Eruption State of Mandibular Third Molar and Morphology of Mandible
Recent studies have indicated that even in cases in which the existence of tooth germs are observed, third molars cannot perfectly erupt because there is too little space for eruption in the distal end of the 2nd molar, and that cases of impaction or semi-impaction are increasing. The purpose of this study was to compared the morphological variation of the mandible as the mandibular corpus and the mandibular ramus among three groups: a group of full impaction of the third molar in the mandibular dental arch (A group), a group of semi-impaction (B group), and a group of full eruption (C group). The following results were obtained. 1) Concerning the measurements representing distance: R (the width of the mandibular ramus), was significantly longer in group A while it was shorter in group C. M (total length of the mandible), C (length of the mandibular corpus) and the distance between Cd and Gn were all significantly longer in group C than in group A. 2) Concerning the measurements representing angles, the Go angle was significantly larger in group C than in group A. 3) All the measurements in group B approached the median value of those of group A and group C. It was suggested that there was no impaction of the mandibular third molar observed due to the reduction of the mandible, and that the eruption of the mandibular third molars appears to be affected by the growth and change in the mandibular corpus and the mandibular ramus and/or the change in the Go angle.
松本歯学 22 (3), 297-303, 1996-12-31