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Canine role in dental wear patterns Macaca nemestrina.

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Canine Role in Dental Wear Patterns: Macaca nemestrina
D e p u r t m e n t of Anthropology, University of Georgia, A t h e n s , Georgia 30602
Canine . Interlocking . Wear . Tooth . Macaca.
A study of variables and patterns in dental wear among
3 0 individuals in a colony of Macaca nernestrina shows that consideration of
age and sex are crucial for understanding differential wear degrees on molar
occlusal planes. With advanced age, this species of non-human primate undergoes obliteration of initial morphological characteristics through the gradual
erosion of enamel. Wear gradients are differential from P M l - M 3 in both sexes.
It appears that there is a functional relationship between degrees of occlusal
plane wear and the degree of wear on the canines, and that females show a
greater degree of wear changes relative to males of equivalent age because of
initial differences in canine length and robusticity due to sexual dimorphism.
It appears that there is a direct relationship between occlusal wear plane
changes and the degree of wear on the canines, with advanced differential
wear showing up in individuals in whom years of maxillary canine honing,
canine damage, and the normal wear of mastication has reduced dimensions
of unworn permanent canines. Other considerations included in this study are
the honing functions of the deciduous first mandibular molars and molar cusp
height relative to canine function.
One of the supposedly unique diagnostic
dental characteristics of hominids is the
flattening of occlusal wear planes of molar
teeth due to “rotary chewing” motions of
the mandible during mastication. Presumably these motions are made possible by
the absence of large, interlocking canines.
However, despite the implications of such
a generalization, supportive data are nearly as scarce as functional, systematic approaches to tooth wear studies.
For example, the role of interlocking
canines, as it pertains to patterns of tooth
wear which might be useful in making
taxonomic assessments, remains speculative and inferential. Studies of the variables in tooth wear for living populations
of Homo are rare, and almost non-existent
for living non-human primates. Only very
recently have the age-correlated patterns
of helicoidal and differential occlusal wear
plane changes in Homo sapiens been abstracted on the basis of objective data
(Butler , ’72).
As St. Hoyme and Koritzer have observed (’71), flattening of molar occlusal
wear planes is not absolutely indicative
of hominid status; they point to the flatAM. J. PHYS. ANTHROP.,40. 391-396
tening of molar crowns in Gigantopithecus
as a n example. A number of workers also
have noted both occlusal plane flattening
and marked interstitial wear in Pan (see
Wolpoff, ’71). Further, Jolly (‘70), in one
of the rare applications of systematic analysis, suggested that in the case of Theropithecus, at least, the dentition may be
regarded as a functional whole: what happens to wear of the cheek teeth may be
directly related to functional aspects of
the anterior dentition. Regrettably, Theropithecus does not make a n ideal laboratory animal for studies on living populations because of size, temperament, and
problems in anesthesia.
In short, those who attempt to follow
the threads of primate evolution via dental
studies are handicapped by the relative
lack of data concerning age and sexrelated variables in tooth wear for either
fossil or recent populations of primates
in general.
Despite the importance of dental wear
This research was supported in part by a grant from
the National Institute of Mental Health MH-13864, and
by a grant from the National Institute of Health PHSFF-00165.
39 1
patterns and their functional elaboration
the statements of many early workers have
not been verified or have been discarded
after the substitution of data for speculation. For example, in the first quarter of
this century, Campbell suggested that interlocking canines in pongids may not
absolutely limit lateral mandibular movement during mastication (‘25). This bit
of speculation, at least, is less dogmatic
than that of Jones, who, working with
Macaca mulatta, comments that “there
are certainly no lateral excursions of the
mandible, movement being practically
straight up and down” (‘47:257). The
author neglects to provide the size of the
sample and does not consider the effects
of differential wear due to age or sex.
