RK^80 e>^t Columliia ©mbersiitp in tbt Citp of jBtefcD gorfe ^clbool of Bental anli (2^ral burger? Reference %ihvav^ ^^^^^^^m ^K^OT^vJ^^nJ^^ ^^^^s^^^^^ ^^^ ^^^^^^^^^m ^^^^5 9 m ^^^w ^s 1 1 ^B ■ s ^h?\^ 1 ^8 m ^^ s 1 ^S 1 ^8 M ^^^x ^^ i 1 H ■ ^^^ ^1 ^^^^^^ ^^^ s^^^ ^ ■\ / '• ^ L. Digitized by tine Internet Arciiive in 2010 witii funding from Columbia University Libraries http://www.ar.chive.org/details/descriptiveanatoOOblac X Descriptive Anatomy OF THE Human Teeth. ^^, \ BY G. V. BLACK, M.D., D.D.S. PUBI^ISHED BY The Wilmington Dbntai, Manufacturing Co. , 14 1 3 Fii^BKRT Street, PHILADEIvPHIA, PA. Copyrighted, 1890, by The Wilmington Dental M'fg Co., Phila. PREFACE. BY my experience as a practitioner, as a teacher, and in my intercourse with fellow practitioners, I have be- come convinced of a serious defect in the teaching of the details of the anatomy of the teeth, and in the systemization of the terms used in their description. This defect has been a constant drawback at the chair, in the laboratory, and, most of all, in the college. The object of the present volume is to remedy, in a measure, this defect. To this end I have had constantly in view the needs of the dental student and practitioner. We have heretofore had excellent general descriptions in human and comparative dental anatomy ; but these have dealt principally with the general forms of the dentitions of the mammalia and other orders of animate beings, rather than with specific descriptions of the forms of the various surfaces, and surface markings, making up the sum of the forms of the individual teeth of man. Valuable as these works have been, they have left the acquirement of a knowl- edge of the details of the specific forms of the human teeth mostly to individual observation. By this means, many have attained to an excellent perception of the various forms of the human teeth ; but it is not reasonable to suppose the profession generally will do this without some fixed guide. "What the dental student wants most in the college, and in the office, is a systematized nomenclature of the several parts PREFACE. of the teeth in detail ; and such a description as will call his attention successively to every part of each tooth, as Gray, in his Anatomy, has called attention to every part of each bone, however apparently unimportant. It should be re- membered that anatomy is not to be learned from books alone, but also by bringing the parts to be studied into view, and closely examining them in connection with the descrip- tions given. Any one who may read the present volume without a reasonable number of human teeth of each denomi- nation before him for examination and comparison, will be but partially benefited. It has been my object to systematize the nomenclature most in vogue with the profession, whenever practical, rather than to introduce new terms. However, the reader will find a few new terms, and possibly a few old ones that are used differently from the former custom. The terms up and down, to indicate direction or parts of teeth, are abandoned, because of their ambiguity. In a few instances, new forms of old words have been used, especially to avoid the terms inner, outer, backward, forward, etc., which are so often mis- leading. The words mesial, distal, labial, buccal, lingual, etc., are used as ad Verbs of direction by adding /y, or the same thing is accomplished by the use of the preposition to. It is as easy to say of a cavity that it extends far beyond, beyond, to, or nearly to, the gingival line, as to say it ex- tends up or down, etc., and the meaning will not be mistaken ; or to say that a cavity extends distally, or to the distal, or lingually, or to the lingual, instead of backward, or inward, either of which have different meanings in different situa- tions. The best rule is to use no extraneous object in the PREFACE. designation of the parts of, or direction on, the surface of a tooth ; but to confine the phraseology to the specific and well defined terms applied to its several parts. The back part of a molar would not mean the same relative part as the back part of an incisor. In many such ways the author has endeavored to systematize, and make more definite, the phraseology applied to the teeth without going to extremes, knowing well that forms of language once in use can be im- proved more easily than they can be displaced by new terms, though more exact. The absence of a Bibliography may be noted. The plan and object of this work has not seemed to call for many references to authorities. This does not imply, however, that authors who have preceded me, as Fox, Carabelli, Tomes, Wedl, Judd, Wortman, and many others, to whom we are greatly indebted, have been either overlooked or ignored. The illustrations have all been made by the author for the 23u.rpose of illustration, rather than as works of art. After experimenting with the various plans of the manage- ment of light and shade, diffuse light has been used because more detail could be shown, esjDCcially in the difficult task of illustrating the occluding surfaces of the teeth. Each picture of the teeth, in all its details, is drawn from accurate measurements of the particular tooth in hand. Much of dental histology might properly find place in this book ; but that subject is well rejjresented by others. Malforms of the teeth, supernumerary teeth, and variations of arrangement, belong to the subject of irregularities, which is amply treated by several authors. Our aim has been to 6 PREFACE. confine the book strictly to normal macroscopic anatomy. However, a very serious difficulty, which has always met the dental anatomist, has been the variations of form met in teeth of the same denomination. The endeavor has been to systematize these under one, two, or more typical forms of each tooth, or its lobes, and point to the character of the changes which occur. This has occasionally led to the men- tion of abnormal forms. The reader will find scattered through the work some hints with regard to the practical bearing of anatomical points on operative procedures, which it is hoped will be of value. DENTAL ANATOMY. 1. Man's food is both animal and vegetable, and his teeth are so formed as to enable him to readily masticate either kind ; therefore, his teeth differ from those of both the carnivorous and herbivorous animals, and form the type of the omnivora. They are formed for catting, tearing, and comminuting many kinds of food. The incisiors, situated anteriorly, have edges for cutting ; the cuspids and bicus- pids, at the angles of the mouth, have fairly sharp, though not very long, points or cusps, well calculated for tearing ; while the molars, situated in the posterior part of the mouth, have broad, tuberculated grinding surfaces, which serve well to grind or comminute the more solid masses. The forms of the teeth of man indicate a design that his food should be taken in rather small masses, considered from the stand- point of the habits of animals in general, and that it should be very thoroughly commingled with saliva before being" passed to the stomach. 2. The adult has thirty-two teeth, as follows : In- cisors, f; cuspids, \; bicuspids, |; molars, § = 32. The teeth are composed of four tissues: enamel, which covers the crown ; dentine, which forms the body of both crown and root; cementum, which covers the roots and joins with the enamel at the gingival line, or neck, of the tooth ; and pulp tissue, which fills the central cavity of the dentine. 3. Each tooth presents for description certain charac- ters common to all, such as crown, neck or gingival line^ root, pulp-chamber, canal, and surfaces of crown and root. The crown of a tooth is that part which projects beyond 7 8 NOMENCLATURE. the gum tissue, and is covered with enamel ; while the root, covered with cementum, is that portion fixed in the bony process of the jaw, by which the whole tooth is held securely in position. The root of a tooth may be single, as in the incisors and cuspids ; divided into two prongs or roots, as in the lower molars ; or into three roots, as in the upper molars; 'Or into a greater number, as in exceptional examples. The root is divided into the body or main portion ; the apex, or terminal end of a root ; and the neck, which marks the junction of the root with the crown. A tooth is also marked with a slight constriction at the neck, and by the junction of the enamel with the cementum. The latter, which forms a visible line encircling the. tooth, is called the gingival line. It is so curved in its course as to present a convexity toward the crown on the proximate surfaces, to correspond with the line of the gum as it passes over the alveolar ridge from the labial to the lingual side of the arch. On the anterior teeth, it is also so curved in passing the labial and lingual surfaces :as to present a concavity toward the crown. These are called the curvatures of the gingival line, or the gingival curvature. The neck of a tooth is common to all of the roots, whatever the number, for the point of division into two or more roots is always rootward from the neck. 4. The crowns of the incisors and cuspids present for ■examination four surfaces and an edge ; and the crowns of the bicuspids and molars, five surfaces. These surfaces are named according to their position and use. Those of the in- cisors and cuspids presenting toward the lips, are called labial surfaces ; those of the bicuspids and molars presenting toward the cheek, buccal surfaces ; all presenting toward the tongue, lingual surfaces, whether in the upper or the lower jaw.* 5. The surfaces of the teeth that present toward, or lie against, adjoining teeth are called proximate, or proximal, *Soine authors use the term " palatine surfaces " for those of the upper jaw, and ■"lingual " for those of the lower. This seems unnecessary. NOMENCLATURE. 9 surfaces. The proximate surfaces are also more closely defined by the terms mesial and distal. These terms have special reference to the position of the surface relative to the central or the median line of the face. This line is drawn along the suture uniting the superior maxillary bones, or perpendic- ularly through the centre of the face and mouth, and passes between the central incisors of both the upper and lower jaws. Those proximate surfaces which, as they are placed in the arch, and following its curve^ are toward this median line, are called mesial surfaces ; and those most distant from this median line are called distal surfaces. The mesial surfaces of the central incisors, both upper and lower, proximate each other ; but in all other cases a mesial surface proximates a distal. Also, a distal surface always proximates a mesial surface, except those of the third molars, upper and lower, which have no distal proximating teeth. 6. The angles formed by the junction of any of these surfaces are designated by combining the names of the two uniting surfaces into a compound word, using the term mesio or disto as a prefix, thus : mesio-buccal, mesio-ocduding ^ disto-lingual and disto-labial angles. 7. The incisors present a cutting edge by the junction of the labial and lingual surfaces along a line. In the cuspids, this joining of the surfaces to form an edge is raised to a point near the center of its length, forming a cusp, hence the term " cuspid," a tooth with one point. The cutting edges of the incisors, and the grinding surfaces of the bicuspids and molars, are those which occlude with the similar surfaces of the teeth of the opposing jaw when the mouth is closed, as in the act of biting ; hence they are called the occluding surfaces. The incisors and cuspids of the upper jaw do not occlude ex- actly on the cutting edges or cusps, but generally just back of them ; though, for convenience, this term is applied to them as if they did. The occluding surfaces of the bicus- pids have two cusps, hence the term bicuspid, a tooth with 10 NOMENCLATURE. two points ; and the occluding surfaces of the molars have- four, and sometimes more. 8. A cusp is a pronounced elevation, more or less pointed, on the surface of a tooth, but more especially on the occluding surface. A slight elevation is often called a tubercle, as that frequently seen near the gingival margin of the lin- gual surface of the upper incisors. These are generally deviations from the typical forms of the teeth. 