Abstract: Objective To explore the value of estimating chronologic age based on the grades of mandibular third molar development. To evaluate whether mandibular third molar could be used as an indicator for estimating the age under or over 18 years. Methods The mineralization status of mandibular third molar of 1 845 individuals aged 10-30 was graded and marked based on Demirjian’s classification of grades reformed by Orhan. Gender difference was examined by t-test. A cubic regression model was established to analyze the correlation between third molar and chronologic age. Each grade of age cumulative distribution diagram and ROC curve was respectively performed to evaluate the relationship between third molar and the age of 18. Using Bayes discriminant analysis, an equation was established for estimating the age of 18. Results The inner-rater reliability was 0.903. Statistical analysis showed a moderate correlation between age and grade. Significant differences of both genders were found only in grade D and H （P＜0.05）. Males at the grades from 1 to D and females at the grades from 1 to C were under 18 years old, and both males and females at grade H were over 18 years old. The area under the ROC curve was 0.797 （P＜0.05）. Conclusion Third molar development shows a high correlation with age, and combined with other indicators, it can be used to estimate the age of 18.

Key words: forensic dentistry, radiography, panoramic, age determination by teeth, molar, third, mandible, han nationality, Sichuan