For dental age estimation of these young adults, three regression formulas were developed for both Thai men and Thai women. In order to obtain the best age determination, all possible age estimation methods suitable for the particular case should be conducted. If possible, all the regression formulas found in this study should be calculated and the mean reported as estimated dental age. The database and corresponding regression formulas provide forensic odontologists at any global location with a scientific tool for estimating the age of majority of a person of Thai origin. The same findings can be important in further investigations where equal data collection of populations with individuals of common nationality provides comparable material and findings. A total of 1,199 orthopantomograms were collected from Thai women and men equally divided in age categories between the ages of 15 and 24. On the radiographs, the developmental stage of the third molars was scored using a modified scoring technique. Inter- and intra-observer reliabilities were tested using kappa statistics. Correlation between the scores of all four wisdom teeth and left-right symmetry were evaluated with Pearson’s correlation coefficient. Student’s t-test on asymmetry was performed, and regression formulas were calculated. Future research on similar database of different nationalities worldwide may reveal ethnic differences in dental development in relation to age. 10 tables, 2 figures, and 47 references