9. Long-shaped elevations on the surfaces of teeth are called ridges, and are named according to their location or form: as buccal ridge, lingual ridge, and marginal ridge. Those ridges which descend from the cusps of the molars and bicuspids toward the central part of the occluding sur- faces are called triangular ridges. They are named after the cusps to which they belong, as, the triangular ridge of the mesio-buccal cusp of the upper first molar, or simply, mesio-buccal triangular ridge. When a buccal and a lingual triangular ridge join they form a transverse ridge. In this way they often subdivide the central fossa of the lower molars and form supplemental fossse. 10. A generally rounded or angular depression on the surface of a tooth is called a fossa. Fossse occur mostly on the occluding surfaces of the molars. When a notable depression is long-shaped it is called a sulcus. Some of these pass entirely from mesial to distal through the occluding surface of a tooth, as in the bicuspids. This term is often erroneously applied to the grooves and fissures. 11. A shallow, long-shaped depression, in the form of a line, on the surface of a tooth, is called a groove. When such a groove follows the bottom of a sulcus it is said to be sulcate. When such a groove sinks suddenly into the sub- stance of a tooth in the form of a fault it is called a fissure."'^ * The words sulcus, groove, and fissure are often used as if they were synonymous and interchangeable, which has given rise to much confusion. It is necessary that the distinctions made in their use in dental anatomy be well understood. A groove is a very fine line in the form of a slight, sharp depression on the surface of the tooth, as repre- sented in section in diagram A, at a in a section cut at the point where the mesial NOMENCLATURE. 11 There are two varieties of grooves in the teeth, differing essentially in their nature and formation. One class marks the lines on which the parts of the teeth first formed sepa- rately, are afterward joined, and is called the essential or developmental grooves, or developmental lines. In their relation to the development of the enamel, they are of the same nature, and resemble the sutures of the bones of the skull, which mark the junction of the separately formed plates. Hence these grooves form the key to much of de- scriptive dental anatomy ; and, when they can be traced, enable the anatomist to unravel complex forms, and assign irregu- larly formed teeth to the groups to which they belong ; to properly name their individual parts, and identify any additional, accidental, or unusual forms or parts that may have become intermingled in the accident of a faulty forma- tion. These developmental grooves, or lines, are subject to fissures, which occur when, from any cause, there is a failure of perfect union of the parts, leaving a fault. 12. The other class of grooves has no especial relation to the developmental lines, and are called supplemental grooves. These are aptly described as wrinkles in the enamel, which, in fact, many of them are. But some are so constant in their location and form as to make up a portion of the typical tooth form. The supplemental grooves are usually groove passes over the marginal ridge of a bicuspid. Diagram B, from a section of a bi- cuspid, a cut across verj' close to the occluding surface grooves are shown at a, a. A very- shallow depression with rounded bottom is also called a groove, as those seen on the labial surfaces of the incisors. A sulcate groove is one that follows a sulcus of notable depth, the inclines of which approach each other at an angle, as represented at a, in Diagram C. A fissure is always a fault in the enamel, a point where the margins of the plates of enamel fail to unite, as represented at a, in diagram D. These are distinctions of im- portance, and there should be no confusion in the use of the words by which we distin- guish them. J ^ C ^ 12 MEASUREMENTS OF THE TEETH. shallow, with well-rounded bottoms, and are not ordinarily subject to fissure. 13. In the mesio-distal direction all of the teeth are a little broader at or near their occluding surfaces than at their necks ; therefore, as they stand in the well-formed arch, their proximate surfaces touch only at or near their occluding sur- faces, leaving V-shaped openings between their necks. These are called inter-proximate spaces. IsTormally, the inter- proximate spaces are filled with gum tissue. 14. The teeth of difterent individuals show considerable variety of form. Some persons have teeth with very long crowns, broad in the mesio-distal direction at their occluding surfaces and narrow at their necks. These present large inter-proximate spaces. They are known as " bell-crowned " teeth. Again, some individuals have teeth that, in their mesio-distal diameter, are nearly as thick at their necks as at the occluding surfaces, making their inter-proximate spaces very narrow, the teeth almost, or quite, touching along the whole length of the crown. These are known as thick-necked teeth. The more common form is midway between these two extremes. The teeth of some individuals and families have very long cusps ; those of others have very short cusps. Some are deeply marked by grooves and sulci, and in those of others the grooves and sulci are shallow. Thus, there is considerable variety of contour without change of type. 15. In the following tables the results of the measure- ment of many teeth of each denomination are given. The numbers we had of the different varieties differed, but in all denominations they were sufficient to insure reasonable accu- racy as to the average size. There are three measurements given, the average, greatest, and least, in the several posi- tions measured. With a greater number, both larger and smaller teeth might be found, so that the tables must not be taken to represent the greatest nor the least that might MEASUREMENTS OF THE TEETH. be found ; but the occurrence of larger, or longer teeth must be rare. The lines of measurement, are : 1st. " Length over all:" Length of the tooth from the cutting edge, or buccal cusp, to the apex of the root. 2d. "Length of crown:" Length of the crown from the cutting edge, or buccal cusp, to the gingival line on the labial or buccal surface. 3d. " Length of root :" Length of root from the gingival line on the buccal surface to the apex of the root. 4th. " Mesio-distal diameter 6f crown:" This is the extent from mesial to distal in the greatest diameter, or at the points of proximate contact. 5th. " Mesio-distal diameter of neck :" This measure- ment was made at the gingival line. 6th. " Labio- or bucco-lingual diameter:" This meas- urement was taken at the greatest diameter of the crown in the direction named. In the incisors it was on the gingival ridge. In the bicuspids and molars it was generally mid. length of the crown, but occasionally it was near the gingival line, especially in the upper second and third molars. 7th. " Curvature of the gingival line :" This is the height or extent of the curve of the gingival line toward the cutting edge, or occluding surface, as it passes from labial to lingual, measured on the mesial surface. Having these tables, the necessity for giving many measurements in the text is avoided. 14 MEASUREMENTS OF THE TEETH. Table of Measurements of THE Teeth of Man, Given IN Millimeters and Tenths of Milli- meters.* 22.5 27.0 18.0 o t-l o o a o o ft a .— TS is 1 si CD ■♦^ <» = a 31 s > UPPER TEETH. 'nisor ^-S: Incisor. Least. 10.0 12.0 8.0 12.0 16.0 8.0 9.0 10.0 8.0 6.3 7.0 5.5 7.0 8.0 7.0 3.0 4.0 2.0 Lateral GleaSt' 22.0 26.0 17.0 8.8 10.5 8.0 13.0 16.0 8.0 6.4 7.0 5.0 4.4 5.0 4.0 6.0 7.0 5.0 2.8 4.0 2.0 Average. Cuspid. Greatest. Least. 26.5 32.0 20.0 9.5 12.0 8.0 17.3 20.5 11.0 7.6 9.0 7.0 5.2 6.0 4.0 8.0 9.0 7.0 2.5 3.5 1.0 First Average. ■R5„..c,.j^ Greatest. Bicuspid. Least. 20.6 22.5 17.0 8.2 9.0 7.0 12.4 14,0 10.0 7.2 8.0 7.0 4.9 6.0 4.0 9.1 10.0 8.0 1.1 2.0 0.0 ^^«<^°4 ., Greatest Bicuspid. Least. 21.5 27.0 16.0 7.5 9.0 7.0 14.0 19.0 10.0 6.8 8.0 6.0 5.3 6.5 4.5 8.8 10.0 7.5 0.8 1.5 0.0 First Average. 20.8 24.0 17.0 20.0 24.0 16.0 17.1 22.0 14.0 7.7 9.0 7.0 13.2 16.0 10.0 10.7 12.0 9.0 7.5 8.0 7.0 11.8 12.0 11.0 2.2 3.0 1.0 Second ATerage. Molar. SSr- 7.2 8.0 6.0 6.3 8.0 5.0 13.0 17.0 9.0 9.2 10.0 7.0 6.7 8.0 6.0 11.5 12.5 10.0 1.6 4.0 0.0 Third Average. 11.4 15.0 8.0 8.6 11.0 7.0 6.1 8.0 5.0 10.6 14.5 8.0 0.7 2.5 0.0 *T]iere are 25.4 millimeters to the inch. MEASUREMENTS OF THE TEETH. 15 Table of Measurements of THE Teeth of Man, Given IN Millimeters and Tenths op Milli- meters. '3 u 0) > o fl 0) 2 o o to a a g"3o o LOWER TEETH. Central _ aleaSt I^"««^- Least. 20.7 24.0 16.0 21.1 27.0 18.0 8.8 10.5 7.0 11.8 16.0 9.0 5.4 6.0 5.0 3.5 5.0 2.5 6.0 6.5 5.5 2.5 3.0 1.5 Lateral ^J^f^e. Incisor. Greatest. Least. 9.6 12.0 7.0 12.7 17.0 11.0 5.9 6.5 5.0 3.8 50 3.0 6.4 7.5 6.0 2.5 3.5 2.0 Average. Cuspid. Greatest. Least. 25.6 32.5 20.0 10.3 12.0 8.0 15.3 21.0 11.0 6.9 9.0 5.0 52 7.0 3.0 7.9 10.0 6.0 2.9 4.0 2.0 First Average. !?•„ -A Greatest. Bicuspid. j^^^^^ 21.6 26.0 18.0 7.8 9.0 6.5 14.0 18.0 11.0 6.9 8.0 6.0 4.7 5.0 4.5 7.7 8.0 7.0 0.8 1.5 0.5 Second ^I^ejfgJ- 22.3 26.0 18.0 21.0 24.0 18.0 7.9 10.0 6.0 14.4 17.5 11.5 7.1 8.0 6.5 4.8 6.5 4.0 8.0 9.0 7.0 0.6 2.0 0.0 First ^-"^'fSe- M«^- Sir- 7.7 10.0 7.0 13.2 15.0 11.0 11.2 12.0 11.0 8.5 9.5 7.5 10.3 11.5 10.0 1.1 2.0 0.0 Second Average. 19.8 22.0 18.0 6.9 8.0 6.0 12.9 14.0 12.0 10.7 11.0 10.0 8.1 8.5 8.0 10.1 10.5 9.5 0.2 1.0 0.0 Third Average. Molar. g^r- 18.5 20.0 16.0 6.7 8.0 6.0 11.8 17.0 8.0 10.7 12.0 8.0 8.3 9.5 5.0 9.8 10.5 9.0 0.2 1.5 0.0 16 MEASUREMENTS OF THE TEETH. Table of Measurements op THE Deciduous Teeth of Man, Given in Milli- meters and tenths of Millimeters. > o to c 16.0 & o u c o to § u o a rO O 6 fH -J ^ o .s a .^ o .2S pt4 .S ° Averages Only. 11 UPPEE TEETH. T3 Central Incisor. 6.0 10.0 6.5 4.5 5.0 4.0 Lateral Incisor. 15.8 19.0 5.6 6.5 11.4 5.1 3.7 4.8 3.7 Cuspid. 13.5 7.0 5.1 7.0 5.5 First Molar. 15.2 5.1 10.0 7.3 5.2 8.5 6.9 Second Molar. 17.5 14.0 5.7 5.0 11.7 9.0 8.2 4.2 6.4 3.0 10.0 4.0 8.3 LOWER TEETH. Central Incisors. 3.5 Lateral Incisors. 15.0 17.0 5.2 6.0 10.0 4.1 3.0 4.0 3.5 Cuspids. 11.5 5.0 3.7 4.8 4.0 First Molar. 15.8 6.0 9.8 7.7 6.5 7.0 5.3 Second Molar. 18.8 5.5 11.3 9.9 7.2 8.7 6.4 MEASUREMENTS OF THE TEETH. 17 Table of Measurements of THE Teeth of Man; in Inches and Hundredths OF an Inch. 1 1 "^ u > o bb a p 3 o ,5 "so a T3 03 8-2 .21 c3 a -^ a UPPER TEETH. Central. ^JS: I°^^^«^- Least. .88 1.06 .72 .39 .41 .31 .49 .63 .31 .35 .39 .31 .24 .27 .21 .27 .31 .27 .11 ,15 .07 ^ntisor ^-S- ^^«^^«^- Least. .86 1.02 .66 .34 .41 .31 .51 .63 .31 .25 .27 .19 .17 .19 .15 .23 .23 .19 .11 .15 .07 Average. Cuspid. Greatest. Least. 1.04 1.26 .79 .37 .47 .31 .68 .80 .43 .29 .35 .27 .20 .23 .15 .31 .35 .27 .09 .13 .03 First Average. "bicuspid, sr .81 .89 .66 .32 .35 .27 .48 .55 .39 .28 .31 .27 .19 .23 .15 .35 .39 .31 .04 .07 .00 .84 1.06 .62 .29 .29 .27 .55 .55 .39 .26 .31 .23 .20 .25 .17 .34 .39 .29 .03 .05 .00 First Average. .81 .94 .66 .30 .35 .27 .51 .62 .39 .42 .47 .35 .29 .31 .27 .46 .47 .43 .08 .11 .03 ijeast. .78 .94 .62 .28 .31 .23 .51 .66 .35 .36 .39 .27 .26 .31 .23 .45 .49 .39 .05 .15 .00 Third Average. Molar. Greatest. Least. .67 .86 .55 .24 .31 .19 .44 .59 .81 .33 .43 1 .27 .23 .41 .31 .57 .19 .31 .02 .09 .00 18 MEASUREMENTS OF THE TEETH. Table of Mt^iasurements of THE Teeth of Man; in Inches and Hundredths OF AN Inch. Is u > o bo g o o "So a 1-1 o o u 1-1 3 2 13 O O Si ^4 o u II 6 S3 .si «M >u o O o ^ ^ ^ 60 60 60 c S c ^ 1-1 H-1 Central Incisor. .63 .23 .39 .25 .18 .20 .16 Lateral Incisor. .62 .25 .45 .20 .14 .19 .14 Cuspid. .74 .25 .53 .27 .20 .27 .21. First Molar. .59 .20 .39 .28 .20 .33 .27 Second Molar. .68 .55 .22 .19 .46 .35 .32 .15 .25 .11 .39 .15 .32 LOWER TEETH. Central Incisor. .13 First Molar. .59 j .19 i .39 I .15 I .11 j .15 | .13 'm~\ .23 I .45 I .19 I .14 I .17 | .15 '!62~| .24 I .38 I .30 I .25 | .27 I .21 Second Molar. .62 .21 .44 .38 .28 .34 .25 UPPER CENTRAL INCISORS." 16. The right and left upper central incisors are sit- uated in the extreme anterior part of the dental arch, one on each side of the raedian line, their mesial surfaces proxi- mating each other. The crown presents four surfaces (five, including the cutting edge), four angles, and a cutting edge, or occluding surface. The general contour of the crown is similar to a wedge, with rounded angles and merging into a rounded form at the thick end, or the neck of the tooth. It * U<^allv ill the descriptions of the teeth, those of one side oulv will be mentioned ^rithout reference to which side in the text. Accompanying the illustrations the side to wMrfithlt(Mth belongs will be given. The student wiU readily determine to which sfdlaliTefeTinple belongs by comparing it ^vith the text and correctly naming its surfaces. 