“2×4”矫治系统中前倾弯弓丝弯折位置变化对其力学行为影响的三维有限元分析

Effect of variation of bending location of tip-forward bending arch wires on its mechanical behavior in “2×4” appliance system:A three-dimensional finite element analysis

目的:建立模拟临床的"2×4"矫治系统的三维有限元模型,探讨三维空间内前倾弯弓丝弯折位置的变化对其力学行为的影响。方法:通过逆向工程法建立包含上颌牙列和直丝弓托槽的"2×4"矫治系统的三维有限元模型,设计弯折位置不同[弓丝弯折点至中切牙托槽中心点的弓丝长度/一侧第一磨牙颊管中心点至中切牙托槽中心点的弓丝长度(A/L)分别为0.8、0.7、0.6、0.5、0.4和0.3]的前倾弯弓丝模型,使用三维有限元分析软件计算弓丝弯折位置变化时各牙齿所受力和力矩及磨牙前倾弯弓丝(A/L=0.8)作用下各牙齿的初始位移。结果:前倾弯弓丝弯折位置不同时,"2×4"矫治系统的力学系统也不相同。A/L=0.41时,第一磨牙垂直方向受力为0N,切牙垂直方向所受合力为0N;不存在一个力的中性点(让所有牙齿的垂直向受力均为0N)。A/L=0.38时,第一磨牙的力矩反转;A/L=0.59时,侧切牙的力矩反转;中切牙整个过程受伸长力,未发生力和力矩的反转。A/L=0.8时,牙齿的初始位移不利于前牙开牙合的纠正。结论:三维空间"2×4"矫治系统中,前倾弯弓丝弯折位置的变化将影响整个力学系统的表达;磨牙前倾弯弓丝对矫治前牙开牙合不利,临床使用时要结合辅助措施。

Objective:To construct a three-dimensional finite element model of“2×4”appliance system simulating the clinical reality,and to investigate the effect of variation of bending location of tip-forward bending arch wires on the mechanical behavior in“2×4”appliance system.Methods:The 3-dimensional finite element model of“2×4”appliance system including maxillary dentition and brackets of tip-forward arch wires were constructed by reverse engineering method and the tip-forward bending arch wires with different bending locations[arch wire length from the point of arch wire to the central point of central incisor bracket/arch wire length from the central point of the buccal tube to the central point of central incisor bracket(A/L)were 0.8,0.7,0.6,0.5,0.4,and 0.3]were designed.The forces and moments of teeth under different tip-forward arch wires and the initial displacement of teeth under molar tip-forward arch wires were calculated by finite analysis software.Results:The force system changed as the bending locations of tip-forward arch wires varied.There were no vertical forces existed at A/L=0.41 for the first molar and incisors.There were no neutral points existed in the vertical force system(make the vertical forces=0 N in vertical direction).The moment of the first molar reversed when A/L=0.38 and the moment of lateral incisor reversed when A/L=0.59.The central incisor was affected under extrusion force without force and moment reverse as the bending location varied.The initial displacement of tooth was not conducive to the correction of anterior tooth apertognathia when A/L=0.8.Conclusion:The force system of three-dimensional finite element model of“2×4”appliance system changes as the varying of bending location of tip-forward arch wires.The molar tip-forward arch wire is unfavorable when correcting the anterior tooth apertognathia and the auxiliaries should be added.