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Enlarged occlusal surfaces on first molars due to severe attrition and hypercementosis Examples from prehistoric coastal populations of Texas.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 78:9-15 (1989)
Enlarged Occlusal Surfaces on First Molars Due to Severe
Attrition and Hypercementosis: Examples From Prehistoric
Coastal Populations of Texas
ANTHONY G. COMUZZIE AND D. GENTRY STEELE
Department ofdnthropology, Texas A&M University, College Station,
Texas 77843
ABSTRACT
During a n examination of prehistoric samples from the Texas
coast, individuals consistently exhibited a suite of traits on the first molars
that included severe wear, hypercementosis, and resorption of the buccal margin of the alveolus. The occlusal surface of the tooth was worn below the
cervical margin, with the subsequent incorporation of the buccal surface of the
buccal roots into the occlusal plane. This expanded occlusal surface, which
extends the buccal surface beyond the normal edge of the tooth, is composed of
a combination of original enamel, secondary dentin, and cementum. There is a
marked rounding of the buccal aspect of the occlusal surface. These conditions
were noted in both maxillary and mandibular first molars. The resorption of
alveolar bone surrounding the buccal roots resembles resorption associated
with periodontal infection and is thought to be the result of severe levels of
stress being applied to this portion of the dentition.
The dentition, like the skeleton, is a dynamic system responding to the forces to
which it is subjected. One of the most common forms of dental response is attrition.
Attrition is produced principally by the normal processing of foods andor the use of teeth
in technological applications (Dahlberg, 1963;
Molnar, 1970, 1971, 1972; Roydhouse and Simonsen, 1975; Sicher, 1960). Lavelle (1970)
described attrition as a “complex polymorphism” resulting from an interactive combination of external forces and the physical
composition and morphological structure of
the dentition. Since work done by Leigh
(19251, attrition has increasingly come to be
viewed as a natural and often desirable process, functioning in the maintenance of
proper occlusion as well as contributing to
the prevention of caries and periodontal infection (Hall and German, 1975; Patterson,
1984; St. Hoyme and Koritzer, 1976; Smith,
1986). In extreme cases, however, the reductive effects of attrition can be pathogenic
(Cawson, 1968; Kraus et al., 1969; Ross, 1970;
Spouge, 1973) and can dramatically alter the
shape of a single tooth or the entire dental
arcade. Regardless of its causes or final effects, attrition is, in principle, a destructive
process, evidenced by the wearing away of
the occlusal surface of a tooth.
@ 1989 ALAN R. LISS, INC
Since duration of occlusion plays a significant role in the level of attrition seen in a
tooth, typically the first molars exhibit the
greatest wear in a normal dental arcade
(Gordon, 1982; Lavelle, 1970; Marks et al.,
1985; Miles, 1963; Reinhardt, 1983;
Schmucker, 1985). Authors describing the
wear of first molars have noted the invariable loss of enamel and exposure of the dentin, and often a shift in the orientation of the
occlusal surface as well (Hall, 1976; Hall and
German, 1975; Murphy, 1959; Smith, 1986;
Reinhardt, 1983). Three other less often
noted, but highly important, characteristics
seen in severely worn molars are exposure of
the pulp cavity, erosion of the buccal alveolar
border (Linn et al., 1987; Tal, 1983), and exaggerated lingual tilting of upper and lower
molars (Reinhardt, 1983; Taylor, 1963).