B i r t h d a t e s a n d s e x of a n i m a l s e x u m i n e d in 1972
1957 2
1958 1.2
1958 1.2
1960 1.2
1960 1.2
20 Nov 64 2
21 Jan 65 2
24 Feb 65 2
23 Mar652
11 Feb662
7 Sep 66 2
4 Dee 66 2
11 Dec 67 2
31 Dec 68 2
19 Apr 69 2
21 Oct 69 2
22 May 70
11 Jul70 2
4 Jul71 2
15 Jul71 2
2 Sep 71 2
24 Sep 71
1956 1.2
1959 1.2
27 Jul64 2
28 Jun 65
19 Jun 66
5 Sep 66
27 Jul67 2
8 Dee 67
19 Sep 68 2
24 Sep 68
2 Jun 69 2
21 Feb 70 2
22 Aug 70 2
15 Sep 71
10 Oct 71
With this background in mind, we chose
a living colony of Macaca nemestrina to
determine dental wear pattern and correlate it with age and sex.
Observations were made on some 37
individuals in the spring and confirmed
on subsequent reexamination for 30 individuals during the summer of 1972 at
the Lawrenceville Field Station facilities
of the Yerkes Regional Primate Research
Center (see table 1). Large adult males
were anesthesized prior to examination,
while younger males and females of all
ages were examined while their limbs
were pinioned. Color slides and black and
white photographs were taken, and data
on wear was recorded on tape. Observations were repeated by the second author
several months after the initial examination, and the data were then oriented with
recorded vital statistics. We regard the
sample as adequate in regard to wear patterns, but it is too skewed in terms of age
and sex to permit precise statements about
such matter as tooth eruption sequences.
Further, no attempt is made to present
data in terms of actual differences in
degrees of occlusal plane wear. The techniques for this form of approach are still
being developed.
All animals lived together in an open
air compound which originally included
the natural vegetation of northern Georgia.
They were maintained on monkey chow
and a variety of fruit and vegetable supplements. In addition, animals were seen
Age estimated i n 1962; all others, including 1957
female, were born in captivity.
Animals reported on in this paper.
eating a variety of insects, small animals
and earth. Animals chewed sticks, mouthed
stones and bit wooden and other objects
in play and exploration. These patterns,
plus horizontal molar and incisor gritting
and vertical canine grinding patterns were
considered within the normal range of
activities for wild specimens based on field
observations in Malaysia by the junior
In this sample of Macaca nemestrina,
enamel loss on the occlusal surfaces of
the tooth leads, as in other genera, to
gradual obliteration of initial crown morphology, exposure of dentin and pulp
chambers, and to degrees of change in
occlusal wear planes. An occlusal wear
plane may be oriented lingually or buccally, or it may be flattened.
In our sample, permanent dentition was
completed by the age of 5 or 6 years.
Enamel loss at this age is more marked
on the anterior teeth, with relatively little
dentin exposure visible on the cheek teeth.
Although we are aware of the significance
of time differentials in tooth eruption sequences as variables in wear, we can state
only generally that M 1 seems to be func-
tionally erupted between the ages of 2
and 3 years, M2 between the ages of 3 and
4, and M 3 by the seventh year at the latest
and usually earlier. Permanent canines
ordinarily follow functional eruption of
M2. In at least one instance, permanent
maxillary canine eruption followed functional eruption of M 3 in a 5-year-old male.
Graduated wear in the cheek teeth is
fully evident by the age of 7 years. Although this age category is represented
only by three females, two of these individuals have sharply-sloped buccal occlusal wear planes on the mandibular M1,
while the maxillary M1 is worn to an even
greater degree in a lingually-oriented plane.
In all age categories, there is considerable variation in regard to both eruption
times and degrees of wear. We do not
overlook the possibility that differential
wear from front to back may be present
at an earlier age.
Obvious sex-related degrees of occlusal
plane changes are apparent in all individuals 8 years and older. Although differential wear is evident in both sexes,
the degree of wear from the age of 8
onward is consistently greater for females,
with M1 worn to a greater degree than
M2, and M2 more than M 3 for both mandible and maxilla.
