Accuracy of Nolla Method for Age Estimation of Northern Chinese Han Children / 法医学杂志

Objective To study the accuracy of Nolla method for age estimation of Northern Chinese Han children aged between 5.00 and 14.99 years based on original transformation tables and multiple regression model. Methods A total of 2 000 orthopantomographs （OPGs） were collected from the Hospital of Stomatology, Xi'an Jiaotong University, including 1 000 males and 1 000 females. Development stage of 7 left mandibular permanent teeth （except third molars） was assessed based on Nolla method, then age estimation was conducted through transformation tables and multiple regression model, respectively. Firstly, the development stage results of 7 permanent teeth were added up and the estimated age was obtained through the original transformation tables. Secondly, 80% of the samples （80 males and 80 females in each age group） were randomly selected from 2 000 OPGs as the train set. The chronological age of the selected patients was taken as the dependent variable, while gender and the development stage results of 7 permanent teeth were taken as the independent variable to establish multiple regression model. The remaining 20% of the samples were substituted into the model as the test set, to verify the accuracy of age estimation by multiple regression model. Results Mean chronological ages of males and females were 10.03±0.09 years and 10.01±0.09 years, respectively. The age estimated by original transformation tables showed an overestimation for males （0.18 years on average） and an underestimation for females （0.02 years on average）, with mean absolute error （MAE） of 0.94 years and 0.97 years, respectively. While the results by multiple regression model showed that males were overestimated by 0.06 years on average and females were underestimated by 0.02 years on average. The MAE was 0.66 years and 0.77 years, respectively. Conclusion The Nolla method is suitable for age estimation of Northern Chinese Han children. Compared with the original transformation tables method, the multiple regression model is more accurate for age estimation.

Research Progress and Prospect of Facial Reconstruction in Forensic Science / 法医学杂志

Facial reconstruction is a way to recover facial morphology by restoring soft tissues based on unidentified skulls using the knowledge of anatomy, anthropology, aesthetics, and computer science. It is applied in forensic science, oral plastic surgery and archeology, and especially plays an important role in the identification of the origin of the unknown corpses in forensic science. Facial reconstruction is the supplementary means of identification when other approaches （such as DNA comparison, imaging matching, dental records comparison, etc.） cannot identify individual identity. Facial soft tissue thickness （FSTT） is the basis of facial reconstruction and with the development of imaging and computer science, the techniques for measuring FSTT are improving rapidly and many related researches have appeared. This paper summarizes the application of facial reconstruction in forensic science, the accuracy of different methods and the research progress of this field to provide reference to this field.

Research Progress of Age Estimation Based on the Demirjian's Method / 法医学杂志

In recent years, individual age estimation has gained increasing attention in forensic practice. Common age estimation methods mainly use developments of teeth and bones. Compared with bones, teeth are stronger and are highly resistant to external factors, therefore plays an important role in age estimation. Demirjian's method is one of the most commonly used methods to evaluate dental age and has been widely used in many countries. In this paper, the accuracy of its application in different populations is reviewed. It is found that compared with the chronological ages, most of the estimated ages are overestimated. By combining research results of many scholars and by analyzing, it can be assumed that this situation may be related with race, region, sex, etc.

Construction of Age Estimation Model of 18-Year-Olds in the Northern Chinese Population Based on the Development of Mandibular Second and Third Molars / 法医学杂志

Objective To establish a linear relationship between age and the development process of the mandibular second, third molars in a northern Chinese population and test its accuracy in inferring whether the subject is over 18 years old. Methods The orthopantograms （OPGs） of 960 northern Chinese people aged between 10.00 to 25.99 years were selected. The gender, birth date, and date of the orthopantograms of each sample were recorded. The development stages of left mandibular second and third molars were divided with Demirjian method. The experimental group （760 individuals） constructed a Logistic regression equation to infer whether the subject is over 18 years old. The validation group （200 individuals） tested the accuracy of the equation. Results When only using third molar, the formula obtained for inferring whether the subject's age is over 18 years is： logit P1=-18.276+0.494 x1+2.953 x3. When combining the second and the third molars, the formula is： logit P2=-21.045+3.177 x1+0.619 x2+2.088 x3. （x1 stands for gender, male is marked as 1 and female is marked as 2; x2 and x3 stand for the development stage of second molar and third molar, respectively）. The accuracy rates of this equation in estimating whether ages of subjects from the validation group were over 18 years old for males and females were 88.0%-92.0% and 85.0%-88.0%, respectively. Conclusion The age estimation formulas based on the development of mandibular second and third molars have important value in judging whether the individual is over 18 years old. Meanwhile, the accuracy of age estimation can be improved by combining the development of second and third molars together.