A Clinical Study On Dentition Distalization With Mini-screw And Segmental Arch

Objective :To explore the clinical effects of mini-screw and segmental arch in the dentition distalization in order to correct mild or moderate crowding;and to compare the effect of dentition distalization using mini-screw and second premolar extraction treatment.And to evaluate the amount of molar distalization and the character of tooth movement.Methods:This is a retrospective study,20 patients with mild or moderate crowding were divided into two groups,10 of which were treated with dentition distalization using mini-screws and segmental arch(group 1),The third molars were extracted before the treatment.The other 10 patients were treated with second premolar extraction(group 2).Before and after treatment,the lateral cephalograms were measured and compared statistically to assess the alteration.Compare the two groups before and after treatment the changes of skeletal and soft tissue and teeth.Paired t-test and the independent sample t-test were performed to determine the treatment effects within the group and between the groups respectively.The average treatment time was counted.Results:In the two groups,all the crowding in the upper and lower dentition was resolved,and incisor retraction was also obtained.In the group 1,the indicators SNA°?SNB°?ANB°?NP/FH°?SGn/FH°?FMA°were not significantly changed for the pre and post treatment and the difference was not statistically significant(P> 0.05).The indicators:U1/SN°?L1/MP°?U1/NA°?U1/NAmm?U1/L1°?L1/NB°?U1/L1 were significantly changed before and after treatment within the group,and the difference was statistically significant(P<0.05).2.3 mm and 2.0 mm of upper and lower incisor retraction were achieved.The distance of upper and lower molar distalization were 3.2mm and 3.1mm respectively.The indicators:UL-EPmm?LL-EPmm?NLA°were significant changed after the treatment;the difference was statistically significant(P< 0.05).The molars move approximate bodily movement with slightly tipping movement during the treatment.In the group 2,the indicators SNA°?SNB°?ANB°?NP/FH°?SGn/FH°?FMA°were not significantly changed for the pre and post treatment and the difference was not statistically significant(P> 0.05).The indicators:U1/SN°?L1/MP°?U1/NA°?U1/NAmm?U1/L1°?L1/NB°?U1/L1 were significantly changed before and after treatment within the group,and the difference was statistically significant(P<0.05).2.6 mm and 2.2 mm of upper and lower incisor retraction were achieved.The upper and lower molars moved forward 3.1mm and 3.0mm respectively.The indicators:UL-EPmm ? LL-EPmm ?NLA°were significant changed after the treatment;the difference was statistically significant(P< 0.05).The changes after treatment between the two groups:the indicators SNA°?SNB°?ANB°?NP/FH°?SGn/FH°?FMA°,the indicators U1/SN°?L1/MP°?U1/NA°?U1/NAmm?U1/L1°?L1/NB°?U1/L1,the indicators UL-EPmm?LL-EPmm?NLA° the difference was not statistically significant(P> 0.05).U6-PFPmm ? L6-PFPmm,the difference was statistically significant(P< 0.05).In the group 1,the average treatment time was 15.8±2.25 months;and in the group 2,the average treatment time was 19.6±3.40 months,the difference between the two groups was statistically significant(P <0.05).Conclusion:The use of mini-screw as anchorage and segmental arch for dentition distalization is one of good methods to correct mild or moderate crowding.There is no significant difference in the treatment result between the dentition distalization with mini-screw and second premolar extraction treatment.The treatment time can be largely shorted by dentition distalization with mini-screw and segmental arch.