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Cementum annulation and age determination in Homo sapiens. II. Estimates and accuracy

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 71:321-330 (1986)
Cementum Annulation and Age Determination in Homo sapiens.
It. Estimates and Accuracy
KEITH CONDON, DOUGLAS K. CHARLES, JAMES M. CHEVERUD, AND
JANE E. BUIKSTRA
Department ofAnthropology, Northwestern University, Euanston, Illinois
60201 K.
C., D.K.C., J. M. C., J.E.B.);Department ofAnatomy, University of
Illinois at Chicago, Chicago, Illinois 60612 K.C.):Department of Cell
Biology and Anatomy, Northwestern University, Chicago, Illinois 60611
(D.K.C., J.M.C.)
KEY WORDS
Cementum, Aging, Teeth, Forensics
ABSTRACT
The cementum annulation aging technique was evaluated in
a sample of 80 clinically extracted premolars (age range 11-70 years). Demineralized thin sections (7pm) stained with hematoxylin were used. The correlation (r) between age and adjusted count (number of annulations added to age
of tooth eruption) was 0.78 for the entire sample (N = 73) and 0.86 for a
subsample in which teeth with periodontal disease were excluded (N = 55).
Standard error of the estimates ranged from 4.7 to 9.7 years depending on sex
and health status of the tooth. The technique provided significantly better
estimates for females than for males. The overall inaccuracy (mean absolute
error) of the technique was 6.0 years, with a bias (mean error) of 0.26 years.
Reduced major axis regression of adjusted count on age produced a slope of
0.797 for the entire sample and 0.889 for the nonperiodontal disease subsample. These slopes are consistent with a hypothesis of annual deposition of
cementum rings given a decrease in cementogenesis with increasing age.
An incremental structure of alternating
light and dark bands has been reported in
the dental cementum of at least 19 families
of mammals, including several primates
(Wada et al., 1978; Kay et al., 1984; Stott et
al., 1980). Counts of these layers, or annulations, have been employed and accepted as
accurate indicators of age among wildlife biologists (see reviews by Grue and Jensen,
1979; Klevezal’ and Kleinenberg, 1967; Morris, 1978; Spinage, 1973). Two recent studies
(Naylor et al., 1985; Stott et al., 1982) have
claimed accurate estimates of age in humans
using cementum layers in thick-cut (100 pm)
mineralized sections. Stott and coworkers
(1982),using a sample of three cadavers (ages
57,67, and 76 years) found 4 years to be the
greatest deviation between layer count
(added to age of tooth eruption) and age at
death. Unfortunately, the small sample size
of the study precludes evaluation of the accuracy of the estimates. In the study by Naylor and coworkers (1985), which was
primarily methodological, neither sample
size nor accuracy of the technique is reported. In neither study are measures of in0 1986 ALAN R.LISS, INC.
ter- and intraobserver error or variability
between and within tooth types in layer formation considered.
In a previous study, Charles and coworkers
(1986) evaluated inter- and intraobserver error in cementum layer counts and inter- and
intratooth variability in layer formation in a
sample of human mandibular canine and
first premolar pairs. Whereas canines produced counts with high interobserver error,
counts based On premolars provided reasonable levels of observer error and intratooth
variability. In an extended sample of 51 premolars, intraobserver variance was 2%, interobserver variance 5%, and intratooth
variance (i.e., variability in counts between
two sections of the same tooth) 4% of the total
variance. Thus cementum layer counts in
Received January 24,1986; revision accepted May 2. 1986.
Address reprint requests to Keith Condon, Department of Oral
Anatomy, College of Dentistry, University of Illinois at Chicago,
801 S. Paulina, Chicago, IL 60612.
322
K. CONDON, D.K. CHARLES, J.M. CHEVERUD, AND J.E. BUIKSTRA
premolars offer a highly repeatable method
of estimating age at death.
This study evaluates the accuracy of age
estimates based on cementum layer counts
in a sample of 80 human premolars. Equations for age estimation and for calculating
the error of these estimates will be provided.
