A Comparative Study Of Skeletal Class Ⅲ Malocclusion Effect Of Maxillary Protraction Treatment In Mixed Dentition Between Two Nationalities

Objective: To compare the craniomaxillofacial morphology of Uygur and Han patients with skeletal Class III malocclusion in mixed dentition period before and after treatment by maxillary protraction,so as to provide some reference for the treatment of this kind of patients.Methods: The subjects were 30 patients with skeletal Class III malocclusion in the mixed dentition period,including 15 Uygur patients and 15 Han patients,who were treated by rapid palatal expansion combined with maxillary expansion in the Department of Orthodontics of the Fifth Affiliated Hospital of Xinjiang Medical University from January 2015 to December 2020.The lateral cephalograms of the subjects before and after treatment were measured and analyzed,and the relevant measures of Steiner,Tweed and Holdaway were selected.Results: There were statistically significant differences in SNA,ANB,U1-NA(°),U1-NA(mm),U1-L1(°),SE and SL in skeletal tissue indexes of Uygur patients after treatment(P < 0.05).There were significant differences in the soft tissue indexes between A-Sn,H line-N’PM’,Si-H line,Sn-H line and PM-PM’(P<0.01).There were significant differences in SNA,SNB,ANB,SND,U1-NA(°),U1-NA(mm),U1-L1(°)in skeletal tissue indexes of Han patients after treatment(P<0.05).In soft tissue indexes,the differences of FH-N’PM’,A-N’Pog’ and SiH line were statistically significant(P<0.05),and the differences of H-N’PM’ and Li-H line were statistically significant(P < 0.01).Before treatment,there were statistically significant differences in skeletal tissue indexes including L1-NB(°),U1-L1(°),IMPA and FMIA between Uygur and Han patients(P<0.05).Soft tissue indexes including Sn-H line,U1-Ls and Si-H line had statistical significance(P < 0.05).The results of comparison between Uygur and Han nationality after treatment showed that there were statistically significant differences in the skeletal tissue indexes U1-NA(mm),FMIA and IMPA(P<0.05).There were statistically significant differences in Ss-Ls and A-Sn in soft tissue index(P<0.01).Conclusion: After treatment,the maxillary forward growth,the A point moved forward significantly,the mandibular moved backward significantly,the labial inclination and protrusion of the maxillary anterior teeth increased,and the soft tissue profile was improved effectively.The comparison between the Uygur and Han patients before treatment and the comparison between the Uygur and Han patients after treatment showed no statistically significant difference in skeletal indexes,while the differences in dental indexes and soft tissue indexes were statistically significant.