C O S G E S I T A L SBSENCE AKD IMPACTION O F THE T H I R D MOLSR I N THE ESKIMO MANDIBLE MARCUS S . GOLDSTEIN Division of Physical Anthropology, 17. S. National Museum A. COXGENITAL ABSENCE The incidence of the absence of the lower third molar in the Eskimo, compared with other peoples, should prove of interest. HrdliEka (’11, p. 407) states that “the tendency toward the loss of the third molar is evidently a n evolutiona r y feature of the human teeth that belongs to the present era, and in some races of man has as yet scarcely begun to be manifest.’’ Some work on the congenital absence of M Jin the Eskimo has already been done. Leigh (’25b, p. 888) states that in fifteen of 324 (4.6 per cent) modern Eskimo crania (U. S. Kational Museum) the third molars had apparently never erupted; it is not clear, however, whether the third molars of the upper, lower, or both jaws a r e meant. Hellmaii (’28) notes 28 per cent congenitally missing third molars in the lower jaws of thirty male Eskimo. My own observations a r e tabulated in table 1. The method of determining congenital absence was as follows. Every mandible was examined f or third-molar absence. When missing, very careful attention was given to any signs of alveolar absorption o r other conditions that would indicate the possibility that the third molar may have once been present. Every case i n which such a suspicion existed, or where the tooth might yet have erupted, was eliminated from the series. The uncertainty arose, however, occasionally when the molar was missing, whether o r not the tooth was impacted o r completely suppressed. Fortunately, Dr. Sterling V. Mead, of Georgetown University, had recently utilized t h e 381 AMERICAN JOURNAL OF P H Y S I C A L AKTHROPOLOGY, VOL. I V I , NO. J AN UA RY - M AR CH , 1932 3 382 MARCUS S. GOLDSTEIK mandibular collections in the C. S. Xational Museum, among which was the Eskimo, in a research on the incidence of impacted teeth, and an x-ray machine had been used in the determinations. Doctor Mead informed me that very rarely was a third molar so completely impacted that i t would not be visible to the eye; so rarely, in fact, that these statistics on the congenital absence of the third molar should not be affected. The d a t a here presented should be, therefore, a faithful representation of the frequency of congenital absence of the lower third molar as observable in the adult Eskimo. TABLE 1 Congrnital absence of $he lower thzrd molar in adult Eskimo __ ____ ________ - I M A MISSING O N O N E SIDE I ~ C , MISSING1 SEX I _. .__ ONBOTH I Males ( 3 6 3 ) Females (380) Totals Per cent of total adult mandibles (759)' ~ ' Sixteen ' Right I, -_ _ Loft I j PEE CENT OFMA TOTAL 'PERCENT w1-m OF J A W S MIssrx(: , CONQENICON I TO Y.. - ' TALLY GENITALLY THAT [HISSING M JY I S S I I G M:i S H O U L D B E lJ.tws I IWITH ~- ~ I 18 GO I 16.50 12.67 ~- JrO - 1 126 21 '1.8 I 3.8 I ~. 16.G I i 13.31 _. ~ mandibles included in t.his total were unsexed. I t is seen that in 16.6 per cent of all the adult Eskimo mandibles the third molar is missing on one or both sides; too, tlie third molar is missing in 13.31 per cent of all the third molars that should normally be present. The absence of the Ma too appears considerably more symmetrical, i.e., occurring on both sides of the jaw, than not. There seems t o be a tendency f o r the absence to occur somewhat more often on the left than on the right side of the mandible. Finally, the third molar is somewhat more frequently missing, absolutely and relatively, in the females than in the males. I n table 2 is recorded the congenital absence of the lower third molar with reference to geographical locality of the individuals represented. The Eskimo a r e divided into the three main subgroups according to HrdliEka's classification ( '30). 383 THIRD MOLAR I N ESKIMO MANDIBLE TABLE 2 Congenital absence of lower third molar of the Eskimo according t o locality _ _ ____ ~ I I.OC.4I.ITY I -- .;-- Southwest and miclwest : Total HISSINQ Ids Both sides .- 1 ’ 46 i Rightside - .- - 7 I Left side .--I I I (mzJ&s) -. - I 18 ! 