachment is roughened. The plate is now immersed in the gold bath to deposit sufficient gold to permit of perfect vulcanization. The teeth are next attached by means of vulcanite, and the piece returned to the gold bath, where it is to remain until three or four pennyweights of gold are deposited. The principal objection to this form of plate is its tendency to tarnish, the gold plating not being impervious. CHAPTER X. THE "BITE" OR OCCLUSION. By Grant Molyneaux, D. D. S, The lower jaw forms, with the temporal bone, a joint called the " teraporo-maxillary articulation." This joint is formed by the con- dyle of the lower jaw, which is of oblong form and is convex from side to side and antero-posteriorly, resting in a concavity of the tem- poral bone called the glenoid fossa. It permits of a hinge-like motion, a gliding motion, and a rotary motion, each of which is limited by the articular ligaments. The lower jaw is endowed with these movements to permit the proper incising and masticating of the food. When all the teeth have been removed and artificial dentures are con- templated these movements become a matter of serious consideration to the dentist, as he is compelled to accurately locate the lower jaw in those positions and in the position of occlusion. The lower jaw has only one position of complete occlusion, and that is when both condyles are resting in the glenoid fossae and the mouth is closed. Fig. 389. Skull showing temporo-maxillary articulation, and natural teeth in occlusion. The position of the jaw is best studied from the skull (Fig. 389), which shows the temporo-maxillary articulation, A, and the teeth striking ao-ainst each other. The teeth as shown in the cut are in the position of 346 BITES FOB ENTIBE ABTIFICIAL DENTUBES. 347 occlusion, and when the mouth is merely opened and closed without any- lateral or forward motion it is called the motion of occlusion. It is the motion of occlusion which it is so necessary to secure when about to construct an artificial denture, for, before we can arrange any of the artificial teeth we must obtain either the position of the teeth of the opposing jaw in occlusion, or, if there are no opposing teeth, the correct relation of the edentulous ridges. The operation of obtaining the occlusion of the jaw is generally termed the " taking of the bite." The taking of the occlusion would seem to be a better term, but, as the former term has the sanction of long usage, is shorter, and is perfectly understood. The " taking of the bite," then, is simply obtaining the relation of the jaws in occlusion. This is best studied, by the beginner, from a patient with all of the teeth, upper and lower, in situ. In its simplest form it consists of placing a roll of soft wax about as thick as the index finger between the teeth, and long enough to extend Fig. 390. Upper cast, with temporary base-plate in position. from the last tooth on one side to the last tooth on the other, and have the patient bite into it. The patient is directed to bite or close the teeth into the wax until the opposing teeth strike each other, and while holding them steadily in this position the soft wax is pressed close against the surfaces of all the teeth, care being taken to prevent the patient from changing the position of the lower jaw after the bite has been secured. The wax should then be chilled by a stream of cold water from a syringe to prevent bending, when the wax-bite can be easily removed. This wax-bite will contain an impression of the upper teeth on one side and the lower teeth on the other. After this is accomplished an upper and lower impression of the teeth in the mouth should be taken. When these casts are recovered from the impression they are to be placed in their respective positions in the wax-bite, and fastened together by a wire or other means to permit of the wax being removed without changing the position of the casts. If after the wax is removed the casts are found to bear the same relation to each other as the teeth in the mouth, the bite is correct. Bites for Entire Artificial Dentures. — The first step in taking a 348 THE "BTTE" OB OCCLUSION. bite for entire dentures is to adjust to the casts, temporary base-plates. These base-plates are about three thirty-seconds of an inch in thickness, and are formed in sheets of either gutta-percha, beeswax, paraffin, or pat- tern tin. The kind usually employed is composed largely of paraffin, with a pink tint — " pink paraffin base-plates." A sheet of this is warmed Fig. 391. Lower cast, with temporary base-plate in position. unifornily to soften it, when it is laid over the entire ridge of a lower cast (Fig. 391) and over the ridge and palatal portion of an upper cast, as illustrated in Fig. 390. In pressing these plates down upon the casts care must be taken not to reduce their thickness at any point by too great force, as they represent the thick- ness of tlie future jjermanent base, and any inequality of the permanent base would materially weaken it. The edges of the wax-plate should now be trimmed to conform to the attachment of muscles on the ridge, which would make the upper plate higher in the incisive and cuspid re- gion and over the tuberosities, and lower in the buccal region, as shown in Fig. 390, B. The lower wax-plate must 1 e trimmed to rest easily on the ridge dthout impinging upon the muscles on ither side of the ridge (Fig. 391). A roll of soft beeswax is now placed pon the base-plate large enough to cover the entire ridge, about half an inch high and about three-fourths of an inch wide. This is pressed down upon the base-plate so that it will cover the labial and buccal side and extend an equal distance over the lingual side of the ridge, as shown in Fig. 392. These plates are called " articulating plates," and after chilling them in cold water they are ready to try in the mouth. The upper plate is now placed in the mouth, and the length Showing the wax base-plates, temporary or trial plates, with bite-wax in posi- tion : A, upper bite-plate ; B, lower bite- plate. BITES FOR ENTIRE ARTIFICIAL DENTURES. 349 of the lip marked by trimming the occluding surface of the bite- wax until it is the exact length of the upper lip, being careful when trimming to take off the wax, so that the occluding edge will repre- FiG. 393. /. ! No. 1. No. 2. No. 3. sent the exact plane of the cutting edges of the incisor teeth. The lower bite-plate is then placed in the mouth, and trimmed ante- 350 THE "BITE" OR OCCLUSION. riorly to represent the desired length of the lower teeth. After the occluding surface of the bite-wax is trimmed to give the length of the teeth, the bite-plates should be returned to the cast, and if they have changed shape they should be again warmed and readapted to the casts, after which they should be cooled and returned to the mouth. The patient should then be instructed to gently close the mouth while the operator holds the plates in position on the ridges. It must now be carefully observed whether the occluding surfaces of the bite-wax strike uniformly against each other. If there is a space between them at any point, either the point which strikes must be trimmed off or w^ax must be added when required in order to have the blocks strike solidly against each other over the entire occluding surface. As the anterior part of the wax has been trimmed to give the length of the teeth, this should not be disturbed. If, however, the plates come together anteriorly and not posteriorly, w^ax should be added in order to prevent them tilting. After the ope- rator has obtained an even contact between the bite-pieces when the patient's mouth is closed, he must " fix " the bite. This is accomplished by making two or three parallel cuts in the two waxes while in correct position ; these cuts, together wnth one marking the central line, will serve as guides in maintaining their correct relation. While this is being done the patient should be in a comfortable position, and no definite instruction given about closing the mouth, being directed to swallow and at the same time to close the mouth. The act of swallowing will involuntarily bring the lower jaw into Fig. 394. Wax-bite plates and casts in position : A, median line of face ; B, high lip-line ; C, low lip-line ; D, occluding surfaces or lip-line. the position of occlusion: the operator instructs the patient to bite hard until directed to relax. The softened edges of the wax are thus brought into such forcible occlusion that they cannot be separated, and the occlu- sion of the jaws, or the bite, is fixed. The wax-plates, upper and lower, may then be removed in one piece. The casts should be adjusted in the base-plates, and with a hot spatula the two bite-plates should be securely fastened to each other by melted wax, when they should be again cooled and returned to the mouth. At this point is determined the exact con- tour of the patient's face by adding wax to the labial surface of the bite- THE ARTICULATOR. 351 wax, or by reducing the latter until the natural expression of the patient's face is restored. The next point to determine is the high and low lip-lines. The occluding edges of the bite-plates represent the length of the lips at rest, as well as the length -of the teeth. The high lip-line is the highest point of elevation of the upper lip, as when laughing ; the low lip-line is the lowest point to which the lower lip is depressed. The next line is the median line of the face, which should be made on the wax perpendicular to the occluding surface of the wax-bite. These lines are marked on the wax with a sharp instrument, and are shown in Fig. 394. The bite with all the markings is now removed, and the casts re- adjusted in their proper positions in the base-plates, when they should be fastened to the bite to prevent slipping, as represented in Fig. 394. The Articulator. — The object of a bite is to secure the proper relation of the jaws for the arrangement of the teeth. Before ar- ranging the teeth, means must be provided for maintaining the casts in their proper relation to each other when the wax-bite is removed. An instrument for this purpose is called an articulator, and is illustrated in Fig. 395. When such an instrument is not at hand, a plaster articu- lator can be arranged by extending the casts posteriorly, as illustrated in Fig. 395. Hinge pm Lower j S. S. White articulator. Fig. 396. In the latter illustration the wax has been removed in order to show the relation of the upper and lower ridges, but before the wax has been removed, as in Fig. 394, the extension of plaster to form the articu- lator is poured around the base of the lower cast. After this has hard- ened soft plaster is poured around the base of the upper cast, allowing some to fall upon the posterior extension of the lower model. In Fig. 396 the position of the casts is shown within the heavy lines, while the plaster extension is shown above, below, and posterior to the lines. 352 THE ''BITE" OR OCCLUSION. The joint at A is to permit of separation when desired ; the dovetail is to ensure a perfect readjustment of the two parts. This is the simplest form of articulator, and, though but little used, it is still of value. Fig. 396. I. ouMlkliuliuiH Showing plaster articulator v, ith wax-bite removed The form of articulator in general use at the present time is illus- trated in Fig. 395. It is made of brass, and consists of an upper and lower plate held together by a hinge pin. The upper plate is held at any desired point by a set-screw, and the upper and lower plates of the articulator are separated or lowered by the bite-screw, A. In mounting cases in this instrument the cast and bite, as shown in Fig. 394, are placed between the two plates of the articulator, raising the upper part by the bite-screw, A, so that it will not quite touch the upper plaster cast. Fig. 397. Showing the plaster casts and bite mounted in the anatomical articulator. The base of the casts should be trimmed to a perfectly horizontal plane, when a thin batter of plaster is mixed and poured over the lower part of the articulator, and the lower cast quickly placed in it, and the plaster brought up around the base of the cast to fasten it. The upper BITES FOB FULL AND PABTIAL DENTUBES. 353 cast is fastened in the same manner to the upper part of the articulator. When the plaster has hardened the bite-wax can be separated at the occluding surface and prepared for the arrangement of the teeth. In using this articulator it should always be observed that the bite-screw is opened a few threads to permit of bringing the casts nearer each other in case the bite was taken too long. Anatomical Articulator. — This articulator is shown in Fig. 397, with the same models and bite as seen in Fig. 394 mounted in it. It is the invention of Dr. W. G. A. Bonwill. The inventor claims for it special advantages, which will be explained in the section on Articulation. Bites for Full Upper or Lower Dentures. — To take a bite for a full upper or lower denture a base-plate and bite-wax are arranged after the manner just described, but in place of an opposing bite-plate of wax there would be the opposing teeth, upper or lower, as the case might be. The same rules for obtaining the length of the teeth, height of lip, median line, and contour are followed, but the wax-bite must be trimmed to allow each of the opposing teeth to strike it squarely. The bite-plate is now removed and the occluding surface warmed slightly, when it is returned to the mouth and the patient instructed to close against it. This will give an impression of the points of the opposing teeth in the oc- cluding surface of the wax. It is now taken from the mouth and returned to the model, after which an impression of the opposing teeth should be taken and an articulating cast made. This cast, when recovered from the impression, is adjusted in the imprints of the teeth on the occluding surface of the bite-plate and fastened with melted wax. The bite and two models are then mounted in the articulator after the manner described for entire dentures. Bites for Partial Dentures. — Any artificial denture requiring less than the full complement of teeth is called a partial denture. If one or two natural teeth only remain, the bite is usually taken after the method just described, but openings should be made in the base-plate to allow the natural teeth to project (Fig. 405). If the case is for one, two, or four artificial teeth, it is not always necessary to construct a base-plate. If two teeth — say a central and lateral incisor — be absent, a roll of soft wax should be placed Fig. 398. over the space, and extend about the width of two teeth on either side. The patient may now bite into this, and after the wax has been pressed close against the teeth and subsequently cooled it may be removed and adjusted in the same position on the plaster cast. After the wax is adjusted the cast should be filled to a level with showing upper cast a, bite-wax CC, and lower the cutting edges of the plasterteeth antagonizing cast b. with a roll of wet tissue-paper. A sheet of wet tissue-paper is now spread over this and the cutting edges of the plaster teeth, and as far forward as the wax. The wax-bite is 23 354 THE ''BITE" OR OCCLUSION. then filled in with thin plaster, which is allowed to flow on the cutting edges of the teeth, but not over the sides. At the posterior extremity of the east the plaster may be allowed to run down to a level with the base of the cast. The paper which has been previously spread over the plaster cast will prevent the two pieces from uniting. After the plaster has hardened the wax is softened in warm water and removed, when the bite and upper cast may be separated. (See Fig. 398. Bites for partial cases are described later, " New Bite- taking Means and Methods.") Bites on a Permanent Base-plate. — Bites for S^waged "Work. — Dentures constructed with a plastic base, such as vulcanite, celluloid, Watts' metal, cast aluminum, etc., require an arrangement of the teeth upon wax plates (temporary base-plates or trial plates). With swaged plates, such as gold, silver, platinum, etc., the bite is taken and the teeth arranged directly upon the permanent plate. After the plate is swaged, properly trimmed, and wired (if a wire is necessary), a ridge of wax is placed directly upon the metal plate, and built up according to the instruction given in the first part of this chap- ter. The principles involved and the method employed for obtaining a bite with swaged work are the same as for vulcanite or celluloid, the only diiference being in the use of the permanent metal plate instead of the wax trial plate. Bites for Crown- and Bridge-work. — " Crown- and bridge-work " are methods of dental substitution which dispense with the usual forms Fig. 399. Showing the manner of mounting a crown or small "bridge." of base-plates. Some forms of crowns are fitted directly to the root of the tooth in the mouth, no bite being necessary. The form usually requiring a bite is known as the ferrule crown. In DIFFICULTIES ENCOUNTERED WHILE TAKING BITES. 355 this case the ferrule is first adjusted to the root, after which a roll of soft wax is placed over it and the adjoining teeth, and the opposing teeth are closed into it. After the wax is chilled it is slipped off and laid aside. If the ferrule is detached from the root with the bite, it is recovered and readjusted to the root and a plaster impression is taken. The ferrule and post usually come away with the impression, and if not they must be removed from the tooth and placed in the impression and fastened in place. The impression is then filled with a mixture of sand and plaster or marble-dust and plaster (plaster, 2 parts ; sand or marble-dust, 1 part). After this cast has hardened the impression is broken off, the surplus plaster trimmed away, and the base made perfectly flat. The bite-wax is now adjusted to the cast, and the whole mounted in a crown articu- lator, as seen in Fig. 399, B. Bites for small pieces of bridge-work, where there are only one or two spaces to be bridged over in connection with the abutments, are taken and mounted in essentially the same manner as for a single crown. In extensive pieces of bridge-work the " true bite-plates " are exceed- ingly useful, though accurate bites in these cases may be obtained with- out the use of base-plates. The method for using bite-plates and of mounting the bite in bridge- work is practically the same as for partial plates, the only difference being that the crowns or caps used as abutments for the bridge must be in position on the natural teeth before the bite is taken. If it is desirable to have something more resistant than plaster an- tagonizing teeth to articulate in bridge-work, " modelling compound " may be used for the bite instead of wax. Into the modelling compound bite a fusible metal, composed of 8 parts tin, 4 parts lead, 2 parts bismuth, and 2 parts cadmium, can be 'Cast, thereby giving a metal antagonizing cast in place of one of plaster. Difficulties encountered while Taking Bites. — By a careful ex- amination of the temporo-maxillary articulation the student will observe that the lower law cannot close farther back than the position of occlusion. Therefore any move- ■^^^- ^0^- ment of the jaw save that of the occluding mo- tion must bring the condyles forward in the glenoid fossae. When a patient has lost all of the teeth from either jaw there is no fixed point of occlusion, and the patient may contract the habit of moving the jaw about to obtain different bearings on the ■edentulous ridges for the purpose of mastication. If this condition continues, it may become diffi- -cult to ascertain when the condyles are resting in the glenoid fossse, and the patient is apt to pro- trude the jaw to one side or the other or directly forward, when the bite is being taken, and thus give a false occlusion.^ From the fact that the lower jaw cannot be drawn back farther than ^ Under some conditions the shape and outlines of the articulating surfaces of the maxillary and temporal bones may undergo permanent alteration. — Ed. 356 THE ''BITE" OR OCCLUSION. the position of occlusion, any instruction given the patient, such as " bite back," or " close naturally," etc., will cause him to attempt to close in a certain way, and he will almost invariably close the wrong way. There have been many suggestions as to how this tendency to pro- trusion can be overcome, but few of them seem to be of any real value. The method which has been found most reliable in securing a correct closure is to instruct the patient to swallow, and just as the act of swal- lowing is complete have him bite firmly until told to relax. When the patient has been for some years without teeth, even the above method fails and something more radical is necessary. A little apparatus, which was invented by Dr. Garretson of Iowa, has been satisfactorily employed in several cases, and is illustrated in Fig. 400» It consists of two steel strips about 6 inches long, at one end of which are projections to enter the external ear, and a leather strap pass- ing over the occiput which prevents the ear-pieces from slipping down. At the other ends of the metal strips is a chin plate which works on a ratchet, and which may be moved forward or backward as the case requires. After placing the ear-pieces in position and tightening the straps, the chin plate is to be moved up firmly against the chin. The patient should now open and close the mouth repeatedly, and as the lower jaw is drawn backward the chin plate is moved upward until il: is certain that the condyles are at rest in the glenoid fossae. In this position the patient can open and close the mouth comfortably, but any attempt at protrusion will meet with resistance by the ear-lugs. The bite-plates are then adjusted and the bite is taken as usual. Fig. 400 illustrates the application of the instrument. The protrusive tendency is always increased by an excess of bite-wax and by failure to properly trim the wax base-plates. Before attempting to take the bite the wax plates should be carefully trimmed to prevent them being forced off the ridges by the muscles of the lips and cheeks. The attachment of the buccinator muscle should be especially observed, for if there be any infringement upon this muscle every attempt to open the mouth will be accompanied by a displacement of the base-plates. The continual displacement of the base-plates causes uneasiness to the patient, and in his or her efforts to maintain the plates in position the lower jaw is forced forward. The bite-wax should also be trimmed to the smallest possible dimensions that will permit of obtaining the proper markings. When the bite-plates are first inserted it is usual to find them in con- tact posteriorly when the mouth is closed, and there is a space be- tween the occluding surfaces anteriorly. This indicates too great depth to the wax at the points of contact, and the wax is to be trimmed off until there is an even contact over the entire occluding surfaces. It sometimes happens, however, that the plates strike anteriorly first, and if the cheeks are then drawn away with the finger and the occluding surface of the wax-bite observed, it will be found in perfect contact. This is often deceptive, for there would frequently be a space between the plates posteriorly if they were held in contact with the ridges. The force of occlusion and striking anteriorly first caused a tilting at the heel, which would give the appearance of proper contact. DIFFICULTIES ENCOUNTERED WHILE TAKING BITES. 357 If dentures were constructed after such a bite, there would be con- siderable space between the opposing bicuspid and molar teeth when placed in the mouth, and contact only with the anterior teeth. When the above condition occurs, it is well to hold the base- plates against the ridges firmly with the fingers, and then instruct the patient to close the mouth two or three times gently ; the space can then be detected and the proper remedy applied-. Another annoying occurrence when taking a bite with base-plates of wax is the spreading of the base-plate under the force of occlusion.^ This is more perceptible when taking a bite for a full upper denture with opposing natural teeth. Some operators, instead of taking a bite for full upper dentures as described in this chapter, place a roll of soft wax on the occluding sur- face of the bite-plate, and have the patient close into this with his teeth, . thereby taking the bite and an impression qf the opposing teeth at the same time. The warm wax, together with the heat of the mouth, causes a soften- ing of the base-plate, and under the force of occlusion the latter spreads. When the bite and base-plate are returned to the cast, it is found that the palatine portion of the base-plate is not in contact with the cast. The operator often attempts a readaptation of this part of the plate by pressing it down, and in doing so draws the impression of the occluding teeth nearer the centre of the mouth. When the denture is finished the articulation of the artificial teeth with the natural is quite diiferent from their arrangement on the articulator. The deficiency may not be so great as to require a complete recon- struction of the denture, but the use of the corundum wheel will be necessary to partially correct it, whereas a little more time and care expended while taking the bite would have afforded more accurate results. jSTo matter how much time is spent in taking a bite with wax base- plates, there always follows a slight deficiency in the articulation. It is impossible to so closely adapt wax or paraffin base-plates to the cast that there will not be some discrepancy between the model and the base-plates. When such is the case the position of the base-plate in the mouth may be slightly different from its position on the model. This is another cause for the difference between the occlusion in the mouth and that of the articulator, and even in entire dentures the use of the corundum wheel is often necessary before precision of occlusion is obtained. Dr. W. S. How described " New Bite-taking Means and Methods, with illustrations of the use of bite-plates," in the Dental Cosmos for Sept. and Oct., 1894, which the author deems of much value. In Fig. 401 is seen an upper bite-plate of suitable thin metal, having a palatal portion A, a plane portion B, and a contoured edge or border C. When a full upper denture is contemplated, the bite is at once taken by placing on the bite-plate (Fig. 401) a sufficient quantity of warmed beeswax to secure a completely good impression, and at the ' To avoid this difficulty many operators prefer swaged temporary base-plates of the metal commonly used for the formation of chambers in vulcanite and celluloid Avork. — Ed. 358 THE ''BITE" OR OCCLUSION. same time afford material for modelling the labial and buccal surfaces in a suitable manner to produce the proper facial expression. Fig. 401. The bite-plate here exhibits its novel and useful functions in enabling the operator to readily lengthen or shorten the bite, and also adapt the bite-plane B to the lip-line, as well as to the occluding lower teeth. When this has been carefully done and the mass removed from the mouth, the appearance will approximate that of Fig. 402. If the bite Fig. 402. then requires an increase of length, the bite-plate is held a moment over the Bunsen flame, when it will fall on a paper napkin held in the hand. It is then covered with a thin sheet of wax, replaced on the modelled wax, trimmed with the wax-knife along the contour border C, again put in the mouth, and comfortably remodelled and adjusted. The quickly transmitted heat of the metal bite-plate permits facile changes in occlusive adaptation and contour, without disturbance of the fit of the impression portion of the wax — an advantage of real consequence and value. If upon further study it is desired to shorten the bite, the mass is removed from the mouth, the plate quickly warmed over the Bunsen flame, all replaced in the mouth, and the patient instructed to close the teeth firmly on the bite-plate, which, while accurately maintaining the plane of the occluding teeth to which it has been conformed, will at the same time cause the softer wax immediately in contact with the plate to gradually yield until the bite becomes suitably shortened. In this connection it is important to note the functional difference of this metal bite-plate from the common wax plate, which yields and is indented by any considerable pressure of the occluding teeth ; whereas in the present instance so soon as the wax has cooled to a slight stiffness the patient is directed to press the teeth hard on the bite-plate (see Fig. DIFFICULTIES ENCOUNTERED WHILE TAKING BITES. 359 403), and the result is a bite-gauge identical in length with that which the finished denture will have under the ordinary pressure of the closed jaws. Many of the usual disappointing discrepancies between the common soft wax-bite gauges and the resulting defectively articulating dentures may now be avoided. Fig. 403. Fig. 404. The smooth and hard surface of the bite-plane B fixes a constant and firm limit to the bite-length, while allowing the utmost freedom of lower-jaw movement in occlusion during the adjusting and modelling ])rocesses to secure a natural oral and facial expression, with a proper lip line, as indicated in Fig. 404. This having been accomplished, a roll of warmed wax is placed on the under side of the bite-plate, which is replaced in the mouth, and the patient while the previous process was going on having been instructed and practised in the correct manner of closing the jaw, the head being thrown back to bring the face horizontal and the jaw held as far back as possible, the teeth are pressed through the wax on to the bite-plate, and kept there while with the finger the labial and buccal portions of the soft wax are pressed in upon the natural teeth. The mass is then carefully removed from the mouth and kept in safe readiness for transfer to the plaster model when obtained from the plaster impression ; and it is unnecessary to dwell upon the advantages of securing a certainly correct bite at the time of the sitting secured for taking the plaster impression. Fig. 403 shows a bite thus taken and transferred to the cast set in an articulator, and represents also the correct bite so obtained. This novel bite-plate provides for the taking of a very short bite. In fact, the bite-plane B may rest directly upon the gums, and the under teeth strike the plate, yet the rigidity of the metal plate is such that the wax impression and modelling will not warp in the adjusting, shaping, and removing manipulations ; whereas by the old mere wax methods a trustworthy very short bite is often almost impossible. For partial upper dentures sections of the bite-plate are with plate- nippers cut out as at EE (Fig. 405), and the bite taken in the way previously described. The lower bite-plate (Fig. 406) is of like character with that of Fig. 401, the lingual portion D being designed to approximate the lingual conformation of the lower jaw, while the bite-plane B and contour 360 THE "BITE" OB OCCLUSION. border C have the bite-taking functions of the upper bite-plate. For partial lower dentures sections may be cut out as at EEF (Fig. 405), to Fig. 405. Fig. 406. permit the passage of the remaining natural teeth through the bite-plate, the intermediate planes of which can be shaped to conform to any plane of the occluding upper tooth or teeth. The Separation of Bites. — After the plaster which fastens the bite to the articulator has hardened the bite should be separated at the occluding surface. This is accomplished in entire cases by passing a heated spatula or thin knife-blade between the occluding surfaces, when they will readily part. To separate partial cases or full upper or lower cases where there are opposing plaster teeth, the bite-wax containing the plaster antagonizing teeth is to be warmed until the bite-wax is softened throughout. The models may then be readily separated and all surplus wax removed. Articulation. The articulation of the teeth is one of the most important steps in the process of constructing an artificial denture. By the term " articulation " is meant the placing or an arrangement of the artificial teeth upon base-plates, so that they will appear like, and perform as nearly as possible the functions of, the natural teeth for which they are a substitute. It has been often observed that under most conditions the more closely is followed the normal arrangement or articulation of the natural teeth the greater will be the utility of the artificial. Therefore, it is of first importance for the student to study the teeth, their names, forms, arrangement, and requirements, in order to apply the principles in constructing an artificial denture. Names, Shape, Surfaces, and Position of Teeth. — The permanent teeth are thirty-two in number, sixteen in either jaw, divided as follows : Upper or f j Superior. \ Central incisors. 2 Lateral incisors. 2 Cuspids. 2 Bicuspids. 4 Molars. 6 Lower or f „ -^ , Inferior "1 .Central Aiueiiui. (. incisors. 2 Lateral incisors. 2 Cuspids. The arrangement is bilaterally symmetrical. 4 Bicuspids. 6 Molars. DIFFERENTIATION OF THE TEETH. 361 Taking a perpendicular line through the centre of the face, it should fall between the central incisor teeth superior and inferior. Beginning at this line and counting either way, we have in order — first, the central incisor ; second, the lateral incisor ; third, cuspid ; fourth, first bicuspid ; fifth, second bicuspid ; sixth, first molar ; seventh, second molar ; eighth, third molar. For the purposes of an artificial denture twenty-eight teeth are found sufficient, the third molars being omitted (Fig. 407). 54 3 21123 4 5 Upper and lower plain teeth in sets of twenty-eight. Each tooth has five surfaces, as follo:ffiB-r'^ 1. Labial surface, next the lips or Buccal surface, next the cheeks. 2. Incisal surface, cutting edge of the incisor teeth, or Occlusal surface, cutting or grinding surface of the bicuspids and molars. 3. Mesial surface, the proximal surface directed toward the median line of the face. 4. Distal surface, the proximal surface directed away from the median line of the face. 5. Lingual surface, next the tongue. Mesial, distal, and lingual surfaces are common to all the teeth, whether upper or lower. The line of junction between the crown and root of a tooth is called the cervical portion, or " neck," of the tooth, and is usually at the gum margin. In dental prosthesis there is use for only the crowns of teeth, and, as artificial crowns are made so nearly like the natural in outward appearance, it is deemed advisable to use them in the further illustration of this subject. Differentiation op the Teeth. Upper Teeth. — In Fig. 408 are represented the half of an upper and a low^er set of teeth for the same mouth, showing the labial and buccal surfaces 1 to 7 and a to G, and the occlusal surfaces of the bicuspids and molars, 0. The perpendicular line represents the median line of the face. No. 1 is the left superior central incisor. It is recognized 362 THE "BITE" OB OCCLUSION. as a " broad, wedge-shaped tooth, and is the largest of this style in the mouth." No. 2 represents the superior lateral incisor of the same general form, but smaller. The side to which these teeth belong is determined by looking at the labial surface and placing the longer mesial surface M Fig. 408. T M N iyiy'tJt/uit_^i tJ' \a\B CD E \ F \ G M N M N X W 1 10 11 U V U ir toward the median line. Also, the more acute angle, where the mesial surface 31 joins the incisal surface /, points toward the median line of the face. N is the distal surface of the central, and points toward the mesial surface of the lateral incisor. No. 3 is the cuspid, so called from its having a " pointed projection or cusp on the cutting edge." The labial surface of this tooth is convex, while that of the incisors is flattened. The cusp has a long and a short cutting edge. K marks the point of the cusp, J the shorter anterior cutting edge, and R the distal and longer cutting edge. The mesial sur- face points toward the distal surface of the lateral incisor. Placing the longer proximal surface and the shorter cutting edge of the cusp toward the median line determines to which side the tooth belongs. Nos. 4 and 5 show the buccal surfaces of the first and second bicuspid teeth, which so nearly resemble the labial surface of the cuspid, except they are smaller, that no further description of these surfaces is necessary. In addition to the labial cusp these teeth have a lingual cusp, shown in ARTIFICIAL TEETH. 363 vertical section Nos. 8 and 9, U. The lingual cusp is usually a little shorter than the buccal cusp V, and not so pointed. The superior molars are the grinding teeth, and have " broad occlud- ing surfaces, possessing four cusps," Nos. 6 and 7, 0, the two anterior or mesial cusps being heavier and longer than the two distal cusps, while the mesio-buccal angle is the most acute. Directing the broader proxi- mal surface, while looking at the buccal surface, toward the median line of the face, will determine to which side the tooth belongs. The second molar 7 very nearly resembles the first molar, except being a little smaller. Lo^wer Teeth. — While the superior central incisor is the largest wedge-shaped tooth in the mouth, the inferior central incisor is the smallest, and is shown in A. It has the same general formation as the superior central, but is longer in proportion to breadth. The inferior lateral incisor 5 is a little broader than the inferior cen- tral, and the crown is usually a little shorter. The inferior cuspid C bears a close resemblance to the superior cus- pid, but is longer in proportion to breadth. The first inferior bicuspid D resembles the inferior cuspid in form more than a bicuspid, but, owing to its extreme narrowness, it would never be mistaken for a cuspid. It ^qry seldom possesses more than a diminutive lingual cusp, as shown in Fig. $08, W, and is much narrower than the second bicuspid inferior. Bicuspid, second inferior, is broader than the first bicuspid, and in proportion to length is broader than the upper bicuspids. The principal distinguishing feature of this tooth is its lingual cusp, No. 11, Y, which is usually more acute than the buccal cusp Z, and quite as long; the lingual cusp is divided into two distinct sections, mesial and distal. The lingual surface is quite as broad as the buccal. Molar, first inferior, is the largest tooth in the lower jaw, is " trape- zoidal in form, has five cusps," three buccal and two lingual, F and O, the lingual cusps beings usually quite as long, and often a little longer than the buccal cusps. The upper molar is more rhombic in form, and has four cusps, the two lingual being slightly shorter.^ The side to which it belongs is determined by the same rule as with the upper molars. Molar, second inferior, has the general shape of the first, but is smaller and possesses but four cusps, G and 0. The same rules are applied for determining the side of the mouth to which the lower teeth belong as with the upper. A careful study of the anatomy of the natural teeth, as found in Black's Dental Anatomy, where the foregoing facts are treated more elaborately than is admissible in a chapter of this character, will be of great service to the student of prosthetic dentistry. Artificial Teeth. Artificial teeth are divided into two general classes — viz. gum teeth and plain teeth. ^ Observation has shown that when the lingual cusps of lower molars are longer than the buccal (of natural teeth) there is a corresponding diminution in the length of the lingual cusps of upper molars, these being just as much shorter than their buccal as the lingual cusps of molars are longer than their buccal cusps. 364 THE ''BITE" OR OCCLUSION. These are again subdivided into several varieties, as follows (see Figs. 409-417) : Fig. 410. Fig. 411. Fig. 412. Fig. 413. Fig. 414. Fig. 415. Gum Teeth. Plain Teeth. Fig. 416. Single gum teeth, Fig. 409. Gum sections, Fig. 410. j Festooned gum sections. Fig. 411. 1^ Gum teeth for metal plates (gum plate-teeth). Fig. 412. ' Are always single, Figs. 413, 414, 415, 416, 417. For mental plates (plain plate-teeth). Fig. 416. For vulcanite plates. Figs. 413, 414. 1 For celluloid plates, Figs. 413, 414. For continuous-gum plates. Fig. 417. 1^ Countersunk-pin teeth. Fig. 415. The teeth are again divided into " long bite " and " short bite," com- mon to both gum and plain teeth. While the labial and proximal surfaces of artificial teeth resemble the natural organs, the lingual side is adapted for attachment to the base-plate of the denture. In this side two or more platinum pins are arranged, the position of which determines the length of the bite, whether long or RULES FOR SELECTING TEETH. 365 short, and is a very important matter to consider in making a proper selection. In addition to the divisions of artificial teeth already given, there are — Teeth with headed pins, Figs. 410, 413, 414, 415, for plastic bases. Teeth with straight pins. Figs. 412, 416, for plate work. Teeth with pins lengthwise, Figs. 412, 416. Teeth with pins crosswise. Figs. 413, 414. Pins lengthwise are arranged in series with the long diameter of the tooth, or w^ith one pin near the cutting edge and the other nearer the neck of the tooth. Pins crosswise are arranged in parallel across the shorter diameter of the tooth. Short-bite teeth usually have the pins arranged crosswise, as have also gum-section teeth, while in plain teeth the pins are arranged either way. Rules for Selecting Teeth. In making a selection of gum or plain teeth, long- or " short-bite " teeth, some rules should be adopted on which to base our choice. By referring to Fig. 418, No. 1, we see represented a vertical sec- tion of the ridge at the median line, showing the position of the upper Fig. 418. lip B at rest, and the same at C elevated to its highest point, as in laughing. The space between C and B must either be filled in with a plain tooth or gum section. If the distance between Cand B would not require a tooth too long for the proper appearance, a plain tooth would be suggested, as is seen in the figure. The second point to be observed in this same case is the " bite " of the tooth. In the illustration we find the pins on the lingual side nearer. 366 THE "BITE" OR OCCLUSION. the cutting edge, and the major portion of the tooth extends above the pins ; and it is at once recognized as a short-bite tooth. It is obvious that a tooth with a longer cutting edge could not be used, because it would project too far below the lip line, B, and would expose too much tooth. Again, if the tooth did not extend as high as A, the base of the denture would be exposed and an unsightly appliance would be the result. Rule. — A long ridge and short lip suggests the use of short-bite teeth. No. 2 illustrates a case w^here a plain tooth is indicated, but where a short-bite tooth is contraindicated. The lip B is longer and the elevation, A, not so great as in No. 1. As for appearance, a short bite-tooth could be used, but by removing the pins so far from the ridge in order to bring the cutting edge of the tooth to the lip line B an unusual thickness of the plate is occasioned, which would be a serious impediment to the tongue in speaking. There- fore we must use a tooth witli the pins nearer the cervical extremity, and with the major portion of the tooth between the pins and cutting edge. This tooth will be recognized as a long-bite tooth, and is illustrated in No. 3. It will be seen that the ridge lap is shorter than in No. 1, for the reason that it is not necessary for the tooth to extend beyond the high lip line A. This character of tooth gives more room for the tongue, and also allows the lower teeth the normal under bite. Rule. — A short ridge and long lip usually indicate long-bite teeth. No. 4 illustrates a case where a plain tooth is contraindicated, but where a long-bite tooth is indicated. The lip line is the same as in No. 3, but it will be noticed that the high lip line is considerably ele- vated, and is as much higher than No. 3 as from C to A in No. 4. It is evident that the space from ^ to -B must be filled in, either with a tooth or a tooth with porcelain gum, but in this case the distance from A to B would give a tooth of too great length for a natural appearance. Therefore we must select a gum section that will give a tooth of the proper dimensions, but with a porcelain gum extension that will reach A, as shown in No. 5 (known as long-bite gum tooth). Rule. — Where the distance between the lip line and high, lip line would require a tooth of too great length for proper appearance, a " gum tooth " is indicated. In No. 5 the length of tooth is shown to extend from B to C, and the extension above C to A is of porcelain, in order to hide the unnatural base of the denture. No. 6 illustrates the use of a short-bite gum tooth. This figure is the same as No. 1, except the high lip line is at A instead of C. It will be noticed now that the distance between A and B would require a tooth too long for a good appearance, as shown in No. 1, A to B ; con- sequently we must reduce the size of the tooth and add a porcelain gum, as seen in No. 6. No. 7 illustrates a case where a gum tooth is contraindicated. Owing to the excessive fulness of the alveolar ridge, the use of a gum tooth would cause an unnatural protrusion to the upper lip, and, if the same method were followed in the construction of a denture in this case as in the preceding illustration, a plain tooth would also be contraindicated. RULES FOR SELECTING TEETH. 367 In this case, however, a plain tooth is indicated in order to prevent dis- figurement of the face, but an entirely different method of arrangement, as illustrated in No. 8. The six or eight anterior teeth must be arranged to rest with their necks slightly imbedded in the gum-tissue covering of the ridge. In order to accomplish this the gum lap must be ground thin, and where this strikes the plaster cast the latter must be trimmed away slightly, as shown in No. 8. When the denture is inserted the front teeth press into the gum-tissue gently and hide the cervical portion of the teeth, thus affording a very close imitation of the natural organs. No. 8 also illustrates another character of tooth — viz. a medium bite, the pins being arranged near the centre of the tooth. The same arrangement of teeth is necessary for No. 7, A, No. 8, except that a short-bite tooth is suggested. No. 9 illustrates a case of almost complete resorption of the ridge. In this case a plain tooth could be used, but, owing to the considerable amount of vulcanite necessary to restore the features, and the danger of not obtaining a good adaptation when so much vulcanite is used, it is better to use a thick gum section in order to reduce the quantity of vulcanite. Therefore, as a rule with vulcanite base in cases of great resorption of ridge a thick gum section is indicated. With a close study of the foregoing illustrations, and the following chart ^ the student should be able to enter upon the study of the more artistic features of the subject. Definition and Illustration of Terms employed to Express "Va- rieties of Styles of Teeth.— Figs. 419-426. Short or Long Ridge Lap. — The form of the heel or butt of the tooth. Short or Long Shut. Fig. 419. Fig. 420. Fig. 421. Short ridge lap. Long shut. Long bite. Long ridge lap. Short shut. Short bite. Short ridge lap. Long shut. Short bite. — The distance between the upper and lower maxillae when the mouth is naturally closed. Shoi^t or Long Bite. — The extent of the lap of the upper tooth over the lower. Shoulder Bite. — The striking of the occluding teeth upon a shoulder. Flat-faced Teeth. — Those intended for cases of ^ Kindly loaned by S. S. W. Dental Manufacturing Co. 368 THE "BITE" OR OCCLUSION. protruding upper jaw. Bow-faced Teeth. — Those intended for cases of protruding lower jaw. The vertical lines represent the facial line. The two horizontal lines represent the lip line in laughing. The following cuts illustrate what is meant : Fig. 422. Fig. 423. Fig. 424. Short ridge lap. Short shut. Short bite. Long ridge lap. Short shut. Long bite. Long ridge lap. Short shut. Short bite. Fig. 425. Fig. 426. Flat-faced tooth for protruding jaw. Bow-faced tooth for pro- truding lower jaw. Occlusion and Articulation. The teeth are arranged in the alveolar process in the shape of a parabola : with the long axis passing between the central incisor teeth, the' arch is a little larger in the superior than the inferior jaw (Fig. — ~). They are also so arranged that when the mouth is closed naturally they will strike against the opposing teeth in a definite manner, as shown in Fig. 427. When in this position the teeth are said to be in occlusion. During occlusion all of the superior teeth overlap the lower ; the six anterior teeth, superior, pass over and cover part of the labial surface of the six inferior teeth ; while in the buccal region the buccal cusps of the superior bicuspids and molars cover to a decreasing extent the buccal cusps of the inferior bicuspids and molars. OCCLUSION AND ARTICULATION. 369 This arrangement makes the upper arch a little more prominent and larger than the lower arch. It will also be observed, by referring to Fig. 427, that with but two exceptions each tooth strikes against two opposing teeth, the exceptions being the inferior central incisor, which is Fig. 427. covered entirely by the superior central incisor, and the last superior molar, which covers about one-half or one-third of the last inferior molar. Beginning at the superior central incisor, it will be observed that it covers not only the inferior central, but also about one-third to one-half of the inferior lateral incisor. The superior lateral covers the remaining portion of the inferior lateral and about one-half of the inferior cuspid. The superior cuspid covers the remaining portion of the inferior cuspid and nearly half of the first inferior bicuspid. It will be seen by this arrangement that the inferior central, lateral, and cuspid occupy a position anterior to the point of the cusp of the superior cuspid — a fact which it is well to remember in the selection of entire sets of teeth, as it fixes the relative size of the six lower to the upper teeth. By referring to Fig. 427 it will be observed that the first bicuspid, superior, covers the remaining portion of the first inferior bicuspid, and also about one-half of the second inferior bicuspid. This brings the point of the buccal cusp of the first superior bicuspid between the inferior bicuspids. The manner of occlusion of the remainder of the teeth is clearly shown in Fig. 427, and needs no further description here. When the teeth in occlusion strike as shown in Fig. 427, they are said to represent a normal articulation. Articulation. — The means for properly masticating the food infers a perfect articulation of the teeth, not only during occlusion of the jaws, 24 370 THE ''BITE" OR OCCLUSION. but also during the various movements of the lower jaw in the acts of incising and grinding the food. The lower jaw is endowed with certain movements by the muscles of mastication whereby the teeth are brought into various relations with each other for the purpose of incising the food when both condyles of the lower jaw move forward and downward in the glenoid fossae, bringing the cutting edges of the incisor teeth opposite each other for the purpose of separating a small portion of food from the main bulk, prior to the process of mastication. During mastication, instead of both condyles moving, one condyle only moves forward and downward in the glenoid fossa, protruding the lower jaw to one side or the other. This lateral protrusion, followed by a drawing back into the position of occlusion, is a provision whereby the cusps of the bicuspids and molar teeth, if they are in proper relation to each other, can be utilized for the comminution of the food. It is a fact that, owing to careless methods in vogue, the movements of the lower jaw for the purpose of mastication, with a large percent- age of artificial dentures, are restricted simply to the up-and-down movements of the jaw or the movement of occlusion. By such a movement of the jaw, instead of mastication the patient is limited to only a crushing of the food, swallowing it without the proper insaliva- tion which follows the free and unrestricted use of the lower jaw. To construct an artificial denture which shall permit of the free and unrestricted use of the lower jaw several points must be carefully con- sidered, and these cannot be better presented than in the language of Dr. Bonwill, who is the author of a series of articles entitled "The Geometrical and Mechanical Laws of the Articulation of the Human Teeth." In these articles he calls attention to a few conditions which exist in every normally articulated natural denture, and with a special apparatus of his own invention, called " the anatomical articulator," he applies his conclusions to the arrangement of artificial teeth. His first important observation is with reference to the shape of the lower jaw, it being of a peculiar tripod arrangement and forming an equilateral triangle. " From the centre of one condyle to the centre of the other four inches is about the average distance, and it will also be found that from the centre of each condyloid process to the median line at a point where the inferior centrals touch at the cutting edge is also about four inches." The sides of these angles, he asserts, never vary more than half an inch, which would make little difference in describing the arc of a circle. " No matter what the width from one condyloid process to the opposite process, the distance is the same from the processes to the median line of the lower jaw at the cutting edges of the central incisor teeth." . . . . " The jaw forms a perfect triangle for the purpose of bringing into contact the largest amount of grinding surfaces of the bicuspids and molars, and at the same time have the incisors on one side at once come into action during those lateral movements." .... " It will also be found that from the cuspids, the bicuspids and molars run in nearly a straight line, instead of a circular one, back toward the condyloid process, enabling them to keep the largest amount of surface always presented for mastication." The next import- ant observation has reference to the position and relation of the incisor OCCLUSION AND ARTICULATION. 371 teeth : " The upper incisors should over-jet the lower incisors, while the lower have a corresponding under-bite ; without this arrangement the incisor teeth would lose their function. Were the incisors to strike directly upon each other, the power to cut off food would be very much lessened. The normal arrangement of the incisor teeth is shown in Fig. 428. Where there is an over-bite and an under-bite of the incisor Fig. 428. teeth, just in proportion to their depth will be the length of the cusps of the cuspids, bicuspids, and molars." The next observation has reference to the curvature of the teeth in the jaw, which is formed by the dipping down of the second bicuspid and shortening of the posterior cusp, with a turning upward of the first and second molar teeth toward the condyle of the jaw, as illustrated in Fig. 430, and is also illustrated in Fig. 427, which is reproduced from a life-size engraving from Black's Dental Anatomy. This vertical curva- ture " commences at the first molar tooth, ' although it shows itself slightly at the bicuspids ; practically, it need only commence at the first molar, and this curvature is proportioned to the under-bite and over-bite of the incisor teeth." The purpose of this curvature at the ramus, as shown in Figs. 427 and 430, is obvious : when the lower jaw is protruded during the incisive function (Fig. 429) the molar teeth are in contact at the same Fig. 429. time as the cutting edge of the incisor teeth, while the cuspids and bicuspids swing free. This prevents anything more than mere contact of the incisor teeth ; and, applying the principle to the arrangement of artificial teeth, it establishes contact at the heel of the plate at the same time the incisor teeth strike, and prevents the displacement of the den- 372 THE ''BITE" OR OCCLUSION. ture. The length of the cusps of the bicuspid and molar teeth has a definite relation to the lateral movement of the lower jaw. The buccal Fig. 430. cusps of the lower bicuspid and molar teeth are usually shorter than the lingual cusps, while the reverse is true of the upper bicuspids and molars. The purpose of this arrangement can be easily seen by refer- ring to Fig. 431. When the lower jaw is extended to the left side, as Fig. 431. in the figure, and mastication is being performed on the left side of the mouth, the cusps, both the lingual and the buccal, are found opposite each other, while the food is pressed into the sulcus between these cusps. Now, if there is no contact upon the opposite side of the mouth, the plate would be in great danger of tilting or dropping on the side oppo- site the one in use. But by the proper shaping of the cusps of the bicuspids and molars we find that we can obtain upon the opposite side of the mouth contact between the lingual cusps of the upper molar teeth and buccal cusps of the lower molars, which prevents displacement of the denture opposite the side in action. " By drawing two lines from T to a and T to e, in Fig. 428, we have the lengths of the cusps of the bicuspids, b in the upper and c in the lower, and also d, the second upper molar. The depth of the under-bite is one-eighth of an inch from the cutting edge of the inferior central incisor, c, to that of the superior central incisor, a. Did the teeth extend as far back as T, there would be flat surfaces at those points. But in articulating artificial teeth, when the superior second molar is reached its distal cusp has to be raised from line Te to Ta (Fig. 428) to allow the molar teeth on the opposite side, not in mas- tication, to touch for merely balancing the plate, as Fig. 431, 31, N; otherwise the second molars would be of no use in lateral movement, nor would the first molars. This curvature at the ramus (see Figs. 42^ and 430) commences at the first molar, although it shows itself slightly in the bicuspids. Practically, it need commence at the first upper molar. This curve, then, will always be proportioned by the under- OCCLUSION AND ARTICULATION. 373 bite at a, e. The length of the cusps or bicuspids will never be more than an eighth of an inch normally ; the groove deeper than that would cut the palatal cusp off and make of it a cuspid. It would in reality be cut in twain. " So that when a first superior bicuspid is seen it can very well be told from the length of the cusps whether the jaw from which it came had a depth of under-bite of one-sixteenth of an inch or more. Where the teeth all strike fairly one upon the other, without over-bite, then there is no occasion for cusps. If originally there, they would soon be worn ofP from the abnormal articulation." As the lower jaw is drawn into position, the buccal cusps of the lower molars travelling into the sulcus and toward the lingual cusps of the upper molars on the side in use, we find the buccal cusp of the opposite lower molar travelling toward the buccal cusp of the upper molar on the side not in use, keeping a constant contact for the pur- pose of supporting the denture upon that side of the mouth during mas- tication on the opposite side. The same principle holds good when mastication is performed on either side of the mouth. Fig. 431 shows the position of molars and bicusj^ids during mastica- tion on the left side, with a balancing contact of the molar teeth on the opposite side of the mouth. The next observation made by Dr. Bonwill has reference to the rela- tive position and size of the teeth in the arch. This is illustrated in Figs. 432, 433. An equilateral triangle is formed with a base of four inches, the distance from the centre of one condyle of the lower jaw to the centre of the opposite condyle, and represented by the points A, A in the figures. From the points A, A a, line is taken to the cut- ting edge of the central incisor teeth at the median line, which repre- sents the apex of the triangle. We now take a pair of dividers and obt,ain the combined width of the superior, central, lateral, and cuspid teeth on one side. A line is now drawn from the point (F), or the cutting edge of the superior central incisors at the median line, to a point between the condyles, or midway between the points A, A (Fig. 433). This line extends from i^ to T in the diagram, and represents the median line of the mouth throughout its entire extent. The point of the dividers is now placed at the cutting edge of the superior centrals at point F, while the other foot of the divider is placed at point I on the median line, or just the distance of the width of the superior central, lateral, and cuspid teeth on one side. The point of the divider resting at / is held firmly in position, while the point of the divider at F is made free, and a com- plete circle described. The anterior segment of this circle which inter- sects the median line at F gives the exact size of the arch as it falls directly upon the cutting edges of the incisor and cuspid teeth. It marks the extreme limit and prominence of the cuspid tooth. If a line be drawn at right angles to the point where this circle intersects the median line at Y (Fig. 432) (or twice the distance of the combined width of the superior central, lateral, and cuspid) from the apex of the triangle, it will fall through the centre of the second molar tooth. After arranging the six anterior teeth according to the measurements given, a straight line is taken from the condyle of one side of the mouth to the distal surface of 374 THE ''BITE" OB OCCLUSION. the cuspid tooth on the opposite side of the mouth. Another line is drawn from the condyle on one side to the cuspid tooth on the opposite side at its distal surface. These lines intersect the median line at B. Dr. Bonwill asserts that a line drawn at right angles to the median line at the point B (Fig. 432) will pass through the centre of the first molar tooth. It may be stated with reference to this line that its position can be slightly altered according as the width of the incisor teeth is greater or less, and also the width of the bicuspid teeth, but the discrepancy is so slight that it makes but very little practical difference in the arrange- ment of an artificial set of teeth. By reference to Fig. 432, which is taken from a life-size engraving in Black's Anatomy, it will be found that the horizontal line passes through the middle of the disto-buccal lobe of the first molar tooth instead of through the centre of the tooth. Fig. 432. The arrangement as shown in Black's Anatomy has been more uni- versal in the measurements made than that shown in Dr. Bonwill's diagram. One point of the divider is next placed at A (Fig, 432), and the oppo- site point at B, and a curve described toward the buccal surface of the mouth from B, and it will be found that this gives a space between the OCCLUSION AND ARTICULATION 375 curve and distal surface of the cuspid tooth, which fixes the width of the first bicuspid tooth. One point of the divider is kept at A and the other point retracted to Y ; a second outward curve is then described, and the space between these curved lines gives the exact width of the second bicuspid tooth. The next line is taken from a point at the distal surface of the cuspid tooth to the condyle of the jaw, which Dr. Bonwill claims will pass through the buccal cusps of the bicuspid and molar teeth — teeth approximating the natural or normal. This line, however, has been found in normal dentures to deviate slightly from the diagram shown by Dr. Bonwill. By reference to Fig. 432 it will be found that the two bicuspids and first molars will fall with their buccal cusps upon this line, while the second molar is turned inward, toward the median line of the mouth, and is missed entirely by the line from A and B (Fig. 432). This seems to be a more advisable arrangement of artificial teeth, for if the diagram of Dr. Bonwill is followed exactly, the disto-buccal cusps of the second molars are thrown too far from the ridge, and there is great danger of excessive leverage at this point, which would not be the case if the second molar was turned toward the median line, as shown in Fig. 432. With the exception of this tooth and the position of the line which defines the centre of the first molar no exception is taken to Dr. Bonwill's measurement. While the drawings represented in Figs. 429, 430, 431, and 433 are theoretical, they are nevertheless true ; but in order to make this subject more practical two engravings from life are shown in Figs. 427 and 432, with the measurements as given by Dr. Bonwill (page 372). Fig. 433. In following out the measurements as given below the reader can make reference to both Figs. 432 and 433, and can make comparison between the ideal and natural. [Dr. W. E. Walker of Pass Christian, Miss., in Cosmos, January, 1869, calls attention to an anatomical feature of the temporo-maxillary 376 THE ''BITE" OR OCCLUSION. articulation, together with its consequent effect upon occlusion, which has been overlooked in previous observations. In the Bonwill articulator the instrument is so constructed that the plane of the temporo-maxillary articulation is parallel with that of the occlusion of the teeth. The opening of the jaws of the articulator to bring the tips of the inferior and superior incisors into contact corresponds with the depression of the inferior maxilla. In the Bonwill instrument the angle formed by the joint portion with the horizontal line is but about 10° to 15°. Dr. Walker shows that the angle in the living subject, from which the con- dyle of the inferior maxilla diverges from the horizontal plane of the glenoid cavity, is, upon an average, 35°. He has studied carefully this forward and downward path of the head of the bone, and has constructed an instrument which follows accurately the movements of the human jaw according to its variations in individuals. Models of a perfect den- ture placed in the Bonwill articulator have not the precise physiological movements observed in the human jaws. Dr. Walker has demonstrated that this discrepancy is due to insufficiency of the angle at which the portion of the instrument representing the head of the bone diverges from a horizontal plane. The models transferred from the Bonwill to the Walker instrument have movements which correspond closely with those observed in the human jaws. — Ed.] Angles of Force during Mastication. When the teeth are firmly imbedded in the alveolar process and sup- ported laterally by one another, a slight change in the angle or position of the teeth is of very little importance practically, but the angles at which teeth on an artificial denture are placed contribute largely to the successful or unsuccessful use of that denture. It is absolutely necessary to consider the lines of force, or the mechanical forces, during mastication, in order to prevent displacement of dentures before the cutting edges of the teeth come into actual contact. Fig. 434 outlines the position of the incisors, bicuspids, and molar teeth on opposite sides of the mouth during the incisive function and during mastication, and the lines of force are indicated by the darts. In a large number of cases where there has been excessive resorption of the ridges it is a rule with a great many operators to project the cut- ting edges of the incisor teeth toward the lip, while the cervix of the tooth is inclined toward the alveolar ridge. The same is true of the lower incisor teeth, and is indicated by No. 12. If the mouth is thrown open, and there is an attempt to incise with the teeth in this position, the pressure from the lower tooth is against the inner or lingual cutting edge of the upper incisor tooth, and the angle of pressure is shown by the dart from B to A, which would cause a tilting of the plate at the heel because, there being food between the incisor teeth, there is no contact between the molars. An arrangement of this kind, as shown in No. 12, would have a tendency, as can be seen by the angle of these teeth, to displace by tilting both dentures at the heel. Referring now to No. 13, we find that by inclining the cervix of the superior incisors labially, the cutting edge of the inferior incisors lingually, the line of pressure is toward the centre of the palate above and against the labial cutting edge of the superior incisors, thereby supporting the denture during the pro- ANGLES OF FORCE DURING MASTICATION. 