Reference and target sample age distribution impacts between model types in dental developmental age estimation.

The performance of age estimation methods may vary due to a combination of method- and sample-related factors. Method development and evaluation necessitates understanding what influences these factors have on age estimation outcomes. In the specific context of juvenile dental age estimation, we used a single dataset and complete factorial design to systematically test four potential sources of difference: age distributions of reference and target sample (uniform, unimodal, U-shaped), Bayesian (multivariate Bayesian cumulative probit) vs. classical regression modeling (multivariate adaptive regression splines i.e. MARS), and model selection bias. The dataset consisted of 850 sets of left mandibular molar scores from London children 5-18 years old. True age and estimated age intervals in target samples were compared for bias, root-mean-squared error, precision, and accuracy using locally weighted smoothing of performance measures across the age range and means of performance metrics between factor-level combinations. We found interactions of model type, reference distribution, and target distribution. MARS models showed consistent evidence of age mimicry. Central tendency of the reference sample corresponded with increased bias while central tendency of the target sample corresponded with reduced RMSE and reduced precision for both model types. We found evidence of model selection bias, mitigated through averaging model metrics. We conclude that reference and target sample distribution influences and model selection bias are sufficient to cause difference in model performance within a single population. We suggest using Bayesian modeling, drawing uniform reference and target samples, and calculating test error on a hold-out sample to mitigate these challenges in method development.

Bone-specific median age of hand-wrist maturation from Sudan.

BACKGROUND: Maturation of bones in the hand-wrist region varies among individuals of the same age and among world groups. Although some studies from Africa report differences to other ethnic groups, the lack of detailed bone-specific maturity data prevents meaningful comparisons. AIM: The aim of this study was to describe bone-specific maturity for developing hand-wrist bones in individuals in Khartoum, Sudan. SUBJECTS AND METHODS: The sample was selected from healthy patients attending a dental hospital in Khartoum with known age and ancestry (males = 280, females = 330; aged between 3 and 25 years). Bones were assessed from radiographs of the left hand and wrist after the Greulich and Pyle Atlas (1959). Median ages of attainment for bone stages were calculated using probit analysis for each stage in males and females separately. RESULTS: Maturity data for stages of the phalanges, metacarpals, carpals and radius and ulna in males and females are presented. Median ages in females were earlier compared to males for all stages. These results are largely earlier than previously published findings or where these could be calculated. CONCLUSION: These results of individual maturity stages of phalanges, metacarpals, carpals and the distal epiphyses of the radius and ulna are useful to assess maturity in growing individuals from Sudan.

An assessment of root stage of canine and premolar teeth at alveolar eruption.

OBJECTIVE: The primary aim was to evaluate the degree of root development of permanent canines at the time of alveolar eruption. We also aimed to assess whether differences in the degree of root development at alveolar eruption exist between permanent canines and premolars and between maxilla and mandible. DESIGN: A cross-sectional study. SETTING: Barts and The London School of Medicine and Dentistry, Queen Mary University of London. PARTICIPANTS: Two hundred dental panoramic radiographs taken as part of routine dental care. METHODS: Radiographs were assessed for canine and premolar root development stage and eruption level with calibration and repeat measurements undertaken. RESULTS: Two hundred and sixty teeth were identified as being at the level of alveolar eruption. The majority of maxillary canines reached alveolar eruption when root formation was complete. Most premolars and mandibular canines reached alveolar eruption when roots were three-quarters developed. At alveolar eruption, canines were statistically more mature than premolars (p<0.001) and maxillary teeth were more mature than mandibular teeth (p<0.05). CONCLUSIONS: Root development appears to be particularly advanced for maxillary permanent canines, being essentially root-complete at alveolar eruption, while premolars and mandibular permanent canines appear to have three-quarters root development at this stage. This information may be used to inform whether and when to extract primary teeth for orthodontic reasons.

Growth of Neanderthal infants from Krapina (120-130 ka), Croatia.

