Expanding Juvenile Age Assessments using 2013
Recovered MCIG Subadult Dental Data
Draft Reading Version
PLEASE DO NOT CITE WITHOUT PERMISSION OF THE AUTHORs
Brianne E. Charles and Emily Mueller Epstein
University of Wisconsin-Milwaukee
Paper presented in Symposium: People that no one had use for, had
nothing to give to, no place to offer: The Milwaukee County Institution
Grounds Poor Farm Cemetery at the 80nd Annual Society for American
Archaeology Meeting, San Francisco, California, April 15-19, 2015.
Charles SAA 2013
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Brianne E. Charles and Emily Mueller Epstein
INTRODUCTION
Subadult skeletal remains expose a single moment in the intricate sequence of human
growth and development. The 2013 MCIG series of unidentified skeletal remains includes 283
subadult individuals with estimated ages ranging from 16 fetal weeks up to 20 years. It is a rare
opportunity to work with such a large number of relatively complete subadult remains and this
nodestructive research is meant to broaden the ability to make focused visual assessments of fetal
and infant stages of human life. The research centers on deciduous dental development within
the first 1.5 months after birth as well as extends a commonly used method of postnatal age
estimation into the fetal period.
BACKGROUND
Sample
The MCIG series of unidentified skeletal remains excavated in 2013 includes 283
individuals with estimated ages below 20 years. A total of 222 subadults have an estimated age
at death below one year based on dental and osteometric analysis. Skeletal analysts estimated
the ages of subadults in two stages during the project’s general analysis of human remains. The
first stage identifies broad age categories based on epiphyseal presence and fusion. The earliest
fusion age group, fetal-infant, encompasses individuals from prenatal up to 2.49 years. The
second stage of age estimation features dental and metric observations that are applicable to the
broad age group identified in the first stage. For the fetal-infant category, osteometric ages were
estimated using Fazekas and Kosa (1978) up to 40 fetal weeks and Maresh (1970) long bone
standards from 1.5 postnatal months forward. Mineralization, formation, and eruption of
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dentition were also analyzed to generate ages (Sunderland et al 1987; Ubelaker 1989a; Moorrees
et al. 1963a).
Dental and osteometric age ranges were identified for each individual and age categories
were assigned from the mean of each age range. Dental and osteometric age categories applied
to the collection of remains are as follows: fetal from 9 to 40 prenatal weeks, neonate from 40
weeks/birth to 28 postnatal days, infant from one to 11.9 months, toddler from one to 2.49 years,
early childhood 2.5 to 5.9 years, late childhood 6 to 12.9 years and adolescent from 13 to 19.9
years. There is noticeable disparity between age categories assigned through osteometric and
dental data. The number of individuals between fetal, neonate, and infant categories is fairly
even for dental ages, whereas osteometric ages skew heavily to the fetal category. This may be
attributed to a lag in skeletal development or may be an artifact of the methods used.
Data from our initial analysis reflects a major disparity in methods. From 40 fetal weeks
to the first month and a half of life, the standards provide no means to estimate age. This
disparity is stark given that fetal osteometric standards identify age in two-week intervals and
Moorrees et al (1963a) also has intervals as small as two weeks between tooth formation stages.
An aging method that spans the time of birth would be applicable for bioarchaeologists and
forensic anthropologists and has additional relevance in the MCIG context. The Register of
Burial for the grounds indicates that subadults buried there were more likely to have come from
the community rather than one of the county institutions. A significant number of subadult
entries are unnamed and listed as unknown, suggesting death was a result of abandonment or
infanticide (Richards 1997) Stillborn, aborted fetuses, or deaths resulting from medical
intervention during delivery are also possibilities among the remains. Refinement of age
estimations at this crucial time would be relevant to further investigations of the medical
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treatment of parturition and postnatal care as well as mortuary treatment of the unborn and
neonates in Milwaukee County during this time period.
Dental development is among the most useful and precise ways to estimate age because it
is relatively sheltered from stressors such as malnutrition and disease (Bowman et al. 1992).
Additionally, mineralization of primary dentition commences early in the fetus. Timing of
primary tooth mineralization, formation, and resorption varies between tooth type, creating a
staggered series of developmental stages that can generate a consistent, predictable, and
relatively precise estimation of age from early fetal life to maturation. Our goal is to fill in the
void between fetal and infant aging methods through the application of dental formation stages to
deciduous dentition.