20 UPPER CENTRAL INCISORS. is slightly bent on its shorter diameter, so as to make the flattened labial surfaces convex ; while the other, the lingual, is concave. The crown is also slightly bent in the mesio- distal direction, so that the labial surface is convex and the lingual concave in this direction. Therefore, there is a general convexity of the labial, and a general concavity of the lingual surface. 17. The labial surface of the crown of the upper central incisor (Fig. 1), in its general form, is an imperfect square, with its gingival side rounded. The mesial margin is a little longer than the distal, so that the cutting edge slopes away toward the distal angle (Fig. 1, A). Both the angles, formed by the proximate surfaces and cutting edge, are slightly rounded, the distal more than the mesial, after which the proximate surfaces converge toward the long axis of the tooth, making the crown a little narrower at the neck than at the cutting edge. 18. . The lingual surface of the crown (Fig. 2) is con- cave in all directions, forming a fossa, bounded by the cutting edge (a), the mesial and distal marginal ridges {n, m) and the gingival ridge, or cingulum [d). The marginal ridges are strong elevations of the enamel, running from the mesial and distal angles of the cutting edge along the borders of this surface to near the gingival line, where they join the gingival ridge. The gingival ridge is a strong elevation of the enamel forming the lingo-gingival border of the crown, sometimes elevated into a tubercle. The lingual fossa is usually smooth, and the ridges by which it is bounded are not prominent. In many instances, however, there is a deep pit at the junction of the gingival ridge with the lingual surface proper ; and in some a groove extends from the pit for a short distance along the border of each marginal ridge (Fig. 3). These latter may, or may not, be fissured. In a few examples the enamel of this surface has irregular wrinkles, or ridges and grooves, running from the gingival Fig. 4. Fig. 5. Fig. 1* (Par. 17).— Right Upper Central Incisor, Labial Surface, a, Cutting edge ; 6, mesial surface ; c, distal surface ; d, labial surface ; e, e, labial grooves ; g, mesial angle ; h, distal angle ; i, body of root ; k, apes of root. Fig. 2* (Par. 18).— Right Upper Central Incisor, Lingual Surface, a, Cutting edge ; b, mesial surface ; c, distal surface ; d, gingival ridge, or cingulum ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root ; m, distal marginal ridge ; n, mesial marginal ridge. Fig. 3 * (Par. 18).— Left Upper Central Incisor, Lingual Surface, showing lingual pit. The cutting edge, a, is considerably worn. The mesial and distal marginal ridges, 6, c, are prominent ; d, linguo-gingival ridge ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root ; m, lingual pit. Fig. 4* (Par. 19).— Right Upper Central Incisor, Mesial Surface, a, Mesial angle ; d, gingival ridge ; /, /, gingival line, showing its labio-lingual curvature ; i, body of root ; k, apex of root. Fig. 5* (Par. 21).— Left Upper Central Incisoe, Lingual Surface. Young, un- worn tooth. The developmental lines, or grooves, are made diagrammatically promi- nent to show the form of the lobes, a, Middle lobe ; b, mesial lobe ; c distal lobe ; d, lingual lobe ; e, e, linguo-gingival groove ; /, /, Ungual developmental grooves ; g, mesial angle ; ft, distal angle. * Illustration, 1}4 diameters. UPPER CENTRAL INCISORS. 23 ridge toward the cutting edge. In malformed teeth this surface is often very imperfect. 19. The mesial and distal surfaces each present the outline of the letter Y, with its lines curved with the con- vexity toward the lips, and the acute angle at the cutting edge (Fig. 4). The mesial surface is almost straight from the angle of the cutting edge to the gingival line. It is convex from labial to lingual, hut nearly flat toward the gingival line; while in some there is even a slight concavity, centrally at, or near, the gingival line. In the labio-lingual direction, the distal surface is rounded, as in the mesial. In the majority of examples it is also convex in the direction of the long axis of the tooth, so that it bellies out toward the lateral incisor. 20. At the gingival line, the tooth is a little constricted, forming a slight furrow; or rather, the root at the neck is a little smaller than the crown, and the enamel slopes down to the size of the root, giving the appearance of a continuous ridge of enamel around the neck of the tooth. This line does not run horizontally around the neck of the tooth. On the proximate side it forms a curve with the convexity toward the crown, and on the labial and lingual surfaces it forms a curve with the concavity toward the crown. This line marks the limit of the attachment of the peridental membrane to the root of the tooth. 21. Developmental lines (Fig. 5). "When any of the incisors first appear through the gums there are three little eminences, or tubercles, on the cutting edge with grooves crossing from labial to lingual between them {a,g,h). These grooves run some distance on the labial surface, becoming broader and shallower till they disappear. In many, these lines appear on the lingual surface between the marginal ridges and the fossa (/,/). Occasionally, they are seen as far as the gingival ridge. The little tubercles are soon removed from the edge by wear, leaving it straight, or slightly curved. 24 UPPER CENTRAL INCISORS. These lines divide this part of the crown of the tooth into three labial lobes. Calcification begins in these tubercles as separate pieces, or plates, and the grooves are the marks of the after-confluence of these plates. This is common to the inci- sors and cuspids. These teeth are sometimes fissured across the cutting edge, marking an imperfect confluence of the primary plates. The calcification of the gingival ridge, or cingulum, is also begun as a separate plate, forming the lingual lobe, but afterward it becomes united to the other parts by confluence, leaving a groove, often very slight, indeed, and soon obliter- ated by wear, marking the line of union. This is the linguo- gingival groove {e, e). In smooth regularly formed teeth it begins at the gingival line just distal to the summit of its labio-lingual curvature, and runs across the marginal ridge at right angles with its length, then runs almost horizontally across the lingual surface to the distal marginal ridge. This ridge is now crossed at right angles, and the gingival line reached. The length of the groove usually includes from a quarter to a third of the circumference of the tooth. When the gingival ridge is prominent, or rises in the form of a tubercle, this groove is subject to much variation in its course. Often, there is a deep pit in the center of its length ; «.e., centrally in the lingual surface, at the margin of the gingival ridge (Fig. 3, m). From this, fissures may extend laterally. Occasionally, especially in the lateral incisors, a sulcus, or a fissure divides the gingival ridge from one of the marginal ridges, and extends into the*cementum. This is the gingival fissure. 22. The root of the upper central incisor (Figs, 1 to 5) is about one and a fourth, to one and a half times as long as the crown. It is conical in form, tapering from the crown to the apex ; less rapidly near the neck, and more rapidly as the apex is approached. Therefore, the body of the root seems a little swollen. However, the root of this tooth presents great variety of figure, as do the roots of teeth Fig. 6. Fig. 8. Fig. 10. Fig. 6* (Par. 24).— Right Upper Lateral iNasoR, Labial Surface, a, Cutting edge ; c, distal surface ; e, labial grooves ; /, gingival line ; g, mesial angle ; h, distal angle. Fig. 7 * (Par. 25).— Right Upper Lateral Incisor, Mesial Surface, a, Mesial angle ; d, linguo-gingival ridge ; /,/, gingival line ; i, body of root ; fc, apex of root. Fig. 8* (Par. 26).— Right Upper Lateral Incisor, Lingual Surface, without lingual pit. a, Cutting edge ; 6, mesial marginal ridge ; c, distal marginal ridge ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root ; m, lingual fossa. Fig. 9 * (Par. 26).— Right Upper Lateral Incisor, Lingual Surface, with lingual pit. o. Cutting edge ; 6, mesial marginal ridge ; c, distal marginal ridge with linguo- gingival groove crossing it ; d, linguo-gingival ridge, or eingulum ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apes of root ; m, lingual pit. Fig. 10* (Par. 26).— Right Upper Lateral Incisor, showing a linguo-gingival fissure. a. Cutting edge ; &, linguo-gingival groove ; /, gingival line ; g, mesial angle ; h, distal angle. Fig. 11* (Par. 27).— Upper Lateral Incisor, Mesial Surface. Very short root, a. Mesial angle ; d, linguo-gingival ridge ; /, gingival line. * Illustration, IJ^ diameters. UPPER LATERAL INCISOR. 27 generally. The root is nearly round at the neck. The cur- vature of the Ungual surface is the arc of a smaller circle than that of the labial. The proximate surfaces are slightly flattened. The flattened portion of the mesial surface is a little broader than the distal. These two converg-e to the lingual, giving the form of a prism with its angles rounded. UPPER LATERAL INCISOR. 23. The description of the lateral incisor may be much abridged, because of its resemblance to the central in its general form and developmental lines. The tooth is a little shorter, and from mesial to distal the crown is about a third narrower. 24. The labial surface of the lateral incisor (Fig. 6) is more rounded in the mesio-distal direction than in the cen- tral. The mesial angle is acute, and the cutting edge slopes away in a curve to a rounded and obtuse distal angle. The cutting edge, at the time of eruption, presents three tubercles, and the grooves crossing the edge between these are projected on the labial surface as shallow labial grooves. 25. The mesial (Fig. 7) and distal surfaces present the characteristic V-shape of all the incisors. From labial to lingual the mesial surface is rounded near the cutting edge, but much flattened near the gingival line. Sometimes a slight concavity exists at this point. Occasionally the mesio- labial angle has a flattened or sunken point of enamel near the middle of its length. This is sometimes broad and of notable depth, and in this case is generally in the labial portion of the mesial surface. In others, it is a small im- perfection in the mesial border of the labial surface. The distal surface is convex in all directions. In its occlusive third, it rounds out freely toward the cuspid, but becomes more flattened toward the gingival line. 26. The lingual surface (Fig. 8) of lateral incisors, is very irregular in the extent of its concavity. Some are almost flat, while others are deeply concave. The mesial 28 THE LOWER INCISOES. and distal marginal ridges are proportionately broader, and stronger, than in the centrals. In the majority of examples the lingual surface is the broadest part of the crown. The rounding of the proximate surfaces is at the expense of the labial surface, so that a moderately acute angle is formed by the junction of the proximate surfaces with the lingual. Generally, the lingual surface is almost smooth, but in many, a pit, with or without lateral fissures, will be found at the junction of the lingual surface proper, with the gingival ridge (Fig. 9). In some of these, the gingival ridge is unusually short, so that the marginal ridges are folded in together at their gingival ends, forming a deep sulcus be- tween them, and there is a deep pit at their junction. Again, some are found in which there is a deep groove, which is often fissured, dividing one marginal ridge from the gingival ridge, and extending into the cementum (Fig. 10). This is some- times nearly central, giving the appearance of a failure of the lingual lobe, or of a division of the lobe centrally, or of the dis- placement of the lobe to one side. This is the gingival fissure. 