377 cess of biting through the food. While this arrangement may not be wholly in accordance with a natural denture, and is slightly exaggerated in the figure, the appearance is much better in an artificial set than the same arrangement might be with the natural teeth. The slight change Fig. 434. No. 15 No. 13 No. 10 No. 12 No. 14 of these angles does not materially aifect the appearance of an artificial denture. It must be remembered that No. 1 3 represents the position of the incisor teeth when the lower jaw is protruded for the purpose of incising. If we refer to No. 14, we observe an arrangement of the bicuspids and molars that usually accompanies No. 12. By the leaning in of the cervix toward the alveolar ridge it can readily be seen that 378 THE ''BITE" OB OCCLUSION. when there is food between the teeth and pressure is exerted, bringing the lower teeth against the upper, the pressure would be represented by a line from B to A, and this pressure toward the buccal surface would tend to displace the denture upon the opposite side of the mouth. It will be observed by reference to No. 15 that the necks of the teeth incline away from the ridge, while their cutting edges lean toward the centre of the mouth. This is the correct arrangement of artificial teeth in occlusion. The position of the teeth in mastication is shown in No. 10, with the lower jaw protruded to the right side. If the food be now grasped between the teeth arranged according to this figure, the line of force would be as indicated in No. 10, the pressure being upon the buccal surface toward the centre of the palate, while in the lower it would be toward the median line of the floor of the mouthy as indicated by the darts. When the jaw is protruded laterally for the purpose of triturating the food, it is gradually retracted, drawn upward and toward the position of occlusion. Until the cutting edges of the teeth strike, the pressure would be toward and against the lingual cusp of the upper molar in the sulcate groove. It will readily be seen that pressure against this point would tend to support the denture on the opposite side of the mouth. If the angles of the teeth are arranged properly, there will be no dis- placement of the denture while biting through the food until the cutting edges of the teeth strike, unless upon the opposite side of the mouth there was no balancing contact. The real act of mastication occurs after the cutting edges of the bicuspids and molars strike, and if at this time we have contact upon the opposite side of the mouth, we find that the den- ture would be constantly supported. By reference again to No. 10 the lines of force indicated are seen until the cutting edges of the teeth strike ; now, as the lower jaw is retracted the molars and bicuspids begin to travel, the food being pressed in the sulcate groove between the cusps upward and toward the position of occlusion, the buccal cusps following into the sulcus of the upper tooth, while the lingual cusps of the lower molar travel over the lingual cusps of the upper molar. During this time we find the buccal cusps of the lower molar on the opposite side travelling into the sulcus of the upper molar and toward its buccal cusps, keeping a balancing contact on the side opposite the one in action. A practical application of the angles of force during mastication can probably be more clearly demonstrated by reference to Fig. 435, No. 16. Here is shown a case of lower central incisors and cuspids, with their abraded cutting edges bevelled away from the lingual surface toward the labial side of the tooth. The second molar tooth tilts forward, owing to a loss of the first molar and bicuspid tooth. No. 17 shows a faulty arrangement of the artificial molars in which the same conditions hold good as in No. 16. No. 18 illustrates an arrangement of the molars by which much greater stability of the denture can be secured. There are other points to be considered in the arrangement of teeth besides mastication. The strength and duration of artificial teeth on a denture or a " bridge," and also the base-plate of the denture as well, de- pend upon the manner in which the occluding teeth strike. If they strike ANGLES OF FORCE DIJBINQ MASTICATION. 379 as shown in Fig. 434, No. 14, there is a great strain on the superior denture throughout the centre of the palatine portions, which eventually results in a splitting or bending of the plate. The individual teeth are also liable to be fractured or forced from the plate, this latter condition Fig. 435. No. 18 occurring more frequently in ridged appliances, such as bridge-work, and is an extremely difficult break to repair. The direction in which force is exerted during mastication and during the incisive function should be closely observed in order to place the teeth in a position which will enable them to resist that force to the highest degree, or in a position which will afford the greatest mutual support between the base of the denture and the teeth. By giving strict attention to these points many annoying accidents will be avoided. With the foregoing basis, it remains to adopt some apparatus by which may be studied and obtained the various movements of the lower jaw out of the mouth. As has been seen by the preceding observations, the over-bite of the incisor teeth, the position of the teeth in the arch, the vertical curvature in the bicuspid and molar region, the length of the cusps, all have a definite relation to each other and cannot be followed abstractedly. It will not be possible to carry out the provisions of this articulation without having the means of actual measurement. There is a vertical curvature in the molar region, but this curvature will be of no service unless properly proportioned to the over-bite. If the incisor teeth are arranged with a very slight overlap, " or only enough to prevent 380 THE ''BITE" OB OCCLUSION. Fig. 436. W. G. A. Bonwill's articulator. hissing/' the incisive function of the incisor teeth is sacrificed, and the appearance of the incisor teeth will be unnatural. If the incisor teeth are arranged regardless of the position of the molars and the natural amount of overlap given, then lateral movements of the jaw will be interfered with, and the patient will be restricted simply to the up-and- down movements of the jaw. Means must be adopted whereby these various conditions can be measured or relatively proportioned out of the mouth, and this cannot be accomplished without being able to obtain the movements of the lower jaw. An instrument for this purpose is the "anatomical articulator." Anatomical Articulator. — The anatomical articulator is composed of brass wire and tubing, and is illustrated in Fig. 436. It consists of a base and two brass bows, the bows being detachable by loosening the set- screws. The articulator as seen in the cut is in the position for use, the uppermost bow being much narrower than the lower bow. The cross-bar or tube, to which the narrow bow of the ar- ticulator is attached, corresponds to the base of the triangle or the line from a to a, Figs. 432 and 433. At either extremity of the cross-bar is an eyelet through which the " condyle " of the ar- ticulator works. The two spiral springs back of the condyle represent the muscles, and serve to keep the casts in the position of occlusion, except when moved about to get the diiferent bearings of the artificial teeth. In mounting cases the narrow bow should always receive the upper model, whether that be an articulating model or the model upon which a denture is to be constructed, and the wide bow should at all times receive the model of the lower jaw. The first step in the process of mounting a case is to loosen the two set-screws and push the brass bows firmly back in their respective sockets, and then hold them by tightening the screws. Second. Trim the base of the models so that the plane of the base A, Fig. 437, will correspond to the plane of the occluding surface of the wax-bite, B. The plane of the base of the models A, A should be per- fectly horizontal, and the wax-bite at B should be also horizontal in the region of'the six anterior teeth, as shown in Fig. 437. Attention to these points enables one to mount the cases squarely in the articulator. Third. Place the plaster models in position in the wax-bite plates, and fasten them at two or three points by melted wax, to prevent slipping of the models during the mounting process. Fourth. Place the articulator with the wide bow resting upon a piece of paper on the plaster bench, and the upper bow turned backward. Fifth. The lower model is now adjusted upon the wide bow, the heels pointing toward the condyles H, H, Fig. 437, with the bite-wax and upper cast also in position when the narrow bow is turned to rest on the upper cast. ANGLES OF FORCE DURING MASTICATION. 381 Sixth. Take a pair of dividers, opened to measure four inches, and place one foot in a depression at the condyle, H, then bring the other foot to the point where the perpendicular (median line) intersects the Fig. 437. B, occluding surface of wax-bite ; F, high lip line ; 6, low lip line. occluding line, B. The distance is now to be measured from the op- posite side in the same manner. Rule. — Let the median line of the mouth, F to T, Figs. 431 and 432, fall midway between the condyles of the articulator, and at the same time let the median line of the bite at the occluding edge of wax be equidistant (four inches) from each condyle. When in this position pour plaster, quite thin, over the narrow bow and upper model, and at once lift the articular up by the base, and make a bed of plaster on the table into which the wide bow and lower cast are placed. When the plaster hardens the excess should be trimmed away. In mounting a cast for an upper denture alone there would be only an upper wax articulating plate, and instead of the lower on the oc- cluding surface of the upper bite an impression of the cutting edges of the lower teeth. Take an impression now of the lower teeth in wax and make a model, and when this is separated from the impression place the cutting edges of the plaster teeth in the impression on the occluding surface of the upper bite-plate, and then mount in the same manner as with entire dentures. The above method is also followed in mounting a full lower denture where there are upper teeth, and will also 382 THE "BITE" OB OCCLUSION. serve in mounting casts for partial dentures where it is necessary to use an articulator. Fig. 397 show bites for entire dentures after mounting on the anatomical articulator. After the plaster which has been used to fasten the models to the ar- ticulator has hardened (the plaster above and below the horizontal lines A, A, Fig. 437, in which the bows of the articulators are fastened), the wax-bite at the occluding surface should be separated to allow the lower model to swing free : the teeth may then be selected. At this point must be measured the distance from D to J5 on the upper cast, and from E to B on the lower, with the dividers. This dis- tance, whatever it is — say one inch and a half — should be marked on the top of the model by two holes one inch and a half apart. The divider is now adjusted to measure the distance from D to F, which is marked on the top of the upper model. The distance from ^ to 6r is now measured and marked on the lower model. The longer distance will be recognized as the length of the upper and lower teeth, or lip line, while the shorter distances will represent the high and low lip lines- The depression at D and E on the median line of the models is usually selected about the centre of the base of the models. If the bites become destroyed, these markings may be referred to, and the bite may be re-established with a certain degree of accuracy. Plain Teeth. Fig. 407 shows a set of twenty-eight plain teeth. The wax articu- lating plates, or bite-wax, should represent the exact length of the lips (lip line), B ; the highest point of elevation of the upper lip, as occurs in laughing, high lip line, F ; the point of forcible depression of the lower lip, low lip line, C ; the proper contour of the face and the median line. Fig. 437. If these points have been faithfully observed, the lower wax articu- lating plate at the median line represents precisely the position of the inferior central incisor teeth. All that is necessary is to cut down to the base-plate through the median line of the wax, and take out a section, upper and lower, on one side only, to admit of placing the cen- tral lateral and cuspid on that side, as shown in Fig. 437, After these teeth are approximately arranged the measurement as given under the heading " Articulator " is to be followed to fix their exact position when they should be waxed fast. Unless some of the occluding surface of the wax is removed, it would require the teeth to be placed longer than the wax-bite. When the amount of overlap is determined, just that much of the occluding surface of the upper wax bite-plate should be removed, as shown in Fig. 437, B to a After arranging the central, lateral, and cuspid, enough wax is re- moved to admit the first lower bicuspid, which is placed in the wax a little lower than the lower cuspid. At the distal surface of the cuspid the circle is broken, as only the six anterior teeth form the segment of PLAIN TEETH. 383 a circle. Next turn the bicuspid so that the groove between its diminu- tive lingual cusp and buccal cusp points straight toward the inner border of the ramus of the jaw. The next tooth is the upper first bicuspid, which is arranged to occlude with its buccal cusp, overlapping the lower bicuspid. Next in order is the second inferior bicuspid, which is set a little lower in the way that the first bicuspid inferior was, with its sulcate groove pointing straight toward the inner border of the ramus. It is followed by the second superior bicuspid. It will now be noticed that the occlusal surfaces from the cuspid to the distal surface of the second bicuspid have been gradually lowered. From this ]wint, the distal surface of the second inferior bicuspid, the occluding surfaces begin to turn upward. The first lower molar is arranged with its anterior cusps on a level with the second bicuspid, but its distal cusps should be raised slightly above that plane. (See A, page 123.) The second molar inferior is inclined still higher, and when the upper molars are placed in occlusion the vertical curvature is formed, and we must now determine whether it is too great or small for the over- bite. Fig. 438 shows the teeth of one side arranged in occlusion, and while the upper model and wax-plate are held in position the lower cast and Fig. 438. Showing the arrangement of plain teeth in occlusion, and the manner of waxing the buccal and labial surfaces of wax-plates. wax are brought forward until the cutting edges of the incisor teeth are opposite each other (Fig. 440). If there is an even contact between the upper and lower last molars and the superior and inferior central incisors, the curvature is correct (Fig. 440). After this point has been ascertained, the springs of the articulator are to bring the models into the position of occlusion again, when the teeth should be fastened to the base-plate by flowing the melted wax around the pins on the lingual side and over the necks on the labial and buccal sides with a hot wax-spatula, illustrated in Fig. 439. The wax should now be chilled in cold water to prevent loosening of the teeth. 384 THE ''BITE" OR OCCLUSION. Fig. 439. when the opposite side should also be arranged after the manner just described. i When both sides are arranged the lower model should be , I' Fig. 440. Showing the artificial teeth arranged for one side, and the lower jaw protruded for incising : also contact of molars ; also of incision while intervening teeth swing free. protruded, first forward, and then to the right and to the left to see that the teeth are all in proper relation to each other. The articulation of the cusps of molar teeth is admirably shown in Fig. 441, which is taken from a life engraving from Fig. 441. Black's Anatomy. It indicates the proper angle at which to place artificial teeth and the manner of deepening the cusps to effect a better masticating surface. I I If a plumb-line were dropped from the lingual border of ' the lingual cusp of the second inferior molar, it would fall L J clear of the body of the jaw, and not through the centre of ^*^ the edentulous ridge, as many artificial teeth are arranged. Wax-spatula, ^j-^gj^ ^}jg teeth are placed too near the cheek it is con- PLAIN TEETH. 385 stantly irritated, and the teeth are, during lateral movement, thrown out of line of use. The position of the molar teeth would be more nearly correct if a perpendicular line falling through the buccal cusps would also fall through the centre of the edentulous ridge. This arrangement might, upon first observation, appear to impede the move- ment of the tongue. Such is not the case, but, on the contrary, the molar teeth are in the best position to receive the greatest assistance from the tongue and cheek in keeping the food in position for mas- tication. The No. 2 Articulator and Gtum Sections. Fig. 442 represents the use of the plain line articulator, or the same as illustrated in Fig. 395. While it is not possible to move the casts Fig. 442. Showing the No. 2 S. S. W. articulator, and an upper and lower set of gum sections. about in this instrument as with the anatomical articulator to get the various bearings of the teeth, the same general rules are followed in the formation of the arch and tlie arrangement of teeth for entire dentures. For partial cases this instrument is quite as successful as any other, because the position of the artificial teeth will be governed to a great extent by the natural teeth remaining; but for full dentures some ad- ditional suggestions are necessary. After the bite is mounted, the arrangement of the teeth should be proceeded with after the manner illustrated in Figs. 438 and 439, but the adjustment of the overlap of the anterior teeth should be slight, the superior incisors barely covering the tips of the inferior incisors. There should also be a slight space between the labial surface of the inferior and the lingual surface of the superior incisors, so that these teeth shall not quite touch in the articulator. The strongest occlusion should be between the superior and inferior bicuspid and first molar teeth, while the inferior second molar should not be in positive contact ; and if there are inferior third molars, with the occluding surface pointing forward, these should not be allowed to quite touch the superior artificial teeth. The reason for this is, that after the dentures are placed in the mouth 25 386 THE ''BITE" OR OCCLUSION. there is a slight settling, and if the incisors were alloAved to strike in the articulator, a more positive contact would follow in the mouth, which would cause a tilting of the plates. Again, if the last molar strikes too forcibly, the denture would be crowded forward, and not only loosened, but the mucous membrane would be considerably irritated by the friction. Fig. 442 illustrates the use of " gum section " teeth, the first section containing a central and lateral incisor and the cuspid tooth ; the next section, the two bicuspids ; and the next, the two molars. It will be seen that the use of section teeth requires a different method of ar- rangement, two or more teeth being placed at the same time. On the proximal margin of each block or section there is an excess of porcelain gum, which is to be ground off to the required amount to permit of articulating the cutting edges. This is called the jointing process, and must be performed very care- fully in order to obtain a properly finished piece. If the joints are not properly made and protected, the dark vul- canite will be forced through in vulcanizing and produce a discolored joint. Fig. 443 illustrates in No. 1 a hori- zontal section through' the gum enamel of a porcelain block and the approximating edges A A, the surface to be joined. If care is not taken, the result after grinding may be as shown in No. 2, the labial sur- face in contact with a V-shaped space back of it, and during the contraction of the vulcanite in the hardening process the two blocks may be drawn so forcibly against each other as to fracture a piece of the porcelain enamel. No. 3 indicates the proper method of forming the joint for vulcanite work. From one-half to two-thirds of the thickness of the blocks toward the labial surface should be joined squarely against each other, while the inner third should be given a slight bevel, as seen in No. 3. Fig. 444. 1, 1, horizontal section of the por- celain gum of a block of three ; ^^, proximal edges to be joined; 2 A, V-shaped or imperfect joint: 3 A, proper method of jointing see- lions for vulcanite ; 4 A. proper method of jointing for plate or solder work. Showing an upper set of single-gum plate teeth on gold plate, illustrating the manner of jointing. After the case is inverted this V-space is to be filled with cement to prevent the vulcanite from being forced through the joint. Single gum teeth for gold plate work should be joined squarely against each other through the entire thickness of the block, as shown in No. 4, while the complete set, so ground, is shown in Fig. 444. TEMPORARY DENTURES. 387 Temporary Dentures. A distinction is made by many operators between " permanent " and " temporary dentures." Strictly speaking, any artificial denture might Fig. 445. A cast showing recent extraction of six anterior teeth. Fig. 446. Showing the arrangement of teeth necessary in a case like Fig. 44-5, where the six anterior teeth were recently extracted. be considered as temporary, and none as permanent. But as these terras have been given a special significance, regardless of their real meaning. 388 THE ''BITE" OR OCCLUSION. " Temporary denture " is a term applied to a denture inserted imme- diately upon or soon after the extraction of the natural teeth, or before the process of resorption is complete. Fig. 445 illustrates a mouth from which the bicuspids and molars of one side had been extracted some six or eight months before the anterior teeth. Resorption has been completed in this region, and the sockets from which the teeth were extracted perfectly obliterated. The anterior portion of Fig. 445 shows the margins of the sockets from which the six anterior teeth have been recently extracted, the impression being taken as soon as bleeding had ceased. In such a case no artificial gum will be required, as the ridge is already sufficiently prominent. The crowns of the artificial teeth should be placed in the position formerly occupied by the natural teeth, with the neck of the tooth extending slightly into the empty socket. The outer wall of the socket is formed by the labial alveolar plate, and the labial surface of the neck of the artificial tooth should fit snugly against this in order to have the natural gum form nicely around it. Fig. 446 shows the arrangement on a plain line articulator, with the artificial crowns projecting from the natural gum, and the appearance for a time is natural and agreeable. Back of the cuspid teeth, where resorp- tion is complete, we see the bicuspid and molar teeth arranged with an artificial gum, Avhich is brought forward to the distal surface of the cuspid tooth. This figure (446) also illustrates the arrangement of a partial lower case in connection with an upper having two molars on either side. The Arrangement of Teeth in Abnormal Protrusion of the Lower Jaw. In the preceding illustrations and text the attention of the student has been directed to normal conditions, and the normal arrangement of artificial teeth with those conditions, in order that he may familiarize himself with the various methods and principles involved, and be able to modify them in the treatment of abnormal cases. Fig. 446 may be considered a fairly normal relation of the edentulous ridges, and one with which all of the rules governing a normal articula- tion can be followed out with a certain degree of accuracy. Fig. 447 shows an extremely abnormal relation of the alveolar ridges, and one requiring a considerable modification of the usual methods in order to arrange the teeth in a manner at all satisfactory. A protrusion of the lower jaw, however, within certain limits may be met with occa- sionally, and a normal arrangement of the teeth obtained, providing that other conditions are favorable to it. But, before attempting to arrange the teeth in such cases, and while the patient is still at hand, the ope- rator must make some careful observations. First, to ascertain whether the low^er teeth can be retracted sufficiently to obtain an over-bite without interfering with the movements of the tongue. It is seldom possible to adjust the lower teeth toward the tongue far- ther than the centre of the edentulous ridge. If such an operation is attempted, the movements of the tongue will not only be impeded and TEETH IN ABNORMAL PROTRUSION OF THE LOWER JAW. 389 speech impaired, but the stability of the denture will be affected by the tongue constantly pushing against it. Second. — It must be ascertained whether the tissues of the upper lip Fig. 447. Showing extreme protrusion of the lower jaw, and with antagonizing casts on the anatomical articulator. are sufficiently lax to permit of bringing the upper teeth the necessary distance forward from the alveolar ridge to obtain an over-bite. Fig. 448. Showing the arrangement of teeth necessary in a bite when the lower teeth close outside of the upper. Third. — Will the removal of the superior incisor teeth from the alve- olar ridge cause a continual loosening of the denture by excessiv^e lever- age on these teeth ? Fourth. — Whether the attempt to obtain a perfect ])rofile will effect too radical a change in the patient's appearance. 390 THE ''BITE" OR OCCLUSION. Fig. 448 illustrates the arrangement of teeth necessary in case of" pro- trusion so extensive as in Fig. 447. The upper incisor teeth are arranged to close inside of the lower, with their labial surfaces gliding closely on the lingual surfaces of the inferior incisors, the incisive function being performed in a reverse manner to that of a normal arrangement. When the superior cuspid tooth is reached the first attempt is made to merge into a normal arrangement. This tooth is placed with its anterior cutting edge covered by the in- ferior cuspid, while the distal cutting edge is turned labially and ground so as to strike directly on top of the mesial cutting edge of tlie first in- ferior bicuspid. The first bicuspid, superior, is ground and brought out slightly more than the cuspid, and from this point distally the teeth assume their normal position. In order to obtain a graceful arrange- ment in such a case, as seen in Fig. 448, it will be necessary to do con- siderable grinding and lapping of the upper teeth, which is not at all unsightly in this character of case. The facial expression following such an arrangement of the teeth will be improved. In marked protrusion of the lower jaw, where the natural teeth close outside of the upper, and M'hen this condition has existed up to middle life with natural teeth, a correction of the facial expression with artificial teeth should not be attempted. The Arrangement of Teeth in Abnormal Protrusion of the Upper Jaw. A case directly the opposite to the one illustrated in Fig. 447 is shown in Fig. 449. In this case the protrusion of the upper ridge was about half an inch beyond the lower, and, while there was an over-bite Fig. 449. Showing pldbter ciituuUtK in 111 aiast with ._ \tu me Drotrnsioii (it tht upper jaw. of the upper teeth, the position of the ridges would not permit of bring- ing the lower into contact with the upper for the natural performance of the incisive function. This function was established between the cutting edges of the lower incisor teeth and the base-plate of the upper denture. The six anterior teeth were permitted to barely strike the base of the ujiper denture when the opposing bicuspids and molars were in occlusion. Another feature of this case was the arrangement of third artificial molars, which with the one natural molar wive a masticating; surface of DIRECT ANTAGONISM OF OPPOSING TEETH. 391 four molars on either side above. The cut shows the exact size of the casts and their relation to each other, indicating the necessities of the case better than if the artificial teeth were shown. Direct Antagonism of Opposing Teeth. A third form of abnormality is shown in Fig. 450. While this case is termed abnormal in comparison to an ideal arrangement, it is not ab- normal, strictly speaking. The abrasion of the cutting edges of the natural teeth from many years of hard use and other causes, together Fig. 450. Showing the arrangement of upper teeth directly upon the abraded ends of the lower natural teeth. with a destruction of the natural over-bite caused l)y the obtusing of the angle of the lower jaw, which occurs with advancing age, is a natural consequence, and direct antagonism of the opposing teeth is perfectly normal under such conditions. Persons of an advanced age, who have lost all of the upper teeth, but who have retained a number of the Tower teeth, as shown in the illustration, are frequently seen. These teeth are so abraded that no signs of cusps remain, and perfectly flat surfaces are presented upon which to articulate the artificial teeth. If an attempt is made tO articulate teeth with cusps to these flat surfaces, only the points of the cusps will be in antagonism, which would deprive the patient of a thor- oughly useful appliance. An over-bite would also be unnatural, for whenever we find the bicuspids and molars abraded there is usually a corresponding abrasion of the incisor teeth, and if the patient had re- tained the upper teeth, they would have been affected in the same manner, and antagonism would have been directly upon the cutting edges. In articulating an upj^er denture to lower natural teeth with the above conditions existing, one feature must be prominently borne in mind by the operator — viz. to offer no obstacle to the perfect freedom of the lower jaw. To this end the artificial teeth should be articulated directly upon the ends of the lower teeth : the cusps of the upper teeth should also be ground off and the flat occlusal surface roughened. Tliis arrangement will permit a free lateral movement of the lower jaw, and mastication will be performed after the manner of the millstones in 392 THE ''BITE'' OR OCCLUSION. crushing grain. While this arrangement may not afford the best means of performing the incisive and masticatory functions, it is tlie best that can be done under the circumstances. When arranging teeth to strike directly upon tlieir cutting edges, the lines of force must be carefully studied, and any point likely to produce leverage upon the denture nmst be shaped so as to offer its portion of support. The upper incisor teeth should not be allowed to strike the labial cutting edges of an abraded lower, but should be placed squarely in the centre of that tooth. The cutting edge of the lower teeth can with advantage be grooved slightly, mesio-distally, and the upper teeth articulated to this groove, as shown in Fig. 435, No. 18. Fig. 450 will also illustrate Fig. 435 as regards the position of the incisors and molars. In the arrangement of the bicuspid and molar teeth in such cases care must be taken not to allow the antagonizing buccal edges of the opposing teeth to strike on the same line. The upper teeth should be projected either buccally or lingually, so that one or the other of the teeth will drive the cheek and tongue away from the line of occlusion ; otherwise there would be great danger of injury to these tissues every time the mouth is closed. Partial Dentures. In the selection and adjustment of the teeth in partial cases the ope- rator is governed largely by the degree of resoi'ption of the alveolar pro- cesses at the edentulous spaces. In Figs. 451 and 453 we observe the loss of the left central and lateral incisor, and, while either case requires an artificial central and Fig. 451. Fig. 452. A cast indicating the need of a gum sec- tion. A cast showing the ajustment of a gum section containing a left central and lateral incisor that will harmonize with the natural teeth of the opposite side, the two cases require an entirely different method of treatment. Fig. 451 exhibits considerable resorption of the ridge between the points A A, and should plain teeth be used here it would require a con- siderable thickness of vulcanite or celluloid gum to properly restore the contour of the ridge. A vulcanite or celluloid gum is contraindicated in such a case — first, on account of its unnatural appearance ; second, because it is not sufficiently strong and is liable to fracture in a short time. PARTIAL DENTURES, 393 Fig. 453. A cast indicating the need of plain teeth. The proper method of treating these cases is with a sectional block of gum teeth, as illustrated in Fig. 452. A block with the porcelain gum as near the natural color as possible is se- lected, with teeth of the proper size, color, and form. Before attempting to adjust the block the plaster model should be scraped slightly, as shown at the points A A, in order to obtain a close joint between the artificial gum and the natural. The block should now be carefully placed in the space, so as not to mar the contiguous plaster teeth. The points of contact should be ground oif slightly from the block until the surface of the artificial gum is con- tinuous with that of the natural, and the artificial teeth on a line with those of the plaster cast. It should now be fastened to the model by melted wax, and the lingual side of the plate prepared for investing. Fig. 453 shows a model similar to 452, where but little resorption has occurred. Plain teeth are here indicated, and should be so adjusted that when the piece is finished their necks will be slightly imbedded in the gum- tissue of the ridge. To accomplish this the ridge on the model should be scraped at the points where the necks of the teeth impinge, as shown in Fig. 453. The teeth should be ground so tliat they may be placed in alignment with the natural teeth represented on the plaster cast. (See Fig. 454.) They should then be fastened with wax, and the lingual side of the base-plate prepared for investing. Aside from the above conditions, which suggest the use of gum or plain teeth, we must consider the bite in order to determine whether we can use teeth with headed pins or those with headless pins (plate teeth). In the two illustrations there is sufficient space between the cutting edges of the lower teeth and the eden- tulous ridge, consequently we can Fig. 455. easily use teeth with headed pins if the case is to be of vulcanite or celluloid. If it is to be a gold plate or silver, then plate teeth should be Fig. 454. used. If, however, the lower teeth almost touch the edentulous ridge, i:he use of teeth with headed pins would be contraindicated, because they would require too much thickness to the plate and would prevent the natural teeth from occluding. When the bite is close and a vulcanite plate is contemplated, plate teeth should be selected and lined or backed with gold, as shown in Fig. 454. The thin gold tag attached to the back- ing may extend posteriorly far enough to receive a firm attachment in the 394 THE "BITE" OR OCCLUSION. vulcanite plate (see chapter on Vulcanite), while the thin gold will per- mit the natural teeth to occlude. The anterior view would not be unlike Fig. 452 or Fig. 455. Fig. 456 illustrates an extensive partial denture and the use of teeth Fig. 456. Showing the use of teeth with extended necks, commonly known as " celluloid teeth." The two centrals and right lateral incisors are natural, and have suffered recession of the gums; the artificial teeth are selected to correspond. with extended necks, commonly known as teeth for celluloid work. It will be seen by the figure that the two centrals and right lateral incisor are natural teeth which have suffered recession of the gums, causing part of the root to be exposed. While the lip of the patient would roll high enough in laughing to expose the neck of the teeth, it did not rise suf- ficiently high to expose the unnatural gum of the denture. Failures with Partial Dentures. — Failures with partial dentures are largely due to carelessness in adjusting the artificial teeth, to avoid which the student is directed to the following observations : Whenever a block or plain tooth is to be placed in contact with the mucous membrane of the ridge, it is necessary to scrape the points of contact on the plaster cast slightly, in order to obtain a clean joint between the natural and artificial gum. In vulcanite work the scraping should be a little more extensive than in soldered, for during vulcaniza- tion the rubber forces the block or tooth away from the ridge a little, which would cause a dark line betw^een the tooth and natural gum, or there would be a space. Scraping is done to compensate for this slight moving of the block or tooth, also to obtain a little pressure upon the natural gum to ensure a clean joint. The degree to which this is to be performed depends upon the compressibility of the gum-tissue in the mouth, which should be examined carefully before an alteration of the model is made. Wherever there are natural teeth which occlude in the mouth requiring a partial denture, these should never be ^^*^^- '^^' ■ held apart by the appliance, except for } i' \flF\ extreme reasons. It not infrequently happens that an appliance consisting of the bicuspids and first molar for both THEs s ^ D M r„. sides is necessary. The bite is very close, not giving enough room for cusps upon the artificial teeth without holding the natural teeth apart. In such a case facings or veneers are used, which have the appearance of the bicuspid and molar teeth, but LINGUAL SURFACES OF DENTAL PLATES. 395 are perfectly flat on the reverse side. (See Fig. 457.) These teeth are made for either vulcanite or solder work, but are most exclusively used for bridge-work. By using veneers or facings the outward appearance of the denture can be made satisfactory, while cusps, if necessary, can be built up with the vulcanite or gold to any required height. As a rule, the artificial tooth should be of the same general form and shape as the natural tooth for which it is a substitute, but this rule can- not always be followed. It is generally better to place a cuspid tooth back of a natural cuspid, even though there be room for the lingual cusp of a bicuspid. The sudden thickening of the denture at this point when beginning with a bicuspid tooth is a serious impediment to the tongue, which would not be so noticeable if the appliance were started with a cuspid — though narrower than the natural cuspid or a veneer — then fol- lowing this with a well-formed second bicuspid. A single artificial incisor or a central and lateral, as shown in Figs. 452 and 455, should be placed with their cutting edges a little longer than the adjoining tooth on the plaster cast, to allow for the settling of the denture. If they are placed the exact length at first, after a few days' wearing they will appear shorter than the natural teeth. Artificial teeth should be selected to correspond exactly with adjoin- ing natural teeth in color, shape, and size. The Proper Conformation of the Lingual Surfaces of Dental Plates. Trouble is often experienced by patients in securing a clear and sharp s sound after they have commenced the use of artificial dentures. A peculiar whistling sound is produced. It is now proposed to give a short description of the mechanism by which these sounds are produced, and to draw attention to the import- ance of giving due consideration to the shape of the lingual side of the plate if it is desired to secure clearness and ease of articulation of the sound above referred to. Inspection of models of the upper jaw in which the natural teeth are in place will show that while the lingual surface of the bicuspids and molars practically forms a continuation of the lateral curve of the palatal arch, the alveolus behind the incisors is thickened. With the rugse a nearly flat triangular space is often produced, bounded by a line con- necting the distal surfaces of the laterals and the edges of the alveolar sockets. Viewed in longitudinal section, a reversed curve is presented, extending forward from the hard palate and merging into the hollow outline of the lingual surfaces of the incisors. Sections of models from different mouths are shown in Figs. 458 to 463. The curves will be seen to present nearly the same general shape, whether the arch be deep, like Fig. 459, or shallow, like Fig. 461. In Figs. 462 and 463 an attempt has been made to show the relative positions of the tongue and teeth in making the -s* and sh sounds. In producing the sh sound (Fig. 463), the upper and lower teeth are held slightly apart ; the tip of the tongue rests against the gum behind the lower incisors, its edges impinging upon the lingual surfaces of the bicuspids and molars at the junction with the alveolus. The result is a narrow passage over the centre of the tongue, the narrowest portion 396 THE ''BITE" OR OCCLUSION. being ju!?t back of its tip, the passage being thus gradually enlarged both behind and before its narrowest portion. The breath, being forced through this narrow passage, follows its curve, and is impelled against the tips of the lower incisors, the result being the .s7/ sound. Fig. 458. Fig. 459. Fig. 460. Fig. 461. Fig. 462. Fig. 463. In giving the .s sound (Fig. 462) all the parts remain in the positions above described, except the tip of the tongue, which is curved upward to the alveolar border on tiie lingual side of the upper incisors, making the passage smallest at its outlet and projecting the current of air against the upper incisors. It will be found bv experiment that if the tongue is drawn Inickward a little from the position described, the hissing sound Fig. 464. Fig. 465. will be changed to a whistle. It will be noticed that the shape of the palatine arch is such that the tongue can readily conform to it, and that a passage between the tongue, palate, and alveolar border can be readily formed by which a clear articulation of the sounds in question can be produced. REMOVAL OF CASES FROM THE ARTICULATOR. 397 As a contrast to the figures already shown, attention is directed to Fig. 464, which is a section of a fairly well-made vulcanite plate. The teeth are well arranged, the joints close and well fitted, the finish good. It will be observed that the palatal curve, if continued, would meet and coincide with the curve of the lingual surfaces of the incisors, there being a break at the point of junction of the teeth and rubber ; and this is so abrupt that it would be impossible for the tongue to follow its out- line, as it does the curve of the natural arch in Figs. 463 and 464. The reversed curve, shown in Figs. 458 to 461, is plainly out of the question. The sketch illustrates what is by no means an extreme case. With thinner teeth and a longer bite the defect noted would be still greater. If the plate which is shown in section in Fig. 464 were tilled in to present the outline shown in a dotted line in Fig. 465, the enunciation of the wearer would be improved, and another very substantial benefit be secured — viz. an amount of strength which will obviate any danger of the plate cracking through the centre. If the imitation of nature be carried far enough to reproduce the rugae upon the plate, it will be found to be a decided benefit both to articulation and in the management of food in mastication. When the lingual side of the plate is smooth the tongue has but little power to hold a morsel of food upon it, while with the rugae the food is easily held and managed. They are easily formed by burnishing a piece of heavy tin- foil over a model showing them prominently, filling the depressions in the tin-foil with wax or paraffin, and then fitting and attaching it to the trial-plate when waxed up and ready for flashing, leaving its edges turned up so that it will be held securely in the plaster when the plate is flasked. The surface of the vulcanite will come out clean and smooth, and will require but little polishing. It will be found that a patient who has once become accustomed to the use of a plate made as above suggested will be extremely loath to return to the use of one as ordinarily made. Removal of Cases prom the Articulator. After the teeth are arranged and the waxing is finished, the cast with the wax-plate and tooth in position should „ . be removed from the articulator. „..^— — '--^ — '.,-^ This is done by trimming off the plaster which held the cast to the ar- ticulator, exposing the brass bows or frame, and then, by passing the point of a knife or spatula between the base of the cast and articulator, the two pieces will readily separate. si^^^i^^ ^ pi^,,^^ cast,^itrtrupo- TOO much force must not be exerted rarybase-plate and teeth in position. . . . , •!! 1 1 removed from the articulator and in this operation, or there will be clanger ready for investing; also the man- of fracturing the cast. ^ The excess of folnt^ of^lum^fertl^^^ plaster must now be trimmed from the vesting. base of the cast, when the case is ready for investing. CHAPTER XL SELECTING AND FITTING THE TEETH ; ATTACHMENT TO THE PLATE; FINISHING. By H. H. Buechard, M. D., D. D. S. Selecting the Teeth. If there be any of the natural teeth remaining, these are to furnish the guide for the choice of the artificial teeth. It is noted, first the color of the natural organs, and a sample shade selected which matches them in this particular. Observe the shapes of the natural teeth, whether they be long or short, broad or narrow, thick or slender-bodied — whether the necks of the teeth be narrow or broad as compared with the width of their cutting edges. A mould of teeth is to be selected in which all the features of the natural teeth are reproduced as nearly as possible. It is noted also whether the lip be long or short, and the extent to which the articulating wax is exposed by the movements of the lip. If the jaws be edentulous, the temperament of the patient is deter- mined by the shape of the arch and vault, by the features, the color of the hair, of the eyes, complexion, etc., as described in the section on temperaments. Teeth appropriate to the temperament are to be selected. The question of gum or plain teeth is determined first by the amount of absorption ; for as the artificial teeth are to replace the lost teeth, so artificial gum is to compensate for deficiencies made by resorption of gum contour. If there be no loss of contour, an artificial gum is mani- festly unnecessary. The material of which the gum restoration is to be made is deter- mined by the exposure or non-exposure of the artificial gum by the movement of the lip. Porcelain gum approximates in appearance the natural gum more closely than artificial gum of any other substance, so that when there is marked exposure of this portion of a denture the porcelain is to be preferred. There are unsatisfactory limitations as to the amomit of arrangement possible with teeth having porcelain gums, so that cases which require an irregular arrangement of the teeth are usually supplied with plain teeth, to which a rim or an artificial gum of one of the vegetable bases is applied. These several peculiarities and indications are noted when the plate is tried in the mouth and the articulation taken. The antagonizing models are made, and usually mounted on an artic- ulator. The line on the wax representing the middle line of the face is extended upward and downward by a scratch on the models. At a 398 SELECTING THE TEETH. 399 point about half an inch above the wax this scratch is intersected by another line ; one point of a pair of dividers is placed at the point of intersection, its other point at the line on the wax representing the length of the lip, which is also the length of the teeth, and the distance between the divider points is then marked on the side of the model for future reference. If a full denture, upper and lower, the middle line and the length of the lower teeth are similarly recorded. The articulating wax having been built to a form restoring the lost facial contour, it is to furnish the guide in setting the artificial teeth in their relation to fulness. If a full denture, it has been determined by the rules of temperament what should be the size, shape, and shade of the artificial teeth, and a mould is selected from the stock of the manufacturer which best corre- sponds with the indications. The shapes of the single gum teeth appropriate to the several tem- peraments are shown in Figs. 467 to 470. This style of artificial tooth does not oifer the same facilities for artistic arrangement that may be made with plain teeth. Fig. 467. Fig. 468. Lymphatic. Fig. 469. Nervous temperament. Bilious. If a single denture or a partial case, the remaining natural teeth serve as guides in selecting the substitutes for the lost organs. As a rule, the best manufacturers make artificial teeth which bear the relative sizes that are found in the natural teeth. Being copied, in the main, after the natural organs, a mould of teeth which has centrals of the correct size and shape will presumably have lateral incisors accom- panying which are in anatomical correspondence, so that in selecting artificial teeth primary attention is directed to the central incisors. It is noted, first, whether the inferior incisors are imusually flat or rounded, whether thick or thin — the superior incisors must be in correspondence ; next the width must be correct : as a rule, a superior central incisor is at its cutting edge as wide as an inferior central and half a lateral incisor. The lengths of the crowns of inferior and superior incisors are about equal, although inferior incisors, through their lesser relative width and by a frequent recession of the gum from the enamel line, appear to be 400 SELECTING AND FITTING THE TEETH, ETC. longer. When set in the proper arch the axis of the superior cuspid should be at the line between the inferior cuspid and first bicuspid. A shade darker than the natural teeth should be selected in preference to one lighter. The shadow of the lip causes artificial teeth to appear of a lighter color when in the mouth than when held in direct light. Cuspids are usually more yellow than the incisors or bicuspids : it is advisable to represent this peculiarity in the artificial teeth. In all cases select well-fired teeth, those in which there is a blending of the point and neck colors. The lighter gum colors are, as a rule, to be preferred ; however, the general colors of the natural gums and of the lips are to form the guide in this particular. It would be obviously an error to place in the mouth of an anaemic patient bright-red or purple gums, and equally wrong to use the light gum shades for a patient who is plethoric and has full, dark-red lips. The gums of blondes are lighter in color than those of brunettes. After determining and selecting the form, size, and color of the crowns and the color of the gum, the configuration of the latter may form an element in .selection, and it should always when block teeth are employed, and may when single gum teeth are indicated. The gum should be thick enough, and yet no thicker than required, to restore the lost contour, and moulds are selected which require the minimum of grinding to adapt them to the indicated degree of contour. Molars and bicuspids are to be selected which shall bring the distal edge of the second molar to about Fig. 471. the rise of the tuberosities (Fig. 471, A): rarely should that portion of the tooth be beyond the middle of this protuberance. Occasionally it is advisable to omit a tooth from either side to bring teeth of the correct width to the point named. In selecting teeth for partial cases it is noted first whether there is such a loss of alveolar contour at the site of the absent tooth as to de- mand restoration by artificial gum. Plain teeth are to be preferred wherever admissible, but lost contour should be restored, so that any marked loss in this particular demands a gum tooth. Teeth should as nearly as possible match in shade the teeth on either side. If these be pulpless and markedly discolored, their shades differing greatly from that of the vital teeth, they should of course be bleached ; but in lieu of bleaching the color of the artificial tooth is to be between that of the vital and that of the discolored teeth. Marked contrasts of color are to be avoided. It is most important that the shape of the artificial teeth corresponds ARRANGEMENT AND FITTING OF TEETH. 401 with that of the natural organs. It is manifestly improper to place be- side a rounded and narrow-necked natural tooth an artificial tooth having a flat grooved face and broad neck. The cervical line, where the artificial tooth touches the natural gum, should correspond with the cervical lines of the natural teeth. Where a plain tooth which is of the proper length anatomically is found to be too short to extend from the correct cutting-edge length to the natural gum, and when long enough to span the space, sets at a more obtuse angle than the adjoining teeth, an artificial gum is the indication : it should be of a size which shall bring the tooth to the proper angle, and to have the crown of the correct length ; that is, in anatomical correspond- ence with its fellows. Teeth having their platinum pins in a vertical line (straight pins) are to be preferred to those having the pins in a horizontal line (cross pins), on account of their greater strength. The break in the tooth represented by the pin is the weak spot, and, as the stress upon an artificial tooth Fig. 472. Fig. 473. tends to fracture it horizontally, it is evident that if both points of lessened resistance be in a horizon- tal line the danger of fracture is increased. In selecting teeth note that the pjns lengthwise. Pins crosswise. distance between the plate and the lower pin of the tooth is great enough to permit adaptation of the tooth without cutting away the pin. If this distance is very short, the use of cross-pin teeth will be necessary. Arrangement and Fitting of Teeth. If the case be one for the replacement of a full upper denture by single gum teeth, a layer of wax is placed around the alveolar ridge and the tips of the antagonizing teeth are imbedded in it. At its anterior aspect the wax is cut away until it merely serves to retain the artificial teeth when their pins are pressed into it. The anterior teeth are placed around the incisive arch, so that the amount and direction of the necessary grinding may be noted. The directions of the axes of the teeth, the lengths and prominence of the cutting edges of the teeth, peculiarities of arrangement, and the spaces to be between the teeth are now determined. A corundum wheel of coarse grit, one-fourth inch thick by one and a fourth inches diameter, having a round edge, is used for the rough grinding. The central incisors are to be first adapted. Note the points at which the under surface of the gum touches the plate when the cutting edges of the teeth are placed at their proper length and their proper distance from the tips of their antagonists. Grind the teeth away at these points, and continue the testing and grinding until there is a fair adaptation of these two teeth. The joint between them is roughly made, outlining the future joint, and leaving sufficient surplus to provide for the finishing gi'inding. At this stage the central incisors receive their general expression. Repeat 26 402 SELECTING AND FITTING THE TEETH, ETC. the procedure with the lateral incisors, giving them the relative position to the central incisors suggested by the positions of the antagonizing teeth, or modifying their position or direction according to any unusual forma- tion of the alveolar ridge at these situations. Rough grind now the joints between central and lateral incisors. The cuspids are next partially fitted after the same manner. The expression produced by these six teeth will determine in a great measure that of the entire denture. There is not a great latitude of choice for the arrangement of single or any gum teeth which are jointed to one another, so that the prosthetist will find exercise for all his taste and ingenuity in using what there is to the best effect. If the teeth are of the proper width, the points of the cuspids will now be resting upon the middle of the labial surfaces of the inferior first bicuspids. The amount of joint-grinding necessary to bring the artificial teeth to their correct anatomical positions is now noted. This amount is to be divided among the five joints. If advisable or necessary to leave spaces, it is preferable to make that between the centrals small but dis- tinct. For the final grinding a smaller wheel of fine grit is substituted. To secure the accurate adaptation of the teeth to the plate some device is employed to show the points of contact between them and to indicate when the contact is perfect. Some prosthetists employ for this purpose small squares of thin carbon-paper pressed against the plate ; the tooth, rubbed against this, is marked at the points of contact. A black or blue crayon, used to give a colored surface to the plate, answers well : the writer commonly marks the plate with a blue pencil. The points indi- cated are ground away until a uniform distribution of the color shows the adaptation of the tooth to the plate to be perfect. The joint between the centrals is now to be finished. Some operators grind the joints upon the side, and not the edge, of the jointing wheel. A wheel of fine grit about two and a half inches Fig. 474. Fig. 475. in diameter and perfectly true is revolved rap- idly, and the joint surface held lightly and steadily against its side, thus forming a plane surface. The tooth is then set in position on the plate, and the amount of necessary grinding noted in its fellow, which is, in its turn, ground Faulty joint. Perfect joint, in such a manner that the joint surfaces are in contact throughout (Fig. 474). Great care must be exercised that there be no V-shaped space at the back of the joint (Fig. 474) : with close contact of the pink borders anteriorly, or almost inevitably when the teeth expand in heating, the gum will flake. The writer believes that better joints are made by using the edge of the jointing wheel. Note the points at which grinding is necessary, and, holding the tooth in the thumbs and index fingers of both hands, pass the joint rapidly across the surface of the wheel backward and forward, using a wheel of fine grit having a narrow, square edge. Adjust and joint the other teeth after the same method ; and now the points of the cuspids should rest between the inferior cuspids and first bicuspids. The centrals, if there be any variations in their axes from the verti- cal line, should point toward, not from, the median line : the laterals, as ARRANGEMENT AND FITTING OF TEETH. 403 a rule, are to be a trifle shorter than the centrals ; the cuspids about the same length as the latter. The distal edge of the cuspid is turned in, so that an arc of a circle would be made by the cutting edges of the six front teeth. In adapting the posterior teeth, although it is impracticable to carry out Dr. Bonwill's injunctions as to correct occlusion with this type of work, the endeavor should be made to attain two of the objects — to arrange the teeth so that, no matter what the positions of the jaws may be, there shall always be three points of contact between the upper and lower dentures ; and to lessen the amount of over-bite progressively to the second molar : these effects are, however, mutually interdependent. The common fault in arranging the posterior teeth is in making them a portion of a circular arch : the figure should be, including the anterior segment, a parabola. Again, the arch is commonly made too wide across the second molars, thus removing the perpendicular of the teeth too far beyond the centre of resistance, the top of the alveolar ridge, and pro- ducing a lessened stability of the piece during mastication. The bicuspids and molars are ground in pairs, exercising the same care in securing close adaptation of the bases of the teeth to the plate and in making good joints as with the anterior teeth. The joint between the cuspid and first bicuspid requires especial care. The latter tooth should be ground well in, so that it is half hidden by the cuspid. Un- due prominence of the first bicuspid is a common fault in the arrange- ment of artificial teeth. The bases of all the teeth should rest solidly upon the plate (Fig. 476, A), thus bringing the strain upon the bodies of the teeth, and not upon the pins (Fig. 476, jB), as occurs when the teeth are improperly adjusted. Ftg. 476. Cases which present a short lip and a full gum contour indicate the use of plain teeth. The thickness of artificial gum necessary to prevent fracture of the latter would cause undue prominence of the lip. If the natural gum itself is exposed through the movements of the lip and the latter is very full, plain teeth are to be so fitted to the natu- ral gum as to appear to be growing from it (Fig. 476, C). When plain teeth are to be employed, the extent to which the labial edge of the plate is exposed through the movements of the lips is noted, 404 SELECTING AND FITTING THE TEETH, ETC. and it is cut away until it is scarcely visible at the angles of the mouth. Behind this the alveolar portion of the plate is permitted to remain. Usually, the anterior edge of the buccal wall of the plate will then be about betw^een the first and second bicuspids, or a little in front of this point. The necessity for this form of plate has been determined when the impression is taken, so that the minimum of cutting away is re- quired. The artificial teeth are set in wax and their proper angle to the vertical determined, which is about that made by the lower teeth with the vertical of their alveolar wall. The lingual tips of the upper teeth should be about one- thirty-second of an inch from contact with the lower teeth. The edge of the plate is filed away, so as to support two-thirds the bases of the artificial teeth, the outer third of the latter to be imbed- ded in the natural gum : the plate is then bevelled to a feather edge. The central incisors are first ground to the natural gum, next the laterals, and, following, the cuspids, giving to the neck of each tooth the curved outline possessed by natural teeth. When these teeth have been adjusted, a fine point is passed around the neck of each, marking their several positions on the models. Within this line a layer of plaster of uniform thickness is scraped away — about one-thirty- second of an inch if the texture of the natural gum be firm, and more if it be soft — and the necks of the teeth placed in these depressions : the small sections of plate visible between the teeth are removed in the finishing operations. The first bicuspid, M^hether a plain or gum tooth, is ground so that its anterior edge at the neck also presses into the natural gum. All of the posterior teeth must rest solidly and firmly upon the plate. The choice of gum or plain teeth to replace the bicuspids and molars is determined by the extent of contour lost : if the loss be sliglit, the restoration is usually made with pink vulcanite, as this material is much stronger than porcelain for such purpose. Grinding Partial Cases. The proper teeth are selected for the replacement of the missing organs, their anatomical forms and sizes corresponding with the natural teeth adjoining. From several samples procured from the manufacturer the teeth best suited in color are taken. This is determined by placing them in juxtaposition with the natural teeth. As stated above, teeth appear in many cases to change shade when placed within the shadow of the lips, and so several are selected, the best of which is determined by the cru- cial test of placing each in the mouth. It is preferable, when and where possible, to use plain teeth for par- tial cases, for when artificial gum is adapted as it should be, its thinness is a decided element of weakness. It is permissible in most cases to make, when necessary, plain teeth a little longer than anatomically cor- rect ; but if the loss of gum contour at the site of an absent tooth be pronounced, a gum tooth is indicated. The teeth are placed on the model, and the amount and direction of the grinding to be done noted. The artificial tooth is in all respects to restore the break in the arch. It is to be ground in until its cutting GRINDING PARTIAL CASES. 405 edge, the antagonizing teeth permitting, is in the common arch line. The neck of the tooth is to have the shape of the adjoining natural teeth and to be at the same height. The rounded extension of the plate at this point is cut away and bevelled, supporting the base of the artificial tooth and yet hidden by it. If a gum tooth be used, the plate tongue should be larger when possible, affording support to part of the porcelain gum. To adjust gum teeth the plaster should be colored by means of a crayon or carbon-paper laid under the artificial gum to indicate the points requiring grinding. At the completion of the fitting the plaster should be scraped beneath the artificial gum, so that the latter will press firmly against the natural gum. The artificial gum, to be properly adapted, should exactly restore the contour of the general gum. It is preferable to have too little rather than too great a fulness. As a rule, it is advisable to have the artificial teeth a trifle longer on the model than the adjoining teeth, or longer than its position should be in the mouth. The yielding of the soft tissues to the pressure of a plate when the latter is in position in the mouth carries the artificial teeth higher than tliey are on the model, so that, particularly in soft mouths, teeth which are placed in correct anatomical position on a model are too short when in the mouth. This yielding of the tissues occasionally so alters the relation as to throw out of position the artificial teeth which have been accurately fitted to the model. It is usual in such cases to fasten the teeth to the plate by means of adhesive wax, and accurately adjust them while the piece is in the mouth: the wax softens sufficiently to permit altering the rela- tions of the teeth, which when properly adjusted are chilled, carefully removed from the mouth, and immediately placed in the investment of sand and plaster. In some instances it may be impossible to maintain the relative positions of teeth and plate while withdrawing the piece from the mouth. This is not infrequently the case when the natural teeth are long and irregularly disposed, and single artificial teeth must be set in odd positions with great exactness. It is advisable to have the patient draw the plate well into position, and then take a plaster impression in- cluding several teeth on either side of the space for the artificial teeth, in Fig. 477. Fig. 478. which the plate is withdrawn from the mouth. This impression is var- nished and a cast made of investing material. When this has set hard it is separated from the impression, and the artificial teeth set in their correct arrangement. Stays are fitted as described below, and additional invest- 406 SELECTING AND FITTING THE TEETH, ETC. ing material placed over and around the artificial teeth, holding them in position, and the model serves as the soldering investment. Cases in which the investment is made in two sections, as described, require slow and gradual heating to prevent separation of the sections during the soldering operation. In well-assorted stocks of the manufacturer, blocks of two or more teeth may be found which are well adapted for special cases (Figs. 477, 478). When spaces for which these blocks are designed may be so fitted by them as to restore perfectly the lost contour, they may be employed. They possess the advantage of dispensing with gum joints, but have the disadvantage of greater liability to fracture. They are to be ground to perfect adaptation with the plate, joining the natural gum by a thin edge. The heads of the pins are cut oif, and a stay of plate No. 26 fitted to their backs beneath the shoulders : they are then invested. Great care is necessary in heating and soldering such blocks to avoid fracturing them. Pull Dentures. To properly adapt, arrange to the best advantage, and to correctly finish a full denture of gum-plate teeth is one of the most difficult ope- rations in prosthetic dentistry. The articulating wax in its upper and lower sections should represent accurately the length of the upper and lower incisors — the fulness and contour of both dentures. The articulation is mounted and teeth selected which will harmonize in size, shape, and color both of teeth and gums with the age, complexion, and physiognomy of the patient. In adapting and fitting the teeth to the plates it is usual to regard the lower wax as the outline of the lower denture, this wax remaining on the plate, and the upper teeth are adapted to the plate, as described above, the labial and buccal tips of the teeth following the external edge line of the summit of the wax. After the upper teeth have been fitted, arranged, and jointed in harmony with the physiognomy, they are cemented to the plate by means of adhesive wax. The lower teeth are now fitted to the plate, articulating with the upper teeth. It will be noted in fitting the teeth of lower dentures that, as a rule, the articulating relations existing with the natural teeth are reversed. If the upper teeth have been adapted so as to have a firm plate support beneath, the lower bicuspids and molars when in position are found to occlude not within, but outside, the upper. The reason of this is found in the different manner of resorption of the alveolar processes of superior and inferior maxillse. The alveolar process of the superior maxilla diverges from the body of the bone so that during resorption it contracts in the arch areas (Fig. 479, A). The process of the inferior maxilla converges so that the greater the shrinkage the wider the arch becomes (Fig. 479, B). If teeth are arranged, therefore, in correct anatomical relation in mouths where there has been extensive loss of process, the upper teeth are inevitably placed beyond the centre of resistance, the apex of the ridge, or by narrowing the width of the arch of the lower teeth gives the lingual FULL DENTURES. 