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Biomechanical association of dental and temporomandibular pathology in a medieval Nubian population.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 85~201-205 (1991)
Biomechanical Association of Dental and Temporomandibular
Pathology in a Medieval Nubian Population
SUSAN G. SHERIDAN, DIANE M. MITTLER, DENNIS P. VAN
GERVEN, AND HERBERT H. COVERT
Department of Anthropology, University of Colorado, Boulder, Colorado
80309
KEY WORDS
Temporomandibular joint, Biomechanics, Tooth
loss, Dental pathology
ABSTRACT
An analysis of the relationship between oral pathology and
degenerative change at the temporomandibular joint (TMJ) was undertaken
on an archaeological sample of 122 adult crania from the Medieval site of
Kulubnarti in Sudanese Nubia. The crania were sorted into 2 groups: those
demonstrating clearly visible bony changes at the joint (TMJ+1 and those
without visible change (TMJ- 1. These groups were compared according to 1)
age; 2) sex; 3) active dental pathologies (abscesses, caries, partial socket
resorption); 4) tooth loss with complete socket resorption; and 5) dental
attrition.
No statistically significant association was evident between degenerative
change at the TMJ and age, active dental pathologes, or dental attrition;
however, sex differences and posterior tooth loss with complete socket resorption revealed a significant correspondence to degenerative TMJ changes. Both
of these factors agree with the clinical literature and with biomechanical
models (most notably that of Hylander) based upon modern populations.
Furthermore, the results support the contention that paleopathological conditions can be analyzed from a clinical and functional biomechanical perspective.
Interest in disorders of the temporomandibular joint (TMJ) has mainly focused on
the clinical and biomechanical as ects of this
joint. A rapid rise in these disor ers among
modern populations has attracted much clinical attention, while biomechanical research
has concentrated on the functional role of the
mandible and associated musculature in
mastication.
It has been estimated that between 5080% of the American public suffers from
some form of TMJ dysfunction (Gerschman
and Reade, 1988; Lewis, 1988).This range in
estimates reflects a continuin lack of systematic methodology for the de inition, diagnosis, and treatment of such conditions
(Weinber 1987).
Biomeckanical considerations have focused extensive1 on the relationship between the mandi le and temporal bone durin mastication, and have led to considerable
de ate as to whether the mandible functions
as a lever (Hylander, 1975; Picq et al., 19871,
rt
B
8
a link (Robinson, 1946;Taylor, 19861,or both
(Gingerich, 1979). Hylander (1975) provided
a detailed description of this debate and
argued strongly in favor of the lever hypothesis.
The lever-action model has important implications for clinical research due to its
predictive value (Fig. 1).According to this
model, TMJ reaction forces are ordinarily
larger on the balancing side than on the
workin side (where the bite force is exerted). f 3 ecause individuals with dental pathologies (such as abscesses and caries) on
one side of the mouth preferentially chew on
the o posite (healthy) side, the lever-action
mode predicts that in these individuals the
masticatory forces should ass mostly
through the teeth on the heaghy side and
through the condyle on the diseased side.
The reverse should occur if there is unilat-
P
%
@ 1991 WILEY-LISS. INC
Received January 18,1990;accepted November 13,1990.
202
S.G. SHERIDAN ET AL
Y
While Hylander’s model has apparent utility in explaining morphological variation in
archaeological PO ulations, its utility for the
analysis of bony $MJ changes in such populations has yet to be determined. Indeed,
althou h degenerative joint changes in the
appenficular and axial skeleton have been of
FORCE considerable interest to paleopathologists,
the TMJ has received little attention in spite
of the clinical interest and biomechanical
modeling available. Reasons for this lack of
attention no doubt include the fact that archaeological remains only provide a partial
BITE FORCE
/
record of TMJ disease, and as Bell (1986)
stated, “mastication involves many structures-bones, joints, muscles, teeth, glands,
Fig. 1. Bite forces in Hylander’s lever-action model. nerves of different types, blood vessels . . .”.
(Adapted from Hylander, 1975).