Suggested relationships between canine
size in their initial, unworn state and wear
on the cheek teeth correlated with age are
seen in two 12-year-old females. One of
these females has drastically worn canines,
with those of the mandible worn to the
incisal level of the adjacent teeth. In addition to wide areas of secondary dentin on
the premolars, molars in this individual
are worn to the extent that not even a
rim of enamel remains around the contour of the molar occlusal surfaces. The
second 12-year-old female has relatively
large canines. Incisor wear is almost to
the gum line, but molar wear is not so
advanced as in the other female, with
large areas of intact enamel and retention of much of the original area of the
It is of some interest that the female
with the well-worn canines shows relatively more premolar and molar wear than
the alpha male, a 13-year-old individual
whose canines remain robust despite a
modest degree of blunting. In the alpha
male, differential wear gradients on molar
surfaces are present, but much of the
crown enamel is still intact.
The oldest male available for study is a
16-year-old individual in whom the maxillary canines are greatly worn and chipped
(fig. 1). The entire maxillary molar series
shows occlusal wear planes which are
sharply sloped lingually, while the wear
planes of the mandibular molars all slope
to the buccal side. Wear is greater in the
maxillary dentition than in the mandibular. It should be noted that, in this old
male, while upper and lower canines show
considerable damage and blunting, the
remaining portions of the teeth are still
relatively robust.
The oldest female, aged 15 years, has
mandibular canines worn nearly to the
level of the incisors. Her right maxillary
canine is severely worn relative to the
left. On this animal, all of the mandibular
molars show sharply-sloped buccal occlusal
wear planes, with the maxillary series
showing a strong lingual orientation of
the wear planes. In this case, as in the
others, M l is worn to a greater extent
than the rest of the series. The 15-year-old
female retains lips of enamel around the
occlusal contour of M2-3, but the upper
and lower M1 show almost no enamel,
with pulp chambers visible although not
actually exposed. No enamel elevations
are visible on any of the molar series in
this individual.
A slightly younger female, 14 years of
age, shows canine wear to the extent that
there is no apparent impediment to lateral mandibular excursion. Incisors are
heavily worn, and all of the mandibular
molars are worn sharply to the buccal
side while those of the maxilla all are
worn to the lingual side. By way of contrast, another 14-year-old female with less
severely worn canines shows a lesser degree of occlusal plane wear on the molars.
In this individual, original cusp sites are
represented by areas of elevated enamel.
In all individuals in whom deciduous
molars were retained, the mandibular M1
is an elongated tooth relative to other
deciduous molars and has a raised anterior surface which seems to function in
much the same way as the permanent
first mandibular molar, as a honing surface for the maxillary canine. It would
Fig. 1 Maxillary dentition of a 16-year-old male shows advanced wear on all teeth,
including the chipped and worn canines. Molar wear is differential but nonhelicoidal.
seem that deciduous upper canines are
honed in the same manner as the permanent upper canines.
Degrees of wear on the occlusal wear
planes of Macaca nemestrina seem to be
more pronounced in females than in males
provided that comparisons are made of
animals of equivalent age. In all cases,
changes of degree in occlusal wear planes
are differential, with PM1 normally showing greater wear than PM2 and M1 showing the greatest amount of wear in the
molar series. In no case was differential
wear found associated with helicoidal patterns. That is, there were no changes in
the occlusal wear planes from buccal to
lingual or vice versa on any of the cheek
teeth as occurs in Homo and earlier hominids (see Butler, '72). In this population,
the pattern with advancing age, regardless
of sex, seems to be for the entire maxillary
molar row to assume a sharply lingual
wear plane, with the opposite true for the
mandibular molars. Data for premolars
are insufficient for generalizations.