Reinhardt (1983) presented a detailed review of lingual tilting and erosion of the buccal margin in severely worn teeth. Lingual
tilting of the teeth, particularly the first molars, was described a s the physical displacement of the tooth from its normal orientation
to one with a pronounced buccal to lingual
slope. This tilting of the tooth often resulted
in extension of the occlusal surface onto the
buccal margin and abandonment of part or
all of the original occlusal surface (Rein-
10
A.G. COMUZZIE AND D.G. STEELE
TABLE 1. Number of individuals from Texas coastal sites who possessed first molars
(N) and the number of these in.dividuals exhibiting hypercementosis and expansion. o f
the occlusal surface
Site
name
Blue Bayou
Palm Harbor
Oso Creek
Cay0 Del Oso
Tot.nl
Site
number
41 VT 94
41 AS 80
41 NU 37
41 NU 2
N
19
4
3
28
54
Individuals
with
hypercementosis
3
1
2
4
10
Individuals
with expanded
occlussal
surface
-I
1
2
1
4
‘Although heavily worn, these teeth do not yet sh ow evidence of expansion
hardt, 1983; Taylor, 1963). Based on observations of lingual tilting of molars in selected
California populations, Reinhardt (1983) believed that lingual tilting, and its associated
characteristics, could be attributed to a “severe attrition syndrome” created by the normal process of mastication and bruxism.
Alternatively, Taylor (1963), Buck (19251,
and Campbell (19251, suggested that the buccally oriented slope of the severely worn occlusal surface on maxillary and mandibular
molars, the extension of occlusal wear onto
the buccal roots, and the lingual tilting of
both upper and lower molars observed in
samples of Australian Aborigines and of
Maoris were created by a specific type of
mastication associated with the processing of
fern rhizomes. In fern root processing, the
buccal extension of the occlusal surface results from a functional expansion of the occlusal surface created by a n expanded use of
the tooth. It did not represent a n occlusal
adjustment as the tooth tilted in its socket.
Other researchers, notably Anderson (1965)
and Saunders (1972),thought that the use as
a tool of the region around the first molar at
least exacerbated the development of some of
these traits, particularly the lingual tilting
of the teeth.
This study documents additional features
associated with severe attrition in a sample
of hunter-gatherers from the Texas coast: hypercementosis and expansion of the occlusal
surface by incorporating cementum in the
surface. This study further documents that
a n extension of the occlusal surface onto the
buccal margin can OCCUT without significant
tilting of the tooth and abandonment of the
original occlusal surface.
MATERIALS AND METHODS
Material from four prehistoric sites from
the Texas coast were examined for evidence
of severe attrition (Table 1).All samples represent Archaic and/or Late Prehistoric
hunter-gatherer societies utilizing a coastal
environment. Several studies have suggested
some degree of biological affinity between
these populations (Wilkinson, 1977; Comuzzie, 1987; Comuzzie et al., 1986). From a sample of 54 individuals with associated first
molars, 10 individuals exhibited two distinct
features resulting from severe attrition: 1)
hypercementosis associated with dehiscence
and 2) the incorporation ofthe buccal surface
of the root and cementum into the occlusal
plane.
Whereas all individuals in this sample displayed high levels of attrition in the entire
dentition, only the first molars exhibited the
inclusion of the buccal roots as part of the
occlusal surface and hypercementosis associated with dehiscence or abscesses. Unfortunately, because of poor preservation of the
remains recovered, none of the affected individuals is represented by a complete dental
arcade. Therefore, it was not possible to compare the pattern of wear on a n affected tooth’s
antagonist in the opposing dental arcade.
However, four individuals possessed left and
right first molars in the arch, which permitted comparison of measurements and wear
patterns from the same individual for both
affected and nonaffected molars.
In a n effort to describe the changes in the
teeth exhibiting the two distinctive features,
measurements were made of those that exhibited occlusal expansion and those that did
not. Two authors have developed techniques
11
PREHISTORIC MOLAR OCCLUSAL SURFACES
TABLE 2. Surface area (mm2)of both affected and nonaffected first molars for the same
individual
Site
Palm Harbor
Tooth
tvDe
Mi
Oso Creek
M1
Cayo Del Oso
Mi
MI
for quantifying the degree of lingual tilting
of teeth. Reinhardt (1983) measured lingual
tilt by use of a protractor and a straight edge,
recording the amount of angulation in increments of 5". This was done by first placing
the 90" mark of the protractor even with,
and approximately parallel to, the alveolar
buccal margin. Next, a straight edge was
placed along the buccal roots of the tooth,
and the degree of tilting was read from the
protractor. Molnar (1971) presented a qualitative method for scoring the tilting of the
occlusal surface of severely worn teeth. Although this method has been suggested to be
quick and reliable (Schmucker, 1985; Hall,
1976; Butler, 1972),it did not offer a complete
description of the form of the occlusal surface. The technique presented by Reinhardt
(1983) also was attempted, but we were unable to measure the tilt of the molars for the
individuals in this study with the precision
we desired.