The relationship between age and layer formation will also be investigated.
MATERIALS AND METHODS
Unfixed clinical extractions were collected
from the Oral Surgery Clinics of Northwestern University and the University of Illinois
a t Chicago and from private practitioners in
the Chicago area. Date of birth, date of extraction, sex, tooth identification and reason
for extraction were requested for each tooth.
The latter information, reason for extraction,
was not always supplied. Additionally, several teeth of known age and sex were generously donated by Dr. K. Bennett of the
University of Wisconsin. Canines and premolars were chosen for analysis, because examination of cadaver dentitions collected for
this study (N = 112) showed a high incidence
of premortem tooth loss for incisors and molars. Cadaver dentitions were not used because the cementum layers were not as
clearly defined in them as in clinical extractions. In a sample of mandibular canine and
first premolar pairs from 42 cadavers, consistent layer counts could not be obtained by
one or both observers in 11individuals (26%;
Charles et al., 1986). In contrast, in a sample
of 115 clinically extracted canines and premolars, there were no instances in which
counts could not be made. This suggests that
some substance in the preservative used in
the cadavers has a n effect on the staining
quality of the layers.
Demineralized root segments were sectioned longitudinally (7 pm) and stained with
hematoxylin following the procedure of
Charles et al. (1986). Thick-cut mineralized
sections were not used because of high rates
of intraobserver error reported for this technique (Charles et al., 1986).The sections were
evaluated using brightfield microscopy a t
magnification x 400. Areas of the cementum
showing 1)clear definition of layers from the
cementodentin junction to the periodontal
ligament and 2) no evidence of resorption
andor remodeling were photographed using
Ektachrome tungsten 160 film. Two to ten
such areas were photographed for each individual. The best two photographic slides
based on criterion 1 above were selected for
counting.
The age distribution of the sample was unknown to both the photographers and observers. The photographic slides comprising the
sample were randomly mixed prior to scoring. The slides were projected to approximately 22 x 28 cm, and repeated layer counts
of the projection were made until a consistent
count was obtained. The mean of these consistent counts was recorded as the number of
annulations for that section. A cementum
layer was operationally defined as a pair of
adjacent dark and light bands. All slides were
counted by a single observer a single time.
The two counts for each individual were then
averaged, and this average was used as the
best estimate of layer number.
Because several tooth types were used,
counts were adjusted by adding the age of
eruption to the mean count (Table 1).Ages of
eruption for the mandibular canine and premolars were taken from Demirjian and Levesque (1980). Sex-specificeruption times were
available for these teeth. Maxillary dental
eruption times were taken from Thoma and
Goldman (1960). The midrange of the age
interval of eruption was used, and sex was
not distinguished. Note that the age ranges
of the maxillary dentition from Thoma and
Goldman (1960)encompass those of the study
by Demirjian and Levesque (1980). These
studies were performed on populations from
northern temperate climates.
Based on the findings of Charles et al.
(1986),the canines (N = 44) were eliminated
from further analysis because of high interobserver error for these teeth. The age distribution of the remaining 80 individuals
(represented by premolars) is shown in Figure 1.
Equations for the estimation of age were
generated by using least-squares regression.
This method assumes no error in the measure of the independent variable (i.e., adjusted layer count; Sokal and Rohlf, 1981).
Although this is clearly not the case, as demonstrated by the presence of observer error
(Charles et al., 19861, least-squares regression is still the preferred technique since we
are interested in estimating age from layer
counts and attaching confidence intervals to
these estimates (Seim and Saether, 1983).
The degree of association between age and
adjusted layer count was measured by correlation coefficient and measures of inaccuracy
and bias. Inaccuracy is the average absolute
323
CEMENTUM ANNULATION AGING TECHNIQUE
12
>
0
z
9
W
3
c
l
W
a
LL
6
3
10
15
20
25
30
35
40
45
50
55
60
65
AGE
Fig. 1. Age distribution of the premolar sample (N = 80). The numbers below each bar
indicate the beginning age in years of the age class.
