B.A., University of Texas at Austin, 1999
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of
Science in Human Biology in the Graduate School of the University of Indianapolis
May 2005
Copyright © 2005 Emilie L. Smith. All Rights Reserved

FORM B
Accepted by the faculty of the Graduate School, University of Indianapolis, in the partial fulfillment of the requirements for the Master of Science degree in
HUMAN BIOLOGY
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Thesis Advisor – Dr. Stephen P. Nawrocki, D.A.B.F.A
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Reader – Dr. Christopher W. Schmidt
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Reader – Dr. Jeffrey A. Dean
5-15-05
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Date i

DEDICATION
This thesis is dedicated with love and gratitude to my family for their extraordinary commitment to my education. Without your constant encouragement and support, I would not have had the courage to pursue my education to this level.
This thesis is also dedicated to my best friend of eighteen years, Meredith M. McQuiston, who stood beside me and urged me at every step of the way. ii

ACKNOWLEDGMENTS
This project would not have been possible without the enthusiasm, support, encouragement, and creative insight of many people. First and foremost, I would like to thank my advisor Dr. Stephen Nawrocki, whose assistance and guidance was instrumental in the completion of this thesis. Additionally, I would like to thank the faculty members of the
Department of Biology at the University of Indianapolis.
I would like to express a special thanks to this study’s Principal Investigator, Dr. Edwin
T. Parks with the Department of Oral Pathology, Medicine, and Radiology at the Indiana School of Dentistry for generously offering his time to be the P.I for this study and for his assistance in gaining access to the charts at the Riley Hospital for Children Pediatric Dental Clinic.
I would also like to thank the proofreaders of the early drafts of my thesis, particularly
Dr. Jeffrey A. Dean, whose extensive efforts to accommodate my needs during the accumulation of my research at the dental clinic will never be forgotten and Dr. Chris W. Schmidt, for his many contributions and limitless knowledge of the teeth.
I would like to express my gratitude to everyone at the Riley Hospital for Children
Pediatric Dental Clinic for all their help, assistance, and guidance, with special thanks to Dr.
Richard D. Jackson, Dr. Brian J. Sanders, Marsha Thomas, Donna Bumgardner, and Rachel
Boruff.
Additional thanks to Dr. Douglas Ubelaker and Taraxacum Inc. Publishers for granting permission to reprint a copy of the1989 Dental Aging Chart and Julia Mead for giving her official permission to include the American Dental Association-copyrighted Development of
Human Dentition Chart within the body of my thesis.
I am quite fortunate to have been surrounded by smart, funny, and caring friends and iii

colleagues who made substantial contributions to my thesis, in addition to my well-being!
Thanks to Jill Masters, Denver Gray, and Nancy Masters for helping me to keep my sanity and a smile on my face - I will always remember and cherish our time as roommates. I would also like to thank Krista Latham, Nicolette ‘Chick’ Parr, and Janene Curtis, who offered their friendship, listened to my numerous concerns, dissipated them with great ease, and provided knowledgeable advice.
Lastly, I would like to thank my best friend (Meredith), my sisters (Gina Marie, Melissa, and Suzanne) and my parents (Ernest and Marie), who provided me with endless supplies of support and encouragement. iv

ABSTRACT
In forensic anthropology and dentistry, the age at death of an unknown individual must sometimes be estimated from the teeth. Various charts are utilized to age subadult human remains by comparing the teeth present with the standardized pictures to obtain a target age estimate. The two main charts used today were published by Schour and Massler (1944) and
Ubelaker (1978; 1989). Each of these charts includes pictures of the teeth at different ages and are very similar in their illustrations, primarily because the latter is derived from the former.
The purpose of this study is to determine whether Schour and Massler’s and Ubelaker’s charts are appropriate for estimating the ages of modern children, to ascertain which one is more accurate, and to see if their target age and associated error ranges are still applicable. Since these charts are used regularly by osteologists, it seems appropriate to subject them to rigorous testing with a known-age sample. Unfortunately, no such tests have been conducted, so the present study fills a void in the literature. In addition, with the increased use of DNA techniques, it has become easier to determine sex from subadult remains. Therefore, it may no longer be justified to combine males and females if indeed there are significant sex differences in dental development. Failure to separate the sexes would result in greater aging errors for both. Thus, a secondary purpose of this study is to determine if dividing the sample by sex would increase the overall accuracy of the charts.
The study sample is composed of 419 modern European American children aged 5-15 years. These children were randomly selected and approximately equal numbers of males and females were chosen for each year of age. Panoramic radiographs were examined to assign a stage of formation and eruption to the teeth as a whole. The target age given by each chart for a v

particular dental stage became the predicted age for each child, which was then compared with the known chronological age.
Various summary statistics were calculated for each chart, including mean age and observed age range per stage. Measures of mean error (bias and inaccuracy) were calculated for each stage and for each chart as a whole. The percentage of individuals correctly falling within the predicted +/-2 standard deviation interval for each stage was also calculated. The data were then evaluated for sex differences using t-tests and analysis of covariance (ANCOVA). New target ages and 95% prediction intervals were calculated for each stage for each chart.
This study found that Schour and Massler’s and Ubelaker’s charts are equally effective at determining age when the new target ages and associated error ranges are applied. Mean ages per stage are about half a year higher than the whole years provided on both charts, meaning that the charts tend to underestimate age at death. Ubelaker’s chart is slightly better with respect to the robusticity of its error ranges, but Schour and Massler’s chart has slightly lower inaccuracy and bias values. Not surprisingly, the narrow error ranges originally provided by Schour and
Massler do not work. Additionally, there are small but significant sex differences in age for some of the later dental stages, which can affect the overall accuracy of age estimation. vi

TABLE OF CONTENTS
Signature Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2: Dental Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Chapter 3: Development of the Dental Aging Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chapter 4: Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Chapter 5: Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Chapter 6: Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 vii

