[The condition of dentition and the prediction of eruption at lower third molars of Japanese adolescent males].

This study was examined the relationships between the condition of dentition of lower third molar and malocclusions and shape of mandibles, and to predict eruption for third molars by their relationships. Data were obtained from 90 degrees and 60 degrees rotated cephalometlic radiographs, orthopantomographic radiographs, mandibular occlusal films and gnathostatic models of 101 males showing a complete permanent dentition anterior to the second molars and who had not had extraction lower their molars and orthodontic treatments, were selected from 147 dental students at Asahi University. they were divided into 8 groups by condition of lower third molar dentitions. Bilateral presence of lower third molar occurred in 69.3% and unilateral in 20.8% on 60 degrees rotated cephalometlic radiographs. Bilateral eruption or half eruption occurred in 24.7% and impaction in 44.6% on gnathostatic models. Coronal arch length of erupted cases was longer than that of impacted cases. A apired t-test revealed the significant difference (p less than 0.05). Over bite of impacted cases were deeper than that of erupted cases (p less than 0.05). Arch length discrepancy of presented and impacted cases were larger. There were normal occlusions in each group. Most mal-occlusions were prognathia, second to deep bite, bi-maxillary. The most frequent lower arch conditions were crowding (65%). I. M. P. A. of bilateral impacted cases were langer. Mandiblar length (Cd-Pog) of erupted cases were longer. The distance from Xi-point to the distal surface of second molar was border at 25mm for lower third molar eruption.