TABLE 1. Dental eruption ages used in adjusting
counts for aee estimates
Demirjian and
Levesque, 1980
Tooth
Male
Female
Thoma and
Goldman,
1960
(combined)
9.6
10.5
9-10
10.3
10.7
10-12
11.2
11.6
-
-
11-12
11-12
~
C
P1
~
-
P2
c
P1
-
-
-
10-11
P2
-
-
10-12
error of age estimation without reference to
over- or underaging, and bias is the mean
over- or underprediction (Lovejoy et al., 1985).
These latter measures (inaccuracy and bias)
are held to be more effective indicators than
the correlation coefficient, which is influenced by the age range and composition of
the test sample (Lovejoy et al., 1985).Inaccuracy and bias were calculated for each decade
of the sample.
Because of difficulties in generating a sufficient sample, no additional teeth were
available to test the equations using an independent sample. This problem was circumvented by using the jackknife technique
(Sokal and Rohlf, 1981).In this test, N regressions are run on sample sizes of N - 1,leaving out a different individual in each run.
Age of the excluded individual is then estimated using the derived regression. The
standard deviation of the residuals or standard error of the estimate was computed using standard jackknife techniques (Sokal and
Rohlf, 1981). Thus the jackknife provides an
evaluation of the standard error of the
regression using an outside sample. Little
difference was detected between standard
and jackknife estimates of parameters or
errors.
Finally, the structural relationship between age and layer formation was analyzed
using reduced major axis regression. This
model assumes measurement error in both
variables and better describes the relationship between the two variables than does
least-squares regression. This model assumes the relative sizes of the two error variances to be equal (Seim and Saether, 1983).
RESULTS
Age estimates
Three of the 80 individuals (4%;two males,
one female; ages 24, 37, 63 years) showed no
areas of layer formation suitable for estima-
324
K. CONDON, D.K. CHARLES, J.M. CHEVERUD. AND J.E. BUIKSTRA
tion. [This percentage was slightly higher in
the canines, where 12% (five of 44) of the
individuals showed incomplete or poorly defined incremental cementum structure.] An
additional four individuals were removed
from analysis following least-squares regression of the remaining 77 individuals. Examination of the residuals showed these four to
be outliers having a very strong effect on the
regression (Sokal and Rohlf, 1981). Examination of the four cases showed all to be
possible cases of “doubling,” a phenomenon
in which twice as many layers are present as
would be predicted given a n annual deposition. “Doubling” has been reported in several species (Grue and Jensen, 1979; Spinage,
1973). All four cases were maxillary second
premolars from males aged 30-59.
The least-squares regression of age on adjusted count for the remaining 73 individuals
produced a regression line with slope 0.973
and a y intercept of 2.4 years (Table 2, equation l).The slope is not significantly different from 1.0, and the y intercept is not
significantly different from 0 years. The correlation coefficient is 0.78, and the standard
error of the estimate is 9.6 years. A breakdown by sex of this sample produced no major differences; neither slope nor y intercept
is significantly different. Similarly, the correlation coefficients for the two sexes were
not statistically different, although the standard error of the estimate was smaller for
females (8.2 years) than for males (10.9
years).
Among the 73 individuals of the sample,
there were 18 reported cases of clinical periodontal disease. Since cementogenesis involves calcification of the periodontal ligament, any pathology altering the integrity of
the periodontium might be predicted to have
a n effect on cementogenesis and cementum
ring formation. As a partial test of this hypothesis, the 18 known cases of periodontal
disease were removed. The resulting regression produced a slope of 0.965 with a y inter-
cept of 0.4 years (N = 55; Table 2, equation
2). Again, the slope is not significantly different from 1.0, and the y intercept is not different from 0.0 years. The correlation coefficient
is 0.86 which is not significantly different
from that of equation 1. However, the standard error of the estimates has decreased to
7.4 years. Partitioning this sample by sex
produced significantly different (P < .0001)
correlation coefficients (males 0.733; females
0.946). However, neither the slopes nor the y
intercepts of the regression lines are significantly different. Standard errors of the estimates are 4.7 years for females and 9.4 years
for males.