CHAPTER 1: INTRODUCTION
Comprehensive knowledge of growth and development is fundamental in gaining an understanding of morphological variation in children. An assessment of the state of an individual’s dental development can be important in the evaluation of his or her overall maturity and can be used to compare growth and health between individuals and populations. In addition, the state of dental development can be used to ascertain the age of an unidentified child.
To determine age, one compares information obtained from the skeleton, in this case the teeth, and then translates this morphology into an approximate chronological age. Dental age is therefore a predictor of actual age. Analysis of subadult dentition for aging purposes seems to be fairly robust, especially since it has been determined that the formation of the teeth is reasonably resistant to environmental influences. Tooth formation is generally viewed as a “progressive, continuous, and cumulative process” (Prahl-Anderson and Van der Linden, 1972:535).
In forensic anthropology and dentistry, age at death is estimated by comparing the decedent’s teeth with a series of standardized images of dentitions at different ages presented on comprehensive charts. A target estimate is then assigned to the unknown individual. The two main charts utilized by anthropologists were prepared by Schour and Massler (1944) and Ubelaker (1978;
1989). These charts are similar and provide line drawings of the teeth in 21 different developmental stages from just prior to birth to early adulthood. However, there are some differences between these charts in their depiction of the development and eruption of specific teeth and in their designated error intervals. These charts are not sex-specific even though many authors have noted a distinct sexual dimorphism in the formation and eruption of the teeth (Schour and Massler, 1941;
Steggerda and Hill, 1942; Gleiser and Hunt, 1955; Lewis and Garn, 1960; Glister et al., 1964;
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Ubelaker, 1978; Smith, 1991).
Morphological vs. Chronological Age
The term ‘chronological age’ is used throughout this thesis to refer to the actual age of an individual. Krogman (1968a:175) defines chronological age as the “birthday - or calendric age of the child. It is based on sidereal time and is constant” (1968a:175). “Dental age,” on the other hand, refers to the morphological state of an individual’s dentition without reference to their actual age. Moorrees et al. (1963a) describe dental age as involving both the formation and the emergence of the teeth. Krogman (1968a:175-6) defines dental age as “the variable to moderately variable registry of biologic time in the developing dentition,” which he divided into two subtypes: calcification age and eruption age. Calcification age is defined as the “stage-sequence of tooth development from first appearance of cusp(s) to root apical closure,” a concept that is similar to
Moorrees et al.’s ‘tooth formation’ (Krogman, 1968a:175-6; 1968b:335). Eruption age is defined as
“the progressive emergence of the tooth from its alveolus into functional occlusion,” which is similar to Moorrees et al.’s (1963a) ‘emergence’ (Krogman, 1968a:175-6).
The term ‘dental development’ is not always defined in the literature and often seems to be
(incorrectly) used as a synonym for dental formation. In this particular thesis, use of ‘development’ will follow Garn et al. (1958), who assert that dental development is composed specifically of calcification (including crown completion and root formation) and eruption. Similarly, Smith
(1991) describes dental development as the combined processes of formation and eruption. She defines formation as the “formation of an organic matrix and its subsequent calcification
or mineralization ” (1991:144). In this study, formation, mineralization, and calcification will all be used interchangeably to refer to the development of the crown and roots.
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Moorrees et al. (1963a:1490) define physiological age as an estimation of “maturation of one or more tissue systems, and . . . is best expressed in terms of each system studied. Maturation is scaled by the occurrence of one or the sequence of multiple events that are irreversible.” The authors state that ‘physiologic age’ and other commonly-substituted words for terms such as
‘biologic’ and ‘developmental’ age are merely intended to describe the morphological status or state of a child, whereas chronological age suggests an approximation of status due to the range in observed development for any age. Shumaker (1974:55) suggests that “chronologic age norms deal with the mean and the physiologic age norms deal more closely with individual development.”
Various authors have compared ‘dental age’ with ‘chronological age’ and ‘skeletal age.’ A common definition of ‘skeletal age’ can be derived from Krogman and is “the registry of biologic time in the developing skeleton” (1968a:175). Scheuer and Black identified three phases that comprise skeletal development including: (1) formation of the centers of ossification, (2) the growth of the centers of ossification, and (3) the time during which fusion of the center with a separate center of ossification occurs (2000:6). Green (1961) examined a sample of 56 European
American males ages 8 to 12 and found that dental age is more correlated with chronological age than with skeletal age. This finding is similar to those of Holz et al. (1959), who noted a closer association between chronological age and dental age than between skeletal age and dental age.
Krogman (1968a,b) and Demirjian (1986) determined that dental development has a close association with chronological age. Lewis and Garn (1960) also found that the stages of tooth formation are less variable than the stages of skeletal development. Kullman (1995), however, found that a determination of dental age was not as accurate as skeletal age when studying children between the ages of 14 to 18. Bambha and Van Natta (1959) found no evidence of an association between skeletal age and dental eruption. Grøn (1962) determined that tooth emergence was
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closely related to the stage of root formation rather than to chronological or skeletal age. Feasby
(1981), however, found a low correlation between the dental eruption rate and root formation.
Various problems in age estimation arise from a lack of rigorous testing, a lack of proper statistical methods, and because of differences in secular and population trends. It has also been noted by various authors that many studies do not include important information on methodology, ages of subjects, sample sizes, and statistical methods used (Smith, 1991; Scheuer and Black, 2000).
Therefore, many studies are not comparable because of the inherent difference between the underlying variables. This problem can lead to conclusions that any differences between samples are due to true population differences, when in reality they are more likely a result of sampling effects or the misuse of statistical procedures.
Anthropological and Forensic Significance
Norms of dental development provide a means for aging subadult human skeletal remains by giving anthropologists a method of estimating the unknown chronological age from known morphology. Estimation is possible because the “growth of the deciduous and permanent teeth takes place over the entire range of the juvenile life span, starting during the embryonic period and nearing completion during the late adolescent . . . period” (Scheuer and Black, 2000:12). After this period, the teeth are in full articulation and begin to undergo attrition and other structural changes.
Dental maturation is, therefore, of “particular significance for … aging skeletal specimens when only jaws remain” (Moorrees et al. 1963a:1490) and is important even with a complete skeleton.
The purpose of this study is to determine whether the use of Schour and Massler’s or
Ubelaker’s dental age charts are appropriate for age estimation in modern American children. Since these charts are both used regularly by anthropologists to estimate age at death from skeletonized
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subadult remains, it would seem appropriate to subject them to rigorous tests with a known-age sample. Unfortunately, few such tests have been conducted, so the present study will fill a void present within the literature. In addition, with the increased utilization of DNA techniques, it has become easier to determine sex from subadult remains. Therefore, it may no longer be justified to combine males and females if indeed there are significant sex differences in dental development.
Failure to separate the sexes would result in greater aging errors for both sexes. A secondary purpose of this study is to determine whether dividing the sample by sex will increase the overall accuracy of the charts.
Chapter 2 gives a general discussion of the dental development of subadults, including rates of formation and eruption, sex differences, ancestral differences, environmental and genetic influences, and methodological concerns. Chapter 3 outlines in detail the evolution and development of the Schour and Massler and Ubelaker dental aging charts and examines the results from previous tests of these charts. Chapter 4 describes the materials and methods used in this study, with emphasis on the selection of the clinical sample, scoring systems, and statistical methods. Chapter 5 presents detailed results for both charts. The study will conclude with Chapter
6, which will give a summary of the findings and a discussion of future research possibilities.
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CHAPTER 2: DENTAL DEVELOPMENT
In their method of formation, structure, and basic functioning, teeth record and retain a history of their development and the events to which they have been subjected. For these reasons, normal tooth development has long formed the primary basis for age determination of children of unknown age. Investigation of the literature reveals numerous studies of dental aging, including formation and eruption. Garn et al. (1959), Lewis and Garn (1960), and Krogman (1968a,b) established that tooth formation was less variable than skeletal maturation, making the former potentially more accurate for age estimation.
For these reasons, it is important to understand the development of the human dentition, including patterns and timing of formation and eruption. These factors are discussed in detail in this chapter, and factors that potentially influence dental eruption (such as sex and ancestry) will be examined. Various dental aging methods are also addressed, producing a comprehensive view of previous research attempting to approximate chronological age from the development of the teeth.
Dental Development
Tooth formation . The development of the dentition occurs in a predictable pattern. At approximately thirteen weeks of intrauterine life, the first deciduous central incisors begin to form, followed by the deciduous first premolars at approximately fifteen weeks. These teeth are followed two weeks later by the lateral incisors and approximately two weeks later by the canines and deciduous second premolars (Kraus, 1959; Kraus and Jordan, 1965; Hillson, 1996). The first permanent molars begin calcification after about 28 to 32 weeks in utero (Kraus and Jordan, 1965).
Among the molars, the mesiobuccal cusp is always the first to begin developing, followed by the
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mesiolingual, distobuccal, and distolingual cusps, respectively. Lastly, a fifth, distal cusp generally develops on the lower molars (Schour and Massler, 1941; Gleiser and Hunt, 1955; Kraus and
Jordan, 1965; Hillson 1996). At birth, the state of development of the teeth is dependent upon the duration of gestation and the overall extent of tooth development while in the uterus (Hillson,
1996).
Postnatal development of the human dentition occurs with the initiation of the permanent incisors (excluding the upper lateral incisors, which follow slightly behind) at around three to four months after birth (Hillson, 1996). At this point in time, the germs of the deciduous premolars occupy the majority of the vertical space of the maxilla, with the total height of the upper jaw being almost double the size at birth (Logan, 1935).
The canine crowns begin to form at about one month after the initiation of the permanent incisors. At six months of age, calcification has advanced in the upper and the lower central incisors with the enamel and dentin cap reaching 1 to 1.5 mm in height (Kronfeld, 1935b). At the end of the first year, the upper permanent second incisors initiate formation, which are then followed consecutively by the first and second permanent premolars and second molars through the end of the second year and into the third year of age (Hillson, 1996).
The completion of the tooth crowns is much more variable than their initiation. According to Schour and Massler (1940b), the tooth crown is completed when the production of enamel stops, and the overall time until completion is dependent on the general size of the crown and the rate of apposition. In deciduous teeth, crown completion takes from 7 to 14 months, and in permanent teeth, completion requires 4 to 6½ years (Schour and Massler, 1940b). The permanent first molar crowns are completed at approximately 3 years of age, incisors at 4 or 5 years, canines and first premolars at about 6 years, and second premolars and second molars from 7 to 9 years of age
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(Fanning and Brown, 1971; Hillson, 1996).
The completion of root formation has been deemed more variable than crown completion and depends on the root’s overall length and the rate of dentin apposition (Schour and Massler,
1940b). However, Lauterstein (1961), in an effort to compare bone age with chronologic age, decided that root formation may be as good of an indicator of age as bones. In general, the deciduous roots require 1½ to 2 years for completion and the permanent roots require 5 to 7 years
(Schour and Massler, 1940b). Churchill (1932) found that the absorption of the root of the first deciduous incisors begins before the roots of the second deciduous incisors are completely formed.
Additionally, the deciduous second premolar is completely erupted with roots fully formed before the permanent first molar erupts (Cheyne, 1947). Among the permanent teeth, first molars and incisors usually complete their roots first, at about 9 and 12 years respectively, and the rest close after the age of 12.
The permanent third molar is highly variable and usually does not begin formation until the other crowns have completed their development, with initiation beginning anywhere from 7 to 15 years of age (Demisch and Wartmann, 1956; Hillson, 1996). The completion of the third molar crown occurs sometime between the ages of 12 and 15, and the roots generally do not close until between 17 and the early twenties (Fanning and Brown, 1971; Hillson, 1996).
Dental eruption.
El-Nofely and İş can (1989:239) define dental eruption as the “tooth breaking through the alveolar tissue until it reaches an antagonist or an obstacle.” The term eruption is used interchangeably throughout the literature with emergence (Miles, 1963). Steggerda and Hill (1942), Gustafson and Koch (1974), and Filipsson (1975) collectively agree that a tooth is erupted when it makes its first appearance through the gums. Hillson (1996:138) defines dental eruption as “the process by which teeth, in their bony crypts, migrate through the jaws and emerge
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into the mouth. It continues as each tooth moves into occlusion and beyond to compensate for the effects of wear, so that eruption is a continuous process that never completely ceases.” Demirjian
(1986:270) believes that eruption is applied erroneously when used to denote the appearance of a tooth in the oral cavity. He claims the correct term for the piercing of the gum is “clinical emergence,” and the piercing of the alveolar bone should be called “alveolar emergence.” Gleiser and Hunt (1955:265-6) had previously defined alveolar emergence as the occasion when “the tips of one or more cusps are at or just above the superior margin of the alveolar process.” Garn et al.
(1958) and Lewis and Garn (1960) later defined alveolar eruption as the time when there is no apparent alveolar bone located above the tooth and the subsequent elevation of the crown above the alveolar margin. According to Hurme (1948), these differing definitions could make comparisons between different studies difficult.
The permanent dentition is much more variable than that of the deciduous in both the sequence and the timing of eruption. According to Hillson (1996), eruption times can be broken into three phases: Phase One includes the emergence of permanent first molars and incisors (5 to 8 years of age); Phase Two consists of the emergence of the canines, premolars, and second molars
(9.5 to 12.5 years); and Phase Three consists of the emergence of the third molars (late teens to early twenties). Bradley (1961) found that the canines and premolars begin to erupt when their crowns are entirely complete and that these teeth reach the occlusal plane before completion of their roots. He also noted that the canine and first premolar began and completed eruption at approximately the same times, followed by the second premolar. Fanning and Moorrees (1969) found that the permanent teeth tend to emerge approximately after 50 to 75% of their root length has been attained and concluded that eruption is more closely related to the stages of root formation than with chronological or skeletal age.
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In various studies it has often been noted that eruption of the teeth usually occurs in pairs.
Lo and Moyers (1953) and later Prahl-Anderson and Van der Linden (1972) both determined that the order of dental eruption was bilaterally symmetrical. However, Steggerda and Hill (1942) noted that while eruption generally does occurs in pairs, many examples of eruption on the one side occurring in a different year than that of its antimere can be found. Their study showed sixteen instances in which the eruption times of the left and the right sides were outside the limit of one standard error. The authors concluded that the differences in eruption of the left and right sides were due to chance variation.
Brauer and Bahador (1942) and Adler (1963) also discovered a lack of symmetry among the right and left sides of the arch. Lauterstein et al.’s (1962) findings supported this disparity and they noted a high incidence of occurrence among the buccal teeth and their antimeres. Lauterstein et al.
(1967) found instances of asymmetries in eruption among the mandibular permanent canines and premolars in 54% of the 242 children studied.
Inconsistencies in eruption between the upper and lower teeth have also been observed.
Schour and Massler (1940b) found that maxillary teeth begin to form before the mandibular teeth, with the exception of the upper permanent lateral incisor. Interestingly, however, they found that the lower teeth generally erupt before the corresponding upper teeth. Brauer and Bahador (1942) and Adler and Gödény (1952) also noted this trend.
Factors Influencing Dental Eruption
There are many theories as to the processes that cause a tooth to emerge from its crypt and erupt through the gums. Brauer and Bahador (1942) explain that the same biological principles that can be applied to the body also control the development of the teeth. Therefore, variation will exist
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in the calcification and eruption of the teeth. Steggerda and Hill (1942) proposed that there are not only biologic forces at hand, but also local factors, such as nutrition and the environment, that influence the time of eruption of individual teeth. The biologic factors that can contribute to the general development of the teeth include genetic factors and endocrine reactions (Steggerda and
Hill, 1942; Garn et al., 1965a; Prahl-Anderson and Van der Linden, 1972; Davidson and Rodd,
2001). Additionally, sex and ancestry are important factors that can influence the eruption of the teeth and will be discussed in detail.
Genetic factors
. Genetic factors are very important in the development of each individual tooth. Wise et al. (2002) state that there are 25 known human syndromes that involve disruptions in the process of dental eruption, with the most frequent disruption being delayed eruption. Some of these genetic disorders include Trisomy 21 Syndrome, cleidocranial dysplasia, achondroplastic dwarfism, and chondroectodermal dysplasia (McDonald et al., 2004). Wise et al. (2002) found that the modes of inheritance of these syndromes were equally distributed between autosomal dominant/recessive and X-linked dominant/recessive forms.
Some additional genetically determined dental traits include teeth that have been modified or reduced in size and an absence of the tooth within the mouth. Modified teeth include peg or barrel-shaped incisors, diminutive teeth, and absent cusps (Dahlberg, 1957).
Lewis and Garn (1960) and Garn et al. (1965a) theorized that tooth formation is genetically determined and in an analysis of monozygotic twin pairings found correlations of tooth formation ranging from 0.75 to better than 0.90. Correlations found among dizygotic pairs from triplet sets were approximately 0.30, the same as for non-triplet siblings (Lewis and Garn, 1960). Garn et al.
(1960) found that among monozygotic triplet pairings, there is a correlation of 0.91 for both sexes.
Garn et al. (1965a) also found strong sibling correlations in tooth development. The findings by
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these authors are consistent with the assumption that the timing of tooth formation is largely, but not absolutely, genetically determined. Twins and siblings generally share the same fetal and postnatal environments, thus it is difficult to distinguish any environmental factors that may play a role in tooth formation. Kraus and Jordan (1965:213) concluded that since twin studies have shown that many morphological traits of the teeth are genetically determined, the “crown morphology of the primary dentition, particularly of the mandibular first molars and lateral incisors, is under the control of genes throughout the period of odontogenesis.”
Endocrine factors
. Recent investigations of how hormonal growth affects dental eruption have reported on individuals with various endocrinopathies. One endocrine condition that effects the development of the teeth is hypothyroidism. In congenital hypothyroidism, without hormonal therapy, the eruption and loss of the deciduous teeth and the eruption of the permanent teeth can be significantly delayed. In addition, while the sizes of the teeth are normal, they are crowded into jaws that are overly small (McDonald et al., 2004). In juvenile hypothyroidism, an untreated case can also lead to delayed loss of the deciduous dentition and delayed eruption of the permanent dentition. This situation can cause a child with a chronological age of 14 to have the dental stage of a 9 or 10 year old (McDonald et al., 2004).
Individuals affected by hypopituitarism, hypoparathyrodism, and autoimmune polyendocrinopathy are much less affected by dental growth retardation (El-Nofely and İş can,
1989). In hypopituitarism, individuals have teeth that are normal in size, however, approximately
25 percent have delayed eruption (McDonald et al., 2004; Garn et al., 1965b). In severe instances the deciduous dentition is retained throughout the person’s life with developed, but unerupted, permanent teeth underneath (McDonald et al., 2004).
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Environmental factors
. While some authors have concluded that environmental factors may play a role in the development of the dentition, Smith (1992) and Konigsberg and Holman
(1999) believe that deciduous tooth eruption is well buffered against these influences. Some environmental factors that have been found to influence the emergence of the permanent teeth include early or late extraction of the deciduous teeth, supernumerary teeth, odontoma, crowding, osteogenic tumors, cysts, and trauma (Prahl-Anderson and Van der Linden, 1972; El-Nofely and
İş can, 1989; Wise et al., 2002; McDonald et al., 2004). Adler (1963) and El-Nofely and İş can
(1989) concluded that these various factors could lead to premature loss of deciduous teeth, which can affect the timing of the emergence of their successors. For example, loss of the deciduous teeth too early while the permanent successor is still in the jaw may result in developmental retardation.
Lauterstein et al. (1962), however, found an accelerated rate of eruption among extracted deciduous premolars.
Bradley (1961) examined the mandibular permanent canine and premolars to determine whether there was a relationship between eruption and crowding of the mandibular permanent dentition. He found that increased crowding in the mandibular permanent dentition had a small but significant correlation with a retardation of the early phases of eruption of the mandibular canine.
Crowding was also correlated with delayed calcification of the second premolar, followed by an increased rate of eruption during the early phases.
Nutritional factors
. Nutrition and socioeconomic factors may also affect the emergence of the permanent dentition. Malnourished children among low socioeconomic environments show retardation in the eruption of the teeth relative to other children in a given population (El-Nofely and İş can, 1989). However, other studies imply that nutritional and social stresses do not have as significant an effect on dental formation as they do on other physical growth criteria such as height,
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weight, skeletal, and sexual maturation (Demirjian, 1986). Garn et al. (1965a) studied the effects of nutrition on dental development by analyzing the degree of fatness in children. They found that fatter children are more advanced in their dental development, however, the effect is small. They found that the teeth were “one-third as responsive to nutritional status as ossification timing or epiphyseal fusion” (Garn et al., 1965a:231).
Sex Differences
Gleiser and Hunt (1955) and Miles (1963) found that the sex differences in the development of the teeth are far less than those found in the skeleton. Gleiser and Hunt (1955) determined that at equivalent stages of permanent dental development, the average age of girls is about 95% of that of boys. Gleiser and Hunt (1955) also found that absolute sex difference in eruption gradually increased with respect to chronological age, with girls becoming increasingly advanced.
Glister et al. (1964) found that females at 10 months of age tend to be about 2 months advanced over males. Konigsberg and Holman (1999) note that such small differences in the eruption of the deciduous teeth are not likely to create serious inaccuracy in age estimates. Hurme
(1949) suggests that the differences in sex are so slight that the ranges of normalcy for boys and girls are approximately equivalent. Hurme (1949) also points out that the actual amount of female advancement generally depends on the tooth in question.
Black (1978) found that sexual dimorphism of the deciduous dentition was small in comparison to the permanent dentition. Lauterstein (1961) found a slight tendency among the deciduous teeth of two-year-old boys to erupt earlier than those of girls the same age.
Lo and Moyers (1953) and Hurme (1957) are in agreement that in girls, the sequence of emergence of the first premolars and the mandibular canines are in the order of mandibular canine,
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maxillary first premolar, and mandibular first premolar. However, in boys, the maxillary first premolar consistently precedes the other two. Carr (1962) and Carlos and Gittelsohn (1965) obtained similar results. Smith and Garn (1987) found that the sequence of eruption among the mandibular permanent canine and first molar may be sexually dimorphic and may differ between populations. Lo and Moyers (1953) justify these differences in eruption as being a result of the earlier onset of puberty in females. Nanda (1960), however, found no correlation between dental eruption and puberty.
Hurme (1957) suggested that sex could be determined by examining the sequence of emergence of the permanent canine and first premolar. He states that the greatest time difference in the emergence of teeth among boys and girls is the mandibular canine, which appears about eleven months earlier in girls than in boys. Ferembach et al. (1980) agree that the canines show the greatest sexual dimorphism among the teeth. Hurme (1957) also notes that the sex difference in the eruption of the permanent maxillary canine is significant and suggests that if subadult remains exhibit this tooth close to or ahead of the eruption of the maxillary second premolar, the remains are likely to be female.
Studies of sex differences in dental development generally agree that the early stages of tooth development are similar in males and female, with differences in development beginning at the crown completion stage and increasing during development of the root. However, there are some discrepancies among the studies. Demirjian and Levesque (1980) attributed this inconsistency to the limited sample sizes used by the researchers. They attempted to reinvestigate the sex difference in dental calcification on a larger scale with an ethnically homogeneous population.
They used a large sample size of 5,437 radiographs from a homogeneous French-Canadian population to examine the differences between males and females in the development of the
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mandibular permanent teeth from the beginning stages of calcification to the closure of the root apex. They noted that there was not a discernable sex difference until the completion of the development of the crown, with girls being more advanced by a mean of 0.35 years for four teeth.
For the subsequent stages of root development, the average difference between sexes is 0.54 years, with the canine having the largest difference of 0.90 years. These results support the earlier findings of Garn et al. (1958) and Nolla (1960) that sexual dimorphism is more important during the later stages of dental development, especially during root development, than during the period of crown development.
Garn et al. (1958) investigated the formation and eruption of the mandibular molar and premolar teeth and noted that girls preceded the boys in almost all teeth. The found that during the eruption stage (which includes alveolar eruption and attainment of the occlusal level) the average sex difference was 0.52 years. During the calcification stage (from follicle to beginning root) the average sex difference was only 0.16 years. Lewis and Garn (1960) found that girls’ dental development was, on average, 0.32 years and in extreme cases up to 0.92 years ahead of boys.
Nolla (1960) found that for all teeth at every stage, girls were more advanced. Lauterstein (1961) also found that girls’ permanent teeth erupted earlier and their root formation was more advanced than boys.
Garn et al. (1956) found evidence that the timing and order of dental calcification was, in fact, influenced by sex. They noted that cases where the second permanent premolar calcified prior to the second molar were more frequent in girls, whereas the calcification of these two teeth simultaneously is primarily a male characteristic.
Sex and ancestral differences . Steggerda and Hill (1942) determined that between different ancestral groups there are sex differences in the eruption time of teeth. They found that of
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the four ancestral groups analyzed, the average eruption time of female European Americans and
Maya is five to six months ahead of that of males, with sexual dimorphism in eruption being slightly greater among African Americans and less in Native Americans. Dimorphism is greatest in the canines. In the four populations they studied, in females the maxillary canines erupted 9.6 months and mandibular canines 10.2 months before males. The canines of African American females erupt more than a year before those of males and as a result, the greatest difference between the sexes occurs during the tenth and eleventh years. At this age, females may have one or more teeth than males. The canines of females were found to erupt before the second premolar in the maxilla in all populations, which is the same eruption order as the corresponding mandibular teeth in males. Female mandibular canines erupt before both the first and second premolars. Among
European Americans, the maxillary second premolar of both males and females erupts before the corresponding tooth in the mandible. This condition was also found among Navajo males and females and in Mayan males. In the Navajo, the maxillary first premolar erupts before the mandibular in females. In all of the other ancestral groups tested, the mandibular teeth erupted before the maxillary, or the differences are not significant
Ancestry
It has been noted in various studies that there are different rates of permanent tooth eruption among the various ancestral groups. El-Nofely and İş can (1989) note that between populations, differences can only be considered in the context of socioeconomic conditions, nutritional status, and other environmental factors. However, in spite of the difficulty in separating genetic factors from external influences, many studies have found that the sequence of tooth eruption varies between ancestral groups in different geographic locations.
Steggerda and Hill (1942) studied the influence of ancestry upon the mean time of eruption,
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including comparisons of sex and the order of eruption. The subjects analyzed within this study are of ancestral groups from significantly different environments. They ranked the ancestral groups studied by their rate of dental eruption. These rages ranged from fast (Navajo, African American) to slow (Mayan, European American). They found that there is no significant ancestral difference in the mandibular first molar. However, this tooth in the Navajo does erupt earlier than in any of the other ancestral groups. Among the Maya, the central incisors erupt later than in the other ancestral groups. This difference occurs in both the maxillary and mandibular teeth, involves both sexes, and occurs about six months after the eruption of the same teeth among European Americans.
All other Mayan teeth except the canines erupt before those of European Americans, with the first premolar and second molar being most pronounced in their early eruption. All the teeth of African
Americans also erupt before those of the European Americans, except for the maxillary second premolar. The teeth of the Navajos have the earliest eruption times of all the groups studied. Their teeth erupt at a significantly earlier age than in European Americans in all instances, except the maxillary and mandibular central incisors and maxillary first molars.
It has been suggested that eruption in African American and Eskimo children may occur from ½ to 1½ years earlier than in European Americans (Bang, 1989; Hurme, 1957). However,
Hurme (1957) also claims that there is not a significant difference between the “Mongolian” groups versus the Europeans and Japanese. El-Nofely and İş can (1989) use flawed logic in attributing this delay in European and Japanese to the fact that they are from industrialized populations and thus have improved nutritional status and medical care, which results in a later emergence of the teeth.
Nyström et al. (1986; 2001) examined Finnish children and determined that they were more advanced in dental maturity when compared to the research by Demirijian et al. (1973) on French
Canadian children. Accelerated dental development was also shown in a South Indian population
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(Koshy and Tandon, 1998). However, Speechly and Liversidge (1998) did not find any population differences in dental maturation for British and Bangladeshi children.
Dental Aging Methods
In 1958, Garn et al. devised five stages of calcification and eruption including: (1) stage of full follicle, immediately preceding first evidence of cusp calcification; (2) crown completion and beginning of root formation; (3) alveolar eruption; (4) attainment of occlusal level; and (5) apical closure. They distinguished calcification as involving stages 1, 2, and 5 and equated eruption with stages 3 and 4. Lewis and Garn (1960) later eliminated the two eruption stages and devised a system of three stages for dental development including: (1) calcification of the crown; (2) completion of crown formation; and (3) closure of the root apices. Gustafson and Koch (1974) also described stages of tooth development, which involved four phases: (1) commencement of mineralization; (2) completion of crown; (3) eruption of the tooth (where the cusp penetrates the gingiva); and (4) completion of the root. These stages were used to construct a simple diagram for age estimation.
A method of aging using dental microstructure was developed by Boyde (1963; quoted in
Bang, 1989) and is based on the fact that the formation of enamel in humans originates at the dentin surface and moves outward at a speed of two to eight microns every twenty-four hours. These lines of enamel deposition are discernible on the surface as “Lines of Retzius.” The “neonatal line” within the teeth forms the border between the prenatal and the postnatal enamel and is found where enamel is forming at the time of birth. Counting the lines of Retzius up from the neonatal line to the surface of the enamel allows for age determination of a young individual (Bang, 1989). This quantitative method, while accurate, is very elaborate. Huda and Bowman (1995) applied Boyde’s
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technique to unknown, commingled juvenile European skeletons recovered from Saint Bride’s
Church in London. They managed to confidently age eight of the ten individuals by analyzing the dental microstructure after unsuccessful attempts to use known skeletal aging methods.
Moorrees et al. (1963a) feel that tooth formation is superior to tooth eruption for the assessment of dental age. They studied radiographs of maxillary incisors and eight mandibular teeth in order to provide norms for their formation. The authors identified several stages in the formation of the crown and root in deciduous and permanent mandibular canines and molars, and root resorption in deciduous teeth. They found that the range of variation is least for crown development and greatest for root apex closure. There were also significant differences between males and females.
Bailit and Hunt (1964) used the Moorrees et al. (1963a) chart to assess sexual dimorphism and the developmental age of twenty-five girls and twenty-five boys using a mandibular canine.
The authors examined radiographs and scored them based on the methods determined by Moorrees et al. (1963a) and compared their results to the known chronological age of the child. The developmental age of the canine for both sexes was determined and compared to the known chronological age. Sex was correctly determined in 70% of the cases. However, Bailit and Hunt
(1964) question this method’s usefulness in medico-legal applications due to the sexual dimorphism of the radiographs being too slight.
Demirjian and Tanner (1973) developed an aging system using an approach used earlier by
Tanner et al. (1962). Their method used a 7-tooth system that was based on eight stages of calcification, and each tooth was given a score based in its phase of calcification. These evaluations were totaled for all teeth, which gave a maturity score measuring from 0 to 100. This maturity age could then be converted into a dental age. The 1973 method for estimating dental maturity was
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later reevaluated and updated by Demirjian and Goldstein (1976). They developed a new system that extended the age range and the number of stages and created a 4-tooth system of analysis. The authors noted in their discussion that their sample was entirely of French-Canadian origin and may not be applicable to other populations. They conjecture that while the scores for the stages will likely not change very much, the maturity standards might change considerably.
Nykänen et al. (1998) used the Demirjian et al. (1973) method for dental age estimation and applied their standards to Norwegian children. They found that their children were somewhat more advanced in dental development than the French-Canadian children. This finding is in accordance with the studies of Swedish and Finnish children that have been analyzed utilizing the Demirjian method (Hägg and Matsson, 1985; Nyström et al., 1986; Staaf et al., 1991). Although the mean differences between estimated and chronological ages were comparatively small, indicating a good correlation between dental maturity and actual age among the Norwegian and French-Canadian children, individual estimates varied considerably, particularly in the older children. This observation of increased variability with age was also found in other studies using various methods for age estimation from dental development (Hägg and Matsson, 1985; Nyström et al., 1986;
Reventlid et al., 1996).
Davis and Hägg (1994), in an effort to estimate chronological age based on tooth formation in Chinese children, used the methods of Demirjian et al. (1973) along with the updated standards by Demirjian and Goldstein (1976) and Demirjian (1986). While they found the precision to be high, the accuracy was low, with the mean difference between dental age and chronological age of the Chinese children being eleven months for boys and seven months for the girls. Davis and Hägg
(1994) believe that their results indicate that Demirjian’s method cannot be accurately used to estimate the chronologic age of Chinese children.
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Loevy (1983) used the methods of Demirjian et al. (1973) to analyze and compare the dental development of European American, African American, and Latin American children from the
Chicago area. He found that each of the populations tested displayed faster development than
Demirjian’s French-Canadian children. Loevy (1983) also determined that Latin American males were not significantly different from European American males and that African American males were significantly different from European American males. For the females, a significant difference was found between European Americans and the other two groups (Loevy, 1983).
Several studies have tested systems of dental aging using children of known age, however, some do not report the actual differences in predicted versus actual ages (e.g., Haavikko, 1974).
Staaf et al. (1991) tested the methods for age determination from dental development and compared the methods of Demirjian et al. (1973), Haavikko (1974), and Liliequist and Lundberg (1971).
Their sample consisted of 541 Swedish children aged 5.5 to 14.5 years. Staaf et al. (1991) found that when Demirjian’s method was used, the age was consistently overestimated by approximately ten months for both sexes. These results were similar to those of Hägg and Matsson (1985), who obtained an overestimate of four to six months for Demirjian’s method. An analysis of Haavikko’s
(1974) method found an underestimate ranging from four to six months, with lower errors attributed to the younger individuals and higher errors for those above approximately ten years of age (Staaf et al., 1991). Liliequist and Lundberg’s (1971) system of assessing dental age displayed a correct estimate for girls and an overestimate of roughly seven months for boys (Staaf et al., 1991). Staaf et al. (1991) explain the differences between Haavikko’s (1974) and Liliequist and Lundberg’s (1971) studies as resulting from the differences of about one year or more between each of their stages.
Hägg and Matsson (1985) compared the methods of Liliequist and Lundberg (1971),
Gustafson and Koch (1974), and Demirjian et al. (1973) to determine which one more accurately
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predicts the age of 150 Swedish children 3.5 to 12.5 years of age. Each case was independently assessed by each researcher. Unlike Staaf et al. (1991), Hägg and Matsson found that the method of
Liliequist and Lundberg (1971) consistently underestimated the age by two to six months, with lower errors for the boys. In addition, they found that this test had, overall, the lowest accuracy despite the fact that it represents standards set from analyses of Swedish children. Hägg and
Matsson (1985) also found that the methods of Gustafson and Koch (1974) were difficult to replicate and the age predictions were poor for females but acceptable for males. Of the three tests, the stages of the development of maturity determined by Demirjian et al. (1973) when used on
French-Canadian subjects gave the most precise age estimates. They determined that the subject’s age could be accurately estimated to within 15 to 25 months with 95% confidence.
Methodological Considerations
Hurme (1948) blames much of the discrepancy in the various dental aging methods on authors’ differing definitions of dental eruption. There also seems to be some confusion among researchers in the use of the terms development, formation, and calcification, which are used interchangeably. There is disagreement as to whether calcification or eruption data is better for dental aging. Some researchers consider dental eruption to be limiting in that it can only be examined for a short period of time compared to formation. In a living individual, a tooth may be lacking at the time of oral examination but may be visible one or two weeks later (Demirjian and
Levesque, 1980; Ferembach et al., 1980; El-Nofely and İş can, 1989; Smith, 1991; Haavikko, 1974).
Formation of the crowns and roots is said to be more accurate in that the process can be followed longitudinally and assessed radiographically, permitting continuous scoring over several years
(Demirjian and Levesque, 1980; Smith, 1991). Formation also allows for the analysis of dental
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maturation in periods where no emergence takes place. Smith (1991) believes that tooth formation is more resistant to environmental influences, whereas dental eruption can be influenced easily by caries, tooth loss, and severe malnutrition. For skeletonized individuals, a cross-sectional approach is the only one available. In these cases, a radiological analysis gives an internal view of the teeth, enabling examination of formation and development at a single point in time.
El-Nofely and İş can (1989) believe that clinical examination of the oral cavity in living subjects is the most common and best manner for studying tooth emergence. Clinical oral data permits an observation of the tooth’s initial appearance in the mouth, including its penetration through the oral mucosa. Additionally, an oral examination involves simple, rapid, and convenient data, does not require expensive tools or equipment, has less intra- and interobserver error, enables a large sample size, and allows intra- and interpopulation epidemiological studies of dental growth and maturation. However, for forensic purposes, these oral data may have limited utility.
The variation in mean eruption times of teeth presented in the literature is noted by
Steggerda and Hill (1942), who believe that some differences between studies could be due to the method of tabulation of the material. They note that in some cases, the researcher’s averages are based upon the nearest birthday, some upon the actual month and year, and others consider the year group to include all individuals up to their next birthday.
Steggerda and Hill (1942) also note that part of the discrepancy between studies could be due to the fact that not all authors take into consideration the uneven distribution of sex in their study samples, which becomes a problem when female dentitions consistently erupt earlier than those of males. An additional source of error could be that researchers often base their studies on relatively small sample sizes, so the real variation in the population may, in actuality, be greater than what is stated (Bang, 1989).
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Numerous studies also have found discrepancies when attempting to use a recognized method of determining dental age on a different population than was originally tested. This disagreement could be due to differences in calcification and eruption patterns between and among various populations. However, it would be interesting to determine if some of these differences were due more to improper application than due to true population differences.
Additionally, there is generally an underlying assumption that the error ranges were properly constructed for the reference population and that the error ranges were then correctly applied to the new population. However, the methods in these studies are rarely questioned and many obtain impressive results from incomplete data, non-random samples, and small sample sizes, and many do not take into consideration differences in sex or ancestry. They rarely give methods or reasons behind their statistical analyses and frequently fail to give enough summary statistics to allow for critical comparison and assessment.
Summary
The importance of the human dentition as a “measure of maturity” and the association of dental age with chronologic age are of interest to both the forensic anthropologist and the orthodontist. An investigation of the literature reveals numerous studies of dental development, including formation and eruption. Various methodologies have been used to establish standards for estimating age at death in medicolegal cases. If the standards determined for dental aging are applied to unknown skeletal remains without questioning the origin or validity of these standards, scientists may be introducing unrecognized error into their predictions. It is important to question these older, but accepted methods of age determination to determine their applicability in modern usage.
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CHAPTER 3: DEVELOPMENT OF THE DENTAL AGING CHARTS
The first chronologies of dental formation can be attributed to Legros and Magitot (1880,
1881; quoted from Smith, 1991:145). These authors developed tables that displayed the appearance of dental tissues and structures for both the deciduous and permanent teeth, with emphasis on prenatal formation. In 1933, Logan and Kronfeld examined children with various dental abnormalities, including cleft palate and linear enamel hypoplasias, and discussed the errors found in Legros and Magitot’s chart of calcification. The authors found that within the table, all permanent teeth, from central incisor to second premolar in both upper and lower jaws, are shown as beginning calcification at one month after birth, whereas “in reality there are differences of almost two years between formation of the dentin of the central incisor and that of the second bicuspid” (1933:392). Logan and Kronfeld also found that although the chart contains many inaccuracies, “the table has for four decades been copied, without modification, by accepted authorities on histology” (p. 392). Smith (1991) cites the errors found in Legros and Magitot’s chart as a result of their data being poorly translated into English and their table of development being partially misprinted. Later developmental charts appeared in American dental journals in
1883 (Black) and 1884 (Peirce) without any description of the methods or sample subjects. Smith
(1991:146), however, believes that these charts were a product of each author’s analyses of hypoplastic banding and found that when “measured against modern studies, all are quite inaccurate.”
Later, in 1924, W.J. Brady printed a chart that pictographically depicts stages of dental development, eruption, and absorption that he developed after more than 25 years of study. He believed that it was a dentist’s duty to know the average time of loss of the deciduous teeth, much
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as they know their multiplication tables, in order to properly care for children’s teeth. Brady laments
“both live-stock and automobiles usually receive better care than children’s teeth. Surely children are as important as pigs or flivvers!” (Brady, 1924:3). His chart displays both the upper and lower dentition beginning at the 17 th week of embryonic life and follows prenatal development through the 20 th , 25 th , 30 th , and 40 th (birth) weeks. The postnatal stages begin at 5 months and are also recorded at 7, 9, 14, 18, 24, and 30 months and then continue consecutively from 3 to 15 years of age.
In 1940 (b), Schour and Massler researched the incremental growth of the teeth and likened their development to tree rings. Their study included a table modifying data from Logan and
Kronfeld (1933) and Kronfeld (1935a, b) on the initiation of calcification of the permanent teeth.
The authors also included a ‘diagrammatic representation of the chronology and mode of development of human upper teeth’ (1940b:1929), which appears to apply some of the Logan and
Kronfeld data as well as their own data (Schour and Hoffman, 1939; Schour and Kronfeld, 1938;
Schour and Massler, 1940a, 1940b). There are some critiques against Schour and Massler using these data because they were based on a very small sample and many of these individuals had died from illnesses, which could, potentially, have had an effect on their dental development (Garn et al.,
1959; Miles, 1963; Lunt and Law, 1974a; Ubelaker, 1987). Additionally, they seem to ignore previous findings that the Logan and Kronfeld ranges (1933; Kronfeld, 1935a,b) were too narrow and that many children “fell outside of the published ranges, occasionally by as much as 3 to 4 years
(Garn et al., 1959; Lewis and Garn, 1960).
Despite using the same manner of presentation, Schour and Massler do not reference
Brady’s (1924) previous diagram representing a pictorial development of the dentition. There are many noticeable discrepancies between the two charts. Most conspicuously, Brady does not
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indicate that the permanent teeth begin their formation until 14 months of age, with the calcification of the medial permanent incisor crown. Schour and Massler, however, show in their chart that the permanent teeth begin their formation at the age of 6 months with calcification of the crowns of both the medial incisor and canine. Schour and Massler’s developmental chart more closely depicts published data for these rates of formation. Schour and Massler’s chart (1940b) shows 21 developmental stages of the upper dentition from 5 to 8 months in utero, birth, 6 months, 9 months, and then chronologically 1 to 14 years of age.
Schour and Massler later modified their pictorial chart in 1941, with 22 developmental stages for the first 35 years of life. They eliminated the 13 and 14-year age stages and included new stages at ages 15, 21, and 35. The authors do not list any prior references used, however, these data are probably extensions of their 1940’s data (a, b). Differences between the 1940b and the 1941 charts are minor, with dissimilarities beginning at the 2 year stage. Their older chart (1940b) shows the second permanent premolar beginning cusp formation at age 2; however, this is not seen in the new chart until age 3. Additionally, the third molar at age 15 in the 1941 chart shows the same stage of root development as eliminated age 13 in the older version. Schour and Massler describe their chart as having six overall phases of development, including Prenatal, Birth/Neonatal, Infancy,
Childhood, Grade-School, and Adulthood. Within these phases are further distinctions. The authors describe the Prenatal period as the time when the crowns of the deciduous teeth begin to grow and calcify. The Birth/Neonatal period is defined as the time during which root formation has not begun and the deciduous teeth are unerupted. It is at this time that the crowns of the deciduous incisors are five-sixths complete, the canine crowns are one-half complete, the cusps of the first premolar are completed and coalesced, and the cusps of the second premolar are one-half formed and still isolated. The Infancy period is designated by an Early Infancy period (Birth to 6 months)
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and a Late Infancy Period (6 months to 1 year). The Early Infancy period is characterized by the growth and calcification of the canines. The Late Infancy period includes the eruption of the deciduous incisors. The Childhood period is also known as the “preschool age” and includes children from ages 2 to 6. It involves the complete presence of the deciduous dentition in the mouth by the end of the second year, the gradual resorption of the deciduous roots, and continued growth and calcification of the permanent first molars and anterior teeth. Schour and Massler also note that during this period, at around 4 to 5 years of age, the deciduous anterior teeth begin to spread apart to accommodate the eruption of the larger permanent teeth. The Grade-School period is characterized by grade-school aged children from 6 to 12 years of age. This stage features a time of mixed dentition and is divided into the Early Grade-School period (ages 6 to 10) and the Prepubertal period (ages 10-12). The Early Grade-School period begins with the eruption of the first permanent molar at 6 years and also features the appearance of the permanent incisors at 7 to 8 years. The
Prepubertal period begins with the eruption of the first and second permanent premolars, the canines, and the eruption of the permanent second molars (at approximately 12 years of age). This stage is characterized by the completion of the permanent dentition, with the exception of the third molar. The Adulthood period of this chart includes the Adolescent period (ages 12 to 15), which features the completion of all the permanent dentition, and the Young Adult period (ages 15 to 21), which is the period when the third molar erupts.
The Schour and Massler chart appears in a slightly modified version in 1944 as a wall-sized chart entitled ‘Development of the Human Dentition’ distributed by the American Dental
Association (see Figure 3.1). This chart notes at the bottom that it is the second edition; however, it is uncertain which version of the previous two charts are considered to be the ‘first.’
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30