71 Distinct differences in the extent of mandibular thirdmolar absence appear to exist in the three main groups of the Eskimo. A coiisisteiit percental increase of individuals lacking one or more lower third molars is noted from the southwest to the northwest to the north-northeast ; in other words, with respect t,o third-molar absence, a phenomenon said to indicate progressive involution in the dentition, the southwest Eskimo appear appreciably more primitive than the northwest-north-northeast Eskimo. This is an unexpected showing which stands i n concordance with the results of the preceding study on the cusps of the lower molars. Racial survey Table 3 considers i n brief a racial survey of the incidence of congenitally missing lower third molars. It is interesting to note that the percentages of Hellman and the writer on the Eskimo a re remarkably close. 384 MARCUS S. GOLDSTEIN TABLE 3 9 l u m l survey of the tnctdence of congenitally massang mandbbular third molar8 ~ RACLAL G R O U P ALID AUTHOB Chiuese : Hellmail ( '28) Eskimo : Hellniaii ( '28) Goldstein ~- ' 19' 30 ! 363 males 380 females 759 total' j I I ! i i I I Australian Aboriginal : Hellmau ( '28) I I i ! I i ~ _ _ _ 3.9 28 25.3 88.9 26.6 i I i I ! I 20 lo.s 17.5 13.8 15.9 17 i 1s i 20 i 13 119 I i 11 i ! I I 55 I i Ancient Egyptians : Ruffer ('20) ____. 21 I American iiegroes : Hellman ( '28) ___ 80 males 58 females 138 total I Anisrieaii Indian: Hellmau ( '28) West African iiegroes: Hellman ( '28) 61 2112a ! Mougoloid Buriats Hellmau ( '28) P E R CENT MISSING YQ . -!- I European : Hellmau ( '28) Golbirscli ( '30) Hawaiians : Chappel ( '27) , NUMBER OF J A W S 156' 3.2 I - I 49 _ 0 _ Hellman's figures throughout table are f o r males only. The total includes sixteen unsexed mandibles. Combined males and females. ' N o sex given. The hlongoloid peoples as a whole appear to be most advanced with respect to congenitally missing lower third molars; the whites, browns, and Australians follow, and the negroes, it seems, a r e the least advanced. Curiously enough, the ancient Egyptians appear to present almost no congenitally absent third molars in the mandible. ~ THIRD iMOLAR IX ESKIMO MAh-DIBLE 385 It is noted that congenital absence of the mandibular M:;, presumably a n advanced stage in the evolution of the human dentition, occurs in a relatively high percentage of the Eskimo mandibles, according either to Hellman o r the writer. It seems, therefore, since the Eskimo use their teeth more than most peoples, a n d as much as any, mere use or function has no large correlation with the loss of the mandibular third molar. Some authorities have proposed a s the cause for the absence of the third molar (Tomes, Chappel, Darwin), in the words of Tomes ( ’23, p. 530), “ a consequence of want of space during its formative period.” The writer, on the other hand, agrees with Hellman, who well sums up the sitnation thus ( ’28, p. 173) : The argument, favoring the idea that the congenital absence of the third molar is due to the reduction in size of the jaw and the crowding of dentition, cannot be corroborated. The American Negro, the Eskimo, the Buriat and the Australian Aboriginal do not show any lack of room due to diniinution in size of the jaw, and yet they all present a very high percent of congenitally missing third molars. Vestigial lower third molars A note may be added on the occurrence of vestigial lower third molars. I n a few cases, four males and two females, the third molar was found to be merely a stump. I n one case where the right third molar was diminished the left was congenitally missing. B. I Y P A C T I O N S O F T H E MANDIBULAR NOLARS I N T H E ADULT ESKIMO The third molar only was found impacted in the mandibles of adult Eskim0.l Table 4 presents the tabulated results. The incidence of impactions is noted to be 5.4 per cent. Hellman (’28) gives the incidence of M3 impactions in thirty Eskimo lower jaws, also examined in the U. S. National Museum, as 9 p e r cent. Mead (’30), using a n x-ray ma- ’ There were three adolescents with five impacted third molars, not iiicluded in the table. 386 MARCUS S. GOLDSTEIN chine on the Eskimo material in the U. S. National Museum, found in 11872 mandibles 4.04 per cent impacted t,hird molars. TABLE 4 Iiicidence of impacted lower third molars in adult Eskimo -. - -. Yale 23 ~- 1 6 . 9 . 4 - .. -. .