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.

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.

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.

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.

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.

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.

Status of Mandibular Third Molar Development as Evidence in Legal Age Threshold Cases.

The completion of the third molar roots has played an important role in ascertaining whether individuals may be at or over a legal threshold of age, often taken as 18 years. This study demonstrates that root apex completion in the third molar is relatively uninformative regarding the threshold of age 18 years in a sample of 1184 males, where mean age-of-attainment of root apex completion for third mandibular molars is about 19.4 years. This paper also considers the legal age threshold problem for cases where the third mandibular molar is not completely formed, and outlines the use of parametric models and Bayes' factors to evaluate dental evidence in statistically appropriate ways. It attempts to resolve confusion over age-within-stage versus age-of-attainment, likelihood ratios versus other diagnostic tests, and prior odds for a case versus the prior density for an age distribution.

A Reappraisal of Developing Deciduous Tooth Length as an Estimate of Age in Human Immature Skeletal Remains.

This study provides an update on a quantitative method for immature age estimation based on postnatal deciduous mandibular tooth length. Two known sex and age skeletal collections from Western Europe were sampled (n = 97). Linear regression models for age estimated were calculated for each individual tooth, each sex, and sex combined sample using classical calibration. Prediction errors, residuals, and percentage of individuals whose real age fell within the 95% prediction interval were calculated. The teeth which develop earlier in life, the incisors and the first molar, showed the greatest precision, while the canine showed the least. This method has greater applicability to archeological skeletons or to children in developing countries than for use in North American or European forensic contexts. The method can be applied to incomplete or poorly preserved remains of unknown sex, particularly when dental radiographs are not an option or when teeth have been removed from the alveolus or crypt.

Estimating age using permanent molars and third cervical vertebrae shape with a novel semi-automated method.

Estimating chronological age accurately in young adults is difficult and additional methods are required to increase the accuracy. This study explored a new semi-automated method to assess shape change of third cervical vertebra (C3) with age in the living; comparing this as a method to determine whether individuals could be categorised into being less than 18 years of age (<18), or at least 18 years of age (≥18) with tooth formation of the second and third mandibular molars (M2 and M3). The sample was panoramic and lateral skull radiographs of 174 dental patients (78 males, 96 females aged 15-22 years). Twelve variables were compared in two age categories: younger than 18 and at least 18 years of age in males and females separately using a t-test. Tooth formation of M2 and M3 was assessed. Mean values of eight variables of C3 in males and one variable in females were significantly different between the two age categories (p < 0.05). Results for males showed that the best age indicator for age ≥18 was the ratio between height and width of C3 and for females, the ratio between diagonals. Results for molars showed that M2 was mature in 69% of males and 83% of females, within the expected age range of 14-16 years. M3 was highly variable ranging from stages 6-14 for both; M3 was missing in 24% of males and 28% of females and mature in 14% of males and 15% of females. The conclusion was that shape change of C3 has potential as an additional method to group individuals <18 and ≥ 18 years of age.

Response to Comment on "The growth pattern of Neandertals, reconstructed from a juvenile skeleton from El Sidrón (Spain)".

The comment by DeSilva challenges our suggestion that brain growth of the El Sidrón J1 Neandertal was still incomplete at 7.7 years of age. Evidence suggests that endocranial volume is likely to represent less than 90% adult size at El Sidrón as well as Neandertal male plus Krapina samples, in line with further evidence from endocranial surface histology and dural sinus groove size.

The growth pattern of Neandertals, reconstructed from a juvenile skeleton from El Sidrón (Spain).

Ontogenetic studies help us understand the processes of evolutionary change. Previous studies on Neandertals have focused mainly on dental development and inferred an accelerated pace of general growth. We report on a juvenile partial skeleton (El Sidrón J1) preserving cranio-dental and postcranial remains. We used dental histology to estimate the age at death to be 7.7 years. Maturation of most elements fell within the expected range of modern humans at this age. The exceptions were the atlas and mid-thoracic vertebrae, which remained at the 5- to 6-year stage of development. Furthermore, endocranial features suggest that brain growth was not yet completed. The vertebral maturation pattern and extended brain growth most likely reflect Neandertal physiology and ontogenetic energy constraints rather than any fundamental difference in the overall pace of growth in this extinct human.

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.

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.