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The library at the American Dental Association in Chicago was unable to locate an earlier edition of the wall-sized chart and the only other versions of the Schour and Massler chart were published by the Journal of the American Dental Association in 1940 and 1941. The newer 1944 chart is similar to the 1941 version; however, one noticeable difference is the addition of error ranges. There are no data accompanying this new chart in the form of published research in a journal, thus it is not certain how the error ranges were derived. Other differences include the elimination of postnatal ages of 6 and 8 months and the addition of an 18-month age stage (1.5 years). The newly added 18month age group most closely resembles the 1941 stage at 2 years. Beginning with 6 months of age, there are apparent differences in the formation of the dentition, with root development in the later Schour and Massler chart being more advanced at almost every stage. Despite this progression, the ages for loss and eruption are still the same for both charts. The phases mentioned by Schour and Massler in 1941 are now partially visualized in their 1944 chart. This chart is grouped by Deciduous Dentition, Mixed Dentition, and Permanent Dentition categories. The
Deciduous Dentition includes two subgroups, Infancy (5 months to 18 months) and Early
Childhood/Pre-School Age (2 to 6 years). The Mixed Dentition includes Late Childhood/School
Age children ages 7 to 10 years, and the Permanent Dentition grouping includes ‘Adolescence and
Adulthood’ individuals aged 11 to 35 years.
The 1944 Schour and Massler chart was printed in their “Atlas of the Mouth and Adjacent
Parts in Health and Disease” (1958) published by the American Dental Association, and includes the same error ranges. This version of their chart is very similar to their 1944 chart with the first difference being seen at age 6, with development of the permanent upper and lower canines beginning root initiation. Root initiation has not begun in the previous chart at this age and does not reach the same stage in the 1958 chart until 8 years of age. At 7 years in the 1958 chart, the
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development of the permanent lower canine is shown with the development of the root half shaded.
This seems to be the authors’ way of displaying the high variability in the formation of this particular tooth. At age 8, the stages again become similar in their formation to the 1944 chart.
In 1978, and again in 1989, Ubelaker expanded and changed many of the error ranges originally given by Schour and Massler in 1944 (see Figure 3.2). This change seems to be primarily due to the fact that Ubelaker’s chart was developed for analysis of Native American Indians and other non-white dentitions after determining that Schour and Massler’s chart consistently overestimated the ages at death of these individuals and underestimates their actual growth rate
(Merchant and Ubelaker, 1977). Despite the modifications made for Native American individuals,
Ubelaker’s chart has now become a recognized world standard for all ancestral groups. Ubelaker also made minor adjustments to the original pictorial depictions of the rates of formation and eruption of the teeth, with the most distinct visual difference being in the development of the canine from the age of 18 months to 2 years. The changes made by Ubelaker are associated with various author’s findings of earlier formation and development of Native American individuals. However, the chart derived and modified from these data should not be a substitute for these original publications (Ubelaker, 1987).
There seem to be spontaneously generated or tacitly modified differences among all of the dental aging charts with no mention as where these differences were generated. For example,
Ubelaker’s 1989 chart was reproduced in a text by Buikstra and Ubelaker (1994:51), and while
Ubelaker’s 1989 text gave a target age with error range as 12 years ± 30 months, the 1994 text gave an error range for the same age of ±36 months with no mention as to why this change was made.
Additionally, Ubelaker’s newer 1999 edition of his 1989 book replicates the chart again with the error age at 12 years ± 30 months, and he notes that his ranges express variability within the
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literature; the error intervals may be inexact by as much as 5 years, especially among the older ages.
Some errors in using these charts are incorrect citations; for example, some say they use the 1941
Schour and Massler chart, however, they have actually examined the 1940 chart (Trodden, 1982:5).
Brauer and Bahador (1942) tested Schour and Massler’s 1940 chart on 315 patients and found that only 45-49% of the patients tested exactly matched the picture given for the appropriate year. The investigators noted difficulties in reconciling anterior versus posterior tooth development.
They determined that “calcification age and eruption age do not necessarily correspond with chronologic age” (Brauer and Bahador 1942:1386).
Miles (1958) tested Schour and Massler’s 1941 chart and found that on individuals up to the age of 12, most were close to their actual estimates, few exceeding their true age by more than one year. After 12 years, Miles found an increasing tendency for the individuals to be scored 2 or more years above or below the actual age. The age estimates found with Schour and Massler’s 1941 chart for individuals over 16 years of age were consistently too low, and the author suggests modifying the chart to correct the development of the third molar.
Miles (1963) again critiques Schour and Massler’s 1941 chart, citing that it is limited to individuals below 15 years because no stages of growth for the third molar are recorded for the critical formation ages between 15 and 21 years. Miles claims that “where material of unknown sex is concerned, estimates of age based on the dentition are more likely to be correct than those based on osseous development” because sex differences in the skeleton are about three times greater than those for tooth development (p. 258). Scheuer and Black (2000) recommend that Schour and
Massler’s 1941 chart is best used when examining infancy and early childhood subjects.
There do not appear to be any tests of Ubelaker’s chart. There was a modification made by
WEA (1980) that can be viewed in Scheuer and Black (2000) that was based on Ubelaker’s 1978
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chart. The only major differences in this newer chart is that the error interval at 15 years has been narrowed from 15 ± 36 months, as was previously found in Ubelaker’s chart, to 15 ± 30 months.
Additionally, in the WEA chart, at 6 months of age the permanent cusps are beginning in the mandible, which is not present in Ubelaker.
The history of these dental charts is long and complex, but it seems that they each lack vigorous testing. Those tests that have been performed do not recommend any major changes.
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CHAPTER 4: MATERIALS AND METHODS
Clinical Sample
The sample for this study was used upon receiving approval from the Indiana University-
Purdue University at Indianapolis (IUPUI) and Clarian Institutional Review Boards and
Subcommittees Reviews, as well as the University of Indianapolis Committee on Research
Involving Human Participants. The subjects for this longitudinal study were located by examining existing records located at the Riley Hospital Dental Clinic in Indianapolis, Indiana. The sample consists of 419 randomly selected European children from 5 to 15 years of age and includes approximately equal numbers of males and females for each year of age. Research was conducted until approximately twenty males and twenty females were obtained for each age or until the existing supply of records for that age was exhausted (see Table 4.1). The age ranges from 5 to 15 were selected because of the available data and because children tended to have their first dental visit at Riley Hospital at around five years of age. By the age of fifteen, permanent teeth (excluding the third molar) are nearing full occlusion (Harris and McKee, 1990; Nanda, 1960).
Individuals not of European-American ancestry were excluded from this study in order to concentrate on variation within one ancestral group and to maximize homogenous sample sizes.
Ancestral information was obtained from the patient’s charts and was based on notations made by the residing dentist. Within these charts, the general notes for ‘race’ were abbreviated with ‘W’ for white, ‘H’ for hispanic and ‘B’ for black. Only those individuals with a ‘W’ notation were included in this study. Additionally, any chart with mention of biracial ancestry (Bi) was eliminated from this study.
36