27. The root of the upper lateral incisor (Figs. 6 to 11) is conical, but considerably flattened on its mesial and distal sides, which is generally maintained to the apex. The root is generally straight, and about one and a half times as long as the crown. In many specimens the apex is curved to the distal. Occasionally the root is very crooked. 28. The ujDper lateral incisor presents much variety of size and form. It is not uncommon to find narrow laterals associated with broad centrals. The lateral incisors are more often imperfectly developed than the other anterior teeth. In these, the crown of the tooth is frequently conical, with a rounded, or even a moderately sharp, point. THE LOWER INCISORS. 29. The lower incisors have outlines similar to the upper lateral, but are, in every way, more slender. Their Fig. 12. Fig. 15. Fig. 17. Fig. 12* (Par. 29).— Left Lower Central Incisor, Labial Surface. Long root. a, Cutting edge ; e, labial grooves ; /, gingival line ; g, mesial angle ; h, distal angle. Fig. 13* (Par. 29).— Left Lower Lateral Incisor, Labial Surface. Long root. a, Cutting edge ; e, labial grooves ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root. Fig. 14* (Par. 29).— Right Lower Lateral Incisor, Labial Surface. Short root. a, Cutting edge ; e, labial grooves ; /, gingival line ; g, mesial angle ; A, distal angle ; i, body of root ; k, apex of root. Fig. 15 * (Par. 30).— Lower Central Incisor, Lingual Surface, a, Cutting edge ; 6, mesial marginal ridge ; c, distal marginal ridge ; d, linguo-gingival ridge ; g, mesial angle ; h, distal angle ; m, lingual ridge. Fig. 16 * (Par. 30).— Lower Central Incisor, Distal Surface. a, Cutting edge ; the edge is worn away as represented by the line ; d, linguo-gingival ridge ; /,/, gingival line ; i, groove along the distal side of root ; k, apex of root. Fig. 17 * (Par. 31).— Right Lower Lateral Incisor, Distal Surface, showing root deeply grooved, a, Cutting edge ; d, linguo-gingival ridge ; /, gingival hue ; i, deep- groove in root ; k, apex of root. * Illustration, l}i diameters. THE LOWER INCISORS. 31 developmental lines are the same, but the grooves are much less marked, and generally cannot be seen except in unworn teeth. The cutting edge of the lower central (Fig. 12) is very nearly at right angles with the long axis of the tooth, and its angles are square and sharp. From mesial to distal, the cutting edge is the widest part of the crown, and from it the proximate surfaces converge equally to the gingival line, reducing the mesio-distal diameter about a third. The lower lateral differs from the central by the cutting edge sloping away to the distal, the mesial angle being acute, and the distal, obtuse and rounded. The distal surface is also convex from the angle to the gingival line, bellying out toward the cuspid. 30. The lingual surface (Fig 15) of the lower incisors is concave from the cutting edge to the gingival ridge, over which there is a convexity (Fig. 16). l^ear the cutting edge this surface is generally nearly flat in the mesio-distal direction, but is sometimes concave or slightly convex ; it becomes convex progressively toward the gingival ridge. In many there is a slight ridge on the center of this surface with a shallow concavity on either side, which marks the junction of the lobes, running from near the cutting edge to the gingival ridge (Fig. 15). The mesial and distal surfaces are convex near the cutting edges, but become flattened, and sometimes slightly concave, toward the gingival line. 31. The roots of the lower incisors are slender and much flattened in their mesio-distal diameter, and not unfrequently slightly grooved on the mesial and distal sides. The labial surface of the crown and root, in its length, forms nearly the arc of a circle (Fig. 1-7), though the curve of the surface of the crown is usually a little greater than the root (Fig. 16). The lingual surface is almost straight, but in the apical third it is convex, sloping away to form the apex. The roots of these teeth are generally straight, but occasionally the apex is curved to the distal side. 32 THE CUSPIDS — THE UPPER CUSPID. THE CUSPIDS. 32. We have four cuspids, one on each side in the upper and the lower jaw. Thej are sometimes called canine, or eye, teeth. They are situated at the angles of the mouth between the lateral incisors and the first bicuspids. They are the third tooth from the median line, and are large, strong teeth of simple form, firmly implanted in the alveolar process by a long, strong root, the longest in the human mouth {q. v. tables of measurements). The name cuspid is given to this tooth because its crown is surmounted by a single strong cusp. THE UPPER CUSPID. 33. The labial surface of the crown of the upper cuspid (Fig. 18) is a little narrower in the mesio-distal direction than in the central incisor, with nearly equal length from the point of the cusp to the gingival line. Instead of a straight, or only slightly curved-cutting edge, as in the in- cisors, the central portion of the crown is extended into a well-formed point (a), with a cutting edge sloping away to the mesial and distal angles (^, h). Of these cutting edges, the distal is a little the longer, and, from the angle to the gingival line, the distal surface is a little shorter, than the mesial. In unworn teeth, the angle formed by the union of the cutting edges from the cusp is usually about ninety degrees, or a square. The point is a little rounded, but the cusp is soon much rounded or flattened by wear. Both the mesial and distal margins of the labial surface of the crown, from the angles to the gingival line, slope toward the central axis of the tooth, — the distal the most, narrowing the crown of the neck nearly one-third from the width of its widest point. The curvature of the gingival line on this surface, marking the termination of the crown, is about a quarter circle. The surface is convex in all directions, and is much more rounded in the mesio-distal direction, than in the Fig. 18. Fig. 19. Fig. 20. Fig. 21. Fig. 22. Fig. 24. Fig 23 Fig. 18 * (Par. 33).— Right Uppee Cuspid, Labial Surface. a. Point of cusp ; d, labial ridge ; e, labial grooves ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root. Fig. 19 * (Par. 34).— Right Upper Cuspid, Lingual Surface. The more common form, a, Point of cusp ; e, e, lingual grooves ; d, gingival ridge ; /, gingival line ; g, me- sial angle ; h, distal angle ; i, body of root ; k, apes of root. Fig. 20 * (Par. 34).— Right Upper Cuspid, Lingual Surface of irregular foi-m. a, Point of cusp ;■. d, linguo-gingival ridge ; e, e, lingual grooves ; /, gingival line ; g, me- sial angle ; h, distal angle ; m, prominent lingual ridge ; n, two small tubercles on linguo- gingival ridge. Fig. 21 * (Par. 35).— Right Upper Cuspid, Mesial Surface, a, Point of cusp ; b, mesial marginal ridge ; e, point of slight concavity of mesial surface ; d, linguo-gingival ridge ; e, labial groove ; /, /, gingival line ; g, mesial angle ; i, body of root ; k, apex of root. Fig. 22* (Par. 37).— Left Upper Cuspid, with a very long and croolied root. Fig. 23* (Par. 37).— Right Upper Cuspid, with a peculiarly crooked root. Fig. 24* (Par. 87).— Left Upper Cuspid, with a very small and short root. * Illustration, IJ^ diameters. c THE UPPER CUSPID. 35 incisors. In the direction of its length, the convexity is about the same as in the incisors. The greater convexity mesio- distally is caused by a strong labial ridge {d) running from the point of the cusp to the gingival line. This ridge occu- pies so much of the surface of the tooth that its margins are imperfectly defined. It belongs to the middle lobe, developed from the middle plate, which, in the incisors, is the smallest of the three, but in this tooth is much the largest. There are two labial furrows (e), or a flattening of the convexity between the central line of the ridge and each angle, marking the junction of the lobes. These furrows are usually lost by becoming shallower before reachino; the center of the lenscth of the crown. In well-formed teeth, this surface presents a uniform enamel, free from pits or sulci. 34. The lingual surface (Fig. 19) presents the same general marginal configuration as the buccal, though it is somewhat narrower toward the gingival line. This is caused by the arc of convexity being a smaller circle, and by the flattening of the proximate surfaces on lines which converge rapidly to the lingual. This surface is usually almost straight from the cusp to the gingival ridge, or cingulum, but is sometimes slightly concave. The gingival ridge is sharply convex and longer from the gingival line to the point of convexity than in the incisors. (Fig. 21, d). Mesio- distally this surface is slightly convex in its central part on account of the lingual ridge which runs from the point of the cusp nearly, or quite, to the cingulum. On each side of this, and between it and the marginal ridges, there is a slight but well defined concavity and furrow, marking the conflu- ence of the lobes. The marginal ridges arise from the mesial and distal angles and unite with the gingival ridge or cingu- lum. These ridges are usually large near the angles, and much less pronounced toward the gingival ridge. The latter is prominent, and is often raised into a tubercle, or slight cusp. Occasionally this part of the enamel is thrown into 36 THE LOWER CUSPIDS. irregular folds, with grooves between, which are sometimes fissured. More rarely the small cusp may be divided by a groove (Fig. 20, n). The linguo-gingival groove is often pronounced in unworn teeth. 35. The mesial surface, near the angle (Fig. 21), is convex in all directions, but becomes flattened, and occasion- ally sightly concave, near the gingival line (c). 36. The distal surface is similar to the mesial, but ia more convex, usually being well rounded in the labio-lingual direction to the gingival line. But in the direction of the long axis of the tooth this surface, on account of the projec- tion of the distal angle, is first convex, and further toward the gingival line is concave, especially near, and at the neck of the tooth. The labio-lingual curvature of the gingival line is about 2.5 m.m., varying from 1.0 m.m. to 3.5 m.m. on the mesial surface, and a little less on the distal. 37. The root of the upper cuspid is the longest in the human mouth, averaging, according to my measurements, 17.5 m.m., and varying from 11.0 to 21.0 from the apex to the gingival line at the buccal surface. It is irregularly conical in form, tapering from the neck to the apex. Its labio-lingual diameter is a little greater than its mesio-distal, which gives the root a flattened appearance, but it is seldom entirely flat on either the mesial or distal surface. In most examples the body of the root is straight, and tapers to a slender point, which is often curved to the labial and distal, though the form of this root presents great variations. Fre- quently, it is very crooked, perhaps, because, when it is taking its place in the arch, it is often crowded by the teeth mesial and distal to it, so that its growth in a right line is inter- rupted. (See Figs. 22, 23 and 24). THE LOWER CUSPIDS. 38. In their general figure, the lower cuspids so closely resemble the upper, a description of their differences will be Fig. 28. Fig. 29. Fig. 25* (Par. 38).— Left Lower Cuspid, Labial Surface, a, Point of cusp ; b, mesial surface ; c, distal surface ; d, labial ridge ; e, distal labial groove ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root. Fig. 26 * (Par. 38).— Left Lower Cuspid, Mesial Surface, a, Point of cusp ; d, linguo- gingival ridge ; /, gingival line ; g, mesial angle ; i, body of root, which is distinctly flattened ; k, apex of root. Fig. 27 * (Par. 38).— Left Lower Cuspid, Distal Surface, a, Point of cusp ; c, labial groove ; d, linguo-gingival ridge ; e, concavity of the distal cutting edge where the groove passes over it ; /, gingival line ; h, distal angle ; i, body of root ; k, apes of root. Fig. 28* (Par. 39).— Left Lower Cuspid, Lingual Surface, a, Point of cusp; d, linguo-gingival ridge ; e, lingual grooves ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root ; I, distal marginal ridge ; m, lingual or triangular ridge ; n, mesial marginal ridge. Fig. 29* (Par. 40).