Predictive factors of third molar eruption

Introduction. We studied the prognosis of upper and lower third molar evolution. Patients and methods. Seventy-eight patients were included after a clinical examination, dental casts, panoramic and lateral cephalometric radiographs on inclusion (T1) and two years after (T2). Five parameters were studied: retromolar space (RMS) between the third molar (M3) and the anterior ridge of the minus; RMS/M3 crown diameter ratio, distances (PTV-M-1) and (X-1-Mi(2)); and third molar angle with occlusal plane. Results. They were noted at T1 and T2. The gain of retromolar space from T1 to T2 reached 1.2 to 2.2 mm without extraction, 2 to 2.7 mm with PM extraction, and 4.5 to 6.8 mm with M1 extraction. The "RMS/M3 diameter" ratio increased in the maxilla from 0.6 to 0.8 and from 0.5 to 0.8 in the mandible (P = 0.01) between T1 and T2. PTV-M1 increased significantly from 17.1 to 19.9 mm (P < 0.001), and Xi-M2i increased significantly from 18.5 to 22.4 mm (P < 0.001) between T1. and T2. Discussion. The extraction of premolars has little influence on the variation of the retromolar space; conversely first molar extraction increases that space. Prognosis techniques for the evolution of third molars are helpful when considering avulsion. (C) 2011 Elsevier Masson SAS. All rights reserved.