TABLE 4.1. Comparison of total number of male and female European subjects per age range.
5.00-5.99
6.00-6.99
7.00-7.99
8.00-8.99
9.00-9.99
10.00-10.99
11.00-11.99
12.00-12.99
13.00-13.99
14.00-14.99
15.00-15.99
14 9 23
25 17 42
25 25 50
27 20 47
22 21 43
21 19 40
23 21 44
18 19 37
21 15 36
19 8 27
13 17 30
Other charts that were eliminated included all patients with considerable orthodontia (such as braces) or more than one absent tooth. Also excluded were any panoramic radiographs that were blurry, washed out, or that had an unlisted date of exam which could not be determined from the file information. In addition, any siblings of a subject previously selected were excluded. Sibling status was determined by a common surname and street address. Some patients’ charts had discrepancies between the date of birth on the radiograph and the one located within the chart. If a discrepancy was found, the birth date used was the one recorded by the parent on the patient information sheet.
The panoramic radiographs used to assess the stages of formation and eruption of the teeth were taken by trained technicians using a Planmeca Proline PM2002 CC panoramic unit before the beginning of this study. Panoramic radiographs were chosen because they provide comprehensive coverage of all teeth, and the film includes the “maxillary region extending to the superior third of the orbit, and the entire mandible including the temporomandibular joint region” (Miles and Parks,
37

