[Stability of molar relationship after orthodontic treatment in Class II division 1 malocclusions treated by extraction].

OBJECTIVE: To investigate the changes of occlusal relationship in posterior teeth among the pre-treatment, post-treatment, and to analyze some possible factors which may relate to the relapse of posterior occlusal relationship. METHODS: 29 finishing Class II division 1 cases treated by extraction with full records selected were included. The sample consists of 12 males, 17 females. The follow-up lateral head films and study casts were taken at least 2 years after orthodontic treatment. The cephalograms were measured by computerized program and the study casts measured by caliper. RESULTS: Improvements of molar relationship were shown during treatment and a little bit changes during follow-up. During the treatment, the amount of mesial movement of the lower molars was more than the upper molars in dental Class II malocclusion and the amount was similar between upper and lower molars in skeletal Class II malocclusion although the ANB angle decreased significantly. During the follow-up stage, the movement tendency between upper and lower molars was reversed. The sagittal growth pattern of mandible and irregularity of upper incisors were nearly correlated with the relapse of molar relationship. CONCLUSION: The stability of molar relationship is acceptable during the follow-up stage in Class II malocclusion. The improvement of molar relationship depends on the difference of mesial movements between upper and lower molars in dental Class II malocclusion. However, in skeletal Class II malocclusion the improvement of jaw relationship does the effect. The positive growth of mandible and crowding of upper incisors may affect the relapse of molar relationship.