COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX00022578 ^ ^ ■ s'iin-:s.;T:> mi^ m^ "A -fit'- >.L6AM FILLING 1 §^W, ImWi WALTER G.CPANDALLD.D.S. W^^^/m ,?> ... . 'l-»7. . ff'^iJ*'."r:,^>-^ *^ -K, iff ''i'il?' ^;-?^^ m m •m. ri2v- ;-i •n: mM^ y^^i: %# Jr.-;''/.-'! '. /^.>.' -J^'tf. i^Sr^' m )^:;^^^;,'v;v,,^'t l>' s^« ^'ii^vf ..^"^-i ^>>:'*^* '■^■■^^. ;.^"■:^^' ;^M^/?^s^;^ ■•-V»V>'-'J''v'''«.' .l;.:>^ hm. ^:^>: c.. 'b^«; C25 Columbia ^nitJem'tp mtl)fCitp0flfttigork College of ^fjpsJicians! anb burgeons! i^ibrarp Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/standardizingamaOOcran STANDARDIZING THE AMALGAM F\ LUNG BY WALTER G.CRANDALL,D.D.S. SECOND EDITION PUBLISHED BY THE CLEVELAND DENTAL MFG. CO. CLEVELAND, OHIO. U. S. A. Copyright 1915-1916 by The Cleveland Dental Mfg. C< Cleveland, Ohio, U. S. A. standardizing the Amalgam Filling Second Edition THE enthusiastic reception accorded by the dental profession to the first issue of "Standardizing the Amalgam Filling," adds to our pleasure in presenting the second edition. The need for a simple and comprehensive treatment of the subject of amalgam manipulation has been revealed by this enthusiasm and we believe that a real appreciation of the importance of amalgam restorations, as a factor in conserving the teeth and health of patients, has resulted from this publication. The present edition of ''Standardizing the Amalgam Filling" has been revised in the interest of unity and convenient reference and some of the results of research in metals, made by a highly competent metallographist at Yale, Sheffield Scientific School, have been added. This work, which represents the first intensive use of metallography applied to dental alloys, has been done under the direction of Dr. Crandall and will be reported fully in a later publication. To those who have gone before us in the investigation of the alloy metals and methods of combining them, we offer our acknowl- edgments. The best of the past has been combined with research and increased practical experience in the evolution of the Crandall Method of Amalgam Restoration. It is offered to the profession with the assurance that it is founded upon scientific principles and that its application, under varying conditions of practice will result in a step in advance of present methods in the restoration of bicuspid and molar teeth. THE CLEVELAND DENTAL MANUFACTURING COMPANY ZW the friends and confreres who have assisted me in the experiments necessary to this work, to those who have offered criticism and suggestion. I ivish to express my heartfelt and sincere gratitude. The list of those icho have disinterest- edly aided in this work has grown to such proportions that it seems impossible to partic- ularize here. It is a pleasure to acknowledge my indebtedness to these men and I offer to each and every one my heartiest appreciation. TF. C. C RAX BALL. standardizing the Amalgam Filling By Walter G. CrandaU, D. D. S. THE earliest use of amalgam as a material for restoring portions of the human teeth is of comparatively re- cent date. It is probably well within the past century that it was first employed and within half a century that its use has become at all common. Many men who are stiU active in the practice of dentistry recall very vividly the contention over the material when its introduction was first becoming general throughout this country as, at that time, amalgam was in such ill repute that its use by any dentist was sufficient to bar him from membership in the dental societies which then existed, and from any associ- ation with his confreres. However, it is not the intent of this article to discuss the amalgam of the past, but the amalgam of the present, and its possibilities. The importance of any mate- rial bears a direct relation to the extent of its use. Judged from this standpoint, the importance of amalgam is at once evident, for a comparison of the number of amalgam fillings inserted with all fillings of other materials, when taken from records of actual practice, has always shown at least seventy -five per cent of the total to be amalgam. In reviewing any scientific research of dental amalgams and amalgam alloys, acknowledgment must be made of the work done in this field by Greene Vardiman Black. If he had given nothing else to the advance- ment of the dental profession, his name should still be held in grateful remembrance for his investigation and classification of the minute actions of the dental amalgam alloy metals. Two decades have passed and we are only beginning to appreciate the heritage that is ours through his efforts and to realize that we have failed, in some par- ticulars, to take advantage of the work which should have given us an unalterable standard for dental amalgam alloys. The cKnical experience of the past has taught us the value of amalgam and has demonstrated its wonderful tooth-saving quafities, even when it has been used in a careless, indifferent manner. Too often it has been considered only as a cheaper sub- stitute for the patient who can not afford, or will not have, a gold filling, inlay, or crown, and the work has been done with little care in the preparation of the cavity, with a plastic alloy, and without regard to the restoration of anatomical form or occlusion, simply as the quickest means of getting rid of the patient. It is possible, however, to save teeth with amalgam when it has become practically an impossibility to save them with other materials. Now and then we have all seen cases in which amalgam fillings have given more than ordinary service, proving the inherent value of the material. The more frequent failures show us the lack of a standardized technic for amalgam work. Notwithstand- ing the more and more frequent discussions of the subject, do we really know the req- uisite qualities of a dental amalgam alloy; in what proportions it should be combined with mercury; whether or not the cavity should have a cement lining for amalgam; how much force is required to condense amalgam; the form and size of instruments best adapted for this purpose; the modi- fications of Black's cavity preparation for gold foil which are permissible or advisable for amalgam; the method of alloying which [6] STANDARDIZING THE AMALGAM FILLING will produce a dental amalgam alloy with the most desirable qualities? It is the purpose of this article to bring before you. as plainly and emphaticall}' as possible, the essentials of a standardized technic for amalgam restoration. A clear and systematic presentation of the subject re- quires the following subdivision into sections : Essentials of Standardized Amalgam Technic Classified I. Proper Cavity Preparation II. Accurately Tested Alloys of the Greatest Strength and Stability III. Correct Amalgamation IV. Correct Instrumentation and Condensation V. Correct Contour and Finish of the Restoration \l. Profitable Fees Section I — Cavity Preparation SCIENTIFIC cavity preparation is as essential for amalgam as for a filling of any other material. Without proper prep- aration of the cavity, no filling material is given a just opportunity to prove its worth, and the writer is inclined to beheve that the lack of such preparation is the most fre- quent cause of failure of amalgam fillings. The entire preparation of the cavity should bear a distinct relation to the condi- tions which surround the tooth. We should study conditions, observe, if possible, the faulty condition which produced the lesion, and attempt to remedj' this, producing an environment which wiU prevent the recurrence of the pathological state. We should study the occlusion and build to withstand its existing force and, if possible, to anticipate future developments. The restoration of a tooth is a surgical procedure and requires expert knowledge in diagnosing and planning. The completed restoration should be fuUy visuahzed and decided upon before the operation is begun. The writer would adA^ise those who wish exhaustive information on the subject of ca\'ity preparation to make a close study of Black's "Operative Dentistr}-" or to take a course of chnical instruction from some master of Dr. Black's scientific system. It is impossible to consider the subject ade- quately within the limits of the present article, but we shall consider brieflj' several forms of cavities occurring most commonly in bicuspid and molar teeth. Its color limits the use of amalgam almost entirely to these teeth. In the main, cavity preparation for amal- gam should be the same as for gold. The ideal ca^'it^' is a box form ^-ith a flat base and walls at right angles to the base. This, of course, becomes complicated in many forms of ca\TLties, but the principle should be followed in any cavity where stress will be apphed to the completed filHng. Dr. Black gives the following as the order of procedure in cavity preparation: 1. Obtain the required outline form. 2. Obtain the required resistance form. 3. Obtain the required retention form. 4. Obtain the required convenience form. 5. Remove am- remaining carious dentin. 6. Finish the enamel walls. 7. IMake the toilet of the cavity. CAVITY PREPARATION FOR AMALGAM We shall consider briefly these various steps, noting especially variations from the usual procedure for gold foil. 1 — Outline Form This form is the outline of the cavity upon the enamel surface; it must be such that it will place all of the margins in areas which are comparatively immune to initial decay. For cavities on proximal surfaces, the gingival wall of the cavity should be just beneath the free margin of the gum, as decay rarely, if ever, begins at this point when the tissue is in a healthy condition. When the gum has receded upon the root, Figure 1 shows an upper molar with cavity preparation for amalgam on the disto- occlusal surfaces. The outline form of this cavity includes all of the area of the distal surface which is susceptible to decay. The buccal and Ungual walls are at right angles to the base of the cavity, with flat base on the gingival and pulpal walls. it will be quite useless, of course, to attempt to place the gingival margin in such an area. The buccal and lingual margins must be so placed in the embrasures that food will sweep over and cleanse them, making it impossible for plaques of bacteria to form and institute a new area of decay. Upon the occlusal surface, under usual conditions, the outline form should include that portion of the occlusal surface which is contiguous to the cavity and should be extended to include all fissures susceptible to future decay. Where the occlusal and proximal portions of the cavity join, the cavity should be cut as broad as conditions will permit, as shown in Figure 1, A-B. Care should be taken not to approach too near the summit of the cusps, where the enamel rods lie in a direc- tion which will cause inferior margins, and not to cut too deeply into the dentin, as the horns of the pulp often extend to a point where they are easily involved. Especial emphasis should be placed upon the broad outline at this point as the narrow connection between the occlusal and prox- imal portions of a cavity is a fault common to many operators. The broad outhne will give strength to the restoration, where strength is most needed, by allowing a greater bulk of amalgam to be placed at this point. Amalgam is not a ductile mate- rial and continued heavy stress upon a small body of it will surely cause it to give way in time; its strength increases rapidly as its bulk increases. We must constantly bear in mind the physical properties of amalgam and adapt our methods to its quaUties to obtain permanent results. If decay has progressed throughout the dentin so that any cusp has become under- mined or weakened, the cusp should be cut away, for at least one-third of the occluso-gingival diameter of the tooth, so that it may be restored with a bulk of amalgam. Representative cases in which this has been done are shown in Figures 2, 3, 4 and 5. The wall, in each case, has been [7] STANDARDIZING THE AMALGAM FILLING reduced with a stone and beveled so that the reproduction with amalgam will lock the cusp and prevent fracture. Verj' often decay has become extensive from both the mesial and distal surfaces and all the cusps are more or less undermined. Figure 2 shows a cavity preparation for amalgam in an upper bicuspid. In this case there were extensive cavities upon both the mesial and distal surfaces to such an extent that the Ungual cusp had become weakened from loss of normal dentin. The Ungual wall at B has been reduced with a stone and beveled so that it may be reproduced with amalgam. This will lock the cusp so that it will not be sub- ject to fracture. The bucco-axial Une angle is shown at A. This is part of the resistance form and is an aid in preventing flow of amalgam from the cavity. Usually teeth in this concUtion are beHeved to be impossible to restore, except with a banded crown, but the writer seldom hesi- tates to restore such teeth vnth. amalgam. Records of these extensive operations, cover- ing a period of years, have yet to reveal the first failure, either from recurrence of decay. fracture, or any other cause. The outhne form for such restorations is shown in Figure 5. The gingival walls, A and F, are ex- tended and squared out as they would be for an operation on either the mesial or dis- tal surface. As both the buccal and lingual walls are weakened by extensive decay, the}' have been reduced so that the amal- gam restoration will have sufficient strength to withstand all the forces of mastication. The outline form of cavities which occur upon the buccal, lingual, and occlusal sur- faces is identical with the form which is used in ca\dty preparation for gold foil. Adjustment of the Rubber Dam If the rubber dam has not been adjusted at the beginning of the operation, this should be done, or some other means should be provided to keep the cavitj^ free from moisture, as soon as the outline form is completed. It is not sufficient to prepare the cavit}' and then dn,' it, since in this case it will be impossible to remove the debris and the dried salts of the sahva from the ca\dty and its margins. Xo moisture should come in contact with the cavit}' after the final cutting is done. 2 — Resistance Form The resistance form of the cavity should be the same for amalgam as for gold, that is the cavity should have a flat gingival wall, ■\\'ith definite angles, and a broad, flat step, or pulpal wall. The base of the cavit}' should be at right angles to the force of occlusion and usually should be at right angles to the long axis of the tooth. This form is illustrated in Figure 1 where the ca^dty sho^Ti has a flat base on the gingival and pulpal walls, with buccal and Ungual waUs at right angles to the base of the cavity. CAVITY PREPARATION FOR AMALGAM 3 — Retention Form The ideal retentive form is a box form, that is a fiat base witli walls at right angles to the base, as this form gives the greatest strength possible to the lateral walls. If amalgam is properly condensed into a cavity of this kind, it will be retained safely. However, as such ideal cavities are not often presented, we must consider the conditions which actually exist. As amalgam tends to flow under pressure, it is permissible, in compound cavities, to use more retention than is necessary for gold. This is accomphshed by carrying the bucco-axial and linguo-axial line angles, in a very slightly retentive form, to a point near the occlusal surface. This statement is not intended to countenance, in any way, deep or decided undercuts which may weaken the walls and, subsequently, permit fracture. These lines are carried out soleh^ for the purpose of resisting the flow of the amalgam. Both Figures 2 and 4 show the correct retention form for the bucco-axial hne angle at A. A part of the retention form shown in Figure 3 is a small slot, at A, cut in the lingual wall gingivally to lock the amalgam from any tendency to flow distally from the cavity. At B the wall has a bevel which, when covered with amalgam, will overcome any tendency of the wall to fracture. In cavities hke that shown in Figure 5, an extensive resistance surface for the anchorage of the restoration is given by the flat, wide, subpulpal wall. This has been broadened so that only a small amount of dentin remains on either the buccal or Ungual waU. As aU the force of occlusion is applied to this subpulpal wall, very little anchorage is required. There is a shght undercut at the base of the cavity at C and a bevel from D to E which adds strength. The cusps have been reduced about two-thirds of the depth of the crown to a very safe and immune area. The gingival form, when restored, is anatomic- Figure 3 represents a cavity in. the disto- occlusal surfaces of a left upper molar. Decay has been very extensive, the pulp has been removed from the tooth, and the disto-Ungual cusp, being weakened, has been reduced so that it may be restored with a mass of amalgam sufficient to give ample strength for any occasion. At A is a small slot cut in the lingual wall gingivally to lock the amalgam from any tendency to flow distally from the cavity. At B the wall has a strong bevel which, when covered with amalgam, wiU over- come any tendency of the waU to fractiure. The pulp chamber, fiUed with cement to the level of the gingival wall, is shown at C. Cavities of this class are encountered very frequently in practice; when they are properly restored with amalgam, the result should be permanent. aUy correct and remains free from the irri- tation which must result when a banded restoration is used. It is permissible, in pulpless teeth, to use the pulp chamber as an aid to retention, as this gives added strength and a base M STANDARDIZING THE AMALGAM FILLING wliich is better, stronger, and more stable for amalgam. A study of the enamel rods, than cement. as shown in Figures 6 and 7, will make it clear that a bevel to the cavo-surface angle 4 — Convenience Form Extension for convenience is less essential for amalgam than for gold. Usualty when the preceding forms of retention have been Figure 4 is an upper bicuspid with a cavity in the mesio-occlusal surfaces, in- volving the Ungual cusp. As shown at B, this cusp has been reduced so that it may be restored with amalgam. At A the bucco-axial Une angle shows the correct resistance form for amalgam. observed, the convenience form is sufficient. It should, however, be observed that suit- able condensing instruments will enter the cavit}' in lines which will produce thorough adaptation. 