2004:72). The use of bitewings was discarded early in the study due to the limited number of teeth represented on them and the lack of notation of which side of the jaw each bitewing film represents.
The only information taken from the patients’ charts was the child’s sex, date of birth, and the date of the radiograph. Radiographs were placed on a lighted mount in a room with subdued lighting to allow for accurate interpretation and ideal digital images. Two digital pictures were taken of each radiograph with a Fuji FinePix 2650 digital camera at one megapixel of resolution to allow for analysis at a different time. All potentially identifying information was blocked out of the pictures with black electrical tape. Consecutive numbering was assigned by the researcher for each individual and a sticker with this number was placed on the radiograph for the purpose of the picture and then removed. This number was recorded, along with the data for that particular individual, on a self-designed Data Recording Form (which is appended at the end of this chapter).
Scoring Systems
Specific dental stage numbers were assigned to Ubelaker’s (1978) and Schour and Massler’s
(1944) dental charts, beginning with 1 for the ‘birth’ stage and ending with 18 at the age 21 stage.
Since the ages in the study range from 5 to 15, stages 9 through 17 were generally assigned for those ages (Nawrocki et al., 1998).
The best digital image for each individual was professionally printed onto Fuji Film Printpix paper. Each picture was then visually compared to Ubelaker’s (1978) dental aging charts and given a dental stage number according to which Ubelaker stage the radiograph most closely matched.
Then all pictures were reexamined using Schour and Massler’s (1944) chart. The left side of the mouth (including both the mandible and the maxilla) was used in all cases to make comparison with the published charts easier. In addition, any developmental abnormalities (e.g., congenitally absent
38