Accuracy of estimating age from cervical vertebral maturation and mandibular molar maturation / A confiabilidade da estimativa de idade pela maturação óssea das vértebras cervicais e mineralização de molares inferiores

Age estimation is required for forensic cases such as minors without documentation and age disputed by asylum seekers. Cervical vertebral maturation (CVM) has potential to estimate age as a new method of analysis of shape change during adolescence and adulthood. The aim of this study was to assess the accuracy of estimating age using Lamparski's method of cervical vertebra maturation, the mandibular second (M2) and third molars (M3) in a group of males. The test sample consisted of lateral cephalograms of 60 boys from the Bolton-Brush online collection and 53 from Burlington online collection aged 10 to 15 years. CVM age was calculated from age category and mean age and transition age of CVM stages, calculated from raw data of 69 boys (aged 9 to 15 years) studied by Lamparski (1972). Dental age was calculated using mandibular second and third molar stages from Liversidge (2009). The mean difference and absolute mean difference between CVM age and dental ages and chronological ages was calculated. CVM and molar tooth stage assessment reliability was assessed by duplicate readings by the first author. Results show that Lamparski's method of CVM mean age was most accurate and had considerably smaller standard deviation and smallest absolute mean difference than other method of M2 or M3 (mean difference -0.49, SD 0.23, absolute mean difference 0.49 years). CVM has potential as a possible method of estimating age for this age group, particularly when M2 is mature or M3 is missing.

A estimativa da idade é necessária em casos forenses como os de menores sem documentação e disputa por comprovação de idade em caso de refugiados. A maturação óssea das vértebras cervicais (MOVC) tem potencial para estimar a idade pela análise de mudança de sua forma anatômica, durante a adolescência e vida adulta. O objetivo deste estudo foi avaliar a exatidão da estimativa de idade pela MOVC proposta por Lamparski (1972), além da análise da mineralização do segundo (M2) e terceiro (M3) molares mandibulares. O material de estudo consistiu em teleradiografias de meninos com idade entre 10 a 15 anos (60 da coleção Bolton-Brush e 53 da coleção Burlington). A idade pela MOVC foi calculada a partir da categoria, média e transição de idade de cada estágio da MOVC, tendo como base os valores encontrados dos 69 meninos (de 9 a 15 anos) estudados por Lamparski. A idade dental foi calculada utilizando os estágios de mineralização dos segundo e terceiro molares mandibulares de acordo com Liversidge (2009). A média da diferença e a diferença média absoluta entre a idade pela MOVC, a idade dentária e a idade cronológica foram calculadas. A confiabilidade das leituras das idades pela MOVC e a idade dentária foi avaliada pela repetição das mesmas pelo autor principal. Os resultados mostraram que a média da idade pelo método da MOVC segundo Lamparski foi mais preciso e teve consideravelmente menor desvio padrão e menor diferença média absoluta do que os outros métodos através de M2 ou M3 (diferença média -0,49, SD 0,23, diferença média absoluta 0,49 anos). MOVC tem potencial como um possível método de estimativa de idade para essa faixa etária, especialmente quando M2 já está mineralizado ou M3 é ausente.

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.

A Reappraisal of Developing Permanent Tooth Length as an Estimate of Age in Human Immature Skeletal Remains.

This study expands on existing juvenile age prediction models from tooth length by increasing sample size and using classical calibration. A sample of 178 individuals from two European known sex and age skeletal samples was used to calculate prediction formulae for each tooth for each sex separately and combined. Prediction errors, residuals, and percentage of individuals whose real age fell within the 95% prediction interval were calculated. An ANCOVA was used to test sex and sample differences. Tooth length for age does not differ between the samples except for the canine and second premolar, and no statistically significant sex differences were detected. The least prediction error was found in the incisors and the first molar, and the highest prediction error was found in the third molar. Age prediction formulae provided here can be easily used in a variety of contexts where tooth length is measured from any isolated tooth.

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.

A radiographic study of estimating age by deciduous mandibular canine and molar root resorption.

BACKGROUND AND AIM: Root resorption of deciduous teeth is an important aspect of dental development; however, the accuracy of using root resorption as a method of estimating age has not been reported. The aim of this study was to assess the accuracy of estimating age from fractions of resorbed root in mandibular deciduous canines and molars, using published reference data. METHODS: The sample was 940 dental panoramic radiographs of dental patients aged 3-16. Deciduous mandibular canine and molar roots were staged into levels of resorption (one quarter, one half and three quarters). Reliability of root fractions was assessed using 193 duplicate readings and calculated using Kappa. Age was estimated using Moorrees et al. (1963), Fanning (1961), and O'Meara and Knott (1967), and the difference between dental and chronological ages tested using t-test. Accuracy was defined as a difference not significant to zero (P<0.05). RESULTS: Results show that assessment of levels of root resorption was excellent (Kappa 0.88-0.94). Some root fractions of molars estimated age accurately; however, the standard deviation was more than 2 years. The average difference between dental and chronological ages ranged from 0.12 to -2.04 years with standard deviation values up to 2 years and the most accurate method was O'Meara and Knott (1967). CONCLUSION: Fractions of deciduous root resorption can help to predict age.