The significantly different correlation coefficients between sexes suggests using sexspecific equations for age estimation. If sex
is unknown, and periodontal disease not
present, then equation 2 should be used.
Table 3 shows the inaccuracy (mean absolute error) and bias (mean error) by decade
for the nonperiodontal disease sample. Normalized values for the entire age range show
a n inaccuracy of 6.0 years, with essentially
no bias.
Error estimates
Plots of adjusted count on residuals showed
all the samples to be heteroscedastic, with
the spread of the residuals increasing with
increased count. This heteroscedasticity produces large standard estimates of the error
for all age ranges, although examination of
the scatterplot (Fig. 2) shows that age estimates for younger individuals will probably
be better than estimates for older individuals. To compensate for the heteroscedasticity,
two alternate error estimates can be used
with equation 2. The first alternate was computed by dividing the sample into two groups,
those with adjusted counts < 30 and those
with adjusted counts > 30. The mean adjusted counts of the two groups were plotted
against the mean of their respective residuals and the slope and intercept of the line
TABLE 2. Regression equations and correlation coefficients
-
Eauation
N
Y
Intercent
Sloue
r
r2
s.e.
1
la: males
lb: females
2
2a: males
2b: females
73
34
39
55
26
29
36.2
37.4
35.3
32.2
34.8
29.8
2.4
5.4
0.0
0.4
2.6
- 1.4
,973
,854
1.085
,965
.775*
.651*
.864*
.858*
.733*
.946*
,601
,423
,746
,735
,537
2394
9.7
10.9
8.2
7.4
9.4
4.7
,884
1.046
325
CEMENTUM ANNULATION AGING TECHNIQUE
TABLE 3. Comparison of inaccuracy and bias ofthe cementum
annulation aging technique with the summary age and revised pubis
techniques
Age group (years)
Cementum
11-17
Inaccuracy
Bias
18-29
_ _ _.
Inaccuracy
Bias
30-39
Inaccuracy
Bias
40-49
Inaccuracy
Bias
50-59
Inaccuracy
Bias
All ages
Inaccuracy
Bias
All aees normalized'
Inaccuracy
Bias
Revised
pubis'
Summary'
3.0
3.0
-
-
4.9
2.6
3.0
2.7
3.1
1.9
8.7
5.8
5.6
4.3
5.5
3.5
4.3
-3.0
5.7
1.2
6.1
0.2
8.9
-7.1
7.6
3.4
7.5
1.7
5.6
0.8
5.2
2.5
5.8
1.3
6.0
0.3
5.2
1.7
6.5
-0.4
-
I
'From Lovejoy et al. (1985;Table 3).
'Normalized error measures are the unweighted averages over all decades.
P
.
P
A&
A
k
>
P
P
P
P
lo
A0
ADJUST!;
COUNT
10
40
60
1
Fig. 2. Scatterplot and regression line of age on adjusted count for the nonperiodontal disease
sample (N = 55).
326
K. CONDON, D.K. CHARLES, J.M. CHEVERUD, AND J.E. BUIKSTRA
connecting them derived. Multiplying the
adjusted count by the slope and adding the y
intercept provides a n error estimate that increases with increasing age. This error estimate is calculated by the following equation:
Sz = 0.342
+ 0.178 (adjusted count).
(3)
The second alternative was derived by regressing the absolute value of the residuals
against adjusted count. Again, the error estimate is obtained by multiplying the adjusted count by the slope and adding this to
the y intercept, i.e.,
S3 = 1.295 + 0.1332 (adjusted count).