teeth) were noted.
The target age for each dental stage was the predicted age given by each chart, which was then compared with the actual chronological age. The chronological age was calculated as a decimal age using the website http://www.simd.org/Tools/age.asp by entering the date of birth and the date that the panoramic radiograph was taken.
All data were entered into a Microsoft Excel 2000 spreadsheet for calculating general statistics and developing tables.
Statistical Methods
Various summary statistics were calculated for each chart, including mean age per stage, standard deviation, and observed ranges. Bias and inaccuracy statistics (measures of mean error) were calculated for each stage and for each chart as a whole. Bias was calculated as
∑  expected age – observed age

/n and inaccuracy was calculated as
∑
(expected age – observed age)/n
The percentage of individuals correctly falling within the predicted +/-2 standard deviation interval for each stage was also calculated. The data were then evaluated for sex differences using t-tests and analysis of covariance (ANCOVA) with SYSTAT v. 5.2.1 for the MacIntosh (Wilkinson,
1992). In the analysis of covariance (ANCOVA), the recorded stage is the semi-continuous
39

dependent variable, sex is a categorical independent variable, and age is a continuous covariate independent variable, resulting in the following model:
Dental Stage = Sex + Actual Age + error
The 95% prediction intervals were calculated for each stage using the formula:
Target age ± t
(0.05)
(1 + 1/n)
1/2
(s) where ‘n’ is the number of individuals within a stage and ‘s’ is the standard deviation of that particular stage being tested. The percentage of individuals correctly falling within the 95% prediction intervals was calculated for each stage and for each chart overall.
40

University of Indianapolis
Department of Biology
Emilie L. Smith – M.S. Thesis Research
SAMPLE NUMBER: __________
BIRTHDATE: __________
SEX: __________
DATE OF EXAM: __________
Date of Radiographs Years Months Decimal Age
Orthopantograms
Bitewings
Other
UBELAKER DENTAL STAGE : _______________
TARGET AGE: __________ ERROR RANGE: __________
S & M (1944) DENTAL STAGE: _______________
TARGET AGE: __________ ERROR RANGE: __________
NOTES: Left side of mouth examined for all stages.
41

CHAPTER 5: RESULTS
Qualitative Results
When analyzing each radiograph and assigning each individual a stage (9-17), certain nuances were observed that influenced how individuals were scored using the Ubelaker (1989) and the Schour and Massler (1944) charts. For example, in stage 9, the first molars have begun root formation in Ubelaker’s chart; however, in Schour and Massler’s chart, they have only just completed crown formation (see Figure 5.1). This difference caused some individuals to be classified as one stage later when using Schour and Massler’s chart. Stages 10 and 11 were very similar between the two charts and no problems were noted in these stages.
Beginning with stage 12, additional differences can be observed between the charts. At this stage in Ubelaker’s chart, the first and second permanent incisors are at stage 13 in Schour and Massler’s. This led to some differences when scoring the study sample. In addition, in
Schour and Massler’s stage 12, the canine is underdeveloped relative to Ubelaker’s chart (the root should be developed at approximately ½ its full length but it is shown at ¼). This difference led to some individuals being placed into Schour and Massler’s stage 13 when the root was further developed (see Figure 5.2).
At stage 13, the second molar in Ubelaker’s chart is shown with roots developing, however, in Schour and Massler, root formation has not yet begun. It was found that Ubelaker’s chart more accurately depicted the state of tooth development in the study sample in this respect.
In Ubelaker’s chart the development of the roots of the first and second incisors at stage 13 were at stage 14 in Schour and Massler’s chart. However, while these differences were noticeable, they did not affect the stage placement because the overall eruption pattern had not advanced to
42

Schour and Massler (1944) Ubelaker (1989)
FIGURE 5.1. Comparison of Schour and Massler’s and Ubelaker’s Stage 9.
Ubelaker (1989)
STAGE 12
Schour and Massler (1944)
STAGE 13
FIGURE 5.2. Comparison of Schour and Massler’s and Ubelaker’s Stages 12 and 13.
43

Schour and Massler’s stage 14.
It should be noted that in evaluations of Schour and Massler’s stage 13, in most cases the mandibular teeth were more advanced than they should be (especially the roots of the 1 st and 2 nd permanent premolars) while the maxillary teeth tended to match the picture very well. Another general irregularity in both charts involves the formation of the permanent second premolar, shown as being developmentally the same as the first premolar. However, the P2 was found to be less developed than the P1 in most cases. This difference was especially noted in stages 13 and 14.
Another scoring difficulty for both Schour and Massler’s and Ubelaker’s charts was distinguishing between stages 14 and 15. The major difference between these stages is the transition from mixed dentition to permanent dentition. Thus, for both charts, even if most of the teeth were in stage 15, if any deciduous teeth were present, they were placed into stage 14. The unintended effect of this strategy was to dramatically reduce the number of individuals in stage
15 (Tables 5.1 & 5.2).
For both charts, the difference between stages 16 and 17 is slight. If root formation for the M2 and the P2 was incomplete, the specimen was classified as stage 16, and if all of the apices were closed, the specimen was placed into stage 17. Differences in the development of the third molar between stages 16 and 17 were observed, but these differences were highly variable and did not appear to be stage-specific.
Overall, it seemed that the Ubelaker chart performed better than the Schour and Massler chart in both placing individuals correctly in the stage that they should have belonged in and in the correct phase of development for each tooth in the diagrams.
44

Quantitative Results
The first method used to compare the two charts evaluates the range of ages obtained per stage. The second method compares the means obtained for the study sample with the predicted means from the original charts. Third, bias and inaccuracy statistics were calculated to assess mean error. The fourth method of comparison evaluated the predicted error ranges as given in each original chart. After these comparisons, I checked for differences between the sexes, and lastly I constructed new target ages and 95% prediction intervals for each stage.
Method 1: Range of ages per stage
. The first method used to assess the Ubelaker and
Schour and Massler charts was a comparison of the distribution of individuals by age per observed stage (Tables 5.1 and 5.2). The largest numerical grouping for each stage is marked with a bold font. As seen by the positions of the bolded values, Table 5.1 shows a fairly linear progression from stages 9-13 for Ubelaker’s chart with some disparity for ages 10, 11, 13, and
14. The trend for Schour and Massler’s chart is also fairly linear. Both tables lack a strong grouping of individuals for stages 12 and 15. Overall, both charts seem to track the age of individuals fairly well. A total of 37% (139/375) of the kids up to and including stage 16 scored with Ubelaker’s chart fell in the predicted “best” stage, while a total of 36% (137/377) of the children scored with Schour and Massler’s chart fall in their predicted “best” stage.
Method 2: Comparing the means.
The second method used to assess the two charts is to compare the mean ages obtained from the study sample with the predicted ages for each stage for the published charts. Summary statistics, including the mean, standard deviation, sample variance, minimum and maximum, and sample size for each of these stages are given in Tables
5.3 and 5.4. The data for these tables are calculated using combined sexes.
45

TABLE 5.1. Comparison of number of individuals by age per observed Ubelaker stage
(sexes combined).
Observed Ubelaker Stage
Totals
5.00-5.99 1 9
6.00-6.99 6 11 1
7.00-7.99 7 15 3
16 11 2
9.00-9.99 2 4 8 9
10.00-10.99 2 4 15 14 3 2
23
42
50
47
43
40
23 7 44
12.00-12.99 1 7 6 19 4
37
13.00-13.99 4 7 36
13
27
Totals 1 19 43 58 45 52 59 16 83 43 419
TABLE 5.2. Comparison of number of individuals by age per observed Schour and
Massler stage (sexes combined).
Observed Schour & Massler Stage
Totals
5.00-5.99 11 23
6.00-6.99 3 10 2
42
7.00-7.99 8 4
50
11 47
9.00-9.99 2 4 5 9
43
14 40
23 7 44
12.00-12.99 1 7 6
37
13.00-13.99 4 7 36
13
27
Totals 0 15 49 52 38 61 92 16 84 42 419
46

TABLE 5.3. Summary statistics for age for each Ubelaker stage (sexes combined).
Stage 9
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
Stage 12
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
Stage 15
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
Stage 10
5.75 Mean
0.529 Standard Deviation
0.280 Sample Variance
5.02 Minimum
6.6 Maximum
19 n
Stage 13
8.43 Mean
0.940 Standard Deviation
0.884 Sample Variance
6.97 Minimum
10.49 Maximum
45 n
Stage 16
11.64 Mean
0.844 Standard Deviation
0.712 Sample Variance
10.12 Minimum
12.96 Maximum
16 n
Stage 11
6.57 Mean
0.942 Standard Deviation
0.887 Sample Variance
5 Minimum
9.29 Maximum
43 n
Stage 14
9.59 Mean
1.046 Standard Deviation
1.093 Sample Variance
7.15 Minimum
12.04 Maximum
52 n
Stage 17
13.34 Mean
1.316 Standard Deviation
1.733 Sample Variance
10.5 Minimum
15.84 Maximum
83 n
7.80
0.908
0.824
6.3
10.44
58
11.14
1.156
1.335
8.84
13.85
59
14.53
1.047
1.097
12.1
15.96
43
47

Stage 9
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
Stage 12
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
Stage 15
Mean
Standard Deviation
Sample Variance
Minimum
Maximum n
TABLE 5.4. Summary statistics for age for each Schour & Massler stage
(sexes combined).
Stage 10
5.69 Mean
0.520 Standard Deviation
0.270 Sample Variance
5.07 Minimum
6.6 Maximum
15 n
Stage 13
8.22 Mean
0.973 Standard Deviation
0.947 Sample Variance
6.97 Minimum
10.49 Maximum
38 n
Stage 16
11.64 Mean
0.844 Standard Deviation
0.712 Sample Variance
10.12 Minimum
12.96 Maximum
16 n
Stage 11
6.51 Mean
0.947 Standard Deviation
0.898 Sample Variance
5 Minimum
9.29 Maximum
49 n
Stage 14
9.42 Mean
1.012 Standard Deviation
1.025 Sample Variance
7.15 Minimum
12.04 Maximum
61 n
Stage 17
13.33 Mean
1.314 Standard Deviation
1.726 Sample Variance
10.5 Minimum
15.84 Maximum
84 n
7.81
0.952
0.906
6.3
10.44
52
11.07
1.195
1.429
8.09
13.85
62
14.58
0.996
0.993
12.1
15.96
42
48