Modern humans have a slow and extended period of childhood growth, but to what extent this ontogenetic pathway was present in Neanderthals is debated. Dental development, linked to the duration of somatic growth across modern primates, is the main source for information about growth and development in a variety of fossil primates, including humans. Studies of Neanderthal permanent teeth report a pace of development either similar to recent humans or relatively accelerated. Neanderthal milk teeth, which form and emerge before permanent teeth, provide an opportunity to determine which pattern was present at birth. Here we present a comparative study of the prenatal and early postnatal growth of five milk teeth from three Neanderthals (120 000-130 000 years ago) using virtual histology. Results reveal regions of their milk teeth formed quickly before birth and over a relatively short period of time after birth. Tooth emergence commenced towards the earliest end of the eruption schedules displayed by extant human children. Advanced dental development is consistent with expectations for Neanderthal infant feeding.

Prior Probabilities and the Age Threshold Problem: First and Second Molar Development.

Dental development has been used to assess whether an individual may be below or above an age that serves as a legal threshold. This study used development of the first and second mandibular molars from a large sample of individuals (N = 2,676) to examine the age threshold for minimum age of criminal responsibility. A bivariate ordered probit model was applied to dental scores following the Moorrees et al. (1963) system, with the addition of a crypt-absent/present stage. Then a 10-fold cross-validation within each of the sexes showed that the bivariate models produce unbiased estimates of age but are heteroskedastic (with increasing spread of the estimates against actual age). To address the age threshold problem, a normal prior centered on the threshold is assumed, and the product of the prior and the likelihood is integrated up to the age threshold and again starting at the age threshold. The ratio of these two integrals is a Bayes factor, which because the prior is symmetric around the threshold, can also be interpreted as the posterior odds that an individual is over versus under the age threshold. It was necessary to assume an unreasonably high standard deviation of age in the prior to achieve posterior odds that were well above "evens." These results indicate that dental developmental evidence from the first and second molars is of limited use in examining the question of whether an individual is below or over the minimum age of criminal responsibility. As the third molar is more variable in its development than the first two molars, the question of dental evidence regarding the age of majority (generally 18 years) remains problematic.

Skeletal maturity of the hand in an East African group from Sudan.

OBJECTIVES: Studies of skeletal maturity from Africa indicate a delay, reflected in a negative relative skeletal age (RSA). This study aims to evaluate the influence of age, socioeconomic status (SES) and nutritional status on skeletal maturation in a large sample of children from North Sudan. MATERIALS: The sample consisted 665 males and 1018 females from 3-25 years from Khartoum. Height, weight, age of menarche and, SES were recorded of patients attending for dental treatment. METHODS: Skeletal age was assigned from hand-wrist radiographs using the Greulich-Pyle (GP) atlas (1952). RSA (difference between skeletal and chronological ages) was compared in groups divided by age, sex, height-for-age and body-mass-index z scores, and SES. Spearman's correlation and student t-test was used to compare groups. RESULTS: Delayed skeletal age was noted across all age in boys. In girls, a delay was observed between ages 6-10, while advancement occurred between ages 13-18. Maturity was delayed in low height groups (p < .05) and low SES groups. RSA was negatively associated with HAZ in low SES males (R = -0.0.27, p < .001) and low SES females (R = -0.32, p < .001). CONCLUSIONS: There were statistically significant skeletal delays in North Sudanese males and most pre-menarche females, low height and low SES groups. Post-menarche females were advanced relative to males and GP references. Low SES impacts were statistically correlated to skeletal delay.

The timing of mandibular tooth formation in two African groups.

BACKGROUND: Ethnic differences in the timing of human tooth development are unclear. AIM: To describe similarities and differences in the timing of tooth formation in two groups of Sudanese children and young adults. SUBJECTS AND METHODS: The sample consisted of healthy individuals from Khartoum, Sudan, aged 2-23 years. The Northern group was of Arab origin (848 males, 802 females) and the Western group was of African origin (846 males, 402 females). Each mandibular left permanent tooth from first incisor to third molar was assessed from dental radiographs into one of 15 development stages. Mean ages at entry for 306 tooth stages were calculated using probit regression in males/females in each group and compared using a t-test. RESULTS: Mean ages were not significantly different in most tooth stage comparisons between ethnic groups for both males (61/75) and females (56/76), despite a tendency of earlier mean ages in the Western group. Mean ages for most tooth stage comparisons between males and females (137/155) were not significantly different within ethnic groups suggesting low sexual dimorphism. CONCLUSION: The mean ages of most mandibular tooth formation stages were generally not significantly different between ethnic groups or between males and females in this study.

