Comparative Study Of Three Kinds Of Maxillary Anterior Teeth Retraction Force System

Objective:To observe the movement of the upper anterior teeth of three kinds of stainless steel arch wire with sliding mechanics assisted by micro-implant anchorage in the treatment of skeletal class?maxillary protrusion,and discuss the mechanism by comparing the effects of the three force systems on en masse retraction,so as to provide theoretical basis and reference for the selection of appropriate retraction method of anterior teeth in clinic.Methods:In this study,33 patients with maxillary protrusion in the Department of Orthodontics,Stomatological Hospital of Lanzhou University were selected.the orthodontic scheme was to remove the first premolars of upper and lower jaw and strengthen the anchorage with micro-screw implant.They were randomly divided into three groups according to the case number.The patients with 0.019×0.025 inch stainless steel straight arch wire combined with 2mm short traction hook with sliding mechanics were used as the control group?C?.0.018×0.025 inch stainless steel 2mm deep rocking chair arch combined with 7mm long traction hook was used to retract the anterior teeth.In the experimental group?E1?,the patients with 0.016×0.022 inch stainless steel V-shaped arch wire combined with 2mm short traction hook sliding method were also used as the experimental group?E2?,each group was composed of11 people.The lateral cephalometric films were taken before the closure of the extraction space?T₀?and after the closure of the extraction space?T₁?,and the maxillary research models were made.There were 19 items of cephalometric analysis and 4 items of model analysis and measurement.1 item of the time taken to close the extraction space.Mann-Whitney U test and Wilcoxon rank test were used for statistical analysis of the data in this study.Results:The bone tissue measurement after closing the extraction space in the three groups showed that there was significant difference in SNA,A-VR,but no significant difference in NA-PA.Soft tissue measurement showed that the protrusion of the upper lip decreased and the nasolabial angle increased in the three groups,but the difference was not statistically significant.There was no significant difference in dental measurement indexes U6-PP and U6-VR between groups,The retraction of incisal ridge in E1 was smaller than that in C and E2,and the difference was not statistically significant.The intrusion of incisal ridge in E1 was higher than that in E2,and that in E2 was higher than that in C,and the difference was statistically significant.The change of upper incisor inclination in E1 was lower than that in E2 and that in E2was smaller than that in C,and there was no significant difference between E1 and C.The change of canine width in control group was significantly different from that in experimental groups.There was significant difference in the time needed to close the extraction space between C and E1,E1 and E2.Conclusions:1.In the treatment of patients with maxillary protrusion,under the condition of micro-implant anchorage,the three force systems combined stainless steel wire of different sizes with traction hooks of corresponding height had closed the space by sliding mechanics,point A moved backward,and the anterior teeth were obviously retracted.The upper lip point moved backward,the retraction volume was large,and the profile of the patients was improved.2.The effect of rocking chair arch force system on labial inclination and intrusion of anterior teeth was better than that of V-shaped arch wire and straight arch wire,and the anterior teeth were closer to the en masse retraction.