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An evaluation of the miles method of ageing using the Tepe Hissar dental sample.

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An Evaluation of the Miles Method of Ageing Using the
Tepe Hissar Dental Sample
GEORGE WESLEY NOWELL
Department of Anthropology, University of Pennsylvania, Philadelphia,
Pennsylvania 191 74
KEY WORDS Ageing methods
Tepe Hissar
-
Miles method
. Dental
wear
.
ABSTRACT
The Miles system of ageing, based upon analysis of the rate of
molar wear, was evaluated using the available dental sample from Tepe Hissar,
Iran. The independently estimated ages for the mandibles and maxillae of the
same individuals were found to be highly correlated (r = 0.87, p < 0.001). Ages
of a subsample of the dentitions were compared with skeletal ages for the same
individuals estimated from pubic symphyseal faces and found t o be significantly correlated (r = 0.82, p < 0.005) with no significant differences in the mean
ages. Although a complete evaluation of the Miles method would require its
testing on a controlled population, the available dental sample from Tepe
Hissar provided evidence of the reliability and validity of the Miles method of
ageing archeological populations on the basis of dental wear.
Due to selective retention of burial remains, the available skeletal sample
from Tepe Hissar 1-111 is not representative of the human populations of the
site and can not be used to generate meaningful demographic statistics.
Since dentitions have more often been recovered and retained for study than non-dental materials, a valid method of determining
ages based upon dental materials is of considerable importance in the study of archeological populations. This paper evaluates a
method of ageing based on dental wear previously described by Miles ('63).
THE SAMPLE
The dental sample used in the present assessment comes from the archeological site of
Tepe Hissar 1-111,Iran and dates to ca. 4000-?
(1900-1300) B.C. (Dyson, '68a,b). The majority
of the dental material dates t o between ca.
2400-1300 B.C. None of the few skeletal remains from Tepe Hissar dating from the
Partho-Sasanian or later periods is considered
in this report. The site was excavated by Erich
F. Schmidt in 1931 and 1932 (Schmidt, '33,
'37) and the skeletal material was studied in
part by Krogman ('40a,b,c) and Kappers ('34).
It was not possible t o derive reliable demographic data from this sample. The basic
conditions necessary for the generation of demographic statistics from archeological skeletal remains are:
AM. J. PHYS. ANTHROP. (1978)49: 271-276.
(1) the sample must accurately represent
the original populations of the cultural levels
of the site, and
(2) each skeleton must be attributable to
its proper level in the site. The evaluation of
the present skeletal sample in these terms
indicates that neither condition is adequately
met.
Since all of the skeletal material was found
on the elevated portions of the site, there is no
assurance in the final site report (Schmidt,
'37) that the skeletal population excavated
was not biased with respect to age or sex by
cultural factors regulating the place of interment. Schmidt ('37) also did not test extensively for alternate burial locations in the
unexcavated portions of the site and in the
surrounding plain. Both Krogman ('40a) and
Schmidt ('37) note a marked predominance of
males over females in each level and it can not
at present be determined why this should be
so. No attempt was made to reassess the sex of
the individuals in the sample during this
study.
Only a small fraction of the individuals excavated were represented in the available
skeletal sample. Although Schmidt ('37) re-
271
272
GEORGE WESLEY NOWELL
corded the excavation of 1,637 burials, Krogman ('40a,b,c) was sent fewer than 250 individuals to study and the author found skeletal
remains of only 479 individuals in the collections of the University Museum of the University of Pennsylvania (table 1).The generally
excellent condition of the bones and their
small number relative to the total excavated
population suggests that Schmidt brought t o
the United States only the best-preserved
bones. A comparison of the age distribution of
this study to Schmidt's ('37) figures shows a
great disparity in the number of juveniles,
aged zero t o six years. In the present sample
there were 19, compared t o 151 excavated during the second working season alone. There
may be a similar bias against the presence of
older individuals (45 years of age a t death)
in the sample available for analysis. The extent of these possible biases is unconfirmable
because of the unreliability of the ages determined in the field.
The excavator's field records and reports
+
TABLE I
Inventories of the Tepe Hissar I-lllskeletal material
Krogman ('40a)
Crania
Mandibles
Post cranial
Individuals represented
Present study
193
138
58 '
216
211
238
299
479
' Parts of 58 individuals
Parts of 299 indinduals
often do not attribute individual burials and
skeletal materials to specific cultural sublevels. Thus, sampling and recording problems
involving the skeletal materials both as excavated and as retained for study preclude their
use as indicators of the demography of the
populations of Tepe Hissar 1-111.