(4)
Examination of the two alternate error estimates shows both to be a function of adjusted
counts. Thus individuals with low adjusted
counts will have error estimates less than
the general standard error of the regression
given in Table 2. For example, a n individual
with an adjusted count of 24 produces error
estimates of 7.4 years (sl; standard error of
the regression), 4.6 years (sz), and 4.5 years
( ~ 3 )For
.
a n individual with a n adjusted count
of 60, the error estimates are 7.4 years (sl),
11.0 years (sz), and 9.3 years ( ~ 3 ) .
Weighted least-squares regression was not
used to correct for heteroscedasticity because
it provides a single point estimate of the
standard error of the regression. We believe
that the standard errors for predicted ages
should increase with age, as provided by the
alternatives (sz and s3) above.
In summary, three error estimates are provided for use with age estimates derived from
equation 2. The first is the standard error of
the estimate of the regression (7.4 years; Table 2, equation 2). This estimate does not
compensate for the heteroscedasticity of the
sample. The other two estimates are derived
using equations 3 and 4 and compensate for
the heteroscedasticity, providing narrower
error estimates for younger ages and wider
estimates for older ages.
Thejackknife
The jackknife analysis yielded standard error estimates essentially identical to those
produced by the regression. In the sample of
73 individuals (equation 11, the standard error was 9.7 years and the standard error of
the jackknife 9.8 years. Similarly, the standard error of the estimate for the nonperio-
dontal disease sample was 7.4 years and the
jackknife, 7.5 years. Jackknife regression
coefficients and associated standard errors
were also nearly indistinguishable from those
obtained by standard least-squares techniques.
Reduced major axis
If cementum rings are produced annually,
then reduced major axis regression of adjusted count on age should produce an axis
with slope 1.0 and y intercept of 0.0 counts.
The reduced major axis of the full sample
has a slope of 0.797 and a y intercept of 5.4
counts. Removing the cases of known periodontal disease increased the slope to 0.889
with a y intercept of 4.3 counts. Subdividing
this sample by sex showed females (N = 29)
to have a n axis with a slope (0.905) and y
intercept (2.8 counts) close to the norm for
annual deposition. The male (N = 26) axis
was flatter (slope = 0.829), with a correspondingly higher intercept (7.6 counts).
DISCUSSION
The results of this study show a high correlation between adjusted counts of cementum layers (i.e., the number of layers added
to age of tooth eruption) and age at extractiorddeath. Thus cementum layers in premolars can be used to estimate age with error
estimates ranging from 4.7 to 9.7 years, depending on sex of the individual and health
status of the tooth.
Table 4 compares the correlation coefficients reported in this study with those reported for a variety of age indicators by
Lovejoy et al. (1985). The correlation coefficient for the entire premolar sample (N = 73;
r = 0.78) is equal to the best single indicator
reported by Lovejoy et al. (1985), a revision
of the Todd pubic symphysis technique. The
correlation coefficient for the nonperiodontal
disease sample (N = 55; r = 0.86) is roughly
equal to the summary age technique, a multivariate composite aging method. However,
whereas the summary age technique reports
higher correlations for males (r = 0.90), the
cementum technique produces a higher correlation for females (r = 0.95).
The inaccuracy and bias of the cementum
annulation technique for the nonperiodontal
sample compare favorably with the \ d u e s
reported for the summary age technique and
are superior to those reported for the revised
pubis technique (Lovejoy et al., 1985; Table
CEMENTUM ANNULATION AGING TECHNIQUE
TABLE 4. Comparison of correlations of age indicators
with. real age
Age indicator
Cementum annulation
Full sample
Nonperio. subsample
Males
Females
Summary age'
Males
Females
Revised pubis'
Revised auricular surface'
Proximal femur'
Revised suture'
Dental wear'
Correlation
0.78
0.86
0.73
0.95
0.85
0.90
0.79
0.78
0.71
0.53
0.53
0.71
'From Lovejoy et al. (1985;Tables 5 and 6)
3). Overall (normalizedvalues), the summary
age technique provides slightly better age
estimates (5.2 vs. 6.0 years) with a bias to
overestimate. The accuracy of the two techniques is similar for all decades except for
the decade of 30-39 years, for which the summary age is superior. The reported inaccuracy of the cementum technique in the decade
of 20-29 years is heavily influenced by a
single case of doubling. If this individual is
removed (age 24; adjusted count 45),the inaccuracy falls to 3.2 years with a bias of 0.7
years. The cementum technique tends to overestimate age until the fourth decade, although overall the technique is unbiased.