407 wall such an inward inclination that the movements of the tongue are restrained and tend to displace the denture. Greater stability is given a denture if the bases of both lower and upper teeth rest upon the summits of the respective alveolar ridges. Fig. 479. While in many or most cases such an arrangement produces undesirable relations as to the articulation of the dentures, divergence from it de- creases the stability of the pieces, so that it is preferable to compromise, giving the tongue as great a latitude of movement as possible without unduly lessening the stability of the denture. When the arrangement of the teeth is completed, they are to be cemented to the plate for trial in the mouth. This is best accomplished by providing a wall which shall hold the teeth in their respective posi- tions while being cemented to the plate. The surface of the model above the plate line has a series of conical depressions made, usually, three on a side, as shown in the chapter on Block Carving (Fig. 270) ; these and the walls of the model are varnished and oiled. A plaster batter is applied over the teeth and walls of the model, covering them by a layer about half an inch thick. The plaster wall so made is grooved at the median line, so that it will divide readily at that point. When the plaster has set it is removed in two sections and the teeth 408 SELECTING AND FITTING THE TEETH, ETC. withdrawn from their beds ; they and the plate are boiled in the acid solution, then dried. The pins of each tooth are straightened and made parallel : this is best done by squeezing them with a pair of flat- nosed pliers, which will also remove the film of tooth enamel which occasionally overlies the pins. The teeth are returned to their beds, the walls containing them adjusted to the model, and adhesive wax is melted and applied, so that each tooth shall be firmly attached to the plate. The denture is now ready for trial in the mouth. Trial of Denture. The plate is placed in position in the mouth, and it is noted, first, whether the joint between the central incisors is in an imaginary line bisecting the face. When the jaws and lips are closed, the edges of the central incisors should exactly mark the length of the lip, except in patients having an unusually short lip, when the teeth may be longer. The occlusion is noted : the teeth of both sides must strike in biting, The patient should feel no greater pressure upon one side than upon the other. The normal lip outline should be restored ; any bulging of the lip shows the gums to be too full : it is rare with gum teeth that the gums are too thin. Teeth unduly prominent or insufficiently prominent should be placed in proper position, and any improvement possible made by altering the positions of the teeth. The teeth of partial cases are to be pressed into correct positions, so that their necks appear to be growing from the gum. If gum teeth be used, their gums are pressed so firmly against the natural gums as to leave an almost indistinguishable line between the natural and the arti- ficial gum. Rimming the Plate. After the teeth of a full upper denture have been tried in the mouth and found to be correct, a protective rim is to be made extending over the upper edges of the gums for about one-eighth of an inch, and attached to the plate wall above the gums. It is designed to prevent the entrance of foreign substances beneath the artificial gums, and to serve as a pre- ventive against fracture of the tops of the gums. Usually these gum sections are fractured by a fragment of some foreign substance getting beneath the gum and acting as a wedge between gum and plate. A wall of plaster, as described above, is made, enclosing the teeth, and when hard is removed. Each tooth is loosened in its bed and re- turned to it. A block of wax is pressed into the lingual surface of the plate, covering enough of the backs of the teeth to hold them in position when the plaster wall is removed. Detach the wall and fill between the block of wax and the teeth with plaster, carrying the latter over the occlu- sal surfaces of the teeth (Fig. 480). When this block of plaster has set it holds the teeth firmly in their relative positions. The artificial gums are marked by a line at a uniform distance from the upper edge line of the plate. The block of plaster containing the teeth is removed from the plate, and the gums are ground down to the line marked on them, bevelled, and the cut surfaces smoothed on a fine corundum wheel. They are returned to the plate, still held by the block of plaster. The surface RIMMING THE PLATE. 409 of the model, the upper portion of the plate-wall, the plate heel over the tuberosity, and the gums are oiled and covered by a plaster batter about half an inch thick and extending for more than a quarter of an inch over Fig. 480. Guide to hold single gum teeth together while adjusting a rim. the porcelain gums. This plaster forms an impression from which a model of that portion of the denture is to be made. It is a more satis- factory measure to make these impressions in two sections, each of which extends a short distance beyond the median line of the plate. From the models dies and counter-dies are made, two of each for each side. A strip of plate of No. 28 gauge is swaged between each, and trimmed so that it shall extend for about an eighth of an inch above the plate edge, the lower edge of the strip covering the tops of the gums to a uni- form depth of about one-eighth of an inch. The heel of the strip should be closely adapted to the tuberosity and its anterior extremity a short distance beyond the median line. The strip for the opposite side is to be similarly made and trimmed. . The plate and strips are boiled in acid, dried, the plate and one strip adju.sted to one another with the arti- ficial teeth in position. The strip is to be held by the clamps of iron. The block containing the teeth is re- moved, and the plate set with its alveolar ^...Jz^^ ^^^' portion resting uniformly upon a solder- ing block. A cream of borax is painted along the joint between strip and plate, and two small pieces of solder placed on the ledge formed by the pro- jection of the strip above the plate edge. The plate is now carefully and uniformly heated under the blowpipe, and by means of a fine flame the solder is melted, partially uniting the strip to the plate. When the plate is cool the teeth are set in position to see that the position of the band strip is correct. A line of borax is painted along the lines of junction between the strip and plate, avoiding the introduction of borax into the space to be occupied by the tips of the gum : plate and strip are to be held by means of three clamps — one at the tuberosity, one at the anterior extremity, and one between them. About four of the small squares of solder are usually sufficient to complete the union. The plate is boiled 410 SELECTING AND FITTING THE TEETH, ETC. ill acid, and the anterior end of the strip cut off by means of a saw exactly at the median line. The second strip is applied to the plate, its anterior extremity cut to make a square joint with the attached half of the band or rim. It is soldered as the first, uniting the ends of the bands by a very small piece of solder. The upper projection of the band is cut down to the plate out- line, rounded and smoothed. The teeth are returned to their positions in the plate, and the next operation proceeded with — the fitting of the stays. Fig. 482. Upper denture rimmed. Another but less neat and accurate method of fitting a rim is as fol- lows : Fit to the upper edge of the plate and for an eighth of an inch over the gums of the artificial teeth a strip of pattern tin : this is to be reproduced in plate of No. 30 gauge. Anneal the strip of metal, and fit it to the plate edge and over the artificial gums with approximate accu- racy. The plate is laid face upward upon a block of charcoal, and a couple of iron pins pressed into the latter, bracing it against the heel of the plate. The strip is placed in its position upon the plate and held against it by means of two or more iron pins. At the points where it is seen the strip is in contact with the plate borax is applied, and small pieces of solder placed at the points of contact. The parts are then tacked by melting the pieces of solder. Transferred to the model and the teeth placed in position, the contact of the edges of band and plate is furthered, and then soldered, the operations described being repeated as often as necessary to perfect the joint between the plate and rim. The edge of the band covering the artificial gums is burnished down until it is within a small fraction of an inch from contact with them. Wiring Plates. When plain teeth have been adapted to a plate, and it is designed to place over them an artificial gum of one of the vegetable bases, it is advisable to attach to the upper edges of the plate a continuous wire, to round the upper edge, increase the means of retention of the artificial gum, and to lend additional beauty of finish to the piece. After the teeth have been fitted and tried in the mouth, the palatal line of the base of the last molar is marked by a scratch on the plate. Beginning at the extremity of this tooth, a wire is to curve over the ridge and follow the upper edge of the plate until it terminates at the base of the oppo- site terminal molar : the stays of these teeth are to abut with the ends of the wire. A piece of triangular wire of No. 18 gauge of the proper length is procured. This is annealed, boiled in the acid solution, and one face of it scraped to exhibit a fresh surface. The middle of the wire WIRING PLATES. 411 is usually attached first. A clamp holds that point of the wire against the plate at the depression for the fraenum, the edge of the wire level with the upper edge of the plate, which is then set on a block of char- coal, the alveolar ridge portion resting upon the surface of the latter. The point of junction of the wire and plate is covered with borax and a small piece of solder placed over it. A fine blowpipe flame is directed against the plate beneath the wire, carefully avoiding contact of the flame with the loose ends of the wire, as these latter fuse very readily. When the solder flows, attaching the wire at this one point, the clamp is re- moved and the plate plunged in the sulphuric-acid solution. The plate is placed upon the model or die and the wire bent, following the line of the plate. For about half an inch on both sides of the soldered point the wire is brought into close apposition with the plate, the upper edges of wire and plate in a line ; the junction is boraxed, a clamp placed at the extremities of the fitted portions of the wire, and joined to the plate by small pieces of solder. The remainder of the wire is, little by little, fitted and soldered until the extremities are attached and are soldered fast to the point at which the disto-palatal corner of the second molar touches the plates. As a final measure the entire length of the joint between the plate and wire is covered by borax, one or two small pieces of solder placed at points where the solder may be deficient in amount, and then the blowpipe flame is passed along the joint, filling the latter completely with the solder. Should the case be one retained by clasps and not by the vacuum chamber, the wire is to be attached before the clasps are fastened to the plate. Before rimming or wiring it should be determined whether Fig. 483. the plate edge is of the proper height or depth, for, should sub- sequent trimming of this portion of the plate be required, it is possible a portion of the wire might need to be filed away, and thus mar the finish of the denture. Cases which have the third molars remaining should have the wire carried around the plate at the bases of these teeth (Fig. 483). The wall made over the ex- ternal faces of the teeth is now cut away at the portions touch- ing the band or wire until the teeth are set in the Avail, the for the succeeding operation. If the teeth are to be attached to the plate by means of vulcanite the wire is continued across the palatal aspect of the palate, following a line which marks the base of the wax. A pair of special, long clamps will be required to hold the wire in contact with the plate during the soldering operation. wall IS in its the proper position, rim, and they are The ready 412 SELECTING AND FITTING THE TEETH, ETC. Fitting Stays. The backing stays which are to serve < as the medium of union be- tween teeth and plate are usually adapted to the teeth of partial dentures while they are in the first plaster wall, so that after removal from the mouth the piece may be placed immediately in the soldering investment. Full upper or lower dentures, or both, when removed from the mouth are set on their models. Should any alterations have been made in the positions of any of the teeth, the gums must be jointed again, so as to restore the continuity of the gum contour. Any slight grinding necessary to perfect the adaptation of the teeth to the plate must also be done. There are two methods of fitting the stays to the teeth — the first by making a second plaster wall and fitting the stays while the teeth are held in this manner ; the second by investing the piece and fitting the stays in the soldering investment. The writer for several years followed the latter method, but has abandoned it for the former, which, although requiring a greater length of time, is more accurate. After the teeth have been enclosed in the second plaster wall the adhesive wax is picked away, not removed by boiling water, as the latter fills the spaces between and covers the surface of the teeth with a film of the cement. A pattern in three sections of the stiff foil is made for the stays — one embracing the molars and bicuspids of one side, the second those of the other side, the third of the six anterior teeth. The line of junc- tion with the plate should be accurate. These patterns are duplicated in platinous gold, the thickness of the latter depending upon the amount of stress to which the teeth will be subjected : the usual thickness is No. 25 gauge. For teeth requiring additional support No. 24 to No. 22 should be employed. The outline of the pattern at the line of the junc- tion with the plate should be cut accurately in the gold. Fig. 484. Occasionally it will be found that the backs of artificial teeth have a very irregular surface, one to which it would be impossible to adapt the platinous gold as it should be — the surfaces of gold and tooth in contact throughout. This difficulty is overcome by making the stays in two layers, that next to the tooth of thin and pliable metal, 24-carat gold or platinum of No. 32 gauge. The gold when used gives a yellow tinge to the cutting edges of the teeth, the platinum a blue tinge ; 22-carat FITTING STAYS. 413 Fig. 485. B plate of No. 34 gauge aiFects the color but little. The gold for stays is first annealed. The following tools are spread before the operator, so that each may be picked up when required : A pair of broad-pointed steel tweezers (Fig. 492) ; the pair accom- panying dissecting cases is the correct form ; A pair of parallel pliers (Fig. 484) ; Two plate-files, one 5 in. long, coarse cut, the other 3 in. long, fine cut ; A pair of plate-punches, a pair being selected which has the shortest distance from the joint to the pin, thus securing the greatest force needed for perforating platinous gold : many punches have the short arm of the punch so long as to require a strong force to perforate the metal ; A countersink engine-bit of about one-eighth edge mounted in the tool handle, for countersinking the holes (Fig. 485, C) ; A chisel having a wedge-shaped edge and mounted in a handle, to split the pins of the teeth (Fig. 485, A, B) ; A small pot of rouge made into a paste with olive oil. In fitting stays to single teeth, those having irregular backs, the head of each platinum pin is touched with the rouge and oil ; a piece of the thin metal is cut the full width and length of the crown and fitted so that it makes an accurate joint with the plate. It is then, while the base is held in contact with the plate, pressed against the lower pin. The position of the latter is marked by the rouge. The pin-punch is placed to cover the mark so made, and the gold is perforated. It is again placed in position behind the tooth, and the second pin marked and the perforation made. By means of a rubber point, the erasing rubber of a lead pencil, the gold is pressed into close apposition with the surface of the tooth. The holes are now countersunk to half their depth from the palatal side. Over the stay so adapted a second stay of platinous gold, No. 27 gauge, is fitted in the same manner. The tooth is now removed from its plaster bed and a sharp point passed around it, marking its exact width and length on the stay, which is then trimmed to this line and given rounded edges. At the cutting edge of the tooth the platinous gold stay is made one-sixteenth of an inch shorter than the other, and given a long bevel. The pins are then cut oif to within one-sixteenth of an inch of the stays, and the projecting portion divided into halves by means of the pin-splitter. Care is necessary in this operation that the pins be not shaved away, instead of being divided. The two pin sections are bent back against the stay, and serve to hold it firmly against the back of the tooth. The edges of the stay are given a rounded form, except at the base, set in the walls, cemented to the plate, and the fixture then invested. In fitting the stays to a full denture it has always been the Avriter's 414 SELECTING AND FITTING THE TEETH, ETC. Fig. 486. Fig. 487. iM practice to begin with the terminal molar of one side, fitting each stay in sequence, so that the second molar of the opposite side is the last stay to be adjusted. Cut from the strip of metal a piece having the width of the base of the tooth. The distal end of the stay for the second molar is made long enough to extend around the gum to the edge of the rim, to which it is ultimately to be attached. If the patterns for the stay pieces are accurate, the section of gold cut by them will fit the plate at the bases of the teeth ; if not, the gold is to be filed so that it does fit closely. The pins of the teeth are touched on their ends with the rouge and oil, and the perforations are made as described. Each stay as it is made is cut to the size and form of the back surface of the tooth upon which it is to be placed. The form of the stay for the terminal molar is as represented in the cut (Fig. 486). The joint between adjoining stays is to be cut square ; its base is also to have a square edge. The other outlines are to be bevelled and to follow the form of tlie back of the tooth, cover- ing it entirely (Fig. 487). The pin-holes are next countersunk. The stay for the first molar is cut and fitted in the same manner, making a close joint with the gum portion of the stay of the second molar. The stays for the bicuspids are similarly fitted, and so on to the terminal molar of the opposite side, the stays being given the forms of the backs of the individual teeth, and extending as far toward the cutting edges as the occlusion will permit, the basal portion of each stay fitting to the plate closely, and its lateral walls in close contact with the stays of the adjoining teeth. If there be spaces between the stays and the teeth, the solder which joins the two frequently draws the tooth from its position when it contracts in cooling. The more accurate the adaptation the less solder is required to unite the parts, hence less likelihood of disturbing the positions of the teeth. The contraction of a mass of solder may also cause an alteration of the form of the plate upon which it is melted. When all of the stays have been fitted the plaster wall holding the teeth is removed. The teeth, stays, and plate are boiled in the acid solution. The teeth are placed in line before the operator, and each stay set beside the tooth to which it belongs. Each is placed on its tooth, and by means of pliers bent until it fits accurately the surface of the tooth. The pins are next cut off to within one-sixteenth of an inch of the surface of the stay, and split. The split sections are bent back, retaining the stay. Each tooth as it has its stay adjusted and fastened is returned to position in the plaster wall, but not before a fine file is passed over the bevelled edges, smoothing the outlines of the stay to those of the tooth. When all the teeth and stays have been so treated, the walls containing them are placed on the model, and by means of adhesive wax the teeth are firmly cemented to the plate. If the operator chooses to assure himself of greater accuracy or more Fig. 488. INVESTING THE CASE. 415 thorough attachment of the stays to the teeth, and a better finish to their edges, the teeth and stays are imbedded in investing material, thus : Make two beds of the material, about one-half of an inch thick, in each ; seven of the teeth are placed in two rows, exposing the surfaces of the stays, the teeth themselves entirely enclosed in the investment (Fig. 488). When this has set each pin is covered by borax, and above each a small square of 20-carat solder is placed. The invest- ments are now heated in a furnace ; next in a charcoal bed under the blowpipe, and when the teeth and stays are made a bright red by the heat transmitted through the base of the investment, the fine flame is turned upon each pin until the solder flows about it, filling the counter- sink. When cool the teeth are boiled in acid, and each stay smoothed and finished on the polishing lathe. This method ensures accuracy, but the experienced operator prefers to have the soldering of stays to the teeth and to the plate in one operation. When the cement which attaches the teeth to one another and to the plates has hardened, the plaster wall is removed. It is noted whether each tooth is in its proper position ; the jaws of the articulator are brought together, so that it may be seen whether the occlusion is correct. The teeth and plate are now ready for investment. Investing the Case. An investment is a device designed to hold the teeth and plate in their relative positions during the soldering operation. It is made of a material having a low degree of conductivity and sufficient coherence to ensure that it shall maintain its form when raised to a very high heat. By its relatively low conductivity it prevents too rapid heating of the porcelain teeth which it encloses, and also the too rapid cooling when the source of heat is removed ; either of which is a prominent factor in causing fractures of porcelain. The same physical property lends to the invest- ing material the feature of maintaining the teeth at a constant tempera- ture during the soldering operation. Plaster is the basis of the invest- ment ; to it are added beach sand and asbestos, so that it will resist fracture in heating. About a gill of water is placed in a plaster-bowl, and to it are added two tablespoonfuls of short-fibre asbestos. Beach sand is added until the materials are just covered by a film of water, and the mixture is well stirred to distribute the asbestos evenly. Plaster of Paris is next sifted in and stirred until a soft, plastic mass is made. A spoonful of this is placed upon a glass slab, making a layer about half an inch thick. The denture is wet so that the investing material will flow freely into the spaces between the teeth. A small portion of the plaster is taken upon the point of a spatula and worked into the deepest portions of the palatal surface of the plate : little by little, more investment is added until the plate is full, when the material is then packed between the teeth, filling the spaces perfectly. It is then inverted upon the bed of the material upon the slab, and the investment built about the teeth until they are covered by a layer half an inch thick. The lingual surface of the plate is covered to within about half an inch of the bases of the stays. To ensure against fracture of the investment, it is the usual practice to imbed in the investment a piece of round iron 416 SELECTING AND FITTING THE TEETH, ETC. wire. This is bent so that its arch shall be about one-quarter of an inch larger than that of the teeth. It is set in position when the investment Fig. 489. Upper denture invested and ready for making the backings, and showing position of wire to guard against fracture. Fio. 490. Lower denture invested and ready for making the backings : A, position of wire to guard against ■fra r>t.n rp fracture is half completed. When the investment is perfectly hard the cement is picked away piecemeal, every particle being removed. Do not use m VESTING THE CASE. 417 hot water for melting out the wax : it is uncleanly, frequently leaving a tenacious film upon the teeth and plate, besides softening the investment. In some laboratories the teeth and plate after trial in the mouth are immediately invested, and the stay-fitting done while in this encasement, using no preliminary wall. The writer followed this method for some years, but abandoned it for the former method described, that being safer and more accurate. The patterns are made, and each stay cut, fitted, and trimmed as with the method first described. By means of pliers they are bent to fit the backs of the teeth as closely as possible, using especial care that the edges of the stay are in contact with the tooth. The stays are boiled in the acid solution, and their line of junction with the plate scraped clean. Each pin is now cut oif to within one-sixteenth of an inch of the surface of the stay and split twice by means of the pin- splitter, the cuts at right angles to one another : the four sections are then bent down, holding upon the stay firmly. Care is necessary in this opera- tion that not enough force be applied to fracture the investment. Some operators grasp the unshortened ends of the platinum pins in the jaws of a pair of pliers, drawing the ends together over the face of the stay instead of splitting the pins. There is more or less danger of splitting the teeth by this method ; besides, the cutting of four leaflets and bending them from the centre gives a form to the pin like that of a rivet head : the likeness is complete when the spaces between the leaflets are filled with solder, so that the attachment is a combination of soldering and riveting. No matter how carefully the stay-fltting may be done by this method, there is not so good an adaptation of stay to tooth as with the first method described. Another objection is that the necessary manipulations tend to loosen, to a greater or less extent, the teeth from their positions in the investment, so that after soldering the alterations of position may become evident. Dr. W. H. Trueman ^ advises a method for overcoming one of the great defects arising from stay-fitting in the soldering investment — viz. the want of accurate contact between the wings of the stays and the lower portions of the tooth back. Each stay is fitted and bevelled as for plain teeth with straight sides. Narrow pieces of thin platinum plate are cut extending from the top of the gum-joint between the teeth to the plate, and wide enough to be firmly held by the sides of the stay. Before the stays are fastened to the teeth these pieces are pressed across the joints, fitting any irregularities of form which may be present, the stays placed in position in pairs, so that by bending down the pins the sides of the stay hold the platinum pieces firmly in position. When all the stays have been adjusted and fastened small pieces of the stay metal are bevelled to fit between the sides of the adjoining stays, and long enough to hide the platinum : before placing them for soldering the surface of the platinum is covered by borax, the base joints are scraped ; the small sections are covered by the flux and placed in position. Should there be any points of imperfect contact between the bases of stays and the plate, the space is to be perfectly filled with small pieces of plate appropriately filed and fitted. Very long teeth, those subjected to unusual stress in mastication, and which might exhibit a tendency to bend at the plate joint, are given the ^ American System of Dentistry, vol. ii. 27 418 SELECTING AND FITTING THE TEETH, ETC. additional rigidity necessary by placing at the base of each joint a section of triangular wire. A cream of borax is applied to all the joints and about each pin. Solder is cut into small squares of about one-sixteenth of an inch size and covered with borax. Above each pin and over each lateral joint one of these squares is placed. At the base of the stays a continuous line of the pieces is placed on the plate. This amount of solder should suffice to solder a denture if the stays have been accurately fitted and spaces or weak joints correctly buttressed by means of additional plate. The following rules are to be observed in soldering ; When two pieces of metal are to be united by solder their surfaces should be as nearly as possible in perfect contact. The solder used for dental appliances should be employed merely as a uniting agent, and beyond the amount necessary to perform this office it should form no part of a fixture. Any additional strength of the piece should be derived from additions of plate, not of solder. Absolute chemical cleanliness of the surfaces to be united is neces- sary, for soldering is a molecular union of the surfaces of metals by means of a metal of greater fusibility than those to be united, and any substance interposed between the metallic molecules prevents their intimate union. The thickest part of an investment is to receive the greatest volume of heat. Solder flows toward the parts of highest temperature, so that in sol- dering the part into or over which solder is to be floAved is made hotter than its ^ surroundings. The nearer a metal is raised toward its melting-point, the more its molecules separate, and it tends to assume a crystalline structure ; there- fore the higher the melting-point of the solder used, the stronger is the union of the solder with the soldered metals, and the tensile strength of the latter is correspondingly lessened. With decrease in the thickness of the solder pieces there is an in- creased surface of oxidation. Solder should be placed at short intervals on the part of the fixture most difficult to heat. Drying of the investment should precede the heating of it. No tooth should receive the direct flame of the blowpipe until it is heated to redness by heat transmitted through the investment from the exterior. Borax must not be placed on porcelain : it forms a contractible glass surface which in contracting produces enamel fracture. In any piece where there may be several soldering operations begin with a high-carat solder — 18-carat solder for 18-carat plate — the second soldering with 16-carat, and if a subsequent one be required, 14-carat. This is not necessary where the heat required for fusion of the second solder is at a distance from the solder first fused. Heating and cooling should be gradual. The case is now set in the base of an old vulcanite flask and placed on a furnace, and warmed until the investment is perfectly dry : the heat is gradually increased until the base of the investment is red hot. Trans- ferred to a Fletcher furnace, the heat is increased until the entire piece is at a low red heat. While the last stages of the furnace-heating are in progress a soldering-pan is filled with small pieces of charcoal and heated INVESTING THE CASE. 419 under a blowpipe (Figs. 68 and 71). The case is transferred to the bed of charcoal, the pieces of the latter being heaped about the sides of the invest- ment. The broad blowpipe flame is then thrown beneath the investment and passed rapidly over its outer wall, until the teeth and stays are made red by the transmitted heat and the solder begins to settle. The fine flame is now thrown upon the line of junction between the stays and plate, and carried from the terminal molar of one side to that of the other, the solder melting and flowing freely. Usually the solder above the pins and lateral joints is fused by the same flame ; if not, if it do not flow freely about the pins and between the joints, a very pointed flame is directed at each pin and joint. To flow as it should the solder pji- hibits a quick fluidity and has a smooth, even surface at the completion of the operation. The case is now returned to the warm tray and per- mitted to cool slowly. When the stays are cooled, this is the test for the proper time of removing the investment ; the latter is carefully broken away piecemeal. The teeth and gums are now examined for any possible cracks or checks, as they are more readily seen while the case is dry. The piece is boiled in the acid solution, washed, scrubbed with soap powder, and dried, and then placed on the model. If the preceding operations have all been done correctly, the plate will have suffered no change of form and the porcelain will be intact. If, however, there have been any neglect of the minutiae, all of vital im- portance, the plate may be warped, the porcelain gums checked, or one or more teeth cracked or in malposition. If the pieces have been accu- rately fitted and no excess of solder used, the succeeding operations are a comparatively light task, but none the less important. A small fine corundum wheel on the lathe is used to grind down the heads of the pins and to make uniform the joint at the bases of the backing. A wheel should never be used when and where it touches any point save the one upon which we desire to operate. Flat and half-round gravers (Fig. 291) are employed for the finishing dressing and scraping. The tops of the joints between the stays are given a uniform concavity by means of engine burrs of the plug-finishing variety. The stays them- selves and the plate are not to be reduced in thickness at any point : for this reason tools and appliances should never be larger than necessary to remove the superfluous solder. It is a prudent measure to make a plaster cast of the interior of the plate to support the latter during the trimming and buffing operation : by this means there is a lessening of the danger of bending the plate and of undue strain upon the artificial teeth. Useful points for the smooth- ing of the surfaces of the stays and their joints are made of old corun- dum wheels softened by heat and drawn out into flat pencils. By alter- ing the shapes of their points these pencils may be formed so that they may be operated in any irregular places. After all of the surfaces have been dressed smooth, water-of-Ayr stones are used to give the final dressing : they are passed over every portion of the plate surface, oblit- erating all of the tool-marks and removing the outer coating of the entire plate. " To prevent the entrance of foreign particles in the spaces between the teeth and plate, and between the teeth themselves, the den- ture may be warmed, and melted paraffin flowed into all interstices : this is permitted to remain, as it effectually prevents the collection of debris 420 SELECTING AND FITTING THE TEETH, ETC. and secretions in parts inaccessible to ordinary cleansing agents " (Bon- will). The piece is now transferred to the polishing lathe, where the smoothing is completed by means of fine felt wheels and powdered pumice. It is customary with the experienced operator to dispense with the use of Scotch stone, except in places inaccessible to the following imple- ment. Select from the stock of the dental-goods dealer the hardest of the felt cones offered. This is placed on the mandrel of the polishing lathe and revolved rapidly, when a sharp knife-blade held against it divides it into wheels of any desired width. A section of this, three-eighths of an inch wide, is kept constantly charged with powdered pumice made into paste with water, and is passed rapidly across all parts exhibiting scratches or tool-marks. The device is for the removal of slight blem- ishes, and should never be applied to reducing protuberances. The case is held with the fingers embracing the outside of the teeth and support- ing the body of the plate firmly, so that no uneven pressure is brought to bear upon the latter. Plates are occasionally warped during the fin- ishing operation if held improperly. The piece is kept constantly in motion, so that while buffing there shall be no prolonged contact of the wheel at any point. The wheels as they are worn down are preserved for buffing small spaces. When the surfaces of the plate and stays are perfectly smooth, the edges of the Fig. 491. plate rounded and freed of all minute irregularities, a brush having a row of stiff bristles is a substitute for the wheel : this is passed rapidly over the surfaces of plate and stays, cleansing well the palatal surface of the former, but removing none of its fine lines. When all the surfaces have received a fair polish by this means, a similar brush is placed on the mandrel, and further surfaced, using a paste of chalk as the polish- ing medium. Succeeding this, a broad brush (Fig. 97) having fine bristles is employed with the chalk paste, to give a high polish to all of the surfaces — a sufficient finish to render the color of the solder undistinguishable. The plate is from time to time washed to observe the progress of these operations, and, after the buffing with chalk and soft wheel, is scrubbed well with soap to free it from all particles of pumice or chalk. A practice followed by the writer, but which appears to have fallen into general disuse, is to succeed the foregoing operation by that of burnishing. It is difficult to procure an effective set of burnishers : the best are of small points and edges made of forged steel, the temper scarcely drawn, and given a mirror-like polish (Fig. 492). A folded towel is placed before the operator and the denture laid upon it, and beside it the burnishers. A block of coarse soap, free Brush wheel, cup-shaped, for surfacing. SPIRAL SPRINGS. 421 Fig. 492. Burnishers. from any grit, and a vessel of water, are set beyond, so that the blades of the burnishers may be frequently lubricated by dipping them first in the water, then rubbing them over the soap. The burnishers are rubbed over every portion of the plate surfaces and stays until a brilliant surface is given them. This operation requires half an hour or more to do thoroughly. At its completion the burnishers are dried and rubbed smooth on a piece of chamois, and returned to a wash-leather wrapping having appropriate pockets for each tool. The case is now washed free from soap, and is ready for the final polishing. The burnish- ing is commonly dispensed with, and the succeeding operation practised immediately after the final buffing with whiting. A brush four inches in diameter, having the softest of bristles, is employed. A thin mixture is made of alcohol and the finest jeweller's rouge (an oxide of iron) : this is painted over the surfaces of the plate and stays, and the brush, revolv- ing as rapidly as possible, is passed and repassed over all parts until the metal portions of the denture have a polish equalling that of the inner case of a watch. Every trace of the polishing powder is removed with soap and water. An attractive finish may be given the palatal surface of the plate with a water-of-Ayr stone. A piece of this material is filed to a pencil point ; the plate surface is wet and the entire palatal surface, except the interior of the chamber, which is highly burnished, is marked by a series of spirals traced by the pencil point, the lines of the spirals radiating from the edges of the chamber : it gives the surface of the plate the appearance of frosting. Any rouge remaining about the joints which is not removable by soap and water may be destroyed by touching the joints with nitric acid, then reapplying the soap. If the burnish- ing operation have been followed, it will be found that the polish of the plate persists for a greater period. Spiral Springs. Prior to the advent of the vacuum chamber formed in plates, the retaining appliance employed with full dentures was that known as the spiral spring. Improvements in laboratory technique, comprised in bet- ter means, methods, and materials for impression-taking, together with a more accurate adaptation of plates, have so limited the use of these springs as to place them in the class of obsolete appliances. It is ex- tremely rare that recourse to this method of retention is ever necessary. Springs are employed only when the anatomical configuration of the parts would render the employment of other retaining devices inapplicable. Examples of such cases are found when any of the following condi- tions exist : Extreme flatness of the arch ; extreme contraction of the area upon which the plate rests ; an exaggerated softness and thickness of the soft tissues of the mouth ; or for attachment to obturators or artificial vela in edentulous cleft-palate cases. 422 SELECTING AND FITTING THE TEETH, ETC. Full denture with spiral springs in position. The appliance consists of two parts — the springs and the arms to which they are attached. The springs are made of wire coiled about a mandrel, so that they have a tubu- FiG. 493, lar form. The arms are in two sections : one section is anchored in the buccal wall of the denture ; the other, freely movable upon it by a swivel -joint, is at right angles to the first. There are four of these double arms — one for either side of each denture. The springs are in pairs — one for the right, one for the left side. The springs are slipped over the free or the movable arms, with the concavity of the spring backward, as shown in Fig. 493. It will be seen that the elas- ticity of the spring tends to press both dentures in their proper positions. They are so attached that the surfaces of the springs will rest upon the buccal aspects of the denture, and not protrude in such a manner as to irritate the soft tissues of the mouth. The springs are made of round platinous gold wire, of from No. 24 to 30 gauge, wound upon a mandrel somewhat smaller than the movable anchorage arm. An ordinary knitting-needle will serve as a mandrel. The wire is to be wound in a coil upon this mandrel in such a manner as to have a uniform tension throughout the coils ; that is, the spring when completed should be perfectly cylindrical. The sj)rings must be accu- rately paired : the degree of elasticity in both must be alike. The method of making them, as described by Dr. Wm. H. Trueman, is as follows •} " The mandrel. A, is attached to the lathe by Fig. 494. its enlarged extremity, B. To support the man- drel when in use a block of hard wood, jB, two inches long by one inch wide and half an inch thick, is arranged as follows : Lengthwise of the block and centrally located upon its upper surface there is formed a groove, C, in depth twice the diameter of the mandrel and of width sufficient for the mandrel to fit it tightly. From the bottom of this groove and about half an inch from one end drill a hole, D, one-sixteenth of an inch in diameter through the thickness of the block, countersinking each end sufficiently to remove the square edge and round the entrance to the hole at each side of the block. With a small round graver increase the depth and width of the groove from the hole just made to the nearest end of the block, as seen at e. The object of this is that the mandrel may be evenly supported by the ^ American System of Dentistry, vol. ii. Apparatus for making spiral springs: A, mandrel; B, por- tion fitted to lathe ; f, loop to ■which wire is fastened ; B, block supporting mandrel ; c, groove in which mandrel turns ; d, hole through which wire p)asses ; e, enlarged por- tion of groove to accommo- date spring wound. SPIRAL SPRINGS. 423 groove in the block when the portion of its length occupying this part of the groove is covered by the wire wound upon it. " In using this device secure the mandrel in the lathe ; the small lathe used for grinding teeth will answer if a stronger one is not available, as the power required is but slight. Pass one end of the wire through the hole in the block and secure it to the loop, r, on the mandrel ; turn the mandrel a few times, guiding the wire so that the coils will be far apart : the object of this is, first, to more firmly secure the wire to the mandrel ; second, to occupy the space upon the mandrel corresponding to the space between the end of the block and the hole through which the wire passes, so that when the winding begins the wire will be drawn through straight, and not at an angle, as would otherwise be the case. This, a little practical experience will quickly prove, is of more import- ance than at first appears. We are now ready to begin winding the spring. Place the end of the block through which the wire passes next the lathe-head, the mandrel lying in the groove opposite the centre of and in line with the axis of the lathe-spindle ; the right hand should hold the block firmly, and the fingers of the left hand, protected with a glove or a piece of cloth, regulate the tension of the wire by making it bear hard against the side of the hole, d. To make a good spring the wire should be held firmly and with a greater strain than would be prudent with the unprotected fingers. Slowly turn the lathe, increasing the speed if the winding is proceeding satisfactorily, and keep the block firmly pressed toward the lathe-head, so as to lay the coils closely together : the wire forces the block forward on the mandrel too rapidly unless resisted by a firm, steady pressure. There are several points to be carefully guarded in winding a spring. It is all-important that the first few coils should be laid closely together ; they are apt to determine the character of all that follow : it may be necessary before proceeding to force them together with a burnisher if they are disposed to separate. See that the wire is not. liable to become entangled in the lathe or with near objects, or to form " kinks," as it is very apt to do. By attaching to the free end of the wire a weight of a few ounces this annoyance may be avoided. There is a constant tendency in the coils to ride over those already formed ; this must be checked by sufficient tension. If the spring is a long one or if the fingers are insufficiently guarded, the friction of the wire passing over them becomes quite painful, naturally causing the tension to be relaxed and spoiling the spring. The end of the wire, if the wire is completely used up, becomes a source of danger as it passes through the block. It may coil around a carelessly-disposed finger or it may be bent into a hook ; in either case it is liable to do serious injury. This will suggest that if a weight is attached to it, it should be secured by tying with a piece of thread that will either slip off or break — never by making a hook or loop in the wire." The arms are made of 18-carat wire, of a size slightly larger than the tube of the springs. Eight pieces of wire are cut, each about three- quarters of an inch long. Four of these pieces are to be made into movable, four into the fixation, arms. For each of the latter two disks of plate, No. 24, are cut : these are perforated in their centres, so that they shall fit tightly over the wires. One of the disks is driven on the wire for about one-eighth of an inch ; the second is then placed at a 424 SELECTING AND FITTING THE TEETH, ETC. distance from the first slightly less than the diameter of the wire. The space on the wire between these disks is to be kept free of the borax with which the lines of junction of wire and disk are touched. An infinitesimal portion of solder is placed outside each disk Fig. 495. and fused, attaching the pieces. The external disk is A ■ ■ ID rounded and smoothed ; the second is to have a square edge. B n : Q The movable arms are made by forming the ends Button and hook of the wires into loops ; the loops are then laid upon ^or attaching spi- ^ smooth anvil and flattened until they are narrow enough to pass between the disks on the first arms. The loop is opened sufficiently to admit the section of wire at that point. The sides of the movable arms are squared so that when rotated into the spring tube a faint retaining thread will be formed on them. As furnished by the manufacturer the arms are undetachable from one another. If the plate be of metal, an arm is to be soldered to the stays of the artificial teeth ; if of vulcanite or celluloid, the end of the wire is bent into a retaining loop. When the plate is of one of ihe latter materials, grooves or gutters may be formed in its buccal wall to prevent pressure of the spring upon the tissues of the mouth (Fig. 493). The arms are attached to the dentures in such positions that the springs shall rest upon the buccal surfaces of the dentures. The arms pass be- tween the second bicuspids and first molars of upper and lower dentures. The arms are passed between these teeth until the inner disk rests upon their buccal surfaces. The springs are next placed over the movable arms and pressed against the buccal surfaces of the artificial teeth, when the arms are to be firmly cemented by their projecting ends to the palatal surface of the plate and to the teeth. When the cementing adhesive wax is hard the springs are carefully detached. The position of the arm must not be disturbed in any subsequent operation. Repairing Soldered Dentures. The common casualties occurring to soldered dentures which demand repair are cracks of the plate, the fracture of one or more teeth, the loss of a natural tooth, leaving a gap in the arch, and, finally, some altera- tion of the form of the plate. When cases present for repair, it is always to be noted whether there be any fault in the adaptation of the plate to the arch and vault. Patients by becoming accustomed to the presence of a denture may have their mouths grow tolerant of a piece, the adaptation of which is markedly faulty. Much chagrin is spared the operator if he invariably call the patient's attention to such faults. It may be that the change of form is due to resorption of the tissues of the mouth producing non-adaptation of the denture, or the latter itself may be bent from its original form. The operator is not infrequently annoyed himself, and unjustly cen- sured for it by patients, by a phenomenon due to physiological processes in the dental arch and vault — to wit : an artificial denture is made and faultlessly adapted ; it is worn by the patient for a period ranging from one to several years ; then gradually develops a discomfort which an REPAIRING SOLDERED DENTURES. 425 examination shows is due to lack of adaptation of the plate to its base. When placed upon the original plaster model it is seen little or no change of its original form has occurred. The mouth itself has altered in its configuration, which alteration may be readily demonstrated to the patient by placing the denture upon the model. This is one of the reasons why models should be marked with the patient's name, together with the date of making, and preserved. These changes almost always occur in the mouths of all patients between the ages of twenty-five and fifty years. In either event, the difficulty complained of being faulty adaptation, it is necessary to again bring the plate surface in contact with the under- lying parts. The first step of the operation is the securing of an accu- rate plaster impression, from which a perfect model is obtained. The latter is given a coating of varnish, and when this is dry the denture is set on the model. If it be a partial case, it will be found, frequently, that it is impossible to place the piece in position on the model without muti- lating the plaster teeth. These latter are for the time removed, and the location of the faults of adaptation noted. The most common fault will be found a lateral bending, the posterior angles of the plate bent away from or against the soft tissues of these parts. If this be the only dif- ficulty, the experienced workman readily and deftly restores the form by bending between the fingers. If the difficulty embrace the entire vault or outlined spaces of it, satisfactory readjustment is only possible by reswaging the plate. As a preliminary measure it is advisable to boil all dentures presented for repair in a strong solution of caustic soda or potash, to saponify fatty matters and destroy all food deposits between or beneath the teeth. If this precaution be not taken, the deposits are carbonized during the soldering operation, and blacken the joints by the insoluble and usually irremovable particles. The case is next boiled in the acid solution to free it of the oxides on its surfaces. A wax-bite is taken and an articulator formed. If it be a partial denture and the bases of the stays are accessible to a fine saw-blade, each tooth is removed by sawing through each stay as close to the plate as possible. Should the teeth be inaccessible to the saw-blade, a small circular saw having very fine teeth is mounted on the lathe and em- ployed for the purpose. In some cases it is necessary to unsolder the teeth from the plate. The teeth and gums are covered by a paste of whiting to a depth of about one-quarter of an inch and the solder sur- faces well boraxed. The denture is set over a stove to warm sufficiently to dry the paste when it is placed in a furnace and heated. It is now transferred to a charcoal bed, leaving the teeth and gums free from con- tact with any pieces which might support them. A blowpipe flame is directed against the encasement until the teeth are at a red heat, when the flame is turned against the plate at the base of each backing, and as soon as the solder is fused each tooth is knocked off the plate and into the charcoal bed, where it is permitted to lie until cool. The plate is cleansed in acid, and the rough solder masses are dressed down by means of coarse files. The plate is bent into as close an adaptation to the plaster model as possible, between the fingers. The inner surface of the vacuum chamber is oiled, and in it is fitted a piece of wax of the same depth as the chamber 426 SELECTING AND FITTING THE TEETH, ETC. and a hair's-breadth smaller on all sides. In the centre of the chamber area on the model a drop of melted adhesive wax is placed, and the plate containing the wax form quickly pressed into position. In a minute or two the plate is removed and the edges of the wax form are pressed, not melted, into contact with the model ; its edges are next smoothed and bevelled, and the entire model is varnished. A die is made, and on it a counter-die of lead, and then one of zinc, are formed. Between the die and lead counter the plate is swaged, interposing between the counter-die and plate a layer of the wet rubber cloth to prevent contamination of the surfa(ie of the plate, always more or less rough. The plate is annealed, and then swaged between the zinc die and counter, when usually it will be found to have a satisfactory adaptation to the model. The teeth are boiled in acid, any ragged edges of solder dressed ofP, and are adapted to the model and articulator as for a new case. The teeth are cemented to the plate, tried in the mouth, and, if found correct, the piece is invested. Any space between the bases of the stays and the plate are to be filled with pieces of plate. The surfaces to be soldered are first covered by the cream borax ; then in the spaces beneath the teeth and stays a piece of pure gold is placed as a matrix ; a fragment of 24-carat plate. No. 36, being bent upon itself, and the folded edge introduced beneath the tooth : the leaflets are then separated, one being brought in contact with the base of the tooth, the other with the plate : the V-shaped depression is filled flush with small bars of plate. The stays and additions are covered by the borax, a greater amount than usual of solder placed on the plate beneath the stay, and the case is heated and soldered as described on the preceding pages. The next class of repairs in point of extent are those which require the addition of plate to overlie spaces left by the loss of a natural tooth or teeth. A plaster impression is taken of the part with the denture in position in the mouth. The plate is to be withdrawn in the impression. A wax-bite, which has also been taken with the plate in the mouth and before taking the impression, is mounted and an articulation made. If the break in the outline be small and of regular form, a die is not re- quired to fit the additional pieces. Tlie edges of the plate surrounding the break are to be bevelled from the palatal side. If the edges of the break be more than one-sixteenth of an inch from contact with the model, a series of saw-cuts are made along it, extending into the plate halfway to the line of contact with the model. A thin piece of 24- or 22-carat gold plate or of platinum is annealed, and made to conform to the surface of the model by means of the rubber end of a lead pencil : its inner edge is to come within the plate line as far as the end of the bevel, its outer edge to be on a line with the plate line. A joint made between the plate and the supplementary piece is stronger when the edges of the plate overlap the patch : the adap- tation is more accurate, and to secure the necessary strength it is not required to leave an unsightly protuberance. The leaflets between the small saw-cuts are now bent down, covering the added piece. The tooth or teeth are fitted to their places, and stays made. The several pieces are cemented together, and the fixture is invested, making the invest- ment immediately underlying the plate joint thinner than at other places. BEPAIBING SOLDERED DENTURES. 427 SO that more heat will be transmitted to this portion of the denture. The cement is picked away, the surfaces well covered by a cream of borax, and in the space between the stay and the plate edge surrounding the break a piece of plate of No. 26 gauge is set, fitting the piece beneath it. Solder is placed around the joints and the case well heated. In the soldering the heat is to be thrown upon the plate beyond the line of the break, so that the solder may be drawn beneath the plate and fill the joint. The deflected heat usually flows the solder about the pins of the teeth and at the base of the stay. Should the space to receive the addition be large or have an irregular form, it is advisable to swage the piece. The plate edges adjoining the open space are to be bevelled, and the line of the edges traced on the model by means of a pin point. The plate is removed from the model, the latter is varnished, and a small die made of the part to be covered by plate. A piece of plate of No. 26 gauge is swaged to fit, and its inner edge cut down until it is slightly broader than the pin scratch on the model. Saw-cuts are made in the plate edges surrounding the break, and the leaflets bent down, holding the swaged section. The teeth are mounted and the pieces united as described. Occasionally it is necessary to make the repair in two operations. It may be impossible to perfectly unite the piece to the plate and the tooth to both in one soldering. Such cases are found in those having a portion of the joint between the supplementary piece and the plate extend far beyond the palatal edge of the artificial tooth ; for instance, where it is required to add an extension to the end of a lower plate, the additional piece being virtually a small plate covering the ridge. In such cases the piece is first swaged, fitted, and soldered to the plate, and the tooth or teeth mounted in a second operation. A common casualty, as noted above, is a crack in some portion of the plate. Such breaks are to be repaired by the addition of a strip of plate, never by solder alone. The case is cleansed thoroughly and the edges of the crack are brought together. Should the edges of the crack be separated more than about one-twentieth of an inch, it is inadvisable to attempt readjustment of the edges : the repair is to be made then with- out any bending. The crack is filled with the cream borax. When this is dry the plate is invested, and a piece of plate of No. 28 gauge, about a quarter of an inch wide and extending the full length of the crack, is fitted to the plate covering the crack. Its upper edges are bevelled, and it is well cleansed, and the surfaces to be united covered by the flux. A piece of solder is laid at each edge, and the case is heated and soldered : in finishing the strip is to represent a rounded ridge. Should the crack be at the portion of a plate embracing the neck of a natural tooth, a semi- lunar piece is to be fitted over the plate and soldered to it. When teeth are broken from a denture an impression is taken with the plate in the mouth, an articulation made, the tooth fitted, stayed, and soldered as with a new case. If the tooth be broken away from its stay and lost, the repair may be made by riveting. A tooth of the same mould and color is selected, the pin-holes drilled, not punched out, as the latter operation invariably bends the stay. The tooth is ground into position : this operation will require some care, owing to the pins hampering the free mobility of the 428 SELECTING AND FITTING THE TEETH, ETC. tooth in its space. If necessary, the pin-holes may be reamed out and made larger. If there be any marked difference in the situations of the pins of the new tooth from those in the old one, the pin-holes are sawn into elliptical openings, and when the tooth is fitted the pins are so bent as to cover as much of the openings as possible. The case is then invested and soldered. Should the other teeth of the denture be of such type as would be endangered by the heating necessary in soldering, it is advisable to rivet the tooth to the stay. A tooth is selected having the pins at the same distance apart as in the old tooth. The pins of the old tooth are care- fully drilled out of the stay, and holes are countersunk at the palatal side. The tooth is fitted to position, and the pins cut off to about one- FiG. 496. Riveting hammer. sixteenth of an inch from the surface of the stay. A folded towel is laid upon an old counter-die, the tooth to be riveted set upon the towel, and no other tooth should press hard against the latter : repeated light blows of a small riveting hammer are directed against the ends of the pins until each is forged into the countersinks, filling them completely and leaving rounded heads, which are then burnished hard to complete the operation. Cases will occasionally present in which the artificial tooth has broken away from its stay, leaving pins projecting from the back of the tooth about one-fiftieth of an inch long. Such a tooth is to be boiled in a test- tube with nitric acid. To its back is burnished a covering of platinum plate. No. 36 or 38. Apertures are made over the stumps of the pins. The tooth and the platinum back are invested, a piece of pure gold is placed over each pin, and the platinum is soldered to the pins. The old pins are drilled out of the stay standing on the plate. The back of the stay is scraped to cleanse and thin it, and its top bent inward slightly. The tooth with the platinum back is set against the stay and cemented to it : the case is invested, and the platinum soldered to the stay, using a low- carat solder. In repairing cases having a gum of one of the vegetable bases, if the stay be standing the following method is frequently applicable : The rubber or celluloid is cut out to receive the neck of the tooth, but the festoon covering the latter is to remain untouched. A plain tooth is fitted to the stays, in which pin-holes have been drilled and countersunk. Phosphate of zinc colored pink with carmine is placed in the depression cut in the gum, and the tooth pressed into position : when the cement has set the pins of the tooth are riveted as described. To properly adjust broken or detached clasps it is necessary to take an impression of the clasp tooth with the plate in the mouth. Should the clasp itself be broken, the surface on either side of the break is filed REPAIRING SOLDERED DENTURES. 429 flat and a piece of thin clasp metal extending for one-fourtli of an inch on either side adapted, cleansed, and perfectly joined to the clasp by means of solder. A method of repairing metallic plates without subjecting the denture to the soldering operation, and, what may be more important, a means of attaching a clasp to a plate or an additional tooth without depriving the patient of the piece except for a few minutes, has been devised by Prof. C. J. Essig. A typical application of the method will illustrate its advantages : A patient is wearing a partial gold plate ; one of the remaining natural teeth is becoming progressively looser, and may be lost at any time ; it is not permissible to deprive the patient of the piece for the length of time necessary to repair it by soldering. A bite and impression are taken with the plate in position. If the operation be the preparation of an artificial tooth to be substituted for a loosening natural organ, as soon as it is removed ; the plaster tooth on the model is cut away, together with an amount of plaster to represent the condition of the soft parts after extraction. A die and counter-die are made, and a piece of plate No. 26 is swaged which shall overlap the plate, as shown on the model, for one-fourth of an inch or more : a tongue to extend into the interdental space is to furnish a support to the artificial tooth. An articulating model is made, a tooth fitted to the model, and a stay adapted to it. The pieces are now invested and united by means of solder, then finished. The edges of the plate piece should receive a bevel, so that there shall be no abrupt line between the new and old plate. To add a clasp, an impression is taken with the plate in position, and a model is made which shall have a perfect representation of the tooth to be clasped. The clasp is fitted to the tooth, and a piece of plate to the general plate, as described above. This is filed away about the base of the clasp tooth until it has a close Fig. 497. joint with the clasp, to which it is cemented, invested, and soldered, and finished as described. To add these pieces to the plate, three holes are drilled through the plate as marked in Fig. 497, and each is countersunk upon its upper side. When, in the first instance noted, the natural tooth is lost, or, in the second, the clasp addition is prepared, the piece is placed in the mouth with the plate itself in position, and by means of a sharp excavator point the outlines of the supplementary piece are scratched on the plate proper. With the pieces held in close apposition a drill is placed through the openings made in the small plate, and the plate proper perforated : the holes are countersunk at the palatal surface. Gold pins upon which rivet heads have been formed are placed through the openings and riveted, thus holding the sections firmly together. CHAPTER XIL ENGLISH TUBE TEETH: THEIR USE IN PLATE-, CROWN-, AND BRIDGE-WORK.i By Charles J. Essig, M. D., D. D. S. English Tube Teeth. The English tube tooth diifers from the ordinary plate tooth in that its attachment to the piece to which it is adjusted is effected by means of a central tube of platinum running through the body of the tooth, and into it a pin or post is introduced (Figs. 498 to 500). Tube teeth may be used in any situation on either upper or lower plates, and they are well adapted for mastication. Being somewhat cubical in shape, they are probably stronger than flat teeth. The tube tooth is supported over its whole lower surface, and the greatest strain" in occlusion falls mostly in a vertical direction, upon the crown and parallel to the line of the central pin ; whereas in a flat tooth, the attach- ment being on one side only, the strain caused by the impact of the bite is more unevenly distributed. The tube teeth allow of easy removal for repair, it being possible to add a new tooth in from ten to twenty minutes. As the quantity of solder used in uniting the backings of flat teeth to the plate is of necessity considerable, the danger of warpage from this cause is proportionally great. By the use of tube teeth this risk is entirely removed — a consideration which alone seems sufficient to com- mend their application in many cases back of the cuspids, where flat-back masticating teeth would otherwise be used. Many English dentists claim that tube teeth are more adaptable than pin teeth : a very long tooth can be cut down to any length, and the body, being of the same texture throughout, can be ground and polished perfectly. They can be used for plate-, crown-, and bridge-work, and in some cases in combination with vulcanite. From the ease with which they may be adapted a small stock of these teeth will meet all ordinary de- mands of private practice — a most important consideration to practi- tioners who are not within easy reach of a dental depot. Being a more faithful reproduction of the shapes of natural teeth, they are likely to feel more comfortable to the tongue and interfere with speech less than do flat teeth. They are, in all probability, more easily kept clean, being without backings, which favor the lodgement of decomposable material, than or- 1 From a paper read before the World's Columbian Congress by John Girdwood, L. D. S. (E. D.), D. D. S. (University of Pennsylvania). 