These sampling problems do not significantly affect the evaluation of the Miles system of
ageing dental remains, since all dentitions
came from one site and the individuals were
exposed to the same general diet. All 268 individuals from Tepe Hissar 1-111represented by
at least one dentition with molars ageable by
the Miles method were aged. The sample used
to evaluate the Miles method consists of all
139 individuals represented by both ageable
upper and lower dentitions and includes 120
adults (aged 15.0 years and older) and 19
juveniles (table 2).
METHODS
The Miles method of ageing (Miles, '63)
assumes general uniformity of dental wear
rates and patterns throughout the population
studied. Only molars are used in the method,
since the molars demonstrate the greatest
degree of consistency in wear patterns and
rates. The Miles method can only be employed
on a dental population which includes dentitions of a t least 20 immature individuals
ageable t o between 6 and 19 years on the basis
of dental development alone. The immature
dentitions serve as the first baseline for the
TABLE 2
Comparison of the age estimates assigned to the mandibles and maxillae of the same individuals
Campanson of means of
estimated ages
Group
Correlation of ages assigned
to same individuals
N
Adult (15.0years and older)
Aged by Miles method
Aged by Miles method
(but nooccluaal partners)
Aged by dental development
Juvenile (younger than 15 years)
Aged by Miles method
Aged by dental development
Entire sample
h t i r e sample (less those with
no occlusal partners)
' Pearson correlation coefficient.
't-test for the significance of r. * p < 0.0005.
All agea in years.
r'
Mean age
t2
Mandible
Maxilla
t
19.14'
19.58'
26.85
27.17
26.87
27.44
0.00
0.09
0.46
0.09
39.50
17.50
32.75
17.44
0.72
0.03
10.05
12.00
9.94
0.55
120
107
0.87
0.89
4
9
-0.31
0.03
19
1
18
0.95
12.04*
0.95
11.67*
9.58
11.00
9.50
139
0.93
29.90'
24.49
24.57
0.02
135
0.95
34.86'
24.05
24.33
0.10
-
-
-
0.51
273
MILES METHOD OF AGEING TEPE HISSAR DENTITIONS
TABLE 3
Comparison of the age estimates assigned to individual mandibles and maxillae on two occasions
(age-reagereliability su bsamplesl
Comparison of means of estimated ages
Correlation of age8 assigned
to same individuals
Dentition
Mandible
Maxilla
Mean age '
"
r2
t 3
Ageing
Reageing
20
0.99
0.99
30*
30'
28.8
28.8
29.65
20
29.8
t
0
0.03
The mandibular and maxillary subsamples used were not identical.
Pearson correlatian coefficient.
3t-test for the significance of r. * p <0.0005.
All ages in years.
I
establishment of the basic rates and patterns
of dental wear used to accomplish the rest of
the ageing.
The development of the baseline is dependent upon the comparison of the wear of the
second and third molars of slightly older dentitions with similar stages of wear of first and
second molars representing functional ages in
the existing baseline. The functional age of a
tooth is the number of calendar years a tooth
is in occlusion with its partner in the opposing
dentition. The older dentitions are assigned
estimated chronological ages as described
above and are integrated into the baseline t o
extend the baseline t o the chronological limits
of the population. Adding the functional age
t o the eruption age of a particular molar yields
an estimate of the chronological age of the individual a t death. Conversely, subtraction of
the eruption age from the chronological age a t
death yields the functional age of the stage of
wear of the tooth. It is through the latter process that the baseline is established and
through the former that the majority of the
individuals are aged. The extended baseline is
expanded during the study by incorporating
into it those dentitions best illustrating each
different pattern or degree of wear assigned to
the same chronological age.
In this study, first the mandibles were
assigned ages in accordance with the Miles
method outlined above. After the maxillae
had been aged by the Miles method independently of the mandibles, each mandible was
articulated with its maxilla if available and
the age estimates were compared.
After the entire dental sample had been initially aged, subsamples of 20 maxillae and 20
mandibles were selected randomly from the
non-baseline materials. The subsamples were
re-aged independently of the initial ageing
against the appropriate baselines in the identical manner outlined above to assess the
reliability of the author in the application of
the Miles method of ageing. Also, all available
pubic bones belonging to the individuals aged
by the Miles method were aged according to
the standards of McKern and Stewart ('57).