The data do support statements by various workers that large projecting canines
impede lateral mandibular motions, pro-
vided that these statements take into account the suggested strong relationship
between degrees of canine wear associated
with age and resultant changes on occlusal surfaces of the molar teeth. This sample further suggests that the degree of
wear on the cheek teeth increases as size
and robusticity of the canines decreases
through mastication, honing, or fighting.
A variable which could not be checked
was the amount of wear advanced by
molar teeth gritting, and canine grinding
which may be part of a general anxiety
syndrome for the species. Finally, this
sample also strongly suggests that canine
length and robusticity attributable to sexual dimorphism should be taken into account when considering either degrees of
wear or patterns of wear on the cheek
Explanations of differential but nonhelicoidal wear in our sample are not
clear-cut, but examination of skeletal material of the same species offers several
possibilities. One lies in the relatively pronounced height of molar cusps and the
functional relationship with unworn canine
size. In young adults, before wear has
proceeded to any marked degree, lateral
mandibular excursion is limited by con-
tact of the distal aspect of the mandibular
canine with the mesial surface of the maxillary canine. As this occurs, unworn
mandibular canines on the opposite side
come into impeding contact with the maxillary lateral incisor. Further, lateral mandibular movement is limited by contact of
the distal aspect of the maxillary canine
with the mesio-buccal aspect of the mandibular PM1. Functionally related to these
basic considerations is the fact that differences in dental arch width at different
tooth positions causes considerable overlap
of the maxillary teeth so that the lingual
cusps of the mandibular teeth fit, in the
unworn state, between the buccal and
lingual cusps of the maxillary teeth. All
unworn molar cusps are relatively high.
It would seem that the initial emphasis
of wear is on the lingual aspect of the
maxillary molars and the buccal aspect
of the mandibular teeth.
By the time individuals of this species
have reached the age where sharply differential occlusal wear planes are evident,
it appears that so much of the original
tooth structure has been lost that even
increased lateral movement of the mandible will not result in helicoidal patterns
(see Brace and Molnar, '67; Molnar, '68)
for a review of experimental work in human tooth wear.
Based on this sample of Macaca nemestrina, we conclude that initial wear patterns are strongly influenced by the devel-
oping canines. The fully erupted canines,
of males especially, limit lateral mandibular movements to the extent that molar
wear is minimal on mandibular lingual
cusps and maxillary buccal cusps. In older
individuals with heavily worn canines increased lateral movement of the mandible
permits wear of these cusps, but the initial
wear emphasis on the buccal aspect of
the mandibular molars and the lingual
aspect of the maxillary molars persists.
Occlusal wear planes thus may undergo
wear changes in terms of degree but there
is no similarity to true helicoidality, including reversals of initial occlusal wear
Butler, R. J. 1972 Age-related variability in
occlusal wear planes. Am. J. Phys. Anthrop.,
36: 381-390.
Brace, C. L., and S. Molnar 1967 Experimental
studies in human tooth wear: I. Am. J. Phys.
Anthrop., 27: 213-221.
Campbell, T. D. 1925 Dentition and Palate of
the Australian Aboriginal. Hassell Press, Ade1aide.
Jolly, C. J. 1970 The seed-eaters: A new model
of hominid differentiation based on a baboon
analogy. Man, 5: 5-26.
Jones, H. G. 1947 The primary dentition of
Homo sapiens and the search for primitive features. Am. J. Phys. Anthrop., 5: 251-282.
Molnar, S. 1968 Experimental studies in human tooth wear. 11. Am. J . Phys. Anthrop.,
28: 361-368.
St. Hoyme, L. E., and R. T. Koritzer
Significance of canine wear in pongid evolution. Am. J. Phys. Anthrop., 3 5 : 145-148.
Wolpoff, M. H. 1971 Interstitial wear. Am. J.
Phys. Anthrop., 34: 205-228.
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patterns, wears, dental, role, macaca, nemestrina, canine
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