Overall, the cementum annulation aging
method seems to be the most accurate single
aging criterion available for adults, being
comparable in accuracy to the best multivariate aging techniques (e.g., summary age;
Lovejoy et al., 1985). The addition of this
criterion to those already available should
increase the accuracy of age estimation in
forensic research.
The technique is also potentially applicable
to archeological material. A moderately well
preserved mandibular canine from a Late
Woodland site in Illinois ( - 1000 years BP)
was sectioned using both mineralized and
demineralized techniques (Charles et al.,
1986). Although the annulations were fainter than in modern material, counts were possible. The demineralized sections appeared
slightly macerated, suggesting that further
experimentation with the technique (e.g.,
gentler acids) will be necessary for archeological specimens.
327
The technique appears to work better for
females than for males, with error estimates
for females being half those for males. The
reason for this disparity is not clear. Although the female subsample has a slightly
younger mean age (29.8 years) than the
males (34.8 years), examination of the respective scatterplots shows females to form a
tighter cluster of points about the regression
line for all ages. It is possible that the sample
of males contains cases of unreported periodontal disease. Unfortunately, it was not possible to identify positively all individuals
with periodontal disease solely by examination of the cementum sections. Although the
presence of periodontal disease does not appear to alter either the slope or the intercept
of the regression significantly, it does substantially increase the error of the estimate
(Table 2). Periodontal disease also lowers the
slope of the reduced major axis of counts on
age, and the males have a shallower slope
than do the females.
The possible existence of unreported cases
of periodontal disease in the male sample
illustrates the difficulty in generating a sample to evaluate the technique. In that most
individuals are reluctant to have healthy
teeth extracted for scientific purposes, and
curators of skeletal samples of known age
are reluctant to allow destructive analysis,
the sample must be generated by clinical
extraction. Except for the relatively rare
cases of trauma and some cases of orthodontia, the majority of extracted teeth are probably diseased (decay, periodontal disease,
etc.). The effect of any or all of these diseases
on cementum layer formation is not clear.
However, comparison of the reduced major
axes of samples with (N = 73) and without
(N = 55) known cases of periodontal disease
shows the presence of this pathology to decrease the slope; i.e., fewer layers are present
than would be expected given an annual deposition. Whether this is a direct result of the
disease or the result of altered tooth function
cannot be determined here. The same effect
can be applied to other dental diseases. For
example, although decay may not effect the
root proper, the presence of decay (and pain)
may result in avoidance of tooth use, thus
altering the mechanical environment of the
tooth and, therefore, possibly cementogenesis and/or layer formation. In other words,
this sample may represent a worse case, with
328
K. CONDON, D.K. CHARLES, J.M. CHEVERUD, AND J.E. BUIKSTRA
better results obtainable in a working sample of healthy teeth.
The technique is not applicable to all individuals. In the premolar sample (N = BO),
three individuals (4%) showed a n incomplete
or poorly defined incremental layer structure
in their cementum. However, this phenomenon is true of all individuals in that most
areas of dental cementum in all individuals
show incomplete incremental structure. Although clarity of definition does differ between individuals, there is no relationship
between clarity of definition and accuracy of
age estimate. The source of this variability
in cementum structure both within a tooth
and between individuals is unknown. Grue
and Jensen (1979) note that among other species there is a broad relationship between
distinctiveness in layer differentiation and
the range between seasonal extremes in climate attributes. For example, in a northsouth gradient, lines are more difficult to
differentiate in animals from tropical regions. Alternatively, the variability in cementum structure may not, in fact, exist.