Dental age estimation in a group of Kenyan children using Willems' method: a radiographic study.

BACKGROUND: Radiographic study of developing teeth provides a reliable indication of chronological age. In Kenya, dentists are often required to estimate age. However, there is a paucity of publications on the performance of dental age estimation methods. AIM: To determine the accuracy of Willems' method of dental age estimation. SUBJECTS AND METHODS: A cross-sectional study was done at The University of Nairobi Dental Hospital. Panoramic radiographs of children aged 3.00-16.99 years old were studied. Dental age was estimated according to Willems' method and compared to chronological age and the difference compared to zero using a t-test. RESULTS: Radiographs of 187 (47%) females and 214 (53%) males were analysed. Willems' method significantly over-estimated the mean overall age by -0.24 ± 1.17 years (p < .000). Age was over-estimated in girls by -0.10 ± 1.18 years (p = .254); however, age in boys was significantly over-estimated by -0.37 ± 1.14 years (p < .000). CONCLUSIONS: Willem's model over-estimated dental age slightly and the method performed better in estimating the age of girls compared to boys. The majority of the children had their age estimated within 1 year of their chronological age. This suggests that Willems' method is suitable for estimating the ages of individual children in Kenya.

Optimal trait scoring for age estimation.

OBJECTIVES: Little attention has been paid to questions about the applicability of parametric models to age estimation data and the related problem of how to adjust trait scoring in light of potential deviations from particular parametric models. This article addresses this deficit. METHODS: A Lagrange multiplier goodness-of-fit test is applied to two datasets to address the question of whether or not attainment ages for stages are log-normally distributed. The first dataset used in this article consists of scores of the Todd ten-phase system for the pubic symphysis obtained from 938 individuals with known ages. The second dataset consists of scores for 15 stages of formation for the second mandibular molar scored in 2,304 individuals of known age. RESULTS: For the Todd ten-phase system there is a significant departure from log-normally distributed ages of attainment. To obtain an acceptable goodness-of-fit statistic, Todd scores consequently are collapsed into an eight-phase system that maintains scores I through VII as individual scores but combines phases VIII through X into one phase. The 15-stage scoring system for the second mandibular molar has an acceptable fit to the log-normal distribution for ages of attainment. CONCLUSIONS: The results from the analysis of the Todd pubic symphysis scores show that researchers should use goodness-of-fit tests for parametric models before deciding to collapse scores. Further, such goodness-of-fit tests are an essential tool in answering questions concerning the suitability of various parametric models. For the 15-stage scoring of the second mandibular molar, the log-normal model is appropriate for attainment ages.

Controversies in age estimation from developing teeth.

BACKGROUND: Numerous dental reference data exist to estimate age from developing permanent teeth. AIM: To compare the performance of reference data that provide a point estimate using the developing second molar. METHODS: Performance of several methods estimating age using mandibular second molar formation was compared using the Maber test sample (age = 3-16) of 946 dental radiographs. Mean difference and mean absolute difference between dental and chronological ages were calculated. The percentage of individuals with mean absolute difference <1 year was counted across age group and tooth stage. Results for the choice of Demirjian or Moorrees tooth staging, pooled-sex, opposite sex reference data, selected stages (initial cusp tips, crown complete, root half and root complete) and statistical approaches were compared. RESULTS: Tooth reference data conditioning on age, particularly probit mean age (age-at-transition) adapted for age prediction performed best. Results using sex-specific reference data, Moorrees stages and selected Moorrees stages were marginally better than other methods. No method performed well for ages 15 and 16 years. CONCLUSION: Adapted maturity data L9a and N25a reference data for this tooth performed best across age categories and tooth stages, with a mean absolute difference of 0.8 year.

