Three Dimensional Effects Of The Archwire With Reverse Curve Of Spee On Arch

Aim:To study the three dimensional effects of Cinching-back on lower dental arch using archwire with reverse curve of spee with different depth, and evaluate the biomechanical effect of intermaxillary traction and archwire with different reverse curve of spee on lower arch.Method: Study models were established using Typodont and 0.019×0.025 stainless rectangular wire were selected as the archwire in all the experiment. The depth of reverse curve of spee were defined as 2,4,6mm. 30 subjects were divided into six group according to endbending or not and the depth of curve of spee. Four group were set up in terms of the depth of reverse curve of spee(0,2,4,6mm),5 subjects were assigned to each group, and intermaxillary traction of 150 gram were facilitated in each subject to observe its mechanical effects. Three dimensional digitizer was utilized to gauge the model to observe any change of the marks on dental arch on X,Y,Z axis. Student test and analysis of variance were used to analyze the data in the experiment using SPSS 12.0.Result:①No significant variation in the width and length of lower arch and the occlusal-gingival position of the marks on the lower arch whereas cinching-back or not.②Increase in intermolar width and the tendcy of the intrusion of the lower incisor and the molar were significantly increased in 4 mm and 6mm group, more markedly in 6mm group and more markedly in cinching-back group.③Almost the same incisor retraction and less molar mesial movement were observed in 2mm reverse curve of spee group with the same time and the same force of intermaxillary traction compared to archwire with no reverse curve of spee.④Effects of 150 gram of intramaxillary traction in 4 mm and 6mm reverse curve of spee group were: no significant change in intercanine width, increase in intermolar width, less incisor retraction, less molar mesial movement and less space closing, intrusion of the lower incisor and molar were more marked in 6mm reverse curve of spee group.Conclusion:①Cinching-back could reduce the increase in arch length, tended to increase the intermolar width and the intrusion of lower incisor and molars with the increase in the depth of the curve of spee.②Archwire with 2mm of reverse curve of spee could maintain the intermolar width,increase the anchorage of the posterior teeth, facilitate incisor retrusion in closing space via sliding mechanics.③Archwire with more curve of spee could facilitate maintaining intermolar width,withstand the increase in the overbite during space closing using intermaxillary traction, however lead to more labial movement of the anterior teeth and more friction ,thus interfere space closing.