— Right Lower Cuspid, Mesial Surface, a, Point of cusp; d, linguo-gingival ridge ;/, gingival line ; g, mesial angle. The root is short and thick. * Illustration, IJ^ diameters. THE BICUSPIDS. S9 sufficient. It is slightly smaller than the upper cuspid, and the crown is a little longer, which makes it appear more slender. The mesial surface is usually nearly straight the entire length of the root and crown (Figs. 25 and 26) ; so that the increased width of the crown over the root is mainly on the distal. This causes a marked prominence of the dis- tal angle. In many examples this gives the tooth the ap- pearance of being bent, with a considerable concavity on the distal side. In young, unworn teeth, the cusp is rather more prominent and pointed than in the upper cuspid, and the distal cutting edge is proportionately longer; but, as the point of the cusp comes directly in occlusion with the upper teeth, it is soon worn to a blunt point, or a flat surface^ inclining to the labial, sloping away to the distal. 39. The lingual surface (Fig. 28) is very smooth, and the ridges are less prominent than in the upper cuspid. A tubercle on the gingival ridge is rare. The developmental lines, or grooves, are the same as those of the upper cuspids,, but less prominent. Yet, generally, they can be seen in un- worn teeth. Fissures are seldom seen in any part of this tooth. 40. The root of the lower cuspid (Figs. 25 to 29) is shorter than the upper, and generally more flattened in the mesio-distal diameter, often presenting deep furrows. la rare instances, there is a division of the root near the ex- tremity. The root is nearly straight, and in many examples the lingual surface of the root is nearly a straight line, while the buccal surface, root, and crown, present a nearly regular convexity. The root is not so often abnormally crooked as that of the upper cuspid, though, like the upper, the root is much inclined to end in a slender apex; which is often slightly bent in the labial direction. THE BICUSPIDS. 41. There are eight bicuspids, or premolars, two on each side in the upper jaw, and two on each side in the lower jaw- 40 UPPER FIRST BICUSPID. Hence tliey are called the first and second bicuspids. They are situated between the cuspids and first molars, and are the fourth and fifth teeth from the median line. The bicus- pids, though unlike the incisors and cuspids in the contour of their crowns, have the same number, and a similar dis- tribution of primary parts, or lobes. They are, indeed, formed on the same general plan. The change of form is the result of a different relative development of the parts, by which the cingulum, or gingival ridge, is elevated into a powerful lingual cusp ; which, in the upper bicuspids, is almost or quite as high as the buccal cusp, but in the lower bicuspids, especiallj" in the first, this is less prominent. The central lobe also forms a relatively larger part of the buccal portion of the crown than in the incisors and cuspids ; while the mesial and distal lobes are relatively smaller. By the de- velopment of the lingual cusp of the upper bicuspids, the linguo-gingival groove of the incisors and cuspids {q. v. 21) is carried to the central part of the crown, which it traverses from mesial to distal in a deep sulcus (Fig. 30). It is natu- rally divided by the mesial and distal pits, found at its junction with the triangular grooves, into three parts : me- sial (o), central (/), and distal [jp). In the lower bicuspids "the lingual lobe is often very small and the course of the grooves irregular. UPPER FIRST BICUSPID. 42. The outline of the occluding surface of the upper first bicuspid (Fig. 30), when seen in a line with the long axis of the tooth, is irregularly quadrilateral, or trapezoidal in form. The bucco-lingual diameter is about two-ninths greater than the mesio-distal. The flattened proximate surfaces converge toward the lingual, so that the mesio-distal measurement of the buccal portion is a little greater than the lingual. The buccal and lingual surfaces are convex. The buccal convexity forms an arc of about a quarter circle, and merges into the proximate surfaces by obtuse, but well Fig. 30. Fig. 32. Fig. 33. Fig. 34. Fig. 30* (Par. 42).— Right Upper Fiest Bicuspid, Occluding Subface. a, Point of buccal cusp ; b, lingual cusp ; c, buccal ridge ; d, mesial marginal ridge ; e, distal margi- nal ridge ; /, triangular ridge of the buccal cusp ; g, distal angle ; h, mesial angle ; i, triangular ridge of the lingual cusp; I, central groove; o, mesial groove; p, distal groove ; n, m, triangular grooves ; r, s, buccal grooves. Fig. 31* (Par. 46).— Right Upper First Bicuspid, Buccal Surface, a, Buccal cusp; c, buccal ridge ; e, e, buccal grooves ; /, gingival line ; g, mesial angle ; h, distal angle ; i, buccal root ; k, lingual root. Fig. 32 * (Par. 48).— Right Upper First Bicuspid, Mesial Surface, a, Buccal cusp ; b, lingual cusp ; c, mesial angle ; d, mesial surface and point where there is often a con- cavity ; /",/, gingival line ; e, lingual root ; g, buccal root. Fig. 33 * (Par. 50).— Upper First Bicuspid, Avith three roots. Bucco-mesial angle. Fig. 34* (Par. 50).— Upper First Bicuspid, with three short roots and of a peculiar form. Fig. 35* (Par. 50).— Upper First Bicuspid, with a single, very long, crooked root. * Illustration, 1}^ diameters. UPPER FIRST BICUSPID. 43 defined, angles (A, g). The lingual surface forms an arc of nearly half a circle, and merges into the proximate surfaces without any angular prominence. 43. The occluding surface has two prominent cusps — the buccal («), and the lingual (6) — and is transversed from mesial to distal by a deep sulcus. The buccal cusp is the larger, and forms the terminal point of the buccal surface. From the point of this cusp, four ridges lead away at right angles. Two of these form cutting edges, which slope away mesially and distally to the mesial (A) and distal angles (^), where they join the marginal ridges. The central buccal ridge (c) leads away centrally on the buccal surface toward the gingival line, forming the convexity of this surface. The triangular ridge (/) slopes down to the central part of the crown and joins a similar ridge from the lingual cusp (i) to form the transverse ride, or ends in a central sulcate groove {I). The lingual cusp (6) is in the form of a crescent ; its convexity forms the occluding margin of the lingual surface. Instead of a well defined point it usually presents a blunt edge, which runs around its elevated central portion, and joins with the marginal ridges at both angles. The lingual triangular ridge {i) leads down from the central point of the cusp to the central groove, to join its fellow from the buccal cusp in the formation of the transverse ridge, or is divided from it by a deep central sulcate groove. The ridge is seldom prominent. Yery frequently the central incline of the lingual cusp is a plain surface. 44. The marginal ridges, mesial {d) and the distal (e), are strong ridges of enamel which rise in the mesial and distal terminations of the cutting edges of the buccal cusp, and form the mesial and distal margins of the occluding surface. They join with the ridge forming the lingual cusp. Or they are usually divided from the latter by the mesial and distal grooves ; though the latter are often indistinct, especially in teeth that have been somewhat worn. 44 UPPER FIRST BICUSPID. 45. The occluding surface of the bicuspid has five developmental grooves ; the central (1), mesial (o), distal (p), mesial triangular (?n), and distal triangular (n). The central groove is deeply sulcate, and divides the triangular ridges, or passes over their junction as a shallow line, and sinks into a triangular pit at either end. The mesial and distal grooves are really continuations of the central, which pass over the marginal ridges as very fine lines, or as more marked grooves, and mark the boundary of the lingual lobe. They are rarely fissured, while the central groove is frequently fissured throughout its course. The triangular grooves, mesial (m) and distal (w), run from the mesial and distal pits toward the mesial and distal angles, dividing the marginal ridges from the triangular. They are occasionally sulcate in the first part of their course, and are generally lost toward the buccal angles by becoming shallower ; but in young, unworn teeth they can often be followed as a fine line running over the cutting edges of the buccal cusp near the angles, and leading into the buccal grooves (r, s). These are the marks of confluence of the mesial and distal lobes with the median or central lobe. In the central incline of the lingual cusp, supplemental grooves are often seen meeting the triangular grooves of the buccal side. The triangular grooves are occasionally fissured for a short distance from their junction with the central. 46. The buccal surface of the upper first bicuspid (Fig. SI) is similar to the labial surface of the cuspid {q. v, 33). The cusp is usually nearer the center of the crown, and generally somewhat to the distal ; therefore, the cutting edges which run from the summit of the cusp to either angle may be of about equal length. In some examples the distal edge is the longer ; but usually the mesial edge is the longer. In the gingival half of its length this surface is smoothly convex from mesial to distal ; but further toward the occluding margin, the buccal ridge, which terminates in UPPER FIRST BICUSPID. 45 the cusp, becomes more prominent, and a shallow buccal groove (e, e) appears at both sides of the ridge, or between it and the angles. This surface is also considerably narrowed toward the gingival border, almost equally on the mesial and distal, so that the crown seems much broader at the occluding surface. 47. The lingual surface is regularly convex from mesial to distal. From the gingival margin to the summit of the lingual cusp it is often a straight line ; but more generally it is slightly convex, in manj examples almost as convex as the buccal surface. 48. The mesial surface (Fig. 32) is much flattened from buccal to lingual, but is generally slightly convex over its whole extent ; yet in many examples there is a slight con- cavity near the gingival line. In the direction from the gingival line to the occluding margin, this surface is slightly convex through its whole length, but not equally so through its buccal and lingual half. The lingual portion is progress- ively more rounded toward the occluding surface ; while the buccal portion is nearly straight to the angle.* 49. The form of the distal surface agrees substantially with the mesial, but is rather more convex in all directions and any concavity is rare. 50. The root of the upper first bicuspid is usually either much flattened and grooved on its mesial and distal sides, or separated into two divisions, one-third to two-thirds of its length, making one buccal and one lingual root. More than half have their roots thus divided. When separated, the roots taper regularly to slender apexes. When not divided, the apex is apt to be obtuse. Occasionally this tooth pre- sents three divisions of the root, two buccal and one lingual * The form of the proximate surfaces is especially important in making contour fillings, for any concavity increases the difficulty of forming good, clean margins at the gingival border. The unequal convexity of the buccal and lingual halves is important, and requires a special adaptation of instru- ments to make a perfect contour and good clean margins. 46 UPPER SECOND BICUSPID. (Figs. 33, 34). In some instances the root of this tooth is very crooked or otherwise distorted (Fig. 35). UPPER SECOND BICUSPID. 51. The upper second bicuspid so nearly resembles the upper first, just described, that a notice of its differences will be sufficient. It is a little smaller, and in every way more slender.* The general form of the occluding surface (Fig. 36) is similar to the first bicuspid. It presents a buccal and a lingual cusp, and similar sulcus, ridges, grooves, and pits. The average height of the cusps is considerably less than in the first bicuspid. The marginal ridges are propor- tionally broader, the mesial and distal pits closer to each other, and the central groove shorter. The triangular grooves join the central groove nearer the mesio-distal center of the tooth, making the buccal triangular ridge narrower and more nearly pointed. In many examples the enamel of the occluding surface is thrown into several shallow wrinkles, or supplemental grooves and ridges, which radiate from the central groove, which occurs but rarely in the first bicuspid. The buccal cusp is a little nearer the mesial than the distal angle, so that the distal edge is slightly the longer. 