Age estimation in fossil hominins: comparing dental development in early Homo with modern humans.

BACKGROUND: Previous studies have used molar tooth eruption as a comparative marker of maturation in early fossil hominins. However, tooth eruption and tooth formation are independent maturational processes. AIM: To determine whether estimates of age for entering a stage of dental development in three early hominin fossils fell within the distribution of a modern human sample. METHODS: This study used a comparative model of dental development to identify the stages of dental development most likely to provide information about length of the growth period in early fossil hominins. Age estimates for stages of dental development in fossils were superimposed onto a normal distribution of the same radiographically defined stages derived from a sample of 6540 children of diverse geographical origin. RESULTS: Both within the dentition of S7-37, from Sangiran, Java, but also for stages of two other specimens (KNM-WT 15000 from Kenya and StW 151 from South Africa), all age estimates for later stages of tooth formation fell within the modern sample range. CONCLUSIONS: A pattern appears to exist in early Homo where, both within and between developing dentitions, age estimates for stages of P4, M2 and M3 tooth formation fell consistently among the more advanced individuals of the modern human sample.

Albert Edwin William (LOMA) Miles (1912-2008) extracts from personal letters on dental matters.

Professor Miles (1912-2008) was a key player establishing dentistry as an academic subject. In the many letters he wrote to Helen Liversidge and me, he describes his involvement as Hon. Curator of the Odontological Museum, Editor Archives of Oral Biology, Assistant scientific editor of the BDJ. He writes about his association with Robert Maxwell and the Pergamon Press and his interests and friendships.

Combining radiographic and histological data for dental development to compare growth in the past and the present.

BACKGROUND: Being able to estimate the age at death of fossil hominins enables meaningful comparisons of both dental and general growth, past and present. AIM: The aim of this study was to use data for modern permanent canine formation derived from separate histological and radiographic studies to estimate the age at death of an early African Homo erectus specimen (KNM-WT 15 000) with a developing permanent maxillary canine. METHODS: Ground sections of 18 sexed modern human canines were used to reconstruct growth in tooth height along the enamel-dentine junction (EDJ) and onwards into root formation along the cement-dentine junction (CDJ). Daily rates of enamel and dentine formation were used to put a time scale to cumulative fractions of tooth height. RESULTS: Age estimates for KNM-WT 15 000 averaged 7.89-8.8 years of age (range = 6.6-10.3 years) and were close to previous histological estimates for this individual (7.6-8.8 years). CONCLUSIONS: Stages of dental development in KNM-WT 15 000 were easily accommodated within this age distribution of a modern sample. However, body mass and stature estimates for KNM-WT 15 000 fell well beyond those reported for a modern sample of 438 Sudanese children aged between 7.0-10 years.

The effect of reference sample composition and size on dental age interval estimates.

OBJECTIVES: Validation studies in juvenile dental age estimation primarily focus on point estimates while interval performance for reference samples of different ancestry group compositions has received minimal attention. We tested the effect of reference sample size and composition by sex and ancestry group on age interval estimates. MATERIALS AND METHODS: The dataset consisted of Moorrees et al. dental scores from panoramic radiographs of 3334 London children of Bangladeshi and European ancestry and 2-23 years of age. Model stability was assessed using standard error of mean age-at-transition for univariate cumulative probit and sample size, group mixing (sex or ancestry), and staging system as factors. Age estimation performance was tested using molar reference samples of four sizes, stratified by year of age, sex, and ancestry. Age estimates were performed using Bayesian multivariate cumulative probit with 5-fold cross-validation. RESULTS: Standard error increased with decreasing sample size but showed no effect from mixing by sex or ancestry. Estimating ages using a reference and target sample of different sex reduced success rate significantly. The same test by ancestry groups had a lesser effect. Small sample size (n < 20/year of age) negatively affected most performance metrics. DISCUSSION: We found that reference sample size, followed by sex, primarily drove age estimation performance. Combining reference samples by ancestry produced equivalent or better estimates of age by all metrics than using a single-demographic reference of smaller size. We further proposed that population specificity is an alternative hypothesis of intergroup difference that has been erroneously treated as a null.