- Total .. , - I 13____ I 10 - 2 I 41 -- :T-- lIncludes twice the numbers under the ‘Both sides’ eolumn; i.e., oue f o r each side. According to locality T h e Eskimo again a r e divided into three main groups, according to HrdliGka ( ’30), and the incidence of impacted molars noted.for each. I n t.able 5 is seen a rather small, yet consistent, decrease in impacted third molars from the southand midwest to the northwest and norbh-northeast. Mead ( ’30, p. 4), in summarizing a study of dental conditions among the Eskimo by Wahl, states that “in the younger generation [of the Eskimo] where . . . . diet consists of, o r is interfered with by the use of, carbohydrates, candies, etc., . . . . caries has become apparent as we!I a s have malocclusion, a n d impactions.” I t would seem from the above that a positive correlation exists between the incidence of caries and that of impactions. To be sure, the order of increase of impactions among the three main groups of Eskimo is identical with that of the incidence of caries in the three groups, as will be indicated in study 111. Hellman (’28, p. 173) comments on the cause of thirdmolar impaction as seeming “ t o have no relation to lack of space [in the mandible]. They [impacted Ms’s] seem to be a The discrepancy between the figures of Mead and the writer with reference to number of mandibles observed is probably due to the f a c t t h a t the former, noting impactions in the whole mandibular dentition, included in his series a considerable number of jaws which the present writer necessarily excluded because of a lack of molar teeth. 387 THIRD MOLAR IN ESKIMO MAKDIBLE associated rather with the position of the tooth crown during the formation period than the room needed for its accommodation.” Very certainly in the Eskimo lower jaws, where impaction of the third molar occurred, there was no lack of space or room. TABLE 5 Zaczdence of ampnctpd l o w ~ rtkard molars in the adult Eskimo accordang t o thew geographacal localtly - -__ _ _ - X U H R E R OF J A W 6 LOCALITY - __ South-midwest : Nuiiirak St. Laareiiee Island Yukon Ricer Tanunuk St. hfichel Islaiid Rocky Point Golofiiin Bay Pastolik Hooper Ray Total Per cent of mandibles ( 4 7 7 ) Korthwest : Point Hope Wales Shishmaref Total P e r cent of inaiidibles (832) Korth-northeast : Greenland -,I AFFECTED I _-- NUMBER OF INPACTIOKS _ _ . -- I I I i I I 12 5 7 4 4 3 2 2 1 1 1 1 1 1 1 1 1 1 -. 21 28 5.9 5 3 - 5 3 2 - 9 10 I 1 4.3 I 11 -3.5 2 1 1 Total Per cent of mandibles (40) Miscellaneous Alaska’ 1 ._ - __ ‘There were tell adult iiiaiidibles from Alaska with tioiied. I 110 _ - --__ precise locallty men- SUMMARY 1. The third molar never appeared on one or both sides of the mandible in 16.6 per cent of adult Eskimo. The absence was usually on both sides of the jaw. 2. The lower third molar is more frequently missing in the females than in the males. 388 MARCUS S. GOLDSTEIS 3. Congeiiitally missing lower third molars occur appreciably less frequently in the south-midwest Eskimo than in the northwest-north-northeast Eskimo, the former group, therefore, being more primitive in this character than the latter. 4. Racially, the Eskimo appear among the most advanced with respect to congenitally missing lower third molars. 5. Impacted lower third molars occurred in 5.3 per cent of 759 adult Eskimo. 6. The lower third molar of the male is slightly more frequently impacted than in the female. 7. A consistent decrease in mandibular third-molar impactions occurs from the south- and midwest to the northwest and nor th-no r t h east Eskimo. BIBLIOGR.4PHT 19.7 Jaws and teeth of ancient IIawaiians. Yem. Bishop MUS., Hollolulu, I X , 251-268. DARWIN, C . 1881 The descent of man. New York. GOLBIRSCH, A. W. 1930 A study of third molar teeth. J. Am. Dent. Assoc., X V I I , 1849-1854. HELLXAX,M. 1928 Racial characters in human dentition. Proc. Amer. Philos. Soc., L X T I I , 2. HRDLICKA, A. 1911 Human dentition and teeth from the evolutionary and racial standpoint. Domin. Dent. J., X X I I I , 9. 1930 Anthropological survey i n Alaska. 46th Ann. Rept. Bur. Am. Ethnol., Washington. LEIGH,R. W. 1925 Dental pathology of the Eskimo. Dent. Cosmos, LXVIT, 884-898. MEAD,S. V. 1930 Incidence of impacted teeth. Internat. J. Orthod., XVI, 3-8. RUFFER,A. 1920 Study of abnormalities and pntliology of ancient Egyptian teeth. Am. J. Phys. Anthrop., 111, 3. TOMES,C. S. 1923 Dental anatomy. Kew Tork. CHAPPEL, 11. G .