Methods
Moorrees, Fanning, and Hunt published their original research on the formation and
resorption of the deciduous mandibular canine, first molar, and second molar in 1963. Samples
were obtained from the longitudinal growth records of Fels Research Institute (Yellow Springs,
Ohio). Radiographs were taken every three months for the first year and semi-annually
thereafter. A total of 136 males and 110 females were included and results of the study are
separated by sex. The dental formation and resorption stages were arbitrarily defined by the
researchers, but they note that they are similar to stages used by other investigators (Gleiser and
Hunt 1955; Demisch and Wartmann 1956; Garn et al 1959; Nolla 1960). The stages begin with
initial cusp formation and continue through the completion of the root apical closure. Separate
line drawings of each stage are provided for canines and molars. Molars have an additional stage
to mark the initial cleft formation between roots.
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Original results from Moorrees et al. (1963a) were published as horizontal line graphs
that plot the mean age of attainment and two standard deviations for each stage of formation.
Each sex has separate lines for the deciduous mandibular canine, first molar, and second molar.
When sex is unknown, the analyst is encouraged to take the average of the male and female
mean for the given stage and tooth. The earliest combined average of the sexes is 7.2 weeks or
1.8 months after birth.
Our sample consists of 152 individuals between the ages of 20 fetal weeks and 9
postnatal months. Prenatal age was generated from petros portion length since the petros portion
of the temporal bone had a high rate of survivability among individuals below 40 fetal weeks in
the sample. For postnatal individuals, we used ages based on the original Moorrees data for the
mandibular canine, first molar, and second molar. We did not attempt to separate the 2013
MCIG subadults by sex so all ages from Moorrees used in this study were an average of
published male and female means.
The sample size was limited by the assessability of the elements used in age estimation as
well as the presence of identifiable and assessable dentition. In some instances, articulated teeth
were assessable from within the alveolar process, although most often our observations were
made from loose teeth. Every identifiable and undamaged tooth was compared to the line
drawings published by Moorrees et al. (1963a) in order to determine the most suitable stage.
Results
This boxplot depicts the median age of attainment for all stages observed during the
study, with stages organized in ascending order from earliest to latest. The new age range based
on median age of stage attainment begins as early as 31 fetal weeks and extends to over eight
months after birth. A total of 14 stages, shown below the solid red line, are identified with a
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median age of attainment before birth. The dashed line marks 1.5 postnatal months, which is the
earliest postnatal age that can be derived from osteometric standards. The highest stage attained
from this sample is R1/2 or root length at one half of the expected length for the maxillary and
mandibular first and second incisors. The lowest stage is the initial cusp formation of the
maxillary canine and first molar. Since we limited our sample to fetal and infant individuals up
to the estimated age of six months at the time of death, newly generated stages do not extend far
beyond the six month mark.
Five stages with median ages between birth and 1.5 months were identified. Each stage
is associated with a distinct tooth, but the range is dominated by incisors at the Cr3/4 stage. The
first maxillary incisor has a median age of attainment at birth for the Cr3/4 stage, followed by the
same stage for its mandibular counterpart. The maxillary and mandibular second incisors have a
common median age of 4.7 weeks. Completion of the maxillary canine cusp outline also has a
median age of attainment at 2.9 weeks.
All median ages of stage attainment progress with dental formation with the exception
of the maxillary first molar. The age of attainment peaks at the initial root formation stage and
then decreases for the following two stages. This discrepancy may be explained by the low
number of specimens that were observed in the Ri (n=2), Cli (n=2), and R1/4 (n=1) categories
for that tooth. Application of the dental formation stages to additional individuals around 6
months and older would likely smooth out this discrepancy.
Discussion
Our results compare favorably with the sequence of tooth appearance and development
published elsewhere (Sunderland et al. 1987; Ubelaker 1989a). In particular, the incisors and
canines have earlier ages of stage attainment than molars and maxillary dentition develop earlier
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than their mandibular counterparts. Fourteen stages extend the Moorrees into the fetal period and
five stages fall between 40 fetal weeks and 1.5 postnatal months. The preliminary results are
promising, but a few additional steps need to be taken in order to validate the method. The ages
for this sample were unknown so the median ages of stage attainment reflect estimations of age
rather than actual age. The extended method should be applied to a sample with documented
ages at death in order to test the correlation between our own generated median ages of stage
attainment and actual biological age. Intra- and inter-observer error associated with the
formation identification process also need to be calculated. If valid, the new stages could be
applied to a series of fetal and infant remains from the 1992-1993 MCIG excavation.
Conclusion
Dental data is valuable because it is more representative of chronological age than
osteometrics, as seen in the variability between dental and osteometric ages for this sample. Our
proposed dental formulation stages narrow age estimations for neonates from 1.5 month
increments to as little as two weeks and broaden the applicability to remains that may have teeth
other than the mandibular canine, first molar, or second molar present. Multiple lines of
evidence for age estimation, such as interquartile ranges for multiple teeth from a single
individual, can narrow age estimations and potentially lead to more meaningful cultural identities
based on survivability past birth.
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