RESULTS
The insignificant differences in the mean
ages and the correlation coefficients of the
first and second ageings of the subsamples of
maxillae and mandibles re-aged by the Miles
method indicate the high degree of reliability
of the author in his use of the Miles method
(table 3).
All individuals in the skeletal population
for whom both the maxilla and mandible were
present were divided into five subgroups on
the basis of age, manner of ageing and the
presence or absence of occlusal partners (table
2). There were no significant differences (p >
0.05) between the mean ages of the mandibles
and maxillae in any of the subgroups, as indicated by the t-test for dependent means. The
correlation coefficients between the estimated ages of the mandible and maxilla for
the same person are r = 0.87 (table 2). For the
entire sample and for each group with a size
greater than ten, the correlation was significant (p < 0.005). These data suggest the
reliability of the Miles method as used in this
study.
The absolute differences between the ages
assigned to the mandible and maxilla of the
same individuals were tabulated. Sixty-six
percent of all the adults have ages assigned to
both the mandible and maxilla of the same
person within two years of each other and 93%
have both ages assigned within five years of
each other. In the absence of those cases in
274
GEORGE WESLEY NOWELL
TABLE 4
Comparison of the age estimates assigned t o the dentitions andpubic bones of the same individuals
Comparison of means of eatimated ages
Subsample
Maxilla-pubic
Mandible-pubic
Correlation of pubicdentition ages
Mean ages
N'
r2
Dental
Pubic
Difference in
mean age
t
12
17
0.82*
0.88*
25.83
28.41
27.67
28.41
1.84years
0
1.46
0
' Eight individuals were common t o both subsamples
Pearson correlation coefficient. * p < 0.005
which all the occlusal partners of the ageable
molars were lost ante-mortem, the correspondence of the estimated ages is notably
closer.
The mean estimated ages of the pubic bones
and dentitions subsamples were not significantly different (p > 0.05) for either the mandible or the maxilla subsamples (table 4). The
correlation coefficients between the estimated ages of each dentition and the pubic
symphyses for the same persons were significant (p < 0.005) (table 4). These data support
the validity of the Miles method.
all three molars appeared and the final baseline well represented the consistent rates and
patterns of wear. The sequence for the third
molars was not as consistent as those of the
first and second molars on a year-to-year
basis, probably because the third molars did
not erupt or become functional as regularly as
did the first and second molars. Although
Miles ('63) employed a wear rate ratio of 6 :
6.5 : 7 (M, : M, : MJ for the Anglo-Saxon population he described, there appeared t o be no
consistent difference in the rate of wear between the first and second or first and third
molars in the present study.
DISCUSSION
The observed differences in wear pattern
To assess the validity of the statistics pre- could not be ascribed to any testable variable
sented above, it is necessary to review the (for instance cusp pattern or sex) and are
hypotheses upon which the Miles method is assumed to be due to differences in (1) individbased, the sources of error inherent in the ual occupations andlor habits, (2) chewing
system, and the results of previous efforts to patterns, (3) diet or manner of food preparaage this population using different ageing tion, (4) tooth composition either due to variations in the genetics or the environment of the
methods.
It is hypothesized in the Miles method (1) developing individuals (or both), or most likethat dental wear is continuous during the ly to some combinations of several of the
functional life of the tooth, (2) that wear on above. The differences in dental wear patterns
all three molars proceeds a t comparable rates are most apparent in several individuals with
through similar states and patterns and (3) dentitions worn relatively flat, but with
that wear and diet are effectively uniform minimal dentine pits. The dental wear patwithin the population. Unfortunately, (1) terns from Tepe Hissar vary substantially
quantification of the effect of tooth loss or de- from those of the Australian population discay on the rate and patterns of wear of the re- cussed by Murphy ('59) and had worn more
maining teeth is a moot point; (2) that wear rapidly than those of the Anglo-Saxons illuson all three molars proceeds a t comparable trated by Miles ('63).
Although the diet of the people of Tepe
rates even in the absence of external changes,
such as loss or decay of teeth, is unproven; and Hissar has been hypothesized t o have been
(3) different patterns of dental wear are ap- uniform and based on the products of domestiparent in this population. There remains no cated plants and animals, the individual diets
conclusive evidence that cultural factors af- undoubtedly varied due to economic exigenfecting dental wear rates and patterns did not cies and social or personal preferences. All
vary significantly through the cultural levels variation in culture, genetics and environment would also adversely affect the validity
of Tepe Hissar 1-111.
