牵引方向对上颌前牙整体内收影响三维有限元分析

Finite element study on the effect of force directions on en mass retraction of upper anterior teeth

目的采用三维有限元法模拟不同方向牵引力内收上前牙,分析前牙位移趋势及应力分布,为临床治疗提供指导。方法研究于2012年在福建医科大学进行。建立唇侧直丝弓矫治器、6个上前牙及其牙周膜和前颌骨的三维有限元模型。模拟在0.48 mm×0.64 mm英寸主弓丝上,以种植钉为支抗、1.47 N矫治力整体内收上前牙,设定前牙区牵引钩为0-6 mm、后牙区种植钉高度分别为8和14 mm。加载后求解,计算出各前牙的位移及牙周膜第一主应力。结果滑动法整体内收上前牙时,牵引钩长度主要影响前牙的矢状向位移方式：牵引钩长度增加至6 mm的过程中,侧切牙在唇舌向上由舌向倾斜运动变为舌向整体平移和舌向控根运动外,中切牙和尖牙的三维位移只有数量的增大,趋势基本保持不变。支抗种植钉高度主要影响前牙垂直向位移：种植钉位置越高,侧切牙的压低位移增大,尖牙的伸长位移减小,即前牙整体压低的趋势更明显。结论种植支抗整体内收前牙时,单纯调整牵引钩长度和支抗种植钉高度难以实现前牙段的整体内收,有必要对前牙段增加适当的垂直向压低力量。

ObjectiveTo simulate en mass retraction of upper anterior teeth with various force system and provide guidance for clinical procedure.MethodsA three-dimensional finite element model of premaxillary bone and anterior teeth with straight wire appliance was established in ANSYS 8.1. En mass retraction of upper anterior teeth with archwire of 0.48 mm ×0.64 mm inch using implant as anchorage and force of 150 g was simulated. The force direction varied with anterior hook of 0 ~ 6 mm and posterior implant anchorage 8 mm and 14 mm gingivally from archwire. After loading,solution was done and displacement and maximum principle stress were calculated.ResultsDuring en mass retraction of upper anterior teeth with straight wire technique,the length of anterior hook mainly influenced sagittal moving pattern of anterior teeth. As anterior hook increased from 0 to 6 mm,labiolingual displacements of lateral incisor varied form lingual tipping to lingual translation and lingual controlling root movement,while 3-D displacements of other teeth only increased in account. Location of posterior implant mainly influenced perpendicular displacement of anterior teeth. As the height of implant increased,intrusion of lateral incisor increased and extrusion of canine decreased,which meant that more intrusion of anterior segment was achieved.ConclusionEn mass retraction of upper anterior teeth is impossible only by changing length of anterior hook and height of posterior microscrew. Proper intrusive force in anterior teeth is recommended for better control.