5 — Removal of Carious Dentin AH carious dentin should be removed after completmg the outline form, to avoid accidents to the pulp. 6 — Finish of Enamel WaUs It is generally beheved by the profession that enamel margins should not be beveled Figure 5 shows an upper molar prepared for an amalgam crown. The gingival walls are extended and squared out as they would be for an operation on either the mesial or distal surface. As both the buccal and Ungual waUs are weakened by extensive decay, they have been so reduced that the amalgam restoration wiU have sufficient strength to withstand all the forces of mastication. The floor of the pulp chamber at B is flat and broad- ened out so that there is only a smaU amount of dentin left on either the buccal or Ungual waUs. As aU the force of occlusion is appUed to this broad flat sub-pulpal waU, very Uttle anchorage is required. There is a very sUght undercut around the base of the cavity at C, the bevel from D to E gives added strength. Though such cavities as this seem difficult, they are reaUy simple to prepare and, when a matrix is properly adjusted, they are not difficult to restore. on the occlusal surface is necessary in in- stances when the margin approaches a cusp or marginal ridge. It is of the greatest importance that all of the surface margins shall be at such an angle that there are no short unsupported rods of enamel at the surface. These are hkely to become dislodged, after the filling has [10] CAVITY PREPARATION FOR AMALGAM been placed, causing an uneven surface for the lodgment of food solutions and, sub- sequently, the failure of the operation. To avoid this, the enamel should be cut with the long axis of the rods in the preparation of the cavity, and in finishing the cavo- surface angle a sharp broad chisel should plane the entire depth of the enamel at an angle which will insure the absence of any short rods at the surface. Dr. Black advocates, in the preparation of the cavo-surface angle for gold foil, a bevel one-fourth of the depth of the enamel. This bevel, which is entirely proper for gold, but would be very unsafe for amalgam, is shown Figure 6 is a diagrammatic representation of the enamel rods, showing the direction in which they are placed in relation to the several surfaces of the tooth. The oper- ator should take advantage of a knowledge of the direction of these rods when cutting and cleaving the enamel for the prepara- ation of cavities for amalgam, especially when forming the cavo-surface angle. at A in Figure 7. The advantage in strength to be gained by the use of the bevel shown at C in this illustration, for amalgam, will be seen at once. Figure 8 shows the manner of holding the chisel when planing the enamel wall. The cavo-surface angle is at A, the dento-enamel junction at B. 7 — Making the Cavity Toilet This represents the final work upon the cavity such as examining thoroughly every margin, surface, and angle with a magni- Figure 7 — A section of enamel through wMch a cavity has been cut into the dentin. At A a short bevel, one-fourth of the depth of the enamel, is shown. This is a bevel advocated by Dr. Black in cavity preparation for gold foil. The correct bevel for amalgam, where the occlusion is a strain to the material, is shown at C. The thin margin of material which is formed when the bevel A is used, is shown at B. A comparison of the bulk of amalgam at D will show the added strength gained by the change in angle. This illustration is adapted from a famihar one in Black's "Operative Dentistry." fying glass of low power and wiping or sweeping all of the cavity surfaces with cotton or spunk to remove fine particles of tooth debris which can not be removed in other ways. Summary of Cavity Preparation for Amalgam Proper cavity preparation for amalgam is identical with Dr. Black's cavity prepara- [11] STANDARDIZING THE AMALGAM FILLING tion for gold foil, with slight modifications. as noted. Outline Fonn: As for gold Modificatioti: Broad outline where occlusal and proximal portions of the cavity join. Resistance Form: As for gold Retetition Form: As for gold Modification: Angles slightly more reten- tive inform. Convenience Form: Not so necessaiy as for gold Modification: Should allow condensing instruments, suitable for amalgam, to enter. Removal of Carious Dentin: As for gold Finish of Enamel Walls: Modification: Bevel entire depth of enamel instead of one-fourth. Cavity Toilet: As for gold Modification: Supply iriissing walls with matri.v. Figure 8 shows a cavity preparation for amalgam in an upper molar, also the posi- tion in vrhich the chisel should be held when planing the enamel to obtain the proper bevel for amalgam. The cavo- stirface angle is at A, the dento-enamel junction at B. Cement Lining for Amalgam Many operators advocate a thin lining of cement for the walls of a cavity about to be filled with amalgam, claiming an advantage in that the cement will act as a seal between the amalgam and the tooth structure. With certain classes of amalgam, this is probably an advantage; however it has certain dis- advantages. Cement in the thin consistency necessaiy to its use in this mamier is neither strong nor impervious, it is Uable to re- crystallization and when this occurs mois- ture will be absorbed at the margins of the ca\'ity and discoloration and future trouble will result. With the accurately balanced dental amalgam alloys, correctly manipulated, it is our experience that a more permanent result is obtained without the cement in- termediary. An amalgam which does not move from the cavity wall will exclude moisture and the bacteria of deca^- suffi- ciently to prevent recurrence of caries. In addition to this, amalgam in contact with the tooth substance, either by exerting an antiseptic action, or bj' some means of wliich we have no formulated knowledge at the present tune, exerts a decided inhibitory action against the bacteria of caries. We do know that some of the metals contained in amalgam have a decided inliibitoiy action against the growth of bacteria and that their salts are among the most effective antiseptics and disinfectants. A further disadvantage of the cement lining, when used in thin consistency with amalgam condensed against it, is that it obliterates the definite form of the ca\'ity preparation and especially tends to fill all angles and line angles so that the amalgam does not have the definite form which we anticipated in the preparation of the cavity. When it is desirable to use cement, either [12] MATRICES FOR AMALGAM RESTORATIONS as a base in the pulp chamber, or as a lining for the cavity walls, a cement of the greatest density should be chosen and, after intro- ducing, should be permitted to harden for several hours in order that the bulk changes, which always occur with the oxy phosphates, may fully take place before the amalgam is introduced. After the cement has thor- oughly hardened, the cavity preparation should be completed, as previously de- scribed, considering the cement as tooth structure and a part of the walls of the tooth. To Prevent Thermal Shock When it is desired to prevent thermal shock to the pulp, a thin solution of resin in chloroform may be used with approxi- mately the same advantage as cement. This will not obhterate the cavity lines, neither is it soluble in moisture, and it will neither shrink nor expand. If the cavity is well dried, it will seal the open tubuU. Matrices for Amalgam In all classes of cavities where one of the walls of the tooth is missing, it is of first importance that some form of matrix should be used to assist in forming the lost contour of the tooth and to aid in conforming the amalgam to the cavity. The placing of matrices requires ingenuity and careful workmanship. An effective matrix must be of such form that it can be adapted closely to the gingival margin, but it should not be adjusted so closely that the amalgam can not be adapted completely; it must have such rigidity of wall that it will not be forced out of position, allowing the amalgam to "landslide" from the cavity and fail to be condensed well at the margins; it must be arranged so that contact with the approximating tooth may be obtained, without loss of space; it must be one which can be removed in a short space of time, without distorting the filhng. The matrix which most nearly meets all these requirements is the tied copper matrix, made from 36 gauge sheet copper. MAKING THE TIED COPPER MATRIX To make the copper pUable it should be annealed by heating it in the flame and dip- Figure 9 shows the steps in the prepara- tion of the tied copper matrix. A strip of metal cut to suitable size with hole for contact point cut out with the rubber dam punch is shown at A. At B button- hole scissors are cutting occlusally and gingivally from the contact point to weaken the matrix so that it can be removed easily. C is the completed matrix. Two forms of ears are shown at D and E. Either may be used to hold the ligature in place. ping it in water, alternately, two or three times. A strip of the annealed metal, long enough to pass sufficiently about the tooth, should be cut as shown in Figure 9; it does not need to encircle the tooth entirely, but should extend past the margins of the cavity as far as it may without inconvenience. In width it should extend somewhat beyond the length of the tooth occlusally, to give the matrix additional rigidity. THE CONTACT POINT With the band in position on the tooth, observe and mark the correct point for the contact with any sharp cutting instrument, as shown in Figure 10. With the rubber dam punch make a small hole where the [13] STANDARDIZING THE AMALGAM FILLING contact should come, as shown at A, Figure 9, then with buttonhole scissors, or a sharp instrument, cut the metal occlusally and gingivall.v from the hole to weaken the matrix so that it may be more easily torn in two when removing it. Occlusally the slit should be cut to or past the occlusal surface so that an instru- Figure 10 — Marking the position for contact point with a sharp instrument. ment may be hooked into it and used to cut the band to the occlusal margin before it is removed. With pliers turn up little ears at the gingival angles, to engage the ligature, and the matrix is ready to be placed upon the tooth and tied. Two forms of ears for the attachment of ligatures are shown at D and E, Figure 9, and the posi- tion of the scissors in cutting slits from the contact point is shown at B. LIGATING THE MATRIX Place a ligature once around the tooth and matrix and make a single knot, as shown in Figure 11, then pass one end of the ligature around the tooth again, so that the ligature surrounds the tooth twice with only a single tie. Now the ligature should be held taut with one hand while, with an instrument, it is adjusted about the tooth and matrix and carried above the gingival margin, as shown in Figure 12. If the opening for the contact is not in the proper place, it may be adjusted by drawing either end of the ligature. Now tie the ligature with a surgeon's knot and continue to wrap it about the tooth mesially and distally, until the form of the inter- proximal space is produced as desired, tying finally on the buccal, as shown in Figure 13. After the first tie, avoid making the matrix too tight; leave it so that some of the amalgam will be forced over the margins Figure 11 shows the matrix, with hole for contact and slits to weaken it for removal, in position upon the tooth; also the first tie of the ligature. as it will be found almost impossible to carry amalgam perfectly to the margins un- less some of it is allowed to pass over them. If the outline of the cavity is extensive and involves, to any extent, the buccal and lingual walls, the matrix should be [14] MATRICES FOR AMALGAM RESTORATIONS burnished to position and a roll of softened modeling compound should be pressed against it and extended mesially and dis- tally against the other teeth. This, when hard, is easily held in position and will support the matrix against the force of heavy condensing. As the amalgam is condensed, it will pass through the hole punched in the matrix and will be forced against the proximal surface of the adjacent tooth at the position desired for contact. Heavy pres- Figure 12 — Holding both ends of the Ugature with one hand, while the matrix is adapted about the gingival margin with an instrument. sure on the amalgam, driving it through this opening in the matrix, will produce a certain amount of separation of the teeth. If more separation is desired, a separator should be placed between the teeth, over the matrix, in such a position that it will not impinge upon the margins of the cavity at any point and so prevent perfect adaptation of the amalgam. This form of matrix has several advan- tages; it can be quickly and accurately applied and is very readily adapted to the Figure 13 - to position. The completed matrix ligated peculiarities of the case in hand; in cases where separation is desired a separator can be placed over it and will adhere to the Figure 14 — Drilling a hole for the point of contact with a small round bur, from the inside of the seamless matrix band. tooth; there is no space lost for thickness of the metal; it is easily removed without disturbing the filling. [15] STANDARDIZING THE AMALGAM FILLING THE SEAMLESS BAND COPPER MATRIX When a complete amalgam restoration, or amalgam crown, is indicated, the seam- less band copper matrix may be used to advantage and can usually be adapted metal immediately around these points should be thinned and made to assume a concave form by grinding with a small round stone. This will produce a better mold for the approximating surface of the Figures 15, 16 and 17 show various methods of slitting the matrix bands. Figures 15 and 17 show bands slit from the gingival through and slightly beyond the contact point. At B, Figure 17, the band is lapped to conform more closely to the tooth. Figure 16 shows bands slit both occlusally and gingivally from the contact point, without cutting to either margin. Small ears turned up to engage the ligature are shown at C, in each illustration. quickly and conveniently. A band which will fit the tooth to be restored, as nearly as possible, is chosen and is trimmed and festooned to the gingival outline. The points of contact are marked with any con- venient cutting instrument, in the same manner as for the tied matrix shown in Figure 10, and the band is then re- moved from the tooth and placed upon a block of soft wood while a small round bur, Xo. 2, is used to drill holes in it at the points of contact, as shown in Figure 1-i. The entire head of the bur should be al- lowed to pass through the band at the contact points and the Figure 18 — The first tie of the Ugature about the matrix band is shown here. The blunt instrument used for holding the Ugature is also used for adapting the matrix about the gingival margin. tooth and when amalgam is condensed within the matrix, it will assume the form of this mold and, passing through the hole at the contact point, will form a smooth, rounded, normal contacting sur- face at the desired point. CLIPPING THE BANDS Figure 15 shows the band after the contact hole has been cut and the band has been slit from the gingival edge at A through and slightly be- yond the contact opening. This slit- ting of the band allows it to be lapped, when this is desirable, as shown at B, Figure 17, so that it will conform more [16] MATRICES FOR AMALGAM RESTORATIONS closely to the tooth when it is tied in place, and also allows the band to be removed easily, by tearing, after the amalgam has hardened. Various methods of clipping the bands may be used as con- ditions and the forms of the teeth vary. It is often advisable to slit the band from the occlusal surface through the contact opening, or it may be slit both occlusally and gingivally from the contact opening, not cutting to either margin, as shown in Figure 16. Small ears, turned up for the purpose of engaging the ligatures which hold the bands in place are shown at C in Figures 15, 16 and 17. PLACING THE SEAMLESS BAND MATRIX The seamless band copper matrix may frequently be used without the ligature; when it is desired to use the ligature, how- ever, it should be adjusted about the tooth in the same manner as for the tied copper matrices, previously described. Fig- ure 18 shows the first tie of the ligature, a single tie with a double loop about the band; this illustration also shows the method of adapting the matrix about the gingival margin with a blunt instrument. It will be noticed that the bands, as shown in Figures 18 and 19, are longer occlusally than the restoration will be when finished. This allows the amalgam to be condensed in excess, producing great density at the occlusal surface. Both the tied copper matrix, for partial amalgam restorations, and the seamless band matrix, for complete amalgam resto- rations, are shown in Figure 19. Figure 19 shows two forms of copper matrices in position on the teeth. At A a matrix which does not entirely encircle the tooth is shown in position upon an upper second bicuspid. At C an opening is punched in the matrix at the point where the filUng should contact with the distal surface of the first bicuspid. To permit the matrix to be torn away more easily after the amalgam is condensed, the matrix is slit both gingivally and occlu- sally from the opening C. A seamless band copper matrix, used in the construction of amalgam crown res- torations, is shown at B. The point for contact with the first molar is shown at D, a similar provision is made for contact with the third molar. After amalgam has been condensed in such matrices, it should be carved until the occlusion is correct and the natural tooth form is restored. If the matrix should interfere with the occlusion it may be ground away until the occlusion is correct. It is usually best to leave such a matrix in position for a few hours at least, as such large restorations must be handled carefully until the amalgam is very hard, otherwise the entire restora- tion may be broken off at the point of anchorage. The ligatures which hold the matrices in position are at E and F. [17] STANDARDIZING THE AMALGAM FILLING Section II. Dental Amalgam Alloys THE second essential for standardized amalgam technic is the selection of the best alloy that it is possible to obtain for the amalgam. The question, "How are we to know the best alloy to use?", is asked of the writer more frequently than any other. The answer to this question will be found by considering those qualities of an alloy which are essential to permanent results when the allo}' is amalgamated and used for the restoration of carious teeth. Practical experience has led to the con- clusion that a dental amalgam alloy must satisfy the following requirements: 1 . It must amalgamate in such a manner that it will be capable of accurate manipu- lation by dentists who are familiar with restoration technic. 