430 ENGLISH TUBE TEETH. 431 dinary pin teeth, and their supports, being surrounded by porcelain, are out of the reach of any impurity (Figs. 495 to 500). Fig. 498. Incisors. Defective. Improved. Fig. 499. Bicuspid. Side. Plan. Side. Side. Side. Plan. Plan. Defective and improved tubing. Plan. For crown- and bridge-work many advantages are claimed for tube teeth, and those who constantly use them find that they can be as perfectly and directly fitted to natural roots as any other form of porce- lain crowns. Being made of porcelain with but a thin central platinum tube baked in them, they retain, when mounted for wear in the mouth, their translucency and natural appearance — qualities so often destroyed by the gold backing on flat teeth. There seems, however, to be one defect in the tube incisors and cus- pids as at present manufactured. In these the base is frequently too small antero-posteriorly, and consequently in many cases it is impossible to cover the root completely with them. Moreover, the tube is very often too near the front, so that the axis of the crown does not always corre- spond with that of the root (Fig. 498, A). The bicuspids and molars, however, are free from any such faults, and are pre-eminently well adapted for crown-work. Yet with the front teeth as now manufactured good work can be done, and if this style of teeth were in greater demand manufacturers would probably produce improvements beyond those at present thought necessary. The setting of tube teeth requires the use of a special set of simple hand tools, which are shown in Figs. 501 to 507. Fig. 501, a countersinker for clearing away the burr which forms upon the end of the tube when ground, and for slightly enlarging the orifice of the tube at its base. A suitable countersinker may be made from an old excavator handle ground to a three-sided pyramidal point and tempered hard. It should be large enough to obviate any danger of forcing it into the tube and so vSplitting the tooth. Fig. 502, a tube-file used to remove the debris from the tube after grinding : it follows the countersinker, and is used before trying the tooth on the pin. Fig. 503, a marker : this is a piece of straight round wire which should fit the tubes easily, but not loosely, and have one end filed almost to a central point. Fig. 504, a pair of flat-pointed pliers with a longitudinal groove in them for holding the pin while it is inserted in its socket in the plate. 432 ENGLISH TUBE TEETH, ETC. Fig. 505, a sharp-pointed graver. Fig. 506, a length of gold pin wire (magnified). Fig. 501. Fig. 502. Fig. 503. Countersinker. Tube-file. Roughing pliers, with gold pin ready for insertion. Fig. 507, a pot of paint, not too thin, made by mixing olive oil and vermilion. The uses of these instruments will be described in the explanation of the method of mounting the teeth for which they are required. Fig. 505. Fig. 507. Sharp-pointed graver. Fig. 506. Length of pin wire. Pot of vermilion and brusli for mark- ing and fine filling. Fig. 508. For the purpose of illustration we will suppose a case of a partial gold upper denture, where the lateral incisor and cuspid on the right side and all the grinding teeth on both sides, except the second superior upper molar, are absent. Having swaged and fitted (Fig. 508) the plate in the ordinary way and adjusted the clasp, a tube tooth is selected for each side. Care must be taken that the teeth chosen shall be longer than is apparently necessary, so that there will be tooth-sub- stance to spare in fitting to the plate and bite. The teeth are now roughly fitted in the positions they will occupy. The countersinker removes the burr from the platinum tube at its ground end, and the ENGLISH TUBE TEETH. 433 tube-file clears out all debris from end to end. The teeth are replaced on the plate to be fastened in their proper positions with hard wax. Fig. 508. Fig. 509. M )c1l1 show 111^ ^t uidin-; tteth Plate and pms for post teeth The marking wire, tipped with vermilion paint, is then passed down each tube till it touches the plate, where it will leave a mark showing the places at which the holes are to be drilled to receive the pins. The teeth are then removed from the plate, care being taken to avoid dis- turbing the color mark. With a sharp-pointed graver a slight pit is made for the drill. The plate need not be taken from the model while drilling the holes for the pins : care, however, must be observed to keep the drill exactly at the same angle as was made by the marker (Fig. 510). By means of a broach the holes in the plate should be enlarged Fig. 510. Showing method of marking pin-posts. till they are nearly, but not quite, large enough to receive the pin-wire : the rough edge or burr left by the drill must be removed by counter- sinking both sides. A suitable length of gold pin-wire should then be cut, and the end which is to fit the socket in the plate should be slightly tapered, so as to fit tightly and project about a sixteenth of an inch through on the palatal surface. A slight groove should be made longi- tudinally on the tapered end of the wire for the purpose of assisting the solder to run more readily from the palatal to the lingual surface. The tapered end of the pin and the pin-hole are then touched with borax, and the wire fixed firmly in place by means of the pliers (Fig. 504), attention being paid to its direction. The tooth is next tried on, and, having ascertained that this particular point is correct, the pins may be soldered in a manner to allow the solder to flow through from side to 28 434 ENGLISH TUBE TEETH, ETC. side. It is not necessary to invest the plate for this purpose, for the tightness of the pin in its socket will support it sufficiently. In solder- ing it is of the utmost importance that the smallest possible quantity of solder be used. It will be at once seen that as the tube tooth fits the pin exactly, any excess of solder at its base must prevent the tooth's touching the plate, unless the former be ground out or the superfluous solder cut away. AVhen the plate has cooled, the flux is removed by boiling in water acidulated with sulphuric acid. The projecting end of the pin should then be cut off, and smoothed down with a corundum wheel and graver until it is level with the plate. The plate is then replaced on the model and the pin filed down until they accurately fit the bite. That this shortening should be carefully done is of some consequence, because when the tooth is put in position on its pin it can be seen at a glance how much of its length may be safely ground away in fitting. The teeth are then placed on the pins, and if the latter should have tilted in soldering, it will be at once seen, and may be corrected by grasping the pin close to the plate and bending as required. Now comes the fine fitting of the teeth, done best with small wheels : Paint is placed upon the plate where the tooth will touch it, and the latter is pressed gently to place : when removed it will I^'JG. 511. show a small red mark where it is too long 0and needs grinding off: having used the |*n| I™! countersinker and tube-file, the' tooth is to \J ^'^ be tried on its pin again, and this process I I I of alternate trying on and grinding is to el, Jl -^ "*^ be repeated until a perfect fit is obtained. ^^ It is well in fitting to the plate to remem- ^^^^^=^-^ ^ ber the bite ; otherwise the operator will . ,. , ^ ^, find, to his annoyance, after havinp- care- Plate and pms, with little teeth r> n r«,, t ,i , ,i ,i , ,• i ,• ready for fixing. lully fitted the tootii, that ou articulating it is too short. The coronal surfaces of the teeth are now to be ground to suit the occlusion of the bite, using the vermilion paint to ascertain points of undue contact. Next the cuspid and first bicuspid on the right side are set and finished, the first bicuspid on each side serving as a guide : the pins for the remaining teeth may be inserted at one soldering. Fig. 511. Let us presume that all the teeth have been fitted to the plate and to the bite : their ground edges should then be lightly touched against the side of a very fine corundum or Arkansas wheel in the direc- tion opposite to its motion. The teeth are then polished, and the coronal ends of the pins are finished to show a rounded end or ground to the bite according to the requirements of the case. This done, the plate is finished in the usual manner. Previous to fixing the teeth a few shallow cuts are made in each pin with a fine file. When the teeth have been properly cleaned and freed from all traces of oil — which can be done by boiling them for a few minutes in a strong solution of soda — their tubes are dried by cotton wound round a broach and their interiors roughened by a clean tube-file. Fig. 512 is a good representation of how the tubes are filled with sulphur. This material is melted in the small porcelain Ber- lin cup marked A, until it is quite fluid, and is kept in this condition and held by an assistant. The operator himself grasps the plate firmly ENGLISH TUBE TEETH. 435 with the pliers (Fig. 512) in the left hand and heats the whole carefully over the lamp. This must be done gradually, and the flame ought not to play on the porcelain. In the right hand he takes the wire spatula Fig. 512. Mode of grasping plate in finally fixing teeth. -B (Fig. 512), and, dipping it in the molten sulphur, conveys it to the heated plate and teeth repeatedly till a surplus begins to show itself. The sulphur runs by capillary attraction under the teeth and along their pins, and when the whole has cooled it sets hard and the teeth are im- movable. The excess of sulphur may be removed with a fine-pointed knife ; the plate is then ready for the final polishing. This description of the method of fitting tube teeth applies in every particular to all cases, whether they be partial or full, upper or lower. Different methods of setting tube teeth are doubtless practised by dif- ferent workmen, but it is believed that the modus operandi herein described is as simple and effective as any. Besides the ordinary tube teeth, single gum teeth of this kind are to be had, and they prove as satisfactory, Avhen judiciously used, as teeth with flat backs. Perhaps it may not be -out of place to indicate here the style of case which will prove most suitable to the use of tubes. Mouths where all the masticators have been lost and the front teeth alone remain are very favorable cases for tube teeth. Again, where alternate teeth are missing they answer admirably. They are, however, not well suited for vulcanite work, because from the weakness of the rubber which radiates from the margin of the plate such dentures would be liable to break under the force of mastication. But if a gold plate and tube teeth be constructed for such a case, the ease with wiiich it can be repaired is greatly in favor of its selection ; and should the inter- mediate natural teeth be lost in course of time, other tube teeth can -easily be added to the old plate to replace them. 436 ENGLISH TUBE TEETH, ETC. English Tube Crowns. In this country during recent years attention has occasionally been called to English tube teeth in crown-work, although no details of their application have been given. This branch of practice, however, is com- mon enough in England, although the usual method of fitting the tooth to a model, fixing pin and tooth together, and finally cementing them upon the root, is open to many objections — among others, loss of time incurred in taking the model and bite and want of accuracy in fitting. An improvement in setting tube crowns has been made by Mr. John Stewart, L. D. S., of Edinburgh. The method is as follows : The root Fig. 513. Single root pin, with post for tube crown. Bifid root pins, with posts for tube crowns. is prepared in the usual manner. If part of it remain above the level of the gum, the rubber dam is applied to one tooth on each side before excising, having first ansesthetized the gum by painting on a 20 per cent, solution of cocaine. A ligature is used in preference to a clamp for fixing the rubber, because the latter interferes with the bite when the pin comes to be adjusted. The rubber dam is pushed up as far as possible on the lingual and labial or buccal aspect of the root, for the reason that thi& kind of crown, being bandless, requires to have its weak point, the union of root and crown, covered by the gum when the dam is taken off. The canal is then enlarged with a twist drill a size larger than the diameter of the wire to be used as a post. If, as often happens in the first bicus- pid, the canal be bifid, a piece of wire may be bent, as in Fig. 513, ta fit into each canal, and to it the straight post should be soldered ; or the straight pin may be "kneed," as in Fig. 514, and an additional "leg'' soldered to it. Both ways are practicable, provided the soldering be done securely. The post may be made of gold, platinum, or English dental alloy. The post, where possible, should have a fine shallow thread cut on it, except where it emerges from the root to enter the crown. This part is the weakest, and its strength should not be impaired even by a screw-thread. Having selected a suitable tooth, it is fitted roughly to the root before applying the rubber dam. On ascertaining that it fits fairly well, the pin is placed in the root and tried on the crown : if it be much out of line with the other teeth, its position must be corrected, either by bend- ing the pin at the junction of root and crown, or by reaming the canal in the direction necessary, or by a combination of both operations. The tooth and the pin are then triecl on once more : if everything is right, the walls of the canal are grooved with a wheel burr ; mix the cement, and, placing a little oxyphosphate cement in the canal and around the pin, the latter is forced to its place with the pliers (Fig. 504). While the ENGLISH TUBE CROWNS. 437 cement is still soft the base of the crown is slightly oiled and slipped on to the pin to ensure its correct position before the cement sets. It should be held in place until the cement sets. Then, having taken oif the crown, the surplus cement is to be trimmed from the end of the root. This part of the root may, if thought desirable, be cut out around the post and filled with gold or amalgam. This, however, is not necessary except in cases where the root has been much weakened by decay. The bite Avill at this point claim attention. The patient is directed to close the teeth, and the post is ground down until it ceases to interfere with complete closure. When no clamp is used, the rubber dam will not interfere to any extent with this part of the work. The tooth is now fitted to the root, as would be done on a plate, but instead of using vermilion paint for fine fitting, a small disk of the thinnest articulating paper, in the centre of which a hole must be made with the rubber-dam punch, is slipped over the pin to the face of the root. The tooth is then pressed to place and ground oflP where it is marked until a perfect fit is obtained. The articulation is then carefully adjusted. The cervi- cal margin is examined, and if the crown overlap the root, the excess of porcelain is to be removed until the sides of root and crown are continu- ous. Previous to setting, the base of the crown should be hollowed out, care being taken to avoid the edges : this provides for the presence of a body of cement between the root and the crown, as in the Logan and other crowns. The tube is to be thoroughly cleaned out and roughened in its interior, as in plate-work, and fastened to the pin and root with cement, pressing it firmly to place with a Bonwill crown-setter. The head of the pin may be riveted with an engine-burnisher, and the bite should be examined before the patient leaves. The shaping of the root is a matter of choice. The two which have found most favor are the well-known '-new Richmond" (Fig. 515) and Fig. 515. Fig. 516. New Richmond. Ordinary saddle-shaped. the "saddle" (Fig. 516) shapes. The crown to suit the former may be fitted by hand with a three-sided corundum file. Many suggestions have been made regarding the posts and pins : some operators prefer that they be made of square or oval forms of wire, in order to prevent rotation ; but if the roots have been properly pre- pared, rotation cannot possibly take place unless the crown first becomes loose — an accident which in practice rarely occurs. Besides being un- necessary, square or oval pins are a positive drawback, and they greatly limit the usefulness of this form of crowns. They demand, in the first place, an unnecessary enlarging of the canal, and consequently weaken the root, and as posts they possess less strength than do round ones ; and it is sometimes found that after the pin has been set the direction 438 ENGLISH TUBE TEETH, ETC. of the crown is not all that could be desired, or that either the mesial or distal corner stands a little out of line. Where a square or oval post has been used this cannot be corrected, except by the removal and read- justment of the post ; whereas when it is round the crown can be turned on its axis in any direction required at any stage of the fitting. For these reasons round posts are generally superior in this class of work to all other forms. Tube Crowns on Metallic Caps. If, for any reason, it is considered advantageous to protect the sur- face of the root by means of a metallic cap and band, the rubber dam must be dispensed with. The root is trimmed, the sides made parallel, and after fitting a collar to it, leaving the gold a trifle high, the canal is prepared and a post loosely inserted into it. A plaster impression and bite of the whole is then taken. The pin and band will generally come away with the impression, or, should they not do so, they can be easily removed from the root and replaced in the plaster. After running the model, a coin-gold cap. No. 30 thickness, is fitted and soldered to the band : through it a hole is drilled for the pin ; it is then placed on the Fig. 517. Fig. 518. Elevation showing blackened bicuspid. Fiepared root. model, the pin is inserted and its direction corrected by bending before soldering to the cap. The pin may be easily bent if nicked with a file, and, as any weakness caused thereby is repaired by the soldering, it in no way imperils the soundness of the post. Having boiled in pickle, the assembled pin, cap, and band are returned to the plaster model, and the crown is fitted as previously described. This done, it is cemented to cap and pin before inserting them in the mouth. This makes a strong and beautiful crown, and, while it is especially applicable to single-rooted teeth, it may also be occasionally employed on some molar roots. Tube Crowns on Living Teeth. It is seldom that tube teeth can be used for this purpose, but Dr. Girdwood reports two cases which he treated with gratifying success. Fig. 517 is the first of these, and represents a lower left first bicuspid, which had a large amalgam filling, extending to the crown, on each of its proximal surfaces. The tooth was much discolored, and by its presence the appearance of an otherwise good set of teeth was spoiled. The patient objected to the extirpation of the pulp. The bite was close, yet the teeth showed considerably. An all-gold crown would have been too conspicuous, a porcelain-faced one worthlessly ENGLISH TUBE TEETH IN BRIDGE-WORK. 439 Fin. '^^^-^2:^^'^^ weak. Therefore, it was decided to grind down the buccal aspect of the root nearly to the gum margin (Fig. 518), leaving the lingual side considerably higher. A cap and band were made to fit the root tightly and to pass a short distance under the gum : a pin was soldered to this and a tube tooth adjusted to it and the bite, and the whole cemented (Fig. 519) on the living root. The buccal side of the 22-carat gold band is almost covered by the gum, and what is seen of it looks like a small cervical filling. The second case reported by Dr. Girdwood does not differ essentially from the first, except that the bite is somewhat closer and the crown, if anything, more severely tested. Elevation showing bicuspid tooth. English Tube Teeth in Bridge-work. As is well known, one of the greatest objections to ordinary bridge- work consists in the difficulty met with in concealing the gold so as not to be seen when the patient talks or laughs. By the use of English tube teeth it is claimed that this objection may be entirely obviated. Fig. 520. Model for removable bridge. For fixed bridges replacing the front teeth tube teeth are less suitable, because of the difficulty encountered in securing proper self-cleansing spaces, the sine qua non of the perfect bridge. The case shown in Fig. 520, where the cuspids are past filling and the molars still stand, will serve to explain the manner of constructing a large removable plate bridge with tube teeth. The crowns of the cus- pids are to be cut level with the gum, and the roots prepared after the usual fashion : the canals are to be drilled to receive a gold or platinum 440 ENGLISH TUBE TEETH, ETC. tube, which should be as long as possible and sufficiently wide to accom- modate a No. 13 post of hard gold. The molars are next trimmed to receive gold crowns, and a considerable notch is cut in the crown and anterior proximal surface of each. This notch (the object of which will be presently explained) should not extend on the coronal surface more than halfway back, nor on the anterior aspect more than halfway from the crown to the gum. Tubes are then placed in the roots of the cuspids and allowed to project about three-eighths of an inch. An impression of the mouth is next taken in plaster, in which the tubes will come away, and it is run out and opened as usual. The plaster teeth and roots are now trimmed, so that the cuspid caps and molar crowns when made will pass a little way beneath the gum margin. The pattern of cap and band for the cuspid is the " Richmond," and care should be taken that each is made level with the gum on the labial side (Fig. 521). Hard gold or platinum tubes are next soldered to them in lieu of the ordinary posts of single " Richmond " crowns. The fixing of these with cement in their proper positions, and the operation of sealing the apical Fig. 521. Fig. 522. Cap, Vjaud, and tube soldered. t^tiuck crown for molar. ends with gold or amalgam, complete the preparation of the roots. They are then ready to receive their posts (Fig. 5:^1). A " Mellotte '_' die of each molar is then taken and a gold collar made to fit it. This collar is notched on its anterior surface (Fig. 523) to suit the corresponding de- pression on the same surface of the natural tooth ; the band is put on the Fig. 523. Fig. 524. Band for molar. Pure gold cap. "Mellotte" cast and a piece of No. 30 pure gold (Fig. 524) is placed over the crown and burnished to fit its upper surface and the floor of the notch referred to. When this is soldered to the collar it gives an all-gold crown without cusps. A pure-gold cap is next struck up and filled in with coin gold : it is ground level on its under surface, and is in turn notched at the same part as the gold crown already made. Having adjusted it to the latter, they are soldered together, and an ordinary all-gold crown is the result, plus the recess on the crown and anterior surface (Figs. 522 and 526). These crowns are cemented upon their respective teeth. Posts with bent ends are now placed in the cuspid tubes and allowed to project from ENGLISH TUBE TEETH IN BBIDGE-WOBK. 441 them about three-eighths of an inch or more. A plaster impression of the whole is now to be taken, and the pins will come away in it if the direction of the cuspid tubes has been carefully considered. Before casting the imjDression a small piece of metal tubing of such a size as will exactly fit the posts is slipped over each : this will prevent any alteration in their direction when they have to be withdrawn and replaced in their sockets during the making of the bridge. Having cast, opened, and hardened the model, the next procedure is to make the clasps for the fixed molar crowns, as follows : First, take a ^' Mellotte " die of each tooth and cut a pattern as in Fig. 525, being careful to leave a portion of it (i?) high enough above the level of the tooth to permit of its being bent down and accurately fitted into the notch. The clasp is next fitted to the tooth, and the portion (B) is thinned down with a file and punched till it fits into the depression as Fig. 525. Fig. 526. Portion of band pattern. Molar crown, notched and completed. just indicated. It is now strengthened and contoured to the normal shape of the crown by the addition of pieces of hard gold soldered to- gether with 21 -carat solder. This forms a strong partial cap or spur, which, bearing on the gold crown, prevents the bridge settling too hard upon the gum. It is better to make the band and spur from one piece of metal, as shown in Fig. 525, than to solder the spur to the band when fitted, for by the former way the continuity of the metal is unbroken. Plan showing bridge-plate The clasp must be prolonged posteriorly to grasp the distal surface of the crown, in order that any tendency on the part of the tooth to back- ward movement by pressure on the spur — which will thus act as an in- clined plane — may be prevented (Fig. 527). 442 ENGLISH TUBE TEETH, ETC. The next step is the swaging of the plate, which is made of two thick- nesses of metal, the first being made of No. 24 gauge ^ and about five- eighths of an inch wide all round. It must be stuck up sharply and made to cover the cuspid caps. Next a piece of plate. No. 26 gauge, and a trifle narrower than the first, is swaged over the latter. When fitted the two are soldered together with 21-carat gold solder. The thick single plate thus produced is trimmed to the shape shown in Fig. 456. After having seen that the plate fits, it is drilled through opposite each cuspid tube to receive the posts, which are introduced into the tubes and allowed to project through the drill holes on the lingual surface. The clasps are then adjusted, and a little plaster placed around them and the cuspid posts. When it is hardened the various parts are removed from the model and fixed in their respective places : they are then invested and soldered with 20-carat solder. If the cuspid tube-tooth posts be thicker than the size of pin wire, they are to be reduced by the file to suit the porcelain teeth. The teeth are now adjusted as described in their plate application, the finished piece is shown in Fig. 528. Modification of this method can be used in the construction of any removable tube-tooth bridge. The point to be especially noted is the treatment of the molars, a plan which can be adapted to suit any of the Fig. 528. Side view of teeth on bridge-plate. posterior teeth. It most surely prevents the " settling " of the denture and the tendency to movement on the part of the natural teeth. Fixed Bridge-work. Fixed bridge-work offers but a limited scope to English tube teeth, for they can, as a rule, be used as substitutes for the masticating teeth only, or, at most, behind the laterals. As already mentioned, the obstacle to their utilization in restoring the front teeth is the much-discussed self- cleansing space, which cannot readily be gotten by any all-porcelain crowns, for reasons which render useless the adaptation of Logan, Bon- will, and other crowns to like purposes. The idea must not be formed, however, that the tube teeth can never be used here ; but, on account of the shape of a front tooth which necessitates a short and weak lingual surface, often to be further destroyed to accommodate the bite, it is in- advisable to use them except in the few cases where the bite of the lower ^ English gauge. FIXED BRIDGE-WORK. 44;^ teeth strikes abnormally far in. Here they may safely be applied. Fig. 529 represents the kind of case in which a fixed bridge with English tube teeth answers admirably. The gap in the dental arch extends from the Fig. 529. Mould for fixed bridge. third molar to the first bicuspid. The first bicuspid is banded and capped^ and a pin which acts as a post both to the root and tube crown is soldered through it (Fig. 530). A gold crown is fitted to the third molar, and a Fig. 530. Posts trimmed. strong ovai-shaped 22-carat gold bar, which will connect the crown and cap, and ultimately carry the teeth, is made. This bar ought not to rest on the alveolar ridge, but must be about one-sixteenth of an inch from it, and its angle with the alveolar border ought to be as represented in the section shown (Fig. 532, A-B). Such a slope down- ward from the lingual to the labial side will secure a perfect self-cleans- ing space. The anterior end of the bar must now be soldered, not only to the bicuspid cap, but to the base of the post itself, so that the strain may be borne by both (Fig. 531). So far, then, the bar and bicuspid cap are in one piece, the molar crown remaining un- attached. These are to be placed in their relative position in the mouth, and any adjusting made that may be necessary between the molar crown and the posterior end of the bar : they are then taken off with plaster, as described in this operation in Bridge with teeth ready for fixing. 444 ENGLISH TUBE TEETH, ETC. Fig. 532. plate bridge, and soldered. A bite must then be taken, and the teeth set up on the bar in the usual way, being fitted to it and allowed to over- hang its buccal edge, as represented in the section (Fig. 532). When the teeth have been cemented to place with sulphur, the bridge should be fixed temporarily in the mouth until it has proved satisfactory, when it may be permanently fastened. A fixed bridge like this may be in- serted on either side of either jaw, and modified to suit such exigencies as intermediate roots, etc. It must not be concluded that the possibilities of tube-work have by any means been exhausted in the descriptions herein given. Their uses seem to be limited by faults in construction of the front teeth, previously mentioned, and shown in Fig. 498, A. A porcelain crown has lately been made which is almost identical with the tube tooth herein described (Fig. 533). Speaking of this special crown, Dr. John Gird wood says : "It is made to replace front teeth and bicuspids. The bicuspids are well designed but as much cannot be said for the fronts, for, although the posi- tion of the tube has been corrected, the crown is still com- paratively worthless, on account of its needlessly weak lingual wall, further undermined in many cases by a too much countersunk base. Because of these, to me, very serious defects, I have never used the new crowns, so I do not on this point speak from experience. Despite their in- troduction, an improved tube tooth is called for." A point of great moment to the tube-worker is the alloys of gold for posts. In plate-work these are made by Eng- lish dentists about 18 carats fine. This comparatively poor grade of metal is good enough for plate-work, but in crown- and bridge- work something finer is required. The qualities most to be desired are toughness and non-liability to tarnish, and these can be secured by alloying coin gold with from 1| to 2 pennyweights of platinum to the ounce : this makes an excellent alloy for all pins, posts, plates, and bars. It is so infusible that it may safely be soldered with coin gold 22 carats fine. The use of sulphur as an agent for fixing teeth on plates and bridges has long been practised by English dentists, and the question of prefer- ence between it and the oxyphosphate cements has been widely discussed by them. Its advocates claim that, except in crowns and other situations where it cannot, from its very nature, be employed, sulphur is much the bet- ter of the two materials ; which will stand in mouths where from the cha- racter of the oral secretion the cements undergo rapid solution, and that none of the oral fluids destroy sulphur. It certainly has the advantage when re- pairs have to be done. Where cement has been the fixing medium the teeth can only be removed with great force — obviously a very unsafe proceeding. Indeed, if the pin and tube have been well roughened, the teeth cannot be, in many cases, gotten oif without fracturing them. By the use of sulphur, however, all this Fig. 533. Side. Ash's new tube crowns. FIXED BRIDGE-WORK. 445 trouble is prevented, for when the plate comes to be repaired it has only to be heated carefidly and gradually until the sulphur melts, when the teeth may be easily lifted from their pins and refixed when the repair is effected. Objection is sometimes made to the appearance of the pins on the coronal surface of tube teeth. This objection may be overcome by cutting as much off the pin as is thought necessary, without impairing its func- tion as a support to the tooth; then cut a piece from a white glass or porcelain rod of proper size in the tube over the pin. This ought to be done before the teeth are finally fixed, so that the section of glass or porcelain will be firmly held by the sulphur. When finished the most critical observer will hardly detect any break in the color of the crowns if the inlays have been well matched. CHAPTER XIII. CONTINUOUS-GUM DENTURES. By Ambler Tees, D. D. S. The variety of artificial denture known as continuous gum consists of a base-plate of platinum, to which plain teeth are first attached by means of solder, the contours of the natural gum and palatal vault being formed of a porcelain body fusing at a lower temperature than the com- ponents of the artificial teeth, over which an enamel closely resembling the gum color is subsequently fused. Our present conceptions of the work and the methods of its con- struction are due to the late Dr. John Allen of New York. The prin- ciples involved have their authorship traceable to the dental fraternity in France, although their experiments and methods were crude compared with those of Dr. Allen. In 1815, M. de Chemant obtained a patent for the manufacture of porcelain or " incorruptible mineral teeth." The denture was constructed in one piece ; the coloring, to imitate the natural gum, was applied by means of brushes subsequent to the vitrification of the piece. The pig- ments employed were destructible by the secretions and fluids of the mouth. In 1818, MM. de Fouze and Delabarre applied jeweller's enamel to the purposes of gum restoration : this was found to crack and flake from the plate. M. Delabarre then conceived the plan of using individual teeth and surrounding them by a porcelain the fusing-point of which was lower than that of the teeth. His experiments were partially suc- cessful, but attracted scant attention, and the manufacture of continuous- gum dentures languished until 1846, when Dr. Allen compounded a porcelain body, now in use, for which he obtained a patent in 1851. We are indebted to him not alone for the formulae themselves, but for methods of design and construction. He first demonstrated the feasi- bility of restoring lost facial contour. In comparing the several features of this variety of artificial dentures with those constructed upon other bases, what have been deemed supe- rior virtues have been claimed for it, and certain disadvantages arrayed against it. It is the most cleanly of all artificial dentures ; its plate-base, com- posed of pure platinum, is entirely uninfluenced by ordinary chemical agencies. There are no interstices in which food debris or secretions may find lodgement and become offensive through subsequent decompo- sition. Worn for a score of years, the piece when scrubbed is practically as clean as when it came from the furnace. Any configuration may be given the porcelain body, so that the ope- rator may at will restore* to a degree limited only by his taste and skill 446 CONTINUOUS-GUM DENTURES. Ml any loss of gum or palatal contour. When the palatal aspect of the piece is exposed, its artificiality is not noted, as with dentures constructed upon other bases. The objections urged against it are, first, its great weight as com- pared with other artificial dentures. This objection is found to be more apparent than real, for a patient rarely complains of the weight of a properly adapted continuous-gum denture. Second, it is asserted that the inevitable contraction of the porcelain body causes more or less change of form of the platinum base-plate. Faults in this direction are largely traceable to lack of skill upon the part of the operator : with increased familiarity with this class of work difficulties in the direction named diminish. The next objection is the liability to fracture : certainly increased care upon the part of the wearer is necessary to avert accidents with a porcelain piece. Fracture occurs usually while the patient is washing the piece : if the precaution is taken to place a folded towel in the bot- tom of a basin of water and wash the denture while held over the basin, or to use a paper basin, it may drop then without fracturing. Breakage while in actual use very rarely occurs. In 95 per cent, of cases of repair the cause of breakage is that first noted, carelessness in handling by the patient. The writer has seen continuous-gum dentures after twenty-five years of use as perfect and beautiful as the day they were inserted. One reason adduced for their limited employment has been, the annoy- ance and difficulty in the operations of attaching the porcelain and enamel. These objections are now largely removed through the im- proved forms of furnaces employed : with these the work will be found a pleasure. They also remove another heretofore objection — the difficulty and expense of repairing a denture in case of fracture. The electric oven of Dr. Custer makes the operation of repairing continuous gum a mere trifle. When upper and lower dentures of continuous gum are worn, it is common to find the teeth produce a clicking sound when occluding. The writer has attributed this to faulty adaptation of the lower piece. The intense heat to which a plate is subjected in fusing the porcelain body upon it causes a change of form to the horseshoe-shaped piece of the lower plate, and upon the completion of the operation the two plates are not uniformly supported by their cushions, the alveolar arches. This warpage may be prevented by a means to be described later. This fault is common to all full artificial dentures, upon whatever base they may be mounted, if the same faults of adaptation obtain. To prevent the clicking Dr. John Meyer has suggested that metallic fillings be placed in the articulating faces of the molars. The term " continuous gum " applies to all pieces in which the arti- ficial gums and teeth are so attached as to form one piece, no matter of what material the base-plate may be constructed ; for example, the portion of an artificial denture composing gums and teeth may be made in an arch of porcelain, and this subsequently mounted upon a plate of vulcanite. Continuous gum is, as a rule, employed alone for full cases, either upper or lower. It is quite possible to construct a partial piece of this material when the teeth to be replaced are in a large and continuous column. Occasionally pieces have been made, and comfortably worn, where the restoration embraced the posterior inferior teeth of both sides. 448 CON TIN UO US-G UM DENTURES. The Impression. The physical properties of plaster of Paris recommend it above all other impression materials, although some operators prefer wax or modelling compound for taking the impression of cases which exhibit uneven density of the tissues of the palatal vault. (See Chapter VIII.) The model is made as for any case in which dies are to be formed. The advisability of a vacuum chamber is a much-mooted question. In cases which exhibit a moderately deep and symmetrical vault a satis- factory adhesion may be secured without the chamber, though a greater adhesion is had where the chamber is employed (Figs. 534 and 535). Fig. 534. Showing form of arch where chamber may not be necessary. The chamber-piece is formed and applied as described in Chapter IX. The plate outline is marked as described in the same chapter : whether for upper or lower case, it must be at such a line, free from im- pingement upon the movable tissues, as shall ensure against future trimming of the plate edge. A layer of wax about one-eighth of an inch or more thick is built upon the wall of the model as shown in Fig. 535. It is carved to meet the plate line at a sharp angle and as acute as may be consistent with accurate moulding. The wax should exhibit a flat shelf-like surface, which when reproduced in the die, serves to form the upper rim. Special care is necessary in forming the wax for lower dentures, as these plates, owing to a tendency to bury in the gum, are Fig. 535. Cast of the upper jaw, with ledge for turning the rim. carried beyond the original plate outline after being worn for a period. In addition the crest of the ridge in lower cases should receive a film of FORMING THE PLATE. 449 wax to compensate for any bruising of the die. The wax wall in lower cases is made continuous, along the entire plate outline, inside and outside. Across the posterior plate outline for upper cases a wax wall about one-eighth of an inch thick is placed, making the line of junction between the wax and model sharp and distinct : this wax is to join that upon the alveolar line, uniting as the lines pass behind the condyles. When the tissues of the palatal vault at the site of the posterior edge of the plate are soft, it is usual to terminate the plate at its heel, with- out raising a rim : the latter is then to be formed as described later. The model is now varnished preparatory to moulding. Matrices are prepared, dies and counter-dies made, as described in Chapter X., using the Hawes flask or cores where and when necessary. Forming the Plate. The best specimens of platinum for continuous-gum work are those prepared in France. Patterns are made of heavy tin-foil (Chapter XL), allowing a sur- plus, in the event of the plate shifting position slightly in the die, or to more readily prevent wrinkling of the plate edge. The pattern is repro- duced in No. 29 platinum for upper plates. For lower plates two laminae of metal No. 29 are employed, one large enough to form its borders into a rim, the second, which is to be superimposed, extending to the angle of the rim. In partial lower cases the body of the plate is to be of No. 29, and to have a supplementary piece of iridio-platinum. No. 26, extending across the lingual wall of the plate behind the natural teeth, and to about one-fourth of an inch beyond the posterior molars. The platinum is well annealed. The surface of the die is covered with wet muslin, to prevent contact of the platinum with tlie zinc, and the annealed plate pressed against the surface of the die by the pressure of the ball of the thumb. The plate annealed, the pressure is resumed. The adaptation is now improved by means of the horn mallet, reanneal- ing the plate as soon as it becomes obdurate. If the operator prefers, he may now employ a partial counter-die to secure primary adaptation of the plate to the vault. The precaution should always be observed of interposing between the surfaces of the plate and those of the die or counter-die a layer of thin wet paper or muslin. Without this medium small particles of zinc or lead may attach themselves to the surface of the platinum, and when the latter is heated the base metal forms an alloy with the portion of the plate upon which it rests. These alloys are very fusible and contaminate the sur- face, or they may perforate the plate. Indeed, it is well to drop the platinum in hot nitric acid as soon as it is removed from contact with the die or counter-die. The partial counter-die set in position, and tapped until the vault por- tions of the plate are in apposition with the die. Removed from the die, the plate is reannealed ; the same care exercised to prevent contact of the platinum with the base metals ; and the horn mallet is employed to adapt the plate over the alveolar walls. Should wrinkles develop, at the incip- iency of their formation the plate is reannealed, and they are removed by 29 450 CONTINUOUS-GUM DENTURES. means of the mallet. When the adaptation is fairly accurate the plate is set in the counter-die, beneath and over it a layer of wet muslin : the die is placed in position and the plate is swaged. It is reannealed and reswaged until the adaptation to the die is complete. The surplus plate is cut away by means of shears and files. Should the plate crack or split at any point, a piece of thin platinum is laid over the break and soldered to the plate by means of pure gold. This is the solder always employed with platinum for continuous-gum work. Alloys of gold, as the ordinary solders, containing base metals, exercise a deleterious influ- ence upon the coloring matter of continuous gum. The imion of plati- num through the medium of pure gold as solder is much stronger than were alloys of gold employed. Vacuum chambers in platinum base-plates are formed in the plate itself, not soldered to it, as with gold plates. The great heat of the fur- nace, required to fuse the porcelain, causes wide diffusion of even pure gold through the platinum, so that the minimum of solder is to be applied in this work. If a second die has been made, the plate is now transferred to it — always a layer of wet tissue-paper interposed, another layer over the plate — the counter-die set in position, and the swaging is completed. The plate is then well annealed. If a lower plate, the second or strengthening piece is swaged and trimmed, leaving a square edge extending to near the angle of the rim. If a partial lower plate, the supplementary piece of metal is adapted, annealed, reannealed, and swaged until it tits the die perfectly and exhibits no tendency toward alteration of form when heated to a bright red. The upper lingual border of such cases is carried about one-six- teenth of an inch above the plate line. The pieces are held together by means of binding wire and soldered with pure gold. The plate, thoroughly annealed, is now bound firmly to the die with wire, and by means of pliers and a light hammer the excess of plate extending above the strengthening piece at the lingual aspects of the teeth, is bent over, forming a slight rim not more than one-sixteenth of an inch broad. After the swaging is completed all base-plates for con- tinuous gum should be annealed at a very high temperature. The adaptation of the plate to the deepest portions of the die is secured through the use of chasers. These are formed of old tooth- brush handles filed to a wedge-shaped edge. Instead of forming a posterior rim by turning over that portion of the plate, some operators prefer ^ adding to the plate a combination of wire and an addition of plate which shall serve as a limiting shoulder to the porcelain : sloping from the latter there is a ledge of platinum which may, by altering its form, increase or diminish at the will of the ope- rator the pressure of that portion of the denture. Aside from the removal of the abrupt termination of the plate, the added heel subserves another purpose — that of lessening the tendency of the plate to suffer alteration of form when subjected to the great heat of the furnace. The addition is made after the following method : Round plati- num wire of No. 19 gauge is bent to fit the plate along a line extending from the alveolar edge of one side to that of the other, and about three- 1 Method of Dr. D. D. Smith. FORMING THE PLATE. 451 sixteenths of an inch from the posterior edge of the plate. It is first attached on its middle by means of a small piece of 24-carat gold. The adaptation of the remainder of the wire is perfected, and it is attached throughout its length. A piece of platinum plate No. 29, wide enough to cover the wire and the posterior edge of the plate, and extending the entire length of the wire, is annealed and swaged. It is better to lightly swage the plate with the wire attached before swaging the supplementary piece. As soon as the outlines of the wire are distinctly marked in the counter-die, the groove made in the lead is deepened by means of a chisel. The piece of plate is annealed, laid in position in the counter-die, and swaged. Reannealed, it is again placed in the counter-die, the plate over it, and they are swaged together. The same precaution is taken to prevent the contact of the die and counter-die metals as in swaging the plate proper. The plate extending over the wire and the posterior edge of the plate is cut away until it is flush with the latter and half covers the wire (Fig. 536). Fig. 536. Showing piece of plate to be soldered over and back of the wire, and the same in place on the plate. The sections are bound together, 24-carat gold placed in front of the wire, and heat applied, drawing the solder under the wire and plate addition. The posterior edge is now smoothed and rounded. The plate is next boiled in a 1:3 solution of sulphuric acid ; then, washed with strong soap, is ready for trial in the mouth and securing of the articulation. It is applied to the plaster model first, to ascertain that its adaptation is correct : if found to be accurate here, it is transferred to the mouth and the patient directed to draw it to position. Should the adhesion be imperfect, a partial adhesion which lessens, the sound of air entering beneath the plate being distinctly audible in some cases, it is first ascer- tained that the plate is of the proper length — that it does not impinge upon the tissues affected by the movements of the muscles of the soft palate. Should this be found, the disturbing element, the plate, is cut away the proper amount. Another source of imperfect adhesion will be found in a lack of 452 CONTINUOUS-GUM DENTURES. accuracy of the adaptation of the plate about the chamber. A sharp edge-graver is passed around the chamber-piece of the die, and a chaser employed to drive the plate into the angle at the base of the chamber. Occasionally minute perforations may exist in this groove, so that the precaution is taken to partially fill the groove with melted wax. Should the adhesion be not yet satisfactory, an examination is made to locate, if there be any, hard areas, upon which the plate may be arrested : if none are found and (if present they should have been seen and allowance made for them in forming the model), it is inferred that the impression itself is inaccurate, so that a new impression may be necessary. Should the adhesion be found correct, it is advised by some operators to exercise pressure by means of an excavator at all parts of the plate, and if unusual yielding of the underlying tissues be found in defined areas, the corresponding areas of the die are scraped away and the plate reswaged, until by trial of the plate in the mouth it is found the bearing is uniform. In the majority of cases a plate so adapted to an accurate model that it does not rock when alternating pressure is applied along its crest will require no alterations. These when necessary are to be made by means of burnishers and swaging, never by bending, as the heating of the piece in the furnace neutralizes changes made by bending, and renders them of no avail. Articulation. The wax-bite is taken as described in Chapter XII., the wax being built so that it restores the lost lip and cheek contour, the middle line of the face marked, and the length of the teeth represented in the length of the wax. The wax block, thoroughly chilled, is to have a layer of softened wax laid over its end, and the patient instructed to bite until the oppos- ing teeth are checked by coming in contact with the hardened contour Avax. A shade tooth is taken, always testing for correspondence in color by placing the tooth under the lip. Should any natural teeth remain, these are to furnish the guide as to the shapes and sizes of the artificial teeth ; if all the teeth are absent, the size, form, and color of the arti- ficial teeth are to be determined by the physiognomy, age, and tempera- ment of the patient. As this class of prosthesis represents the acme of dental art as far as plate dentures are concerned, this step of its con- struction must receive the attention its importance merits. A distinctive variety of tooth mould is designed for the forming of the teeth for continuous-gum work (Fig. 537). The teeth are made with long porcelain extensions corresponding with the roots ; they are designed to ensure the tooth resting upon the platinum plate, no matter what length may be required. Their pins are single, placed beneath the shoul- der ; they are designed to limit the extent of the artificial gum, and are sufficiently long to serve to hold the tooth to its future backing. When the teeth are to be unusually short, teeth designed for mounting upon celluloid or vulcanite may be employed. The teeth are selected the proper shape, shade, and size, being long enough to extend from the plate to the length marked on the wax, which length has been noted by scratching the model with a pair of dividers. In selecting the teeth the operator may at will follow any individual ARTICULATION. 453 indications of the case in hand : the cuspids may be selected more yellow than the incisors ; the shade of a bicuspid may be different from that of the adjacent teeth, etc. Fig. 537. Teeth for continuous-gum dentures. If the models are mounted upon the common hinged articulator, its set-screw is placed at its proper length. If a Bonwill articulator be employed, the posterior portions of the wax are permitted to remain until the anterior teeth have been articulated and arranged. Any irregularities in the positions of the teeth known to have been present with the natural organs may be reproduced in the artificial teeth. Occasionally the positions and arrangement of the occluding teeth will form a valuable guide in this particular. The centrals are first set, the amount of grinding necessary to bring the cutting edges of the teeth at their proper lengths, with the artificial roots resting firmly upon the plate, noted and done. The remaining teeth are set to accurate v.~' y^\-,^^ / .vi^%:-iv|r >^: ; SIDE VIEW, DISPLAYING THESE DEFECTS. 577 Fto. 716. found such as shown in Fig. 715. Here is a well-developed inferior dental arch, with proportionately well-developed teeth, characteristic of one parent, while in the superior dental arch the teeth resemble those possessed by the other parent, and are too small in proportion to the size of the jaw. The result is interspaces between nearly all of the teeth in the superior dental arch. Fig. 716 is a side view, displaying these defects, the cusps of the superior falling in between those of the inferior teeth. The few preceding cuts serve to illustrate how well zylonite or celluloid is adapted to meet the requirements as a base for artificial dentures, and it must be admitted that, so far as experience has gone, this material in combination with single teeth and mounted on metal- lic lining has given as much satisfaction as any other base. No op- portunity of testing the zylonite under the microscope, as has been done with celluloid proper, has presented, but sufficient has been learned of its qualities to indicate that it is superior in every partic- ular as the two are now presented to the profession. The color is better, and always uniform : cel- luloid is not uniform in color, sometimes running into a very objectionable greenish tinge. By comparing the two it will be no- ticed that there is a translucency or depth to the surface of the zylonite not found on the celluloid, which has a thoroughly dead surface. The celluloid has a tendency to scale or disintegrate unless the blanks are very carefully selected. This is not the case with zylonite ; nor has any tendency to soften, or "wash out," from about the pins, as observed with celluloid. The zylonite company, having benefited by the experience of other manufacturers of this material, has attained an excellence in the manu- facture — first, of the dinitro-cellulose, which is so delicate a process ; secondly, in the perfect admixture of the necessary ingredients to make the compound, resulting in an article that is uniform under all vicis- situdes of weather, possessing great resiliency, beauty, and diminished inflammability. 37 CHAPTER Xyil. THE TEMPERAMENTS AND THE TEMPERAMENTAL CHA- RACTERISTICS OF THE TEETH IN RELATION TO DENTAL PROSTHESIS. By Alton Howard Thompson, D. D. S. " Temperament/' says Dr. D. H. Jacque/ " is a constitutional con- dition produced by the mixing in different ^proportions of various physi- cal elements. The functions of life are not performed in all persons with the same degree of force or rapidity. These diiferences are the results and indications of what is called temperament, the corpori habitus of the ancients. It is by the combination of these constitutional elements in various proportions that the body is tempered, the predominating element determining the prevailing temper or temperament, and the others the modifications which may be present. A particular temperament is the result of the preponderance of one of these elements over all the others. The ancients, assuming the possibility of these elements all being equal in a given case, were accustomed to speak of the temperamentum tem- peratum, the temperable, harmonious, or balanced temperament ; but it is scarcely to be conceived of a single instance in the human species in which there is perfect equilibrium in all parts, although near approach to this condition may be found. " It is evident that in an ultimate analysis the temperaments must be as numerous as the individuals of the human race — no two persons, probably, having precisely the same physical organization or the same proportion of each elemental ingredient of the compound structure in which each lives, moves, and has a being. '- It is essential for practical purposes, therefore, to reduce these numberless individual peculiarities to their simplest elements, and group together such persons as resemble each other in certain particulars or who have a similar organization. To this end writers on the subject have generally considered the temperaments under from three to five general heads, which are subdivided." The ancients first observed the differences of bodily action and func- tional activity which distinguish individuals, and four temperaments, founded on constitutional conditions, were recognized and described by Hippocrates. The temperaments, according to his theory, depended upon what were then known as the four primary components of the human body — the blood, the phlegm, the "yellow bile, and the black bile." Persons in whom the blood predominates, he said, have the sanguine tempera^nent ; if phlegm be in excess, the phlegmatic temp)era- ment ; if yellow bile, the choleric ; and if black is in excess, the melan- cholic temperament. This was the original classification, and has influ- enced writers and students more or less in all systems of description down to our own times. " The doctrines of Hippocrates and the ancient physicians were often ^ The Temperaments, etc., Dr. D. H. Jacque, Fowler & Wells, 1878, p. 30 et seq. 678 TEMPERAMENT. 579 discussed, but never greatly modified, until the advances in physiology and humoral pathology in comparatively recent times rendered their defects too obvious to be overlooked ; and even then the same classifica- tion and general nomenclature were generally adhered to. At a later date Dr. Gregory added to the four temperaments of the ancients a fifth, which he called the nervous temperament. The ancients, and the modern writers following them, were accustomed to look upon the tem- peraments from a merely physiological or pathological standpoint, and but little was said or known of the reciprocal influences of mental and physical qualities and states." Dr. Spurzheim's classification is that upon which later systems were founded: (1) the lymphatic; (2) the sanguine; (3) the bilious; and (4) the nervous temperaments, which are determined by the presence of the lymphatic, the sanguine, the bilious, or nervous elements. Some of these Dr. Jacque considers more or less pathological, three only being perfectly normal bodily conditions ; and two, the lymphatic and the ner- vous, are pathological or diseased. But they are none the less real, though being aberrant or unnatural. Such states of the constitution are far too common to be ignored, and must be taken into account. Dr. Jacque proposed a later classification (in which he eliminated the patho- logical and abnormal conditions) which he thought was simpler and more natural. He included under three heads all the various normal condi- tions. These he named — (1) The motive or mechanical system ; (2) The vital or nutritive system ; and (3) The mental or nervous system. These are divided into several branches, which include all the organs and dominate all the functions of the physical man " First, the bony framework bound together by ligaments and overlaid with bundles of muscular fibres, by means of which its parts are moved and locomotion produced ; second, the vital or nutritive system, whose principal masses lie in the chest and abdomen, and consist of the lymph- atics, blood-vessels, and glands performing the functions of digestion, secretion, circulation, etc ; and third, the mental or nervous system, having its principal seat in the cranium, but extending itself in ramifi- cations through every part of the body and furnishing the medium of sensation and volition." A classification may be adopted which will include these under the older headings, with the addition of the pathological temperaments, as he calls them, which are equally important and entitled to study and consideration. For a diagnosis of the temperaments it will be best to present their leading characteristics in tabulated form, for convenience of reference. The groupings of indications under various headings will facilitate the study of an individual under observation. The indications are those given by Spurzheim, amplified by Dr. Jacque's wise criticisms and learned observations. To this is added a table of Dr. Jacque's later system of classification, by way of illustration and comparison. After that a table of the ordinary combinations, and then tables of the temperamental characteristics of the teeth. 580 THE TEMPERAMENTS, ETC. TEMPERAMENT. 581 55 o 6 e g ^ ^f^ iT'q) -o c cS--^ ^-syi a) 03 g <" c^ "^-o ^§^ W E3 --a «g1 5^-§ U)o3 Nrt -O.^n >> ill tH O "^ fl •'-* ,ci o oj «§ '=^.2 03^. g H »* a> ojt: l>^ O 03 ^^^ (U o o g +^ . +^ 5^3 o •rt ftcd .st 02" .=) O O te -•s ^ •^ai+^;;q=l S 03+3 43 +i lOrS 0) S5 S s a o 'SJJ^ o ■fl« (D OS fl ggs flex's o g 0) .03 '2"S'2 fee's a fl 3 fl p! g ^^ > 03 o o3 OJ c3 O o3 OJ.rt ft ,£5 -t^-d 51 .s 'S K2 dJ -LJ ^ • !h 3 "3 o 3 "3 C fl t> r-( ^ tH (;j cfi M 03 O^ o3 'H^'^ mS '§ ..^ 2 o a o o S o s 35 bcP< 2? ^ aJ "> 03 0) >^3a o .o ^m-^ "2oa M'g!;: WC^ tB.-i +3^ m o3^ -d c3 a fl t'P^ +3 o a-ft>. o O a^a 3 0) OD 03 CO OJ o3 2 £-1 ^^a (p ■- • •*j 1 aj'd la O ft ai o to oi O !> CO S-2 51 '3 03 jj •- o3 3 cp 03 ft43 to r- OJ > .S°a 'd ij ^ ^ 3 oa ^.3 "S o3 'r; ^ "C to ? o o^S a WH m ©a .,3 ^ iog IftS'Sg fi 03 . ^ss o o :3 S >• kj . — ^ ^^ 03 CO 1 C3 m ^ > a) o •^ Oj > «2a Black or dark, coarse or curly; not usually abun- dant ; beard full; eye- brows straight. Dark, wavy, and luxuri- ant, and fine in texture ; beard full; eyebrows arched. Hair and beard dark, full, and wavy ; e y e - brows straight and heavy. Dark, moist, straight; beard heavy and dark; eye- brows straight Dark ; decid- edly curly; beard sparse and irregular. Rather smooth ; little color, or dark and yellow- ish. Skin smooth ; so ft and creamy, vary- ing to rosy olive. Rather rough and and dark-col- ored, with tendency to ep h elides, moles, etc. 3 aj 03 Inclined to dark, and often sallow and pallid. i o Rather an- gular ; high cheek-bones ; nose large ; lips full and large. Cheeks full ; forehead large ; jaws large and round ; chin heavy; mouth large ; lips full and red. Face full ; fore he ad large ; jaws and chin round ; mouth lar^e ; lips thin and bluish. Cheek-bones large ; fore- h e a d full; jaws large and square ; mouth large; lips thin. High cheek- bones ; fore- head large ; jaws small, and chin small and pointed. 1 d' .2 d 2 3 Full in both arterial and venous sys- tems ; heart strong and active. Strong and dark ; heart quick and full. Full, but not red or vigor- ous ; heart ir- regular. Weak and thin, or dark ; heart irregu- lar. Thin and dark blood ; heart irregu- lar and weak, or active and cord-like pulse. d o d 6 Disposed to irregularity; mostly sharp and angular. Broad shoul- d e r s ; full chest ; and strong, round limbs. Well-round- ed and in- clined to ful- ness in wo- men. d aj M o3 w (D o o 1 M 1— 1 1— i '^d d ft o o 1^ Full and well-develop- ed, but not graceful. Knotty and hard ; modi- fled by san- guine round- ness. It ajpl "5 Wiry and cord-like ; or may be rath- er full and strong. ^ ai d0 O ft Oi o m'3 Strong and heavy ; head square; jaws large. Wide and strong, bones large ; articu- lation full. Rather coarse and irregu- lar ; articula- tions large. Large and coarse, with- out strength or grace. 2g.3 .rt fe d '^ bo d 03 aj d Above aver- age size. >° . O aj cd -d -d bo o TO -4-s ^ CD o >. 5 > 03

