Objective To investigate the changes of occlusal relationship in posterior teeth among the pre-treatment, post- treatment, and to analyze some possible factorswhichmay relate tothe relapse of posterior occlusal relationship.Methods 29 fin- ishing ClassⅡdivision 1 cases treated by extractionwith full records selected were included. The sample consists of 12 males,17 females. The follow-up lateral head films and study castswere 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 uppermolars in dental ClassⅡmalocclusion and the amountwas similar between upper and lower molars in skeletal ClassⅡmalocclusion although the ANB angle decreased significantly. During the follow-up stage, the move- ment tendency between upper and lowermolarswas reverse. The sagittal growth pattern of mandible and Irregularity of upper inci- sors were nearly correlatedwiththe relapse ofmolar relationship.Conclusion The stability ofmolar relationship is acceptable dur- ing the follow-up stage in ClassⅡmalocclusion. The improvement of molar relationship depends on the difference of mesial move- ments between upper and lower molars in dental ClassⅡmalocclusion. However, in skeletal ClassⅡmalocclusion the improve- ment of jaw relationship does the effect. The positive growth of mandible and crowding of upper incisors may affect the relapse of molar relationship.