2. It must possess inherent structural strength and impart this quahty to the resulting amalgam. Its amalgam must be sufficiently strong to withstand the con- tinued force of mastication; it must not flow from the cavit}^ under this stress; its margins must endure this force without fracture. 3. It must be chemically and electro- chemically resistant to deterioration by tarnishing or corrosion. 4. It must be of the type known as balanced aUoy, that is, when properly amalgamated and condensed in the cavity, the amalgam must remain tight to the cavity walls, it must not contract, and must have a minimum and regulated amount of expansion. 5. It must conform to metaUographic principles. 6. It must require the minimum amount of mercury. 7. Its color should be pleasing. 8. It must not contain materials which will injure the tissues or discolor them. It is not an easy matter to incorporate all of these quahties in one alloy, but it is possible and we should not be satisfied with an alloy which fails, in even one particular to meet these requirements. A careful study of the physical and chemical properties of the various metals which have been used for dental alloys permits us to predicate the probable qualities which the metal will confer upon the alloy and, together with a consider- ation of methods which have been used for combining the alloy metals, should be helpful in choosing the best alloy. Dental Amalgam Alloy Metals Although experiments with other metals have been made none seem to have been found which have added sufficient desir- able quahties and the only metals which have been used to anj- extent for dental amalgam alloys are silver, tin, copper, gold, and zinc. A tabulated comparison of important physical and chemical charac- teristics of these metals will be found on the succeeding page. Some characteristics which especially affect their use in dental amalgam alloys are noted as follows: SILVER Silver occludes twenty-two volumes of oxygen, when molten, which it gives off with great vigor upon sohdification. In order to avoid undesirable oxides and resulting eutectics, from this cause, it should be melted in the electric furnace, under hydrogen. Silver increases in volume when amalga- mated, can not be easily manipulated, and is subject to sulphide blackening. In dental amalgam alloys it lessens flow, [18] PHYSICAL PROPERTIES OF ALLOY METALS o O CO O CO o ^ t^ o CO i-H CO (M CO 1> o o o ^ d CO LO CO o > K O Of .2 ^ 9 fl W [19] o o CO o o o o o o o J> o d o CO o o o CO o d CO > >: O > O T3 O S3 .g5 WW 00 t^ CO lO I CO 05 GO (M O CO CO O lO .-H C-l o o O o3 '^ o 00 ^ O CO --I (M (M O CO t^ CO lO 05 05 o o Ph .1:3 c .2 S o a> HJ P-l -^J O 0^ 1i •-H hC -^ -r ^« o -ij ^ .b ^ « I- 3 --H 03 O ^ oi f^ hJ pq P^ ^ bC M ^§ >>-^ o -^ t-( bC ^ 1 '*"■ QJ .-, O !- >w >^pq -tj bJD faC WW P^ y^ pq P5 pq ^ >. x> -fj a ;J2 5 O >5 H O C o bC c o o CO c3 sj d 5 >», O w STANDARDIZING THE AMALGAM FILLING hastens hardening, forms the primar\^ freezing network upon which amalgam largely depends for strength, and adds other desirable qualities which may be deduced from its characteristics as indi- cated in the table of physical properties. A homogeneous silver amalgam can not be made by triturating silver filings with mercury, since these merely envelope, that is, each grain becomes coated with amalgam, resisting establishment of equi- librium, even when heated moderately. Uniform silver amalgam is produced at the boiling point of mercury, 357° C. Bomb Amalgam To determine the structural constituents actually present in silver amalgams, a constitutional study of the series was made by preparing amalgam in the bombs shown in Figure 20. Weighed portions of silver and mercury were placed in the bomb, the Figure 20 — Steel bombs used to contain alloy and mercury, when amalgamated by heating to the boiling point of mercury. screw plug was inserted, and the whole was heated in the electric furnace for a suitable period of time, at temperatures ranging near the boiling point of mercury. Naturally the time and temperature neces- sary for thorough amalgamation increase with the increase in the percentage of silver. Figure 21 is a photomicrograph of a bomb amalgam containing 43 per cent of mercury; this shows large masses of primary-freezing silver-rich solid solution embedded in the darker, softer mercury- rich solid solution. Up to the percentage of mercury established as correct for dental practice, the silver amalgams are solid solutions of considerable strength and toughness, but the consistency of amalgams containing the percentage of mercury found in the so-called Arbor Dianae (AggHg^) reminds one of lumps of moist table salt. This hardens slowly when exposed to the air, supposedly due to the loss of mercury bj^ volatilization, since the vapor tension of the latter is relatively high. Our research indicates that what has hitherto been considered the fundamental reaction of amalgamation: Ag,Sn+4Hg = AggHg^+Sn, rests on slight foundation and does not concern dental amalgams. Neither "affinity" nor "absorption" de- scribes amalgamation. Silver-mercury al- loys of any desired percentage of mercury may be prepared readily and, in the dental range, only solid solutions appear. A recent publication states "When silver is amalgamated alone it does not harden to any extent, nor does it disintegrate readily." This statement stands unsup- ported by data and actual research shows that silver amalgam may be as hard and tough as brass when silver-rich or decid- edly different when mercury-rich. "Crepi- tation" is due neither to silver nor tin amalgam, but to the cold working of primar}^ freezing crystalhne grains of the dental amalgam. TIN Tin forms a very mobile fluid, when molten, having low chemical affinities thus, in some respects, approaching the precious metals in its chemical behavior. It forms a series of solid solutions, when amalga- 20 EFFECT O F ZINC O N AMALGAM ALLOYS mated, with decrease in volume. In dental amalgam alloys it retards setting, decreases edge strength, increases flow and produces an easily worked mass. It imparts to the alloy its property of solubility, making possible the more ready amalgamation of the copper and silver. Tin readily dissolves in mercury, the solid solutions rich in tin being reasonably Figure 21 is a photomicrograph of a bomb amalgam of silver and mercury, contain- ing 43 per cent of mercury. hard and tough, but rapidly losing their desirable industrial qualities with increase in the mercury content. COPPER Like silver, copper readily forms solid solutions with mercury, near 357° C, amal- gamation being correspondingly more dif- ficult at ordinary temperatures and in the copper-rich portion of the series. The amalgam will stand a considerable degree of heat without suffering loss of mercury through volatilization. Copper is an element of strength in dental amalgam alloys, decreases flow in the amalgam, and possesses a desirable coefficient with respect to change of volume upon amalgamation. GOLD Gold makes amalgam springy and dif- ficult to pack. It has low tensile strength, is liable to flow, and has a rather high electric potential. ZINC Although the use of zinc in dental amalgam alloys has long been condemned by those who speak with authority in the dental profession, its use is still continued and defended by manufacturers of alloys, and it seems well, for this reason, to take up in some detail the physical and chemical characteristics of this metal which may affect the alloy, the amalgam which is made from it, and the general health and welfare of the patient for whom the amalgam is used. Volatilization and Oxidation Reference to the table of physical prop- erties shows that the boiling point of zinc is below the melting point of silver and copper. Unless the metals are alloyed at a temperature below the boiling point of zinc, this will cause a volatilization error as an undetermined percentage of zinc will burn out or distil. This error is suffi- cient to destroy the balance of metals which are placed in the crucible in correct proportions and is further increased by the rapid oxidation of zinc, when molten, even at low temperatures. Dr. Black: "Zinc is Inadmissible" As Dr. Black's research has recently been construed to favor the use of zinc in dental amalgam alloys, it seems well to quote here his conclusion on this subject as published in "Operative Dentistry," Volume II, page 312, where he states: "Experiment in watching fillings for five years shows also that one-half of one per [21] STANDARDIZING THE AMALGAM FILLING cent of zinc is inatlniissible for the reason that the amalgam will continue to change bulk very slowly for that time and perhaps much longer. Though this change is not large (not more than one to one and one- half points per year, with one per cent of zinc), it will finally destroy the usefulness of the filling. This effect is so subtle that it was not at first discovered." Dr. McCauley: "100 Points Expansion" In a paper entitled "Amalgams: Their Manufacture, Manipulation and Physical Properties," read before the National Dental Association, July 25, 1911, and published in "Dental Cosmos," February, 1912, Dr. C. M. McCauley says: "Zinc is very unfavorable in its action upon other metals in a dental alloy. I made two fillings containing only one per cent of zinc. They behaved very well under the ten days test at first, but measurements made three months later showed nearly 100 points expansion." Adhesiveness For the first time in the annals of metallog- raphy, the quality of adhesiveness or stickiness has recently been attributed to a metal. It has been stated, erroneously, that zinc adds this quality to dental amal- gams. No recognized authorities are quoted in support of this theory. For one substance to adhere to another, it is necessary for one to moisten or wet the surface of the other, to have gummy or viscous quality. Amalgam might be de- scribed as cohesive, while in the plastic state, in the same manner that gold foil is cohesive, but it has no quality of sticking to or adhering to tooth substance. Zinc does not cause amalgam to adhere to the walls of the cavity or its margins; on the contrary, its tendency to produce flow and change of form causes the amalgam to draw away from the margins and walls of the cavity. Moisture proof fillings are obtained by condensing a balanced alloy, properly amalgamated, so tight to the cavity walls that penetration of the oral fluids is prevented. Toughness It has also been claimed that zinc toughens amalgam by raising the breaking point. Reference to the table of physical properties shows that zinc has the lowest tensile strength of any of the metals used for dental amalgam alloys. A Comparison of the Electrolytic Single Potential Diflferences for a Zinc Alloy Amalgam with Those for a Non-Zinc Alloy Amalgam Zinc Alloy Amalgam Non-Zinc Alloy Amalgam Positive Negative Positive Negative VOLTS VOLTS Zinc +.493 Copper — .607 Tin — .083 Silver —1.075 Mercury —1.027 Copper — .607 Tin — .083 Silver —1.075 Mercury —1.027 Addition of Single Potentials Gives the Total Voltage Between Any Pair of Positive and Negative Elements Example: The voltage between zinc and copper is .493V. plus .607V. equals I.IOV. The production of electrical energy in a zinc-copper cell is accompanied by the consumption of zinc. [22] EFFECT O F ZINC O N AMALGAM ALLOYS A series of tests made by Dr. H. A. Merchant to determine the strength of amalgams, under different methods of manipulation and varying conditions, has a direct bearing on this subject. The tabulated results of these tests will be found on page 46. Test No. 1 made with a non-zinc alloy, containing 5 per cent of copper, amalgamated according to direc- tions, showed a crushing strength averag- ing (for sixteen specimens) 437.5 pounds. Test No. 6, made with a zinc alloy, con- taining 5 per cent of copper, amalgamated according to directions, showed a crushing strength averaging (for sixteen specimens) 352.5 pounds. After heat treatment of thirtj^-five minutes at 150° F., approximat- ing the effect of hot drinks and food, the non-zinc alloy amalgam showed a loss of strength of 50 pounds, while the zinc alloy amalgam lost 150 pounds, leaving a net crushing strength of only 202.5 pounds, compared with 387.5 pounds for the non- zinc amalgam. While the strength of amalgam contain- ing zinc, or other impurities, may be suffi- cient to resist fracture, it must be remem- bered that strength is the only safeguard against flow and that resistance of amalgam to flow is increased as the strength increases. The result of these tests for strength, as well as any other tests outlined in this article, may be verified by any individual dentist or any study club of dentists and all possible assistance in making the tests will be given by the publishers. Corrosion A consideration of the effect of zinc on dental amalgam alloys requires some ex- planation of the phenomena of corrosion of alloys. The process of corrosion may take place in several ways. The simplest of these may be described as chemical cor- rosion in which the alloj' is merely dissolved in the Kquid, in the same way that a simple metal is dissolved in an acid, as zinc in an organic acid. A more complicated process of corrosion occurs from the combined influence of a corrosive liquid and the atmosphere. This occurs very commonly and is frequently observed in the case of copper-zinc alloys. The maximum effect of the corrosion takes place at the surface of the Uquid, or when the metal is alternately immersed in the liquid and exposed to the air. Perhaps the most interesting as well as the commonest type of corrosion is that which may be described as electrochemical. This occurs when two bodies possessing different electrical properties are immersed in contact with one another in a corrosive or conducting fluid. Owing to the difference of potential between the two bodies, an electromotive force is set up, or in other words a galvanic battery is formed and one of the bodies passes into solution. As zinc is electropositive to the other metals used in dental amalgam alloys, we have, when the alloy is amalgamated and placed in the mouth, all the necessary con- ditions to produce electrochemical corro- sion. The zinc is in contact with the other metals of the amalgam, immersed in a con- ducting fluid, the saliva, and is dissolved from the amalgam, leaving pits and net- work oxidation. The voltage between zinc and any of the negative elements found in dental amalgams may be found by adding their single potentials as found in the table of physical properties or the table on page 22. The voltage between zinc and silver, for instance is .493Y plus 1.075V, which equals 1.568V. [23] STANDARDIZING THE AMALGAM FILLING Galvanometer Tests To show the existence of electric currents, local action, and electrochemical corrosion of dental amalgams containing zinc, the following tests were made with the aid of the set up shown in Figures 22 and 23. This is an accurate galvanometer and two copper wires by means of which contact is made with a specimen of