The assessment and interpretation of Demirjian, Goldstein and Tanner's dental maturity.

BACKGROUND: A frequently reported advancement in dental maturity compared with the 50(th) percentile of Demirjian, Goldstein and Tanner (1973, Hum Biol 45:211-27) has been interpreted as a population difference. AIM: To review the assessment and interpretation of Demirjian et al.'s dental maturity. SUBJECTS AND METHODS: Dental maturity of boys from published reports was compared as maturity curves and difference to the 50(th) percentile in terms of chronological age and score. Dental maturity, as well as maturity of individual teeth, was compared in the fastest and slowest maturing groups of boys from the Chaillet database. RESULTS: Maturity curves from published reports by age category were broadly similar and differences occurred at the steepest part of the curve. These reduced when expressed as score rather than age. Many studies report a higher than expected score for chronological age and the database contained more than expected children with scores>97(th) percentile. Revised scores for chronological age from this database were calculated (4072 males, 3958 females, aged 2.1-17.9). CONCLUSION: Most published reports were similar to the database smoothed maturity curve. This method of dental maturity is designed to assess maturity for a single child and is unsuitable to compare groups.

The usefulness of dental and cervical maturation stages in New Zealand children for Disaster Victim Identification.

Age estimation of young victims of natural and un-natural disasters remains a crucial and challenging task during the process of Disaster Victim Identification (DVI). The purpose of this study was to compare dental maturity using the Demirjian and Cameriere methods and to explore the relationship between dental age and cervical vertebral maturity (CVM) using the Hassel and Farman method for a group of New Zealand children. The study used lateral cephalometric and panoramic radiographs of 200 orthodontic patients aged 7-17 years. Dental age was calculated from mandibular tooth formation stages using the Demirjian and Cameriere methods by calculating the ratio of tooth length to apex width for these teeth. CVM was assessed using stages from Hassel and Farman. Reliability of maturity from reassessment of 20 radiographs showed good agreement for the three methods. Chronological and dental ages were compared using a mixed model. Descriptive statistics of dental ages by CVM stage were calculated. The results show that both dental methods were similar in assessing maturity. A disadvantage of using the Cameriere method was that all seven teeth reached maturity at 13.69 and 14.06 years in females and males respectively, compared to age 16 using the Dermijian method. Females reached CVM stages at earlier chronological and dental ages than males. Mean chronological age for CVM stages 2-5 is about 1 year earlier in females than males. The Demirjian and Cameriere methods of dental maturity and CVM are reliable and useful in assessing dental and skeletal maturity. Ideally in a DVI situation, both the methods of Demirjian and Cameriere, together with CVM, should be employed in the ageing of individuals suspected of being between 7 and 16 years.

Prevalence of Moderate to Severe Periodontitis in an 18-19th Century Sample-St. Bride's Lower Churchyard (London, UK).

The aim of the study was to determine the prevalence of moderate to severe periodontitis in 18-19th century skulls in the St Bride's Lower Churchyard in London, UK. MATERIALS AND METHODS: A total of 105 adult skulls (66 M: F 39) from the Museum of London collection were examined for evidence of dental disease. The primary method was to measure the presence of moderate to severe periodontitis. Other dental pathologies were recorded such as tooth wear, calculus, and caries. RESULTS: Overall, the prevalence of moderate to severe periodontitis in the sample was 21-24%. Males were observed to be more susceptible to periodontal disease than females. The severity of bone loss in the skull collection also increased with age. There was no significant difference in the amount of calculus deposition when comparing either age or sex. A total of 14% of the individuals in the sample showed signs of smoking. CONCLUSION: The results of the study indicated that the prevalence of moderate to severe periodontitis in an 18-19th century skull sample was 21-24%, which was higher than in previous studies. This may be due to the lack of basic personal mouth care and professional dental treatment as well as known risk factors such as smoking, stress, low socioeconomic status, and malnutrition.

