Clinical Comparative Study On Anchorage Consumption Of Maxillary Molars Between PASS And MBT With Continuous Tip-back Bends

Objective: To compare the physiological Anchorage orthodontic technique(Physiologic Anchorage Spee’s-wire System referred to as PASS)and the MBT straight wire orthodontic technique with 30 degree continuous backward bending on each main arch wire in class Ⅱ division 1 malocculsion tooth extraction cases,whether there is any difference in the Anchorage consumption of maxillary molars at the alignment and completion stages,respectively.The purpose of this study is to provide a certain reference basis for orthodontists to select appropriate orthodontic methods for the treatment of Angle II class I cases.Methods: From August 2017 to January 2020,40 adult cases(22 males and 18 females,mean age 25.6 ±1.6years)with class Ⅱ division 1 malocculsion were randomly selected from the Orthodontic Department of the first affiliated Hospital of Wan Nan Medical College.They were randomly divided into two groups with 20 cases in each group.Group A: 13 males and 7 females,with an average age of 25.8 ±1.2years,were treated with physiological Anchorage technique((PASS)).Group B: 9 males and 11 females,with an average age of 25.2 ±1.8years,were treated with MBT appliance combined with 30 °continuous backward bending of each main arch wire.The basal bone width of maxillary first molar segment was measured before treatment,after dentition alignment and at the end of treatment in each group.The maxillary models of 120 cases were measured by the same orthodontist for 3 times,and the average values of 3 times were taken.The change of the width of the basal bone of the maxillary first molar indirectly reflected the change of the anterior and posterior movement of the maxillary first molar,and then compared the Anchorage consumption of the maxillary molar by the two orthodontic methods in the stage of dentition extrusion and the stage of completion of treatment.Results: In the alignment stage of PASS group,the width of basal bone increased by 0.85 mm compared with that before treatment,and the paired t test after alignment was significantly lower than that before treatment(P < 0.01).In the completion stage,the width of basal bone decreased by 0.98 mm compared with that before treatment,and the paired t test after treatment was significantly lower than that before treatment(P < 0.05).The difference was statistically significant.The alignment stage of MBT + 30 ° arch wire group: after alignment,the width of the base bone decreased by 0.10 mm on average compared with that before treatment,and the paired t‐test after alignment and before treatment showed no significant difference(P > 0.05).Completion stage: after treatment and before treatment,the width of the base bone decreased by 2.08 mm on average.After treatment and before treatment,the paired t‐test,P < 0.01.The difference was statistically significant.Comparison of the changes of the width of the first maxillary molars in the two groups with different treatment methods: alignment stage: the width of the first maxillary molars between the two groups was tested by two independent samples t test,P < 0.01,the difference was statistically significant;completion stage: the width of the first maxillary molars between the two groups was tested by two independent samples t test,P < 0.01,the difference was statistically significant.Conclusion: 1.In PASS group,the maxillary molars in the alignment stage had a retroversion effect.There was no loss of anchorage in these 20 patients,which maintained the position of the molar well and had a significant effect on the anchorage of the molar.At the completion stage: the loss of anchorage occurred after the treatment compared with that before the treatment 2.MBT with continuous tip‐back bend treatment group: in the process of alignment,the maxillary molars had the effect of molar retroversion,.There was no loss of anchorage in these 20 patients,which maintained the position of the molar well and had a significant effect on the anchorage of the molar.At the completion stage,the loss of anchorage occurred after correction.3.Comparison between groups: in the exclusion stage,pass appliance has better anchorage preparation than MBT appliance with retroversion;in the whole process,pass appliance has better anchorage preparation than MBT appliance with retroversion.MBT + 30 ° retroversion method consumes more anchorage than pass appliance in this study.