amalgam held in the mouth and a gold crown in the same mouth. Amalgam cylinders about the size of the crown of a tooth were made up from the most widely known zinc alloys, accord- ing to directions given for those alloys. Upon making connections the one per cent zinc alloy amalgams gave a deflec- tion, as shown in Figure 22, ranging from 20 millivolts to beyond the largest scale division of the galvanometer, which is 25 millivolts. In marked contrast the non- Figure 23 — The deflection, when contact is made with a specimen of amalgam made from a non-zinc alloy and a gold crown, is hardly discernible, ranging from 1.75 to 2 millivolts. Figure 22 — A galvanometer with contact made with a specimen of amalgam made from a zinc alloy and with a gold crown. In a series of tests the deflection ranged from twenty to twenty-five millivolts. zinc alloy amalgam gave a deflection of only 1.75 to 2 millivolts, as shown in Figure 23. In time a smaller deflection results due to polarization or coating of one electrode with hydrogen and in the case of zinc to local action between the metals contained in the one amalgam. This local action practically short circuits the cell (zinc alloy amalgam vs. gold) so that the galvanometer receives only a portion of the original current, resulting in a lesser deflection. The consumption of zinc from the amalgam, due to this galvanic action, is accompanied by pits and network oxi- dation, as previously described. Galvanic shock is frequently experienced when a fork or spoon comes in contact with an amalgam filling or the familiar electric tingle may be experienced by in- serting the tongue between a sheet of zinc and a piece of silver, such as a silver coin, placed in contact. [24] EFFECT O F ZINC O N AMALGAM ALLOYS Eutectics and Impurities An alloy whose constituents separate on cooling, or form eutectics which separate on cooHng, will almost certainly be corroded on account of the difference in electric potential between the constituents. It is for this reason that alloys forming solid solutions are usually better able to resist corrosion than highly eutectiferous alloys. Figure 24 shows the large proportion of eutectic in an alloy containing 1 per cent of zinc. Impurities, such as dross, slag, oxides, etc., due to improper treatment of the alloy, are the cause of a similar form of corrosion. The influence of impurities on corrosion has received more attention in the case of metals than in the case of alloys. It is well known that many metals in a pure state are only soluble with difficulty in acids, while the same metals in an impure state are readily soluble in the same acids. FINDINGS BASED UPON FACTS In addition to Dr. Black's and Dr. McCauley's charges of change of bulk, it would seem that the charge of responsi- bility for loss of strength, for pitting, cor- rosion, and galvanic shock, are amply sustained by the evidence. We conclude, therefore, that a comparison of the physical and chemical quahties of the metals con- sidered, indicates that only silver, tin, and copper should be used for dental amalgam alloys, that gold does not add desirable properties, and that zinc is inadmissible. Preparation of Dental Amalgam Alloys Having determined the metals which are suitable for dental amalgam alloys, there remains the determination of a method for combining them in such proportions that their desirable properties shall be retained and their undesirable features eliminated or minimized. Many methods for the preparation of dental amalgam alloys have been detailed and many theories of abstruse interest have been expounded, but the one prin- ciple which has proved to have scientific Figure 24 — The eutectic structure of a dental amalgam alloy containing 1 per cent of zinc. and practical value is that of balancing molecular movements. Dr. Black was the first to devise an amalgam micrometer sufficiently accurate to determine the balancing principle as the correct one for alloying silver and tin in such proportions that shrinkage would be eliminated. Vari- ous efforts had previously been made to determine the shrinkage or expansion of amalgam, both by the specific gravity test and by means of direct reading instruments, but these experiments were not carried to a point where authoritative results were secured, and had little practical value in improAdng the quality of alloj's ofl'ered to the profession. The following experiments to determine the proportions in which silver and tin [25] STANDARDIZING THE AMALGAM FILLING should be combined to effect a balance between their diametrically opposed quali- ties are only corroborative of Dr. Black's work. AMALGAM MICROMETERS Figure 25 shows the micrometer used by Dr. Black in his research upon amalgam. The smallest divisions are 0.0001 inch and Figure 25 — Dr. Black's Amalgam Microm- eter. Unit of measurement 0.0001. (From Black's "Operative Dentistry," Vol. II.) the microscope is used separately to check the readings of the micrometer. The micrometer used by Dr. Black has been replaced, for these experiments, by a micro-micrometer of original design, which is the most exact and delicate instrument ever used for the measurement of the volume changes of amalgam. As shown in Figure 26, it is a combination of microm- eter mechanism with the powerful micro- scope. Four revolutions of the calibrated wheel measure one millimeter, the wheel bears 250 divisions, thus the least count is 0.001 millimeter, one micron, or 0.00004 inch. With careful work readings may be made as fine as 0.1 micron, or 0.000004 inch, and these readings may be repeated, moving the instrument in either direction. In checking tests made with micrometers of other design, we find that they often give inaccurate results because of friction, lost motion, complex design, and errors in calibration. The Wedelstaedt tubes, shown at the left of the micro-micrometer and in Figure 27, are those standard in making amalgam tests. They are hardened steel tubes with a definite diameter and depth. The cavity is grooved at the bottom so that the amalgam, when condensed in it, will be held from moving away from the base. While the amalgam is still plastic, a hard- ened and polished steel point is placed at the center of the filling. The touch point of the micro-micrometer makes contact with this and communicates the amount of expansion or contraction. If the amal- gam expands, it can not change the form of these tubes, on account of their strength, but is necessarily forced to protrude from the cavity. Figure 27 shows empty and filled W^edelstaedt tubes. These tubes fit into the micro-micrometer and are locked in such a way that they may be removed and replaced, at any time, in their exact original position. This is an essential factor in securing accurate results in a [26] PREPARATION OF DENTAL AMALGAM ALLOYS series of tests which is to be carried over a period of several months and leaves the instrument available, in the meantime, for other tests. To further substantiate the readings of the micro-micrometer, the test filling is placed in a sliding rack, under the objective, and the margins about the tube are examined with the aid of reflected arti- ficial light. In case of shrinkage of the amalgam, the width of the ditch between the amalgam and the tube can be measured. BALANCING To determine the composition at which the shrinkage of the tin amalgam offsets the expansion of the silver amalgam, the following tests were made: An alloy containing 40 per cent silver and 60 per cent tin was amalgamated, according to the usual technic, and con- densed in Wedelstaedt tubes. A touch point of polished steel was placed in the center of the filling, the tube was inserted in the micro-micrometer, and measure- ments were taken and recorded. As the Figure 26 Dr. Crandall's Amalgam Micro-Micrometer, least count 0.00004 inch. [27] STANDARDIZING THE AMALGAM FILLING amalgam continued to harden, successive readings were recorded at five minute intervals for a period of one hour, then at successive lengthening intervals. These readings indicated excessive shrinkage. A filling was next made from an allo^' of the formula 45 i>er cent silver, 55 per cent tin: shrinkage was still present, but was a Kttle less than before. These tests were continued by advancing the silver content of the alloy 5 per cent each time, unto the ratio 65 per cent silver. 35 per cent tin was reached. At this point, fillings made from fresh cut filings gave two microns ex- pansion, while fillings which were made from annealed filings gave twenty -seven microns shrinkage. As alloys have the property of aging, or undergoing poh-morphic change, further research was conducted upon aged or annealed alloys. At 70 per cent silver, 30 per cent tin, the shrinkage was fifteen microns, at 75 per cent silver. 25 per cent tin, an expansion of twenty-eight microns was noted at the end of two hours, followed by a shght contraction, resulting in a final expansion of 24.5 microns. The silver content was next reduced in stages of 0.1 per cent until, at 74.3 per cent an expansion of three microns was noted after a period of five days. In a manner entirely analagous to this, the point of balance must be redetermined when copper is introduced into the alloy. When the point of balance is determined, £♦ B A A and B, empty; filling, sho'Ting Figure 27 — Wedelstaedt Tubes. C, tube with test filling; D, te great expansion; E, steel tube used to standardize the micro-micrometer to varying temperatures; F, side view of tube, showing guiding slot it holds good only for the lot of metals tested. Variations in the purity of metals obtainable, variations in heat treatment which they have received, vart'ing methods by which they have been manipulated, and other factors necessitate the determina- tion of the fineness of even,^ lot of metals procured and micro-micrometer tests of everj' lot of the finished product. It is e\'ident that the determination of the balance point for each lot of metals is the onlj^ accurate method of arriving at cor- rect proportions to produce a bal- anced alloy. If the alloj^ is de- ficient in silver as much as 0.1 per cent a shrinkage of five microns may occur about the margins of large ca\ities. This would ob^doush" destroy the utiUtj^ of the restora- tion, regardless of the quahty of the technic emploj^ed. One micron, as determined b}' micro- micrometer measurement, corresponds to a ditch or space 0.00004 inch in width, between the fiUing and the ca\dt3' wall. The micro-organisms productive of caries varj^ in size from 0.4 micron to 0.8 micron. If the width of the ditch, 5 microns, is divided by the diameter of the bacteria, 0.4 or 0.8 micron, it will be seen that a small army of these bacteria could march into the space from six to twelve abreast. Recurrence of caries must attend this invasion of bacteria. We leave for j^our consideration the possibOities which may occur with those alloys which show a con- [28] PREPARATION OF DENTAL AMALGAM ALLOYS traction of from ten to seventy-five microns. Without the aid of precision instruments which will detect the minutest movements of an amalgam while it is hardening, it is impossible for the manufacturer to give assurance of a desirably balanced alloy. The Proximate Analysis of Alloys The physical properties of alloys which give them their industrial importance de- pend largely upon their proximate compo- sition, or constitution, as revealed by thermal analysis and microscopical exami- nation. The chemist reports the anah'sis of brass, for instance, as 70 per cent copper, 30 per cent zinc, while the report of the metallographist is concerned with such data as the character and distribution of the solid solutions, defects in the metal, heat treatment, mechanical defects, results of strength of materials tests, grain struc- ture, extent of deformation, and bene- ficial modifications in composition or pro- duction. In the great majority of cases, two or more metals can be mixed with one another, in the molten condition, in any relative proportion, and in a manner analagous to the formation of well known organic or inorganic solutions. However, compounds may form, and metals varying widely in such physical properties as melting point may form mutual solutions to such a slight extent as to be practically immiscible. According to the number of metals con- tained in the series, alloys are classified into binary, ternary, and higher systems; while, according to their behavior in the molten state and upon soUdification, they are classified as chemical compounds, solid solutions, and eutectics. CHEMICAL COMPOUNDS The chemical compounds of one metal with another do not, in general, follow the law of valence, but are of the type known as molecular. The resulting chemical com- pound differs much less in its properties from those of its component metals than is the case with strong chemical compounds. It is in accordance with this general idea that it is concluded that even those metals which do form definite chemical com- pounds are relatively feebly combined. The metallic compounds usually have a limited range of stability and at certain points in the equihbrium diagram are resolved into other bodies. Great difiiculty is experienced in isolating most of these compounds and the chemical constitution of comparativeh^ few of them has been determined with certainty. The evidence for considering that a structural constituent is a definite com- bination of two metals, instead of a soKd Figure 28 — Photomicrograph of Ag^Sn, a well established metallic chemical com- pound. solution, is not always as conclusive as would be desirable. On the hquidus the formation of a compound is often indicated by a sudden change of curvature and the whole range of composition throughout which the compound separates from the [29] STANDARDIZING THE AMALGAM FILLING liquid mixture corresponds to a distinctly separate branch of the liquidus. At other times the change of curvature is almost or (luite indistino-uishablc, but in this case the compound usually forms solid solutions with the component metals, or with other compounds of the series, and can not be isolated. When the occurrence of a com- Figure 29 — Cold-rolled brass, a well known example of metals in solid solution. pound is shown by a distinct branch of the liquidus, this frequently exhibits a point of maximum temperature, which is the freezing point of the pure compound. The composition of the mixture which shows this maximum freezing point is difficult to determine with exactness, since the curve is somewhat flat, but it is found to agree closely with a simple atomic propor- tion of the two metals. Under the micro- scope this compound is distinguished as a new structural constituent which differs in properties, such as color, hardness, and rate of etching, from the component metals, eutectic, or solid solution. At a certain composition the whole of the section appears to consist of this new constituent and, if analyzed, the alloy is found to contain the metals in proportions corre- sponding very nearly wdth those represented by the peak of the Uquidus curve. It is reasonable to suppose that a chemical com- bination of the metals in a series of alloys exists only when — 1. At a certain composition, it consti- tutes the whole of a just solid metal; 2. On chemical analysis is found to con- tain the metals in approximately simple atomic proportions; 3. Gives rise to a separate branch of the liquidus curve, showing a temperature maximum at a composition very close to that given by analysis; 4. Has physical properties such as color, hardness, density, electrical conductivity, etc.. which differ sharply- from other struc- tural constituents of the series. A well established metallic chemical compound which fulfills all these condi- tions is Ag.