Studying one portion in isolation from the
others can prove difficult. In addition, ancient populations fre uently ex erienced a
magnitude of dental isease an associated
tooth loss during life far in excess of that
era1 disease in the TMJ rather than the anticipated by most biomechanical models
teeth; that is, masticatory forces should pass (Armelagos, 1968; Bergman and Hansson,
primarily through the teeth on the side with 1979; Brothwell, 1972).
the diseased joint, but through the condyle
Therefore, an examination of the cranial
on the healthy side. Both these adaptations remains from a Medieval Nubian population
serve to reduce pain during mastication; was undertaken to determine the presence
however, they result in as mmetrical stress and extent of degenerative bony changes in
on the TMJ, and may lea to eventual joint the TMJ, and to assess the relationshi between dental disease, tooth loss and MJ
de eneration.
fn addition to lefthight asymmetry, poste- degeneration in light of the lever-action
rior (molar) tooth loss has been observed to model. Excellent preservation of complete
contribute to TMJ degeneration in living crania and dentitions make this an ideal
populations. With the loss of posterior teeth, population for study. High rates of dental
the frequency of anterior (incisal) biting and wear during life resulted in rapid and early
associated joint loading increases. Hylander antemortem tooth loss, particularly in the
(1978) has demonstrated that the mandible posterior dentition. This population thereacts symmetrically as a lever during incisal fore, provides an excellent Sam le for a debiting and asymmetrical1 during molar bit- termination of the extent to w ich a wide
ing. It is to be ex ected t at abnormal joint divergence from a healthy dental arcade conforces such as t ose produced by severe forms to Hylander’s predicted association
asymmetric lefthight molar chewing or ex- between chewing patterns, joint forces and
cessive anterior chewing may lead to tissue TMJ changes.
remodeling and subsequent degeneration in
MATERIALS AND METHODS
the TMJ (Bell, 1986; Faulkner et al., 1985).
The relationshi between TMJ mor holThe skeletal population used in this study
ogy and anterior ite forces has also een was excavated by the third author in 1979
examined from an evolutionary pers ective. from the site of Kulubnarti in Northern
Hinton and Carlson (1979) observe a sub- Sudan. Kulubnarti is located in a region
stantial size reduction in the glenoid fossa called the Batn et Hajar (“belly of rock), an
and mandibular condyle in ancient Nubian area described by Adams (1977, .26)as “the
opulations excavated near Wadi Halfa. most barren and forbidding o all Nubian
!his pattern of decreased joint size from environments.” Subsistence in this re ion
Mesolithic through Christian times was in- was marginal, even with low population enter reted as a res onse to facial reduction, sities. The ancient inhabitants of this area,
re uced anterior ite forces, and reduced like their modern counterparts, existed as
reaction forces in the TMJ.
sedentary agriculturalists practicing small
3
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5
RIOMECHANICAL ASSOCIATION OF DENTAL AND TEMPOROMANDIBULAR PATHOLOGY
scale farming along the banks of the Nile
(Carlson et al., 1974).The principal cultigens
were cereal grains, including millet and sorghum. Milling, combined with the blowing
sands of the Nubian Sahara, led to gritty
contamination of foodstuffs. This resulted in
a rapid rate of toothwear, a hi h fre uency of
apical abscess, and tooth loss y mi life.
Two cemeteries were excavated at Kulubnarti yielding a total of 418 individuals, representing both sexes and ages ranging from 5
months in utero to 51+ years. Preservation
of the remains was remarkable. Many were
naturally mummified due to the exceptionally dry climate; annual rainfall averages
less than a millimeter per year. The earliest
of the cemeteries is dated from early Christian times (c. 550-750 A.D.), the other from
the remainder of the Christian era (c. 7501500 A.D.).
The sample selected for the present study
consisted of 122 adult (18 to 51-t years)
crania from the combined Kulubnarti cemeteries. Subadults were excluded from the
present analysis due to a lack of observable
TMJ change and in order to avoid the complicatin factor of dental eruption.
Fol owing sample selection, a systematic
macroscopic examination of the crania was
undertaken to determine those individuals
with clearly visible de enerative changes in
the temporomandibu ar region (Fig. 2).
Those demonstrating significant porosity of
the articular eminence and/or bony exostoses in the TMJ were labeled as TMJ+. Due
to the multicausality of such disorders, no
attempt was made to determine the etiology
of the problems in this category (Gerschman
and Reade, 1988). Those displaying no evidence of joint change were classified as the
TMJ- group.
