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Differences in the pattern of the second lower molar tooth.

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DIFFERENCES I N T H E PATTERN OF THE SECOND LOWER
MOLAR TOOTH
LOUIS R. SULLIVAN
American Museum of Natural History, New York City
It is well known that the third upper molar and the second lower molar
teeth are unstable in form, the former tending to become secondarily
tritubercular and the latter secondarily quadritubercular. Accurate statistical data on the frequency of these transitions in the
various types of mankind are not, with a few exceptions, easily accessible. For the most part such data lie buried in the body of larger
craniometrical treatises and even here we find only occasionally
accurate percentages based on a sufficiently large number of cases t o
warrant their being accepted as an indication of the true state of
affairs. This is by no means the fault of the various observers but
may be attributed in the most part to the condition of the skeletal
material. In all collections of crania, mandibula are present in only
a small percentage of cases. Of this number a large proportion has
lost the teeth in life or after death, some even in the process of collecting
and storing. I n still another large percentage the teeth are worn
t o such a degree that relatively few remain suitable for the study of
cusps and tooth patterns.
We have it on the authority of dentists that modern European
man shows in a large majority of cases the secondary quadritubercular
pattern in the second lower molar teeth. This observation is borne
out by statistical studies in several collections of European crania.
The hypoconulid disappears, leaving only the four cusps protoconid,
metaconid, hypoconid, and entoconid.
This is apparently a late development since the Mauer mandibula
shows the primitive five cusps in the second lower molars as do also
certain Neanderthaloid mandibula. Cunningham says the second
lower molar has four cusps as a rule, five in only 24 per cent of all
skulls examined. Martin gives the occurrence of 5 cusps in 6 per cent
of Europeans and 15 per cent of the Lapplanders. Schwerz gives
the following data: five cusps in 73 per cent of the Australians, 34
255
AMER.JOUR.Pays. ANTHROP.,VOL. III., No. 2
256
LOUIS R. SULLIVAN
per cent of Negroes, 3 per cent of Alamans and 2 per cent of
Hungarians. The number of cases upon which these percentages are
based is not stated. HrdliEka52on the basis of teeth of the Munsey,
Arkansas, Louisiana, Zuni and some Mexican Indians, gives the frequency of five cusps as 21 per cent; of 4% cusps as 25 per cent; and
of 4 cusps as 54 per cent, But in 67 second lower molars of the Sioux
he observed five cusps in 68 per cent, 4% cusps in 6 per cent, and 4
cusps in 36 per cent of the cases. In the male Sioux the proportion
of the teeth with 5 cusps reached in fact as high as 77 per cent, that
of 4 cusps being reduced to 20 per cent.
There are in the American Museum of Natural History two collections of mandibula3 especially favorable for the study of tooth patters.
The first is a group of 43 Tarascan Indians from Mexico and the second
a group of 30 crania from southern India. The latter collection
consists largely of crania of the modified Mediterranean type similar
t o the Singhalese described by the Sarasin brothers. A few approach
the Veddah type. Both of these series are made up almost wholly
of young adults with complete dentition and show little or no wear.
The condition in the two groups are quite different. In the collection of Tarascan Indians from Mexico the second lower molar has
5 cusps in 76.8 per cent of the cases and 4 cusps in only 23.2 per cent.
The mandibulse from southern India on the other hand show five
cusps in only 16.6 per cent of the cases and four cusps in 83.4 per
cent. These results as well as those mentioned above may be summarized as follows.
NUMBER OF CUSPS ON THE SECOND LOWER MOLAR TEETH
Percentage
Group
Negro ..........................
Southern India. . . . . . . . . . . . . . . . . .
Lapplander .......................
European. ......................
Alaman .........................
Hungarian ......................
Author
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30
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5 CUD8
4 CUSW
76.8
73.0
34.0
16.6
15.0
6.0
3.0
2 .o
23.2
27.0
66.0
83.4
85.0
94.0
97.0
98.0
Sullivan
Schwerz
Schwerz
Sullivan
Martin
Martin
Schwerz
Schwerz
That the condition found in the Tarascan Indians may be taken as
representative of the condition in a t least some American Indians I
feel fairly certain. It has been my experience that a second lower
molar tooth with only four cusps is relatively rare in American Indians.
MOLAR TOOTH
257
I n the case of the Tarascan Indians the fifth cusp (hypoconulid) in
question is in a majority of cases as large and well formed as is the
corresponding cusp in the Mauer jaw and the tooth correspondingly
large.
Whether the differences revealed in the above table are indicative of
racial or functional differences is not quite clear. The Australians and
the American Indians stand close together in this particular characteristic yet they are undoubtedly quite distinct racially. The Negro,
famed for his supposedly perfect and primitive dentition, is apparently
quite modern and specialized in this particular respect. The Europeans
are uniform in showing a high percentage of cusp reduction. It is
obvious that more detailed data are needed before generalizing on the
cause of this reduction. From the above it is not altogether clear
how closely this reduction is correlated with the diminution of function.
While the skulls from southern India show a high percentage of cusp
reduction their dentition can in no sense be considered degenerative.
They show a very high percentage of normal occlusion and the teeth
are in most cases well formed and free from caries.
The reduction in question is important from an evolutionary standpoint and worthy of separate study. It is for this reason that the
above observations are placed on record. It is to be hoped that more
data will be forthcoming on the Negroid and Mongoloid types.
BIBLIOGRAPHY
Cunningham, D. J.-Textbook
of Anatomy. Edited by Arthur Robinson, New
York, 1917.
HrdliEka, Ales-Physical Anthropology of the Lenape or DeIewares, and of the
Eastern Indians in General. Bureau of American Ethnology, Bulletin 62,
1916; Skeletal Remains from Arkansas and Louisiana, J. Ac. Nat. SC. Phila.,
1909, XIV, 209 and personal information.
Martin, Rudolph-Lehrbuch der Anthropologie, Jena, 1914.
Schwerz, Franz-Die Volkerschaften der Schweiz von der Urzeit bis zu Gegenwart,
Buschan, Studien und Forschungen zur Menschen-und Volkerkunde, Vol. XIII,
Stuttgart, 1915.
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