不同角度后倾曲作用下近中移动下颌第二磨牙的牙周膜应力分析

目的了解不同角度后倾曲及不同加力方式下近中移动下颌第二磨牙的牙周膜应力分布和大小。方法将0.046cm(0.018英寸)澳丝上不同角度后倾曲对下颌第二磨牙的作用力分别加载于牙体相应部位,并分别采用颊侧单独加载和颊舌侧同时加载方式对下颌第二磨牙施加1.0、1.5和2.0N的近中牵引力,模拟牙齿在不同加力方式下近中移动时牙周膜初始应力的分布和大小。结果后倾曲作用下近中移动下颌第二磨牙时,应力集中区位于牙周膜颈缘。后倾曲为15°、20°和25°时,分别相应于颊舌侧同时加载1.0、1.5和2.0N的近中牵引力,牙周膜应力分布较颊侧单独加载均匀,但后倾曲为5°加载2.0N和后倾曲为30°加载1.0N的近中牵引力时,颊舌侧同时加载的应力分布并不比颊侧单独加载均匀。后倾曲为10°、15°、20°时,加载1.0N的近中牵引力牙周膜最大Von Mises应力接近理想牙移动的牙周膜最佳应力范围。结论近中移动下颌第二磨牙时应尽量选择低摩擦力矫治系统,临床治疗中应首先充分排齐整平;以0.046cm(0.018英寸)澳丝作为主弓丝时使用15°至20°弓丝后倾曲匹配接近1.0N的近中牵引力颊舌双侧加载进行加力,牙周膜应力分布更加均匀,应力大小更接近于牙周膜最佳应力范围。

Three-dimensional Finite Element Analysis of Stress of Periodontal Membrane of Mesially Moved Mandibular Second Molars under Tip-back Bends with Different Angles

Objective To analyze the stress of periodontal membrane of mesially moved mandibular second molars under tip-back bends with different angles and forces.Methods Forces formed by Australian Wire(0.018 inch)archwire with 5°,10°,15°,20°,25° and 30° tip-back bends were loaded on mandibular second molar and mesial forces of 1.0,1.5 and 2.0 N were loaded at buccal side or at both buccal and lingual sides respectively.Distributions of stress of periodontal membrane were analyzed by ANSYS software.Results Stress of periodontal membrane concentrated at the cervical site when the mandibular second molar was moved mesially under tip-back bends with different angles.Stress distributions were relatively more uniform when the mesial forces of 1.0,1.5 and 2.0 N were loaded at both buccal and lingual sides under tip-back bends of 15°,20° and 25° respectively than forces loaded at buccal side only.But the same features could not be found when 2.0 N was loaded with 5° tip-back bend,and 1.0 N was loaded with 30° tip-back bend.The maximum stress values of Von Mises closed to optimal stress of periodontal membrane could be obtained when the mesial force of 1.0 N was loaded at both buccal and lingual sides under tip-back bends of 10°,15° and 20°.Conclusion In order to obtain an optimal stress of periodontal membrane when the mandibular second molar was mesially moved,low friction system should be chosen.The loading pattern should be a mesial force of 1.0 N loaded at both buccal and lingual sides on Australian Wire(0.018 inch)archwire with 15° to 20° tip-back bends after fully aligning and leveling.