> ft .(-1 !»£ .2 TEMPERAMENT. 583 Small; hazel to light, or dark brown to black. 4J t-i ,a 03 .^.2 V^ o • - ^ o o S 2 o Blue or gray; full; large and expres- sive. >>o gap bE_2 .KS-d ci Large, light- colored ; with placid expres- sion. Variable, light or dark, sometimes light hair with dark eyes, or vice versa. Dull, gray- ish; inclined to green or hazel in color. Ranges from dark-brown to dark red; beard dark to red; eyebrows arched. Hair and beard sandy to red. full and wavy; eyebrows light and arched. Light and curly, but fine, with tendency to baldness; beard scanty ; eyebrows light and arched. Blond or light chest- nut, inclined to curl ; beard medium ; eye- brows dark and arched. Dark to light chestnut, sometimes luxuriant; beard full. Variable in color ; slight- ly wavy; beard light. Light in col- or; slight in quantity; eye- brows straight -a c a*^ O m .is) O O Hpjg P. fe a a Fair and smooth, with tendency to ruddiness. Very smooth and fair, pink- ish, inclined to florid; sometimes freckled. Soft and smooth; ivory- white to pink complexion. Dark to light ; usu - ally pallid, with little color. Light, pal- lid, coarse skin, inclined to blotches. Cheek-bones high and prom i n e n t ; lower face thin and con- tracted. Cheeks full ; fore head round ; jaws and chin well shaped. Fo r e h e a d high and broad ; cheek- bones promi- nent ; lower face rather thin : chin small. Face round ; cheeks full ; jaws large ; mouth shape- ly, and lips full and red. Large and full ; forehead high ; jaws and chin round and full ; lips full. Face round ; fore h ead large; cheeks full; lips thick. Face thin, or full and heavy ; fore- h e a d high and bulging; mouth weak; lips thin. ^?> ^.a «o- ? OS Blood red and bound- ing ; heart ac- tive. Blood full, but light-col. ored ; heart active. Good me- dium as to blood, color, and heart ac- tion. Blood thin and full; heart weak ; pulse irregu- lar. Blood light and thin; heart weak and nervous. ■d o 1^- " o3 o «'^§ |^.§ bD^ o S|2 §3 Well-mould- ed, fine limbs and broad shoulders. Rather slight, but s m e- times full and rounded. Round and shapely; full and graceful, but disposed to obesity. Inclined to irregular ful- ness, often corpulent. eS a * ad ^ !-. 0) c3 i: d ••-* m-d-^ P a a 03 .Q -d a d oi a « Ojj-d «"Sa CO ci g^ PT; ■ S o o 03 P-ft a'd2 02 d a) 03 > Full and well - shaped ; strong and g r a c e f u 1 in movement. 11^ ■3*2 a !h a op m 03 ho Fairly well- developed, and rounded ; rather s f t and medium in activity. Full, but not hard, active, but not en- during. Rather full, but moderate- ly strong and active. o'a >-^ a^ J -d .-^ ^aa Small, weak, and irregular. Strong and shapely ; ar- ticulations finely propor- tioned. 03.^. ^ oi 03 •3 .-a as.2 •1-1 ra Bones good and well-de- veloped ; ar- ticulations well-shaped. Bones long and well -de- veloped ; ar- ticulations shapely. Usually large, with coar s e-n e s s ; articulatio n s full, but ill- shaped. Bones mod- erate in size; of low struc- ture. a . a> c„M J aj 5 TO tS3 ^ c3 fcH lis 2^ u Oo3 «.d.S S-a f-t bo Above aver- age in size ; inclined to be tall. Stature very irregular, but usually above average. ,. 22 0) Bilious and nervous ele- ments, the former pre - dominating. Nervous and sanguine ele- ments , the nervous pre- dominating. Sanguine and nervous elements, the sanguine pre- dominating. Lymphatic and sanguine elements, the first predomi- nating. Sanguine and lymphat- ic, the san- guine pre- dominating. Lymphatic and nervous elements, the first predomi- nating. Nervous and lymphatic elements, the nervous pre- dominating. • ^^ t^ o o a ^•g be OS > •j3 oi "Sa ■a d ® ga >>^ 6 . .S.2 p* ?r.d CKg "&2 a «~ . p. > 584 THE TEMPERAMENTS, ETC. THE BINARY TEMPERAMENTS. 585 The Binary Temperaments. The basal temperaments are never found alone, but usually in com- bination with other elements which modify the original base. The com- pounds are generally binary — i. e. a base with one prominent modifying factor. This combination is called a binary temjiei'ament. They are named in accordance with the base and the most important modifying element. Thus, the sanguino-bilious means that the sanguine tempera- ment is most prominent, and the modifying element is the bilious. Other elements may be present, but these cannot always be diagnosed with certainty. The table of binary compounds (on page 582) is based on the indica- tions given by Dr. Ives.^ By comparison of this table with the preceding one of temperamental indications the proper teeth can be readily selected ; i. e. having diag- nosed the binary compound of the person under observation, turn to the table of temperamental characteristics of the teeth which accompany that compound, and select the proper mould and color, and arrange them ac- cording to the indications given. This will give a more artistic appear- ance to prosthetic work than it usually attains. As Dr. J. W. White said •} " What is needed is such an appreciation of the law of correspondence that the dentist can cipher out, as by the rule of three, the character of teeth required in the case of an edentulous mouth with the same precision that the comparative anatomist can from a single bone indicate the ana- tomical structure of the animal to which it belonged. The probability is that in many, perhaps in most, of the cases of artificial dentures the fault is not in the carelessness or indifference of the dentist, but in his failure to recognize the requirements of temperaments. A certain family resem- blance to each other in a set of teeth is considered essential, but the adaptability of the set as a whole to a given case should be esteemed of even greater importance. A set of teeth in which not only the relative length and breadth, but every line and curve, characterizes it as belonging to a certain temperament may be made of a coloi" never found in nature connected with such forms. Thus are seen repeatedly such incongruities as the association of the massive tooth of the bilious temperament with the pearl-blue color of the nervous temperament, and the long, narrow tooth of the nervous temperament with the bronze-yellow color never seen in any but those of a bilious temperament — showing that the laws of correspondence had not been sufficiently observed. The first study of the dentist when proposing to replace a lost denture should be how to restore the natural appearance of his patient, and this can only be effected through an appreciation of the temperamental characteristics and the law of correspondence or harmony. Age and sex may somewhat modify the requirements in a given case, but the basal fact on which he should proceed is temperament. A failure to recognize its demands will result in failure from an sesthetic standpoint. A knowledge of the dis- tinguishing characteristics of the various temperaments and the style of teeth which conform to nature's type in the physical organization marks the difference between the dental mechanic and the dental artist." ^ Amer. Si/st. of Dent. 586 THE TEMPERAMENTS, ETC. '^ I I w- ■a ■ _^- 'O -c £8 c3 a> s S a; g ci W) CU t^ pi Q) e: 03 c« s a M 03 ^P bo :=! J' !-r , CD > S m 2 ^1 •S a 3 « M ;h CD 03 ? Ph ^ a -^ - OS a^'d .^5 bo ,2 t. bo<^ o§S Pi -o ll^ (U agcrc a 2- . > C-C^ =^3-=! ■^ te^ a SS- 03 ^-O 2 ^ a u ^-C^ fH w'^^ boo* g boa „S A ■^05 'SC2 S d 03 oj 0) r 3 ;i o a< O C o ■§ a Sj5« S^^2 1=1 o c3^ £ i 6 CD a^-c CS ^■^.-S o3 ftiU 9 Q> O o3 > S^ft ■■s 03 trt 5 ftS§ <1 h^ a Ph 9 ■ 1^ O Oi ° 03 M-^ bn -2 ^-^^ CD ft-Mr^TH OS a> o 1-^ -O -C -a -a Sh 'o J< Cusps and edges. rt a; d P^ oi a . hoS fig, 5 i a 11° So ^ 2 ^ 02 a ;^ ^2=g O.S3 o -c m eg aj cfi -cf ■c) 'C « . *5 J 2 bco >" . S^O) §■3 1=1 bc.rt g'S'3 03 r-t O^ s CD S rig "3 ■Q"^ " 2 3 cs ^ ^1 o o OS 0^1 1 Or^ Q .a P5 QJ fctO;z! '^ Z^ !=' 2 !=i C cs H 0373 !-. ? bio° bCm=M CS 03 cs 25S^S m^a= I '■^ 0) ^ jog i ffl £ bo s a . •^ U bo (2 a5 c3 be 03 bocs a . .2S, 1 . •-a5 >§• a w O O Ph P ^ bD U o ^ o^ o , ■» -0^03 Round r round V ; much sub- ject to abnormal forms. 1 1 5 M d .Goo "P PI > ^ 03 Close, deep, and firm ; the plane curved. OJ ho 8ft£ og-53 •d m Soft bD 0) PI ^.'tl O£o3 o.tJ'-' hJ ft 'd ^• i^i'S 03 bJOftbo I3ga3 CO ^ Close and shapely, but strong- ly disposed to mal- position. Well set, but in- clined to crowding. Well ar- ranged, roomy, and often sp a c e d , Well-ar- ranged, but disposed to spacing. Rather ir- regular, and disposed to crowding. 03 .2 S 03 O^ ft Well- marked and shapely. •a ft o ^ Good shape; round and full. PI >« q '^ Usually sharp and well- shaped. ■^ftg o-^a Smooth, b r i 1 1 i ant, and strong. Smooth, bright, and trans- lucent. a« CO pj 03 Smooth, but rather opaque. Smooth and clear, or dull and rough. Smooth, soft, and trans- lucent. rt(D pi 02 .S OS n CO 0) Soft and poor in quality. ■S'«g J^ PI o o> Soft, weak, chalky, and sensi- tive. Rich cream - col- or to blu- ish. ^o las «» bi 03.P! rH r- U P5 m;3 a Well shaped and moulded; narrow necks. PI . Broad and round ; angles rounded. a ^^ p O bD o 03 a CJg-03 a) . MO > a (0 < o5S OJ o ^ 03 O is (7) Nervo- san- guine. . o 3 CO PS !-i H (9) Lym- ph atico- san- guine. (10) Sanguo- lym- phatic. (H) Lym- phatico- nervous. ^ 6 . ci ^ ft CHAPTER XVIII. ARTIFICIAL CROWNS. By H. H. Burchard, M. D., D. D. S. Fig. 717. When the crowns of teeth have suffered such extensive loss of sub- stance that restoration by means of filling material is inadvisable^ the restoration is an operation of prosthetic dentistry. The term "artificial crown," as technically applied, includes only such devices as are made in the dental laboratory and subsequently set as a single piece upon a prepared root or remnant of tooth. The pieces known as " partial crowns " are also included in this category. The first example of crown substitution, mounted according to the principles governing contemporary crown operations, was the setting of a crown of a natural tooth upon a prepared root, the support being afforded by a post extending from the enlarged pulp- chamber of such a crown into the enlarged canal of the root. The mechanical principle involved in this mode of support has had constant applica- tion. The next variety of crown employed is that of porcelain, the post support being, as in the preceding form, a hickory post (Fig. 717). Subsequently metallic posts were substituted for those of wood, and this variety is the typal form of one of the two great classes of crowns in present use. Metallic crowns resembling those of the present day were employed early in the present century. Classes of Crowns. All of the varieties of artificial crowns may be divided into two great classes, according to their means and modes of support. The first class Fig. 718. B C Fig. 719. A B includes all of those crowns which depend for fixation upon a post anchored in an enlarged pulp-canal (Fig. 718). The second class in- 588 ANATOinCAL RELATIONS. 589 eludes those which have their retention secured by raeans of a continuous band encircling the neck of the root (Fig. 719). Class 1 is subdivided into two orders : First, those in which the post is an integral part of the artificial crown, being baked in it or soldered to it (Fig. 718, A and B) ; second, those in which the post is firmly Fig. 720. Class 1, Order 1. anchored in the pulp-canal, as a primary measure, and upon this support the crown itself is fixed as a second operation (Figs. 718, C-721, 722). A sub-order includes the collar and post crown (Fig. 718, D), the band encircling the root acting as a subsidiary support to the root, pro- tecting it against fracture, the post being the retentive device proper. Fig. 722. Class 1, Order 2. Class 1, Order ; All of the artificial crowns in present use will be found to be a variety or some modification of one of these classes. Each variety is designed and fitted to meet definite indications, and the application and choice of variety are determined by the anatomi- cal, physiological, and pathological condition of the root to be crowned and, it may be, of the surrounding parts. Anatomical Relations. The first consideration is the position of the root to be crowned ; and the second, its form. Its position includes the class of tooth, whether it be an incisor, cuspid, bicuspid, or molar ; next, its relative position to its neighbors and to its antagonists, and what will be the relations of the artificial crown in these particulars. Each class of tooth has a definite office to perform, and there is in- volved in the performance of its function an amount and variety of stress governed by the position of the tooth — i. e. the class to which it belongs. This demands in the supporting structures of the crown and root sufficient resistance to secure the integrity of the crown and root in the performance of their normal functions. Incisors by their positions and forms are designed to receive and resist stress in one direction, that tending to force them outward. Cuspids in their normal relations receive stress in two directions : two forces act at an angle upon the axis of the tooth, and the resultant of these forces is a line outward. 590 ARTIFICIAL CROWNS. Bicuspids are subjected to three stresses — vertical, outward, and inward ; the relative amounts of stress are in the order given. The amount of the outward and inward stress is governed primarily by the lengths of the buccal and palatal or lingual cusps ; the vertical stress, by the area of the occlusion surface. Molars. — The vertical stress is greatest, and in the direct ratio of the extent of masticating surfaces ; the lateral stress is governed by the lengths of the cusps. Artificial crowns should be made of varieties to meet and resist the several directions of stress. The line of greatest mechanical resistance in any root is in its ver- tical axis, and is the only line of stress which does not tend to mechan- ically displace the tooth. As to the vital resistance of a root, this rule is but partially true, for roots appear to rebel against stress in any other direction than that due to their normal anatomical positions. In normal occlusion the stress upon any individual tooth is lessened or modified by the occlusion of the other teeth of a denture, so that the conditions of any tooth as part of a denture are not those of the same tooth standing alone. For example, the incisors normally receive a stress which ceases as soon as the molars and bicuspids are in perfect contact ; in the absence of these latter teeth the entire force of occlusion falls upon the incisors, and they are unduly strained. The incisors receiving stress in a direction tending to their outward displacement, the indication in crowning is to provide a fixture which shall best resist this direction of stress. Evidently, the device would be a rigid rod extending through the longitudinal axis of the root ; hence, post crowns are selected for incisors. The condition of the root, as discussed later, may demand modification of the variety of post croAvn applied. The same considerations apply to the crowning of the cuspidati. With the bicuspids, as the great stress is vertical, firm support by the root face is the first consideration and, as the lateral stresses are considerable, auxiliary support may be derived through posts. The lateral stress upon a first bicuspid being greater than upon the second, owing to its greater over-bite, a bifurcated pin furnishes the increased support required. The same ends are gained in the bicuspids by the use of barrel crowns ; the cement underlying them forms a perfect contact with the face of the root, thus affording the full measure of resistance to the ver- tical stress ; the collar embracing the periphery of the root protects it from lateral displacing forces. With the molars, the greatest stress being vertical, support is de- manded from the entire root area underlying the crown. The latter represents primarily a block resting firmly upon a broad base. The lateral stress is guarded against by having one or two posts in the axes of the roots or by the periphery of the crown grasping that of the root- walls. It is evident that the crown best adapted to meet these stresses is that having a barrel form, grasping firmly the periphery of the root ; the retaining cement becomes mechanically part of the tooth, so that these crowns rest uniformly upon the entire area of the root-face. Pin crowns of the variety placed upon bicuspid roots are occasionally PHYSIOLOGICAL RELATIONS. 591 employed upon molar stumps, but, as a rule, their intrinsic resistance is not as great as that offered by barrel crowns. Although by their position and form molars receive less lateral stress than bicuspids, the stress transmitted to any one root has greater effect than with the bicuspids, as the line of stress in a ^ „^o molar operates at a greater distance from the line of resistance than it does in a bicuspid, and the leverage represented is correspondingly increased (Fig. 723). As on the natural crowns of molars the lateral stress is less than the vertical, artificial crowns placed upon their roots should be formed so that this is not in- creased by their presence. Dr. Bonwill has shown the anatomical necessity that the cusps of any tooth be not longer than those of the teeth anterior to it.^ When it is desired to lessen the lateral stress upon molar stumps the end is accomplished by a shortening of the cusps of the crown. The Forms of the Teeth. The great consideration as a governing factor in the placing of arti- iicial crowns is the forms of the teeth. This includes the shapes and sizes of the roots to be crowned as factors determining the type or variety of crown selected. How does the area of root-section compare with the length of the root ? and, again. How do these factors compare with the length and breadth of the occlusal surface of the artificial crown ? For example, two roots may have the same length and the same sectional area : one requires a crown half again as long as the other (Fig. 724), or the stress of occlusion may be more severe ; obviously, the Fig. 724. mechanical stress upon the root is increased in the ratio of the extent of its occlusion or the amount of increased lever- age represented in the crown of greater length. Or, again, two roots having the same length, and artificial crowns of the same length and breadth, but the sectional area of the face of one root greater than that of the other, it is evident that the resistance afforded by the root of smaller section will be correspondingly decreased. A long heavy root will bear safely a crown which if set upon a short and narrow root and subjected to an equal stress would result in the loss of the root. Physiological Relations. Under this heading are considered the vital conditions of the tissues of the teeth or roots and of their sources of nutrition and support ; if the pulp be alive, what its condition ; and whether it is possible or advisable to place an artificial crown without effecting the destruction of that organ. Teeth are occasionally broken in such a manner as to render restoration of form by filling material inadvisable, and yet not uncovering the pulp, the latter being healthy and the dentine normal. ^ Proceedings of Columbian Dental Congress. 592 ARTIFICIAL CROWNS. It is possible in some of these cases to adjust an artificial crown without destroying or disturbing the pulp : it is evident that modifications of the barrel crown are alone applicable. Next, what is the texture of the dentine ? Highly organized dentine will bear safely a strain which would inj ure dentine of poorer type. The latter type of tissue is non-resistant to the progress of dental caries, and thus needs protection against contact with or the access of the active causes of caries. The condition of the enamel rarely is a factor in the plans, except that faulty enamel, through its liability to fracture or crumbling, will sooner or later leave part of a natural crown or a stump for the attention of the prosthetist. It may be that a tooth crown consisting in large part of thin and discolored enamel is removed for aesthetic considerations and replaced by an artificial crown. The Condition of the Pericementum. — This includes a consideration of the existing vital relations of this tissue, and the possible sources of irritation to it formed by the placing of an artificial crown, or acting after the crown is set. Pathological Relations. As teeth which require artificial crowns have been brought to their condition by the action of pathogenic agencies, these if unchecked will ultimately cause the loss of the root itself: they are therefore the most important of the factors requiring attention. The question of existing pathological conditions and their treatment belongs properly to the province of dental pathology and therapeutics ; but the present subject is the common ground upon which the therapist and prosthetist meet : their offices are the two steps of a common opera- tion. If a tooth contains a vital pulp, and it is designed to retain that organ, the infected dentine, that invaded by the carious process, should be removed with the same care as though it were being prepared for the reception of a filling. Should the pulp be, or have been, the seat of inflammation, it is destroyed and removed. If it is to remain alive, the same care is observed in guarding it against thermal shock as with fill- ings, so that after placing an artificial crown upon a stump containing a vital pulp there should be no increased response to applications of heat or cold. When post crowns are indicated the pulp is to be, necessarily, de- stroyed. The extent to which the carious process has invaded the dentine is a large factor for consideration, for the greater the loss of the dentine the weaker the root becomes, the less mechanical resistance it affords, so that support may be required to guard the weakened structure against frac- ture. Again, the more extensive the carious process the greater is the probability of such deep infection of the dentine that an increased length of time is required for sterilizing the infected tissue. The present condition of the pericementum and its past history are the most important of all considerations. It is possible that a form of crown may be required which will permit of ready removal in case of PREPARATION OF ROOTS; THERAPEUTICS. 593 recurring pericementitis ; however, in a properly treated root such a contingency should be a remote possibility. The liability or disposition of the pericementum toward inflammation may enforce a lessening of the stress brought to bear upon it through the artificial crown. It is a recognized principle of surgery, and never to be lost sight of in crown- and bridge-work, that a part once inflamed has an increased tendency toward subsequent inflammation. It is an inflexible rule that before the setting of an artificial crown the root bearing it must have such preliminary treatment that its pulp- canal and substance of its denture are rendered aseptic, and if possible antiseptic, and the pericementum must be brought to a condition of health. Unless the root be firmly fixed and supported by sound alveolar structures the following operations prove abortive just in the degree that the root is the subject of anatomical or physiological perversion. It must be remembered that the setting of an artificial crown places beyond access the most important means of combating disease of the crowned root, so that the assurance of continued root-health is a necessary preliminary. Preparation of Roots; Therapeutics. Under this heading are included, first, the therapeutic measures necessary to secure the continued health of all of the dental tissues and their supports ; and next the mechanical preparation necessary to form the root into a resistant base to which a crown may be fitted with exactitude. If the tooth contain a live pulp which has been the seat of morbid action ranging from congestion to suppuration, it is to be destroyed and thoroughly removed. In single-rooted teeth this destruction may occa- sionally be effected by the driving process. A piece of orange-wood is made into a long sharp point ; the pulp is exposed so that there is direct and perfect access to it : if it be hypersesthetic, a crystal of cocaine is placed upon it and permitted to remain for five minutes, when the pointed stick is insinuated between the pulp and its walls and driven into the root by a quick blow of a plugging mallet. The stick is then withdrawn, and usually the pulp is found clinging to it. In other teeth, those in wdiich such direct access to the pulp-canal cannot be had, the nozzle of a hypodermic point, attached to a syringe containing a solution of cocaine of from 4 to 10 per cent., is inserted beside the pulp and a drop of the solution forced out ; in a few seconds the point of the syringe is thrust quickly into the substance of the pulp, and the injec- tion made.^ The pulp is then removed by means of broaches. If the necessary apparatus be available, the pulp may be placed under cocaine anaesthesia through the agency of a cataphoretic current. The usual practice is to destroy the pulps by means of a paste of arsenic : I^. Acid, arsenosi, Cocain. muriat., da. gr. j ; Ol. caryophyll., q. s. M. et ft. paste. 8ig. A minute portion of the paste placed on a small pledget of cotton is laid over the point of exposure. 1 Dr. Masfield, Proc. N. J. State Le.nt. Soc, 1894. 38 694 ARTIFICIAL CROWNS. This preparation is sealed in the tooth preferably by zinc phosphate mixed thin, and before it is hardened the access of the fluids of the mouth to its surface is permitted. The pain following arsenical applications to the pulp is caused in great part by the pressure of the retaining filling material. Zinc phos- phate flowed in the cavity causes no pressure, and its Avetting, before hardening occurs, renders it easy of removal. In from twenty-four to forty-eight hours the pulp is then removed by means of broaches. If the pulp be the seat of purulent inflammation or of moist gan- grene, it should be removed, so that none of the pathogenic organisms may be forced into the tissues about the apex. The root and the de- generated pulp-tissue are filled with a strong penetrating antiseptic, such as meditrina (a solution of hypochlorites), and this is permitted to exercise its properties before the broach is applied. It is a wise pre- caution to wash the mouth well with this solution prior to opening any pulp-chamber in which there is putrescible material. When possible, the rubber dam is applied, the cavity dried, and a strong solution of sodium peroxide carried into the canal, gently stirring it with an iridio-platinum broach : as soon as eifervescence ceases wash out the canal with sterilized water, and repeat the applications of the peroxide until access is had to the apex of the root. The dentine of roots which have contained gangrenous pulps is the seat of more or less albuminous decomposition, so that ample time should be taken in sterilizing it, preferably by the sodium peroxide, as this sub- stance is itself decomposed into sodium hydrate and free oxygen : the former saponifies the fatty products of decomposition and dissolves the protoplasmic filaments ; the oxygen drives out the dissolved materials, and eflPectually destroys any organisms present. If there be no exudation from the apical tissues into the canal, it is the common practice to dry out the canal by means of alcohol and hot blast, and fill the apical portion of the canal with a gutta-percha cone which has been covered by an antiseptic oil — cajuput, cinnamon, or cassia. Should the apex of the root be the seat of an abscess, this is to be cured before the apical foramen is sealed. The canal is washed out with the sodium peroxide and cleansed thoroughly : no harm is done if the solution be forced through the root. Succeeding this, a solution of caustic pyrozone is pumped through the canal into the abscess-sac until the pus is driven through the fistula. As a rule, these roots may be filled at once, and the abscess-sac is soon obliterated by the formation of new tissue about the apex of the root. It occasionally happens that the fistula does not close after one injection, so that as a precautionary measure the per- manent hermetical sealing of the apex of the canal is deferred until it is seen the fistula heals and the normal color of the gum over the aifected tooth is restored. Cases present at times which give a history of a fistula alternately healing, then opening. Even after repeated injections the-fistula will open periodically, and a discharge of pus or serum occur. A condition is present at the apex of the root which demands removal by amputation of the apex. Before the pus formed at the apex of a root makes its escape through a fistulous opening in the gums the destruction of tissues incidental to PBEPABATION OF ROOTS; THERAPEUTICS. 595 Fig. 725. or characteristic of abscess proceeds in all directions, so that by the time a fistula is established the end of the root is extending into an irregular cavity, the pericementum destroyed for some distance above the apex, and the uncovered portion of the cementum saturated with noxious material. When the pus above the dotted line (Fig. 725) discharges, the fis- tula may heal, and remain closed until an increased pus-formation again re-establishes the fistula. The gum is to be divided above the apex of the root, the perice- mentum is scraped from a small area, and free entrance is gained to the abscess-cavity by means of sterilized burs. As soon as the bleeding is checked a fissure bur is passed through the opening and the denuded portion of the root cut off and rounded. The sterilization of the canal and its filling have preceded the amputation. In what are known as blind abscesses, those without a fistulous tract leading from them and discharging externally, it is advisable where possible to make an artificial fistula. The mouth is sterilized and a crystal of cocaine placed on the gum over the apex of the root. The length of the root is measured by a broach in the canal, and this length measured on the gum over the root. A crucial incision is made through the gum, the bone denuded of periosteum over a small area, and a spear-pointed engine drill is quickly passed through the bone and into the abscess-cavity. The case is treated then as a simple abscess. The operation may be made almost painless by injecting a few minims of a 4 per cent, solution of cocaine. The canal is filled after a thorough sterilization, and pending the healing of the abscess-cavity the external opening is kept patulous by means of a couple of strands of floss silk acting as a tent and means of drainage. Persistent endeavor should be made to enter freely and cleanse out perfectly to the apex all the fragments of pulp-tissue in the roots of teeth, even in the most minute canals. The introduction of the use of sulphuric acid, in connection with broaches, for gaining entrance to, enlarging, and cleansing canals, by Dr. J. E,. Callahan,^ has added to the operations of dentistry a most valuable expedient, and furnishes a means for the removal of a common cause of apical pericementitis, imperfect removal of pulp-fragments. A drop of a 50 per cent, solution of sul- phuric acid is placed over the mouth of a fine canal, and pumped into it by means of a fine Donaldson broach. Much patience will be required to effect the desired end in some teeth, but so long as there is an imperfectly cleansed canal there is the ever-present fear of the possibility of abscess, and if the crown be prop- erly set, it is most difficult to cure the diseased condition. Roots or teeth which have a portion of their surface overgroAvn by a hypertrophied gum-tissue must have the latter removed, so that the ^ Dental Cosmos, vol. xxxvi. p. 329. 596 ARTIFICIAL CROWNS. field of operation may be open. If it be a pendulous mass, the gum is excised sufficiently to free the root outline. If the margins of the root be covered by the gum, it is to be pressed back until the field of opera- tion is free. The canal and the pockets beneath the gum margins are washed out with meditrina and the canal and face of the root dried. A block of temporary stopping is made and formed into a truncated cone,, the small end of which is pressed against the face of the root, and the mass is flattened so that it presses the gum away from the root on all sides. " Should there not be sufficient concavity in the root to hold the stopping, a large-headed carpet tack may be pressed into the canal and the gutta-percha wedge built around the post." ^ Mechanical Preparation of the Root. The manipulations included in the mechanical preparation of teeth or roots for the reception of artificial crowns are of two varieties : first, the reduction of the existing volume to the necessary form and dimensions ; second, those cases in which it is necessary to restore in part the form of the root lost by decay, so that it will serve as a base for a crown. Fig. 726. Fig. 728. Crowns supported by posts should be so adapted to the roots upon which they are placed that their peripheral junction is as nearly perfect Fig. 729. Herbst's rotary flies. as possible ; there should be nothing between their surfaces but an attenuated layer of the retaining medium. At no point should the ^ Win. H. Trueman. MECHANICAL PREPARATION OF THE ROOT 597 surfaces overlap ; an instrument passed around the line of union should discover no projection of the crown beyond the root. Roots should be so prepared that they furnish adequate mechanical support to their artificial crowns. As they represent also restoration of form, their bases should be so shaped as to permit the Fig. 730. accurate adaptation of anatomically correct substitutes. The first class of root- or tooth-shaping operations are found in those cases where it is necessary to reduce an entire crown or a considerable portion of one to desired dimensions. When decrowning is necessary to fit teeth contain- ing vital pulps for service as the bases of abutment crowns of dental bridges, they may be removed after the following manner : The edge of a diamond or sharp corundum disk is applied to the outer and inner walls of the tooth until it is deeply grooved (Fig. 726) ; the edges of a pair of excising forceps are then placed in the grooves, and by a sudden pressure the crown is broken off, leaving the pulp protruding. This organ is then destroyed by the driving-out process or extirpated after cocaine injection. This method, if practised upon teeth containing dead pulps, is occasionally followed by obstinate pericemental disturbance. The crowns of pulpless teeth may be readily re- moved by making with a spear-pointed drill a series of perforations from the outer to the palatal surface of the tooth ; these should all be in one line, about one- sixteenth of an inch above the gum margin (Fig. 727). A dentate fissure bur (Fig. 728) is passed through the middle opening, and by cutting laterally the crown is soon removed. Irregular fragments of crowns may be \ J I i Fig. 731. o o O Pivoting. Facers. Root-facers. chipped away piecemeal by means of a small pair of excising forceps until they are almost on a line with the gum margin. The shaping of the root face may be accomplished by means of oval files made for that purpose (Fig. 730). Stump corundums are eifective instruments 598 ARTIFICIAL CROWNS. for the same purpose, but better than either are the rotary files of Herbst (Fig. 729), which shape the root face as it should be, its edge parallel with the gum margin. The trimming is continued until the root face is at uniform depth of about one-twentieth of an inch beneath the gum line. At its labial aspect the cutting should be slightly deeper, so that the line of junction of crown and root may be effectually concealed. A safe and rapid method of reducing the faces of roots or of cutting down broken teeth is by means of Ottolengui's root-facers. Their action and application are illustrated in the cut (Fig. 731). Reducing Teeth for Barrel Crowns. It is essential that the edges of all barrel or collar crowns shall form a perfect joint with the periphery of the root. This portion of the root should have a greater sectional area than any portion of the tooth over which the barrel is passed in adjusting it. The walls of the root and tooth should therefore be at least parallel above the crown edge line, and it is better if they be given a slight slope, so that in placing the bar- rel it is being thrust over the frustum of a rounded pyramid (Fig. 732), It will be noted in the appended figures that the periphery of the roots of the teeth are usually larger at the gum margin than at a point one- sixteenth of an inch beneath this margin ; moreover, the form changes, so that a tooth or root must be so formed that the portion of the crown or root extending beyond the gum has a less circumference than the portion one-sixteenth of an inch beyond the given margin. The evils attending and following the placing of this class of crowns are due in great part to inaccurate adaptation of the edge of the collar to the periphery of the root. It is a task of some little difficulty to properly shape a root for the reception of a collar crown, and no easy operation to accurately fit a metallic band to the prepared root. It is a common observation that very many, perhaps a great majority, of these crowns are imperfectly fitted or the root improperly prepared. An instrument passed around their borders discovers the existence of an irregular shoulder produced by the lack of adaptation of the barrel edge (Fig. 733, a). Such spaces form pockets in which food deposits and secre- tions find lodgement, so that the irritation produced by the projecting collar edge is increased by contact with the products of fermentative decomposition of the deposits, and localized gingivitis and pericemen- titis are liable to occur. The sectional area at the gum line is greater than beneath it, so that a barrel fitted to a root cut off at the gum margin would necessarily leave projecting edges if forced above that line. The line of crown and root adaptation should be as shown in Fig. 734. In cutting down large tooth remnants, such as molars, to the slightly tapering form required, a large revolving disk of corundum or a diamond disk (see Fig. 726) is held against the four walls, and its edge carried slightly beneath the gum margin until the tooth represents a truncated pyramid : the disk is carried over all accessible portions of the walls. The corners of the teeth or some of them are usually inaccessible to the disk, so that they are to be shaped by means of smaller implements, BEDUOINQ TEETH FOB BABBEL CBOWNS. 599 small corundum points, tapering burs. An effective instrument for this purpose is found in Dr. C. S. Case's enamel-cleaver (Fig. 735). A crown or tooth remnant entirely freed of its enamel has the correct form for the proper adjustment of barrels or collars, so that 600 ARTIFICIAL CROWNS. in broken-down teeth tlieir walls may be shaped by the removal of the enamel through the aid of these instruments. The instrument of Dr. W. S. How (Fig. 736) and those of Dr. R. W. Fig. 733. Fig. 735. Starr (Fig. 737) are used to give the proper form to roots for the reception of collars. Fig. 734. Crowns which depend for retention upon a barrel are to have as much of the tooth stump left as possible compatible with perfect adaptation of the crown^ and, if for anterior teeth, with the non- exposure of the gold. Restoring Root Forms. It is necessary that the root of a tooth should possess sufficient strength and such form as to furnish a firm support to the artificial crown. Occasionally cases present in which there has been such extensive loss of tooth-substance that hypertrophied gum is found overhanging the edges of a root which has been extensively invaded by the progress of caries. In such cases the root form is to be restored sufficiently to furnish a good base. After the free application of powerful but unirritating antiseptics to the recesses of the gum and the cavity of the root, masses of temporary stopping are employed as described to free the interior of the root and its face from the overlying gum. The root is thoroughly sterilized, its pericementum brought to a condition of assured health, and the apex of the canal sealed. RESTORING ROOT FORMS. 601 It is now required to restore the root form by means of some rigid and insoluble material. All things considered, a good amalgam is the material best adapted for this purpose. If the root is that of a bicuspid or a molar, one on which a collar crown is to be placed, the filling mass is built down so that the collar encloses it, finding its support in the filling, and, if possible, through some grasp upon the root also. The first step is fitting a matrix to the root in whi(!h the amalgam is to be packed. A small cylinder of moldine is packed over the root face, its external portion being left as a bulbous protrusion. While the mol- dine is in position a small impression-tray filled with the same material is used to secure and withdraw the mass covering the root face. Into this impression a fusible-metal cast is run, on which is adjusted a tube of German silver or copper, fitting the root accurately and being deep enough to grasp the periphery of the root firmly and to extend one- eighth of an inch or more above the edge of the gum. This tube is placed in position — the rubber dam adjusted over it and the adjoining teeth. The root is next dried well and filled with a strong antiseptic. The canal is cleaned and tapped for the reception of a metal screw ; after placing a small piece of soft phosphate of zinc on its extremity it is screwed into place Fig. 738. (Fig. 738). The root is given an undercut and groov- ed to aid in retaining the amalgam. Amal- gam is packed about the pin, over the root face, until the tube is filled to dotted lines (Fig. 738) ; this is done by using a ball of bibulous paper, which is held in a pair of pliers and applied to press out all surplus mercury, which is then removed, and the fill- ing completed with amalgam from which the surplus mercury has been wrung by means of heavy pliers. When the tube is full, use sponge gold to rub into the amalgam and absorb any free mercury. The filling should be hard before removing the rubber dam. An alloy containing at least 55 per cent, of silver and 5 per cent, of copper should be used. After twenty-four hours the tube should be split by cutting through it with a hatchet excavator, the ends bent back and removed. At the external (labial or buccal) edge the amalgam should be ground down to a level with the border of the gum. If desired the tube may be made of thin Fig. 739. Fig. 740. platinum, which is to remain, covering the amalgam mass. For anterior teeth, when a pin support is required in addition to the collar, special provision must be made for it. After placing the cylinder over the root and adjusting the rubber dam, a plat- inum tube is made of thin plate and of a diameter to receive a No. 17 wire. This is to be anchored for the reception of a post of that size. The wire, one-eighth of an inch longer than the tube, is touched with vaseline and inserted in the tube, a small pellet of zinc phosphate is placed in the canal, and the tube and wire pushed into position. This tube and walls Correct cervical outline. Faulty outline. 602 ARTIFICIAL CROWNS. of the cylinder encircling the root must be parallel, or the finished crown cannot be placed properly. Undercuts are made and amalgam packed as described before. When the amalgam has set the wire may be with- drawn from the inner tube, having been greased lightly ; the zinc phos- phate does not retain the distal extremity. If the outer tube is of platinum, it may remain if the operator desire. In shaping the external cervical margins or edges of roots care must be exercised to give them such an outline that the artificial crown has a cervical edge of the same outline as that of the adjoining teeth. Disre- gard of this precaution produces unsightly results. Particular care must be taken in shaping the external border of collar crowns, as upon this detail depends not a little of the artistic success of the piece (Figs. 739 and 740). Requisites of a Crown. Artificial crowns should, as nearly as possible, restore the appearance and function of the natural teeth. Moreover, by their presence they should afford no more opportunity for tho action of disease-producing agencies than when a natural crown is upon a pulpless root. This rule is impossible of exact fulfilment, but it is possible that by a correct artificial crown, properly placed upon a healthy root, the possibilities of disease processes arising may be reduced to a minimum, and by an im- properly made or placed crown the probabilities of subsequent disease are increased. All crowns must rest firmly upon the face of the root upon which they are placed. The contact must be at all points of the edge of a crown with the tooth surface. If of porcelain, it must correspond in shape, size, shade, and position with its fellow, and must subserve the purposes of a crown in mastication. There should be at no part any projection which can form part of a pocket, nor any point which can act as an irritant to vital tissue. The line of junction between tooth and crown should be clean and clear, so that neither the surface of the root projects beyond the edge of the crown nor the edge of the crown beyond that of the root. If a barrel or collar crown, the upper edge of the collar or barrel must be in close contact with the root surface. It should extend far enough beneath the margin of the gum to grasp the root firmly, but should not extend to the alveolar border. A limited portion of perice- mentum is destroyed in trimming a root, and the collar should not extend beyond this point : as the collar represents or replaces the upper border of enamel, it should not extend much beyond the depth of the enamel line unless the gum should have receded from about the tooth. Porcelain crowns should have the porcelain protected against frac- ture, either by the inherent strength of all porcelain crowns themselves, their bulk supplying the strength required, or, if a porcelain facing, the facing should be protected by a metallic backing against the force or shocks of mastication. For posterior teeth the details as to correspondence of size and con- tour are equally important, and in addition their articulating surfaces •should have such an arrangement of cusps and sulci that the normal masticating surface is restored. PARTIAL CROWNS. 603 Type Selected. As a general rule, no root anterior to the second bicuspids should be crowned with an all-gold crown. None of the incisors or cuspids should show any but a porcelain surface. Healthy roots which have not been invaded by caries, if of good size and structure, as a rule, may be fitly crowned with some form of the pin crown. Logan crowns are adapted when the root is of good structure and when form and color corresponding exactly to the adjoining tooth can be had, and when the bite is not too close to cause weakening of the porce- lain by the necessary grinding, and where the correct cervical surface outline can be had. The pin and plate crown is adapted for use on sound roots. This variety produces a greater mechanical strain upon a root than does the Logan, as the force received by it is directed first upon the anterior wall of the pulp-canal ; second, upon the outer surface of the root. With the Logan crown the force received is transmitted primarily to the outer surface of the root, and stress is exerted secondarily upon the walls of the pulj)-canals. The Logan crown can therefore be used upon more frail roots than the pin and plate variety, as the stress tending to fracture a root longitudinally is greater with the latter. Partial Crowns. Occasionally cases are seen where the loss of tooth-substance is not sufficient to demand the sacrifice of an entire crown to be replaced by one of the artificial crowns described, and yet is so extensive or in such situations that restoration by means of filling materials is impracticable : it is at times advisable to apply one of the devices known as partial crowns. The first variety of such cases are those in which one of the anterior teeth has been fractured transversely at about the middle, without expos- ing or destroying the vitality of the pulp. Usually these cases have the contour restored by means of heavy rolled foil at the hands of the operator. As the appearance of a mass of gold in so conspicuous a place may be objected to by the patient, the ope- rator is compelled to resort to the use of porcelain to effect the restoration. The difficulties of this substitution are — securing sufficient support for the porcelain tip ; accurately matching the color of the natural tooth ; disguising the line of juncture of Fig. 741. tip and tooth ; and lack of strength in a porcelain f ■ ^-<^^ piece of such size. 'r'Til' (^]Sm The surface of the broken tooth is smoothed and squared, and dressed to as great a depth as pos- sible without exposing the pulp. Upon this pre- pared surface a piece of platinum plate No. 3-5 is burnished to close adaptation (Fig. 741). At three points holes are drilled, the middle one not on a straight line with the others, as deep as may be without encroachment upon the pulp : these cavities are to be made while the platinum plate is on the tooth ; in each of the openings a- screw is placed, fitting the cavities easily. Adhesive wax flowed over 604 ARTIFICIAL CROWNS. the projecting ends of the screws attaches screws and plate, which are removed in one piece, invested, and the screws nnited to the plate by means of 24-carat solder. The piece is transferred to the root, the exposed ends of the screw dressed to within one thirty-second of an inch of the plate, and the plate burnished to perfect adaptation with the tooth surface. At the labial aspect the platinum is dressed to the tooth outline, and made so thin that its edge is almost imperceptible. A plaster impression of the parts is taken in which the small plate is withdrawn. A model of sand and plaster is poured with the utmost care, and when very hard the impression is picked away. A cross-pin tooth having the pins very close to the cutting edge is selected. Its color should match as nearly as may be that of the tooth upon which it is to rest. It is better to have the tooth a trifle more yellow than its fellow, as the presence of a platinum backing gives a bluish tinge ; if the tip is blue, a 24-carat gold backing produces a yellowish tint. The porcelain is fitted by means of fine corundum wheels until the line of union is as nearly perfect as can be made. It is backed with platinum No. 28 or 24-carat gold No. 27, attached to the plate with adhesive wax, and then sand-and-plaster investment is used to cover the porcelain and retain it in position. At the palatal aspect the porcelain is dressed out to expose the heads of the screws. When the investment has set the adhesive wax is removed, and small pieces of thin platinum plate are used to fill the little space be- tween the base of the porcelain and the plate. Solder with 24-carat gold if the plate and backing are of platinum, or with 22-carat solder if of gold. Finish and set with zinc phosphate, permitting the cement to set half an hour before removing the rubber dam. If the pulp has been exposed, it is destroyed and anchorage secured in the canal by means of a long pin. Incisive edges may be made of gold for pulpless teeth after the fol- lowing method : The labial edge of the tooth is filed square. A piece of thin platinum. No. 36, is pressed into accurate apposition with the broken edges and surface of the tooth, and burnished over the edges for about one-sixteenth of an inch. The plate is perforated over the pulp-canal, and a platinum wire of No. 18 gauge is thrust through the perforation : the platinum film grasping it tightly on all sides, it is with- drawn, bringing the plate with it. The pieces are united by means of pure gold as solder, and returned to the tooth and burnished into perfect apposition. A bite is taken, and next an impression, in which the post and plate are withdrawn. A model and articulating model are made ; the amount of restoration required is noted. A stick is carved to repre- sent the cutting edge, and is driven into an asbestos mat deeper than the necessary height of the tip. Pure gold is melted in this depression, and while molten its upper surface is flattened by quickly pressing against it a smooth piece of charcoal. The protruding end of the post is filed down to within one thirty-second of an inch of the plate. The gold ingot is filed to a close joint with the labial edge of the plate : its inner surface may be short of contact to perfectly admit solder. The cutting edge is filed to an accurate occlusion, but left a trifle PARTIAL CROWNS. 605 long to allow for loss in finishing. The surface of the platinum and the base of the tip are covered by borax. If the model has been made of investing material, enough of it is placed over the tip to hold it in posi- tion. If of plaster, an opening is made in the model to gain access to the base of the pins. The tip is cemented to the plate by means of wax flux ; pressure upon the end of the post pushes the fixture from the model. It is invested and soldered from its palatal surface with 22- carat solder. Its surfaces are dressed down to the proper contour, the overlap of the platinum at the base giving the base outline, to which the piece is to be tiled. It is smooth, polished, and set with zinc phosphate. A better method is constructing the tip entirely of porcelain ; this may be accomplished by selecting the tip of a porcelain tooth, adapting it to a plate as described ; the attachment of the two is made by adding fusible porcelain and baking in a furnace. (See also methods in Chapter VI.) Shells of gold having the appearance externally of large fillings are occasionally employed in restoring the contour of teeth. The method is particularly applicable to cases requiring a large phosphate filling. The gold serves as an outer shell which by its smooth surface and protection of the phosphate from the action of the fluids of the mouth preserves the cement from disintegration for a long period. A satisfactory method of forming these pieces is as follows : The tooth is excavated as for a phos- phate filling ; the enamel edges are made smooth, clear, and distinct, then bevelled. Should the cavity occupy only the masticating surface of the tooth, a piece of softened modelling compound is placed in the cavity and the patient directed to close the bite. A piece of heavy pattern foil is then laid over the compound and bitten upon. When the foil is re- moved the compound is short of occlusion about the thickness of No. 30 plate. The cavity edges are cut clear of the compound, showing their outlines distinctly. An impression is taken in moldine and a die made. A piece of pure gold of No. 30 is annealed, swaged on this die, and its edges filed to fit the cavity outlines perfectly. Small openings are drilled through the cap to receive the ends of wire loops. Pieces of No. 22 wire about one-quarter of an inch long are bent into U form ; four of them are required to hold the cap perfectly. The loops have their ends thrust through the Fig. 742. openings, a minute piece of No. 22-carat solder placed beside each exposed end, the cap laid on a block of charcoal, and the solder fused by a fine blowpipe flame. It is safer to cut de- pressions in the die corresponding to the positions of the loops, then dress down the ends and reswage (Fig. 742). Should the cavities include the approximal walls, the tooth form is restored by means of zinc phosphate ; the cavity edges, which have been dressed, are scraped free from the cement. Particular care is required when the gold extends over the masticating surface that the phosphate be cut down to allow for the lamina of gold. An impression is taken and a fusible metal die made. When the approximal space is minute, it will be necessary to pass a saw-blade between the teeth on the die to represent the space. A piece of 24-carat plate No. 30 is swaged and burnished to fit the outlines on the die, and openings made for two loops — one on the masticating, the other on the approximal wall. 606 ARTIFICIAL CROWNS. The piece is transferred to the natural tooth and its edges burnished into accurate apposition with all the bevelled enamel edges. Removed from the tooth, the wire loops are placed in position and sol- dered. It is advisable to flow solder in the angle to stiffen the piece. (See Fig. 743.) The rubber dam is adjusted and the greater portion of the cement is cut out. A mix of jjlastic phosphate is made ; small portions are packed in the loops, and next the cavity itself is filled, when the facing is pressed into place. The piece should now remain undisturbed for at least fifteen minutes. In cavities involving both approximal walls and the masticating sur- face the piece is shaped and the retaining bar placed as in Fig. 744. Another application of the device is seen in Fig. 745. Fig. 744. Fig. 745. Gold blocks, to be placed in lieu of gold fillings made of foil, are constructed after the following method : The cavity, usually in an incisor, is to have its edges trimmed and squared. A piece of annealed platinum No. 50 is pressed and burnished into the cavity and over its margins. In the platinum form adhesive wax is placed and carved to the proper con- tour. It is chilled, withdrawn from the cavity, and invested in a mix- ture of pumice and plaster. The wax is burned out, and in the matrix pure gold is melted under a fine blowpipe flame. The piece is trimmed :and smoothed to correct contour. It is retained in the tooth by means £)f zinc phosphate. The Post and Plate Crowns. These are crowns which have posts fitting the enlarged pulp-canal for support. The proper size and shape of this post are about those used in the familiar Logan crown. A root which has lost no substance, or no more of the periphery of its pulp-canal than will receive a post of this size, is usually a fit root for the application of a post crown. Should there be a loss of sub- stance in excess of this amount, a supporting band is advisable. The size of the post may also be had in a flattened wire of 14 B. & S. gauge and somewhat tapered toward its extremity. The flattening increases the resistance in the long diameter, which occupies the antero- posterior line of the pulp-chamber, the line of greatest strain. Round and square posts are needlessly strong for one diameter, insufficiently so in the other. When the pin is double, as in bicuspids and molars, round or square pins may be employed. The old type of post, the wood pivot, has been so entirely super- seded that it scarcely needs description. These crowns Avere anchored by THE POST AND PLATE CROWN. 607 means of round hickory sticks, which were compressed immediately before using. A suitable crown selected was ground to the root face, the compressed wood set in its base, and then the post was thrust into the enlarged pulp-canal. Roots have been split, frequently, through the swelling of the compressed wood. The form of made-up post crowns most commonly employed is selected as the typical form : it is the pin and plate crown. A detailed description of this will serve to illustrate many of the principles govern- ing the making of all crowns. The method of making is as follows : An incisor or cuspid root which is in a perfectly healthy state is thoroughly sterilized, and the apical foramen hermetically sealed by some unchangeable material which has been coated or saturated with a strong antiseptic ; usually a gutta-percha point is used for this purpose, one which has been soaked in one of the antiseptic oils. The pulp-canal is enlarged for about two-thirds its length, in such shape as to receive a flattened pin of iridio-platinum wire of No, 14 B. & S. gauge, which is to fit the enlarged canal easily enough to permit ready removal. Fig. 746. Fig. 747. Fig. 748. Fig. 749. The face of the root is shaped to follow the outline of the gum margin, and to have its surface about a line below this margin (Fig. 747). At its anterior aspect the cutting should be a trifle deeper than at the other parts, to ensure perfect hiding of the joint. The operator may now, if he prefers, take an impression of the face of the root, and fit the root-plate on a model prepared from it. An effective method is as follows : After shaping the post-canal and face of the root and fitting the post, Mellotte's moldine is placed around the pin, covered by damp tissue-paper, and inserted in the root ; an impression in moldine is then taken ; after removing from the mouth the post is withdrawn and placed in position in the impression, and a die of fusible metal made. Should the paper and moldine be scraped from the post in removing it from the canal, it is to be again covered by moldine enclosed in the paper before placing it in the impression. The thin layer of moldine covering the post permits its withdrawal from the die. A small piece of soft platinum plate No. 31 or 24-carat gold plate No. 30 is well annealed and placed upon the root face represented on the die, and pressed into rough adaptation (Fig. 746) : a piece of erasing rubber answers well as an elastic counter-die for this purpose. A buckshot or a small piece of soft lead is placed over the root face on the die, and struck with a hammer until it is fit to serve as a counter-die. 608 ARTIFICIAL CROWNS. The small plate, again annealed, is placed between die and counter and swaged with a light hammer. A hole is made in the plate to un- cover the root opening, small enough to require force in pushing the post Fig. 750. through it, so that the post, when in position, is closely embraced on all sides. The post is then withdrawn, the plate coming with it ; borax is applied at the line of junction, and if the plate is platinum it is soldered with a small piece of 24-carat gold, or, if the plate be of gold, with a Fig. 751. Fig. 752. minute piece of 22-carat solder. The plate is then trimmed to follow the root outline ; at its labial aspect it is filed to a thin edge (Fig. 748). The post and plate are placed in position on the natural root, and with an orange-wood stick and a light mallet tapped at all points until the adaptation is perfect. A bite of wax which includes the adjoining teeth is now taken, re- moved, and chilled. Next a plaster impression is secured, in which are withdrawn the post and plate ; if not withdrawn in the impression, a depression is seen, in which the top of the pin is inserted. A shade tooth is selected at this time. The impression is double varnished with thin shellac and thin sandarac, allowing each varnish to dry well. Pins are placed in the impressions of the teeth adjoining the root to be crowned, and poured carefully with rather thin plaster, to be sure the impressions of the tips of the teeth are perfectly filled. Let this set well before separating the model from the impression ; place the wax-bite in position on the model, and make an articulation on a crown articulator. COLLAR CROWNS. 609 Varnish with thin shellac the teeth of the models. Saw off the protruding end of the post to within one-sixteenth of an inch of the plate ; the anterior edge of the post may be bevelled even with the plate ; removing more than this weakens the post attachment to the plate. A plain plate, straight pin tooth, having a shape, size, and color corresponding with the adjoining tooth, is then selected. Sti-aight pin teeth are stronger than than those with cross pins; but the lower pin must be in such situation that it will not be ground Fig. 753. out in the fitting. Grind the tooth with fine grit corundum wheels until the cervical portion fits perfectly the outer edge of the plate and has the same contour : the cutting edge should be precisely on a line with its fellow and restore the general curve of the incisors, repairing the break of the arch line. Bevel the palatal aspect from about one-eighth of an incli beneath to the cutting edge, and bevel the porcelain beneath the lower pin to expose the head of the post (Fig. 753). Make a small plaster wall to hold the tooth while fitting the backing stay. Should the tooth be a little too blue in color, use 24-carat plate for backing ; if a trifle yellow, use platinum plate. A closer adaptation of the backing may be made by using well- annealed plate of No. 35 gauge, and placing over this plate of No. 28 or 27 gauge. The thin plate should be well burnished over the entire palatal aspect, and turned under at the cervical portion. The stay should extend clear to the cutting edge of the tooth to ensure protection to the porcelain during mastication (Fig. 749). With a wedge-shaped chisel split the pins and turn back the sections, so that the backing is firmly held. Boil the tooth and plate in pickling fluid ; place in posi- tion on the model ; unite plate and tooth with adhesive wax. Remove from the model and invest in sand and plaster. The removal from the model without deranging the parts may be readily effected as follows : At the palatal aspect cut away the plaster of the model until the post is exposed (Fig. 750) ; the fixture may then be pushed out by pressure on the end of the post. The piece is then invested in sand and plaster (Fig. 751). When the investing material has set, remove the adhesive wax ; fill the V-shaped space between tooth and plate with thin pieces of 24-carat plate ; apply borax ; cover with small squares of 20-carat solder ; dry out ; then heat slowly from the investment side ; when the tooth shows red by heat transmitted through the investment, turn the fine blowpipe flame on the plate and backing, and the soldering will be perfect. Cool gradually ; pickle and finish with all the care a jeweller exercises in the finish of his work. The outlines of the crown should then be in exact correspondence with the outlines of the root (Fig. 752). Collar Crowns. The second class of crowns are those in which retention is by means of encircling collars or bands. As the band is the distinctive feature of this class, it will be first described. 39 610 ARTIFICIAL CROWNS. The first requisite of this band is that it shall fit absolutely, not approximately. Faults in this direction are the most common and those to be most guarded against. The second requisite is that these bands shall not be irritating to the vital parts, and yet shall offer a perfect protection against the ingress of pathogenic organisms or their products to the parts we design to protect. This implies that the band shall not impinge on the pericementum, nor must it have any roughened edge or surface to irritate the overlying gum. It should extend to such depth beneath the gum margin that the gingival margin shall form a barrier, not the wall of a pocket. The band should grasp, but not irritate; a trifle over one-sixteenth of an inch in depth will be sufficient in the majority of cases. The surface having the greatest sectional area should be at the edge of the collar or barrel. This requires that the root be so trimmed that Fig. 754. Fig. 755. Incisor. Outer lines represent original con- Molar, tour ; inner lines, the form to re- ceive barrels or ferrules. Patterns for collars. its walls are at least parallel (Fig. 754). It will save the patient dis- comfort and the operator material if after shaping the root an accurate impression of the parts be taken. On a model made from this impres- sion a pattern, following the gum line, should be shaped. From this pattern a piece of plate is cut, 22-carat, No. 29 or 30 (Fig. 755). This is annealed and bent to fit the root or tooth on the model. Annealed and transferred to the mouth, the band is pressed into close adaptation, and a scratch made indicating the amount of overlapping of the edge. Remove this and cut a trifle — say one-twentieth of an inch — beyond the scratch to allow for stretching. File the edges square, ajjply borax, and hold them in firm contact with one another, either by use of binding wire or by overlapping the edges, and then bringing back into direct contact, so that they will be held together by the elasticity of the metal itself. Place on the inside of the collar a small piece of 20-carat solder, and fuse by holding in a small Bunsen or large alcohol flame. Another method of fitting the collars is as follows : The perimeter of the root is taken by means of annealed brass wire of No. 33 gauge. The ends of the wire are passed through the end openings of a dentimeter, one end being caught fast upon the side pin of the instrument, and by drawing upon the loose end the nose of the dentimeter is drawn to within an eighth of an inch of the outer face of the root, when the instrument is turned, twisting the wire and drawing it closely about the neck of the teeth. The opposite edge of the wire loop is held down by means of an instrument to prevent it slipping off* the root. COLLAR CROWNS. 611 The loop is removed (Fig. 756) and divided at a point opposite the twist and straightened. The line of greatest distance between the gum line of the root to be crowned and the antagonizing tooth is measured, and a rectangle of plate of that width and the length of the straightened wire is cut. Should the area of the root face be Fig- "56. noticeably less than that to be filled by the articulating face of the crown, the plate is to be cut in the form of a trapezoid, its short parallel side somewhat shorter than the length of the wire. The ends to be joined are filed perfectly square and covered by borax and soldered. The cylinder may be then placed upon an appropriate man- drel, and pressed up on it until it fits tightly, giving an approx- imate form to the cylinder. If the operator prefer he may employ a seamless gold collar procured from the manufacturer, and form this upon a man- drel (Fig. 757). Making a soldered cylinder for each case is, however, a more precise method ; moreover, it permits of making the circumference of one edge of the collar greater than that of the other when this difference in the sizes is demanded. The exact neck forms may be given in the following manner : Lay the wire loop as it comes from the tooth upon a smooth flat lead surface, and place over it an old tool- handle sawn square and given a smooth surface. Strike the wood a hard blow, driving the wire into the lead and wood, leaving both lead and wood marked by the outline form of the wire (Fig. 758). The wire is straightened, the gold measured, and the cylinder made as described. It is then bent to fit the indentation made by the wire in the wood, and next further adapted to the groove in the lead. It is then transferred to the root in the mouth, the outline of the gum margin marked on its surface, and the collar trimmed to this line. It is set upon the root until one portion of it touches the gum, when the outline to which the edge of the collar must be cut is noted, so that it shall be at a uniform depth below the gum line. The collar is cut to this line, transferred to the root or tooth, and pushed into position. Subsequent manipulations depend upon the class of tooth to be replaced, for there are many modifications of the sub- sequent operations depending upon whether the tooth has or has not a vital pulp, and whether the root is that of an incisor, cuspid, bicuspid, or molar. As the molar is the commonest of barrel crowns, it will be described first. There are many time-saving methods recommended and applied in the inaking of these crowns, but in most of them time-saving is at the expense results. The following is a method devised about ten years ago by the writer, and followed ever since to the exclusion of all others : The band is first made as described above, and cut down to within an eighth of an inch or of esthetic ^;^^"- 612 ARTIFICIAL CROWNS. Fig. 757. No. 1. No. 2. No. 3. No. 4. No. 5. No. 6. Mandrels for shaping seamless tooth-root collars. No. 7 COLLAR CROWNS. 