^Sn. A photomicrograph of this compound is shown in Figure 28. While a number of ])inary metallic com- pounds have been established, according to Dr. Rosenhain no ternary metallic com- pounds have been determined to date. SOLID SOLUTIONS The distinguishing characteristic of a solution is that the particles of the dissolved substance can not be detected and can not be separated by mechanical means. For example, in a mass of copper containing tin, the tin can not be detected under a microscope of the highest powers, nor can it be separated by mechanical means. The allo\^ solidifies and crystallizes as though it were a pure metal and the mixture of the two metals is so intimate that there is a strong analogy between it and a liquid solution. Examples of metallic solid solutions of wide industrial use are shown in the photo- micrographs of cold rolled brass, Figure 29, and copper-tin alloy, Figure 30. The [30] PREPARATION OF DENTAL AMALGAM ALLOYS latter is an alloy of tliQ bronze series which was cooled too rapidly for the beta to gamma transformation to take place. The black areas represent primary crystal skeletons of beta, chilled at 725° C. The particular solid solutions, i.e., alpha, beta, gamma or delta, found in this series of alloys, have a very important effect upon physical properties. Mechanism of the Formation of Solid Solutions of Two Metals Let us assume that a certain proportion of the metal tin, of relatively low melting point, is alloyed with, or dissolved in, the metal copper which has a higher melting point. The copper may be considered as the solute and the tin, as the solvent. It is believed that, when solidification begins, homogeneous crystals of tin and copper are formed, but that they contain a smaller proportion of the fusible metal, tin, than the liquid bath, which is thereby enriched in tin. On further cooling these crystals grow, but the crystalline matter now deposited contains more of the metal tin than the crystals first formed, although still less than the molten bath which is further enriched in tin, and so on, the crystals growing through successive ad- ditions of crystalline matter, containing increasing proportions of the dissolved and readily fusible tin, and approaching, there- fore, although not reaching the composi- tion of the molten metal, until finally the last drop sohdifies. A homogenizing an- neal will bring the whole mass to the same composition. Figures 31, 32, 33 and 34 show a balanced silver-tin-copper alloy in process of homo- genization. Figure 31 shows the dendritic structure of the alloy upon solidification, while Figure 34 shows the completely homogenized alloy. Figures 32 and 33 are intermediate stages during homo- genization. EUTECTICS The eutectic is a conglomerate of metals, has a constant composition, always freezes at the same temperature, and is the lowest freezing alloy which can be obtained in the series. The eutectic structure is composed of the different constituents in juxtaposi- tion. The constituents of a eutectic may occur in curved plates or laminae, or in globules, and either or both may be simple metals, solid solutions, or compounds. Types of eutectic structure are shown in Figures 35 and 36 ; they are very character- istic and are not easily mistaken. The manner of employing cooling curves in the construction of the equilibrium dia- Figure 30 — Another example of metals in solid solution. Copper-tin alloy, 73 per cent copper, magnified 45 diameters, etched with acidified ferric chloride. gram for a eutectiferous series, is shown in Figure 37. The eutectic E has the longest eutectic halt, corresponding to the greatest evolution of heat on cooling. The other alloys of the series evolve an amount of heat at the eutectic temperature propor- [31] STANDARDIZING THE AMALGAM FILLING tional to the amount of eutectic which they contain. In the ternary dental amalgam alloy, silver-copper-tin, properly balanced, the copper content should be within the solid solution range, and the tin content small Figure 31 — A balanced silver-tin-copper alloy remelted and slowly cooled, showing solid solution. enough to prevent extensive formation of eutectic. The silver content should be sufficiently high to form the strongest primary freezing amalgam network. Ther- mal analysis and photomicrographs are used to indicate the proportion of eutectic and solid solutions, the latter being the desirable constituent of dental amalgam alloys. Silver can not be reduced beyond a certain point without producing an alloy which is highly eutectiferous and weak upon amalgamation. Aging and Annealing of Dental Amalgam Alloys Annealing, and heat treatment in general, effects profound changes in the physical properties of alloys. The freshly cut dental amalgam alloys require a high percentage of mercury for their amalgamation, and are so extremely rapid setting that very few operators are able to emploj' them satis- factorily. Aimealed alloys require less mer- cury and are modified in their setting qualities so that they may be correctly manipulated. DR. BLACK'S EXPERIMENTS After a series of experiments which are outhned on page 308, Volume II, "Opera- tive Dentistr}^," Dr. Black reached the following conclusion in regard to the changes produced in alloys by annealing: "Conclusion: The cut alloy is made abnormally hard by the violence in cutting, the same as metals are made hard by ham- mering. By the processes above detailed, it becomes annealed to normal. The Figure 32 — A balanced silver-tin-copper alloy partly homogenized. change was produced by heat. This effects a change in the affinity for mercury and the rapidity of combination with the results named above. Why, is unknown, but the Jact stands all tests. It is a primary physical phenomenon." [32] PREPARATION OF DENTAL AMALGAM ALLOYS FURTHER RESEARCH UPON AGING PHENOMENA Incidental to our research upon dental alloys and amalgams, the following obser- vations have been made. It would seem that they offer a reasonable explanation of the slower rate of amalgamation which characterizes aged fihngs of dental amal- gam alloys. Freshly cut alloy is rapid setting for a number of reasons, chemical, physical, and physico-chemical. The particles from the cast ingot are in a state of metastable equilibrium, due to suspended transfor- mation of part of the alloy into the normal proportions of compound, solid solution, and eutectic. Filing, or cold work, endows the freshly cut particles with strain potential which, Figure 33 — Another stage in the homo- genization of a balanced silver-tin-copper alloy. according to the electrolytic theory of solution, favors more rapid amalgamation. In order to better understand the effect of cold work and annealing, it should be pointed out that the structure of metals is crystalline. It appears that the particles of freshly cut alloy are full of cracks, thus presenting more surface to the attack of mercury or, more accurately, the severely strained metal has developed a finer crystalhne structure and, of course, the fine crystals '^ ^ ' * ',- \ ' '■'■'""- • ■ : *V "■-^"' *'' y ■■"■ - -.1 U^V- .:^;^J.-- ^ : ■ -•-^'■, "-' - ' ~- «-\-"*^' .-'-.-,- ' ' J -"- -" ' • ■ * -:■-' ^ ■*. i^^^^#f:-..;--v- ^^\^- -^ Figure 34 — A balanced silver-tin-copper alloy fully homogenized. will dissolve more rapidly in mercury than the same amount of material in the form of large crystals, or crystals of a more resistant system. Changes in temperature and pressure frequently give rise to different crystal structures and change in physical state, or molecular arrangement, is accompanied by alterations in physical properties. When metals or alloys are severely strained by compression, tension, or bending, the original crystals are broken up and re- placed by much finer units. Microscopical examination of a metal strained beyond the elastic limit reveals fine hnes on the crystal grains termed sUp bands. These sHp bands are cleavage planes, for the most part intimately connected with the formation of new small crystals. [33] STANDARDIZING THE AMALGAM FILLING UNAGING AN AGED ALLOY Alloy which had been aged by annealing was unaged, during these experiments, after repeated grinding in a mortar fol- lowed by heavy pressure exerted by a ^3©3 r***^? Figure 35 — Photomicrograph of silver- copper eutectic. modified Brinnel machine. The freshly cut allo}^ amalgamated with equal parts of mercury was quick setting and only a minimum of mercury could be expressed in a vise after amalgamating. The annealed alloy was slower setting and much more mercur}^ was expressed with the same amount of pressure applied with a vise. After the annealed alloy had been subjected to the grinding and heavy pressure men- tioned, it reassumed the properties of a freshly cut alloy, in regard to time of setting and the amount of mercury which it was possible to express in a vise after amal- gamation. The appearance of "amorphous layers" marks an increase in the following physical properties: hardness, tensile strength, vol- ume, heat of solution, and solution pressure. Amorphous material etches and amal- gamates more rapidly than crystalline or annealed metal. Howe states that, "The plasticall}' deformed metal etches faster because, being lighter, that is bulkier and less closely packed, it offers greater surface for attack; because its amorphous metal lacks crystalline bond which in itself opposes solution and every other kind of attack; and because in being a mechanical mixture of amorphous and crystalline metal, it has local differences of potential, which are such frequent accelerators of corrosion." Our dissolving agent is mercury and, digressing, we have found it to be a valu- Figure 36 — Copper-Antimony eutectic. TMs illustration and Figure 35 show characteristic eutectic structure. AMORPHOUS MATERIAL Another important factor affecting a freshly cut alloy is the formation of so- called "amorphous material," upon filing or severely straining by heavy pressure. able etching reagent, which enables us to watch the growth of amalgam crystals under the microscope, and to bring out upon a polished surface constituents of an alloy not readily amalgamated. [34] PREPARATION OF DENTAL AMALGAM ALLOYS ANNEALING If thorough amalgamation took place, equilibrium conditions in the alloy filings would be of less importance, but as a matter of fact partial amalgamation takes place and the alloy particles are enveloped with amalgam, and not completely dis- solved. In order that the balance point of an alloy may remain constant for at least a year, it has been found advisable to anneal, or age, the filings in a manner determined by careful experiment. This heat treat- ment reduces the setting rate of a high grade alloy so that it comes within the range of careful manipulation, makes possible the use of a lower percentage of mercury and reduces the amount of expansion of the alloy upon amalgamation. The effective annealing period and tem- perature is a function of the chemical elements of which the alloy is composed and also of the proportions of its structural constituents. The proper annealing tem- perature and period must be determined for each alloy in order to obtain the par- ticular condition desired. OVERANNEALING Overannealing enlarges the crystalline grains of the alloy, reducing its strength, and affecting its working qualities upon amalgamation. This change may take place through the use of too high temper- ature for a short period of time, or from exposure to ordinary room temperature over a longer period of time. In regard to this change Dr. Black says, in "Operative Dentistry," Volume II, page 311: "Tubes of alloy were put up for time tests, some of which yet remain after twelve years, and frequent tests have been made. Shrinkage and expansion remain unaffected. The amount of mercury re- quired diminishes, the amalgamation be- comes easier, the setting becomes slower, and the strength of the amalgam is grad- Figure 37 shows the manner in which cooling curves are employed in the con- struction of an equilibrium diagram for a eutectiferous series. ually reduced. An alloy that makes a crisp amalgam which sets quickly, such as should always be used in practice will, if kept two or three years at ordinary room temperatures, come to make rather a sloppy, slow-setting mass. If the alloy is exposed to the heat of the sun or other- wise to unusually high temperatures, these changes will be rapid in proportion." CRUSHING STRENGTH OF OVERAGED ALLOY To determine the loss of strength of amalgam made from overaged alloy a series of dynamometer tests has been made with alloy two years old. Alloy and mercury were used in equal parts, heavy mallet force was used for condens- ing, and some excess mercury was ex- pressed during condensing. The average strength shown over a period of two and one-half months was 348 pounds, while tests made under the same conditions with alloy less than one year old showed a crushing strength averaging about 500 pounds. [35] STANDARDIZING THE AMALGAM FILLING We conclude that dental amalgam alloys should not be annealed beyond the zero point, except for cases where extremely slow setting alloys may be desirable, and where the strength of the amalgam is not an essential factor. As even low temper- atures bring about this change if continued over a long period, it is not advisable to use alloys which have been manufactured for a considerable length of time, or alloys of which the date of manufacture is unknown. Bibliography Metallography — Desch. Alloys and their Industrial Applications — Law. The Heat Treatment and Metallography of Iron and Steel — Howe. Metallic Alloys — Gulliver. Physical Metallurgy — Rosenhain. Practical Alloying — Buchanan. Operative Dentistry — Black. Dental Cosmos. Section III. Amalgamation HAVING considered correct cavity preparation and the requisite quali- ties of dental amalgam alloys, we come to the third essential of standardized amal- gam technic, correct amalgamation, of equal importance with these and the succeeding steps of the operation. Amal- gamation may be described as a process of melting and selective freezing. SELECTIVE FREEZING In order to make the process of selective freezing somewhat clearer, there may be constructed a hypothetical binary solid solution diagram, as shown in Figure 38, considering the tin amalgam as one element and the silver amalgam as the other. Let the tin amalgam contain 30 per cent mercury; likewise, the silver amalgam. Suppose the tin amalgam freezes at 100° C. and the silver amalgam at 400° C. Let A- B be the amalgam under consideration; at K, 300° C., a drop or so of silver-rich solid solution, having the composition shown at 0, freezes out; the remainder being liquid. This selective freezing con- tinues until the last drop freezes at L, 175° C., having the composition shown at N or M. Thus the resulting alloy froze in the area KOLM; it will show core structure and consist of the summation of alloys ranging in composition from O to M. The primary freezing silver-rich network, or core structure, possesses a composition in the neighborhood of 0; the crystalline grains are relatively fine; the whole is a fairly strong structure. This represents the amalgam when first placed in the mouth. Now suppose the amalgam to be at blood heat and every meal up to the temperature of hot drinks. The amalgam becomes homogenized; the whole returns to the composition B; the grains become larger, weaker, and coarsely crystalline; the proc- ess is accompained by volume change. This change is the more readily accom- plished the larger the proportion of low melting metal or eutectic. AMALGAM MANIPULATION Dental amalgams are partial solutions of a metal or alloy in mercury; the state and condition of the solution have a decided effect upon the final result of an operation [36] AMALGAMATION O F ALLOY AND MERCURY for which the amalgam is used, the method of manipulation affects the result to an equal degree. There is a wide variation in the abihty of dentists to manipulate amalgam and an unwilHngness on the part of some to spend Figure 38 — Hypothetical silver-tin-mer- cury Diagram. the time necessary for the manipulation of an amalgam made from a balanced alloy. Many dentists insist upon using alloys which produce an amalgam which is plastic and easily manipulated, although it is well known that such amalgams do not produce permanent results. Neither should an alloy be used if its amalgam sets so quickly that it is beyond the ability of the skillful operator to manipulate it. Such alloys require high percentages of mercury to make their amalgam sufficiently plastic to permit good manipulation, and it may be stated, as a principle of amalgamation, that the strength of amalgam varies inversely with the mercury content. The best alloys, of necessity, make a rather quick-setting amalgam, but it is possible to regulate their setting qualities so that any operator should be able to manipulate them successfully. MERCURY Mercury seems to affect the physical properties of most metals injuriously; for instance, if mercury is alloyed with nickel, under the influence of heat and pressure, the metal develops a coarse granular structure and will not bend, as formerly, without breaking. Fortunately silver and copper require larger percentages of mercury than those used in ordinary practice, before their valuable properties are decreased beyond the permissible limit. The purity of the mercury used is a factor in the success of an amalgam opera- tion, as the mercury of commerce frequently contains, in addition to the oxides and sulphides noted as scum upon the surface, copper, lead, zinc, or tin, which when added to the alloy may so change its pro- portions that the permanent usefulness of any operation for which it is used will be destroyed. At ordinary temperatures mercury coats a particle of alloy and forms a protecting or uniting envelope of amalgam, while very little mercury diffuses to the center and none will be found at the center of a fairly large specimen. In this process, termed partial amalgamation, there is a gradient in the mercury percentage from the mercury-rich exterior to the center con- taining, perhaps, none. Figure 39 shows this gradation in the composition of an alloy particle partially dissolved in mercury. [37] STANDARDIZING THE AMALGAM FILLING PROPORTIONS OF MERCURY AND ALLOY The correct ratio of alloy to mercury is an essential factor in the final result, as an excess of mercury will cause a shrinlcing alloy to shrink more, an expanding alloy to expand excessively, and a very closely balanced alloy to shrink first and then expand. Obviously this is because there Figure 39 — Diagram showing mercury gradient in a partially dissolved alloy granule. is sufficient mercury present to produce the maximum action possible from the metals, while if the mercury is limited, it can only produce action on the amount of alloy dissolved and must then cease. To avoid this sloppy excess of mercury, which not only produces excessive movement, but weakens the amalgam, both alloy and mercury should be weighed with a reason- ably accurate balance. Weighing will prove a decided economy as one soon acquires the ability to judge the approxi- mate amount required for cavities of various sizes, while it is impossible to guess the amount when