Dental pathology, degree of socket resorption, and dental attrition were also examined. Dental athologies (caries, abscesses)
were recorde per tooth for each individual.
Socket resorption was classified as either
partial or com lete and recorded for each
tooth. Degree o tooth wear was scored using
rocedures described by Smith (1984).
mith’s method was selected because it allowed inclusion of the anterior dentition and
provided an eight-step method of seriation.
Subjects were categorized according to 1)
age; 2) sex; 3) active dental pathologies at
time of death including caries, abscesses,
and partially resorbed sockets; 4) complete
socket resorption; and 5)tooth wear. Age and
sex for all individuals were previously estab-
203
$3.
f
P
B
f!
E
Fig. 2. Example of degenerative bony changes in the
TMJ+ group.
lished by Van Gerven et al. (1981) using
multiple criteria.
Mean number of cavities, abscesses, and
partially and completely resorbed sockets
per individual were calculated for those in
the TMJ+ and TMJ- groups. Mean stage of
tooth wear was also calculated and compared for these two groups. RightAeft wear
asymmetry was determined by taking the
absolute difference between the wear scores
for left and right tooth antimeres. Variance
was also computed for each group.
RESULTS AND DISCUSSION
As indicated in Table 1, of the 122 adult
crania examined, 17 were classified as
TMJ+, 105 as TMJ-. Comparison of the two
groups by age using Student’s t revealed no
statistically significant differences (Table 2).
Mean age at death for the TMJ+ (34 yrs) and
TMJ- (35 yrs) individuals differed by less
than a year. However, small sample size may
have contributed to this lack of association.
Indeed, when grouped by decade, 50% of the
TMJ+ individuals fell in the 40-51+ age
group, suggesting a possible age effect.
There was no significant difference in the
roportion of females to males in the
!MJ- group. However, in the T M J t grou
the ancient Nubians conformed to the mo,: ern clinical pattern. As with moderns, Nubian females outnumbered males (x’ = 2.88;
one tailed, P < 0.05). Indeed, the near 3:l
Nubian ratio approximates the modern clinical female-to-male ratio of 4:l (Gerschman
and Reade, 1988).
Analysis of active dental pathologies revealed that members of the TMJ+ group
204
S.G. SHERIDAN ET AL.
TABLE 1. Association of sex and condition of TMJ
TMJ+ = subjects with TMJ degeneration and
TMJ- indicates those without bonv degeneration
Sex
TMJ-
TMJ+
Male
n
50
47.6
55
29.4*
12
70.6*
55
52.4
67
5
sil
Female
n
w1
Total in)
Total (n)
17
105
*Significant using the chi-square test at P
122
< 0.05
demonstrated fewer abscesses (0.241
individual) and carious lesions (0.71/
individual) compared to their TMJ- counter arts (0.79 and 1.39 respectively), the
dif erences were not statistically significant.
Mean number of partially resorbed sockets
was highest in the TMJ+ group (2.88 compared to 2.27). However, overall, the number
of active pathologies remained highest with
the TMJ- individuals (4.45 vs. 3.82).This is
not sur rising given the expected delay between isruption in mastication and resultant bony chan es at the TMJ.
f
in mastication was
Long-term C isruption
assessed using complete socket resorption as
a measure of protracted tooth loss prior to
death. The analysis proved highly significant at P < 0.01 using Student’s t. TMJ+
individuals displa ed nearly two times as
many resorbed soc ets (10.24/individual) as
the TMJ- group (5.46hndividual). Of the
10.24totally resorbed sockets per individual,
80% were associated with the posterior dentition. This highly significant association between posterior tooth loss and disorders of
the TMJ conformed to predictions based
upon current clinical literature which lists
such tooth loss as a major contributor to TMJ
disorders (Bergman and Hansson, 1979;
Christensen and Ziebert, 1986; Faulkner
et al., 1987; Furstman, 1965; Granados,
1979; Hatjigiorgis et al., 1987; Weinberg,
1987).
Anal sis of tooth loss produced patterns of
sex dif erence and anteriorJposterior loading
consistent with the clinical and biomechanical literature (most notabl Hylander 1975,
1978);however, analysis o tooth wear as an
indicator of lefthight asymmetry, was less
successful. Based on Hylander’s model one
would expect to find evidence of preferential
chewing in the TMJ+ group on the same side
as the disorder. No such trend was evident.