613 so short of occlusion, leaving a square edge. A wax-bite is taken on this, including two or three adjoining teeth and removed. A plaster impres- sion is then taken, in which the barrel is imbedded and withdrawn. A Fig. 768. model and articulating model are made and mounted, preferably on a Bonwill articulator, but usually upon the crown articulator, as in Fig. 759. While the barrel is upon the plaster model the walls are to receive their correct contour. The catalogues of the manufacturers exhibit an ever- FiG. 759. growing list of pliers designed for this purpose. The two forms figured subserve all the needs — one the form known as the Johnson pliers (Fig. 761). The curves of short radius maybe given collars with these. The second pair is made by bending the beaks of a pair of round-nose pliers (see Fig. 379) ; the curve given the jaws represents the average curve of the buccal walls of the natural teeth. The contouring is done before the barrel has been removed from the model, as the cervix is held in shape by the plaster and the barrel suffers no change of shape at that part. The occluding teeth are varnished and oiled slightly, the barrel filled with soft plaster, and the occlusion made. When the plaster has set it is to be trimmed to expose the square shoul- der made by the top of the band and scraped down uniformly to the thickness of No. 30 plate. Cusps and sulci are then carved in such a manner as to get the greatest amount of masticating surface and natural effect. Natural teeth of the same class should form the models from which to copy. 614 ARTIFICIAL CROWNS. The surface plaster at completion of the carving is short enough to allow for the thickness of plate used for the cap. The collar and plaster cusps are then imbedded in plaster to a level with the shoulder ; when set, this plaster is cut to a tapering prism or a truncated pyramid (Fig. 761, A). Varnish and make a Babbitt metal die ; this, driven into a block of soft lead, makes its counter. Annealed 22-carat plate, No. 29 gauge, is swaged between die and coun- ter-die and the surplus gold X B trimmed oif. The junction of this cap with the barrel forms then but a line ; pickle the sections ; apply borax to the inner sur- face of the cap and the top of the band ; hold them in apposition with binding wire or between the jaws of self-closing pliers, and solder with 20- carat solder over a Bunsen flame. When finished there are but two faint lines rep- resenting the two joints of the piece (C). Fig. 761. The die for swaging the cap may be more quickly made with Dr. Mellotte's devices of tray, ring, moldine, and fusible alloy. A small tray is filled with moldine, the surface of the latter is flat- tened ; the plaster cusps are pressed into the moldine until the collar leaves a distinct and perfect outline. The rubber ring is placed around the tray, forming a well, the crown imprint in its bottom. A die of fusible metal is then formed. Another method almost exact is to fill the gold barrel with soft plaster or modelling compound while the bar- rel is in the mouth, and direct the patient to bite into it, then perform the movements of mastication. The crown is removed from the root, tlie plaster or modelling compound scraped away the thickness of No. 30 plate, and a die formed as above described. COLLAR CROWNS. 615 These appliances of Dr. Mellotte are invaluable in many small laboratory operations. But few of the many methods advanced secure the accuracy of adap- tation of cap to root and of articulation which would warrant their general endorsement. With a view to making an artificial crown what it should be, an instrument for the restoration of a lost function, it will be seen that accuracy of articulation is an essential. The exposure of the least sur- face of solder is desirable from aesthetic considerations. Should it be desired to use this form in replacing bicuspids, porcelain faces may be attached after the following method, and the same may apply in making crowns for the anterior teeth containing vital pulp which it is decided to retain. The operation in nearly all cases up to and including the mounting of the articulation is the same. The labial or buccal aspect of the band is to have a saw-cut made at the cervix, following the gingival margin, to the depth of the thickness of a plain plate tooth which has been selected — if a bicuspid, a cross-pin cus- pid is used. Vertical cuts are made from the top of the band joining the saw-cut, detaching a section of the gold (Fig. 762). The tooth is Fig. 763. Fig. 764. Fig. 765. ground to make a perfect joint at the cervical shoulder and to fit the lateral walls of the barrel (Fig. 763). The tooth is bevelled for one- fourth of an inch or less at the cutting edge, and a stay of 24-carat gold No. 29 fitted to extend to all edges of its back (Fig. 764). This stay makes a close joint with the sides of the barrel. The pins are to be split. Pickle, unite tooth and barrel with adhesive wax, and invest in sand and plas- ter, so that the investment repre- sents an open tunnel (Fig. 765). Remove the wax, apply borax along the joints and around the pins, use four minute pieces of solder, one at each lateral joint, one over each pin ; heat gradually to a red heat ; then turn the fine blowpipe flame into the tunnel and unite the parts. The subsequent making of the cap is as described for the all- gold crown ; it extends to the top of the backing, which is at the cutting edge of the tooth. Prepared for soldering, the cap is waxed to the band, and the piece invested in sand and plaster, cap down, so that the interior of the crown represents a well in the centre of the investment ; the investment over the cap should form but a thin layer. Solder sufficient to fill the joints well is boraxed and placed in the 616 ARTIFICIAL CROWNS. cap. The piece is heated. Transferred to the charcoal, the blowjiipe flame is directed against the base of the investment until the solder -„„ flows. When cool it is boiled in acid, and every joint is dressed down with small files and corundum pencils until smooth ; then bufled, burnished, and polished (Fig. 766). A similar process may be used for the anterior teeth, as described on p, 618 for those cases in which it is thought advisable to retain a vital pulp. Occasionally, where there is not a suflicient amount of a broken bicuspid extending above the gum line to aiford adequate support to a collar crown, a post is attached to either the root itself or made part of the crown. If anchored in the root, the pin is made after the form of an inverted U, and securely fastened by means of amalgam. If it is de- signed to attach the pin to the crown, the pulp-canal is enlarged for half its length ; if the root has a bifurcated or double canal, the palatal root is reamed out to that depth. An iridio-platinum post is set in the canal and the collar adjusted. A wax-bite and plaster impression are taken, a model and artic^ulation made. The collar face is cut out for the reception of the porcelain tooth, and the post is loosened from its plaster canal. The facing is fitted and a stay adapted ; adhesive wax unites the facing to the collar and the post to the backing stay. The pieces are next with- drawn, invested, giving the investment the tunnel form of Fig. 766, but the investment is carried over the pin sufficiently to hold it. The cap is formed and fitted as described, attached to the collar and facing by means of wax, and invested in an inverted position, carrying the invest- ment up on the pin, but leaving space enough between the post and palatal portion of the collar to permit the ready introduction of the solder. The investment overlying the cap should be thin. When this has set the wax is removed ; a liberal amount of borax and sufficient solder are applied to fill the cap. The piece is heated and the solder flowed by directing a flame against the base of the investment. Another method of attaching porcelain facings to the gold barrel crown is by making the entire crown first of gold, the barrel and articu- lating surface complete. The external wall of the erown has the seg- ment made visible by the movements of the lips sawn out, and the cut edges of the metal bevelled, A porcelain facing is selected of a size to fit the space with the minimum grinding. It is to be ground in until all of its edges fit those of the barrel. A stay of No. 34 pure gold is bur- nished over the back of the porcelain tooth. The edge of the stay should be accurately adapted to the barrel. The crown and facing are cemented together with adhesive wax, covered by a thin investment and soldered by means of a blowpipe flame ^^'J^\ ^ ^ .-.r^ directed against the portion of the in- vestment covering the facing. The buccal and articulating faces of molars and bicuspids , may be made of porcelain, the attachment of the crown to the root being secured by means of a gold barrel. The barrel is made as for an all-gold crown, A wax-bite and impression are taken, and an articulation mounted. Before cutting away the buccal wall of the barrel for the reception of the porcelain, measure by means of a wire and COLLAR CROWNS. 617 dentimeter the circumference of the upper portion of the barrel. The loop made is taken to the d6p6t, and a saddle-back or a plain rubber tooth is selected, the circumference of which agrees with that of the barrel (the wire loop). The tooth should have but little thickness of porcelain above the pins (Fig. 768) ; the S. S. W. cusp crowns are designed for Fig. 768. Cusp crowns. this special use. A scratch is made along the buccal portion of the barrel, marking it slightly above the gum line and between the adjoining natural teeth along the line of exposure. A fine saw is used to cut away the buccal walls to these lines. The palatal wall of the barrel is cut down if necessary to admit the face, so that it will articulate with the antagonizing teeth. Should there be any lack of correspondence between the outlines of the barrel top and the cusp crown or tooth, the gold is bent to fit the latter accurately. By means of fine-grit corundum wheels the edges of the porcelain are closely adapted to the cut edges of the gold at the cervical and approximal borders, and articulated perfectly with the antagonizing teeth. The tooth and barrel may now be set with cement : it is preferable, however, to solder the porcelain to the barrel. A piece of 24-carat gold No. 33 is fitted as a stay to the under surface of the porcelain and burnished into accurate contact. The tooth and stay are set in the barrel, and the latter is cut away at points interfering with its correct placement. It is boiled in the acid solution, and invested so that the interior of the barrel and the stay exposed form a well. Borax is painted around the line of junction and over the pins, a small piece of solder placed over each pin, and three or four pieces around the joint, and the piece is gradually raised to a high heat ; a fine flame directed into the well fuses the solder, uniting the pieces perfectly. In finishing the crown the gold should be dressed down to the porce- lain, making a perfectly smooth joint. No projection of the gold beyond the surface of the porcelain should remain. Fused porcelain may be used in lieu of solder to attach the crown to the barrel, as described by Dr. Robert Huey : ^ " The barrel is fitted and cut out as described. One of Ash & Sons diatoric teeth is selected and fitted to the barrel. Openings are drilled through the mesial and distal walls of the barrel, which shall exactly uncover the openings of the tube in the tooth. A piece of platinum wire is thrust through holes and tube, holding the porcelain to the gold. The platinum wire is now either riveted or soldered to the barrel. The line of junction between gold and porcelain is painted with a paste of dental glass, which is then fused in a Downie furnace." 1 Penna. State Dental Soc, 1896. 618 ARTIFICIAL CROWNS. Porcelain-faced Crowns for Teeth containing Vital Pulps. When collar supports are to have porcelain faces, those cases where crowns are to be placed over teeth containing vital pnlps, the tooth to be „ _^Q crowned is to be trimmed so that a sufficient covering of /v ^' ' dentine is left to act as a protector to the pulp. At the /| \ labial or buccal aspect the tooth is sloped to the gum mar- / 1 \ A, gin, carefully avoiding uncovering the cornua of the pulp I m \ ll Jwik C^^S- '^^'^^ ^)- The root is trimmed for the reception of a ■\r"J pP—l collar, which is fitted and permitted to project about one- 1 ^^ sixteenth of an inch above the edges of the tooth. The v./' parts of the band in contact with the antagonizing teeth "" when the jaws are closed are ground to about one-sixteenth of an inch short of occlusion. The labial portion of the band is cut away, following the slope given the labial aspect of the tooth and level with it. A cross-pin tooth is carefully adapted to these edges. The palatal surface of the porcelain tooth is given a long bevel toward its cutting edge. A stay of No. 27 plate is closely adapted to the tooth, its lower edge in contact with the collar (Fig. 770). The tooth and barrel are invested ; the pins Fig. 770. are soldered to the stay, and the stay to the collar. The crown in this condition is transferred to the model and the articulation noted. If the collar is almost in contact with the antag- onizing teeth, its palatal surface is formed of a single piece of plate bent to conform to the open top of the collar, and as far up on the stay as the bite will permit. It is desirable, where possible, that the stay should be made double throughout. Should there be a necessity for contouring the palatal surface of the crown, the articulating teeth are varnished, a batter of plaster is placed in the collar and over the stay of the crown, and the articulation closed. The plaster is, when hard, scraped down uniformly to allow for the thickness of the piece to be added — No. 30 plate. It is then carved to the desired form, freeing from plaster the edges of stay and collar. A small die is made of fusible metal poured in moldine and a cap swaged. The pieces are boiled in acid. The surfaces to be united are touched with flux wax and brought together, and the piece invested. Along the joint — or, rather, beneath the joint on the collar — three small pieces of solder are placed, one in the middle, one on each side. In soldering direct a fine flame beneath the joint, never on the cap, as, this being the portion most readily heated, the solder has a tendency to run from the collar to the surface of the cap. In finishing such caps each edge should be carefully rounded. Application to Abraded Teeth. — This form of crown is frequently applicable to abraded teeth. The remaining teeth of a denture being worn down to within a short distance of the gum line, it becomes neces- sary to protect each tooth from further progress of this formidable destruction. Each remaining tooth is to have its crown length restored by the substitute. The molars and bicuspids are covered by all-gold crowns ; where possible the anterior crowns are made with porcelain faces, without destroying the receding pulps. It is advisable, first, to make and set three crowns — one on each side and a central incisor : these fix the bite in its altered relations ; the remaining crowns are then fitted and adjusted in pairs. POST AND COLLAR CROWNS. 619 Post and Collar Crowns (Richmond Crowns). When it has been determined that the use of a band upon one of the anterior teeth is desirable, whether from undue loss of tooth-substance or because an unusual stress is to be borne by the root, the Richmond or collar crown is the one commonly employed. A band is made to fit the properly shaped root according to the method described. This is placed on the root, and is trimmed a little below the margin of the gum. At the palatal aspect the trimming need not be so deep. The curve at the cervix should be the same as that of the ad- joining tooth (see Figs. 722, 723), so that in the completed crown the cervical outlines may be alike. The collar is then removed, pickled, and Fig. 771. its upper surface laid upon a flat piece of 24-carat gold plate No. 31, the points of junction boraxed, a minute particle of solder (22-carat) placed at the junction ; the plate is held over a Bunsen flame until the solder flows and fixes the band at one point. The plate is then bent down to fit the entire edge outline of the band, and soldered as before, using a piece of solder of the size of a pin's head for this purpose. The cap is then trimmed, placed in position upon the root, an opening made uncovering the root-canal, and a pin which has been fitted thrust through this open- ing into position. Withdraw the post, and, if the collar comes with it, unite them with a small piece of 18-carat solder ; the soldering may be done over the Bunsen flame. As a rule, it is necessary to unite the wire and cap by means of adhesive wax to enable the operator to withdraw both pieces together. They are to be invested, and the post attached to the cap with a small piece of solder. Place the post and collar in position, and take a wax-bite and plas- ter impression as for the post and plate crown. The subsequent operations are the same as those in making the latter forms of crown. (See ante.) The three varieties of crowns described are those which are commonly and most acceptably used as supports in bridge-work. A removable porcelain facing to place upon a post and collar base has been devised by Dr. W. L. Mason of Red Bank, N. Y.^ The post and collar are made as described. Dr. Mason's device consists of two pieces — one a drop-forged backing of heavy gold plate, which has a triangular slot throughout its length, ^ Dental Cosmos, Aug., 1896. Fig. 772. 620 ARTIFICIAL CROWNS. the base of the triangle in the body of the backing (Fig. 772). The second piece is a porcelain facing, having baked in the longitudinal axis of its lingual face a triangular platinum bar, which readily slips into the slot of the backing. A portion of the post extends beyond the cutting edge of the tooth. Both teeth and backings are made in standard sizes and forms. The tooth is slipped into its backing, and both are ground to fit the ferrule tops. The backing is attached to the ferrule by means of hard adhesive wax. When the latter is hard, the platinum extension is grasped and the tooth withdrawn from the backing ; the metallic pieces are next invested and united to one another by means of solder. The piece is now chilled, smoothed, polished, and adjusted to the root. The lingual surface of the tooth and the platinum are to be covered with a thick solution of chloro-percha and slipped into position ; the pro- truding platinum is sawn off and the edges of the metal are burnished. Ready-made Crowns. Of the ready-made porcelain crowns there are two varieties — first, those designed for fixation upon a post which is previously fastened in the root ; second, those having a pin baked in them. To the first class belong the Bonwill, the Foster, and the How ; in the second class are included the Logan, the Brown, and the new Richmond crowns. Crowns which are formed and adapted by means of sets of ready-made appli- ances, such as the Hollingsworth and the mandrel systems, belong to the class of built-up crowns. The crowns of How and of Brown are no longer manufactured. Of all the ready-made porcelain crowns, that offering the widest range of application is the Bonwill. It is made entirely of porcelain, and is perforated for the passage of the Fig. 773. ^ supporting post (Fig. 773). At its bases it is concave, the upper portion of the per- foration formed into a shape which pre- vents the displacement of the crown after it is fixed upon its post. The edges of the porcelain are designed to rest uniformly upon the outer edge of the prepared root-surface. An eminently satisfactory method of fitting these porcelain crowns is as follows : After the root face has been trimmed as for the reception of any post crown, take a wax-bite of the side having the crownless root, and then a plaster impression. In the plaster impression a model of fusible metal, one melting at about 150° F., is poured. A shade tooth is selected, and an articulation mounted. A crown of the proper form, shade, and size is selected. Select one the base line of which corresponds closely with that of the root outlines represented in the model. By means of fine-grit corundum wheels the crown is well adapted to the edges of the root face and correctly articulated with the antagonizing teeth. In adjusting these, and indeed all post crowns where the roots can be grasped firmly by thera, the Ottolengui root clamps are invaluable (Fig. 774, Nos. 126 to 129). A pin of the largest size admissible (Fig. 776) is set in the root- BEAJDY-MADE CROWNS. 621 canal and the crown set in position over it (Fig. 775). Should there be lack of correspondence between the directions of the root-canal axis and Fig. 774. No. 126. No. 127. No. 128. No. 129. Fig. 776. Root-clamps for crown-work. Devised by Dr. Otlolengui. the perforation of the crown, the post is to be bent and filed until the crown slips readily over it, the palatal wall of the tooth perforation resting against the post. The latter is withdrawn __ from the root, and by means of a small wheel bur the walls of the root-canal are cut to a semblance of a screw thread. After the crown edges have been adapted to the root face, a small corundum point is passed around the basal concavity of the crown, removing sufficient amount of the porcelain to give almost a featlier edge. This is to prevent the amalgam at the junction from being reduced to a thin sheet, which might be broken, forming a space at such points in which fermenting materials might find lodgement. Slow-setting zinc phosphate is mixed and a small pellet carried to the end of the root-canal, and the post pressed firmly into it ; the crown is then passed over the post into its proper position and permitted to remain until the cement is hard. The crown is removed and soft amalgam is packed about the pin and root-canal walls for about half the length. The remaining amalgam is wrung out to remove the excess of mercury, and packed in small pieces about the post. Place the crown over the post for assurance that the post has not changed in position. In packing the amalgam a more homogeneous mass is made by using pellets of bibulous paper, as recommended by Dr. Bonwill, to compress the mass and force out the surplus mercury. A fresh mix of amalgam, wrung half dry, is banked up about the post, and when more than enough to fill the concavity in the base of the crown has been so 622 ARTIFICIAL CROWNS. Fig. 777. Fig. 778. packed, the crown itself is firmly and steadily pressed into position by means of an appropriate crown-driver until the junction of the crown and root is represented by a faint blue line. Amal- gam, mixed very dry, is now packed about the end of the pin in the cavity of the ar- ticulating face, using bibu- lous paper to express any free mercury ; when this cav- ity is more than full sponge Crown adjusters. gold is rubbed into the amal- gam until it ceases to be amal- gamated, when the surplus is removed, dressing the amal- gam flush with the crown surface. If the amalgam employed contains at least 60 per cent, of silver, and cut in fine grains, it will be well hardened at the end of the ope- ration described. It must be well hardened before the crown is subjected to the stress of mastication ; otherwise the crown will be displaced. The writer occasionally defers the packing of the amalgam about the end of the pin to the next day, filling the articulating surface cavity with zinc phosphate, permitting this to set and hold the crown in position for twenty-four hours, so that the amalgam supporting the crown may set perfectly before any force is applied to it. The cement is subsequently removed and its place filled with soft amalgam, which is well compressed by means of bibulous paper ; the soft portions of amalgam then cut out, and the filling completed with dry amalgam, packing more than full, then cutting it down to the surface of the tooth. In applying this crown to the restoration of molars a post is to be used in each root. For the upper molars a large-sized post is used in the palatal root, and smaller ones in the buccal roots. These may be fixed in position by means of zinc phosphate to hold their distal ends, as described above. The How screw posts will be found frequently applicable with the Bouwill, as with other crowns of the same class. The Gates, Foster, and How dovetail crowns are all of analogous forms, and are to be attached in the common method, a screw anchored in the root, which has been drilled and tapped to receive it, amalgam filling every remaining space in the root and crown and also between them. Their mode of applica- tion is seen in the illustrations. The all-porcelain crowns, such as the Foster, Gates-Bon will, dovetailed crown (Figs. 781 to 783), and others, have been set in various ways, prominent among which has been the use of solid-headed screws ; but Fig. 779. Fig. READY-MADE CROWNS. 623 firmer and more satisfactory work can be done by first fixing the screw- post in the root (Fig, 785), thus permitting the crown to be slipped over the end of the post and properly adjusted to the root, after which the cavities in both root and crown may be partly filled and a nut Fig. 781. Fig. 782. Fig. 783. Foster crown. Gates-Bonwill crown. Dovetailed crown. screwed on the end of the post to condense the filling and firmly secure the crown in its place. These appliances are very simple. They con- sist of a nut-driver, over which is placed a split tube for carrying the nut. (See sectional view. Fig. 784.) The sole object of this tube is to Fig. 784. AA A B How screw-posts (A, with nut). AA A B Headed screws. Nut-driver witli split tube. hold the nut and prevent its falling into the mouth or on the floor during the process of attaching or detaching it from the post. The nuts and nut-drivers are made of three sizes to suit the How screw-posts aa, a, and b, and the old form of headed screws, which are made of the same sizes as the How posts with nuts. Fig. 785, A and B, illustrates the application of the double screw in connection with molar crowns. The next class of crowns is composed of those having their platinum posts baked in them : they are the Logan, the Brown, and the new Rich- mond crown. The first of these has the widest range of application, and is the form in most general use. Being composed of porcelain alone, and having no underlying mass and backing of metal, they present a translucent appear- 624 ARTIFICIAL CROWNS. ance not to be had with those forms of crown which are built up in part of metal. An excellent method of selecting and adapting these crowns Fig. 785. B Fig. 786. is as follows : The root face is trimmed by means of rotatory files or the Ottolengui root-facers to the level of the gum margin. The canal is sterilized, and the upper third hermetically sealed, the remainder of the canal enlarged to about one-sixteenth of an inch in diameter. A wax- bite is taken, including several of the adjoining teeth. A piece of iron wire one-half of an inch longer than the reamed portion of the canal, and small enough to slip very freely in it, has its end bent into a loop and the canal portion covered with gutta-percha, Avhich is then oiled and slipped in the root. A plaster impression is taken in which the coated wire is withdrawn, and a model made of fusible metal melting at about 150° F. A shade tooth and a crown corresponding with the natural teeth are selected. The direction of the axis of the root-canal is noted, the angle which it makes with the root face, and compared with the direction of the axis of the selected crown : not infrequently it is necessary to bend the pin at an angle with the axis of the crown itself (Fig. 786). The opening in the root, made by with- drawing the gutta-percha and wire, is enlarged sufficiently to receive the post of the crown. The pin is bent, if necessary, so that the axis of the crown is parallel with that of the natural fellow, bringing the cutting edge of the artificial crown in the arch of the natural teeth. The points of contact between the edges of the crown and the face of the root represented in the metallic model are ground from the porcelain until there is a uniform contact throughout the crown edge. The grinding is done by means of square- edged corundum wheels on a laboratory lathe or by an engine wheel, as shown in Fig. 787. The cutting edge of the artificial crown should exactly repair the break in the arch. Its palatal surface is cut away, if necessary, to articulate with the antagonizing teeth, in which event the cut surface should be smoothed and polished. The canal is enlarged by means of fissure burs or Ottolengui's reamers (Fig. 788) until the pin slips readily into place and the surfaces of crowns and root are in contact. Should either the edge of the crown or the edge of the root project beyond the common line at any point, it is to be trimmed down BEADY-MADE CROWNS. 625 until the line of junction is uniform. Any slight imperfections of con- tact are to be remedied by means of the carbon-paper test : small pieces of this material, large enough to cover the face of the root, are pressed Fig. 787 Fig. 788. to its surface and perforated by the crown post. The crown is now pressed firmly into position and withdrawn : should there be any breaks in the black line, the crown is dressed down at all parts marked until there is a continuous black line at the outer edge of the crown. The crowns may be accurately adapted to the roots without the use of a model, but, as it is desirable to make a model to serve as a guide in selecting a crown of the proper size and form, the same model may fur- nish a base and guide for adapting it. The operation described in reality saves time. Fig. 789. Prepared articulating paper. In fitting these crowns without a model the canal is enlarged suf- ficiently to receive the metallic post, the root surface trimmed to the proper form by means of the root-facers, and tlie crown is fitted as follows : Dr. E. C. Kir¥s 3Iethod of Fitting a Logan Croivn to a Tooth-root. — Cut several small pieces, about one-quarter inch square, from a strip of thin articulating paper. In the centre of each punch a hole with the tool shown in the margin. Having prepared the root-end, slip the per- forated piece of articulating paper over the pin of the Logan crown and 40 626 ARTIFICIAL CROWNS. press it firmly into position, in contact with the root. Upon withdraw- ing the crown and removing the articulating paper, the points of contact will be found to be marked black. Grind these off carefully, readjust on the root as before, grind again, and continue the operation of fitting and grinding until the mark made by the articulating paper on the con- tact surface of the crown presents as a uniformly unbroken black ring. When this has been accomplished, the crown will be found to fit the root-end with the utmost accuracy. The advantages of fitting a crown directly to the root are, it would seem, self-evident from the mechanical standpoint, and involve besides the least expenditure of time.^ A Method for Perfectly Adjusting- the Logan Crown. — " By making a considerable change in the present form of the Logan crown, as shown in Fig. 790, 1, A and B, we have a crown that can be adjusted in a few minutes, and with a degree of perfectness not yet obtainable by any crown on the market, nor, within my knowledge, by any so far sug- gested method. "The manner of making the adjustment is certainly as simple as could be desired. "After preparing the canal for the reception of the 'Logan pin,' select a tooth in the usual way, having regard to correct length, width, and color, and if care has been exercised to select one as near the right length as possible, it will only be necessary to touch the buccal or labial point of the neck of the crown a few times with the corundum wheel, and the proper length or bite will be obtained. Next take a disk or small piece of thin platinum foil, about No. 50, and push through this the pin of the tooth, carrying the disk up against the porcelain, as represented in Fig. 790, 2. With a little drop of Parr's fluxed wax dropped in the triangular space, formed by the backing and the pin, the disk is held securely in place, and the platinum is trimmed around with small scissors, that there may not be any overlapping. Now place around the pin on the platinum a ball of Parr's wax, stick the pin through the second disk of the foil, and rub the platinum with a hot instrument, that the wax and disk may be sealed together, as shown in Fig. 790, 3. Place this in ice- water to harden the wax, so as to resist pressure. It is now ready to insert, and by pressing the tooth up until the labial surface strikes the end of the root, and having the patient to close the jaws, the correct bite will be secured with the opposite tooth. It will be found on the removal of the crown that the platinum next the root has been perfectly swaged to the root-end. This second disk is now trimmed according to the out- lines of the root. When it is so desired, the palatine side of the root having been left a little high, or just above the gum, the platinum can ^ Dental Cosmos, June, 1894. BEADY-MADE CROWNS. 627 be split with scissors, lapped, and burnished around the exposed side of 'the root, to form a partial band (Fig. 790, 4). " After having dried the wax with bibulous paper and shaped up the approximal sides, these sides are covered with small, triangular pieces of platinum (Fig. 790, 5) by lapping the platinum on the wax and rubbing over it a hot burnisher. The crown is now ready to invest, and the in- vesting mixture is poured on a small piece of wire netting, which will prevent its cracking during the soldering operation. The wax having been burned out, this triangular box is filled flush with solder in the usual way and polished. The result is a beautiful and perfect crown, in every respect the most substantial porcelain crown we have. '' I frequently make the crown without using the triangular piece of platinum to form the box (Fig. 790, 5), relying on the investment to form the sides. This saves a little time ; but it frequently happens, unless care has been taken to make the wax flush, that the approximal surfaces are not well rounded, and consequently do not finish well. It is there- fore safer to use the triangular pieces of platinum foil to form the sides of the box, as described, before filling with solder. This plan is partic- ularly adaptable to those cases of fracture which have resulted in a rough root-end, and where it is often next to impossible to get them smooth. "Where it is convenient or if it is desired, the triangular box can be filled with ' body,' and baked in a Parker furnace from six to eight minutes. This gives us an all-porcelain crown which fits perfectly to the end of the root. In this case the first disk next the porcelain is left off entirely." ^ Caution. — The Logan crown contains a large tapered pin with its large end baked in the tooth, and when heated to flow solder over or around it, care must be taken that the porcelain is made as hot as or hotter than the pin, thus preventing uneven expansion and cracking of the porcelain. These crowns may be adapted upon frail roots, those which demand the supplementary support of a band encircling their necks. It is a matter of but little practical moment whether the collar is or is not attached to the crown : the object sought, the protection of the root against longitudinal fracture, is secured by banding the root first, forming an artificial root face by means of metal. The root face is trimmed as for a collar crown ; the collar is fitted and a cap soldered to it, the edge of the top being hidden at its labial aspect by the gum. While the cap is on the root an opening is made in it considerably larger than the size of the crown post. A piece of metal longer than, and slightly larger on its sides than, a full Logan post is greased with vaseline ; the root is dried, zinc phosphate is packed into it for more than half its length, the ferrule partly filled by the same mixture and pressed into position. While the cement is soft the metal wedge is thrust into the cement as deep as a Logan pin, and left until the cement hardens, when it may be readily withdrawn. The crown is now adjusted to the canal in the cement and to the edges of the ferrule top. The gold of the cap may be dressed away, together with a portion of the cement, until but a nar- row retaining rim of gold is left. Logan crowns adapted after this manner are to be cemented into ^ Gordon White, D. D. S., Dental Cosmos, January, 1893. 628 ARTIFICIAL CROWNS. Fig. 791. position as follows : An appropriate root clamp (Ottolengui's) is placed on the root, and the rubber dam slipped over several adjoining teeth and' the clamp. The root is well dried by means of alcohol and the hot blast ; the canal is wiped with a pellet or cone of paper saturated with the cement fluid to facilitate the flow of the cement. A paste of cement is made just thick enough to be formed into perfectly plastic pellets ; one of these is rolled into a cone, and before the latter bends by its own weight it is carried into the canal : another is pressed into the concavity in the base of the tooth ; the grooves in the post are filled ; the crown is then thrust into position and pressed home, when the cement will ooze from the edges, and the joint should be a very thin line. The crown is left un- disturbed for at least fifteen minutes, when the cement will be found hard enough to resist fracture. The advantages possessed by cement, hardness and rigidity, may be combined with the virtue of gutta-percha, insolu- bility in the fluids of the mouth, after the following method : " First prepare and treat the pulp- canal of the natural tooth-root in the ordinary way, the canal being provided with undercuts or retaining points, and fit the crown in proper alignment with adjacent teeth as usual. Fill the cup or recess in the neck of the porcelain crown with gutta-percha, which can best be ac- complished by slipping a washer or per- forated disk of gutta-percha, cut to cor- respond approximately with the size of the neck of the crown, over the crown- pin, and after softening by holding it in the flame of a burner, press the crown to its place upon the root. After it has been held in position until the gutta-percha has cooled, remove the crown from the root and trim off" any surplus gutta-percha. JSTow coat the end of the root with shellac varnish, fill the root-canal with a suitable amalgam or cement, or, if preferred, pack it with prepared gutta-percha points, using such an amount of points as will allow the crown-pin to enter the canal not quite the full length of the pin. The opening for the pin in the gutta- percha in the canal may be made with a heated instrument having a tapered Logan crown with gutta-percha. BANDING LOGAN CROWNS. 629 point. Having packed the crown-recess with the proper quantity of gutta-percha, as above explained, place the crown in position in the mouth, heat the copper end of a crown-setter sufficiently to soften gutta- percha, and place the grooved end of the setter over the crown with the heated copper in contact with the porcelain. Hold the setter against the crown until the gutta-percha becomes soft, when pressure should be applied to the setter and the crown with its pin forced to its proper posi- tion. After the gutta-percha becomes cool, which can be hastened by dipping the crown-setter in a tumbler of ice-water and holding it against the tooth until it is cold, cut off any surplus that may be squeezed out from between the crown and root, with a sharp knife, and then with a hot tool smooth the edge of the gutta-percha between crown and root. If the cutting is attempted while the gutta-percha is soft, it will be dragged out of place. "■ The use of gutta-percha for packing the root-canal, thus making the entire attachment with this material, possesses the advantage over the use of cement or amalgam in that, should the root become abscessed, the crown may be removed with a pair of forceps after first heating it with the setter, the root-canal treated until the disease is cured, and the crown reset. Heating the porcelain crown when a cement is used to fill the root around the pin hastens its setting. Do not heat the crown if amalgam has been used," Banding Logan Crowns. There are several methods of banding the Logan crown, so that the ferrule becomes an integral part of the crown. One method of making the attachment is as follows : Adapt the collar to the root, and fit the cap inside, not over the band, soldering with 22-carat solder. Fit the Logan crown to the ferrule, perforating the latter for the passage of the post, which should be grasped tightly by the cap. At the palatal side cut out the porcelain for about one-sixteenth of an inch, leaving only the labial crescent of porcelain in contact with the ferrule. Perforate a circle of 24-carat gold No. 40, and pass over the pin and burnish into the con- cavity in the base of the crown. Perforate other pieces of thicker gold and pass oyer the post, pressing them firmly into contact w^th the pieces previously placed, until the concavity is filled and the last piece extends to the palatal edge of the crown. The pieces are covered by Parr's adhesive wax ; the same material is flowed over the top of the ferrule and the crown pressed into position ; the crown and ferrule are placed on the root and adjusted to position; the wax is chilled by having the patient hold ice-water in his mouth for a few moments. An excavator point is passed beneath the upper edge of the collar, and it is withdrawn and invested. The wax between the last, the broadest piece of gold, and the ferrule top is picked away and small pieces of gold are used to fill the space. A liberal amount of 18-carat solder is laid over the gold, and the case heated under the blowpipe, directing the flame against the investment over the labial portion of the crown, drawing the solder through from the palatal side, adding more solder if necessary to fill the joint flush. Dr. Townsend's method of attaching a band without the top is appended : 630 ARTIFICIAL CROWNS. Fig. 792. How to Band a Log-an Crown. — " Prepare the root as usual for a band crown, and enlarge the root-canal to receive the Logan pin. Grind a Logan crown to fit and articulate it. Construct a band of No. 30 gold (or of No. 32 crown-metal, which is better) wide enough to project beyond the end of the root, say three thirty-seconds of an inch. Cut a wooden peg about an inch long, and taper one end of it to the general size and shape of the pin in the Logan crown. Place the band on the root, insert the peg in the canal, and fill up the band with Melotte's moldine or with stiff putty, pressing it closely about the peg. Remove all together, and, holding the die over the flame of an alcohol lamp to melt the fusible metal, place them — the band, peg, and mold- ine, in the same relative positions they occupied in the root — on the die, with the pin in the socket, and press down until the moldine rests on the sur- face of the molten fusible metal. Chill ; in cooling, the fusible metal takes a firm hold on the lower edge of the gold band, holding it securely in place during the remainder of the operation. Remove the peg and the moldine, and with a wooden mal- let drive the Logan crown into the band until the porcelain rests upon the fusible metal. Burnish the band smoothly about the crown. When the gold is perfectly adjusted to the porcelain melt the fusible metal to release the band and crowm. If the work has been carefully done, the crown with its band will then be ready to be set, as the artic- ulation and fit will not have been disturbed." Method of Mounting a Log-an Crown with a Gold Cap. — " With regard to crowning teeth, some have no doubt met with cases like the following, where ordinary methods are not available : Miss L called at my office to have a lower right first bicuspid crowned. There was a considerable portion of the lingual part of the crown standing, the buccal surface being decayed almost to the gum-margin. The coronal portion of the pulp was calcified, and she objected to having it destroyed, nor did I think such a course necessary. Here an all-gold or even porcelain- faced crown would have been too conspicuous, so I decided to apply a Logan crown, — not, however, with its ordinary pin, but with a cap and collar. I trimmed the root, leaving the lingual side a little high, and took a model and bite of it. A cap and collar were made to fit the root accurately and tightly. A suitable Logan crown was next selected, and the pin cut off. Into the countersink and around the stump of the pin I floioed pure gold, and then proceeded to fit the crown to cap and bite. A hole was next cut in the cap, and enlarged till it nearly corresponded in size to the gold base in the countersink of the crown. Cap and crown were now waxed together, and invested crown downward in plaster and marble-dust. This left the interior of the cap and band exposed, and through the aperture in the former all except the edge of the pure gold could be seen. The wax was then removed and the Avhole soldered. A 1, socket ; 2, fusible metal. BANDING LOGAN CROWNS. 631 slight groove was cut round the remaining portion of the root to assist retention, and the crown was cemented in place." ^ Another method is appended, the principle the same as the first described : Dr. HoUingsworth's Method for Accurately Adapting and Mounting a Logan Crown with a Band. — " Prepare the root in the Fig. 793. Fig. 794. Fig. 795. usual way for banding. (See Fig. 793, front view, and Fig. 794, side view.) " Grind the abutting surface of the crown to fit the root under the free margin of the gum, along the labial face only. (See Figs. 793, 794, a to 6.) " Cut the crown away slightly at the lingual surface, so as to leave a space between it and the end of the root. (See Fig, 795, c.) " Make a band only wide enough to give a good hold on the root, but not to extend beyond margin of gum to fit the root and trim off even with the end of it. (See Fig. 795, d.) After fitting the band properly, remove it and solder a piece of pure gold plate, say about No. 34, on the outer end. (See Fig. 795, e.) This can be done quickly by placing the plate in the hand and pressing the band on it with the thumb for a fit, then soldering in the flame of a Bunsen burner. Punch a small hole through the plate to take the pin in the croAvn, and replace Fig. 796. Fig. 797. FiG. 7i in position on the root after trimming off the exposed edges. Now take a piece of thin pure gold, say No, 34 or 36, with ears as shown in Fig. 796,/; punch a hole through it, slide it over the pin of the Logan crown, and burnish tightly to the base of the crown. (See Fig. 796, l\ l£i^^rT.l by flowing gold over them, or, what is ' *^i ^^-^^^ preferable, adding thick pieces of plate to each side and joining them by means of 22-carat solder. The shoulders are soldered to the crowns, the slots are adjusted to the shoulders, their ends attached to the stays of the dum- mies. It is necessary that the slots should be immovably held against the stays to ensure their correct position in the finished piece. Soft adhesive wax is placed around them, attaching them to the backings, an unusually large amount of the wax being used. The piece is chilled and the dummies and sockets withdrawn. If both sockets come away without detachment, the piece is immediately invested ; if one or both have broken away, the sharp line of fracture of the brittle cement fur- nishes the guide for their accurate replacement. The writer advises that the free ends of the shoulder-piece be left as extensions which are adapted to the wall of the abutment crown, the socket piece to have similar wings which shall outline the terminal wall of the bridge body in its finished state. In the Curtis bridge^ (Figs. 920 and 921) the long arms (1, Fig. 921) are made of heavy platinous gold plate, the heads formed in the matrix E Fig. 921. 2 1 (Fig. 922). Sockets (2) of thin gold are made fitting these arms closely. The dummy crowns have had their caps fixed by solder to hold them in position. The sockets, with their ends projecting beyond the borders ^ G. L. Curtis, Cosmos, vol. xxxii. p. 109 et seq. REMOVABLE BRIDGES. 687 of the dummies, are attached to the latter by means of fluxed wax. The pieces are invested, and the sockets are attached by means of solder, completing in this soldering the contour of the dummy block (C, Fig. Fig. 922. 920). The surfaces of the dummies are cut away until the block fits closely between the crowns. The block is now smoothed and buffed. The arms are placed in their sockets, from which they project at their under surfaces. The palatal surface of the cast is varnished ; the dummy block containing the arms is set in position : attach the block to the cast by a drop of adhesive wax melted at the junction of the porcelain with the cast. In the depression beneath the dummies pour soft investing material. When this has set remove the bridge, and a depression is seen in the investing material, in which the bar which made it is placed. Enough investment is added to hold the bars in position, which are to be perfectly united to the abutment crowns by means of solder. These bridges are attached by cementing both crowns to their abut- ments with one mix of cement, and while this is still soft quickly set- ting the body of the bridge in position. A variety of removable bridge, the design of which suggests it as one of wide application, is that of Dr. C. M. Richmond.^ A model and zinc die are made of the abutment molar with its crown. Around this crown a telescoping collar is made, fitting it tightly : this is made of crown metal, about one-sixteenth of an inch longer than the crown. The die is driven into this collar, and the surplus length is swaged to overlap the occlusal surface of the crown. A second collar is adapted to the first and the two united with solder, form- ing a removable, rigid, and closely- adapted abutment piece. The other ex- tremity of the bridge, its second abutment piece, is a removable post crown. Dr. M. L. Rhein ^ has devised, applied, and furnished the models for Fig 923 Cosmos, vol. xxviii., No. 8, p. 497. ■^ Cosmos, vol. xxxvi. p. 97. 688 AN ASSEMBLAGE OF UNITED CROWNS. one of the most ingenious forms of removable bridge yet presented. It is designed to overcome the several disadvantages incidental to the pla- cing of a fixed bridge, to obviate the necessity for the occasionally great mutilation of abutment teeth, to enable the operator to apply a correctly fitting barrel, and to reproduce the slight movement possessed by the natural teeth in normal occlusion. Fig. 924. The distinguishing feature of the bridge (Fig. 924, 3) is the abut- ment crown made in such a manner as to fit closely the neck of a Fig. 925. crown, smaller at this part than at its occlusal edge, without mutilating the walls of the crown. In constructing the crown an accurate plaster REMOVABLE BRIDGES. 689 impression of it is to be secured and a perfect model made in it. [The writer suggests the advisability of making this cast of one of the fusible alloys poured in the plaster impression.] The cast is trimmed away so that the band may go one-thirty-second of an inch beyond the gum line. The natural crown is shortened sufficiently to allow for the proper thickness of an articulating face on the crown after the impression has been taken. A piece of plate, 20-carat, 29 gauge, is swaged to cover the occlusal face and the walls of the crown to the swell of the tooth {B, Fig. 927). A pattern is made of heavy foil. This may be done readily by bending a piece of tin to fit approximately the joint at the middle of the anterior face of the abutment crown : the ends of the pattern, left long, are grasped between the jaws of a pair of pliers and drawn tight against the walls of the crown : the edge of the tin is cut out to follow the gum outline closely, and again drawn tight by means of the pliers ; the ends are left extending some three-sixteenths of an inch (C, Fig. 927). The Fig. 927. Ftg. 928. pattern is reproduced in 22-carat plate, gauge 30. A piece of pure gold is sweated to the free edge of the band, which is then closely adapted to the model tooth. A piece of mica is placed in the joint of the pro- jecting tips, to prevent their union in soldering on the cap, which is adjusted in position and soldered to the band. The shortest distance between the abutment crowns is marked on a piece of card-board, which is then squared to that width. Its edge,^ ap- plied to the gum (Fig. 928), is cut to conform to the gum outline in a line which marks beneath the narrowest distance between the abutments. The second abutment crown is constructed and both are set in position on the model. The card-board is placed in position, resting upon the projecting ends of the collar ends, and the lines of its edges marked on these by means of a sharp blade. Pieces of perfectly triangular wire, half the width of the gib and longer than the crown itself, are cut, two 44 690 AN ASSEMBLAGE OF UNITED CEOWNS. for each crown. One of these has an edge placed along the knife- mark and cemented into position by means of wax flux (Fig. 927, E). A piece is placed on the second arm, exactly opposite and parallel with the first, and it is similarly attached. A thin shaving of mica is placed Fig, . between the projecting arms of the crown ; the piece is invested, and the wires attached by the minimum of solder. The crowns are boiled in acid ; the projecting ends of the wires are cut off, and the upper ends given a rounded bevel. The projecting ends of the crown arms are filed flush with the edges of the wires (Fig. 927, F). [The wires them- selves are filed flat to present a common surface anteriorly.] The key (Fig. 927, 6r) is formed of platinous gold in the following COMBINATIONS OF PLATE- AND BRIDGE-WORK. 691 manner : A piece of steel wire (triangular) is slightly flattened upon one side {A, Fig. 929). A small rectangle of platinous gold, 29 gauge, its short side wider than the length of the gib, is cut (Fig. 929, B), and on its surface the greatest width of the gib is marked. The plate is bent over at one of these lines, placed in a vise, the short arm of plate against the wire, F ; an arm is made, C. Turn the metal in the vise, and form the other side, D, the base of the piece measuring the extreme width of the gib. Saw-cuts, made at the angles to the depth of the bevel of the gib, will permit bending arms together and forming a cap to the key {G, Fig. 927) : the joints are soldered and the key cut away until it is the length of the gib. The gib and key are accurately fitted to one another. The pieces adjusted in position, the crown is represented in J (Fig. 927). A second piece, similar to the key, is fitted over the latter to serve as the slot of the bridge. The body of the bridge is formed with the slots attached, as described ■on p. 686. The abutment crowns are set by removing the keys, placing in the crowns sufficient zinc phosphate, and carrying them into position, when the keys are adjusted and forced fully into position, drawing the edges of the crowns into close apposition with the necks of the teeth. The pure gold edges are now burnished into perfect contact with the teeth. A bridge made and attached after this method is shown in Fig. 930. Combinations of the Principles op Plate- with those of Bridge-work. The principle involved in this class of mechanism ^vas utilized early in the present century as a means of retention for partial dentures. There is a combination of the support represented in the bearing of a plate upon the alveolar ridge, together with the rigidity secured by having terminals or extensions from the plate anchored in the roots of teeth or embracing them as closed and rigid cylinders. The principle of anchorage in the roots of a natural tooth is illus- trated in Figs. 932 and 933 ; that of embracing the natural teeth by 692 AN ASSEMBLAGE OF UNITED CROWNS. closed cylinders, in Fig. 934 ; a combination of the two means of reten- tion, in Fig. 935. These devices possess certain advantages over clasp plates, in that there is no elasticity of the retaining cylinders : they slip over the abut- FiG. 932. Fig. 933. ments prepared for their reception, and, being closely adapted to them, there is a greater rigidity of the dentures than with the ordinary clasp. For their employment it is obviously necessary that the abutments should have sides which are parallel and the axes of both mutually Fig. 934. Fig. 935. parallel. They are usually designed for application in cases where the natural teeth are in such positions and have forms which would fit them to serve as bridge abutments, but the contour of the gum is such that it is necessary to employ gum teeth (Fig. 936). They are, to all intents and purposes, removable bridges, having a greatly multiplied support from the natural gum. It was stated (p. 671), in describing the bulkhead bridge, that should the contour of the gum be lost to such an extent as to preclude the ap- plication of a bridge, owing to the impossibility of correctly adapting plain teeth, a removable plate bridge might be employed. A removable bridge may be adapted to such a, case as follows : The cuspid roots are properly trimmed and capped. Removable crowns are fitted to them. A gold plate is swaged to fit the gum be- tween the teeth, extending high enough on its labial aspect to furnish adequate support to the artificial gums, and the palatal edges far enough to furnish adequate support to the stays of the teeth. The plate is to be made of two layers — that next the natural gum of No. 32 pure gold, and covered by a plate of No. 32 platinous gold : the two are accurately adapted to one another and united by means of 20-carat solder. The ends are to be accurately adapted to the abutment crowns. Plate and crowns are set in position in the mouth, and a wax-bite taken : this is removed and set aside. While the pieces are in position an impression of modelling compound is taken. Modelling compound is preferred to plaster, because the pressure upon the plate forces the latter into accurate contact with the soft tissues. Should plaster be employed, a ridge of softened wax, wide enough to fit between the abutments, is set in the impression tray, and over it the plaster. Now, when the impression is PORCELAIN BRIDGE-WORK. 693 taken the plate is pressed up by the wax sufficiently to ensure that the natural gum shall furnish support to the finished bridge. A model is made and an articulation mounted. Should the plate be exposed by the movements of the lips, it may be necessary to adapt gum teeth (Fig. 936) ; Fig. 936. Fig. 937. if not, plain teeth are fitted ; the gum is to be subsequently formed of pink vulcanite. The teeth are to have stays fitted. The abutment crowns are removed from the model, and they, the teeth, and the plate boiled in acid. They are returned to the model and joined together by means of adhesive wax : a wire laid across the backs from one abutment crown to the other, and covered by adhesive wax, holds them in position. They are invested, and when the investment is set pieces of triangular wire are placed at the junction of the plate with the abutment crowns, and the pieces are attached to one another by means of 20-carat solder. If plain teeth have been employed, and, contouring is indicated, a vul- canite gum is attached to the plate. Porcelain Bridge-work. The general plan and methods followed in this class of bridge-work are those of Dr. E. Parmley Brown, who originated it. The objections urged against bridge-work composed of fine gold and porcelain facings united by means of fine solders — that the spaces be- tween the gum and the palatal surfaces of bridge were unclean ; that the oxidation of the base metals of the solder permitted the accumulation of offensive materials ; and that the porcelain facings were, through lack of bulk, in constant danger of fracture — led to the devising of this method, designed to overcome the several objections specified. The bridge as made and recommended by Dr. Brown consists of a rigid supporting and anchoring bar, to which are adapted porcelain teeth, subsequently united to the bar and to one another by means of porcelain fused about the parts. The usual method of anchoring the bridge is by means of arms ex- tending from the ends of the bridge, which are anchored in cavities formed in the natural teeth for their reception. Instead of what are called " self-cleansing spaces," the base of the bridge presses firmly upon the natural gum, with a view to excluding even the secretions of the mouth. A base-plate of iridio-platinum may be accurately fitted to the gum, to which the porcelain of the bridge is to be attached. A typical case for the application of this variety of bridge is that of the bulkhead — two cuspid roots supporting six artificial crowns. The abutment roots are prepared, a platinum cap fitted to each ; the edges of 694 ^.V ASSEMBLAGE OF UNITED CROWNS. the caps are left projecting beyond the edges of the roots, then slit (Fig. 938, A) — bent over and adapted to the walls of the roots in the mouth Fig. 938. (Fig. 938, B). The root-canals are enlarged and deep- ened, and metal posts filed to fit them are placed through openings made through the caps into the root-canals. A bite is taken ; then an impression is obtained, in which the caps and wires are withdrawn. An articulating model is made, and facings selected and ground into position. The face of the model is varnished and oiled, and a plaster wall formed about the teeth and model, holding the former rigidly in position. A piece of annealed brass wire, three inches long, has one extremity filed to occupy the pulp-canal of a cuspid root to the depth it is designed to carry the anchoring bar ; the wire above the cap is flattened to a distance which shall permit perforating it for the reception of the pins for the cuspid teeth. The wire is bent at right angles, then carried across the posterior surfaces of the incisor crowns ; it is to occupy the space between the pins of these teeth. Above the upper pin of the opposite cuspid crown it is again bent at right angles ; the lower end is shortened to adjustment with the depths of the pulp- canal. This wire forms a pattern which is reproduced in iridio-platinum wire from 13 to 15 gauge, which is annealed and flattened so that a por- tion of it will present a flat surface to the backs of the cuspids, and the transverse portion flattened to rest upon the backs of the incisors be- tween the pins. The wire is bent to the conformation of the brass wire pattern (Fig. 939). The caps over the root-faces are loosened, returned to position, and the iridium bar set in position. The wall holding the porce- lain facings is applied, and the perpendicular arms of the flattened Fig. 939. Fig 940 Porcelain metal band. wire perforated for the passage of the pins of the cuspid crowns. The wall is removed, the bar is cemented to the caps, and these and the bar withdrawn from the model invested and soldered with the minimum of pure gold. The piece and teeth are boiled in a 1 : 3 sulphuric-acid solu- tion. The bar and caps are set in position on the model. The teeth are returned to the plaster wall, the pins of the cuspid crowns passing through the perforations in the bar. The pins of the incisor crowns are bent over the bar, holding each tooth in position. The wire may be grooved or notched at the site of the pins to form retaining slots. The piece is now carefully lifted from the model and prepared for the appli- cation of the porcelain (Fig. 940). FOR CELA IN BR ID GE- WORK. 695 Depressions are made in a fire-clay slab which shall support the bars and the teeth. Porcelain body, made into a paste with water, is applied, giving a contour in consonance with the articulation and the contact with the soft tissues. The body is applied as the second body of a continuous- gum piece. It is set on the supporting slab, and the porcelain fused in a proper furnace, as with continuous-gum pieces. Gum contour of similar cases may be restored after the following method : Caps are fitted to the prepared cuspid roots as for the preceding case. A pair of cuspid facings are selected, and also four incisors of the continuous-gum variety. The cuspid caps are set in position and an impression in modelling compound taken, which presses firmly upon the anterior gum. A model of investing material, and next dies, are made, and an iridio-platinum plate No. 32 is swaged. This plate should extend upon the outer alveolar wall as high as it is desired to have the artificial gum. At its palatal aspect the edge should be formed to represent Fig. 941. Fig. 942. about the usual neck sections of natural incisors. The lateral edges of the plate should overlap or lie firmly against the sides of the cuspid col- lars, to which it is united by means of a small amount of 24-carat gold as solder. The piece is transferred to the mouth ; wire posts the size of the canals-are fitted ; a bite and next a plaster impression are taken. A model of investing material is made and an articulator mounted. The porcelain teeth are now adjusted to position ; the incisors, as though for the usual continuous-gum operations, and their stays are fitted to the teeth ; a support and posts of the form previously described are adapted, over which the pins of the incisors crowns are bent (Fig. 941). More investing material is applied to cover and jirotect the porcelain, and the teeth are united to the bar and stays, and the posts to the collars by means of the minimum of 24-carat solder. Fig. 942 shows labial aspect. The porcelain is next added. Sufficient body is applied to give the desired contour, the piece is baked, and the gum enamel is then added and a final baking given. Porcelain bridges for the replacement of the bicuspids and molars may be constructed after the same method. Fig. 903 illustrates a typical case. A plate is swaged, being only of sufficient size to support the bases of the teeth and the artificial gum. When the plate abuts the natural teeth a surplus of metal is left. The teeth are adapted and the post and bar support formed. The teeth are 696 AN ASSEMBLAGE OF UNITED CROWNS. to have their stays adapted. The ends of the plate are burnished about the bar, and the pins are next bent down, holding the teeth in position Fig. 943. (Fig. 944). The piece is detached from the model, invested, and sol- dered by means of 24-carat plate. The porcelain is to be added as in the preceding case. Fig. 945 shows the finished case. Fig. 944. Fig. 945. Figs. 946 and 947 illustrate the application of porcelain bridge-work to a common class of cases. A pulpless central incisor, which has not Fig. 946. Fig. 947. Fig. 948. lost too much of its substance through the invasion of caries, and whose crown has not discolored, a cuspid which may contain a vital pulp or be pulpless,— these serve as the abutments. The anchorage in the cuspid, if it contain a vital pulp, should not be deep enough to endanger that organ, and yet should be sufficiently deep to ensure immobility of the bridge when anchored by a filling of cohesive gold. SETTING BRIDGES. 