pouring the materials from a container. We should plan to have plenty of amalgam for each filling, without repeating the mix, but it is useless extravagance, especially in the case of large fillings, to amalgamate two or three times the required amount. Sufficient mercury should be used to produce an amalgam of such consistency that fluid mercury will appear on the sur- face of the mass, while it is being rapidly rolled in the palm. The manufacturer should determine the ratio of mercury which will produce this consistency for each lot of alloy, as the dentist can only estimate unless he uses the micro-microm- eter and dynamometer, and spends con- siderable time. It is necessary to determine the ratio for each lot of alloy, as it is im- practicable to make all batches of alloy so that the proportion of mercury required will be the same. For this reason, we should pay no attention to the directions for the ratio of mercury if the same direc- tions are used with every batch of alloy. There should always be a slight excess of mercury, to make the best amalgam, but this excess should be expelled as manip- ulation progresses. THE MORTAR AND PESTLE Many methods of amalgamating alloy and mercury have been advocated, and all, perhaps, have some advantages for certain varieties of alloy. The accurately balanced dental amalgam alloys have proved most successful when triturated in the wedg- wood mortar. One of these will be found in nearly every dental office, but the pestle which accompanies it is usually worse than useless because of its shape and size. The pestle should be so shaped that it will fit into the contour of the mortar and large enough to cover most of the floor, so that as much as possible of the alloy will be worked continuously. The handle of the pestle should be generous in size to permit 38 AMALGAMATION OF ALLOY AND MERCURY a firm grasp. A pestle wliich is correct in form is shown in Figure 40. The roughness and porosity of the new wedgwoocl will prove to be a source of considerable annoj^ance at first, as the amalgam will adhere to the mortar and is difficult to remove. The deeper pores will become filled with the amalgam, in time, and the trouble will then cease. It will hasten matters to grind the inner surface Figure 40 — Wedgwood mortar, with large pestle fitting into the contour of the mortar, correct in form for triturating alloy and mercury. of the mortar with powdered emery, or other suitable abrasives, until it is smooth. PRECEDING AMALGAMATION Before the amalgamation of the alloy with the mercury is begun, everything about the cavity should be in readiness for condensation and the completion of the operation. The instruments for condensing should be at hand and should be tested in the cavity, to make sure that they have the proper form to reach the angles of the cavity. There should be no delay after the alloy and mercury are amalgamated before condensing is begun. AMALGAMATION To amalgamate the alloy, begin with a circular motion of the pestle, using very light pressure so that the mercury will not be forced away from the alloy. As soon as the alloy has taken up the free mercury, shghtly heavier pressure should be used on the pestle, and this should be continued until all of the granules of the alloy have been coated and free mercury is not apparent in the mortar. When this point is reached, the amalgam should be removed to the palm where it should be rolled and worked rapidly. This rapid rolhng seems to bring out the excess mercury better than other methods and also insures a better solution by rapidly changing the position of all of the alloy granules. As the amount of mercury used is in- sufficient to form a chemical combination with the metals of the alloy, the particles of alloy are onlj' partially dissolved and a uniting envelope of amalgam is formed, lea\'ing an undissolved integral granule which assists in retaining the original strength of the alloy. A series of dynamometer tests made to determine the comparative effect of partial and thorough amalgamation upon the strength of amalgam resulted as follows: ALLOY No. 178 Alloy eight parts — Mercury ten parts. Ground with mortar and pestle ^4 minute. In palm 3I4 minutes. Total 4 minutes. Granules well dissolved in mercury. All excess mercury removed. Heavy mallet force for condensation. Average crushing strength test over a period of 2^2 months, 375 pounds. ALLOY No. 178 Alloy and Mercury equal parts. Ground with mortar and pestle -2 minute. In palm 52 minute. Total 1 minute. Granules weU coated but not dissolved in mercury. All excess mercury removed. Heavy mallet force for condensation. Average crushing strength test over period of 2 months, 464 potmds. [39] STANDARDIZING THE AMALGAM FILLING THE AMALGAM DYNAMOMETER The dynamometer used for this and other tests of the compressive strength of amal- gam, described in this article, is shown at Figure 41. Cubes of amalgam .085 inch are made in the block shown in the lower that amalgam is but slightly ductile and that the full force of occlusion is often exerted upon frail margins, which are tested to their utmost to resist fracture. Not only this, but as the strength of amalgam is increased, the tendency to flow Figure 41 — Amalgam Dynamometer used for measuring the compressive strength of amalgam. part of the illustration; these are placed in the steel jaws of the instrument and a compressive force is applied, by means of the screw head at the right. As the pres- sure is increased, the dial registers the pressure in pounds; when the amalgam is crushed, one hand of the dial remains stationary, registering the exact amount of force which has been required to crush the amalgam. A good amalgam resists a pressure of from 350 to 600 pounds; many amalgams are fractured before the pressure reaches 200 pounds. It must be borne in mind that these tests are made with very small fillings, .085 inch, with fillings of ordinary size the strength would be increased proportion- ately. It is evident that this large factor of safety is necessary when one considers is diminished. It is as important that amalgam should resist flow as that it should resist fracture. The leaking margins that we so frequently observe are more often from flow than from shrinkage. Flow of amalgam is its tendency to move under pressure, either sustained or inter- mittent; it is only a change of form and not, in any way, an increase in the bulk of the filling, hence, if the filling moves in the cavity in the least degree, a leak must be created at some point. Tests of amalgam for flow are also made with the dynamometer. Cubes of amalgam of the same size as those used for measuring strength, .085 inch, are placed in the jaws of the dynamometer and pressure is applied until the dial registers one hundred pounds. The small micrometer dial, at the right of the large dial, is set at zero. [40] AMALGAMATION O F ALLOY AND MERCURY As the amalgam is compressed the microm- eter dial registers the amount of com- pression. EXPRESSING EXCESS MERCURY The excess mercury, necessary for amal- gamation, should be removed from the amalgam by expressing it through muslin with flat nosed pliers. In experiments with annealed alloys we have found that a lesser amount of pressure applied through an interval of time will remove more mercury than a greater amount of pressure applied and immediately removed. It is difficult to state the exact con- sistency at which amalgam should be placed in the cavity. The most desirable consist- ency is that obtained by expressing all of the mercury in excess of the amount required for perfect adaptation, as the greatest strength in the amalgam is secured by bringing the undissolved particles of alloy as closely together as possible. Unless the operator realizes clearly how very difficult it is to adapt amalgam thoroughly, he should experiment on cavities in ex- tracted teeth, under conditions as nearly normal as possible, splitting the teeth and examining the adaptation with a magni- fying glass after the filling has thoroughly set. Possibly a magnifying glass will not be necessary. Because of this difficulty of adaptation and because amalgam with all the excess mercury removed sets very rapidly, it is very rarely advisable to begin condensing with amalgam as dry as it is possible to make it. MIXING SOLUTIONS Amalgam should be kept free from water, saliva, and chemical solutions, during its manipulation, as any moisture which comes in contact with it tends to decrease its strength about one-third. There are on the market a variety of solutions for "washing alloys, to make them white and aid amalgamation." These solutions may possibly remove tarnish from some alloys, but this does not make the filling any whiter. Their principal harm lies in moistening the granules and preventing amalgamation. The effect of a two per cent HCl solution when used for this purpose is shown by the following result of tests made with the dynamometer: ALLOY No. 10 Alloy five parts — Mercury six parts. 2% HCl mixing solution used. Amalgam packed with heavy hand pressure. Average crushing strength, 283 pounds. ALLOY No. 10 Alloy five parts — Mercury six parts. No mixing solution used. Amalgam packed with heavy hand pressure. Average crushing strength, 389 pounds. Other tests show that alcohol, water, or saliva, coming in contact with the alloy before amalgamating, have a similar effect. Section IV. Instrumentation and Condensation HAVING made all preparation possible for the completion of the operation before amalgamating the alloy and mer- cury, we should begin to place the amalgam in the cavity and condense it immediately after the excess mercury is expressed from the amalgam. To secure the greatest strength in the amalgam, we must express a still further amount of excess mercury while condensing [41] STANDARDIZING THE AMALGAM FILLING and bring the undissolved portions of the alloy granules as closely together as pos- sible. This is best accomplished by the use of properly shaped condensing instru- ments with the hand mallet. The hand mallet not only supplies the stress necessary Figure 42 — Photomicrograph of dental amalgam, showing accidental voids result- ing from insufficient condensation. to condense the mass but, in addition, agitates and vibrates the alloy granules, reducing the void volume and bringing to the surface further excess of mercury which may then be removed. Dr. Black found that the average amalgam filling contained about fourteen per cent of air space. It is unnecessary to say that these air spaces or voids are not desirable. ACCIDENTAL AND INHERENT VOIDS Voids are of two kinds, accidental and inherent. Accidental voids, which are much the larger, result from insufficient condensation. They may and should be minimized by proper condensing, with heavy pressure. Inherent voids are due to the diffusion of excess mercury from the mercury-rich portion of the alloy into the alloy-rich portion. The black areas seen in Figure 42 are accidental voids in a mercury-rich amalgam, poorly condensed. Figure 43 shows the same amalgam thor- oughly condensed and containing a smaller proportion of mercury. The alloy-rich portion of the amalgam appears as large white grains, the small dark areas are almost entirely inherent voids. Amalgam of this structure possesses the highest crushing strength and the minimum volume change. It is the structure which should be attained in amalgam restorations, as determined by physical tests, metallo- graphic investigation, and actual clinical observation. THE RELATION OF VOIDS TO VOLUME CHANGES We find that the phenomena accompany- ing voids throw some light on the volume changes of amalgam. An observed fact ^n^^^ ^^H Figure 43 — Photomicrograph of dental amalgam with smaller inherent voids, resulting from the diffusion of mercury into the alloy granules. is that with excess mercury a tin-rich alloy shrinks more and a silver-rich alloy expands more than normally is the case. As pre- viously noted tin forms a shrinking solid [42] PROPER CONDENSATION O F AMALGAM solution with mercury, and silver an expand- ing one. When an excess of mercury is used, it finally becomes effective in form- ing more tin-rich amalgam, accompanied by increased shrinkage; contrarily, more silver-rich amalgam is accompanied by increased expansion. A secondary phenomenon causing ex- pansion in the silver-rich amalgam arises from the fact that the particles grow in diameter as the envelope of amalgam in- creases in thickness and the interstitial adhering mercury diffuses toward the center, leaving inherent voids. On the other hand, tin simply melts in mercury without formation of particles of larger diameter and voids. The explanation of this behavior involves a discussion of molecular physics and physical chemistry which will be considered in a later publi- cation. BEGINNING CONDENSING In placing the amalgam, it is often advisable to begin with a small piece that is not as dry as the remainder of the mix. It can be condensed and adapted more per- fectly than the very dry amalgam and the excess mercury can be removed from it, as it makes its appearance, during the condensing. Instruments which will carry the amalgam into the angles and over the margins of the cavity, as shown in Figure 44, should be used to begin condensing. Force should be applied first in the angles of the cavity, then the condenser should be stepped so as to reach the margins last. HEAVIER PRESSURE After the base of the cavity is covered, larger pieces of amalgam and larger con- densing instruments may be used, as the size of the cavity will permit, and the force may be greatly increased as the size of the condensers and the density of the amalgam increase. This stage of the operation is shown in Figure 45. ADVANTAGES OF HEAVY CONDENSING Amalgam is treacherous in that it readily gives the appearance, on the surface, of thorough condensation, and only careful examination will reveal the defects caused by a failure to thoroughly seat and con- dense it. One of the advantages of con- densing it to the density described is that this may compress the dentin walls, that Figure 44 — Beginning condensation with a small instrument, condensing into the angles and margins of the cavity. is it may spring them apart so that their elasticity will produce a continued force upon the amalgam, an effect similar to the advantage gained by the use of gold foil. This continued force exerted by the com- pressed walls will, to an extent, overcome the disadvantage of any minute volume changes occurring in the bulk of the resto- ration and will produce a contact of the filling with the cavity walls which is proof against leakage. [43] STANDARDIZING THE AMALGAM FILLING CONDENSING OVER ALL MARGINS SIMULTANEOUSLY The excess of mercury which will come to the surface as a result of the heavy force used in condensing should be removed with suitable instruments and drier amal- gam should be added. Finally, to fill the Figure 45 — The use of a condenser as large as the cavity will permit. cavity, a large excess of amalgam should be added and a condensing instrument, sufficiently large to cover all of the margins simultaneously, should be used, with the hand mallet, to drive the amalgam tight on all margins. This simultaneous pres- sure over all of the margins is necessary as on account of the semi-plastic nature of amalgam it would be impossible to make a wide area of margins tight by passing from one point to another. Naturally pressure down at one point will produce pressure up at another point and a leak will result. The large excess of amalgam used has the advantage of absorbing any excess of mercury from the cavity margins and gives strength at this point, where strength is most essential ; it also protects the margins from the blows of the condenser and makes possible closer adaptation to the cavity walls and margins. Figure 46 shows the use of a large con- densing instrument which produces pres- sure over all the margins simultaneously. EFFECT OF HEAVY CONDENSING To determine the comparative strength of amalgam from which the excess mercury has been removed and which has been thoroughly condensed by the method out- lined here, the following tests were made: Fifty fillings, .085 inch cube, were made in steel dies, all from the same alloy. Twenty- five had the excess mercury removed by placing the amalgam in a small piece of muslin and expressing it with flat-nosed pliers and were thoroughly condensed by mallet force. Twenty-five were made by expressing the mercury between the thumb and fingers and were condensed as thor- oughly as possible by hand pressure. At varying intervals the same number of fillings from each lot were crushed in the dynamometer and a record was made of the crushing strength. The average strength of those which had been thoroughly con- densed by mallet force, after removing the excess mercury through muslin with pliers, was 514 pounds; of those with the usual amount of mercury remaining and con- densed by hand pressure, 385 pounds, that is, 129 pounds or dS}4 per cent in favor of mallet condensing and a minimum of mercury. CORROBORATIVE TESTS A series of tests made recently by Dr. H. A. Merchant confirms the result of previous tests of methods of manipulation and condensation and also shows the effect [44] EFFECT O F UNDUE EXCESS OF MERCURY of heat upon amalgams manipulated and condensed in various ways. The object of the heat treatment is to produce an amalgam of the same structure that occurs in fillings subjected to changes of temperature from hot food and drinks. It may be objected that 150° F. is the maximum temperature experienced in the mouth; however, the same effect occurs at lower temperature but requires a longer period of time. The maximum tempera- ture was chosen merely to obviate unneces- sary delay. Dr. Merchant's findings are tabulated on page 46. Some of the more important are noted following: TESTS OF A BALANCED NON-ZINC ALLOY Test No. 1 was made with a non-zinc alloy of 80 mesh filings. The alloy and mercury received only light initial trit- uration. With mallet force for condens- ing, the small granules were driven to- gether so that the excess mercury was largely driven off. As little of this mercury was absorbed by the alloy, the resulting amalgam was silver-rich. The loss of strength resulting from heat treatment was small. Test No. 2. The only variation from test No. 1 was the use of pressure for grinding the alloy with mercury so that the granules were partly crushed. This cold work partially unaged the alloy, so that it retained more mercury than in test No. 1. The effect of this higher percent- age of mercury is graphically shown in the resulting loss of one-half the strength of the amalgam under heat treatment. Test No. 3. In this test the same alloy was used as in test No. 1 and No. 2. The object of this test was to learn the effect of large percentages of mercury such as have been advocated, recently, by a num- ber of prominent dentists for the purpose of making air-tight fillings in steel tubes. Amalgam of this strength would flow and leave a crevice about the margins of a tooth which would soon defeat the object of the operation. The fallacy of a mercury- rich amalgam is evident when its weakness is considered. Tests Nos. 4 and 5 show the volume change of a non-zinc alloy, due to heat treatment. It will be noted that heat produced practically no change in the volume of amalgam when the parts of mercury were only slightly in excess of the parts of alloy. However, in test No. 5 Figure 46 — Condensing a large excess of amalgam over all the margins of the cavity, by the use of a large condenser which win cover all the margins simultane- ously. where the percentage of mercury is too high, the sloppy amalgam resulting suffers great volume change. This effect should be borne in mind by those inclined to use amalgam in a sloppy condition. N STANDARDIZING THE AMALGAM FILLING ^ ^ b£ i: 1. /. jc i 7. ■f. 3 ;-i !