外展曲与支抗磨牙所受舌向力的关系

The relationship of wire offset and lingual component force on first molar

目的 观察拉尖牙向远中移动时 ,在不同规格的弓丝作用下 ,牵引力对支抗磨牙所产生的舌向分力的大小以及在不同磨牙外展曲宽度下该牵引力舌向分力的大小。方法 利用与北京大学力学系合作研制的力测量仪在Typodont专用蜡上测量使用不同规格、不同刚度的弓丝 [0 4 0mm、0 4 5mm的不锈钢圆丝 ,0 4 0mm、0 4 5mm的澳丝以及 0 4 1mm× 0 5 6mm (0 0 16英寸× 0 0 2 2英寸 )、0 4 6mm× 0 6 3mm(0 0 17英寸× 0 0 2 5英寸 )的不锈钢方丝 ],分别在不同的磨牙外展曲宽度 (1mm、2mm、3mm)下 ,支抗磨牙受到的 15 0 g沿磨牙颊面管牵引钩至尖牙托槽远中翼中点方向的拉尖牙向远中移动力所产生的舌向分力。结果 (1) 15 0 g拉尖牙向远中移动力会使支抗磨牙受到舌向分力。 (2 )支抗磨牙受到的牵引力的舌向分力随弓丝粗度和刚度的增加而减少 ,弓丝抵抗磨牙所受到的舌侧力作用与弓丝的刚度、粗度成正比。 (3)支抗磨牙受到的牵引力的舌向分力随磨牙外展曲宽度的增加而减少且二者间呈线性关系。结论 拉尖牙向远中移动时支抗磨牙受到舌向分力 ,为避免磨牙向舌侧移动 ,应选择较大刚度且较粗的弓丝或适当加大磨牙外展曲。

Objective To measure the strength of lingual component force on first molar while retracting canine by 150 g tractive force with different sizes of arch wire and with different widths of molar offset on the wire Methods Wires with different sizes and different materials [0 40 mm and 0 45 mm stainless round wires, 0 40 mm and 0 45 mm Australia wires, 0 41 mm×0 56 mm(0 016×0 022 inch)and 0 46 mm×0 63 mm(0 017×0 025 inch)rectangular stainless wires] were ligated in ideal arch Typodont when the canine was retracted with 150 g force in the direction from the molar buccal hook to the central point of canine bracket′s distal wing under different widths of molar offset(1 mm?2 mm?3 mm) The lingual force applied on the first molar was measured by a self made dynamometer Results 1 There is lingual component force applied to the first molar while retracting canine with 150 g tractive force 2 The bigger the cross section area of the wire and the stronger the rigidity of the wire, the smaller the lingual component force turns The ability of the wire in deducting the lingual component force is in direct ratio with the cross section area and the rigidity of the wire 3 While the width of wire offset increases, the lingual force produced by the tractive force applied to the first molar decreases lineally Conclusion There is lingual force produced on the anchorage molar when retracting canine In clinic for avoiding the lingual movement of the first molar, increasing the size of wire or increasing the width of wire offset is suggested