The maximum buccolingual and mesiodistal widths of the occlusal surface of the tooth
were measured by use of dental sliding calipers and recorded to 0.1 mm. The occlusal
surface was identified on the basis of tooth
orientation and polishing of the dentin and
cementum. These measurements were used
to estimate the area of the effective occlusal
surface of the tooth.
Epoxy casts of two specimens, produced following Rose's (1983)guidelines, were further
examined with the electron microscope. Micrographs were produced with a Jeol JSM
25SII scanning electron microscope, using a n
accelerating voltage of 15 kV and magnifications of x15 to ~ 7 0 Electron
.
micrographs
were also taken of a nonaffected third molar
from this same sample for comparative
purposes.
Surface area
nonaffected
molar
Surface area
affected
molar
109.8
83.7
94.1
106.1
118.7
116.6
111.6
110.9
RESULTS AND DISCUSSION
The attrition in these ten first molars was
extreme, with the complete loss of enamel
from all tooth surfaces (Fig. 1A). Along with
the extreme attrition, there was a marked
reduction in crown height. Whereas the original occlusal surface of these molars is still
relatively flat, it does curve onto the buccal
margin, with pronounced wear continuing
onto the buccal surfaces of the buccal roots
in four instances (Fig. lB,C). In these cases,
there is a deposition of adventitious dentin,
usually of a clear, glassy variety (Taylor,
1963), surrounding the outer margin of the
molar. The roots of these extremely worn
molars were enlarged as a result of hypercementosis (Spouge, 1973) (Fig. lB,C). These
affected molars exhibited evidence of dehiscence or abscessing of the buccal alveolar
border in conjunction with the inclusion of
the buccal surface of the buccal roots into the
functioning occlusal surface (Fig. lB,C).
There did, however, appear to be some variation in the degree of expression of the hypercementosis between individuals.
A visual examination of the affected molars failed to reveal marked tilting of the
tooth in its socket and abandonment of portions of the original occlusal surface as Reinhardt (1983)suggested. However, the increase
in the effective occlusal surface of these molars could be documented (Table 2). The average increase in surface area, in the four
individuals for whom affected and nonaffected teeth could be compared, was 15.5 mm2
over first molars in which the roots were not
incorporated into the occlusal surface. In all
cases, the expanded portion of the tooth was
along the buccal margin.
Electron micrographs documented buccolingually oriented striations on all first
12
A.G. COMUZZIE AND D.G. STEELE
PREHISTORIC MOLAR OCCLUSAL SURFACES
molars. Although all molars displayed buccolingually oriented striations to some degree, those first molars displaying a n
increase in area of their occlusal surface revealed a greater predominance of well defined buccolingual striations than those
occurring in the nonaffected molars (Fig. 2AC). Striations were as long as one-half the
width of the tooth. Some began on the original occlusal plane and extended onto the buccally curved extension of the occlusal surface.
This suggests that the original occlusal surface plus the sloped surface on the lingual
border functioned as a n expanded occlusal
surface. A nonaffected third molar (Fig. 2D)
exhibited fewer and shorter striations, which
were more varied in their orientation. Gordon (1982) documented the decreased number of striations in posterior teeth in Pan,
proposing that these differences were a result of changing amounts of shear and
compression, and differences in the length of
transverse movement of the occluding partners from the first to the third molars.