-■ 05 c b£ fcC O -3 00 ^ o a rf DC 00 a: Si -1-3 a 'V^ T-H S ^ B 00 >-. o ^ o o l> 1—1 >— 1 <© '^ o <-H eS lO 1—1 P3 00 o < :« r/3 M lO J2 Si H O 00 a -U3 c3 o -tJ O cc CC cc ■<* -C5 3: O ^ i> -^ -i^ s >-. __o o ^ CO "S 1—1 -. o ;m j5 3 -*J c K >-. o ^ H zn aj >. "^ C ^ ^ \ \ ^r rf, o ^ 3 3 O ^ -tJ :/- a i-H c^ Tl -13 a -t^ — O _3 < if •~ -5 •1 ^ ^ S 3 -1-= 3 JO poq^gjv: \J ui ill =3 C c3 t- . 03 P-. o o fe -^ i: — 1 IC ~ ^1 CO t^ '— ' "—I ^ IM lO ^ --^2 ^"^ -v CO 4^ '"' '-'^IC CO .— 1 00 »o o ^ t^ lo =os CO ■ oo 1— ( ^ IC -^2 ^ 1 CO 4- '"' ^ IC ^2 CO 4- ^ ^ LC X 13 s a> o ^ ^ T3 X c3 3 a §o V; o o -t3 -t^ c5 c5 o QQ iz; o GO »o CO lO 1—1 rt '^ hr o bt ^ ^^ ;^ T Ci > j_ < O E^ X i O lO o (M X jQ -O IC o (M iC O 1—1 (N X X sn Xi lO O (M LO 1—1 1— ( T— 1 X X ^ J2 in O h-^ (M o X _Q ■ ' -O lO t^ o 00 lO CO X o fcC ^ ox;.:: br tx o :3 o o > z S-c -*3 -tJ "^ " w-hjf^^-^ _.. k J ',»"• _/9^y^^ I'i Is -^ 'H ^ --^r-->^^^^i»_ M mf' ' ^^^m ^ ■'^^«»i<^.' - :. ^^^2,:i Imp' -^mM?;-^- 1 Figure 51 — Mr. Sellner weighing the metals for Crandall's Scientifically Tested Non-Zinc Alloy. importance, are much more intimately concerned with proximate composition, revealed by the metallographic microscope, than with ultimate chemical composition. The application of metallography to dental products possesses novelty and offers a considerable advantage. While it is necessary to know the percentage compo- after cutting, or merely heated up blindly? What structural constituents are formed upon its amalgamation? Does its amalgam shrink or expand, corrode or waste away, and how much? Such is the nature of the numerous questions which must be answered. The living organism demands that modern science study, with extreme care, [61] MAKING STANDARDIZED DENTAL AMALGAM ALLOY the metals and alloys which may affect its health and general welfare. The anatomy of a metal is its physical and chemical composition; its biology, the in- fluence exerted upon its constitution by various treatments, thermal and mechani- Figure 52 — Dendritic or "tree" structure in a sample of copper containing 0.3 per cent phosphorus. Magnification 150X. Reichert metallographic apparatus. cal; its pathology, the action of impurities and defective treatments upon its normal constitution. Metallographic dissection reveals the physical association of proxi- mate constituents and features relating to desirable or objectionable attributes. It is pleasing to know that the dental profession is becoming very aggressive in metallographic research as witnessed by the papers appearing under the auspices of the National Dental Research Association. The preliminary work necessary to the production of a standardized alloy has been done by men whose devotion to the dental profession has led them to spend time and effort in making the investiga- tions which have been the foundation for our work. Our task has been to adapt their methods to the production of allo}- in larger quantities, without deviating from the scientific methods and accuracy which were responsible for the results which they obtained. An outline of the method of manufac- turing a balanced alloy follows: Selection of Materials As gold has not proved to add desirable qualities to dental amalgam alloys and zinc has proved to be decidedly deleterious, the onh" metals used for Crandall's Scien- tifically Tested Non-Zinc Alloy are silver, Figure 53 — Cast copper with 0.1 per cent oxygen. Even this very slight impurity unfavorably affects the physical properties of the copper to such an extent that it should not be used for dental alloys. tin, and copper. Our problem of the selec- tion of materials resolves itself, therefore, into the effort to obtain these three metals in the purest possible state. The utmost precaution is taken to purchase only the purest metals obtainable and these undergo 52 MAKING STANDARDIZED DENTAL AMALGAM ALLOY further purification and rigid physical and chemical tests in our laboratories. Photo- micrographs of the structure of these metals reveal the character and distribution of impurities and afford an absolute check on claims made for purity. It is a comparatively easy matter to obtain silver and tin of the necessary purity for a balanced alloy. Silver is fur- nished to us in the form of ingots from the United States Assay Office. Our tests for fineness must show 999.8. The allowable impurity for tin and copper is 0.01 per cent. Copper of this high standard of purity is obtained with considerably more diffi- culty than is the case with silver and tin. Regularity of crystalline structure has been pointed out as the ultimate test of the purity of metals. The fallacy of this con- Figure 54 — Cast copper with 0.2 per cent oxygen. tention is shown by the following state- ments summarized from Sauveur's Metal- lography : Microstructure: When a properly pre- pared sample of a pure metal is examined under the microscope, the revealed struc- ture generally presents the appearance of a polygonal network, an indication that the metal is composed of irregular, poly- hedral grains, each mesh or polygon of the network representing a section through a polyhedron. Idiomorphic Crystals: When the fiuidity of a substance and other conditions are Figure 55 — Cast copper with a small per- centage of impurity, causing core structure. such that the formation and growth of the crystals are given free play, perfect, and sometimes very large, crystals are pro- duced. These perfect crystals, with fault- less geometrical outlines, perfect cubes, for instance, are called idiomorphic crystals. Allotrimorphic Crystals: When the free development of the crystals is hindered by less favorable crystallizing conditions such, for instance, as collision or contact with other crystals likewise in the process of formation, the regular external form is not preserved and the resulting imperfect crys- tals are called allotrimorphic crystals, also, but more seldom, anhedrons or faceless [53] MAKING A STANDARDIZED DENTAL AMALGAM ALLOY crystals. Such crystals are said to have taken their shape from their surroundings. It should be noted, however, that allotri- morphic crystals, like idiomorphic crystals are composed of crystalline matter. An allotrimorphic crystal may be regarded as resulting from the mutilation of an idio- morphic crystal, the mutilation affecting the external shape only and not the crys- talhne character of the substance. That is, a pure metal usually exhibits irregular grain structure. The tree-hke or dendritic structure sometimes observed in photomicrographs of copper has also been erroneously taken for an evidence of purity of the metal. It may be caused by 0.3 per cent of phos- phorus as in Figure 52. Figure 56 — Electrolytic copper. Ordinary copper may contain impurities of lead, antimony, tin, iron, arsenic, cuprous oxide and, in some instances, zinc, bismuth, sulphur, selenium, tellurium, or other elements pecuhar to copper from a certain district, or to certain methods of refining. In general, metal dealers are limiting im- purities to cuprous oxide, arsenic, anti- mony, and bismuth. Phosphorus used for reducing cuprous oxide (2P+5Cu2O = P205 + 10Cu) slags off or sublimes, for the most part. It has been argued that cuprous Figure 57 — Another specimen of impure copper containing dendrites or "trees." oxide, within the commercial limits of 0.4 per cent to 1.2 per cent may oxidize impuri- ties and permit formation of copper arsen- ate, bismuthate, and so on, but we have found that this brittle constituent is unde- sirable for obvious reasons in a product which must be balanced. Again 0.1 per cent oxygen, meaning 0.9 per cent cuprous oxide, forms 25.7 per cent of eutectic. Figure 53 shows such a copper which is unfit for use as its conti- nuity and desirable physical properties are too greatly affected. Small percentages of oxygen are hardly accurately determined by ordinary analytical methods, but micro- metric analysis of the eutectic appearing in a photomicrograph presents most accurate 54 MAKING STANDARDIZED DENTAL AMALGAM ALLOY results. This is accomplished by measure- ment of the eutectic areas with a planim- eter, or by the count of squares method. Copper is unique in its capacity for absorbing oxygen and furnace gases, hence the use of the electric furnace for melting Figure 58 — Conductivity copper, used in the manufacture of Crandall's Scientifi- cally Tested Non-Zinc Alloy. Note its beautiful, clear structure, as compared with coppers containing slight impurities. Magnification SOX. it is imperative, as all effort to obtain pure metals avails very little if they are after- ward contaminated by melting in a gas furnace. Figure 54 shows copper with 0.2 per cent of oxygen; Figure 55 copper with a slight amount of impurity showing core structure; Figure 56 electrolytic copper; Figure 57 another impure copper with tree structure or dendrites. The copper purchased and used for Crandall's Scientifically Tested Non-Zinc Alloy is of that highest quality known as conductivity copper; its beautiful clear structure is shown in Figure 58 and Figure 59. Melting To those unfamiliar with the manufac- ture of dental amalgam alloys, it might now appear that, having assembled the pure metals, it would be a simple matter to melt them together, and that the result- ing ingot would be pure, containing silver, tin, and copper, in the same proportions which were originally placed in the crucible. Various obstacles, however, prevent this. If the metals were simply melted together, under ordinary conditions, the mass would absorb oxygen with a resulting partial oxidation of the copper and tin which would entirely nullify the exact propor- tions originally taken. Reducing agents, such as carbon, prevent oxidation, but the alloy takes up some car- Figure 59 — Another specimen of conduc- tivity copper. The black spots are polish- ing and etching pits, the large grains are due to anneaUng. Magnification SOX. bon and the benefit of this addition may certainly be questioned. As the quantity taken up is variable, and generally un- known, we prefer to eliminate it altogether. The use of plumbago or clay crucibles is N MAKING STANDARDIZED DENTAL AMALGAM ALLOY also subject to criticism; the former may impart graphitic carbon and the latter iron oxide. As an absolute safeguard from any possi- bility of oxidation and to eliminate the Figure 60 shows the electric furnace used for melting, together with apparatus for generating and purifying hydrogen. A pure silica rod is used for stirring the alloy during its melting. Figure 60 — Melting silver, copper, and tin in a closed electric furnace, under hydrogen gas. necessity for conjecture as to the effect of ever-changing quantities of carbon, the metals used for Crandall's Scientifically Tested Non-Zinc Alloy are melted in a pure silica crucible, in an enclosed electric furnace, under pure hydrogen gas. The hydrogen gas is generated simultaneously with the melting of the alloy, passing through a purifying train, and flowing over the surface of the metals throughout the melting. No heat is applied to the crucible until the air has been replaced by hydrogen. Dental amalgam alloys are frequently made by placing silver and copper in the furnace first, adding the tin after these are melted. It requires a high degree of heat to melt the silver and copper alone and various alterations take place at this tem- perature which are not conducive to the formation of a homogeneous mass upon subsequent addition of the tin. In order to prevent oxidation, volatilization, and other complications, we alloy at as low an effective temperature as possible. The tin, [56] MAKING A STANDARDIZED DENTAL AMALGAM ALLOY melting at 232° C, is introduced into the electric furnace first, and copper is added over a rising temperature gradient deter- mined by pyrometric methods. There- upon is formed the copper-tin soHd solution which is converted into the correct ternary alloy by the addition of the silver. At no time is the melting point of copper or silver approached within several hundred degrees. Throughout the melting of Crandall's Scientifically Tested Non-Zinc Alloy, met- allographic control is maintained with respect to fusion period and maximum temperature; temperature gradient, as observed by means of the thermo-couple, with Siemens-Halske galvanometer and adjusted by a critical point rheostat; the rate of hydrogen flow, as affecting oxidation and reduction reactions; and homogeneity through mechanical agitation. Casting When the galvanometer records the casting temperature, Crandall's Scientifi- cally Tested Non-Zinc Alloy is run into molds in an atmosphere of hydrogen and is cooled in a manner found to promote desirable physical qualities. Filing As the undue heat generated by friction in some cutting devices, produces unde- sirable physical changes in alloy, anneahng it to an undetermined extent, Crandall's Scientifically Tested Non-Zinc Alloy is divided by hand files used in specially con- structed machines. These are run so slowly that the generation of heat sufficient to cause physical changes in the alloy is avoided. The filings produced by this method are rough and jagged in form, and offer a bright, clean surface to the attack of mer- cury. The size of the filings has been carefully determined to produce the maxi- mum of strength in the undissolved integral unit, while permitting careful adaptation at the margins. Annealing To anneal a small amount of alloy, such an amount as a test tube would contain for instance, is a simple matter. It can be brought to the desired temperature im- mediately, maintained at that point for the desired period, and cooled at once. To obtain this definite result with the comparatively large quantities of alloy which must be handled in a manufacturing laboratory involves problems which have been overcome by our method of anneahng Crandall's Scientifically Tested Non-Zinc Alloy. The continued and indefinite an- nealing which would be produced by slowly bringing the alloy to the desired tempera- ture and by slow coohng is avoided by a method which brings the whole amount of alloy immediately to the desired tempera- ture. It is maintained at this point, with- out fluctuation to a higher or lower point, for a definite period of time, during which the alloy is kept constantly in motion. The return to room temperature is quickly made. Formula The balancing principle is generally con- ceded to be the correct one for combining the dental amalgam alloj^ metals in such proportions that shrinkage is eliminated and a minimum and controlled amount of expansion is obtained. This, of course, precludes the use of a formula, or we might say necessitates the determination of a formula for every lot of metals obtained. Testing After remelting, refining, and testing a lot of metals, a sample melt of fifty ounces [57] MAKING STANDARDIZED DENTAL AMALGAM ALLOY is made up into alloy and sent to Dr. Crandall for his test. This alloy is amal- gamated by him and subjected to micro- micrometer tests. If it does not prove to be desirably balanced, but shows shrinkage or undue expansion, he corrects the per- centage error