Abstract: [Abstract] Objective： The purpose of this study was to investigate the correlation between shape of chin and probability of orthognathic surgery for class Ⅲ adult patients .To develop a discriminant method to predict probability of Clinical diagnosis and treatment. Methods： A total of 61 class Ⅲ adult patients were collected from the orthodontic department .thirty-one patients were treated by orthodontic appliance only, and others were treated with orthodontic and orthognathic surgery. Significant difference in age and sex distribution were not found between the two groups. Conventional Cephalometric analysis was made to compare hard and soft tissue structures before treatment between the two groups. The mean and standard deviation of each measurement were calculated for all the variables with SPSS. The correlation analysis, t-test and Discriminant Analysis were applied. Results： 1.Statistical analysis showed that the probability of orthognathic surgery is significantly correlated with B-Pg、Y、Co-Go、ODI、NSAr。2. The results showed that the B-Pg is closely correlated with MP/SN、MP/FH、MP/PP、L1/MP、ODI、ArGoGn in the orthognathic surgery group. Conclusion： The Shape of chin plays an important role in determining treatment plan about orthognathic surgery or orthodontic only for class Ⅲ adult patients. The probability of orthognathic surgery increases with the increasing in the degree of chin protrusion.

Key words: chin, adult patients, class Ⅲ malocclusion, surgery, relationship