The mean ages for each chart are summarized in Table 5.5, and it can be seen that the study sample tracks the predicted ages on the charts fairly well but are mostly overestimated.
Much of this overestimation, however, is due to the authors of these charts rounding down their age designations in each category to obtain whole numbers. In both charts, it was observed that stages 14 and 15 appear to have similar mean ages, and t-tests indicate that the mean ages for these stages are not statistically different (Ubelaker: t = 1.34, p = 0.18, df = 64; Schour and
Massler: t = 1.32, p = 0.19, df = 63). Therefore, in order for these charts to be used in a rigorous fashion, stages 14 and 15 may need to be combined into a single stage. However, the similarity may simply be a result of the small sample size for stage 15 (n = 16). The mean age for stage 16 for the study sample shows the greatest difference from the chart means, probably because at this age, juvenile dental formation and eruption has slowed and both Ubelaker and Schour and
Massler combined 12, 13, and 14 year age groups, so the use of age 12 as the predicted age for stage 16 is misleading. Stage 17 is underestimated when comparing the obtained mean age with
TABLE 5.5. Obtained mean ages for Ubelaker and Schour and Massler stages
(sexes combined).
9
10
11
12
13
14
15
16
17
Actual
Stage
Ubelaker
Obtained
Mean
Age
(n)
Ubelaker
Predicted
Age
Actual
Stage
5.75
6.57
7.80
8.43
19
43
58
45
7
8
5
6
9
10
11
12
9.59 52 9 13
11.14 59 10
14
11.64 16 11 15
13.34 83 12 16
14.53 43 15 17
Schour & Massler
Obtained
Mean
Age
(n)
S & M
Predicted
Age
5.69
6.51
7.81
8.22
15
49
52
38
7
8
5
6
9.42 61 9
11.07 62 10
11.64 16 11
13.33 84 12
14.58 42 15
49

the charts’ predicted ages probably because the study sample was restricted to individuals under the age of 16, resulting in artificial truncation.
Method 3: Assessing mean error.
The mean error for each chart was determined by calculating bias and inaccuracy statistics for the study sample for each stage, using Ubelaker’s and Schour and Massler’s predicted ages. The bias for both charts was negative across all stages
(see Table 5.6), indicating a systematic underestimation of the true ages by about seven-tenths of a year. This underestimation is largely a result of the target ages for each stage on the original charts being rounded to the nearest whole year. Therefore, any juvenile age estimate based on these charts will always underestimate the actual age of the subject unless the radiograph was taken on their birth date. For example, for a random sample of 5-year-old children, it would be expected that the mean age would be approximately 5.5 years of age. Consequently, for each dental stage given in whole years, the expected baseline bias should be -0.5 years. When the rounding error on both charts is taken into account, the obtained bias values in Table 5 are reasonable and not much more than the predicted 0.5 years, indicating that overall, the chart diagrams perform well. The only exceptions that are readily observed are stages 14 and 16 in both charts, which seem to underestimate the ages of the study sample more than would be predicted by the rounding errors.
Inaccuracy values are predictably higher than the bias values, ranging from about 0.7 to
1.5 years. Again, 0.5 years of this error is due to the rounding of the chart ages to the nearest year. As before, stages 14 and 16 performed less well than the others. Overall, Schour and
Massler’s chart performs slightly better than Ubelaker’s with both lower inaccuracy and bias values for nearly every stage.
50

TABLE 5.6. Inaccuracy and bias values (in years) for Ubelaker and Schour and Massler’s
charts (sexes combined).
One individual in Stage 8 is included in the totals.
Actual
Ubelaker
Stage
13
14
15
16
9
10
11
12
17
Avg
Error (all stages)
Ubelaker
Bias Inaccuracy (n)
Actual
S&M
Stage
-0.75 0.75 19
9
-0.57 0.82 43
10
-0.80 0.93 58
11
-0.43 0.75 45 12
-0.59 0.99 52 13
-1.04 1.20 59 14
-0.64 0.88 16
15
-1.34 1.55 83
16
-0.47 0.85 43
17
Avg stages)
Schour and Massler
Bias Inaccuracy (n)
-0.49 0.69 15
-0.57 0.81 49
-0.73 0.95 52
-0.14 0.71 38
-0.54 0.88 61
-1.05 1.20 62
-0.64 0.88 16
-1.34 1.53 84
-0.40 0.80 42
-0.66 1.03 419
Method 4: Assessment of predicted error ranges
. The fourth method of evaluating the performance of the charts is to calculate the number of individuals correctly falling in the predicted error ranges as given for each stage (Table 5.7). For Ubelaker’s chart, the actual age correctly falls within the predicted age ranges 91% of the time for the entire sample, and no stage performs below about 79%. Schour and Massler’s chart, however, performed less well, with only 44% of the individuals falling within the predicted ranges for the entire sample. The difference in success between the two charts is due in part to Ubelaker’s predicted age ranges including two standard deviations around each mean age, while Schour and Massler’s ranges are considerably narrower, using only one standard deviation. However, even when Schour and
Massler’s error ranges are doubled, only 69.7% of the individuals fall within the range limits.
Stage 16 performs very poorly with only 18% success when using the non-doubled error range.
51

TABLE 5.7. Comparison of correct age assessment using Ubelaker and Schour and
Massler’s charts (sexes combined).
Observed
Ubelaker
Stage
Predicted
Ubelaker
Range (in years)
13
14
15
16
17
9
10
11
12
3.70-6.30
4.00-8.00
5.00-9.00
6.00-10.00
7.00-11.00
7.50-12.50
9.00-15.00
TOTAL (all stages)
# Individuals
Within
Range
%
15/19
40/43
52/58
41/45
49/52
52/59
71/83
379/418
78.9
93.0
89.7
91.1
94.2
88.1
85.5
90.7
Observed
S & M
Stage
Predicted
S&M Range
(in years)
# Individuals
Within
Range
%
13
14
15
16
17
9
10
11
12
TOTAL (all stages) 185/419 44.0
Note that between stages 16 and 17, there is a gap between ages 12.5 and 14.5 years in which no individual can be placed. Therefore, it is technically impossible to age an individual at, say, 13 years with their chart. Their most accurate stage was stage 12, with 65.8% of the individuals correctly falling within the (narrow) error range.
In sum, these results suggest that Ubelaker’s (1989) dental aging chart is superior to
Schour and Massler’s (1944) with respect to the robusticity of its error ranges. However, Schour and Massler’s chart has lower inaccuracy and bias values. Both charts produce similar mean ages for each stage and demonstrate equivalent regularity across the age range.
Sex Differences
Tables 5.8 through 5.11 present the distribution of individuals by age per observed stage, but this time separated by sex. Again, the largest numerical grouping for each stage is marked with a bold font. As would be expected, each of the tables shows a clear trend with the
52

TABLE 5.8. Comparison of number of individuals by age per observed Ubelaker stage
(females).
Observed Ubelaker Stage
5.00-5.99 3
6.00-6.99 1 4 1
7.00-7.99 1 7 3
8.00-8.99 3 6 2
9.00-9.99 1 2 3 4
10.00-10.99 1 7 2
11.00-11.99 1 8 4 8
13.00-13.99 1 2
14.00-14.99 5 3
19
21
19
15
8
9
17
25
20
21
191
TABLE 8. Comparison of number of individuals by age per observed Ubelaker stage
(males).
Observed Ubelaker Stage
5.00-5.99 1 7 6
6.00-6.99 5 7
8.00-8.99 1 5
9.00-9.99 1 2 5
9
5
10.00-10.99 1 4 8 5 1 2
11.00-11.99 1 4
12.00-12.99 1 5 9
13.00-13.99 3 5
Grand 1 12 27 34 25 24 33 7 39 26
22
21
23
18
21
14
25
25
27
13
228
53

TABLE 9. Comparison of number of individuals by age per observed Schour and Massler stage (females).
Observed Schour & Massler Stage
5.00-5.99 4
6.00-6.99 3 2
7.00-7.99 1 3
9.00-9.99 1 2 1 4
10.00-10.99 1 6 2
11.00-11.99 9 8
13.00-13.99 1 2
14.00-14.99 5 3
9
17
25
20
21
19
21
19
15
8
191
TABLE 10. Comparison of number of individuals by age per observed Schour and
Massler stage (males).
Observed Schour & Massler Stage
5.00-5.99
6.00-6.99 3 7
7.00-7.99 7 9 8 1
8.00-8.99 1 8 6
9.00-9.99 1 2 4 5
10.00-10.99 1 3 8 6 1 2
11.00-11.99 2 4
12.00-12.99 1 5 9
13.00-13.99 3 5
22
21
23
18
21
14
25
25
27
13
228
54

progression of age. However, a closer analysis of Ubelaker’s chart (Tables 5.8 and 5.9) shows that the females show a more regular progression of stage per age, while the male’s pattern displays more irregularity. Ages 11 and 13 seem problematic for both sexes. Similarly, Schour and Massler’s chart (Tables 5.10 and 5.11) is fairly linear among females but more irregular among males. A total of 43.7% (76/174) of the females younger than 14 scored with Ubelaker’s chart fall in the predicted “best” stage, while only 32.6% (70/215) of the males do. A total of
41.4% (72/174) of the females younger than 14 scored with Schour and Massler’s chart fall in the predicted “best” stage, while only 33.5% (72/215) of the males do. Overall, then the two charts seem to perform equivalently.
An analysis of covariance for both Ubelaker’s and Schour and Massler’s observed stages was performed on the data to assess the effects of sex. These results can be seen in Table 5.12.
The semi-continuous dependent variable is the observed stage, with sex as the categorical independent variable and age being the continuous covariate independent variable:
Observed Dental Stage = Sex + Decimal Age + Error
The independent variables (sex and age) were found to be highly significant for both Ubelaker’s and Schour and Massler’s charts, indicating that both variables significantly affect the expressed dental stage.
Additionally, t-tests were utilized to compare mean age by sex for each stage (see Table
5.13). The differences between sexes in most of the stages are not significant. However, in
Ubelaker’s chart females and males are significantly different ages at stages 13 and 14 (ages 9-
10) and are approaching significance at stage 12 (p = 0.077). For Schour and Massler’s chart, stages 12, 13, and 14 are significantly different between the sexes. These findings are consistent
55

TABLE 5.12. Analysis of covariance results for sex and age using observed stage as the dependent variable.
Observed Ubelaker Stage
(n) Multiple R
419 0.93
Squared Multiple R
0.87
Observed Schour and Massler Stage
(n) Multiple R
419 0.93
Squared Multiple R
0.87
Source df Mean-Square Source
Sex
Age
Error
1
1
416
9.61
2169.47
0.77
12.42 0.00
Sex
2804.57 0.00
Age
Error df Mean-Square p
1
1
416
12.30
2078.62
0.77
15.88 0.00
2683.92 0.00
with published data that females’ teeth tend to develop faster than males. As a result, females are reaching these stages earlier than males, as seen with a lower mean age. The mean age by stage is always absolutely higher in males in both charts, except for stage 16. This stage includes individuals ages 12-14, which is the age at which puberty begins. Males may begin to developmentally catch up with girls in this age range due to a later growth spurt. For those stages that are significantly different, there may be a need to differentiate them by sex.
TABLE 12. Sex differences in age for each Ubelaker and Schour and Massler stage.
Bold values indicate which sex is older for each stage.
Ubelaker Schour and Massler
Stage
Obtained
Female
Mean
Obtained
Male Mean t-Test
Significance
(p)
Stage
Obtained
Female
Mean
Obtained
Male Mean t-Test
Significance
(p)
9
10
11
12
13
5.54
6.45
7.72
8.15
9.33
5.87
6.64
7.85
8.65
9.90 ns ns ns 11
0.077, df = 43
12
0.048, df = 50
9
10
13
5.45
6.37
7.75
7.75
9.10
5.81
6.60
7.85
8.53
9.79 ns ns ns
0.014, df = 36
0.007, df = 59
14
15
10.80
11.44
11.40
11.91
0.046, df = 57 ns
14
15
10.72
11.44
11.39
11.91
0.027, df = 60 ns
16 13.37 13.31 ns 13.31 ns
17 14.30 14.68 ns 17 14.30 14.68 ns
56