which usuallj'^ does not exceed 0.1 per cent. When the alloy meets with his approval Dr. Crandall furnishes us with a certificate of his tests, showing the date of testing, setting or hardening period, expansion in twenty-five thousandths of an inch, and the parts of mercury which should be used to obtain this expansion. The whole lot of silver is then made up in exactly the same proportions as the sample melt which has been tested and the information contained in the certificate given us by Dr. Crandall is copied on a certificate which is attached to everj^ bottle of Crandall's Scientifically Tested Non- Zinc Alloy which is put up from the lot tested. Research Laboratory Tests Thermal analysis is an invaluable aid in research and enables us to verify or refute the claims made for alloys received by our laboratory'. It has been found that asser- tions as to chemical composition, definite formula, annealing conditions, and other claims, are often entirely unsubstantiated. For instance, an alloy bearing the definite formula, "Ag-jSnCu," and "aged 20 min- utes over water at 100° C," shrunk upon amalgamation, and showed evidence of incorrect annealing. This alloy did not anah'ze for AgoSnCu, and a photomicro- graph showed the eutectic structure of Figure 61, which was further verified b}^ the long eutectic halt in the cooling curve obtained by thermal analysis. In order to indicate the status of research upon ternar}' compounds the statement of the eminent metallographist, Dr. Rosen- hain, is quoted: "Unfortunately the difficulty of making a complete metallographic study of a sys- Figure 61 — Eutectic structure of alloy represented as Ag-SnCu. tern of alloy's increases very rapidly with the number of component metals; for fifty determinations required for the elucidation of a binary system of alloj^s, 1250 would be required for a system of three metals, while no attempt at the complete system- atic study of a quaternary system (of four metals) has yet been made, but for corre- sponding completeness over 30,000 deter- minations would be needed. In the case of a ternary system (of three metals) it is still possible to employ a graphic repre- sentation; the concentration of a system of ternary alloys may be plotted in the form of an equilateral triangle, each corner representing one of the pure component metals; each side of the triangle then repre- sents one of the three limiting binary systems, while the position of any point within the triangle represents the com- [58] MAKING A STANDARDIZED DENTAL AMALGAM ALLOY position of an alloy of a ternary system, on the principle of trilinear co-ordinates. Upon this equilateral triangle as a base, the 'equilibrium diagram' can be erected as a three dimensional model, ordinates representing temperature being erected upon each point of the area of the triangle. A few such equilibrium models of ternary systems have been more or less completely determined, but the field is still largely unexplored. It is interesting to note how- ever, that no tri-metallic compound has yet been discovered." The location of Crandall's Scientifically Tested Non-Zinc Alloy upon the ternary diagram is shown in Figure 62. 3EGINNING OF PERITECTIC ABOUT HERE CRANDALL'S SCIENTIFICALLY TESTED NON-ZINC ALLOY 26.9% Sn in AG3SN 25% Sn end OF PERITECTIC AT 480 SOLUBILITY DECREASES TO SOME 20% Sn at low TEMPERATURES 28.2% Cu IN EUTECTIC SATURATION LIMIT Cu IN AG SOLID AT EUTECTIC TEMPERATURE 779° Figure 62 — Ternary diagram showing the location of Crandall's Scientifically Tested Non-Zinc Alloy. [59] Instruments, Materials and Appliances used in the Crandall Method of Amalgam Restoration IN the following pages instruments, materials, and appliances which have been developed by Dr. Crandall or have been designed to meet his requirements are shown. To these have been added amalgam condensing instruments designed by Dr. Prime and amalgam carving instruments designed by Dr. Frahm. An equipment may be selected from these pages which will fully meet the demands of a standardized amalgam technic and, in all cases, the Clev-Dent standard of quality has been maintained. Crandall Demonstrating Case THIS case has been devised as an aid in explaining to patients the desirabihty of amalgam restorations as com- pared to inferior work. It is a small leather case, velvet lined, with space for twelve steel rings which are used to hold teeth with various forms of cavity preparation, amalgam restorations, and other features of the work which it is desired to bring to the patient's attention. The teeth are not supplied with the case, but may be pre- pared by each dentist with a view to meeting the particular needs of his practice. The case, shown here, con- tains restorations which include nearly all of the forms usually encountered in practice, includ- ing several restorations of the entire crown, such as A. At B is shown the cavity preparation for an amalgam crown, at C a cavity preparation in the medio-occlusal surfaces of an upper molar. At D are five extracted teeth which have been lost because of the poor adaptation of gold crowns. 60 CrandalFs Scientifically Tested Non-Zinc Alloy Authoritative information regarding the effect of zinc and overaging on dental alloys has long been accessible, but dentists have failed to demand an alloy made to conform to the highest standards and have even been content with unbalanced alloys because of their plastic, easy-working qualities. The manufacturer has been content to deal in glittering generalities in describing his alloys, avoiding definite facts and figures, specifica- tions, and tests. 5 OZ. TROY SCIENTIFICAULY TESTED NON-ZINC ALLOY ^leV-DENL The Cleveland U.S.A. Contrary to this plan, investi- gation of all methods of alloy making has preceded the manu- facture of Crandall's Scientifically Tested Xon-Zinc Alloy and fullest advantage has been taken of all authoritative information obtain- able. Much of original research has confirmed or rejected various methods and has evolved new refinements of the process. In addition to chemical and metallographic tests of materials and micrometer tests of the finished product made in our own laboratories, every lot of Cran- dall's Scientifically Tested Non- Zinc Alloy is tested by Dr. Crandall. [61] Crandall's Scientifically Tested Non-Zinc Alloy CERTIFICATE OF TEST Spencer, Iowa..._<~r- *^..... ..19' This certifies that I have tested Lot No. /^../P./.. manufacturecl...ifr^7.'rv/^^/'^..of Crandall's Scientifically Tested Non-Zinc Alloy and find the following results: With 10 parts alloy ..v^...- parts mercury should be used. Expansion is..^.. / 25000 of^n inch. Setting ..M4^.^ CERTIFICATE OF TEST Spencer, \oyNa...^*^^h^.././. W..'^.. This certifies that I have tested Lot Wor-^/D /^/.. manufactured-.-7^..T'-.yr""/^-of Crandall's Scientifically Tested Non-Zinc Alloy and find the following results: With 10 parts alloy ___// parts mercury should be used. Expansion is.-?!^. / 25000 of an inch. Setting i/^v^^^r^trT?:::^:: ^.^^lj^^^^.. •f' B. ^Y S. QX^ F The Cleveland Dental Mfj*. Co. N Woodbury-Crandall Instruments for Cavity Preparation t t ^^ Design Patent Applied for 1 1111 1 IHlllli R 6 8 12 5 8 7 7 12 12 15 15 15 15 ? 2 4 6 I'/a 4 85 85 85 85 95 95 80 80 23 12 14 14 23 23 2 2 5 5 10 10 10 10 6 6 6 6 12 12 12 12 L R L R L R L R 2 3 4 5 6 7 8 9 10 11 12 13 14 15 5^=3 20 3 10 L 26 4>^4 ^ 20 3 10 R 27 20 10 28 20 10 29 30 IS 10 31 15 10 32 10 16 33 g=i 5=3 34 35 [66] Woodbury-Crandall Instruments for Cavity Preparation THE forms which make up this new set of instruments for cavity prepara- tion have been carefully chosen and adapted by Dr. Charles E. Woodbury and Dr. Walter G. Crandall from some of the best known and generally approved sets of cutting instruments. Their form has been modified some- what and a radical change has been made by shortening the neck, bringing the handle much nearer the cutting edge of the instrument and affording a very firm finger grasp with increased leverage and control. The diameter of the handles of the instruments varies, being carefully adjusted to balance the width of the cutting edge. The instruments are practically universal in their application and include all the necessary forms for the preparation of cavities on any surface of the teeth. For the most efficient use of these instruments, we suggest the duplication of those forms oftenest in use, so that an instrument need never be used after it has been sufficiently dulled to cause pain. An economical and time saving arrangement may be made with us for sharpening these and all other hand operating instruments for a fixed sum per year. Nos. 1 and 2 are hatchets for forming angles in the anterior teeth. Nos. 3, 4, and 5 are contra angle hoes, and 6 and 7 are right angle hoes, instruments of the widest application in cavity formation. Nos. 8, 9, 10, and 11 are right and left angle forming instruments designed especially for carrying out the sharp line angles in cavities in the anterior teeth. Nos. 12, 13, 14, and 15 are right and left, mesial and distal gingival margin trimmers. Nos. 16, 17, 18, 19, 20, 21, 26, and 27 are right and left spoon excavators. Nos. 22, 23, 24, and 25 are right and left enamel hatchets for breaking down enamel and shaping cavity walls in bicuspids and molars, one of each pair is marked with a ring to distinguish the direction of cut without examina- tion of the cutting edge. Nos. 28, 29, 30, and 31 are front and back cut enamel cutting chisels. One of each pair is marked with a ring so that those which cut on the back may be distinguished from those which cut on the face, with- out examination of the cutting edge. These enamel instruments have a special temper, differing from that of the other instruments of the set. On account of their special hardness, they not only are better suited for cutting enamel but will hold their edge longer. Nos. 32 and 33 are special instruments for cutting mesially and distally in molar cavities which are difficult of access. Nos. 34 and 35 are finishing knives designed for finding and removing overlaps along the gingival margins of fillings on the proximal surfaces. [67] Prime Amalgam Instruments Patent Applied for AYith the advances recently made in the development of amalgam technic, the necessity for instruments which may be used with the mallet to carry pressure or force directly into the angles of the cavity has become apparent. Dr. J. M. Prime has met this need by designing the set of amalgam condensing instruments shown here. These instruments are necessarily heavy in construction, to avoid any tendency to spring under pressure. The bayonet is sufficiently long to permit of access to the distal portion of posterior teeth, and the opposite end of the instrument has a cor- responding offset so that force applied to the end of the handle with the mallet will be in direct line with the condensing point. [68] K.'^f] Prime Vmalgam Instruments All of the condensing points are con- cave that they may grasp and force forward the amalgam, eliminating the clogging feature so inconvenient in serrated instruments. Instruments No. 11 and No. 12 have a concave outline as well as a concave con- densing surface. This adapts them for use on the buccal surface of the teeth, where the convexity of the surface necessitates the use of an instrument of this form to produce equal pressure over all of the mar- gins simultaneously. Instrument No. 13 is used for condens- ing amalgam into cavities occurring at the buccal groove, also providing equal dis- tribution of pressure into the angles of the cavity. The trimming knives Nos. 14 and 15 are used for removing small particles of amalgam overhanging at the gingival mar- gins, for carving the correct anatomical form at the gingival and restoring the inter- proximal space. These instruments are so delicate that they will detect a very slight overhang, which may afterward be removed with finishing files or strips. 69 25 30 15 40 55 S 15 30 20 40 S 8 8 10 12 12 12 12 12 12 2 3 4 5 6 15 40 50 60 SO 30 18 35 50 so S 10 10 12 12 10 11 12 13 14 70 20 30 90 8 15 12 6 S 12 8 3 6 20 20 15 16 Crandall Amalgam Instruments THESE instruments have been designed by Dr. Crandall to fit into the proximal and occlusal portions of such cavities as are usually made in bicuspid and molar teeth for amalgam fillings. As wUl be noted from the illustration, they have shortened shanks bringing the working point of the instrument closer to the grasp which controls it and affording great leverage and very accurate control. When used as pluggers to carry a mass of amalgam and condense it under heavy hand pressure, supplemented by mallet force, they will produce the greatest possible density and strength in the filling. Xos. 1 to 7 are for cavities in the inferior teeth which are inaccessible to the bayonet shaped instruments, Xos. 8 to 1-i. Xos. 7 and 14 are especially valuable as their size allows them to condense a mass of amalgam over all the margins of the cavity, simul- taneously, thus avoiding the movement away from some portions of the margins which is always produced by the use of small pluggers. X'os. 15 and 16 are amalgam formers for reducing the excess of amalgam to the cavity margins and for preliminary carving in the restoration of the natural tooth form. §_s:j III Frahm Carving Instruments THE occlusal surface of amalgam restorations is easily and correctly carved with these instruments so that normal masticatory form and function are restored. There are four sets of the instruments, each made up of a straight instrument, a right, and a left. The four sets differ from one another in the cutting angle of the blades, which is 75°, 90,° 105°, or 120°. These angles will take care of all the varieties of fissure formations found in the human teeth. The set illustrated has cutting blades at an angle of 105°. The other angles are shown, in comparison with this, in the drawing at their right. Dr. F. W. Frahm, who supplied the patterns for these instruments, has also furnished us with the following technic for their use in the mouth or upon models: "In the case of the occlusal surface of an inferior first molar involv- ing all the fissures: Place the blade of the straight instrument (No. 1) at the point 'a' where the buccal fissure joins the central fissure, embedding the blade in the wax or amalgam until the blades touch the margin of the cavity. Draw the instrument forward, allowing both sides of the blade to cut to their full depth, until the medio-occlusal marginal pit 'b' is reached. Then using either the right or the left instrument, according to the tooth, place it in the fossa end of the buccal fissure 'a,' pass it to the buccal side, following the course of this fissure, releasing the pressure as 'c' is neared. Then, using the straight instrument, cut from 'a' to 'd' with a push cut; from this point, push the instrument distally to the juncture of the disto-buccal and distal fissures 'f.' Select the proper right or left instrument, as indicated, place it at 'd' and draw lingually to make that fissure, then with the same instrument placed at 'b' draw to 'i' and 'j' to finish the medio-marginal pit. Then place it at 'f and draw to 'g' and 'h.' "When passing a triangular ridge the pressure should always be released somewhat, but always start in a pit and end in another with a steady clean cut. In case of lingual or buccal fissures the pressure should be released when the coronal ridge is neared or crossed. "The angle of the set of instruments to be used on the tooth should be selected to conform to the fissures found in other teeth of the same mouth. "Supplemental fissures may be made by placing one edge of the blade on the material and gouging slightly until they are the desired depth. "The cutting should be done with a firm hand and clean cut. The use of the instruments is only limited by the anatomical variation of the tooth." [71] Crandall Carving Instruments Design Patent Applied For g-ii 11 12 85 14 85 14 85 l33 5 6 6 li 23 2 18 3 18 4 For carving and finishing amalgam restorations, so that the natural form of the occluding and other surfaces is fully re-established, Dr. Crandall has designed these four instruments and advocates their use in connection ^-ith other in- struments chosen from the cavity preparation set and the amalgam set shown on preceding pages. Nos. 15 and 16 from the Amalgam Instruments are used for reducing the excess of amalgam upon occlu- sal surfaces to the point where the final car^'ing and reproduction of natural detail may be taken up by the Instruments following. Nos. 28, 29, 33 and 34 from the Woodbur>"-Crandall set are used for shaping the cusp surfaces and planes. Nos. 10 and 11 from the Wood- bury-Crandall set are for push cutting, and Nos. 1, 2, 3 and 4, shown above, for pull cutting, in forming sulci and pits. 7D m Prime Condensing Mallet This mallet was designed by Dr. J. M. Prime for affording the pressure nec- essary to condense amal- gam. The illustration shows the actual length and diameter of the head. The hickon,- handle is nine inches long, the head weighs five ounces. A brass tube, heavily nickel- plated and filled with lead forms the head of this mallet. The ends are faced with leather, inset so that it covers the entire face of the mallet and prevents the instrument from coming in contact, accidentally, with the metal edge. r2] provided by the rules of the Libniry or 1 ngement with the Librarian in charge. )y special ar- E BORROWED DATE DUE DATE BORROWED DATE DUE M.V ^ • - 3e)M50 RK54-4 Crandall 085 , T fTc^-ri -P-4 1 '1 n ^