52. From mesial to distal, the buccal surface (Fig. 37) is not so broad at the occluding surface, and is a little broader at the neck, so that it has not so much of the bell-crown ap- pearance as the first bicuspid. Otherwise, this surface has the same, but less definitely defined, outlines and markings. The mesial and distal surfaces (Figs. 38 and 39) are generally slightly more convex, and the crown more smoothly rounded. The mesial surface seldom shows a concavity. The lingual surface is usually a little more rounded toward the cutting edge or crest of the cusp. Generally, the distal side of the lingual cusp is rounded to such an extent as to bring the summit of the cusp to the mesial of the central line of the * The popular opinion is that the second bicuspid is the larger. Fig. 36. Pig. 40. Fig. 41. Fig. 36* (Par. 51).— Eight Upper Second Bicuspid, Occluding Surface, o, Point of buccal cusp ; 6, lingual cusp ; e, buccal ridge ; e, mesial marginal ridge ; d, distal margi- nal ridge ; /, triangular ridge of the buccal cusp ; g, mesial angle ; U, distal angle ; i, tri- angular ridge of the lingual cusp ; I, central groove ; m, n, triangular grooves ; o, p, buccal grooves. Fig. 37* (Par. 52).— Right Upper Second Bicuspid, Buccal Surface, a. Point of buccal cusp ; c, buccal ridge ; e, e, buccal grooves ; /, gingival line ; g, mesial angle ; h, distal angle ; i, body of root ; k, apex of root. Fig. 38 * (Par. 52).— Right Upper Second Bicuspid, Mesial Surface, a, Buccal cusp ; b, lingual cusp ; /, gingival line ; i, groove in the mesial side of the root. Fig. 39 * (Par. 52).— Right Upper Second Bicuspid, Distal Surface, a, Buccal cusp ; 6, lingual cusp ; c, carous cavity near the proximate contact point ; /, gingival line ; i, groove in distal side of root. Fig. 40* (Par. 53).— Upper Second Bicuspid, with a very crooked root. Fig. 41* (Par. 53).— Upper Second Bicuspid with a very short crook of the root. ' Illustration, IJ^ diameters. LOWER FIRST BICUSPID. 49 tooth. The gingival line, in its course round the neck of the tooth, makes but a slight labio-lingual curvature on the mesial surface. Generally there is no curvature on the dis- tal surface. 53. The root of the upper second bicuspid is a little longer than the first, while the crown is slightly shorter, which makes the proportionate increase of length appear considerable. The root is rarely divided in any part of its length, but is much flattened from the neck to the apex. The mesial side is often deeply grooved in the apical third of its length ; the distal side is less frequently grooved. The root tapers very gradually, remaining broad in the bucco- lingual diameter, and ends in a blunt apex. A few have a root that tapers rapidly, becomes more rounded, and ends in a slender apex. Crooked roots are more frequent in this than in the other bicuspids. (Figs. 40 and 41). LOWER FIRST BICUSPID. 54. This tooth is the smallest of the bicuspids. The occluding surface diflfers much from the upper first bicuspid. Indeed, the lingual cusp is so nearly wanting, it would hardly be called a bicuspid except for its association. The buccal cusp is large and prominent, and so much is the buccal surface inclined toward the long axis of the tooth, that, when seen in a line with the long axis of the tooth, its jDoint occu- pies a position about one-third distant from the buccal to- ward the lingual outline of the crown (Figs. 42 and 43). The buccal cusp presents the same ridges leading from its summit as described for the upper first bicuspid (43), but the pair which form the cutting edges usually form a curve with its convexity to the buccal, and merge into the marginal ridges by more rounded angles. The buccal triangular ridge is narrow and prominent (/), and joins the elevated lingual ridge, or cusp (6), forming a complete transverse ridge. In many instances, this is deflected to the mesial or distal. In 50 LOWER FIRST BICUSPID. young teeth, the central groove often crosses the transverse ridge as a fine line, which soon disappears by wear. How- ever, in many examples the transverse ridge is divided by a deeply sulcate groove. There is a deep pit at the mesial and the distal ends of the central groove, or on either side of the transverse ridge (c, d) from which the triangular grooves, which divide the marginal ridges from the triangular, or transverse ridge, run toward the distal and buccal angles. These are often sulcate in the first part of their course. In many young teeth these grooves may be traced over the euttino; eds-es onto the buccal surface, markino; the confluence of the central with the mesial and distal buccal lobes. 55. The lingual lobe varies much in its size and outline. It is divided from the three buccal lobes by the mesial, distal, and central grooves ; and often occupies but a small portion of the lingual margin of the occluding surface. The grooves which mark its outlines are often indistinct, and often obliterated by wear. The lobe may form a ridge of even height, and join the marginal ridges, or it may be elevated into one or more tubercles. It may, also, be raised into a small cusp, located centrally, or to either side of the central line of the tooth. 56. The marginal ridges are occasionally quite small, but in most examples they are well developed, and cause the mesial and distal surfaces to stand out prominently, giving the tooth a strong bell-crowned appearance. The length of the marginal ridges vary with the size of the lingual lobe. 57. The buccal surface (Fig. 44) is convex in all direc- tions. The cusp is to the distal of its perpendicular line, and its figure similar to the upper first bicuspid, except that its surface is more convex. As the occlusion is directly on the point of the cusp, as with the anterior lower teeth gener- ally, it is soon so worn down that its prominence is lost. 58. The mesial and distal surfaces are convex from buccal to lino-ual. In the direction from the occluding Fig. 45. Fig. 46. Fig. 47. Fig. 42* (Par. 54).— Right Lowee First Bicuspid, Occluding Surface, a, Point ot ■buccal cusp ; &, lingual cusp or ridge ; c, buccal ridge ; d, mesial marginal ridge ; e, dis- tal marginal ridge ; /, triangular ridge of buccal cusp or buccal triangular ridge ; ff, m.esial angle; h, distal angle; i, central groove crossing the transverse ridge; I, mesial pit ; 0, p, buccal grooves. Fig. 43 * (Par. 54).— Lower First Bicuspid, Occluding Surface, a, Point of buccal cusp ; 6, lingual cusp or ridge ; c, triangular ridge of buccal cusp deflected to one side ; d, triangular groove with fissure ; e, mesial marginal ridge ; /, distal marginal ridge. Fig. 44 * (Par. 57).— Right Loaver First Bicuspid, Buccal Surface, a, Buccal cusp ; d, buccal ridge ; e, e, buccal grooves ; /, gingival line ; g. distal angle ; h, mesial angle ; i, body of root ; k, apes of root. Fig. 45* (Par. 58).— Left Lower First Bicuspid, Mesial Surface, o. Buccal cusp; b, lingual cusp or ridge ; c, distal marginal ridge ; d, triangular ridge of buccal cusp ; e, mesial marginal ridge ; /, gingival line. Fig. 46 * (Par. 59).— Left Lower First Bicuspid, Lingual Surface, a, Buccal cusp ; b, lingual cusp or ridge ; c, distal marginal ridge ; d, triangular ridge of buccal cusp ; e, m.esial marginal ridge ; /, gingival line. Fig. 47 * (Par. 59).— Right Lower First Bicuspid, Lingual Surface, a, Buccal cusp ; b, lingual cusp or ridge ; d, triangular ridge of buccal cusp ; e, e, marginal ridges ; /, gingival line. = Illustration, IJ^ diameters. LOWER SECOND BICUSPID. 53 margin to the gingival line, they are generally concave, after passing the convexity of the immediate occluding margin. This latter stands out boldly to both mesial and distal, giving a marked bell-crowned form. The concavity of the mesial and distal surfaces is not so well seen from the buccal view as from the lingual. The greater over-hang of the crown (over the root), and the greater concavity, is toward the lingual portion. 59. The lingual surface (Figs. 46 and 47) is smoothly rounded from mesial to distal, and slightly convex in the direction of the length of the tooth. It is only about half as long as the buccal surface (in unworn teeth), and when viewed at right angles with the long axis of the tooth, all of the occluding surface on the lingual side of the buccal cusp is seen except the pits and sulci. 60. The neck of the tooth is much constricted, and has a deep gingival line at the junction of the enamel and ce- mentum. This makes the proper adjustment of a band for an artificial crown particularly diflacult. The curvature of the gingival line is much less than in the upper first bicus- pid, the average being less than one millimeter {q. v. table of measurements). 61. The root of this tooth is somewhat flattened at the neck, on lines that converge rapidly toward the lingual, and often grooved on its mesial and distal sides, and sometimes the root is bifurcated. It tapers regularly, with a tendency to a more nearly round form at the apex, and generally ends in a slender point. The root is generally straight, or the lingual surface is straight, and the buccal surface convex. This convexity extends from the apex of the root to the point of the crown, which gives that characteristic appear- ance so peculiar to the anterior lower teeth. LOWER SECOND BICUSPID. 62. The lower second bicuspid is a little longer than the lower first, and of much the same figure, except that the 54 LOWER SECOND BICUSPID. lingual cusp is proportionately higher and more nearly, hut never quite, on a level with the buccal, but the lingual sur- face is about equal to the buccal in mesio-distal breadth. These teeth are regular in general contour, but the grooves of the occluding surface are much diversified. These differ- ences may be classified under three forms : 1st. The central groove joins the triangular grooves in such a way as to form a half circle with the convexity to the lingual, with or with- out a transverse ridge crossing its line. In these, when the transverse ridge is high, only a deep pit appears on either side (Fig. 48). 2d. The lingual cusp is divided by a sulcate groove, which runs over centrally, or nearly so, to the lingual surface, making a three-cusped tooth (Fig. 49). The central groove forms an angle at the junction with the lingual, or is crescentic in form. It joins with the triangular grooves in such a way that the point of junction cannot be told except by finding the mesial and distal grooves, which are often very indistinct. 3d. The central groove is straight, and generally sulcate, with a deep pit at both ends. In many examples these pits are crossed by the triangular grooves almost at right angles with the central (Fig. 50). By trac- ing the fine mesial and distal grooves carefully in young, unworn, teeth, it will be found that the lingual lobe is much larger than in the lower first bicuspid, and almost as large as in the upper bicuspids. In the three-cusped forms the two lingual lobes are usually a little broader from mesial to dis- tal than the buccal portion of the tooth. 63. The buccal surface (Fig. 51) of the lower second bicuspid does not differ from the other bicuspids, except in being shorter, the cusp lower, and the lingual surface (Fig. 52) broader and smoothly convex ; in the three-cusped forms it is often somewhat flattened and grooved in its occluding third, giving the crown a squarish appearance, or even triangular when the lingual lobes are large. 64. The mesial and distal surfaces in these bicuspids are Fig. 49. Fig. 50. Fig. 51. Fig. 52. Fig. 53. Fig. 48* (Par. 62).— Left Lower Second Bicuspid, Occluding Surface, a, Buccal cusp ; 6, lingual cusp or ridge ; c, e, marginal ridges ; d,f, pits ; g, h, triangular grooves. Fig. 49* (Par. 62).— Right Lower Second Bicuspid, Occluding Surface, with, three cusps, a, Buccal cusp ; b, disto-lingual cusp ; c, mesio-lingual cusp ; d, lingual groove ; e, e, mesial and distal grooves. Fig. 50 * (Par. 62).— Right Lower Second Bicuspid, Occluding Surface, with straight central groove, a, Buccal cusp ; 6, lingual cusp ; c, e, marginal ridges ; d, triangular ridge of the buccal cusp ;/, central groove ; g, h, triangular grooves. Fig. 51 * (Par. 63).— Left Lower Second Bicuspid, Buccal Surface, a, Buccal cusp ; d, buccal ridge ; e, e, buccal grooves ;/, gingival line ; g, mesial angle ; /(, distal angle ; i, body of root ; k, apex of root. Fig. 52 * (Par. 63).