Abstract The third molar tooth is one of the few anatomical sites available for age estimation of unknown age individuals in the late adolescent years. Computed tomography (CT) images were assessed in an Australian population aged from 15 to 25 years for development trends, particularly concerning age estimation at the child/adult transition point of 18 years. The CT images were also compared to conventional radiographs to assess the developmental scoring agreement between the two and it was found that agreement of Demirjian scores between the two imaging modalities was excellent. The relatively wide age ranges (mean A? 2SD) indicate that the third molar is not a precise tool for age estimation (age ranges of 3a??8 years) but is, however, a useful tool for discriminating the adult/child transition age of 18 years. In the current study 100 of females and 96 of males with completed roots were over 18 years of age.