Effect of the lower third molar on the treatment of Class III malocclusion

Son, Myung Ho; Chang, Young Il

Abstract

The purpose of this study was to evaluate the effect of the lower third molar on treatment time and distal en masse movement of the lower dentition in Class III malocclusions. Thirty subjects (9 males and 27 females) were selected, all of whom were diagnosed as Class III malocclusion and treated by fixed appliances without premolar and/or molar extraction. They were divided into three groups. Group 1 consisted of 12 subjects, whose lower third molars were not extracted during the whole orthodontic treatment. Group 2 consisted of 8 subjects, whose lower third molars were extracted after MEAW application and before removal of the orthodontic appliances. Group 3 consisted of 16 subjects, whose lower third molars were extracted before MEAW application. For each subject, overall treatment time and duration of MEAW application were determined. In addition, pre-treatment and post- treatment lateral cephalometric radiographs were analyzed. All data were processed statistically with ANOVA, and the conclusions were as follows: There was no significant difference among the groups in overall treatment time. However, duration of MEAW application was longer in Group 2 than in Group 1 or Group 3. The overjet that was established after orthodontic treatment was largest in Group 3, in which the lower third molars were extracted before MEAW application. After orthodontic treatment, IMPA decreased in Group 3, but increased in Group 1 and Group 2. There was no significant difference among the three groups in the translation of lower second molars. However, the tipping movement of lower second molars was significantly different, highest in Group 2 and lowest in Group 1. Therefore, it is thought to be better for the orthodontic treatment of Class III malocclusions to extract the lower third molars before MEAW application. In Group 2, the mandibular plane angle was decreased as a result of forward rotation of the mandible. This skeletal change was thought to bring about the difficulty of treatment.