However,in both the maxillary and mandib- of the dental ages assigned to the degree that
ular baselines, a generally consistent, clear it affected the rates of wear of the permanent
progression of degrees and patterns of wear in molars. However, one of the strengths of the
MILES METHOD OF AGEING TEPE HISSAR DENTITIONS
Miles method is its population specificity
which enables a properly constructed baseline
to reflect the normal range of dental wear
rates and patterns resulting from such variations. By establishing the baseline on the basis
of dental development through 19 years, the
circumstances reflected are those of adults as
well as juveniles. A baseline specific to one
population can be used with another population only if variations in the factors affecting
the rates and patterns of dental wear are nonsignificant.
An important source of error in the Miles
method is that any inaccuracies in the earlier
parts of the baseline based on dental development would be retained throughout the extensions of the baseline. In fact, Garn et al. (’59)
report that Kronfeld’s (‘54)chart, relied on by
Miles (‘63) and in this study, is too narrow in
its range of variation attributed to the stages
of deciduous and permanent dentition formation. However, (1) elimination from the baseline of those dentitions with a large variation
in the assigned molar ages reduces the potential error due to using one or more of the divergent molars; (2) the incorporation into the
baseline of dentitions with different wear patterns expressly recognizes variation in the
progression and patterns of dental wear; and
(3) the averaging of the ages arrived at for
several molars, each compared with different
parts of the earlier baseline, helps to reduce
the effects of any single part of the baseline
and yields a more reliable age for the individual. It is unlikely that the baselines developed
in this study were markedly skewed from
their true chronological analogs, since the differences between the means of the ages of the
maxillae, mandibles and pubic symphyses of
the same individuals aged according t o independent baselines and methods are not significant (tables 2,4).However, since it is assumed
that the first, second and third molars become
functional during the sixth, twelfth and nineteenth years respectively, an individual whose
teeth erupt or become functional irregularly
or uniformly late/early would be aged more
inaccurately than other individuals. The more
variable the age of eruption or commencement
of function of the third molars, the more difficult it is to establish a valid baseline and
accurately age the adult population.
Although table 2 indicates the high reliability of the Miles method, there were 17
cases where the difference between upper and
lower dentition is five or more years. Esti-
275
mated age differences between the mandible
and maxilla of the same individual of up to
five years may be accounted for completely by
the differences in the wear patterns of the two
baselines in all cases but one. Differences of
five years and greater in the age determinations were due to: (1) the ante-mortem loss of
the occlusal partners of all ageable molars (4
cases) ; (2) ante-mortem loss and/or presence
of caries or alveolar abscesses in the vicinity
of the occlusal partners of one or more molars
probably contributing to peculiar wear patterns and rates of parts of each dentition (4
cases); (3) extremely different, but common
wear patterns or rates of the mandibular versus maxillary molars for no discernable reason
yet so different as to suggest that the dentitions represent two different persons ( 3
cases); (4) unique wear pattern of one or both
dentitions (3 cases); and (5) the small number
of molars available (3 cases). These data indicate that although a careful ageing of both the
mandible and maxilla of one individual will
usually yield age estimates within five and
even two years of each other differences of
nine years can be due solely to different wear
rates or patterns of the maxillary and mandibular molars. By articulating and evaluating
the mandibles and maxillae before estimating
the age of the individual, peculiar circumstances affecting the wear of the molars can
be noted and a more valid age estimate developed. In this study, mandibles and maxillae
of the same individuals were not articulated
prior to ageing only in order to evaluate more
objectively the reliability of the Miles method
by comparing independently aged maxillae
and mandibles.
The validity of the Miles method can be
assessed by comparison of its age estimates
with those based on endocranial suture closure or on the pubic symphysis. In this case,
comparison of the results of the Miles method
with the results of each alternate method is
not completely satisfactory since the samples
are not the same. In the case of endocranial
suture closure, Krogman (‘40a) aged 154 adult
crania and reported a mean age of 29.1 years.
The present study aged maxillary or mandibular dentitions of 133 of the Krogman sample
with a mean age of 28.1 years. Mandibles or
maxillae with no ageable molars were available for 11 more members of the original sample with no dental evidence apparent for the
remaining 10 members. Since the samples
were not identical, the 11 unageable individ-
276
GEORGE WESLEY NOWELL
uals would probably be aged older than 30
years if molars were present and there is
usually some difference between dental and
skeletal ages, the observed differences in t h e
estimated mean ages are not important.