— Right Lower Second Bicuspid, Lingual Surface, a, Buccal cusp ; b, lingual cusp ; c, distal marginal ridge ; d, triangular ridge of the buccal cusp ; e, mesial marginal ridge ; /, gingival line. Fig. 53* (Par. 64).— Left Lower Second Bicuspid, Mesial Surface, a, Buccal cusp; 5, lingual cusp ; d, triangular ridge ; e, mesial marginal ridge ; f, gingival line ; i, groove in mesial side of the root. * Illustration, IJ^ diameters. THE MOLAR TEETH — THE UPPER MOLARS. 57 a little flattened, but remain convex from buccal to linsual. Ifrom the occluding margin to the gingival line, they are nearly straight, though some are convex and some in part concave. 65. The root of the lower second bicuspid is larger and longer than in the first bicuspid. It is flattened on the mesial and distal surfaces on nearly parallel lines. In some examples they are concave or grooved. In rare instances the root of this tooth is grooved on the buccal and lingual sides, with a tendency to a division into a mesial and distal prong. In the greater number it tapers regularly to a slender apex, but in many, the apex is large and obtuse. The root is generally straight, but occasionally very crooked. THE MOLAR TEETH. 66. The molar teeth are very different in form and plan of construction from those previously described. They are particularly designed for grinding or comminuting food ; for this purpose have broad, occluding surfaces, broken by ridges, grooves, and fossse. The ridges are raised at intervals into powerful cusps, which fit with more or less accuracy into the sulci and fossae of the opposing teeth. There are twelve molars, three on each side of both jaws. They are the sixth, seventh and eighth teeth from the median line, and are com- monly named the first, second and third molars, upper and lower. The last is also called the wisdom tooth, or Dens Sapientia. The upper and lower molars are much alike in size and general contour, but in the detail of the arrange- ment of their lobes, cusps, fossae and grooves, they are dif- ferent. It will, therefore, be necessary to describe the upper and lower molars separately. THE UPPER MOLARS. 67. The three upper molars are similar, but present minor differences of detail, consisting mostly in a less pro- 58 UPPER FIRST MOLAR. nounced, or typical development of certain parts, or lobes, of the second and third molars. The upper first molar being the typical form, will be described first, and afterward the deviations from this type that occur in the second and third, molars. UPPER FIRST MOLAR. 68. The occluding surface of the upper first molar (Fig. 54), when seen in a line with the long axis of the tooth, pre- sents an outline of irregular rhombic form, with the mesio- buccal and disto-lingual as acute angles. The angles are rounded, with more or less convexity of the marginal lines. This surface presents two principal fossae, and four devel- opmental grooves. These grooves divide the crown into four lobes, or primary developmental parts, each of which is surmounted by a strong cusp. These lobes, or cusps, are the mesio-buccal (Fig. 54, a), disto-buccal (6), mesio-lingual (c), and disto-lingual {d). Of the grooves which outline these parts, three rise from the ceutral pit of the central fossa : The mesial (A), which runs to the mesial margin ; the buccal (^), which runs in a deep sulcus to the buccal margin, and over it onto the buccal surface ; and the distal (^"), which runs distally, and lingually, over the transverse ridge and ends in the distal fossa {k). The remaining groove — the disto-lingual (^, k) — begins a little to the buccal of the cen- tral part ot the distal margin, and runs diagonally in a straight line, or in a curve with the concavity toward the disto-lingual angle, to the lingual margin, and over it onto the lingual surface, to become the lingual groove. Except that part crossing the distal marginal ridge, this groove is usually deeply sulcate. 69. In their origin, each distinct portion begins its calcification as a separate piece, plate, or cusp, and moves apart from the others as growth proceeds, till the proper di- mensions of the occluding surface is attained ; then they coalesce on the lines marked by these grooves, and thus com- Fiff. 58. Fig. 54* (Par. 68.)— Right Upper First Molar, Occluding Surface, witli four cusps. a, Mesio-buccal cusp ; 6, disto-buccal cusp ; c, xaesio-lingual cusp ; d, disto-lingual cusp ; f, mesial marginal ridge ; g, distal marginal ridge ; h, mesial groove ; i, buccal groove ; j, distal groove ; k, k, disto-lingual groove ; m, mesio-buccal triangular groove ; n, disto- buccal triangular ridge ; this unites with the distal ridge from the lingual cusp to form the oblique ridge ; o, disto-buccal triangular groove ; p, mesio-buccal triangular ridge ; q, central pit. Fig. 55* (Par. 70).— Right Upper First Molar, Occluding Surface, with five cusps. a, Mesio-buccal cusp ; 6, disto-buccal cusp ; c, mesio-lingual cusp ; d, disto-lingual cusp ; e, fifth cusp ; /, mesial marginal ridge ; g, distal marginal ridge ; h, mesial groove ; i, buccal groove ; j, distal groove ; k, k, disto-lingual groove ; I, k, mesio-Ungual groove. The Ungual cusps are faceted by wear ; m, mesio-buccal triangular groove ; n, disto- buccal triangular ridge. • Fig. 56* (Par. 78).— Right Upper First Molar, Buccal Surface, a, Mesio-buccal cusp ; 6, disto-buccal cusp ; c, mesio-lingual cusp ; d, disto-lingual cusp ; e, buccal ridge ; f, gingival line ; g, mesial angle ; h, distal angle ; i, buccal groove ; k, mesial root ; I, dis- tal root ; m, lingual root. Fig. 57* (Par. 79).— Right Upper First Molar, Lingual Surface, a, Mesio-buccal cusp; &, disto-buccal cusp; c, mesio-lingual cusp; d, disto-lingual cusp; e, fifth cusp; f, gingival line ; g, disto-lingual groove ; h, mesio-lingual groove ; i, lingual groove ; k, mesial root ; I, distal root , m, lingual root. Fig. 58* (Par. 80).— Right Upper First Molar, Mesial Surface, a, Mesio-buccal cusp ; b, disto-buccal cusp ; e, mesio-lingual cusp ; d, disto-lingual cusp ; e, fifth cusp ; f, f, gingival line ; h, mesio-lingual groove ; k, mesial root ; I, distal root ; m, lingual root. * Illustration, 1^ diameters. UPPER FIRST MOLAR. 61 plete the occluding surface. When the union has been com- pleted, nothing but fine lines remain, which, on any plain parts, are often quickly obliterated by wear. But on parts meeting at an angle, forming a sulcus, as in the buccal and disto-lingual grooves, there is usually a sharp groove, and at any point where the union has been imperfect, there is a fis- sure. This fissure is most frequent at the ends of the grooves, near the central pit, or where they are deeply sulcate, and in the central portion of the disto-lingual grooves ; but they may occur in any part of these lines. 70. In many examples of the upper first molars, but in no others, there is a small fifth lobe or cusp (Fig. 55, e). This is situated on the lingual side of the mesio-lingual lobe, from which it is divided by a fifth groove, the mesio-lin- gual (^, Z:), which runs from the lingual portion of the mesial margin diagonally to the lingual margin, and joins the lin- gual groove. This cusp, when it occurs, is always bilateral, i.e., on both the right and left upper first molars. It is hereditary, appearing regularly in the teeth of children when present in the teeth of both parents. It occurs also, in a modified form, when present in but one parent. Therefore, the cusp will be found in all possible varieties of develop- ment, from its largest size, as represented in Fig. 55, to the merest line marking its position on the lingual side of the mesio-lingual cusp. 71. The occluding surface of the upper first molar has four marginal ridges, broken by the grooves described (68), so as to form four principal eminences or cusps. These are the buccal, lingual, mesial, and distal-marginal ridges. The buccal-marginal ridge begins at the mesio-buccal angle, in the form of a blunt cutting edge, and rises in a curved line to the summit of the mesio-buccal cusp (Fig. 54, a), from which it descends distally to the buccal groove (z). From the summit of this cusp the mesio-buccal triangular ridge (^) descends to the mesial side of the central pit {q). This ridge 62 UPPER FIRST MOLAR. is divided from the mesial-marginal ridge by the mesio-buccal supplemental groove (m), which is sometimes deep, but gen- erally shallow, and occasionally absent. From the buccal groove the marginal ridge rises rapidly to the summit of the disto-buccal cusp (b), then descends in a curve to the disto- buccal angle, to join the distal-marginal ridge (g). From the point of this cusp the disto-buccal triangular ridge (or tri- angular ridge of the disto-buccal cusp, n), runs down to the distal side of the central pit, where it joins a ridge from the mesio-lingual cusp to form the oblique ridge, or is divided from this ridge by a sulcate distal groove. 72. The lingual-marginal ridge begins at the mesio- lingual angle as a rounded edge, and rises in a curve to the summit of the mesio-lingual cusp (c), and descends, continu- ing its curve, into a ridge, meeting the triangular ridge of the disto-buccal cusp to form the oblique ridge. However, in a less pronounced form, this marginal ridge descends from the summit of the mesio-lingual cusp to the distal, where it is deeply broken by the disto-lingual groove. On the distal side of this groove it rises abruptly to the summit of the disto-lingual cusp (d), from which it slopes away in a curve to join the distal-marginal ridge. 73. The mesial-marginal ridge (/) is a strong band of enamel running from the mesio-buccal to the mesio-lingual angle of the tooth. It forms the mesial boundarj- of the occluding surface, and the angle of junction of the mesial and occluding surfaces, or the mesio-occluding angle. It is low in the center of its length, and rises toward both angles. It is crossed near its center by the mesial groove, usually as a fine line, which is often obliterated by wear early in life. Occasionally one or more small tubercles appear in the cen- tral portion of this ridge, inclosed in what seems to be a division of the mesial groove. 74. The distal-marginal ridge (g) is a band of enamel forming the distal boundary of the occluding surface, from UPPER FIRST MOLAR. 63 angle to angle, and forms the angle of junction between the occluding and the distal surfaces, or the disto-occluding angle. It is low in the centre of its course, and is crossed ■by the distal end of the disto-lingual groove as a fine line, usually a little to the buccal of the central point. 75. The central fossa is irregularly circular, and is formed by the central inclines of the mesial marginal ridge, Tuesio-buccal cusp, disto-buccal cusp, mesio-lingual cusp, and oblique ridge. It is made irregular, and sometimes angular, by the depth of the several sulcate grooves, or by the prom- inence of the triangular ridges, especially that from the mesio-buccal cusp. The central incline of the mesio-lingual cusp is generally a plain surface, but is sometimes slightly concave, and in about a fourth of its examples there is a low, triangular ridge running from its apex directly to the cen- tral pit. The oblique ridge is occasionally cut through by a deep and wide distal sulcus, thus connecting the central with the distal fossa. In a few examples two supplemental grooves or wrinkles arise from the mesial groove at about the center of its length, and run, one toward the mesio-buccal, and the other toward the mesio-lingual angle of the tooth. These are often of such depth and width as to form a small sup- plemental mesial fossa. Of these grooves, the mesio-lingual is generally absent, and the mesio-buccal (m) is generally present, though often very shallow. 76. The distal fossa is formed by the distal incline of the disto-buccal and mesio-lingual cusps and oblique ridge, which meet the central incline of the disto-lingual cusp and distal-marginal ridge. It is traversed by the disto-lingual groove, which is generally sulcate, and deepens into a pit at the point where it receives the distal groove. From the buccal portion a supplemental groove, the disto-buccal, runs M^ell up toward the summit of the disto-buccal cusp, divid- ing its triangular ridge from the distal-marginal ridge. 