The various stains used in evaluating cementum layers are not specific for either of the
bands, as is demonstrated by the general
staining of all the tissues in the section. The
stains are used simply to dye the essentially
transparent sections and render them optically opaque. Therefore, the failure of the
various stains to define the layers cannot be
interpreted as a n absence of incremental
structure.
Another problem associated with the technique is the phenomenon of “doubling,” in
which approximately twice as many layers
are present as would be predicted by the age
of the specimen given a n annual deposition.
The doubling phenomenon has been reported
previously in humans (Stott et al., 19821,
marmosets (Stott et al., 1980), black bears
(Sauer et al., 19661, and other species (Klevezal’ and Kleinenberg, 1967). In this sample,
there were seven cases (9%)of possible doubling based on visual examination of the
scores (six males, one female; four maxillary
second premolars, three maxillary first premolars). Only four of these were removed
from the regressions (all males, all maxillary
second premolars) on the basis of high leverage. Unfortunately, examination of the suspected sections revealed no a priori way of
identifying doubling except in cases involving older individuals. For example, if layer
counts exceed 100, then one might logically
suspect a case of doubling and divide the
counts in half for a n approximate count estimate. Although the majority of doubling
cases in this sample were male, and all involved maxillary premolars, the sample size
is too small to determine if this is a bias.
Therefore, in estimating age from layer
counts in premolars, there is roughly a one
in ten chance that doubling is present.
The accuracy of the technique appears to
diminish with age and is therefore similar to
other physiological aging methods. Johanson
(19711, in a n evaluation of the Gustafson aging technique, noted that the general relationship of a n increase in cementum
thickness with increase in age tailed off in
the higher age ranges. Gasaway and coworkers (19781, Lowe (19671, and Ransom (1969)
noted among other species, a n increasing discrepancy between layer count with age in
moose, red deer, and white-tail deer, respectively. The origin of the age-related discrepancy is not known simply because the
underlying physiological process leading to
the deposition of cementum in alternating
light and dark bands is essentially unknown,
although various explanatory hypotheses
have been proposed (summarized in Morris,
1978; Spinage, 1973). The annual character
of the layer is most commonly assumed. Grue
and Jensen (1979) suggest a complex interaction of nutritional, climatic, genetic, and
functional factors to be responsible, but a
multifactorial model has yet to be formulated.
Reduced major axis analysis shows all the
samples to depart from the theoretical norm
of a n annual deposition. All the slopes were
less than 1.0, suggesting that age (years) accrues faster than cementum layers. If the
slopes are interpreted literally, then this suggests that layer counts do not represent annual depositions and that rates of formation
potentially can vary between populations,
thus requiring population-specific equations
for age estimates. Further, this indicates that
the counts provide a measure of physiological
rather than chronological age. It is possible
that the alternating light and dark bands
represent simply the method of cementogenesis, analogous to growth reversal lines in
bone.
However, a n axis with a slope of less than
1.0 does not negate a n annual deposition if
cementogenesis and layer differentiation are
independent processes. (Note that a n axis
with a slope greater than 1.0 does negate any
CEMENTUM ANNULATION AGING TECHNIQUE
329
annual hypothesis.) For example, if cementogenesis is a response to functional stimulation (i.e., occlusal forces) and the deposition
of the dark (or light) layer the result of some
annual environmental stimulus, then the
corresponding band would be produced only
if the root was undergoing cementogenesis at
the time of the stimulus. As noted by Johanson (1971), the increase in cementum width
with increasing age tails off in the older age
ranges, suggesting decreased cementogenesis with age. It is also documented that the
cross-sectional areas (and therefore probably
force) of the masticatory muscles decrease
with age (Weijs and Hillen, 1985). A decrease
in masticatory force might alter tooth loading and therefore alter cementogenesis. If
this model is correct, one would predict a
decrease in cementogenesis with age and
therefore a decrease in band formation, resulting in a slope of less than 1.0. Note that
a decrease in layer formation in the older age
ranges would not only decrease the slope but
correspondingly increase the y intercept,
which is the relationship seen in this study.