697 Fig. 948 illustrates a bridge for a similar case, in which the crown of the central incisor is too frail to successfully resist the stress of mas- tication, or which has lost so much of its substance that decrowning is the indication for aesthetic considerations. Setting Bridges. Before cementing a bridge to its abutments it is tried to them, and, should any points interfere with its ready placement, they are cut or ground away until the piece may be slipped into position with easy facility. When the abutment crowns are of the barrel type, a minute opening is made in the sulcus of each crown. The zinc phosphate used for bridge-setting should be moderately slow setting ; it should remain plastic long enough to permit the deliberate and careful setting of the bridge ; should flow freely even through almost microscopic openings ; should harden in about fifteen minutes with a glazed surface ; should quickly lose an acid reaction. In an hour it should be extremely hard, and it is of great importance that it should be but slightly soluble. Fresh specimens of bridge cement are to be tested to see that they answer these requirements. For setting the variety of bridge mentioned, a few large drops of the cement fluid are placed on a clean mixing slab, and beside it an excess of powder. Powder is gradually and thoroughly incorporated with the fluid until a paste is made which drops reluctantly from the tip of the spatula. The paste, as it is, is carried into the deepest p^ rtions of the crowns. The abutment teeth, having been washed with chloroform to remove any fatty deposits and to dry them by its evaporation, are protected by napkins ; the bridge is quickly carried into place and steadily pressed into its position. The napkin is removed and a piece of heavy tin-foil is laid over the entire masticating surface of the bridge, and the patient directed to close the teeth against it, and to keep them closed for twenty minutes. Patients should receive explicit injunctions not to masticate upon a bridge for at least two hours after it has been set. In setting bridges, one or more of the abutment crowns of which are post crowns, the canals of the teeth should be cleansed with hydrogen peroxide and dried by means of alcohol and a hot blast. A wisp of cot- ton containing 25 per cent, pyrozone is passed around the neck of each root ; this will prevent exudation and keep the root free from the con- tact of secretions until the collars are set in position. The cement is made slightly thinner for setting such crowns : the concavities of the crowns are filled with cement, a portion placed in the root-canal, and the bridge is carried into place when the occlusion is tested, the tin-foil between the teeth as before. In setting a bridge, one abutment of Avhich is a bar anchorage to have a metallic filling built around it, no attempt should be made toward making the filling until the cement about the other abutments is rigid. It is, however, a wise precaution to place a layer of amalgam upon the floor of the cavity before the bridge is adjusted, and then press the bar into the amalgam. A better practice is to line the cavity with filling material, shaping a cavity in it to engage the bar, and finish- ing the margins before setting the bridge. Then, Avhen the cement of the other abutments has set, the filling about the bar is Completed with 698 AN ASSEMBLAGE OF UNITED CROWNS. cohesive foil malleted about it, holding it firmly. When perfect dryness can be maintained rolled foil No. 30 is annealed and packed with a mallet. In setting double-bar bridges the thinnest of rubber dam is adjusted, the cavities prepared, and the bridge set in position ; the portions of the cavity which would be made inaccessible by placing the bars are filled as a preliminary measure — filled a little more than necessary ; then slots cut in them which shall engage the edges of the bars, and the edges of the filling filed flush with the cavity margins. The bridge is set in position, and cohesive foil malleted about and over the bar, completing one filling. During the packing of the gold the bridge has been held rigidly in position with the left hand. If the veneer filling has been properly shaped, it almost retains the bridge of itself during the pack- ing of the gold. The second filling is completed in the same manner, and both are trimmed and polished. The rubber dam is stretched, and a cut made, joining the openings embracing the abutment teeth, and is removed. The Repair of Bridge-work. The difficulty of properly repairing bridge-work is one of the objec- tions persistently urged against it since its introduction. Any accidents to removable bridges are readily remedied by detaching the pieces and repairing in the same manner as the individual part was originally con- structed. The common accident affecting fixed bridges is fracture of a porcelain facing. This occurs usually in consequence of the porcelain facings being improperly or insufficiently protected from the direct stress of mastication, and not infrequently by the tooth being split in one of the soldering operations. If the dummies and facings have been properly constructed, made from strong teeth, and due care exercised in soldering^ porcelain facings should never break, as they are never subjected to stress. To accurately replace a broken facing or to remedy any marked defect of a bridge piece, it is in the majority of cases necessary to remove it from its abutments. If the abutment crowns are of the bar- rel variety, it is usually necessary to split the barrels to effect their removal. By means of a fine hatchet excavator the crown is marked from its edge to its cutting surface by a gradually deepening groove made in its buccal wall. When the gold is cut through a fine instru- ment is passed into the cut and the cement detached piecemeal. The crown may be quickly split by means of the cap crown-slitter (Fig. 949). An effort is now made to loosen and detach the bridge Avith- out splitting the second cap ; if this is not possible, it is also divided at its buccal wall. Should one abutment crown be of the post-and-collar variety, a drill is passed through the palatal side of the cap, severing its attachment to the post. A square-edged instrument is passed above the edge of the collar, and traction in all directions is exerted until the bridge is detached. It may be necessary to divide the collar of this abutment also : this is done at the palatal side. Should it be the facing over a post crowm that has broken, the division of the post from the cap may be made through the angle at the base of the stay ; however, the perforation through the back should be made also for the introduction of the new post. The case is boiled in strong nitric acid, which will THE REPAIR OF BRIDGE-WORK. 699 The sections of the Fig. 949. dissolve the old cement and cleanse every crevice, crowns are bent back into their orig- inal positions, and the post removed from the root, as described in Chapter XVIII. Along the cuts of the crowns, in their interiors, small strips of thin platinum are attached by means of flux wax. The bridge is set in posi- tion in the mouth ; a new post is passed into the root-canal of the ante- rior abutment through the opening in the cap made for its passage ; the end of the post is to extend beyond the opening. A bite is taken if necessary, and an impression ; a cast is made of investing material. A porcelain facing is fitted to the cap as described in Chapter XVIII. (Repairing Crowns). A porcelain dummy to be re- placed is adjusted in the following manner : A dummy the size and shape of the one broken is selected ; a spear-pointed drill is passed through the backing and gold body in the positions of the pins ; these openings are enlarged to easily receive the pins of the facing, A deep gutter is cut, burred away between the holes on the palatal side until the platinum pins protrude through them, when the facing is ground in. A thin layer of gold is scraped away from the backing, and the facing backed with very thin platinum. The surface of this stay and that of the gold with which it is in contact are covered with borax, and the fac- ing set in position and held by means of adhesive wax melted over the ends of the pins. The porcelain surfaces are covered with investment material, all the parts to be soldered left uncovered. The wax is removed, and the cast cut away to fully expose the gum edge of the platinum stay. A large piece of 14-carat solder is placed over each pin and a piece at the line of juncture between the platinum stay and the gold block, and over all Cap-crown slitter. 700 AN ASSEMBLAGE OF UNITED CROWNS other parts to be joined additional pieces are placed. The casse is heated : a fine flame is directed against the investment, and when the porcelain is red hot a touch of the flame will fuse the solder over the line of division of the barrel crown. The investment quickly turned over, the flame directed against the solder at the base of the dummy stay will fuse the solder there and that placed over the pins ; it will! run through and fill the spaces between the parts. The soldering of the anterior abutment crown is next done. This general method applies for all thorough repairs to bridge pieces. The difficulty of removing bridges, the dangers of irremediable muti- lation, and the necessary expense attending such a complicated repair have led to the devising of many methods for repairing while the bridge is in position without detaching it. One of the methods is that of Dr. Mason, described in Chapter XVIII., where a removable porcelain facing has been used, anticipating possible fracture. If a facing of one of the anterior teeth should be fractured, the pins are cut from the backing ; a new facing corresponding with the old one is selected ; its pins are to have their edges touched with a mixture of olive oil and vermilion, which marks the backings ; holes are drilled through the backing by means of a spear-pointed drill, and are coun- tersunk at their palatal sides. The tooth is to receive any grinding necessary to adapt it to the backing, and the pins are riveted in the fol- lowing manner : One arm of a pair of plate punch -forceps is covered by a concave block of lead which rests upon the labial surface of the facing. The other jaw is armed with a broad punch, and between them the platinum pins are compressed into the countersinks, filling them and forming rivet heads. The heads are rounded by means of burnishers. A method of replacing a molar or bicuspid facing is as follows : Holes are drilled through the backing, and at their palatal aspects are elongated divergingly. A facing is adapted to its surface and Fig. 950. the pins covered with zinc phosphate, and it is pressed into ~ position ; the pins are immediately separated, being jaressed against the far walls of the slots. When the cement has set any excess of pin or cement is removed. Prof. E. T. Darby suggests a method which he has found to serve well : A cross-pin facing is selected. A slot is cut in the metal backing by means of burs, giving the cavity a pyramidal form, as in the Mason backing, its small end external. A metallic bar is soldered to the tips of the pins, which have been bent to diverge slightly, uniting them ; the facing so prepared is cemented in the cavity made in the backing. Dr. Emory A. Bryant^ describes a novel and effective method of attaching a new facing. A tap and die the size of tooth-pins are neces- sary, together with a special countersinking tool and a screw-driver (Figs. 951 to 954). The pins are cut from the old backing, and holes are drilled the size of the pins of the new facing, and in the proper posi- tions. With the countersinking tool held in a right-angled hand piece, the holes are countersunk exactly to the outer wall of the backing — no ^ Cosmos, vol. xxxvi. p. 469 et seq. THE REPAIR OF BRIDGE-WORK. 701 more, no less. The nuts are made, or have been made, the size of the countersink. By means of the oiled die a thread is cut on the pin of each tooth, exercising great care that the pins are not twisted, the thread Fig. 951. Fig. 952. Fig. 953. Fig. 954. Fig. 955. to be continued to the back of the facing. Nuts are tried on each of the threaded pins, and marked to denote the pins they fit. The facing is set in position, and each nut is loosely adjusted, then alternately screwed into place, drawing the facing close to the stay. The protruding portions of nut and pin are ground down and polished. Dr. Bryant states that this substitution may be made in twenty-five minutes. CHAPTER XX. HYGIENIC RELATIONS AND CARE OF ARTIFICIAL DENTURES. By Charles J. Essig, M. D., D. D. S. There can hardly be room for doubt that a well-planned and prop- erly adjusted artificial denture contributes to comfort and health, and prolongs the life of the individual who by reason of premature loss of the natural teeth finds it necessary to wear one, but the usefulness of the fixture and its influence on the mind and general health of the patient depend very largely upon the manner in which it is planned and con- structed. It may be made an instrument of discomfort, if not of torture, by constructing it upon a faulty impression. It may entirely fail to meet the demands of a masticating apparatus by imperfect articulation of the teeth. It may so interfere with speech, through want of adhesion, that the wearer is at all times conscious of its presence, and he is thus sometimes forced to give up social intercourse, or if, as in the case of lawyers or clergymen, professional duties require the individual to ad- dress audiences, the patient feels that his usefulness is abridged, and mental depression and departure from a normal standard of health follow. Prosthetic dentistry requires in its successful practice good judgment, artistic taste, and a high degree of manipulative ability. Xo two cases are ever precisely alike, and each one demands careful study and a definite plan of procedure. The choice of material, means of attach- ment, style of teeth, and the arrangement of the latter to ensure the greatest attainable degree of efficiency in mastication are to be con- sidered. With the materials at the present time within the reach of every prosthetic dentist, and the light of the experience of other workers in that branch in the recent past, it is not claiming too much to say that artificial dentures may be so constructed and adjusted to any or all mouths as to restore the functions of mastication and speech, as well as natural appearance, in a manner but little short of absolute perfection. The hygienic conditions incident to the use of artificial dentures may be local or systemic. Many morbid phenomena of a local character may be observed as resulting from their presence, and marked constitutional disturbances have been traced to the causes above alluded to, as well as those arising from long-maintained local irritation caused by mal- adaptation or the unsuitable character of the materials used in their construction. 702 ARTIFICIAL DENTURES. 703 In the insertion of an artificial denture a foreign body is introduced into the oral cavity which may act as an irritant to tissues and organs with which it comes in contact. This is particularly liable to occur in all lower dentures, on account of the pressure being confined to a nar-- rower area and the muscles and integuments being attached well toward the top of the ridge, as in the case of the buccinator muscles ; painful abrasions frequently result in this class of cases soon after the introduc- tion of the fixture. Abrasions produced by undue pressure of the edge of a plate cause an amount of discomfort and suffering entirely out of proportion to the extent of the injury. To avoid a continuance of this trouble and to give immediate relief the patient should always be cau- tioned to return the moment the presence of the denture becomes painful. Artificial dentures are held in place by atmospheric adhesion, by clasps, by spiral springs, or by permanent or immovable attachments to natural teeth or roots. Either of these may become the cause of irrita- tion to the teeth or contiguous parts. In the case of clasps the tendency invariably is to produce morbid phenomena, and this tendency is in- creased or lessened by the character of the materials of which they are made, and the manner in which the clasjDS are adjusted and the parts of the teeth embraced by them. The result produced by clasping natural teeth is a loss of tissues, either through caries, mechanical abrasion, electro-chemical action, or by the joint action of all three. The rapidity with which the disintegrat- ing process advances depends largely upon the quality of the tooth-sub- stance, the condition of the oral fluids, the size and form of the clasp, the portion of the tooth which is embraced by it, and the material of which the clasp is constructed. A partial lower denture must be secured either by clasps or contact with natural teeth. In that class of partial lower dentures designed to replace the second bicuspids and molars on each side clasps adjusted to the first bicuspids are generally employed : caries of the approximate surfaces of the first bicuspids is more or less quickly induced, probably because the enamel is thin at that point. Incipient caries, produced by clasps at the positions above indicated, manifests itself by great sensitive- ness of the tooth, which is exceedingly painful when exposed to extremes of temperature and certain kinds of food, such as very sweet or salt arti- cles. Painful mechanical abrasions are frequently caused where mere contact with natural teeth is the means adopted for securing stability to partial dentures. Badly-fitting clasps, as may be expected, rapidly hasten the progress of caries by favoring the lodgement between the tooth and clasp of particles of food mixed with the oral fluids, which undergo fermentative decomposition and produce agents destructive to the enamel and dentine. Clasps should be accurately fitted to the broadest part of the tooth, which is usually found at or near the masticating portion of the crown, and never at the necks of the tooth. They should not be allowed to impinge upon the gum, as recession of that tissue and exposure of the cementum, with subsequent softening and caries, will almost certainly supervene. In addition to the liability to caries alluded to, the author has observed that when clasps are fitted to bicuspids for the purpose of re- 704 RELATIONS AND CARE OF ARTIFICIAL DENTURES. taining partial lower dentures in situ, those teeth are very liable to be loosened and speedily lost by the strain brought to bear upon them dur- ing mastication. For these reasons he has abandoned clasps in this class ■of cases wherever possible, using instead the outside bar shown on page 344. The result of observation as to the eifect of clasps upon the natural teeth is undoubtedly in all cases unfavorable, yet there are many in- stances in which clasps are indispensable ; but their capacity for doing harm may be very greatly reduced by adjusting them with accuracy to the most convex portions of the teeth, avoiding impingement upon the necks and cementum. It has been observed that clasps exert an influence upon teeth vary- ing in degree according to the condition of the oral fluids and the kind of metal of which they are made. Silver clasps have been found to exert a much more rapid disintegrating influence than those made of gold. Dentures with clasps or attachments made of platinum or iridio- platinum act more injuriously than the same appliances fitted with gold clasps. These difi'erences in the effects of the metals upon the teeth are undoubtedly due to a galvanic current between the tooth-structure and the metal forming the plate, aided by certain conditions of the oral fluids. Silver and platinum should not be used in the formation of clasps, or indeed for any purpose which demands contact with tooth-structure. It has been observed that platinum wire when employed as a means of retaining teeth, the positions of which had been changed in the cor- rection of irregularities, showed erosions in a comparatively short time after its application. An example of the action of silver upon the natural teeth was observed a number of years ago in the case of a man who had in an election fracas sustained a severe fracture of the jaw. When he pre- sented himself for treatment at the college clinic, nearly a year after the injury had been received, it was found that the jaw was in three parts, no union having taken place. He had received a blow from some heavy instrument upon the mental portion of the bone ; the fractures were on each side between the first and second bicuspids. The individ- ual, for some reason best known to himself, had been obliged to remain in concealment for several weeks after the injury, during which time he received no surgical treatment whatever. The appearance of the lower part of the face was greatly changed by the displacement of the disunited parts of the jaw, and mastication was impossible. As a temporary or palliative remedy for the latter difliculty a dental surgeon had fitted a bar of stout half-round silver wire entirely around the lower teeth, so as to hold the parts in juxtaposition and restore the articulation of the teeth. The individual had not worn the fixture many weeks before the posterior surfaces of the second molars, where the brunt of the force was borne, became unbearably sensitive. An examination showed deep grooves in these teeth, rapidly approaching the pulps. As the neighboring teeth appeared of good quality and entirely free of caries, the abrasion on the second molars was probably due to galvanic action between the silver support and the tooth-structure. The wearing of artificial dentures at night is a subject upon which there is much difiference of opinion : there is hardly room for doubt, HYGIENIC RELATIONS. 705 however, that disintegration of the tooth -substance when clasps are used IS likely to proceed much more rapidly where the piece is worn con- tmuously; besides, careful observation has shown that at night the oral secretions assume a slightly acid character. This has been demon- strated particularly in patients subject to enamel erosion by carefully testmg the oral secretions with litmus after waking and before the sali- vary fluids have started their usual flow. If the necks of the teeth are highly sensitive or there is well-marked tendency to softening or erosion of the tooth-structure, the patient should be directed to remove the plate each night before retiring, and to apply to the affected teeth, after thoroughly cleansing, a small quantity of pre- cipitated chalk, lime-water, or milk of magnesia. Too much stress cannot be laid upon the necessity for cleanliness, and every patient who wears a denture secured by clasps should be partic- ularly instructed in the means of removing the deposits which are usually found on the inside surfaces of the clasps. This is not generally well done by patients with the tooth-brush alone, so that a piece of soft wood armed with fine pumice is necessary to do it thoroughly, and the addi- tion of aqua ammonia is efficacious. Patients suffering from any chronic conditions of the system which are likely to be accompanied with acidity of the oral fluids must be cau- tioned to exercise the most scrupulous care in cleansing the artificial denture; and this caution is particularly demanded when partial dentures are worn. In these cases lime-water and bicarbonate of sodium are re- commended as alkaline mouth-washes, which by neutralizing the acid condition of the fluids are often effective in preventing sensitiveness and the tendency to softening of the tooth-substance. In attaching clasps to the elongated molar teeth of elderly patients the clasps should be arranged so that no broad metallic surface will be in contact with the exposed neck of the tooth. This may be accomplished by attaching the clasp to the plate by two narrow posts, as shown in Fig. 956. In the mouths of young persons whose teeth show unmistakable evidences of a tendency to rapid decalcification clasps should never be em- ployed ; and this is a matter to be decided by the dentist himself even when the patient expresses the strongest preference for the small plate attached by clasps and an equally forcible objection to the larger atmospheric plate. Of the hygienic relations of spiral springs, which as a means of re- taining artificial dentures antedated all other devices now in use, very little need be said, since the appliances are no longer used except in rare cases of edentulous mouths complicated with cleft palate, wherein atmo- spheric adhesion would be impossible. Three principal objections may be urged against the employment of spiral springs for theretention of ordinary dentures, as follows: their liability to chafe and abrade the delicate mucous-membrane lining of the cheek, the tendency of one or the other to break, and the difficulty of thoroughly cleaning them. The materials used in the construction of artificial dentures, other conditions being equal, do not differ to any great extent in their effect 45 706 RELATIONS AND CARE OF ARTIFICIAL DENTURES. upon the tissues with which they come in contact. On the other hand, the frequency and extent of oral irritation associated with the wearing of artificial dentures, irrespective of materials employed, varies with dif- ferent individuals. It is not, however, denied that modifications of that portion of the surface of the mouth covered by the artificial denture is more frequent in cases where rubber and celluloid are worn. The author has always believed that the real cause of the inflammatory condition so generally attributed to vegetable bases will be found in the following conditions : (1) The non-conducting quality of the substances ; (2) the rough condition of the surfaces of the majority of rubber or celluloid dentures, due to carelessness or want of skill in construction ; (3) want of care on the part of the wearer in not frequently cleansing the denture of deposits of food and secretions of the mouth, which are likely to un- dergo chemical change by long confinement in contact with the tissues, and thus become irritants. Either one or all of the conditions named may cause inflammation of the mucous membrane, but always, so far as the author's observation has gone, limited to the area covered by the plate. Similar conditions are frequently noticed when the dentures were of gold or silver, but always in cases where the plate was seldom removed or cleansed. And if the trouble referred to is more common in rubber or celluloid dentures than where metallic plates are worn, there are doubtless more conditions favoring such a result in the former than are found in the latter ; and the facts that the symptoms are not constant, and that by far the greater number of mouths in which rubber or cellu- loid is worn are not in the least aflFected by it, would seem to confirm the view that the inflammation referred to is due to contact with irritating products of food and secretions, and that these are equally active in all dentures, irrespective of the material of which the denture are made. Rubber sore mouth as described in the American System of Dentis- try, if met with at all, must be exceedingly rare, and the " rubber sore mouth" which passes the stage of redness and slight tenderness and extends to the tonsils and walls of the pharynx, with the parts greatly swollen and painful, rendering the wearing of the plate impossible for the time and the formation of abscesses, the author has never seen. Acute inflammatory conditions of the mouth which appear with some degree of suddenness may often be traced to persistent efforts on the part of the patient to obtain atmospheric adhesion in a badly-fitting denture by powerful suction of the tongue in the effort to exhaust the air from the chamber : violence of this kind, aided by the other unfavor- able conditions referred to, may cause occlusion of mucous follicles and the usual inflammation resulting from interruption of the secretions ; but it would be manifestly wrong to class such conditions under the heading of " Rubber Sore Mouth." The great majority of cases of local irritation associated with the wearing of dentures are not usually cases calling for the exhibition of drugs, but as the rules of hygiene extend to all conditions which may cause departure from a normal standard of health, whether local or general, the first step in the treatment of so-called " rubber sore mouth" should be an examination of the plate to determine — 1st, if there is accu- racy of adaptation ; 2d, is the surface of denture smooth enough, and in proper condition to be constantly worn in contact with the delicate EXCESSIVE ABSORPTION. 707 tissues of the mouth ? 3d, is the denture free of deposits of food and secretions ? A cure will usually be promptly effected by the fulfilment of the three conditions named. Rubber dentures favor the deposition of material composed of food and mucus secreted from the follicles of the tissues covered by the plate, which often escapes the observation of the patient and is always difficult to remove thoroughly. The patient should be carefully instructed as to the best! means of keeping the denture free from this deposit, which will consist in the frequent use of a strong solution of soda, in which the plate should occasionally remain immersed over night, and when the deposit is thoroughly softened by the soda solution the careful use of the tooth-brush armed with soap and tooth-powder. Salivary calculus, which often deposits in large quantities on lower plates, may be removed by immersing the denture over night in vinegar and water ; but if crowns of natural teeth have been reset on metallic plates, the salivary calculus must be removed by instruments, as any form of acid would dissolve the enamel and ruin the teeth. If a chronic state of inflammation of the surface covered by the den- ture has become established by violation of the conditions essential to maintenance of a normal state of the oral tissue, local applications of phenol sodique, thymozone, or listerine, diluted in the proportion of one part of the remedy to three or four of water, will generally relieve the tissues of redness and tenderness. In cases of long standing and unusual severity zinci sulphas in solu- tion, in the strength of gr. j or ij to f ^ss of water, will be found of great service as an application to the inflamed parts. Some authorities state that chronic stages of so-called " rubber sore mouth " are curable only by the substitution of a denture made upon metal. Such cases the author has never met with, and he believes that careful fulfilment of the conditions of precision of adaptation, smooth- ness of surface in contact with the tissues, and absolute cleanliness will generally be found sufficient to restore the mouth to a normal state. Excessive absorption of the alveolar ridge, ending in the entire obliteration of any semblance of a ridge, is extremely rare, and not a single instance of the kind has been met with by the author in his entire practice. The few cases of absorption of the anterior portion of the ridge which have come under his notice have been mouths in which metal plates have been worn. This phenomenon has been attributed to the poisonous action of vermilion used in dental rubbers as a pigment ; im- perfect vulcanization, causing porosity of the plate, thus favoring the absorption of secretions or the growth of micro-organisms on that por- tion of the plate in contact with the mucous membrane ; but it is quite probable that excessive absorption of the alveolar ridge is an inherited tendencv. The author has observed that condition in more than one member of the same family, and he has very recently made dentures for a gentleman of advanced age and his daughter, in both of whose mouths the anterior portion of the alveolar ridge has quite disappeared, while the ridge in the posterior part of both mouths is unusually broad and prominent. Pure vermilion, in combination with rubber, is not likely to produce deleterious effects when worn in the mouth, nor is it probable that this 708 RELATIONS AND CARE OF ARTIFICIAL DENTURES. compound can be decomposed chemically and converted into a poisonous salt of mercury by mere contact with the saliva. The mechanical dentist will, however, do well to avoid the use of nitrohydrochloric acid in removing tin-foil from the surface of unfin- ished vulcanite dentures. (See chapter on Metallurgy : Mercury.) Regarding the presence of free mercury in rubber before or after vulcanizing, Prof. Austin stated that the researches of Prof. Johnston with the microscope, and of Prof. Mayer by chemical analysis, failed to discover the slightest trace in samples of that which had been used for several years. Prof. Wildman observed that sulphur sublimed during vulcanization, but did not find the smallest trace of free mercury. Prof. Austin further stated that he never during his entire experience with indurated rubber as a base for artificial dentures detected the slightest particle of metallic mercury on the surface of any finished jjiece. In the belief that mercuric sulphide (vermilion) may be the cause of the different phases of so-called rubber sore mouth, the substitution of black for red rubber has been recommended as a means of overcoming the tendency to excessive tenderness of the mucous membrane covered by the plate. Black rubber is but a doubtful improvement upon the red variety so far as influence on the health of the tissues is concerned. As it contains lampblack as a pigment, it is uncertain whether it is more den.se and less liable to absorb secretions. The best quality of rubber for dental purposes, the one affording the greater density of surface, is that which is composed simply of caoutchouc 48 parts, sul- phur 24 parts, without any pigment whatever. This rubber is of a dark drab color, and it differs so widely from the color of the tissues that it has never been employed to any great extent in prosthetic den- tistry. Vulcanizable rubbers, of whatever composition, require great care both in investing and indurating. Campbell, the inventor of the " New Mode Heater for Rubber and Celluloid Work," demonstrated that the only way to obtain fine texture and density of surface in rubber and celluloid is to expose them to low temperature, dry heat, and contact with metallic surfaces.^ This produces a harder rubber, less porous and less liable to absorb the secretions than can be obtained by contact with plaster, or indeed by any other means ; but where the modus operandi suggested by Drs. Campbell and Evans is practised the preliminary "waxing" of the case must be done with such precision that the surface thus obtained need not be subsequently disturbed by the scraper. (See chap- ter on Vulcanite and Celluloid Work.) The theory presented by Dr. G. V. Black, that the sore mouth pro- duced by artificial dentures is due to the growth of certain fungi which elaborate an acid secretion which acts as an irritant to the mucous mem- brane, is probably correct. He asserted that he found these fungi upon the surfaces of all plates without regard to the material of which they were constructed, but in the greatest number upon the surfaces of vul- canite dentures ; which he attributed to the fact that the irregularities and roughnesses of the surfaces of such plates afforded lodging-places where they rapidly developed on account of the greater difficulty in ^ The manufacturers of rubber articles of jewelry and ornamentation long since aban- doned the use of steam as a heating medium and plaster as an investment. PARTIAL ARTIFICIAL DENTURES. 709 thoroughly cleansing them, and he regards absolute cleanliness as a complete protection from inflammation. Prof. E. C. Kirk stated, as the result of repeated tests of the mucous secretion in cases of sore mouth associated with the rubber denture, that the mucus in such cases generally showed an alkaline reaction as it was eliminated ; and he suggests the possibility that alkaline sulphides might be eliminated to a sufficient extent to exert a slight solvent action upon the mercuric sulphide of the plate, and thus form an active salt of mercury. But this theory seems to be at variance with the more practical reasoning and experience of many others who have given much thought and attention to the subject. Prof. Kirk's suggestion, how- ever, that the non-conducting quality of the vegetable bases plays an important part in the production of every kind of inflammatory action undoubtedly carries with it much force, for, as he states, "the effect on the tissues continually enclosed by the non-conducting plate is to main- tain a hypersemic condition, with slight increase of temperature : this in addition to the pressure, which, if it does not result in inflammation, is a source of irritation sufficient to bring about greatly increased func- tional activity of the cells of the parts." It was at one time thought, and so claimed by many of its advocates, that the substitution of celluloid for rubber dentures would prove an effective remedy in cases of sore mouth ; but that material is open to the same objections as rubber, and to a greater degree in consequence of the sponginess of surface incident to the evaporation of camphor. Partial artificial dentures immovably attached to one or more natural teeth or roots of teeth, or the attachment of several crowns to one or more roots as in bridge-work, present many points for consideration from a hygienic standpoint. The operation of substituting an artificial crown for a natural one should not, if properly performed, affect the integrity of any of the surrounding tissues, and yet if the work is ill- fitting and done in a slovenly manner, with the cap or ferrule extend- ing so far under the free margin of the gum as to impinge upon the alveolar border of the socket, persistent irritation may be established, which can only end in disorganization of connective tissue and loss of the root if the cause be not removed. The experience of the author has been that roots upon which artificial crowns have been fixed are less liable to pericemental inflammation and abscess than are devitalized teeth with natural crowns, the greater success in the treatment of the crownless root being probably due to its accessibility and the better opportunity which undoubtedly exists of filling the latter with thoroughness to the full extent of the canal. The fact, too, of restoring occlusion, whereby roots are brought into use, helps to keep them in a healthy condition, and prevents their gradual extrusion and premature loss from the alveoli. As is well known, there are a variety of methods of setting artificial crowns to roots. Any one of these methods, if lacking in the ele- ment of precision of adjustment, may favor the establishment of patho- logical conditions. The Richmond crown, properly so called, with an accurately fitted cup or ferrule, is perhaps less liable to cause irritation to the surrounding tissues than any of the methods of crown-setting in use. The worst results have been" noticed in that class of crowns, without 710 RELATIONS AND CARE OF ARTIFICIAL DENTURES. caps or ferrules, in which the attachment to the root is secured by means of amalgam. If the latter is allowed to project at the point of union of the crown and root, it soon becomes exceedingly irritating to the mar- gins of the gum — a condition marked by redness, tumefaction, and a tendency to bleed, particularly in the recumbent position at night, and a nocturnal flow of saliva similar to that noticed in pyorrhoea alveolaris becomes established. The only remedy for chronic dental irritation due to this cause is the removal of the crowns and the substitution of others which are not dependent upon amalgam as a means of attachment. Bridge-"Work, which consists of the bridging of interdental spaces by one or more crowns fastened together and attached to natural teeth or roots, frequently causes pathological conditions from a want of care and exactness in their construction, and by requiring two or more roots to sus- tain an amount of force in mastication greatly in excess of that for which they were intended. As a result of the excessive strain to which they are subjected under such conditions, fracture of the roots, chronic in- flammation of their pericemental membranes, abscesses, or protracted tenderness may occur, either of these being sufficient to seriously inter- fere with mastication and render the denture useless. Cases of serious local irritation from unusual causes are occasionally met with in so-called bridge-work. The author recently met with a case in which a bridge had been constructed for the purpose of replacing two right superior bicuspids. The attachment consisted of a wire of ordinary 18-carat gold fastened with amalgam in the cuspid and first molar, both of which were devitalized. The wire had gradually yielded under the pressure of mastication until the necks of the two artificial teeth had become imbedded in the gum tissues, which were so much swollen that only the points of the porcelain teeth were visible. The general health of the patient was greatly affected by the persistent irritation caused by the displaced bridge : no time was therefore lost in removing it. This was done with the greatest relief to the patient, the tissues returning within a few days to their normal condition. Although skilful and experienced bridge-workers generally plan and construct dentures of this class with special reference to complete clean- liness, yet it is doubtful whether all parts of the best of them can be reached by the tooth-brush as thoroughly as is the case with the ordinary removable denture. In many cases the irritation induced by the impac- tion of food-debris and fermenting secretions, and the unusual strain upon roots of diseased teeth, will cause hypertrophy of the surrounding tissues or rapid loosening from absorption of their alveolar borders. These conditions are always accompanied by more or less vitiation of the secretions of the mouth and foulness of breath, constituting in many cases potent arguments against their introduction. Of the different methods of constructing this class of dentures, the removable bridge introduced and described by Dr. C. M. Richmond is probably open to fewer objections than any of the other forms ; yet even that plan requires good judgment in determining the capability of teeth or roots to sustain the extraordinary strain to which they must neces- sarily be subjected, and the greatest skill and care in the construction and adjustment of the different parts of the fixture. The introduction of immovable " bridge " dentures has undoubtedly IMPORTANCE OF CLEANLINESS. 711 in a great many cases caused so much discomfort and irritation to sur- rounding tissues as to render mastication almost impossible, and it is doubtful whether extensive operations of this class, considered from their hygienic relations, are as satisfactory as properly planned and constructed removable dentures retained in position by atmospheric adhesion. Care in cleansing artificial dentures of whatever form, size, or material is of the utmost importance. The cleansing should be performed imme- diately after eating, and particularly before retiring for the night. If this be not done with some degree of thoroughness, debris of food mixed with saliva and mucus forms an adherent mass upon the plate which undergoes fermentation and decomposition, with the result of irritating the mucous membrane and producing a general inflammation of the oral cavity, and the irritation of the oral secretions may cause serious de- rangement of the digestive function. It is the duty of the dentist to instruct his patient as to the import- ance of cleanliness and in the proper means by which that result may be accomplished. The thorough cleansing of an artificial denture, although apparently a simple operation, seems to be a matter of great difficulty to the majority of patients, and but few are capable of maintaining a fault- less condition of their dentures ; yet the tooth-brush armed with soap and ordinary tooth-powder is quite sufficient to maintain a clean and highly polished surface. The patient should be cautioned against the danger of bending partial lower dentures of gold or other metals by grasping them with too much force while brushing, and in the case of vulcanite dentures to avoid " boiling them out " in hot water. Many individuals who have previously worn gold dentures resort to that means of ridding the fixture of deposits of food, etc. which have found a lodgement under the teeth and behind the backing. The author has met with several instances where recently constructed vulcanite dentures have been completely ruined within a short time of their completion by immersion in boiling water. In the construction of metallic plates for partial dentures the plate should be accurately fitted around remaining natural teeth, so that there will be no spaces between the plate and the teeth to admit of pinching of the gum between the edge of the former and the neck of the tooth ; and where a point of the plate extends betAveen two teeth — as, for instance, the central incisors — such projection must be made to fit the space accu- rately, or it will be certain to cause inflammation which may result in permanent impairment of the teeth. Defects of this kind may be cor- rected by soldering an addition to the edge of the plate in order to bring it almost in contact with the teeth, or else by cutting away the plate so freely that its distance from the teeth will preclude the danger of pinch- ing the tissues. CHAPTER XXI. PALATAL MECHANISM. By Rodeigues Ottolengui, M. D. S.^ Cleft Palate. Cleft palate may be divided into two classes — acquired and con- genital. Acquired lesions include all of those cases where the indi- vidual, having been born with a normal oral cavity, later in life suffers Fig. 957. a division of the hard, or of the soft palate, or of both. This unfortu- nate mischance may be caused by an accident, such as a knife-thrust ; the sequence of disease, usually syphilis ; or the result of a surgical opera- tion for the removal of malignant growths. ^ I am indebted to Dr. Norman W. Kingsley for the use of his large collection of models from which to choose for illustrations, as well as for the privilege of referring to cases from his practice in order to more clearly expound the theories and principles set forth 712 CLEFT PALATE. 713 Tlie acquired lesions may be very slight, as a mere perforation of the hard palate, or they may be most extensive in character, comprising a complete cleft of the hard and soft palate, with total destruction of the vomer and turbinated bones, as well as the bridge of the nose, and sometimes the nose itself. Such an extreme case, of course, would only have its origin in disease. Between the two extremes cited an endless variety of cases are found, many of which will tax the ingenuity of the operator to its utmost. The conditions which may follow upon unsuc- cessful^ surgical operations frequently add to the complexities of cases. Fig. 957 shows such a case, the absence of the uvulse, and the adhesions which have united the posterior borders of the divided soft palate to the pharyngeal wall, making this case readily distinguishable from one of congenital origin. Nevertheless, whether the acquired lesion be of small or great extent, the prognosis is more certain than in the congenital cases, because it has been demonstrated that if the operator succeeds in replacing the lost parts with an instrument properly constructed and suited to the indi- vidual requirements, normal functions will be restored almost imme- diately. The patient needs but to accustom himself to the new and Fig. 958. strange condition in which he finds himself, to be able to speak as well as ever ; this because he had acquired all the normal habits of articu- late speech before meeting with disaster. He has lost part of the natural organs with which he was endowed, but, having known their uses, he readily accustoms himself to the artificial substitute, which enables him to produce the same sounds by the same movements of the organs which remain intact. As the instruments to be made for persons 714 PALATAL MECHANISM. suifering from such misfortune are to be constructed on the same general principles which must guide the dentist in the treatment of congenital lesions, description at this point is unnecessary. Congenital cleft palate is a division of the roof of the mouth of more or less extent, which is present in the infant at the time of birth. Congenital clefts come to the dentist for treatment in one of three conditions : The cleft of the soft palate only, which may extend to the posterior border of the hard palate or be scarcely more than the division of the uvula, as in Fig. 958 ; the cleft of the soft and hard palate, in which the cleft may penetrate the bony tissue but slightly or pass through the hard palate and also the dental process, obliterating entirely the intermaxillary bones, as in Fig. 959 : any of the above con- FiG. 959. ditions complicated in an endless variety of ways through unsuccess- ful surgical operations. In these latter cases the most common pre- sentment is a bridging of the gap, with the soft tissues drawn together tensely, leaving an aperture through the hard palate anteriorly and an inadequate length of soft palate posteriorly, the tightly drawn tissues which form the surgical bridge not being long enongh to occlude with the posterior pharyngeal wall ; or where there has been only a cleft in the soft palate, the cleft is usually found partially closed, with no advantage to the patient, and offering a greater obstacle to the success of the dentist. In some of these cases the intervention of the dentist is rendered useless, while in those where it is possible to make an instrument, the CLEFT PALATE. 715 difficulty of constructing the same is greatly increased, owing to the complexities of the altered conditions. The modern instrument which the skilled dentist supplies to a cleft- palate patient, is either an artificial velum or an obturator, both of which are admirably adapted to the correction of the abnormal speech of these suiFerers, and either of which may be requisite in a special case. It may be stated, however, as a rule for guidance in general practice, that the artificial velum will more quickly enable a cleft-palate patient to acquire the aft of speaking correctly, whilst after having learned to speak prop- perly the obturator may afford him equal satisfaction. The above statement is an important truth which should be promi- nently borne in mind ; and, moreover, it is this fact which accounts for the many recorded cases where dentists have replaced artificial vela with obturators, often poorly constructed, and then have hastily pub- lished the statement that the patient liked his instrument so much better than_ the other, and that " she talked perfectly as soon as my obturator was inserted." In making obturators for persons who have never worn an instrument of any kind tlieir results would be much less favorable. The knowledge of how best to serve a cleft-palate patient, and what manner of instrument is best adapted to his requirements, necessitates an intelligent comprehension of his needs, as well as of the principles upon which obturators and vela are constructed, together with the uses which they are meant to serve. In the production of articulate sounds the normal individual is sup- plied with a soft palate, or natural velum, of great mobility, suspended from the posterior border of the hard palate. This natural velum serves two important purposes : First, it is needful, in the production of many sounds, that they should be free from nasal resonance, which would result if permitted to escape through the nasal passages. That the nasal and oral cavities may be completely separated, the posterior wall of the pharynx rises, forming a well-defined ridge, against which the vehnn occludes, being drawn backward and upward to meet it. Thus the sound is forced to pass exclusively through the mouth, and is rendered clear and distinct. Second, the natural soft palate serves as an abut- ment against which the tongue rises in the formation of such sounds as Ic, g, and ng. A cleft of the palate consequently leaves the patient with no means of shutting off the nasal passages, and with an inadequate organ with which to produce the sounds specified as well as many others. The artificial palate, therefore, whether velum or obturator, must enable the patient to completely shut off the nasal passages, and it must stop the gap in the roof of the mouth, restoring the normal vault, and rendering possible the production of all the sounds with which the cleft interfered. The artificial velum and the obturator both accomplish this, but their modes of action are quite distinct. The artificial velum which has proven to be the simplest and at the same time the most universally efficacious is the invention of Dr. Xorman W. Kingsley. It is made of soft rubber (vulcanite), from which fact it is clear that the theory of its action is to simulate the movement of the natural organ which it replaces. Being exceedingly mobile, it responds to the movements of the muscles which it engages, rising and falling 716 PALATAL MECHANISM. exactly as a natural velum would, while it is so fashioned that at the same time it occludes with the ridge of the pharyngeal wall, completely shutting off the upper passages. The Kingsley velum (Figs. 960-962) consists of two flaps joined throughout the median line. The lower flap, the one which completes Fig. 960. Fig. 961. Fig. 962. the palatal dome, extends from the apex of the fissure posteriorly as far as the bases of the uvulse. Its general form is that of a triangle, the apex of which occludes with the apex of the cleft, the base extending across from one uvula to the other. This flap overlaps the soft parts sufiiciently to prevent its being pushed through the cleft into the upper cavity. The other flap is of a similar triangular shape, the posterior border, however, being curved and thinned out to a feather edge, so that when in occlusion with the pharyngeal wall it curls up, thus presenting a flat surface for better contact, while its thinness prevents irritation to these sensitive parts. This flap is above the fissure and rests upon the upper surfaces of the divided palate. The two flaps are united along the median line, so that when complete they form a single appliance. The flaps having but a narrow line of union, grooves are produced laterally, and when in position the two halves of the soft palate rest in these grooves. In connection with the artificial velum a metal plate is constructed, clasped to the teeth, having a pin upon the upper surface which passes CLEFT PALATE. Ill through a hole in the velum, and thus holds it in place while allowing it lateral motion. Fig. 963 shows an instrument in position, the uvulse appearing pendant below the grooves of the artificial palate. Note the relation between the posterior border of the velum and the wall of the Fig. 963. pharynx. The rationale of this appliance is as follows : In the effort to close off the upper passages the sides of the divided natural palate approximate each other, and at the same time are drawn upward. Thus they first hug the artificial velum tightly, and then, owing to its elas- ticity, carry it upward. Coincidently, the wall of the pharynx rises, forming a ridge which meets the feather edge of the artificial velum, Fig. 964. curling it up, thus accomplishing perfect contact, completely preventing the escape of sounds through the nasal passages. At the same time the velum, completing the proper arch of the vault, is rigid enough to serve as an efficient abutment for the tongue when necessity compels such con- 718 PALATAL MECHANISM. tact. Fig, 908 shows the upper view of the instrument seen in Fig. 963, and is introduced to give a clearer idea of the attachment of the vehim to the plate, as well as the general character of the grooves. As stated above, the flaps which constitute the velum are triangular in shape, yet it will be observed that the velum shown in Fig. 962 is square at the anterior end. Where the cleft is in the soft palate only the triangular velum is required, but where the cleft passes forward, entering the hard palate, it is frequently more desirable to fill the aper- ture in the hard palate by vulcanizing hard rubber upon the upper side of the metal plate, the soft-rubber velum having a square end to meet a similar surface of the hard rubber. Such an instrument is seen in Fig. 965, the abutment of the hard and soft rubber being clearly indicated. The projecting point seen in this Fig. 965. figure was for a special purpose, and is not ordinarily required. This patient was a girl aged fourteen, and presented an extensive fissure through hard and soft palate, complicated with a hare-lip, upon which a fairly good result had been obtained by a surgical operation in early life. Fig. 966 shows a model of her mouth, the aperture seen above the incisors representing the passage of the fissure through to the nose, but somewhat exaggerated, having been enlarged with a knife for convenience in constructing the instrument. The girl's articulation was bad, but the greatest difficulty of understanding her arose from the excessive nasal quality of her voice. Externally, she was much disfigured by the fact that the ala of the nose, on the side where the hare-lip had been, was more sunken than is usual — so much so, indeed, that the nostril on that side was completely closed. If the reader will read aloud a few lines on this page, and while doing so will close one nostril by pressing down the ala with one finger, he will readily discover that such closure of the nostril produces considerable nasal quality of voice. Thus it was very desirable, both from a cosmetic standpoint and for the benefit of her speech, that the sunken ala should be raised. Indeed, the father of the child earnestly solicited an attempt of this nature. Thereupon the writer adopted what proved to be a simple and effectual method of accomplish- CLEFT PALATE. 719 ing the desired end. The metal plate having been fitted, a square platinum bar was soldered to the upper side and bent so that it protruded through the nostril, when it was cut off short enough to be out of sight. The hard rubber intended to plug the aperture in the hard palate was then Fig. 966. """"UHjliiBgi)" attached, and with the soft-rubber velum in position the result is seen in Fig. 965, the end of the platinum bar being shown at a. The next step was to make a square tube which should telescope over the platinum bar, fitting accurately, so that motion would be prevented. To the end of this tube was soldered a platinum button, so placed that when in position it rested against the inner surface of the sunken ala and lifted it to a proper position. Two views of this tube and button attachment are shown (Fig. 965, b and c). In use the instrument is placed in the mouth, the platinum bar passing readily into the nostril ; then the but- ton attachment is slipped over the bar through the external orifice of the nose, the ala being thus distended, and at the same time exerting sufficient pressure to prevent its dislodgement. The fixture is worn with comfort, and the button attachment is tolerated by the nose, the pressure not being sufficient to produce ulceration or absorption. More- over, while the child's speech, of course, was not immediately improved by the introduction of the palate instrument, the nasal resonance was very markedly lessened instantly by the lifting of the ala. Consequently, it will be but a question of time when her speech will be rendered normal, which it never would have been with one nostril closed. It may be well to emphasize the fact that the mere insertion of an artificial palate cannot be expected to enable the patient to speak cor- rectly, any more than the possession of a piano or violin would make the 720 PALATAL MECHANISM. owner an accomplished musician. The artificial palate, properly con- structed, supplies the patient with the means of perfecting his speech, but perfection itself must come through practice. Education by a teacher who thoroughly comprehends the needs of the cleft-palate patient will greatly shorten the time required for improvement, as well as ensure a better final result. But the co-operation of the patient is a requisite which is, strangely enough, not always to be counted upon. And it is those persons who have no ambition to help themselves, who have claimed that artificial palates have done nothing for them. An instance of this is noted in a young man at college and approaching manhood who seems to have no conception of the wretched sound of his speech. An instru- ment admirably adapted to his needs, and one which undoubtedly made it possible for him to attain perfect speech, was worn by him but three months, and then discarded as of no value to him. One reason why the artificial palate cannot be expected to enable the patient to speak properly at once is this : With normal organs one pro- duces articulate sounds by utilizing the normal actions of his throat- muscles and the tongue and lips. With abnormal organs, as with a cleft palate and hare-lip, the individual, in the effort to produce the sounds which he hears from others, compels his tongue, lips, and throat-muscles to adopt habits which are totally dissimilar to normal movements. When, therefore, the artificial palate is inserted, with which perfect speech can be attained only by normal movements, it is evident that the incorrect habits must first be overcome ; and, secondly, the correct action of the organs must be acquired. Consequently, those dentists Avho report that instruments of their devising correct the patients' defective speech in- stantly, simply report what is not, and cannot be true if the case be a congenital one. Since the acquirement of wrong modes of speech must prove so deter- ring to the patient who essays to improve his speech by resorting to an artificial palate, it is a reasonable corollary that the earlier the instru- ment is made the less will the patient have to overcome. It is therefore both wise and feasible to insert appliances even before the appearance of the permanent teeth. The co-operation of the patient, however, being of such importance, especially where lessons in articulation are to be given — which is always desirable — it is scarcely wise to undertake a case until the little patient is old enough to appreciate the conditions and their remedy. Therefore, except in rare cases where the child is un- usually well developed and mentally bright, it is best to wait until the fifth or sixth year. This statement is introduced at this point because, whatever doubt there may be in older patients as to the choice between the soft velum and the obturator, with children, and especially young children, the velum is the one and only best dependence. An obturator is an instrument designed to merely fill a gap or close an opening in the palate. To be of any service the instrument must be so constructed that it accomplishes all that the artificial velum enables the patient to do, even though in an entirely different manner. It must accurately fill the cleft when the parts are at rest; it must also fill the fissure whenever and no matter how far the movable sides of the cleft are draron upward. To serve such a purpose the obturator must be so thick CLEFT PALATE. 721 that when the sides of the palate are drawn upward to their greatest limit they still rest against the sides of the obturator. Moreover it must be of sufficient length to be reached by the posterior wall of the pharynx, and it must be thick enough at the back end, so that when the pharynx does come into contact with it the closure of the posterior nares will be complete. When using the term '• thick," allusion is made to the diameter through the obturator from the oral to the nasal surface, not to the thickness of the rubber, for these obturators are hollow bulbs and the rubber has but the thickness of a single sheet. In Fig. 967 is shown a model with an obturator in position. The Fig. 967. plate is made of iridio-platinum and the obturator is a hollow bulb of hard rubber. This figure shows the length of the obturator in relation to the uvulse, as well as the manner in which the oral surface of the instrument fills the gap and completes the arch of the vault. In Fig. 968 the same instrument is shown in profile. It is seen that the rubber Fig. 968. bulb is attached to the metal plate by passing over a bar which is sol- dered to the plate, a nut holding it fast. Thus the bulb may be removed in order to repair or alter clasps or to do anything requiring the ope- ration of soldering, which would be difficult to properly perform were the rubber bulb permanently attached. The figure also shows the thick- 46 722 PALATAL MECHANISM. ness of the obturator, which is so shaped that as the divided palate rises contact is preserved. This instrument is a modification of the original Suersen device. In use, an obturator of this kind, unlike the artificial velum, is sta- tionary in its position, but it is of such form that the pharyngeal muscles of the throat in the movements incidental to the production of articulate sounds hug the obturator, and so separate the cavity of the nose from the cavity of the mouth. In the American System of Dentistry (vol. ii. p. 1068) there is figured a Suersen obturator, modified by the addition of a hinge, for which the following claim is made : " The main advantages of this appliance are — that it is made of a durable material, is easily constructed, and that articulation can be learned vnth it more readily than ivith any other appli- ance.''^ This claim appears to be based upon the operation of the hinge which unites the obturator with the plate, but this is a misleading device. To the inexperienced it might appear to be an improvement, but in actual practice it will be found to possess no advantage over the Suersen obturator without the hinge. Fig. 969. That the reader may better comprehend the explanation of this fact, illustrations of a hinged obturator have been inserted. Fig. 969 gives a view from the oral aspect, while Fig. 970 shows the upper side. In both figures A represents the metal plate, B the hinge, and C the rubber bulb or obturator. Unlike the artificial velum, the obturator may be immovable and yet subserve its purpose, because the soft parts throughout all their varied motions are always in contact with the instrument, the utterance of articulate sounds being thus rendered possible. The addition of the hinge is intended to allow the lifting of the obturator. Even granting that the levator muscles would be powerful enough to accomplish this, the question arises. What will be gained? Unfortunately, nothing, because the same benefits will obtain with an instrument of exactly the CLEFT PALATE. 723 same shape, immovably attached. But when further examination of this sort of appliance is made in the mouth, it is readily seen that the Fig. 970. levator wuseles do not lift the hinged obturator, hut, on the contrary, they raise the sides of the cleft, which slide along the bidb exactly as though it were immovable. The original of the instrument shown in Figs. 969 and 970 was made for a patient who for years had been wearing a soft-rubber velum, with which he had learned to speak correctly. This hinged obturator did not rise and fall as it was expected to do, and the patient discarded it and reverted to the velum. Nevertheless, with the hinged instrument this patient talked very well, the reason being that, having learned to speak with his velum, he could speak with the obturator, and this in spite of the failure of the hinge action. One of these appliances was made for a young lady who was assured that she would speak well within a year, but at the end of three years no improvement was noticed. An examination of the appliance in the mouth showed that the levator muscles did not lift the bulb at all, and it was more of an embarrassment than an advantage. Unlike the pre- vious case, where the patient had learned to speak with a soft velum, this hinged instrument was the initial effort made for her relief. Again the hinge failed, and the obturator was practically the same as one con- structed without a hinge. But this patient found her appliance of no benefit to her, whereas when she was given the same plate with the same hinge, but with a soft-rubber velum attached to it, a course of instruction covering a few weeks enabled her to speak quite well, and she will unquestionably continue to improve until her speech is perfect. These two cases emphasize the fact, which should be prominently borne in mind, that the soft-rubber velum is the instrument best adapted for correcting the speech of cleft-palate patients : that having learned to speak by using a soft-rubber velum, these persons will do well with a Suersen obturator, with a hinged obturator whether the hinge works or not, and in some cases even with the crude class of instruments designed for no other purpose than to stop the opening in the hard palate. There is but one possible condition where a hinge is needed in con- nection with a hard-rubber bulb, and that is where a surgical operation has failed, a bridge having been constructed across the centre of the fissure, leaving a cleft posteriorly and a perforation anteriorly. The instrument for such a case may be a hard-rubber bulb which passes through the anterior opening, filling the posterior cleft and reaching to 724 PALATAL MECHANISM. the pharyngeal wall during the act of speaking. Such a bulb is hinged to the plate, and it necessarily rises and falls, because it rests upon the upper side of the surgical bridge, and the levator muscles cannot elevate the halves of the divided palate without raising this bridge and with it the extension which carries the obturator. It is rare that such an ante- rior opening will permit the passage of the hard bulb, though such cases have been treated. The history of an instructive case which passed through the writer's hands a few months ago is here given. Before describing this case refer- ence must be made to another sort of obturator which had been employed in this instance. The object in hinging a hard-rubber obturator is to furnish an instrument which will simulate the action of the artificial velum. In Germany the same result had been sought in a different manner, I do not know who claims to be the inventor of the method, but the one which was seen in this case was made by Dr. C. Schultsky of Berlin. This was merely a soft-rubber obturator — in other words, a soft-rubber bulb — hollow like the hard-rubber bulbs, but so fashioned that it could be inflated something after the manner of the pneumatic bicycle tire. The idea evidently is that the soft-rubber ball, placed in the back of the throat, may be compressed by the muscles, thus serving to fill the gap under all circumstances. The history of the patient is as follows : Mr. F was born in Posen, Germany, in 1861, and was thirty- four years of age when he presented himself for treatment. At birth he had a fissure of the soft palate which reached forward to the border of the hard palate, but did not extend into the bone. Nevertheless, he had a hare-lip, which was operated upon during infancy with but partial suc- cess, an opening being left near the nostril. At thirteen Dr. Suersen made for him an obturator having a hard-rubber bulb. This was worn for a year, when the clasp on one side was broken and the fixture was abandoned. At the age of twenty Prof. Wolf of Berlin accepted him as a patient at his private clinic and undertook to close the cleft surgi- cally, and at the same time performed a supplementary operation on the lip. This latter operation was a complete success, and Mr. F — has now a good lip both in appearance and usefulness. A heavy moustache almost completely covers the scar, so that there is no external evidence of his deformity The operation upon the cleft, however, was another addition to the list of cases where the failure of surgical measures has rendered the dentist's work more complicated, without compensating advantage to the patient. The cleft originally extended to the border of the hard palate, so that it would have been comparatively simple to provide for him an artificial velum similar to that shown in Figs. 963 and 964. After learning to speak he could then have had an obturator should he have desired it. The operation, however, by partly closing the cleft constructed a bridge of soft tissue over which a plate could not be worn, so that it became necessary to have an extension to the plate which should carry the appliance used to fill the gap. Thus the patient was very much worse off after, than before his operation. A year later he placed himself under the care of a dentist, Dr. C. Schultsky of Berlin, who made for him a soft-rubber obturator. All that remains of this instrument is shown in Fig. 971. This consists of a vulcanite plate clasped to the. CLEFT PALATE. 