TABLES. Betweengroupcomparisons of agp,sex, active
dental pathologies, complete socket resorption, and tooth
wear for subjects with TMJ degeneration ( T M J I )
and those without (TMJ-I
Variables
x Age i w 9
x Total active pathologies
U Number of partially resorbed
sockets
i Number of apical abscesses
Number of carious lesions
% Number of completely
resorbed sockets
X Dental attrition
F L/R differences
(average of all antimeres)
Variance of L/R difference scores
Samole size
*Significant using the t-test a t P
TMJt
34
TMJ-
2.88
35
4.45
2.27
0.24
0.71
0.79
1.39
3.82
10.24%
5.16
0.87
0.72
17
5.46%
4.97
0.73
0.46
105
< 0.01
f
B
i
P
F
Analysis of 1eftJright differences in wear using Smiths 8-stage system produced no corres ondence between wear asymmetry and
T& degeneration. Mean stage of wear for
the TMJ+ group was 5.16,4.97for the TMJindividuals. The avera e difference between
wear on the left and rig t sides was less than
one stage in Smith‘s system for the TMJ+
group (0.87), as well as the TMJ- group
10.73).Asymmetry was also assessed by computing variance values from the TMJ+ and
TMJ- groups. While the TMJ+ variance
was larger (0.72 vs. 0.46), the values were
not significant at the 95% confidence level.
In summary, while the present analysis
failed to demonstrate a significant association between degenerative changes in the
TMJ and active dental pathology or 1eftJright
chewing asymmetry, sex differences, and
posterior tooth loss revealed a significant
correspondence to bon TMJ degeneration.
Age differences also s owed a strongly related trend, although not significant at the
95% confidence level. These associations
were highly consistent with the clinical literature, as well as Hylander’s lever hypothesis. Furthermore, the results support the
contention that aleopathological conditions
can be analyze from a clinical and functional, biomechanical perspective.
a
i
1
CONCLUSIONS
1. Of the 122 Nubian crania examined,
13.9% demonstrated degenerative changes
in the temporomandibular joint.
2. A trend toward increased degeneration
with increased age was evident, with 50% of
BIOMECHANICAL ASSOCIATION OF DENTAL AND TEMPOROMANDIBULAR PATHOLOGY
the TMJ+ individuals aged 40 to 51-t. The
results were, however, insignificant at
P > 0.05.
3. Sex differences related to TMJ degeneration corresponded to the modern pattern.
There were more Nubian female sufferers
than males; this agrees with current clinical
of a greater female-to-rnale ratio
(Gerschrnan and Reade, 1988;
et al.,
1987).
4.Active dental pathologies, as indicators
of more recent disease events, showed no
significant relationship to degenerative
changes in the TMJ.
5. Total resorption of the alveolar bone was
much more prevalent in the TMJ+ individusocket
Such tooth loss with
resorption illdicated a longer history of oral
disease.
6. In the TMJ+ group, 80% of the cornpletely resorbed sockets occurred in the pasterior dentition.
7. ~
~of dental~attrition
l provided
~ no
evidence for preferential left/right chewing
among TMJ sufferers.
These results indicate a highly significant
association between long term tooth loss and
disoders of the TMJ. This agrees with the
current clinical literature which lists loss of
occlusion as a major contributor to such disorders (Bergman and Hansoon, 1979. Christensen and ziebert, 1986; Fau]kne; et
1987; Granados, 1979; Hatjigiorgis et a].,
1987; Weinberg, 1987). It ap ears that
within this population extensive oss of posterjor teeth and subsequent anterior chewing was the principal factorin degeneration
of the TMJ. Posterior loss led to increased
loading at the TMJ, resulting in degenerative changes in the joint. The clear associatjon between a shift in bite force from the
molars to the incisorsin the TMJ+ group is
if the
is
as a lever (Chrktensen
viewed as
P
ACKNOWLEDGMENTS
This research was partially funded by
NSF grant N ~ 9077-5-535~.
.
we wish to
thank Drs. Matt Cartmill and William Hylander, as well as the anonymous reviewers,
for their extremely useful comments and
suggestions.
LITERATURE CITED
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Allen Lane.
205
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