Although we present no evidence for or
against this model, it illustrates the difficulty in demonstrating the annularity of cementum rings in the absence of knowledge
of band etiology. However, the fact that the
axes approach the theoretical norm and do
not exceed a slope of 1.0 is consistent with an
annual deposition. This model is also consistent with the lower slope and higher y intercept found in the sample containing cases of
periodontal disease, the presence of which
one would predict to inhibit cementogenesis.
In that periodontal disease is most common
in older age groups, the effect would be to
decrease the slope and increase the y intercept of the major axis.
mates being approximately half those for
males. The presence of periodontal disease
also increases the error of the estimate. The
technique is not applicable in all cases; a
minority of individuals (4%) showed incomplete or absent incremental cementum structure. Another 9% exhibited the phenomenon
of “doubling,” for which there appears to be
no a priori means of identification.
Reduced major axis analysis of age on adjusted counts produced slopes not inconsistent with the hypothesis of annual deposition
of cementum rings given that cementogenesis decreases with age. Thus the technique
may be population-independent. However,
since the reduced major axes departed from
the theoretical norm of slope equal to 1.0 and
y intercept of 0.0, the issue of annularity of
cementum ring formation needs further
evaluation.
CONCLUSIONS
Charles, DK, Condon, K, Cheverud, JM,and Buikstra,
JE (1986) Cementum annulation and age determination in Homo supiens. I. Tooth variability and observer
error. Am. J. Phys. Anthropol. 71:311-320.
Demirjian, A and Levesque, G-Y (1980) Sexual differences in dental development and prediction of emergence. J. Dent. Res. 59:lllO-1126.
Gasaway, WC, Harkness, DB, and Rausch, RA (1978)
Accuracy of moose age determination from incisor cementum layers. J. Wildlife Management 425.58-563.
Grue, H, and Jensen, B (1979) Review of the formation
of incremental lines in tooth cementum of terrestrial
mammals. Dan. Rev. Game Biol. 11:l-48.
Johanson, G (1971) Age determination from human teeth
a critical evaluation with special consideration of
changes after fourteen years of age. Odontologisk Revy
22 [Suppl. 211 :1-126.
Kay, RF, Rasmussen, DT, and Beard, KC (1984) Cemen-
Adjusted counts of cementum rings using
7pm demineralized thin sections stained with
hematoxylin can provide reasonable estimates of age a t deathlextraction. Error estimates range from 4.7 to 9.7 years depending
on the sex of the individual and health status
of the tooth. Overall, the inaccuracy of the
technique is 6.0 years, with essentially no
bias. This compares favorably with the summary age technique of Lovejoy et al. (1985)
and is superior to any single macroscopic
technique reported to date.
The technique appears to provide better
age estimates for females, with error esti-
ACKNOWLEDGMENTS
This research was funded by NSF grant
BNS-8318587 to J.E.B. and J.M.C. Kerry
Knox and Rita Quinn assisted in the study.
We thank the directors of the Oral Surgery
Clinics of Northwestern University and the
University of Illinois at Chicago, Drs. Peccar0 and Blaustein, respectively, for their cooperation. The following dentists generously
provided additional specimens: Drs. Bertoglio, Borden, Bork, Brown, Cottrell, Fine,
Foertsch, Gargiulo, Grotz, Huddleston, A.
Martin, E. Martin, Maxson, Mayr, McGahey,
Messina, Nelson, Newton, Recktenwall, Scapino, Schleifer, Schultz, Soderstrom, Sokoloff, Urban, Van Hoozen, Varland, and
Wallace. Dr. Kenneth Bennett of the University of Wisconsin-Madison also generously
donated teeth for this analysis.
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