725 natural teeth and carrying a few artificial teeth. Immediately at the pos- terior border is a small extension [a), also of vulcanite, which is connected Fig. 971. with the plate proper by a gold slide (6) which moves forward and back- ward in a metal slot, thus providing for antero-posterior movement. Next there is a gold spiral spring (c), which permits the obturator to follow the play of the muscles in any direction. At the posterior end of the gold spring was permanently fastened a soft-rubber bulb or ball [d). Judging from what was left of this bulb, it may be inferred that originally it was quite thick along that portion which formed the palatal surface and was intended to complete the arch of the vault. Into this thick portion the spring was fastened. Thinner walls extended upward, completing the bulb and leaving it hollow. There was some sort of orifice and stop- valve, inadequately described by the patient, through which he was instructed to inflate the bulb every morning, the air gradually escaping during the day. He wore this instrument for five years ; during this time, however, the bulb burst, whereupon he continued to wear it in its ruptured condi- tion. Then he had a second bulb attached by the same dentist, which after a brief time also burst. Nevertheless, he continued to use this appliance for eight years more, and the figure shows the fixture as I found it. Two facts in connection with this case are peculiarly instructive : so long as the original bulb remained whole there was no improvement in the patient's speech ; second, after it had burst he noticed a very rapid change, and Avithin two years he was speaking with approximate correctness. Thus the ruptured bulb was better than the soft-rubber obturator which it was intended to be ; and the point of 726 PALATAL MECHANISM. great interest here is that, though in a very crude way, still in principle, the bulb became a Kmgsley soft velum as soon as it was ruptured. This can be better comprehended by comparing Fig. 971 (Dr. Schultsky's instrument with bulb ruptured) with Fig. 972 (which shows the appli- ance constructed for him by the writer). It will be seen at a glance that the velum here appears to differ from the typical form shown in Figs. 960, 961, and 962 in that there is but a single flap. It is there- fore necessary to explain how it is that the principle is the same though the form is different. The typical velum has two flaps, one of which lies in the upper cavity resting upon the sides of the cleft, while the lower flap is below, the two forming grooves in which the sides of the Fig. 972. cleft move. When closed, the uvulse, or extreme posterior ends of the split velum, approximate one another, hugging the artificial velum closely. Fig. 973. Fig. 973 shows a model of Mr. F 's mouth, and the absence of the uvulse will be observed. The uvulte were originally present, but were destroyed by the surgical operation, and the sides of the cleft poste- CLEFT PALATE. 727 riorly are now continuous with the pillars of the fauces. Here, there- fore, there was no need for grooves, there being no possibility of the close approach of the sides of the cleft. A single flap was made^ such as is shown in Fig. 972. The anterior edges were made heavie/ than usual, to offer sufficient resistance to ensure the raising of the hinge ex- tension which connected the velum with the plate in the roof of the mouth. The single flap is similar in the theory of its office to the single flap of Dr. Sercombe, but modified to assume the more practical form seen in the upper flap of the Kingsley velum. Dr. Sercombe claimed that the flap should not reach the posterior wall of the pharynx ; in this he made a grave error. Here, tlien, may be indicated the reason why the hinge is of no value with an obturator, and yet becomes a necessity with such a case as the last two — viz. where the apex of the fissure is distant from the posterior border of the hard palate. Obturators are constructed of hard rubber, have sloping sides, and are highly polished. In the efforts to close the cavity of the nares the levator muscles draw the sides of the cleft upward and slightly backward, and if a patient can be made to swallow with the mouth open, the operator will readily discover that the tissues slide along the smooth sides of the obturator, but do not raise it. The hinge, therefore, is useless. With the other condition a totally different result obtains. The soft velum, lying entirely upon the upper surface of the cleft, and the anterior edge of the velum being stiff" and wide, while the apex of the fissure presents the usual angle, it fol- FiG. 974. lows that the natural palate cannot rise without carrying the superincum- bent velum with it. This it could not accomplish if the extension which connects the velum with the plate were unyielding. Consequently, the hinge is a positive necessity. Fig. 974 shows the model of Mr. F- 728 PALATAL MECHANISM. with appliance in position, the dotted line indicating the border of the velum, which is above the fissured sides of the palate, and making it clear that no movement can displace it, while the least retraction of the tissues must be followed by a responsive movement of the velum and the hinged extension. In the figure the velum is seen at a and the hinge at b. The plate in this instance was made of vulcanite to suit the wishes of the patient, his original plate having been of that mate- rial. Metal would have been preferable. Fig. 975 is of special interest : it shows a similar instrument having a hinged extension, but the soft velum is of the typical form, because, Fig. 975. although there was a great space between the border of the hard palate and the apex of the fissure, thus necessitating the hinged extension, nevertheless the fissure itself was fairly regular, the uvulse being pres- ent, and the two sides of the cleft when shutting off the cavity of the nares working co-ordinately. The model of this case is seen in Fig. 958, while the instrument with tiny velum is shown in Fig. 975. In connection with hinged artificial palates it is also of interest to record the fact that this case was treated by Dr. Kingsley some twenty years ago. Taking the Impression op Olept Palate. No appliance made by the dentist needs to be more accurately fitted than an artificial palate. It is obviously a corollary, therefore, that the plaster model should be as nearly as possible an exact reproduction of the mouth which it represents. To obtain such a model requires skill, but not more than should be possessed by the qualified practitioner. Yet the difficulty of taking the impression is the obstacle which has hindered many from attempting to treat these cases, while the ultimate failure of many others who have essayed to make instruments is directly traceable to their inaccuracy in this initial step. The ordinary impression taken for artificial dentures is easy, because a model is required only of that portion of the mouth, the tissues of which overlie bone. Therefore, whether the impression material be introduced hot or cold, hard or soft, in large or small quantity, the resultant im- pression is approximately the same, because of the resistance oflFered by the roof of the mouth against which it is pressed. When, however, too much material is carried into the mouth, so that it extends beyond the border of the hard palate, the common experience is what is called " gag- ging." A consideration of what tliis "gagging" is, will make more readily understood a fundamental principle involved in all cleft-palate cases. The soft palate is sensitive, and when the impression material is brought into contact with it, the result is an irritation or tickling, where- TAKING THE IMPRESSION OF CLEFT PALATE. 729 upon the involuntary muscles of the throat endeavor to draw the parts away from the intruding substance. Thus the velum is elevated, and consequently were a model to be made from such an impression it would be inaccurate as to the posterior portion of the mouth, in that it would not be a representation of the parts at rest. With the velum divided as in cleft palate, the disturbance of these sensitive tissues upon the introduction of the impression material is even greater. The two halves of the soft palate are not only drawn upward, but they also approach each other. Thus the resultant model will show the cleft narrower than it really is when the parts are at rest, and the pose of the divided palate will be wrong, so that no proper calculation can be made for restoring the true arch of the vault. This will obtain whether the impression be taken with plaster of Paris, or with impression com- pound softened by heat. Where the impression comi)ound, however, is not very soft, or where the divided palate is lacking in vital response, the impression material will merely press the soft tissues before it, the final model being absolutely worthless. Thus it is seen that no one can obtain an absolutely accurate impression of the divided velum in its normal pose. Nevertheless, a model may be made which will be as accurate as any model of the mouth can be. The method of procedure is as follows: Select an impression-tray of the ordinary form, just large enough to embrace the arch without stretch- ing the mouth, and long enough to reach slightly beyond the posterior border of the hard palate. In the majority of cases this will answer all purposes, but occasionally it may be advantageous to extend the cup by adding to it a flap of sheet gutta-percha. This may be carried back as far as the uvula, but should not touch the velum at any point. This is to be ascertained by introducing the cup empty. Plaster of Paris is mixed in the usual way, a little salt being added to hasten the setting, and warm water used to render it more acceptable to the mouth. A pinch of powdered vermilion will color the impres- sion, which will aid in separating, and is preferable to placing the color in the plaster for the model. The plaster is placed in the tray in quan- tity proportionate to the height of the roof, less being used where the cleft is in the velum only, than where the fissure enters the hard palate also. The use of too much plaster is to be avoided, lest it escape and trickle down the throat. The impression-tray is to be carried into the mouth just as the plaster gives evidence of setting, and is pressed up quickly and firmly, and then held steadily until sufficiently hard for removal. With a little practice the calculation can be made with such nicety that the time required will be not more than one minute. The plaster which remains in the vessel in which it was prepared will be a guide to its setting, and as soon as it will fracture sharply the impres- sion should be withdrawn. Where the fissure extends into the hard palate it will occasionally occur that the plaster which passes up into the nasal cavity cannot be withdrawn with the impression ; but if the impression be removed at the proper moment, the plaster will fracture along the line of the fissure, and that portion left up in the nares may be taken away with the tweezers. 730 PALATAL MECHANISM. Fig. 976. Before passing to a consideration of constructing the model one or two other points in relation to the impression are to be considered. Ordinarily, all that is required in a model from which to make an instrument for a cleft-palate patient will be absolute accuracy as to the oral aspect of the parts and the borders of the fissure from its apiex to the uvulae. It will very rarely be essential to procure a perfect impres- sion of the upper or nasal side, except that the ope- rator should observe the thickness of the tissues along the borders of the cleft, the position of the vomer, and Avhether it is likely to interfere with the design of the instrument, as it often will where the fissure only slightly enters the hard palate. In such cases it becomes important to know how close the insertion of the vomer is to the border of the cleft at the apex. This is readily accomplished by pla- cing a small quantity of plaster up into the nasal cavity at the apex of the fissure, carrying it into place with a narrow-bladed knife, or other suitable instrument, just before introducing the impression. This may come away with the impression, or it may fracture and remain in place, in which case it is to be removed with tweezers and added to the impression. A method of obtaining the impression of the upper nares is described in the American System of Dentistry as follows : " This impression, if prop- erly obtained, will show a distinct outline of the cleft and uvula. The portion of the plaster occupy- ing the fissure or cleft is next cut down to a smooth surface, and a little forward of the median line of the cleft a hole is drilled through the cup and impression ; in addition to this, two pits are made in the smooth surface which represent the cleft, in the same manner as would be done in a cast for a spider articulator, to receive corresponding elevations in the second half of the impression. The whole surface of the impression is then painted with san- darac varnish, vaseline, or solution of soap to prevent adhesion. The next procedure is to pass a rubber tube through the hole in the impression, replace it in the mouth, one end of the tube extending through- on to the nasal surface, the other being carried for- ward and held with the cup in position by an assistant. In the outer end of the tube is placed the nozzle of a syringe ; a two-ounce vaginal syringe answers the purpose (Fig. 976). After withdrawing the piston the required quantity of plaster should be mixed to the consistency of cream in a vessel with a spout, by which it can be poured into the syringe. These preparations having been made, the assistant is instructed to hold the syringe in posi- tion, and the plaster is poured into it and the piston replaced. Slight pressure on the handle will force the plaster through the rubber tube on TAKING THE IMPRESSION OF CLEFT PALATE. 731 to the smooth surface and adjacent parts of the impression already taken, ihe patient being instructed to incline the head forward if the plaster is felt to be running down the throat, or backward if it runs too far in the opposite direction, the object being to keep it on a level if possible. " Precaution should be taken before the plaster sets to remove the rubber tube and syringe and cleanse them thoroughly for future use. When the impression is ready for withdrawal— and it is not necessary for the plaster to set very hard — remove the lower or palatal portion with the cup; the nasal portion can be readily withdrawn afterward with a pair of tweezers." If this method is intended to be utilized in cases where the fissure is exclusively in the soft palate, it is lacking in utility, /or no possible occa- sion for an impression of the nasal cavity is conceivable, the position of the vomer and turbinated bones being normal, and the artificial palate never needing to reach farther forward than the apex of the fissure. Where the fissure partly enters the hard palate, as has been already stated, the exact position of the vomer must be comprehended. The reason is that where an artificial velum is used, it engages the fissure, so that a flap extends slightly over the border at the apex on the nasal side. In some cases the insertion of the vomer into the hard palate is so near to the border at the apex that the artificial velum might rest against it and cause irritation, unless provision be made to guard against this. But the simple method of carrying a little plaster through the fissure at this point before inserting the impression, as previously described, accomplishes the required result perfectly, without resort to such an intricate process as the one quoted. Where the fissure involves the whole or greater part of the hard palate it may occasionally be required to secure an accurate model of the nasal cavity as well as of the oral. An example of such an instance is shown and described in connection with Figs. 909 and 910. The impression here is obtained by carrying the plaster, mixed fairly stiff, up into the nasal cavity, filling it to the borders of the fissure, whereupon the tray with additional plaster is carried to place. As the plaster in the tray unites with that which is in the nares, great care must be observed to remove the impression at the first moment when a sharp fracture is possible. With a sudden sharp movement the impres- sion comes away, leaving the plaster in the nares, the fracture along the borders of the fissure being sharp and clean, so that, when the nasal portion is removed by sliding it back toward the throat and allowing it to drop down upon the tongue, it is readily replaced in proper posi- tion upon the impression. If the operator is timid about attempting this, after filling the nares with plaster he may allow it to set. Then after oiling the exposed portion of the plaster, which now finishes out the arch of the roof, the impression may be completed without danger of the two parts adhering. In accidental fissures resulting from disease or other cause we some- times find merely an aperture in the palate, which may be quite small. In taking an impression the plaster would ooze through this hole and form a knob or button upon the upper side, which of course would remain after the removal of the impression-cup. Then, as the posterior portion of the soft palate would be normal, it might become a very dif- 732 PALATAL MECHANISM. ficult matter to remove this plaster without permitting it to pass down into the pharynx. In these cases the precaution should be taken to lay across the aperture a bit of Japanese tissue-paper folded two or three times. This paper will yield sufficiently to allow the plaster to take a perfect impression, yet resists its passage through. The model made from the most accurate impression will represent the cleft with its sides drawn somewhat together and possibly pressed backward. The next step, therefore, will be the correction of these errors, and the production finally of a model which will be an accurate reproduction of the mouth. A trial-plate made upon the model, with an extension fitting into the fissure, will indicate at once, when carried to the mouth, how much wider the natural cleft is when the parts are at rest. The natural cleft is to be observed closely in connection with this trial-plate, and the cleft in the model is widened and altered by cutting away the plaster with a knife until a trial-plate which exactly follows the outlines of the cleft on the model will similarly fit the cleft in the mouth. At the same time the edges of the cleft in the model may be rounded, and the pitch of the palate corrected to agree with the mouth, by adding plaster with a small camel's-hair brush. In the end the model will not only appear to agree with the mouth, but the trial-plate will demonstrate that it does agree. It is not guesswork, but absolute accuracy, even the bulbs of the uvulae being perfectly reproduced. The Making of Artificial Vela. With an accurate model from which to work an artificial velum could be made without further reference to the patient, though it might be best for the inexperienced to try in the model of the velum before pro- ceeding to the construction of metal moulds. The first step in the production of the artificial velum will be to make a model of the palatal flap. The model of the velum, if it is not to be tried in the mouth, may be made of wax, otherwise it will be best to use sheet gutta-percha. The palatal flap is a triangle with rounded angles. The apex of this triangle coincides with the apex of the fissure, and the base extends across from one uvula to the other. This flap should be made just large enough to bridge the gap, as it will be easy to widen it later by scraping the mould should it become needful, whereas if made too large at the outset it might become necessary to make a part of the mould over. The pattern of the flap having been cut out from gutta- percha, it is to be slightly softened and then pressed against the model, so that it assumes the proper form to lie close to the surface of the latter. It will often occur that the edges of the natural cleft are rounded or rope-like, thus showing a depression between the border of the cleft and the maxillary bone. In these cases the upper flap, when moulded upon the model, will assume quite a curl or crimp, especially near the uvulae. If the model is accurate and the flap is made to properly conform to this peculiarity, when placed in the mouth it will lie close against the soft tissues. Were it left comparatively a plane, the edges would stand off and be quite noticeable to the tongue. This curling is made more apparent because of the fact that the flap is slightly depressed between THE MAKING OF ARTIFICIAL VELA. 733 the sides of the cleft, so that it forms a part of the arch of the mouth and completes it. As soon as the flap has been moulded into proper form, all the edges being quite thin, it is plunged into cold water, so that it shall retain its shape. The second or upper flap is moulded upon the model in a similar manner, the form being again triangular. But the base must now be fashioned so that its posterior edge will meet the ridge of the pharynx at a slight angle. The general adaptation of the flap to the model having been obtained, it is placed in position, and the model and flap firmly held in the left hand, while with the thumb and fore finger of the right hand the operator grasps the flap at the centre of the posterior part and simply bends it up, whereupon it asumes the form shown in Figs. 960, 961, and 962. Usually the guide for bending this tail-piece is to form it so that the plane of that surface will be on a line with the incising edges of the anterior teeth. The two flaps are next placed upon the model at the same time and waxed together with hard wax. The velum is then ready to be tried in the mouth, when the operator may correct any discrepancies as to fit or length. The model of the velum having been satisfactorily made, it becomes necessary to produce metal moulds in which soft rubber may be vulcan- ized into the desired form. Fig. 977. A convenient form of flask for holding these moulds is round and in two parts, one of which has a square hole cut at the centre. In constructing the moulds the model of the velum is placed in that half of the flask which has the hole, so that the smaller or palatal flap 734 PALATAL MECHANISM. rests over the hole. The flask having been freely oiled, plaster is poured into it and around the model. When hard it is knocked out readily and carved into shape. It is then varnished, replaced in the flask, and oiled. The model of the velum still being in position, plaster is poured over it and the plaster mould, which now surrounds it, and the opposite half of the flask, well oiled, is put on and pressed flrmly to place. When this is hard and separated the two parts of the mould are complete. The third is made by pouring plaster through the hole in the top of the flask, Fig. 978. completely filling the space left within the flask, and covering the top flap. These three pieces of plaster are then reproduced by moulding in sand and casting in type-metal. The general appearance when complete is shown in the accompanying illustrations. Fig. 977 is the bottom-piece, in which a pin appears : this is best made of iridio-platinum wire, and is driven into a drilled hole after the mould is cast. In some cases it will be tight enough, but occasionally it may be requisite to fasten it Avith soft solder. Its purpose is to produce a hole in the velum through which the bar on the plate passes. The two aspects of the central piece of the mould are shown in Figs. 978 and 979, while Fig. 980 shows the top-piece. The surfaces for moulding the rubber are to be smoothed with a pine stick and pumice. The metal moulds are returned to their respective positions in the flask sections. In vulcanizing the soft rubber it is well to slightly soap the surface of the moulds before packing, as this facilitates removal after vulcaniza- tion, and avoids a tendency on the part of the rubber to adhere to the metal, especially should any rough places be left, which of course should be avoided. THE MAKING OF ARTIFICIAL VELA. Fig. 979. 735 The flask should be opened and excess of rubber removed ; otherwise it will be pressed against the unpolished portions of the mould, and ren- FiG. 980. der it extremely difficult to open the flask after vulcanization. As soft rubber swells considerably during vulcanization, the mould need not be 736 PALATAL MECHANISM. quite full, but care should be taken to avoid creases in the rubber, as they will not be filled out however much the rubber may swell, probably owing to the imprisonment of air. The best results in the vulcanization of soft rubber are obtained by observing the following directions : Place charcoal or other substance in the bottom of the vulcanizer high enough to stand above the water which is poured in. Allow the flask to rest upon this charcoal. In this man- ner the rubber is vulcanized in steam. The thermometer which registers the heat should indicate 240° for two hours ; 250° for one hour ; 260° for one hour ; and 270° for one hour. The velum when taken from the flask will have a peculiar odor if overdone, as though it had been burned. In that case, however perfect and elastic it may appear, it will be worthless within a very few weeks. The Construction of an Obturator. An obturator may be made for a patient where the cleft involves the soft palate only, but will be more commonly resorted to where both soft and hard palates are fissured. The process in connection with the latter condition is described, as it is the more intricate. A correct model having been obtained, the fissure in the hard palate is filled with wax, so that the arch of the vault is restored. Dies are made and a plate of iridio-platinum swaged to fit this reconstructed model, with the result, of course, that when carried to the mouth it bridges over the gap in the hard palate. The plate is provided with an extension at the posterior part which shall support the obturator, and it is attached to the teeth by gold clasps. For this purpose it is best to rely upon the sixth-year molars as ofl'ering the best anchorage, and where these teeth are badly decayed it is often advisable to crown them with gold before fitting the clasps about them. Thus the anchorages may be permanently protected against loss by decay. No matter how valuable teeth may be to ordinary persons, they are doubly so to the cleft-palate patient, who must depend upon, them not alone for mastication, but also for speech, since they serve to sustain the instrument which enables him to overcome his infirmity. The metal plate and clasps having been accurately fitted to the mouth, a loop of copper wire is soldered temporarily to the upper side of the plate (with soft solder) and extended backward about two-thirds the length of the fissure. The object of this is to hold a mass of impression material which is to be used for forming the model of the obturator. This mass of impression material is wrapped about the wire loop and then fashioned into the general shape of the fissure, when it is hardened in cold water. A trial in the mouth will indicate wherein it must be altered by trimming with a sharp knife. The mass having been brought to an approximation of the proper form after this manner, it is then slightly softened in warm water and again placed in the mouth, where- upon the patient is directed to swallow several times. This compels the levator and constrictor muscles to close upon the softened mass and mould it into such shape as will be required to enable the patient to completely close the opening to the nares. Upon removal the mass will THE CONSTRUCTION OF AN OBTURATOR. 737 have assumed an irregular shape, which now must be altered to furnish the final model of the obturator. The palatal surface is trimmed into a continuous flat surface, so that in connection with the plate the arch of the vault is completed and the gap in the back of the mouth bridged over. The upper surface is similarly cut away, and is usually best formed with a depression curved laterally, experience having taught that such a form is best adopted for the obliteration of the nasal quality of the voice. Thus the sides and the posterior end are left undisturbed as they were moulded by the action of the muscles. It must be remembered that no matter how yielding the mass may have been, it is also sufficiently resistant to have prevented the muscles from closing to their utmost limits. It is therefore necessary to trim these surfaces so as to still further reduce the size of the bulb, especially at the posterior end, where the ridge of the pharynx is ex- pected to touch it. In the region of the uvulae the sides must be trimmed away so that they may close under the obturator, and to this end that part of the bulb may be narrowed at the lower and widened at the upper side, thus producing inclined planes against which the leva- tors will play and be in contact at all times during their contractions. In the region of the uvulae the bulb may be cut away on a line with the bases of the uvulse, so that the surface produced will be a plane which if extended by an imaginary line would reach the incisive edges of the anterior teeth. Figs. 981-983 are introduced to show the great variations in the forms of bulbs, the size and shape being dependent upon the peculiarities of Fig. 981. Fig. 982. Fig. 983. the fissures and the activity of the throat muscles. In Figs. ^81 and 983 a indicates the flat surface where, as has been described, the bulb is cut away near the bases of the uvulse, while 6, b show the slanting sides against which the levatores play. Fig. 982 shows the nasal surface of a large obturator, and along the centre is seen the depression, which, experience has taught, is serviceable in many cases in correcting the nasal quality of the voice usually present. Upon the upper surface the depression alluded to is seen at c, but it must be borne m mind 47 738 PALATAL MECHANISM. that this is not always a necessity, being less so in small obturators (as in Figs. 981 and 983) than in large. The model having been brought to this point, plaster is mixed as for an impression, and a little placed upon the upper side of the plate, ex- tended from where the impression material ends sufficiently forward to reach the anterior end of the fissure when placed in the mouth. The plate, with plaster upon it, is then quickly carried into place, and upon removal the plaster will have taken an impression of the forward part of the cleft. It is cut away to a level with the upper side of the im- pression material, and with it completes the model of the obturator, which must now be reproduced in hard rubber. Plaster moulds are next made in which to reproduce the bulb in hard rubber, and when flashed and ready for packing the bulb is made as follows : Patterns of the upper and under surfaces are cut from thick tin-foil, and a single pattern to extend around the sides and end. These are similarly cut from sheet rubber, and are united in the general form of the bulb by placing the edges together and pinching them fast with a pair of tweezers. Before finally closing, water should be intro- duced, filling the bulb about three-quarters full, great care being observed lest the edges of the rubber should become wet, which would prevent perfect union and allow an escape of steam during vulcanization, the result being a collapse of the bulb. If these steps are accurately taken and the flask tightly closed, the bulb will be thoroughly well filled out and will be a perfect reproduction of the model. The bulb is next to be fitted to the plate, the proper position being determined by models which were taken while the plate and wax (im- pression material) model were united. A hole is then drilled through the bulb and plate, through which an iridio-platinum bar is passed and soldered to the plate, the opposite end being screw cut and supplied with a nut. The hole drilled through the bulb for the passage of the bar also serves for the removal of the water used in vulcanizing. The surface of the plate over which the bulb is to lie is smeared with gutta-percha, the bulb slipped over the bar, and the nut turned down until it im- pinges. Then by warming the plate over a Bunsen burner the gutta- percha is softened and the nut screwed down, driving the obturator tight against the plate, the gutta-percha serving to form a water-tight joint. The plate and bulb are then polished and are ready for the patient. INDEX ABSCESS, blind, treatment of, 595 recurring, 595 Absorption, excessive, of alveolar process, 707 Accessories of plaster table, 21 Acid pan, 60 solutions, 60 Adhesions, cicatricial, 274 treatment of, 274 Alexander's removable bridge, 685 Alloy or alloys, 82 aluminum bronze, 144 and mercury, 144 with zinc and tin, 144 Bean's, 468 for cheioplastic operation, 148 copper and gold, 136 and nickel, 136 and platinum, 136 and silver, 136 decomposition of, 85 density of, 83 table of, 84 ductility of, 84 fusibility of, 85 fusible, 149 gold for clasps, 204 and copper, 108 fineness, 102, 107 and mercury, 108 and palladium, 108 plate, tables of, 103, 104 and platinum, 108 and silver, 109 and tin, 108 and zinc, 108 influence of constituent metals, 85 Kingsley's, 468 lead, 132 and gold, 133 and meicury, 132 and platinum, 133 and tin, 133 table of, 84 liquation of, 86 malleability of, 84 with mercury, 148 preparation of, 86 properties of, 82 color, 84 Reese, 148, 468 temper 86 tenacity, 84 tin and gold, 148 Alloy, tin and lead, 149 and palladium, 149 and platinum, 148 and silver, 148 and gold, 148 varieties of, 83 zinc and copper, 139 and gold, 139 and lead, 139 and mercury, 138 and platinum, 139 and silver, 139 and tin, 139 Aluminum, alloys, 144, 145 annealing, 143 bronze, 137 solders for, 144 casting, 145 Carroll's method, 145 plates of, 475-478 compounds of, 147 history of 142 methods of obtaining, 143 its occurrence, 141 forms of, 141 plates, 146 rubber attachments, 523, 527 I reduction of, 142 steel, 129 soldering, 146, 147 uses and properties, 145 Amalgam, aluminum, 144 copper, 134 making, 135 gold. 109 tin, 148 zinc, 138 Anvil, swaging, 19 Arch, maxillary, effects of resorption, 407 shape of, 368 upper and lower, 368 Arrangement of full cases, 406, 407 Articulating models, 353 et seq. metal, 355 mounting models in, 353 full cases, 353 partial cases, 354 plaster, 352 teeth, 382-384 Walker, 375 Articulation, 360 for rubber dentures, 482 Articulator, 351, 352 anatomical, Walker's, 376 739 740 INDEX. Articulator, anatomical, Bonwill's, 376 application of, 380 et seq. Bonwill's, 352, 353 crown, 354 S. S. White's, 351 Artificial crown, preparation for, mechan- ical, 596 by excision of crown, 596 by tiles, 596, 697 Ottolengui's process, 597 roots, mechanical, 596 sterilization of pulp-canals, 594 therapeutics of pulp, 594 teeth, history of, 210 varieties of, 210 vela, function of, 715 Assaying, 111 Aurous chlorides, 109 BABBITT metal, 149 Fletcher's, 150 Haskell's, 150 Backing stays, 411-415 fitting, Trueman's method, 417 forms of, 414, 415 for irregular surfaces, 412, 413 patterns for, 412 Bailey's moulding flasks, 19 Baking continuous gum, 460-462 Bands, clamp. Angle's adjustable, 166 Farrar's, 166 material for, 1 69 to solder together, 169 Barrel crowns, 589 to detach, 643 preparing teeth for. 598 to repair, 543 Bars for regulating appliances, 154 Bending rubber plates, 535, 536 Bellows, Burgess's, 41 Fletcher's, 42 Bench, laboratory, 17 Binary temperaments, tables of, 582, 583 Bites, abnormal, 388 direct antagonism, 391 protrusion of lower jaw, 388 of upper jaw, 390 consequences of inaccurate, 257 difficulties in taking, 355 to remedy, 355, 356 plates for (How's), 357-360 to take, 347 Black on sore mouth, 708 Blowpipe, automatic, 48 Downie's, 28 Fletcher's, 31, 32 gasoline, 47 hand, 45 hot blast, 48, 49 Lee's, 46 Mellotte's, 45 mouth, 43, 44 oxy hydrogen, Knapp's, 27 Bonwill crown, 620 fitting of, 620, 621 for molars, 622 Ottolengui's clamps, 621 Bonwill crown, setting of, 621-624 Bows, labial and lingual, 178-180 for regulating, 192-194 for regulating. Angle's, 201, 202 Case's, 197 extrusion, 196 Farrar's, 196, 200 ' in protrusion, 194 for rotation, 194, 195 Case's, double, 197 their action, 199 Brass moulds for porcelain teeth, 243 Bridges or bridge, dental, 648 et seq. classes of, 649, 650 extension, 650, 681, 682 plate, 691-693 conditions of abutments, 692 removable, crowns with, 692 restoring contour by, 692, 693 porcelain, fitting caps to abutments, 694 setting of, 697 barrel crowns, 697 bars, 697, 698 cement for, 697 filling retaining slots, 697, 698 post crowns, 697 Bridge-work, advantages claimed for, 650 of removable, 710 anterior bridge, 672 with post and collar crowns, 673 attaching caps to facings, 664 breakage of, 698 case showing indications for, 679 casting bodies of, 669, 670 for changing bite, 679 method of making, 679 change of stress by, 652 combined with plate-work, 691-693 constructing parts, 661, 662 definition of, 648 and dental diseases, 655 aesthetic requisites of, 659 to detnch fixed forms, 698 die-i)lates i'or, 666, 667 with discontinuous body, 679 and engineering principles, 652, 653 extensive, adjusting sections, 678 soldering of, 678 faults of, 654, 655 filling of caps, 664 dummies, 667 fitting facings for dummies, 663 incisors, 673 stays to incisors, 673 fixed, 649 to form occlusion, 663 forming incisor dummies, 673 with four abutments, 676, 677 preparing abutments, 677 history, 648, 649 HoUihgsworth's method of forming occlu- sion, 664 hygienic relation of, 709, 710 requisites of, 659 ill effects of, 710 for incisors, 671-675 indication for, 651 INDEX. 741 Bridge-work, limit of, 682 Litch's method of, 672 making bodies of bridges, 562 manufacture of, 661 precautions, 661 measuring stress upon, 653 mechanical aspect of, 651 Mellotte's, 671 forming collars 671, 672 modes of attachment, 649, 650 objections against, 650 porcelain, 693 preparation of abutments, 656-659 proper forms for bars, 658 reducing abutments, 657 removable, 649, 682-691 Alexander's, 685 choice of, 683 Curtis's, 686 definition of, 682 objects of, 682 Eiiein's, 687-691 construction of, 689, 690 Eiclimond's, 687 sockets for, 686 Willis's, 684 Winder's, 684, 685 repair of, 698 repairing of, Bryant on, 700, 701 Darby method, 700 dummies, 699 Mason's, 700 post abutments, 699 splitting crowns, 699 requisites of, correct, 659 rules in making, 654-656 selection of variety, 660 shaping of teeth, 656-659 of abutments, reasons for, 656, 657 and adjusting bars, 677 slots in abutments, 678 for bars, 658 to split crowns, 698, 699 stress upon abutments, 651-653 anterior bridge, 654 pin anchorages, 654 pALCIUM sulphate, 22 \J Callahan's method of entering canals, 595 Cap and bit, 203, 204 Angle's, 204 Goddard's, 203 Mattheson's, 165 occipital, 202 Carroll's method of casting aluminum, 475- 477 Carving block teeth, 231 et seq. Case's double bows, 197 Cassius, purple of, 109, 221 Cast metal dentures, 468 base- plates for, 469 stiff, for, 470 beads upon palatal surface, 469 chamber forms (Chupein'sj, 468 finishing, 473 flasking, 471 Cast metal dentures, flasks for, 471, 472 fusing alloy, 472 gates in investment, 471 in Watt's flask, 472 grinding gum teeth, 470 investment for, 468 luting flask, 472 pouring, 473 repairs, 473 requisites of alloys for, 468 to solder, 473 teeth for close bites, 469 plates, aluminum, 475-478 Bean's method, 475 Carroll's method, 475-477 crucible, 476 gates for, 476 finishing, 477 flasks for, 476 pouring, 477 Carroll's alloy, 477, 478 clasps for, 475 vulcanite attachments, 474 plaster, pouring of, 299 separating from impression, 300 partial. Case's, 301 Cavities in teeth, 241 Celluloid, 553 alleged deficiencies of, 566 cases illustrating artistic features, 567- 577 composition of, 555 cooling of investments, 565 dentures, arranging teeth, 562 baking, 564 base-plates for, 561 carving wax for, 562 impression for, 561 investing, 563 models for, 561 selection of teeth for, 561, 562 stippling of, 563 trimming wax, 562 vents in investments, 564 history of, 553, 554 manufacture of, 555 moulding of, 556, 565 dry heat process. Hunt's, 556 glycerin process, 566 machines for " Best," 556, 557 Camf)bell's, 558 Evans', 558 oil-bath process, 556 in steam, Alexander's, 556 nature of, 554 physical structure of, 567 properties of, 555, 556 to remove cases from flask, 565 repairing of, 565 texture of, 560 teeth for, altering forms, 468 warping of plates, 567 work, plaster for, 566 models for, 566 Chamber metal, 480 Chambers, vacuum, 303 Cheioplastic alloy, 148 742 INDEX. Chin retractors, 205, 206 Chlorides, metallic, 87 Choice of material for plate, 274 Clasps, 337 alloy, 104 attached to plates, 341 Bon will's, 342 bracing, Essig's, 344 broken to repair, 428 upon cast-metal plates, 475 fitting of, 340 forms of, 338, 341, 342 indications for, 276 making of, 339 partial, 341 plates, 334 et seq. on rubber plates, 514-516 teeth, 273 for upper dentures, 334 et seq. uses of, 337 precautions, 338 in porcelain teeth, 214 Cleft palate, 712 acquired, extent of, 713 artificial vela for, 715 congenital cases, conditions presenting, 714 education of patient, 720 necessity for, 720 ill efiects of surgical measures, 713, 714 impressions of, 728 Kingsley's velum for, 716 action of, 717 prognosis of congenital cases, 713 acquired cases, 713 varieties of, 712 vela for children, 720 Coffin split plates, 164 Collar crowns, 609 to detach, 643 to fit new facing, 644 fitting barrel, 611 forming articulating surface, 613 band, 610 Huey's method of attaching facings, 617 mandrels for, 612 measuring root, 610 with molars, 616, 617 porcelain facings, 615-618 for bicuspids, 615 and post crowns for bridge-work, 673 with post in roots, 616 preparing teeth for, 610 requisites of, 610 shaping barrel, 611 swaging caps for, 614 Mellotte's method, 614 Color frits, 216 blue. Hall's, 216 gold in, 216 platinum in, 216 Wildman's, 217 Colors used in porcelain teeth, 215 (.'ombination dentures, 521-529 silver and rubber, 522 Combination enamels, making of, 218 Hall's formulae, 218, 219 Continuous-gum dentures, advantages of, 446 Allen's, 446 arranging, 446, 453 bites for, 452 Chemant, 446 clicking of, 447 to prevent, 447 electric furnace, Custer's, 456 enamelling, 461 finishing, 462 fitting stays, 454 forming plate for, 449 care in, 449, 450 lower plates, 450 second coating, 461 forms of stays, 455 fracture of, 447 to avoid, 447 enamel, 458 furnace fuel for, 457 fire-building, 458 care of, 458 heel to plate, 450, 451 impression for, 448 investing for soldering, 454 mounting teeth, 453 upon vulcanite, 464-466 forming block, 465 objections to, 447 office of body, 458 of second body, 461 plates for soldering, 451 testing adaptation of, 452 remaking, 463 repairing, 463 setting up furnace, 457 single teeth added to, 464 soldering, 455 Tees furnace, 456 teeth employed, 452 treatment of models, 447-449 vacuum chamber, 448 omission of, 448 when employed, 447 Copper, 133 alloj's, 136 amalgams, 134 properties, 134 reduction from ores, 134 strips with Hollingsworth system, 642 tests for, 137 Cores for vulcanite plates, 537, 538 Corundum wheels, 64 Cotton wedges in regulating, 175 Counter-dies, 316 metals for, 312 Crib, Jackson, 185 its construction, 185, 186 Crowns, accidents to, 643 for abraded teeth, 618 in column, 618 artificial, anatomical relations of, 589 classes, 588, 589 collar variety, 609 INDEX. 743 Crowns, artificial, condition of enamel, 592 detaching barrel crowns, 643 forms in relation to stress, 591 function of barrel, 590 post, 590 history of, 588 hygienic relations of, 709, 710 over vital pulps, 591 pathological relations, 592 of pulp, 592 of dentine, 592 pericementum, 592, 593 physiological condition of dentine, 592 of pericementum, 592 relations of, 591 post and plate, 606 support, 588, 589 preparation of roots for, 593-601 teeth, therapeutic, 593 relations to stress, 590 requisites of, 602 selection of type, 603 what constitutes, 588 barrel, 598 preparing teeth for, Case, 599 How, 600 Starr, 600 Bonwill, 620 Brown, 632 cervical outlines of, 601, 602 to detach, when set with gutta-percha, 644 Downie, 622 Gates-Bonwill, 623 use of screws with, 623 Hoi lings worth system, 636 Logan, 623-631 Mason's detachable, 619, 620 partial, 603-606 incisors, 603, 604 shells, 605, 606 for molars, 605 for incisors, 606 porcelain faced for vital teeth, 618 post and collar, 619 ready-made, 620 removable, 634-636 with removable pins, 636 repairing of, 643, 644 restoring root-forms for, 600, 601 retaining media for, 645 Richmond, 619 Crucibles, 35 Custer electric furnace, 456, 458 method of fusing platinum, 29, 30 Curtis removable bridge, 686, 687 sockets for bridge-work, 686, 687 Cusp crowns for molars, 617 DENTIMETER, Kirk's, 611 Dentures of all porcelain, 255, 256 artificial cleansing of, 705, 711 acid mouths, 705 care in, 711 clasps, effects of, 703-705 evil effects of, 702 et seq. functions of, 702 Dentures, artificial, hygienic conditions aflected by materials, 702 effects of spiral springs, 703 of bases, 705, 706 relations of, 702 et seq. requisites of clasps, 703-705 ill effects of uncleanliness, 706 means of retention, hygienic effects, 703 to prevent irritation by, 711 wearmg at night, 704, 705 upon celluloid without anterior gum, 573 changes effected by altering arrange- ment, 568 effects of spacing teeth, 575 of omitting, 575, 576 for elderly persons, 568-570 illustrating artistic features, 567-577 imitation of irregularities, 576, 577 with spiral springs, 574, 575 for young adult, 578 combination, 521-529 partial, 392 use of gum teeth, 392 plain teeth, 393, 394 plate teeth, 393, 394 temporary, 387, 388 trial of, in mouth, 408 type selected, 276 conditions governing, 276 Dies, 309 advantages of zinc, 310 for bridge-work, 662, 663 counter-; 139, 312, 316 and counter-die metals, care of, 23 making by dipping, 318 of fusible alloys, 318 metals. Babbitt's, 311 requisites, properties of, 310 Spence's, 311 use of, 311, 312 used, 310, 31 1 zinc, Bertiia, 311 plates for forming caps, 666, 667 pouring, 316 Babbitt metal, 316 zinc, 316 separating from counter-die, 318 Dinitro-cellulin, 554 Downie's crown, making, 262 furnace, uses of, 262, 263 Drag screw, 183 Angle's method of using, 184 Goddard's methods of using, 184 Draw-plate, 38 Drawing wire, 157 EBONITE, 479 plate with pink rim, 513 flasking, 513 Electric furnace, 29, 264 to fuse platinum by, 265 Electro-deposit plate, 345 Electrolysis, reduction of metallic salts by, 93 Enamels for continuous-gum work, 223 Allen's, 224 Hall's, 219 ^44 INDEX. Enamels for continuous-gum vrork. Hun- ter's, 223 Moffeii's, 223 Smith's 223 Wildman's. 217 their application. 220 Enamelling continuous gum, 462 English teeth, 26-5 Eruption, appliances for forcible. 182 Essig's clasp for lower dentures. 344 method of mounting natural teeth, 429, 516, 517 of repairing bv riveting, 429 Evans celluloid machine, 5oS. 559 use of, 559, 560 Expansion of arch, appliances for. 1S9-190 Extension bridges, 6*1, 682 Parr's. 682 Extruded teeth, appliances for, 181 for construction of, ISl FACIXGS for bridge-work. 662. 663 Feldspar in porcelain teeth, 212 Files for plate work. 413 rubber work, 510 Finishing palatal surfaces of metal plates, 421 soldered dentures. 419 means employed. 419, 420 Flasking cases for rubber dentures, 491 Flasks for anificiai vela. 733. 734 Brown, 491 for cast-metal dentures. 471. 472 for celluloid work, 560 Griswold. 489 Hayes, 491 moulding. 19 Bailev%. 313 Hawe's, 313 for rubber work, 488-491 Seabury, 494 Star. 488 Whitney, 4S9, 490 Flexible rims, 539 Fluorides, 88 Forces applied in regulating teeth, 171 received by teeth. 376—379 Forcible eruption of teeth, 182, 183 Formulas for continuous-gum body, 467 enamel, 467 Fracmred jaw, impression of 296 Furnaces for baking porcelain teeth, 258 Downie's. 261 Land's. 259 Verrier's, 260 carbon, 26 electric. 29 Custer's. 264 gas. Downie. .35 Fletcher. 24, 32, 34 gasoline, 25 muffles. Meyer's. 263 Fusible alloys. 149 Mellottes. 149 Eichmond's, 149 /"lAERETSON'S bite-guide. 355 Ijr Gasoline furnace, Geofrorers. 25 Gauge. Brown and Sharpe, 154 Gauge-plate, 38 Gear's shaded rubber, 535 , Genese crown, 635 1 German silver, 136 - Girdwood's method of banding Logan I crowns. 630 i Gold. 93 ' alloys of 102-108 tsoldei-s). 105, 106 analysis of native, 94 assays of 110 by scorification. 111 brittle, treatment of 98 chemically pure, preparation of, 99 for clasps, 207. 404 compounds of, 108 chlorides. 108. 109 with chlorine. 108. 109 discrimination of, 110 extreme tenuity, 94 . _ I fulminating, 110 methods of obtaining. 95. 96 iiy amalgamation. 96 by washing, 95 native forms of, 95 occurrence and distribution. 93 precipitation of from solution, 100-102 properties of. 93. 94 recovery of. from sweeping, 112 reducing fineness of, 106 refining. 96. 97 by chlorine. 98 nitric- acid process. 97 quartation process. 96 sulphuric-acid process, 97 shredded. 101 silicate of 217 making of 217 and sodium hyposulphite (^sel d'orj, 109 tests for. 110 " volatility of, 94 Grinding blocks, 405 full c-ases plate teeth, 406, 407 teeth. 402-405 gum. 402. 403 Gum frit. 221 making of, 221. 222 Gums, natural structure of, 270 m' rbid conditions, 270, 271 to remove from root faces, 595, 596 spongy, 272 wash for. 272 Gntta-percha heater. How's, 647 indications for using to set crowns, 645 setting crowns with, 646, 647 HEATEE for rubber, 496 Hippocrates on temperament, 578 Hollingsworth method of banding Logan crowns, 631 of casting bridges, 669, 670 of making dummy caps, 665 system of copper strips, 642 of crowning, 636—643 of forming dies, 638, 639 solid cusps, 640 IXDEX. 745 Hollingsworth system of gold crowns, 638 et seq. %for incisors, 640, 641 inserting porcelain facings, 641, 642 Hooks, application of, 176 for regulating appliances, 167 How's gutta-percha heater, 647 Huey's method of attaching porcelain to collar crowns, 617 Hypertrophied gum, to remove from root faces, 595, 596 TMPEESSIONS of cleft palate, 728 X fusible metal casts of, 296 of irritable palate, 2S8 materials employed, 277 beeswax, 277 mixtures of, 278 plaster of Paris, 277 for obturator. 736 partial dentures, 289-295 in plaster, taking of, 285 et seq. preparation of patient, 286 selection of material, 284 plaster, 284 taking, for fractured jaw, 296 in heat-softened materials, 285 loose teeth. 295 palatal defects, 296 trays, 278 altering forms of, 282 for special cases, 292-294 Bean"s method of making, 284 Catchings, 289 for lower jaw, 279 office of, 278 partial lower cases, 280, 281 upper cases, 280 adjustable, 280 for special cases, 283 treatment of, for casting, 297 Incisors, partial crowns for, 603, 604 of gold. 604 of porcelain, 605 Ingot moulds. 36 Interdental splints, 547 Investing dentures, 415 Investment material, 415 Iodides. 88 Iron, alloys, new. 129 to distinguish from steel, 132 distribution, 127 malleable. 132 properties of. 127 Irritable palate in impression-taking. 288 JACK'S regulating plate, flasking for. 547 for retaining. 546 for traction, 546 Jack-screws. Angle's, 171 application of. 173 Farrar"s, 171. 172 Jacque. definition of temperament, 578 table of temperaments. 581 Joints between gum-blocks. 386 discolored in rubber work, 486 to prevent ingress of rubber into, 496 KAOLIX in porcelain teeth, 214 Key-making, 161 Kingslev's slotted regulating plate, 545 velum, 715, 716 Kirk on sore mouth, 709 Kirk's dentimeter, 611 method of fitting Logan crowns, 625 Knapp's blowpipe, 27 LABOEATOEY workbench, 17 accessories of, 18 Ladle-melting, 24 Lamp, alcohol, 50, 51 I Lathes, 61-64 accessories, 61—68 chucks, 62 corundum wheels, 64 Lead, alloys, 132 reduction of, 132 Ligatures in regulating, 175 silk, 175 wire, 176 Lining, Vulcan, 529 vulcanite plates, 529, 530 Lip line, 351 Liquid silex with rubber dentures, use of, 497 Litch's pin attachment, 672 Local effects of artificial dentures, 702, 703 Logan crown, 623-631 to band, 629-631 fitting of, without model, 625 Kirk's method, 625 selection and fitting of, 624-631 to set with gutta-percha, 629 zinc phosphate, 628 "White's method of attaching porcelain, 627 of fitting, 626, 627 Lower jaw, articulation of, 346 movements of, 346, 375 plates, 329 MAXDEELS for shaping barrels, 612 Mason's detachable crown, 619, 620 Matrices for forming blocks, 242 brass, 243 Maxillary arches after resorption, 407 Mellotte's bulkhead bridge. 671 Melting metals, appliances empiloyed. 22-35 by electric current i Custer ), 29. 30 modes of, 24 Metals, agents which volatilize, 82 conduction of electricity, 79 of heat, 78 crystallization of, 81 ductility of, 79 employed in metallic condition, 75 expansion, 77, 78 (alloys), 78 fusiug-points of, 76, 77 gauge. 154 ingot. 153 malleability oi, 79 noble. 75 plate, 153 properties of, 75-82 746 INDEX. Metals, properties of, color, 76 lustre, 76 odor,, 76 taste, 76 reduction of, 90 for regulating appliances, 154 specific heat of, 77 table of, 74, 75 tenacity of, 80 volatility of, 81 Meyer's mnfiles, 263 Mills, rolling, 37 Models for celluloid work, 566 plaster, trimming of, 301 waxing to prevent bruising, 302, 303 preparation of, for moulding, 307 waxing for rim, 308 to prevent pressure, 308 Mono-nitro-cellulin, 554 Moulding box, 18 accessories of, 19 celluloid, 565 conditions complicating, 314 cores in, 315 flasks, Bailey's, 19, 313 Hawes', 313 process of, 313 et seq. Moulds, ingot, 36 NATUEAL teeth to mount on plates, 516, 517,429 Nut-making, 160 OBTUEATOR to attach to plates, 738 attached to plate, 721 construction of, 736 forming model for, 736 patterns for, 738 function of, 722 with hinge, 722 impressions for, 731, 736 indications for use of hinge, 723 ineffectiveness of hinge, 722 making plate, 736 mode of attaching to plate, 721 of investing, 738 of packing rubber, 738 pattern for, 737 requisites of, 720, 721 Schnltsky's, 724, 725 shapes of, 737 Suersen's, 722 for syphilitic lesion, 538 value of natural teeth for retention of, 736 with velum, 718 making of, for special case, 718, 719 Occipital cap, 202 Occlusion, 346 et seq. balance of, 372 Bonwill on, 370 et seq. complete, 346 curvature of, 372 movements of, 347 normal, 369-371 obtaining, 347-349 overbite, 371 wax blocks, 350 Occlusion, wax blocks, trimming of, 351 Ottolengui's root-clamps, 621 root facers, 597 Oxides, reduction of, 88, 89 Oxyphosphate, setting crowns with, 645, 646 PALATAL defects, impression for, 296 Palate, cleft, 712-738 Parallel pliers, 414 Parr's extension bridge, 682 sockets for bridge-work, 686 Partial cases, vulcanite, 514, 518 dentures, arranging teeth, 392 lower plates, 330-333 Patterns, forming of, 321 Pickling, forming, 60 Pin punch, 413 splitter, 413 Pink rubber on soldered dentures, 540 investing, 541 Plaster cast, pouring of, 299 for casting, requisite properties of, 298 for impressions, 23, 284 for models, 23 of Paris, 22 rules for using, 284, 285 table, 20 accessories of, 21 Plates, articulating wax, 348 attaching chamber piece to, 325 bridges, 691-693 clasp, 334 et seq. making of, 336, 337 configuration of palatal surface, 396 effects of, 395, 396 draw-, 38 electro-deposit, 345 files, 413 forming chamber cap, 324 cutting out, 324 upon die, 322 malleting, 323 pattern for, 321 gauge, 38 lower, 329 making of, 329, 330 partial, 330-333 classes of, 331 forming upon die. 333 models for, 332 strengthening pieces foi", 333 uniting sections, 330 metal, indications for, 274 metallic, indications for, 320 metals, properties of, 320 outline, marking of, 301 full upper cases, 301, 302 lower cases, 302 partial lower cases, 302 for regulating, 162, 163 Coffin, 164 to rim, 408-410 strengtiiening pieces for, 328 swaged metals for, 319 swaging aluminum, 326 of partial, 326 et seq. rim, 325 INDEX. 14:1 Plates, swaging, without cut-out chamber, 326 testing adaptation of, 324 thickness of metals used, 322 vacuum chamber, 275 lateral, 275 vulcanite, indications for, 275 wiring, 410, 411 Platinum, 121 alloys, 125 black, 125 chemical properties, 125 chloride, 126 discrimination of, 127 effects of, upon tissues, 704 to fuse, 265 fusing of, by electricity, 29, 30 fusion of, 124 and gold frits, making, Hall's method, 216 impurities, 124 oxides, 126 properties, 124 reduction from ores, 122 separation of, 123 solder for, 126 solvent of, 125 spongy, 127 sulphides, 127 welding, 123 Plumpers for vulcanite plates, 537 Polishing soldered dentures, 420 Porcelain body for continuous gum, 458, 467 first coat, 458, 459 forming, 459 fusing, 460 bridge-baking, 695 fitting caps to abutments, 694 stay and bar, 594 teeth, 694-696 incisors, 69.6 upon bicuspids and molars, 696 incisors, 695 plates, 695, 696 with post crown, 696 for restoring contour, 695, 696 work, 693 dentures, 254 teeth, bodies of, 211 burning, 257, 258 enamels of, 212 history of, 210 materials used in making, 211 Posts for artificial ci'owns, size of, 606 and collar crown, 589 crowns, 588, 589 and plate crown, 607 backing, 609 fitting tooth, 609 finishing, 609 making of, 607-609 preparing base, 608 soldering, 609 shaping root, 607 swaging plate, 607 Powders, finishing, 67 Precious metals, care of, 240 Protrusion of lower jaw, 388 of upper jaw, 390 Pulps, to devitalize, 593, 594 Purple of Cassius, 109, 221 preparation of, 109 Wildraan's methods, 109 /QUARTZ in porcelain teeth, 213 REDUCING fineness of gold, 106 teeth for barrel crowns, 598 Reduction of metallic chlorides, 91 of metals, 90 sulphides, 91 oxides, 92 salts by electrolysis, 93 Regulating appliances, bars for, 154 Coffin's, 541-543 to form wires, 542, 543 nuts for, 155, 170 rubber, 541 et seq. retaining, features of, 544 screws, retaining, 155 swaged caps for, 155 tools required in making, 155 tubes for, 154, 170 wire for, 154, 170 piano, for, 155 plates, rubber, for protruding teeth, 544 for rotating teeth, 545 Kingsley's slotted, 545 for traction. Jack's, 546 teeth, forces applied, 171 Removable bridges, 682-691 bridge-work, Cnrtis's, 686 Rhein's, 687-691 crowns for, 689 sockets for, 690, 691 Richmond's, 687 crowns, 634-636 Repairing bridge-work. 698 cast-metal dentures, 473 celluloid, 565 crowns, 643 facings, collar crowns, 644 post and plate crown, 644 soldered dentures, 424 adding tooth, 427 clasps, 428 cracks, 427 faulty adaptation, 425 modus operandi of, 425 patches, 426 remaking, 425 resorption necessitating, 425 ■ riveting, 427 riveting, Essig's method, 429 using old tooth, 428 vulcanite plates, 518-521 Retaining appliances, 207 bands, 207, 208^ and wires, 207 plates, 209 twisted wires (Case's), 208 media for artificial crowns, 645 plates, rubber, 544 748 INDEX. Retractor, chin, 205, 206 Ribbons, metallic, for regulating appliances, 165 Eichmond crowns, 619 attaching cap, 619 to post, 619 fitting band, 619 Richmond's new crown, 632-634 fitting crown, 633 precautions, 634 setting, 633 shaping tooth for, 632 uses of, 634 removable bridge, 687 crown, 635 Rimming plates, 408-410 Rims, flexible, 539 for vulcanite attachments, 523-526 Rolling mill, 37 Root forms, restoring, 600, 601 Roots, neck sections of, 599 of teeth, mechanical function of, 589, 590 stress upon, 589, 590 Rotation, double, 178 by hooks, 177 sockets and level's for, 179 Rubber, or caoutchouc, 479 attachments, 522-529 dentures, articulation for, 482 models, 483 points observed, 483 base-plates for, 481 gutta-percha, 481 black with pink rim, 513 buffing, 512 ^ carving wax, 487 casts for, 480 cause of discolored joints, 486 clasps, 514-516 finishing, 509 files for, 510 flasking, 491 cases without i-ims, 475 undercut cases, 494 flasks for, 488-491 flexible rims, 539 gauging quantity of rubber, 498 by weight, 498 rubber for pink rim, 499 heater, 496 partial, 514r-518 lower, 515 bars in, 516 gold in, 515 pink rubber rim, 484 plate teeth on, 514 polishing, 512 presses for, 500 to prevent discolored joints, 486, 496 removing wax from matrix, 492 repairing, 518-521 scraping, 511 smoothing, 511 softening rubber, 499 teeth in, 484. See Plate on p. 485. advantages of single, 484 tin-foil in matrix, 497 Rubber dentures, use of liquid silex, 497 vacuum chamber, 481 omission of, 481 vents for surplus rubber, 492, 493 vulcanizers, 500-504 wax carvers, 486 waxing cases, 487 effects of, as base, 706, 707 causes of, 707 hard, 479 impurities of, 479 origin of, 479 plates, absence of free mercury in, 708 beading, 535, 536 fracture of, 518, 519 hvgienic reasons for perfect vulcanizing, 708 sore mouth, 706 tubing for regulating, 174 bands made of, 174 vulcanizable composition of, 480' dentures upon, 480 wedges in regulating, 175 Rules for soldering, 418 SAND for moulding, 309 preparation of, 309, 310 Schultsky's obturator, 724, 725 its value as compared with velum, 725 Scrapers, Kingsley's, 512 Selecting teeth, 398 Separating media, 21, 22, 299 collodion, 297 soapsuds, 297 varnishes, 298 Sercombe's velum, 727 Shapes of teeth, 224 Sheet metal or plate, 153 Shot, swaging with, 344, 345 Silex, liquid, 497 Silica in porcelain teeth, 213 Silver, alloys, 119, TiO compounds of, 117 discrimination of, 117 dry process, 118 wet process, 118 electro-deposit of, 121 German, 136 hygienic effects of, 702, 704 its occurrence and distribution, 113 properties of, 113 pure, 118 obtaining, 119 precipitation of, 119 reduction of, 115, 116 separation from ores, 114, 115 solders, 120, 121 whitening of, 121 Sockets for removable bridges. Parr's, 686 Sodium silicate, 497 Soft gums, 272 solders, 133 Solder silver, 120, 121 Soldering cast-metal dentures, 473 accessories, 39, 40, 56-59 clamps, 58 Mellotte's, 58, 59 INDEX. 749 Soldering, accessories, tweezers, 56, 57 apparatus, 39 furnaces, 54, 55 precautions, 39 rules for, 418 stays to plate, 419 supports, 51-55 carbon basins, 52, 53 charcoal, 51 graphite and fire-clay, 52 tables, 40 Bishop's, 41 Solders, 82 gold, 105, 106 soft, 133 Speech, mechanism of, 715 Speyer's adhesion forms, 530 plates, 530 Spiral springs, 421 et seq. arms for, 424 with celluloid, 574, 575 making of, 422, 423 Splints, interdental, articulation for, 548 Bean's, 547 Gunning's, 547 impressions for, 547, 548 Kingsley's, 551, 552 models for, 548 packing rubber for, 550 investing for, 550 waxing for, 549 Split plate. Coffin's, its uses, 187, 188 Goddard's modification, 188 Spring, Matteson's, 174 Talbot's, 173 Springs, spiral, 421 et seq. Spiirzheim on temperament, 579 Staining porcelain teeth, 268, 269 teeth, 240, 241 Starr's removable bridge, 683, 684 Stays, backing, 411-415 for bridge-work, 673 Steel, 128 aluminum, 129 Bessemer, 129 case-hardening, 132 < chrome, 130 copper, 130 hardening and tempering, 131 temperatures of, 131 making of, 129 manganese, 130 nickel, 130 Stippling wax, celluloid dentures, 563 Stomatitis, treatment of, 271 Suersen's obturator, 722 Sulphides, 90 Swaging anvil, 19 block, 19 with shot (Parker), 344, 345 Syphilitic lesion, 538 obturator, denture for, 538 TABLE, plaster, 20 soldering, 40 of temperatures and pressures of steam, 507 Tables of temperaments, 580-587 Taps and dies, 158 Teeth, actual and relative sizes of, 226, 227 adapting to plate, 402, 403 alteration of forms of porcelain, 228 anatomy of, 362, 363 arrangement of, 229, 230, 401 ethnological features in, 230 artificial classes of, 364 their application, 365 et seq. blocks, bisciiiting, 237 carving guide-walls, 282 instruments used, 234, 235 mixing body for, 233 moulding, 236 trimming, 237 enamelling, 238, 239 errors in baking, 240 fitting sections of moulds, 251, 252 forming matrices, 242 plaster moulds, 247, 248 making brass moulds, 248, 249 foundation plate, 245 frame, 246 moulding in brass moulds, 252, 253 moulds for special cases, 253, 254 plaster blanks for, 243, 244 moulds, 245 precautions in baking, 240 staining, 240, 241 trimming brass moulds, 250 unusual forms, 567 carving of blocks, 231 et seq. clasp, 273 for continuous-gum work, 267 Land's, 267 countersink, 266 English, 265 extraction of, 271, 272 discrimination in, 272 forms in temperaments, 225 geometrical arrangement of, 373, 374 Walker's, 376 grinding of, 402 jointing of, 402 natural, to utilize in prosthesis, 273 j)inless blocks, 265 positions of ai-tificial, 401, 402 selection of, 398 et seq. of gum, 398 shapes of, 224 sizes of, 224 staining, 268 surfaces of, 361 occluding, 362 tinting, 268 unusual shapes, 228 Temperamental characteristics of the teeth, table of, 584, 586,^587 Temperaments, analysis of, 578 the balanced, 578 bilious (Spurzheim), 579 binary, 585 cause of (Hippocrates), 578 choleric (Hippocrates), 578 definition of, 578 by Hippocrates, 578 750 INDEX. Temperaments, Jacque's classification, 579 J. W. White on, 585 lymphatic (Spurzheim), 579 melancholic (Hippocrates), 578 mental (Hippocrates), 579 motive (Jacque), 579 nervous (Gregory), 579 (Spurzheim), 579 pathological, 579 phlegmatic (Hippocrates), 578 sanguine (Hippocrates), 578 (Spurzheim), 579 Spurzheim on, 579 table of binary compounds, 582, 583 for the diagnosis of, 580 illustrating dental relations, 584 of Jacque's anatomical classification, 581 vital, 579 Temperamentum, temperatum, 578 Temporary dentures, 387, 388 Temporo-maxillary articulation, exact move- ment of, 376 Thread-cutting, 159 Tin chlorides, 151 detection of, 152 foil with rubber dentures, use of, 497 history and properties, 148 obtaining pure, 150 solvents of, 151 in the vulcanizing process, 151 for weighting dentures, 151 Tools, bench, 71-73 care of, 73 Tooth bodies, 214 formulae for, 214 Hall's, 215 Wildman's, 215 Townsend's method of banding Logan crowns, 629, 630 Traction apparatus with tubes and bands, 179 by hooks, 177 Trays, impression, for lower jaw, 279 Treatment of impression for casting, 297 Tri-nitro-cellulin, 554 Tube teeth, 430 alloys for posts, 444 attaching to plate, 435 for bridge-work, 439 making bridges, 440 base for, 441 clasps for, 442 (fixed), 442-445 construction of, 430 for crown replacement, 436 crowns upon living teeth, 438 as crowns, 436-438 posts for, 436 fitting posts for, 433 fixation with zinc phosphate, 445 Girdwood, 430, 434 grinding, 434 with gums, 435 to hide posts, 445 over metallic root-caps, 438 on partial cases, 435 on plates, 432 et seq. Tube teeth, soldering posts for, 433 tools used in mounting, 431, 432 uses of, 430, 431 Tubes, application of, 176 for regulating appliances, 154 as sockets, 180, 181 to solder to band, 168 their uses in regulating, 178 upon traction apparatus, 180 Tubing, making of, for regulating appli- ances, 158 TTNDEECUT ridges, to flask, 494 VACUUM chambers, 303 horseshoe, 306 lateral, 307 position of, 304, 305 conditions governing, 306, 307 Vela, artificial function of, 715 correction of models for, 732 flasks for investing, 733, 734 impressions for, 728, 729 for, causes of inaccuracy, 729 foi', parts embraced in, 730, 731 of nasal cavity, 731 investing in flask, 733, 734 metal moulds, 734 making of, 732 models of, 732, 733 of fitting, 733 for plaster, 728 moulding metal forms for, 734 packing rubber in moulds, 735 trial plates for, 732 vulcanizing, 736 Velum, artificial, Kingsley's, 715 choice of, for children, 720 with hinged extension, 726, 728 mode of arranging with hinge, 727, 728 with obturator, 718 Sercombe's, 727 Vulcanite attachments, 522-529 aluminum not suited for, 523 cleats for, 524 on fusible alloy, 522 Vulcanizable rubber, 479 Vulcanizers, Davis's, 501 escape of steam from, 508 explosion of, 508 gas regulators for, 504-506 Hayes's, 500 Lewis's, 501, 502 pressure in, 507 Seabury's, 503, 504 thermometers, 507 broken mercury column, 507 mercury bath for, 508 scales for, 508 time regulators for, 505, 506 rule for setting, 505 Vulcanizing process, 509 on tin, 151 WALKER'S discovery in regional anat- omy, 376 INDEX. 751 Walker's granular gum, 534 Wax, adhesive, 69 fluxed, 69 spatula, 70 heater, 71 Wedges in regulating, wood, 174 cotton, 175 rubber, 175 Weighted rubber, 536 use of, 536, 537 Wheels, corundum, 64 brush, 66, 67 White, J. W., on temperaments, 585 White's method of fitting Logan crowns, 626, 627 Williams' bridge, 680 construction of, 681 Willis' removable bridge, 684 Winder's removable bridge, 684, 685 Wire, pinched in regulating, 176 Wire for regulating appliances, 134 to solder to band, 168 Wire-drawing, 157 Wiring plates. 410, 411 Wood compressed in regulating, 174 Wunsche's plates, 531 application of, 532, 533 ZINC, alloys of, 138 antiquity of, 138 compounds of, 141 counter-dies, 140 uses of, 140 dies, 139 ores of, 138 properties of, 138 phosphate, setting crowns with, 645, 646 Zylonite, 553, 555 advantages over celluloid, 577 Date Due ^^2 3 1^ '^s. -miUM^B JM ^w nAi nov^6 [3'***' $) M651 Essig ^erican text- dentistry-*, Es7 «^'t-book of prosthetic ./ '/'^i i?lv I COLUMBIA UNIVERSITY LIBRARIES (hsl.stx) RK 651 Es7 C.1 ^ ^ ^^ The American text-book o pros hetic den "H ''%^^i^«- ,>^