Comparison of dental and pubic symphysis
age estimates (table 4) is conservative because of t h e difficulty of positively attributing the pubic bones and dentitions to the same
individuals and t h e normal variation between
the dental and skeletal ages of the same individual. Since McKern and Steward validated
their procedures while working with a contemporary all-male sample, the application
of their method to a 4,000- to 6,000-year-old
population and especially to female pelves
would introduce an additional source of error
(Gilbert and McKern, '73). The favorable
comparison of the dental ages with skeletal
ages for the same individual further substantiates the equation of one dental functional
year with one chronological year. It is apparent from these results that the Miles method can be a valid method of ageing skeletal
populations.
ACKNOWLEDGMENTS
Special thanks is owed Erich Schmidt for his
preserving so much skeletal material from
Tepe Hissar at a time when excavators usually discarded bones. Doctor W. M.Krogman has
been very helpful throughout this study both
because of his past meticulous study of the collection, and his continuing interest in t h e relationship of physical anthropology to archaeology and forensic medicine. I thank Doctor
Robert H. Dyson, Jr., Professor of Anthropology and Curator of the Near Eastern Section
of the University Museum a t the University of
Pennsylvania, for his helpful criticism of the
manuscript in its early stages.
I am grateful to Doctor Alan E. Mann, Associate Professor of Anthropology at the University of Pennsylvania, who as my advisor gave
encouragement, constructive criticism, time
and help throughout this project. I thank Mr.
Robert White and the members of the Department of Radiology a t the Hospital of the University of Pennsylvania for their generosity in
the preparation of the X-rays used in this
study. And, I am especially indebted to my
wife, Carla Senders Nowell, for her critical
reading of the manuscript and her advice on
the statistical content of this paper.
LITERATURE CITED
Dyson, R. H., Jr. 1968a Annotations and corrections of
the relative chronology of Iran. Am. J. of Archaeology, 72:
308-313.
1968b The archaeological evidence of the second
millennium B. C. on the Persian plateau. Cambridge
Ancient History (Rev. Ed.) fascicle 66. Cambridge University Press, Cambridge.
Garn, S. M., A. B. Lewis and D. L. Polacheck 1959
Variability of tooth formation. J. of Dental Research, 37:
135-148.
Gilbert, B. M., and T. W. McKern 1973 A method for aging
the female 0s pubis. Am. J. Phys. Anthrop., 38: 31-38.
Kappers, C. U. A. 1934 An Introduction to the Anthropology of the Near East in Ancient and Recent
Times. N. v. Noord-Hollandsche uitgevers maatschappij,
Amsterdam.
Krogman, W. M. 1940a Racial types from Tepe Hissar,
Iran from the late fifth to the early second millennium,
B. C. Verhandelingen der Koninklijke Nederlandsche
Academie van Wetenschappen, Afdeeling Natuurkunde
(Section 21, 39(2):1-87.
- 1940b The peoples of early Iran and their ethnic
affiliations. Am. J. Phys. Anthrop., 26: 269-308.
194Oc The skeletal and dental pathology of an
early Iranian site. Bulletin of the History of Medicine, 8:
28-48.
Kronfeld, R. 1954 Development and calcification of t h e
human deciduous and permanent dentition. In: Basic
Readings on the Identification of Human Skeletons. T. D.
Stewart and M. Trotter, eds. Wenner-Gren, New York,
pp. 3-10.
McKern, T. W.,
and T. D. Stewart 1957 Skeletal changes in
young American males. Quartemaster Research and Development Command Technical report EP-45, Natick.
Miles, A. E. W. 1963 The dentition in assessment of individual age in skeletal material. In: Dental Anthropology.
D. R. Brothwell, ed. Pergamon, New York, pp. 191-210.
Murphy, T. 1959 The changing pattern of dentine exposure in tooth attrition. Am. J. Phys. Anthrop., 17:
167-178.
Schmidt, E. F. 1933 Tepe Hissar Encavations 1931. The
Museum Journal (University Museum, University of
Pennsylvania), 23: 323-487.
1937 Excavations a t Tepe Hiasar Damghan.
University of Pennsylvania Press, Philadelphia.
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