Prediction of lower third molar impaction from the frontal cephalometric projection

Abstract

The purpose of the present investigation was to analyse the eruption path of the lower third molar (M3), as seen in the frontal cephalometric projection, in an effort to contribute to an improved prediction of impaction. A total of 31 subjects (23 boys and 8 girls) representing 41 erupting (Group I) and 18 impacting (Group II) lower third molars were included in the study, the cases were drawn from a larger sample, who had been followed with annual observations and measurements from childhood until adult age. On the frontal head films the inclination of third molars was measured annually from the time of complete crown calcification until the inclination of M3 was stable. Based on the longitudinal data on M3 inclination, individual and mean curves were produced for both groups. The relationship between eruption/impaction of M3 and skeletal and dental development was analysed. The eruption pattern for Group I and Group II was markedly different. The difference seemed to be more pronounced, than in previous studies based on the lateral cephalometric projection. The dental development stage produced the earliest and most significant separation of the mean curves for the two groups. In extreme cases, reliable prediction would seem possible, based on the inclination observed in a single frontal head film at the time of appearance of the bifurcation.