Patterns of permanent incisor, canine and molar development in modern humans, great apes and early fossil hominins.

OBJECTIVE: The objectives of this study were to quantify the variation in coincident stages of incisor, canine and molar eruption and tooth formation in modern humans and great apes and then to ask if any early fossil hominins showed a dental development pattern beyond the human range and/or clearly typical of great apes. DESIGN: Four stages of eruption and 18 stages of tooth development were defined and then scored for each developing tooth on radiographs of 159 once-free-living subadult great apes and on orthopantomographs of 4091 dental patients aged 1-23 years. From original observations, and from published images of eleven early fossil hominins, we then scored formation stages of permanent incisors when M1 was at root formation stage R»-R½ and R¾-RC. RESULTS: Incisor and canine eruption/development was delayed in great apes relative to molar development when compared with humans but there was overlap in almost all anterior tooth stages observed. Molar crown initiation was generally advanced in great apes and delayed in humans but again, we observed overlap in all stages in both samples. Only two fossil hominin specimens (L.H.-3 from Laetoli, Tanzania and KNM-KP 34725 from Kanapoi, Kenya) showed delayed incisor development relative to M1 beyond any individuals observed in the human sample. CONCLUSIONS: For certain tooth types, the distribution of formation stages in our samples showed evidence of generally advanced or delayed development between taxa. However, it would rarely if ever be possible to allocate an individual to one taxon or another on this basis.

Similarity in dental maturation in two ethnic groups of London children.

BACKGROUND: The existence of ethnic differences in dental maturity is uncertain. AIMS: The aims were to assess the impact of ethnic group and sex on tooth formation and report two new dental age estimation methods. SUBJECTS AND METHODS: The sample was radiographs of White and Bangladeshi dental patients in London, England (529 males, 521 females) of 2-22 years. Mandibular permanent teeth were staged after Moorrees et al. (1963, J Dent Res 42:1490). Average age entering tooth stages was calculated using logistic regression with ethnic group and sex as explanatory factors. Maturity data were adapted for age prediction (N25a) and mean age within stage (N25b) was calculated. RESULTS: Mean ages between ethnic groups was not significantly different in 83 of 91 individual tooth stage comparisons in males and 77 of 91 comparisons in females. Variation within each group was greater than variation between groups. For the combined ethnic group comparison of males and females, results show that average age of most canine and premolar root stages in females was significantly earlier than males and third molar root formation was later in females compared to males (p < 0.05). CONCLUSION: Dental maturity of permanent teeth was similar in these ethnic groups.

Bias and accuracy of age estimation using developing teeth in 946 children.

Developing teeth are used to assess maturity and estimate age in several disciplines. The aim of the study was to determine which of the most well known dental age estimation methods was best at estimating age. The target sample of dental radiographs (N = 946, ages 3­16) was described by Maber et al. (Forensic Sci Int 159 (2006) S68­S73). Seven mandibular permanent teeth (I1­M2) were assessed, and dental age was calculated using four dental maturity scales and fifteen methods that use data for individual teeth. The mean difference between dental age and real age was calculated (bias) as well as several other measures of accuracy (mean/median absolute difference, percentage aged to within six months and to within 10% of real age). Most methods estimated age with significant bias and standard deviation of bias ranged from 0.86 to 1.03 years. Analysis by age group showed most methods over-aged younger children, and considerably under-aged older children. The method that performed best was the dental maturity scale of Willems et al. (J Forensic Sci 46 (2001) 893­895) with bias of −0.14 ± 0.86 years (N = 827), mean absolute difference of 0.66 years, 71% aged to 10% or less of age, and 49% aged to within six months. Two individual teeth, P2 and M2, estimated age with bias not significantly different to zero for most formation stages using methods based on a large reference sample (L9a Demirjian stages) and a uniform age distribution (N25a Moorrees stages). Standard deviation of bias was least for early crown stages and most for late root stages. Methods that average ages for individual teeth improve if schedules for 'mean age entering a stage' are adjusted for prediction. Methods that directly calculate 'mean age within stage' can be improved by drawing from a uniform age distribution.