Prediction Intervals
The 95% prediction intervals were calculated for all stages using the formula:
Target age ± t
(0.05)
(1 + 1/n)
1/2
(s) where n is the number of individuals within a stage, and “s” is the standard deviation of that particular stage being tested (Hahn & Meeker 1991). The data for the 95% prediction intervals can be found in Tables 5.14 and 5.16 for Ubelaker and Tables 5.15 and 5.17 for Schour and
Massler. These tables display a new target age based on the observed data for this study and the limits of the prediction interval. In addition, the percentage of individuals that correctly fell within these parameters was calculated.
Based on the significant differences found between the sexes for Ubelaker’s stages 13 and 14 and Schour and Massler’s stages 12, 13, and 14, the 95% prediction intervals were also calculated for males and females separately at these stages (Tables 5.16 and 5,17, respectively).
TABLE 5.14. Target ages and prediction intervals for each stage based on Ubelaker's chart (sexes combined).
Intervals are not provided for stages 9 or 17 because they were artificially truncated by the sampling strategy, and target ages for those stages are suspect.
9
10
11
12
13
14
15
16
17
Observed Range s
(in years)
43
58
45
52
59
6.57
7.80
8.43
9.59
11.14
0.94
0.91
0.94
1.05
1.16
5.0-6.6
5.0-9.3
6.3-10.4
7.0-10.5
7.2-12.0
8.8-13.9
16 11.64 0.84 10.1-13.0
83 13.34 1.32 10.5-15.8
43 (14.52) 1.05 12.1-16.0
95% Prediction
Interval
4.97-8.17
6.27-9.34
6.83-10.03
7.81-11.37
9.18-13.10
10.12-13.16
11.13-15.55
% w/in PI
95.4
94.8
91.1
90.4
89.8
100.0
91.6
57

TABLE 5.15. Target ages and prediction intervals for each stage based on Schour &
Massler’s chart (sexes combined).
Intervals are not provided for stages 9 or 17 because they were artificially truncated by the sampling strategy, and target ages for those stages are suspect.
13
14
15
16
17
9
10
11
12
15 (5.69) 0.52
49
52
6.51
7.81
0.95
0.95
38
61
62
16
8.22
9.42
11.07
11.64
0.97
1.01
1.20
0.84
84 13.33 1.31
42 (14.58) 1.00
(in years)
5.1-6.6
5.0-9.3
6.3-10.4
7.0-10.5
7.2-12.0
8.1-13.9
10.1-13.0
10.5-15.8
12.1-16.0
95% Prediction
Interval
4.90-8.12
6.20-9.42
6.56-9.88
7.72-11.12
9.06-13.08
10.12-13.16
11.14-15.52
% w/in PI
95.9
96.2
89.5
93.4
88.7
100.0
89.3
TABLE 5.16. Prediction intervals separated by sex for stages 13 & 14 based on Ubelaker’s chart.
13 - females
13 - males
14 - females
14 - males
(in years)
28 9.33 1.08 7.2-11.3
24 9.90 0.88 8.5-12.0
26 10.80 1.18 8.8-13.9
33 11.40 1.04 9.6-13.5
95% Prediction
Interval
7.46-11.20
8.36-11.44
8.75-12.85
9.61-13.19
% w/in PI
85.7
91.7
96.2
87.9
TABLE 5.17. Prediction intervals separated by sex for stages 12, 13, & 14 based on Schour
& Massler’s chart.
12 - females
12 - males
13 - females
13 - males
14 - females
14 - males
(in years)
15 7.75 0.66 7.0-9.3
23 8.53 1.00 7.2-10.5
33 9.1 0.93 7.2-9.1
28 9.79 0.96 7.7-12.0
29 10.72 1.23 8.1-13.9
33 11.39 1.05 9.6-13.5
95% Prediction
Interval
6.56-8.94
6.77-10.29
7.49-10.71
8.13-11.45
8.60-12.84
9.58-13.20
% w/in PI
93.3
91.3
90.9
89.3
93.1
87.9
58

For the 95% prediction intervals separated by sex for stage 12 based on Schour and
Massler’s chart, both males and females scored higher than when sexes were combined. The
95% interval for stage 13 individuals evaluated with Ubelaker’s chart was slightly lower for females than for sexes combined, while the male’s percentage was slightly higher. For Schour and Massler’s 95% prediction intervals for stage 13, both males and females scored lower than with sexes combined. At stage 14, for Ubelaker’s chart, the prediction intervals for both the males and females performed better than the sex-combined interval. However, when the 95% prediction intervals were based on Schour and Massler’s chart for stage 14, the females’ percentage was higher than the combined sex percentage and the males’ score was lower than the sex-combined interval.
A comparison of the 95% prediction interval ranges with Ubelaker’s predicted ranges are presented in Table 5.18 and a comparison of Schour and Massler’s ranges are presented in Table
5.19. The prediction intervals calculated here when compared to Ubelaker’s intervals have a higher percentage of individuals falling within the determined parameters for all stages except stage 13, with an overall accuracy of 92.4% for stages 10 to 16. This figure is slightly better than
Ubelaker’s overall accuracy of 90.7% (or 90.2% accuracy for stages 10 to 16). Likewise, Schour and Massler’s newly determined prediction intervals gave an excellent performance with 92.3% of individuals falling within the found range. This highly outperforms the overall accuracy of the original chart of 44%. When these prediction intervals were recalculated with the division of sexes for Ubelaker’s stages 13 and 14 and the new ranges determined (seen in Table 5.16) the overall accuracy increased to 93%. Schour and Massler’s division of sexes for stages 12 to 14 did not increase the overall accuracy, remaining constant at 92.3%. It is, therefore, important to note that while the knowledge of sex at stages 13 and 14 when using the Ubelaker chart can
59

TABLE 5.18. Comparison of prediction interval ranges with Ubelaker’s predicted ranges and percents of individuals within these ranges.
Stage
Predicted
Ubelaker Range
(in years)
% of
Individuals
Within Range
Stage
95% PI
Range (in years)
% of
Individuals
Within Range
9
10
11
12
13
14
15
16
17
3.7-6.3
4.0-8.0
5.0-9.0
6.0-10.0
78.9
93.0
89.7
91.1
9
10
11
12
7.0-11.0
7.5-12.5
94.2
88.1
13
14
8.5-13.5 100.0 15
9.0-15.0 85.5 16
12.0-18.0 100.0 17
TOTAL (all stages) 90.7 TOTAL (stages 10-16)
4.83-6.68
4.97-8.17 95.4
6.27-9.34
6.83-10.03
94.8
91.1
7.81-11.37
9.18-13.10
90.4
89.8
10.12-13.16 100.0
11.13-15.55 91.6
12.73-16.31
92.4
TABLE 18. Comparison of prediction interval ranges with Schour and Massler’s predicted ranges and percents of individuals within these ranges.
Stage
13
14
15
16
17
9
10
11
12
Predicted
S&M Range
(in years)
% Schour &
Massler
Samples
Within Range
Stage
4.25-5.75 60.0
9
5.25-6.75 57.1
10
6.25-7.75 53.8
11
7.25-8.75 65.8
12
8.25-9.75 45.9
13
9.25-10.75 40.3
14
10.25-11.75 50.0
11.50-12.50 17.9
14.50-15.50 45.2
15
16
17
TOTAL (all stages) 44.0
95% PI
Determined
Range (in years)
TOTAL (stages 10-16)
% Within PI
Determined
Range
4.74-6.64
4.90-8.12 95.9
6.20-9.42
6.56-9.88
96.2
89.5
7.72-11.12
9.06-13.08
10.12-13.16
11.14-15.52
93.4
88.7
100.0
89.3
12.88-16.28
92.3
60

increase age prediction accuracy, it is not entirely necessary to identify the sex in order to get a good age estimate.
While the differences are not absolutely great, a general evaluation of the new prediction intervals compared to Ubelaker’s ranges show that the new parameters have smaller ranges, allowing for tighter estimates of age. The lower limits of the new intervals are always higher
(and frequently substantially so) than Ubelaker’s lower limits, while the upper limits are more comparable. A noteworthy example can be seen in stage 14, where Ubelaker’s age range is 7.5-
12.5 years. This study, however, produces a prediction interval beginning 1.7 years later and ending 0.6 years later, at 9.18-13.10 years for the same stage. This range is with the sexes combined, even though they were shown to be significantly different at this stage. It is of importance to note however, that this difference could be due to the scoring strategies at this stage. At stages 14 and 15 the transition begins from mixed dentition to permanent dentition.
Thus, for both charts, even if most of the teeth were in stage 15, if any deciduous teeth were present, the individual was placed into stage 14. This could have skewed the data.
61

CHAPTER 6: DISCUSSION AND CONCLUSIONS
The objective of this study was to reevaluate and test known standards of skeletal aging using the Schour and Massler (1944) and Ubelaker (1989) dental aging charts, to determine their accuracy when applied to modern subadults, if their target age and associated error ranges are still applicable, and whether or not these charts need to be differentiated by sex. It is hoped that these results will assist in improving the accuracy of estimating age for unknown subjects from their teeth and that this approach will assist in their identification.
To date, both charts are widely duplicated and both are utilized by anthropologists and dentists. Therefore, it is the suggestion of this author that the line drawings remain the same, but modifications must be made on the target ages and their associated error intervals. When this study’s 95% prediction intervals were calculated, both charts performed equally well, thus this study suggests that the prior error intervals be modified for stages 10-16 (ages 6 to 14) to include the newly determined mean age and intervals (see Table 6.1).
Accordingly, the question remains as to which of the two charts is better. With the newly determined prediction intervals, they are now equally useful in their age determinations. Thus, the slight differences in formation and eruption between these charts are accommodated by the new means and error intervals.
An analysis of covariance found that sex and age are highly significant for both
Ubelaker’s and Schour and Massler’s charts, indicating that both variables affect the expressed dental stage. Additionally, t-tests were used to compare the mean age by sex for each stage with differences between sexes in most stages not being significant. However, in Ubelaker’s chart, males and females are significantly different at stages 13 and 14, and in Schour and Massler’s
62

TABLE 6.1. Comparison of Schour and Massler and Ubelaker’s mean ages and 95% error intervals (sexes combines) derived from this study.
Schour and Massler Ubelaker
Stage 10
Stage 11
Stage 12
Stage 13
Stage 14
Stage 15
Stage 16
6.51 ± 0.95
7.81 ± 1.61
8.22 ± 1.66
9.42 ± 1.70
11.07 ± 2.01
11.64 ± 1.52
13.33 ± 2.19
6.57 ± 1.60
7.80 ± 1.54
8.43 ± 1.59
9.59 ± 1.78
11.14 ± 1.96
11.64 ± 1.52
13.34 ± 2.21
TABLE 6.2. Comparison of Schour and Massler and Ubelaker’s mean ages and 95% error intervals for males and females derived from this study.
Schour and Massler Ubelaker
Stage 12
Stage 13
Stage 14
Female
Male
Female
Male
Female
Male
7.75 ± 1.19
8.53 ± 1.76
9.10 ± 1.61 9.33
9.79 ± 1.66 9.90 ± 1.58
10.72 ± 2.12
11.39 ± 1.81
10.80 ± 2.10
11.40 ± 1.82
63

chart stages 12, 13, & 14 are significantly different between the sexes. Therefore, in order to obtain the most accurate age estimate, when sex is known, there is a need for both charts to have these ages separated by sex for these stages (see Table 6.2). It is recommended that these new prediction intervals be used when the sex of an unidentified individual is known.
Since these newly derived intervals have not been widely used, any potential limitations have not been delineated. Thus, replication on a larger scale with known-age samples is required to examine the robusticity of this study’s results. It is also important to note that these intervals were derived solely from modern individuals of European ancestry, and thus application to individuals from different time periods or of different ancestries must be made with caution.
64

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