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

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.

Three dimensional finite element analysis of the phenomenon during distal en masse movement of the maxillary dentition / 대한치과교정학회지

This study was designed to analysis the displacement and stress distribution of individual tooth by orthodontic force during distal en masse movement of the maxillary dentition. In this study, three dimensional finite element analysis was used. Author made the finite element model of maxillary teeth, periodontal ligament, alveolar bone and bracket with anatomic and physiologic characteristics on computer. Author analysed and evaluated the displacement and stress distribution of individual tooth when extraoral force, Class II intermaxillary elastics, ideal arch wire, MEAW and tip back bend were used for distal en masse movement of the maxillary dentition. These analyses were also applied in the case of the maxillary second molar were not extracted. Author compared the results of the cases which maxillary second molar were extracted or not. The results were expressed quantitatively and visually. Author obtained following results, 1. When anterior headgear was applied, the posterior translation, posterior tipping, and vertical displacement of teeth were produced more in the anterior segment of the dentition. 2. When Class II intermaxillary elastics were applied in the ideal arch wire, the teeth disp acement were usually produced in the anterior segment. But when tip back bend were added in the ideal arch, the orthodontic force produced by elastics were transmitted to the posterior segment. As increasing the tip back bend, posterior translation and lingual tipping of anterior teeth were decreased, posterior translation and tipping displacement of posterior teeth were increased, and extrusion of anterior teeth by Class II elastics were decreased. 3. When MEAW and Class II elastics were applied, the teeth movement were similar with the case of ideal arch wire and Class II elastics, but more small and uniform teeth displacement were produced. Compared with the ideal arch wire, posterior tipping of the posterior segment were more produced than lingual tipping displacement of the anterior segment. 4. When the maxillary second molar without orthodontic appliance existed, the displacement of maxillary first molar were decreased.