Study On The Stability Of Maxillary Molars Distalization With Different Anchorage Methods In The Treatment Of Adult Class Ⅱ Malocclusion

Objective: Through cephalometric analysis and model measurement analysis,the treatment results of maxillary molars distally moved by different anchorage meth ods with clear aligners were compared,and the three-dimensional stability of ma xillary first molars,maxillary central incisors and soft tissue profile stability were evaluated,in order to provide reference basis for anchorage mode selection and stability evaluation of distal maxillary molars in the treatment of adult class Ⅱ malocclusion.Materials and methods: In this retrospective study,32 class Ⅱ patients who were treated in the Department of Orthodontics of Hefei Stomatology Hospital from April 2016 to November 2022 were selected,including 16 patients with auxiliary intermaxillary anchorage and 16 patients with auxiliary implant anchorage.The lateral cephalograms and models of patients before treatment(T0),after treatment(T1)and 1 year after treatment(T2)were collected,and the bone parameters(S NA,SNB,ANB,MP-SN,MP-FH),soft tissue parameters(UL-EP,LL-EP,N’-SnPog’)were measured,and dental indexes(U1-SN,U1-Apo,Ptm-U6,U6-PP(°),U6-PP(mm),L1-MP,OB,OJ),and the intermolar width of maxilla(U6L-U6R)w as measured on the model.SPSS26.0 software was used for statistical analysis.Paired t-test was used to compare the measured data in the two groups,and inde pendent sample t-test was used to compare the data between the two groups.Results: 1.In intermaxillary anchorage group,Ptm-U6,U6-PP(°),OB and OJ d ecreased at T0-T1 stage,in which U6 shifted distally and distally tilted 2.53°±2.33°,L1-MP increased,L1 average lip inclination 1.22°±2.04°,U6L-U6 R increased,suggesting that the intermolar width of the first molar tended to widen,but there was no significant difference in other indexes.There was no statistical significance in all the indexes in T1-T2 stage.2.In the implant anchorage group,the average values of U1-Apo,Ptm-U6,U6-PP(°),OB,OJ and UL-EP in the T0-T1 phase were significantly lower than those in the implant anchorage group.The average adduction of U1 was 1.63 ±1.38 mm,U6,the distal inclination was 2.75°±2.02°,and the average adduction of the upper lip was 0.66 ±1.07 mm.The U6L-U6 R increased and the width between the first molars widened.There was no significant difference in the parameters of T1-T2 stage.3.The comparison between the two groups showed that the retraction movement of U1 and the distal displacement of U6 from T0 to T1 in implant anchorage group were larger than those in the intermaxillary anchorage group,and the labial inclination of lower incisor in the intermaxillary anchorage group was larger than that in the implant anchorage group.There was no significant difference in the parameters of T1 and T2 between the two groups(P>0.05).Conclusion: The distal movement of maxillary molars with different anchorage a ssisted by clear aligners can achieve 2-3mm distal displacement,and the stability is good after one year of treatment.1.In the intermaxillary anchorage group,the three-dimensional direction of the maxillary first molar was stable,and the maxi llary central incisor and the profile of soft tissue was stable.2.In the implant an chorage group,the three-dimensional direction of the maxillary first molar was st able,and the maxillary central incisor and the profile of soft tissue was stable.There was no significant difference in stability between the two groups.