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The majority of age estimation models based on third molar development are constructed on samples from populations with described and outlined origin. Due to unlike research protocols these studies can rarely be compared for the evaluation of possible geographical or ethnical influences on third molar development. The aim of this study is to evaluate country specific third molar development on standardized collected and analyzed data. On panoramic radiographs selected from subjects out of 9 country specific populations (Belgium, China, Japan, Korea, Poland, Thailand, Turkey, Saudi-Arabia and South-India) the four third molar scores were registered, according to a modified Gleiser and Hunt methodology. To obtain for each subject a (factor) score which represents the degree of third molar development, a generalized linear mixed model for multivariate ordinal data was fitted on the repeated third molar scores. Differences between countries are analyzed using gender-specific regression models for these factor scores with age and country as predictors. Comparisons between countries revealed differences in speed and onset of development. However, although reaching statistical significance, differences in actual value were small and not constant over the considered age range. In all countries, at all ages, males were ahead in third molar development compared to females., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

Unquestionable forensic age investigations are based on statistical models constructed on a sample containing subjects of identical origin as the examined individual. In cases where corresponding models are unavailable, the established report has to describe the possible effects of this unrelated information on the predicted age outcome. The aim of this study is to collect country specific databases of third molar development and to verify how the related dental age estimations are influenced if we were to use dental developmental information only from Belgium or from all collected countries together. Data containing third molar developmental stages scored following Gleiser and Hunt (modified by Köhler) were collected from 9 country specific populations (Belgium, China, Japan, Korea, Poland, Thailand, Turkey, Saudi-Arabia and South-India). Age predictions were obtained from a training dataset and validated on a test dataset. Bayes rule using the repeated third molar scores is applied to get age predictions and prediction intervals. Three age predictions were compared for males and females separately. For the first prediction, the training dataset contains only Belgian subjects. For the second prediction, the training dataset for each country consists only of subjects of the country itself. For the final prediction, subjects from all countries are pooled into one common training dataset. Besides the (absolute) difference between the chronological age and the predicted age, specific interest lies in the juvenile-adult distinction. In the age range from 16 to 22 years 6982 subjects (3189 male and 3793 female) were analyzed. Using information on third molar development from Belgium compared to information from the country specific databases hardly increased the mean absolute differences (MAD) and mean squared errors (MSE): the MAD and MSE increased on average with 0.5 and 2.5 months with maximal increases of, respectively 1.6 and 7.3 months. Using information from all countries pooled compared to country specific information provided even on average negligible increases (0.05 and 0.2 months for MAD and MSE, respectively). For the juvenile-adult discrimination, using information from all countries instead of country specific information yielded comparable performances. Using Belgium instead of country specific information increased the percentage of correctly identified juveniles, but decreased the percentage of correctly identified adults. The adult-juvenile discrimination based on information used from Belgium provides judicially the best applied reference., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)