The unusual characteristics of these severely worn molars are the presence of hypercementosis and the incorporation of the
cementum into the occlusal surface. The roots
of these molars are markedly enlarged, with
secondary deposition of cementum present.
In these teeth, the roots were commonly exposed either by abscesses or dehiscence of the
buccal alveolar border, causing the hypercementosis to be readily apparent. In all these
cases, the occlusal surface of the tooth incorporated this cementum layer. It is believed
that both dehiscence of the alveolar border
and hypercementosis are often symptomatic
of traumatic occlusion or severe wear
(Spouge, 1973; Linn et al., 1987; Tal, 1983).
Consequently, it has been suggested that the
deposition of secondary cementum functions
to strengthen the anchoring of a tooth in the
face of extreme occlusal stress (Spouge, 1973).
Although this increase in tooth size is generally confined below the gum line, and
within the alveolar margin, it has little effect
on the occlusal function of the affected tooth.
However, in the molars from this sample, the
buccal roots were exposed antemortem by
dehiscence or abscessing, and the enlarged
-~
~
~
~~
Fig. 1. Maxillary dentition of individual from Palm
Harbour Site (41 AS 80), Texas. A Occlusal view. B:
Distal view of first molar illustrating hypercementosis
of roots and rounded occlusal surface on buccal margin
of crown. C: Buccal view of first molar illustrating antemortem exposure of roots and extentsion of occlusal surface onto buccal margin.
13
surfaces of the buccal roots were incorporated into the functioning occlusal surface.
As a result, the secondary effect of hypercementosis was to increase the occlusal surface
of the afYected molar even in the face of extreme attrition. In this respect, it may appear to function analogously to the buccal or
lingual cingula seen in some of the non-human primates. Furthermore, this lateral expansion and rounded buccal margin
superficially resembles lingual tilting as described by Reinhardt (1983) and Taylor
(1963).
Normally, in a worn dental arcade, the occlusal surface of the first mandibular molar
slopes buccally, and its maxillary antagonist
slopes lingually. To account for a buccally
sloped maxillary molar, Reinhardt (1983)
proposed that the maxillary tooth shifted
from a buccally oriented tooth to a tooth that
tilted lingually. More specifically, he proposed that the loss of intercuspation in worn
teeth allowed greater lateral mandibular excursion, which increased incursive lateral
force. This, in turn, traumatized buccal aspects of the alveolus, allowing the tooth to
begin to tilt lingually. As the tooth tilted
lingually, the buccal side of the tooth was
incorporated in the occlusal surface as the
lingual side was abandoned. With this model,
wear extending onto buccal surface of the
tooth, and incorporating the buccal roots, occurred if the tooth became tilted. The Texas
coastal samples document that expansion of
the occlusal surface onto the buccal surface
can occur without significant tilting and can
result in the expansion of the functional occlusal surface.
SUMMARY
In summary, hypercementosis can be affiliated with severe attrition, and, if the tooth
wears to the point where the roots become
included within the occlusal surface, the occlusal surface may become larger than the
original. Furthermore, incorporation of the
roots into the occlusal surface on the buccal
margin of the tooth can occur without appreciable lingual tilting or loss of the effectiveness of the original occlusal surface. This
condition has been documented only on first
molars, and only in Texas coastal populations.
ACKNOWLEDGMENTS
The authors thank E. Miller for technical
assistance and Virginia K. Massey for preparing the electron micrographs.
Fig. 2. Electron micrographs of selected molars of individuals from Palm Harbour Site (41 AS 801, Texas. A
buccal margin of mesiobuccal cusp of left first maxillary
molar. B: Lingual aspect of occlusal surface of left first
maxillary molar. C: Close-up view of buccal margin of
mesiobuccal cusp. D: Distolingual cusp of lower third
molar. Electron micrographs A-C are of left first molar
illustrated in Figure 1.
PREHISTORIC MOLAR OCCLUSAL SURFACES
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