77. In some molars many supplemental grooves or 64 UPPER FIRST MOLAR, wrinkles radiate from the centers of these fossse on the in- clines of the ridges and cusps, and in some poorly developed teeth these are deeply fissured. The growth of enamel seems to have reached out toward the line of junction in the form of spiculse, and to have failed to fill out the space. 78. The buccal surface of the upper first molar (Fig. 56) is irregularly convex. Its length is about equal to the mesio-distal breadth at the gingival line, while the width at the widest point, near the occluding margin, is about three- tenths greater. Therefore, the mesial and distal margins converge toward the neck. The mesial margin is almost straight, after the rounding of its angle, but the distal is convex. The occluding margin is surmounted by the buccal cusps (a, 6), between which there is a deep notch, through which the buccal groove passes from the occluding to the buccal surface. This groove passes centrally toward the gingival line about half the length of this surface, dividing the occluding portion into a mesial and a distal buccal ridge. In some examples the groove continues across the gingival line to the bifurcation of the roots. There is a bucco-gingi- val ridge of enamel (e) near the gingival line which the buccal groove generally does not cross. The mesio-buccal convexity is greatest on this ridge, and diminishes toward the occluding margin. The summit of this convexity is on the mesial half, in a line with the mesial root, and the sur- face falls away rapidly toward the distal. 79. The lingual surface (Fig. 57) is divided in a line with the long axis of the tooth into a mesial and distal lobe by the lingual groove (z). Both lobes are smoothly convex from mesial to distal, and in a less degree from the gingival line (/) to the occluding margin. The gingival line is nearly horizontal, and so sunken as to give the appearance of a gin- gival enamel ridge. The occluding margin is surmounted by the mesio- and disto-lingual cusps (c, d)^ of which the mesial is usually the larger. In the five-cusped molar the Fia:. 59. Fig. 60. Fig. 61. mp:0^^yJ^'M^^-^''^^^^'-: Fig. 62. Fig. 59* (Par. 81).— Right Uppee, First Molar, Distal Surface, a, Mesio-buccal cusp ; b, disto-buccal cusp ; d, disto-lingual cusp ; /, /, gingival line ; k, mesial root ; I, distal root ; m, lingual root ; o, concavity of tlie distal surface. Fig. 60* (Par. 82).— Left Upper First Molar, Buccal Surface. A bell-crowned tooth. Fig. 61 * (Par. 8b).— Upper First Molar showing the mesial and distal roots united at their apexes. Fig. 62* (Par. 86).— The Right Upper Molars showing the progressive diminution of the disto-lingual cusp from the first to the third molar. * Illustration, 1% diameters. UPPER FIRST MOLAR. 67 fifth cusp (e) is seen on the mesio-lingual lobe. The mesial and distal margins are convex, converging rapidly toward the lingual root. In the few examples in which the lingual groove is not apparent, the lingual surface is smoothly con- vex from mesial to distal. 80. The mesial surface (Fig. 58) is nearly flat in all directions, and its margins are rounded to the buccal and lingual surfaces. Toward the mesio-buccal angle, the flat surface is continued well up to the occluding surface, which it meets in a fairly sharp angle ; but as it approaches the lingual portion it is progressively rounded toward the oc- cluding surface. In many molars, near the gingival line, half way from mesial to distal, this surface is a little concave. 81. The distal surface (Fig. 59), in its lingual half, is convex in all directions, but in its buccal half there is often a concavity formed by a considerable distal protrusion of the disto-lingual lobe. This is a shallow, but marked, depression (o), running from the bifurcation of the distal and the lingual roots toward the disto-buccal cusp. It crosses the gingival line at a point about one-third distant from the buccal to- ward the distal margin. In many examples this depression is more central, and receives the distal termination of the disto-lingual groove, which may often be traced as a flne line nearly or quite to the gingival border of the enamel. This complication of the surface makes the finishing of fillings, and the fitting of bands for crowns, specially diflicult. This depression falls short of forming a concavity in about one- fourth of the first molars. 82. The root of the upper first molar (Figs. 56 to 61) is divided into three prongs* — the mesial, or mesio-buccal * The divisions of the root of a tooth are usually called " the roots," and the upper molars are said to have three roots. The neck of the tooth is, however, common to all, and, more strictly, there is one root divided into several prongs, or fangs. Some authors follow this form of expression. For instance, Prof. Judd says: "The root of a molar is divided into three fangs." I see no good reason, however, for not calling them roots, the term generally in use by the dental profession. 68 UPPER SECOND MOLAR. {k), the distal or disto-buccal {I), and the lingual (m). These are usually quite widely separated, giving the tooth a firm seat in its alveolus. The lingual root is the largest ; it diverges boldly to the lingual, and is straight, or slightly curved with the convexity to the lingual. It is conical, and tapers regularly to an obtuse rounded apex. In most molars it has a groove, a continuation of the lingual, on its lingual side, running nearly, or quite, its whole length. In rare examples this root bifurcates. 83. The mesial root (k) is larger than the distal ; broad from labial to lingual, and thui from mesial to distal, with the lingual portion the thinner, and grooved on its flattened sides. It diverges first to the mesial and buccal, and then curves to the distal. It tapers mostly at the expense of the lingual thin edge, and ends in a flattened or rounded apex. 84. The distal root {I) is the smallest of the three. It diverges to the distal and buccal, and is straight, or slightly curved, sometimes to the distal, sometimes to the mesial, so that its apex approaches the mesial root. It is flattened on its mesial and distal sides, but less than the mesial root, and tapers to a more rounded form, ending in a slender point. 86. The roots of the first molar are, perhaps, more regular in form than those of any other of the molar teeth; but even in these, considerable deviation from the forms de- scribed will occasionally be observed (Figs. 60 and 61). UPPER SECOND MOLAR. 86. The most constant difiference between the occluding surfaces of the upper first and second molars is that the latter tooth is smaller, and has an almost constant tendency to a relatively smaller size of the disto-lingual lobe. This tendency is well seen in Fig. 62, in which the upper molars of a very well formed denture are drawn from the cast. This shows the disto-lingual lobe progressively diminished, so that in the third molar it is very small. When a large Fig. 65. Fig. 66. Fig. 67. Fig 68. Fig. 63* (Par. 86).— Right Uppee Second Molar, Occluding Surface, witli three of the cusps faceted by wear. Tooth large and especially well developed, a, Mesio-huccal cusp ; 6, disto-buccal cusp ; c, mesio-lingual cusp ; d, disto-lingual cusp ; /, mesial mar- ginal ridge ; g, distal marginal ridge ; h, mesial groove ; t, buccal groove ; j, distal groove ; k, disto-Ungual groove ; I, distal fossa ; m, mesio-buccal triangular groove ; n. central pit ; 0, mesio-buccal triangular ridge ; p, disto-buccal triangular ridge ; r, mesio-lingual tri- angular ridge, Fig. 64* (Par. 86).— Right Upper Second Molae, Occluding Surface. Tooth of medium size and imperfect form, a, Mesio-buccal cusp ; h, disto-buccal-cusp ; c, mesio- • lingual cusp ; d, disto-lingual cusp ; /, mesial marginal ridge ; g, distal marginal ridge ; h, mesial groove ; i, buccal groove ; I, distal fossa. The disto-lingual groove is imperfect ; m, mesio-buccal triangular groove ; o, mesio-buccal triangular ridge ; p, disto-buccal tri- angular ridge, which unites with the ridge from the mesio-lingual cusp to form the oblique ridge. Fig. 65* (Par. 87)— Right Upper Second Molar showing a form of deformity peculiar to this tooth that is not very common. Fig. 66* (Par. 89).— Right Upper Second Molar with the roots inclined to the distal. Fig. 67* (Par. 90).— Right Upper Second Molar, Distal Surface, with the three roots compressed into one. Fig. 68 * (Par. 90).— Right Upper Second Molar, showing the distal and lingual roots united. * Illustration, 1}^ diameters. UPPER SECOND MOLAE. 71 number of second molars are examined, it is fomid that the central fossa is not so regularly formed as in the first, being often small, even in large, well-developed teeth (Fig. 63), and the cusps comparatively low, with a relatively greater inclination of the lingual surface toward the summit of the mesio-lingual cusp. In many examples the distal fossa is reduced to a mere pit (Fig. 64), and the lingual marginal ridge is continued from the summit of the mesio-lingual cusp distally to the disto-lingual angle, where it joins the distal marginal ridge, as in Fig. 64, making practically a three-cusped tooth. In many of these, after the tooth is a little worn, the disto-lingual groove cannot be traced across the lingual marginal ridge, nor on the lingual surface ; but a fine line is generally seen crossing the distal marginal ridge. 87. The upper second molar is liable to a peculiar deformity, which I have not seen in any other tooth. The crown is greatly flattened from mesial to distal, occasionally to such an extent as to present none of its usual lines. In the extreme cases (Fig. 65) there is one central, long-shaped sulcus running from buccal to lingual , formed by the central inclines of a ridge encircling the occluding surface. This ridge may be broken at intervals by shallow grooves crossing it. Usually, much of the central inclination of this ridge is wrinkled, and often there are many small fissures. The mesial surface is commonly deeply concave, and the distal convex. 88. In well-developed second molars, the form of the buccal, lingual, mesial, and distal surfaces are much the same as in the first molar, though rather more convex, and concavities in the mesial and distal surfaces are not so frequent. Howeyer, in teeth with large distal cusps, the concavity of the distal surface is about the same as in the first molar (81). The lingual groove is generally not sulcate, though it is usually seen as a fine line in unworn teeth. It is often near the disto-lingual angle, and, when. 72 UPPER THIRD MOLAR. sulcate, it generally disappears by becoming shallower about half-way toward the gingival line ; rarely, it runs across the gingival line, and in that case the lingual root is grooved, as in the first molars. 89. The neck of the tooth is less regular in its outline than in the first molar. In the average, it is more flattened from miesial to distal, and on lines that converge more to the lingual. On the buccal surface, the mesio-buccal ridge is relatively more prominent, and at the neck the surface slopes away more toward the distal, so that, in many examples, the distal root seems compressed between the mesial and lingual roots. 90. The roots of this tooth are the same in number and general form as in the first molar; but they spread less, and are curved more to the distal (Fig. 66). There is also much more variety of the comparative size of the root and crown than in the first molar. In many the root is single, with the outlines of the division marked by grooves of variable depth (Fig. 67); or two of the roots may be connected, while the third is free. Sometimes this union is the lingual with the "distal (Fig. 68) ; but oftener it is the lingual with the mesial root. UPPER THIRD MOLAR. 91. The upper third molar deviates from the typical form of the first more than does the second. Yet, in dent- ures of the best form, it presents the same developmental lines, fosspe, and cusps (Fig. 69). The disto-lingual lobe is very much smaller, and in many examples is entirely want- ing. Of the examples in my possession, about twenty-one per cent, show a diminutive disto-lingual cusp ; thirty-two per cent, show a pit in the position of the distal fossa, and some portion of the disto-lingual groove, but no depressed groove over the lingual-marginal ridge ; it is similar to that shown in Fig. 64. The remainder, or about forty-seven per cent., have no disto-lingual lobe. Of the latter, three-fourths ^.\r^.