不同部位种植体支抗前牵引上颌的三维有限元分析

目的采用三维有限元方法分析不同部位的种植体支抗前牵引对上颌复合体的影响,为种植体支抗前牵引治疗骨性Ⅲ类错牙合提供客观的理论依据。方法运用已建立的上颌复合体和种植体的三维有限元模型,在上颌骨唇颊侧三个不同部位(上颌中切牙与侧切牙牙根间;尖牙与第一双尖牙牙根间;第二双尖牙与第一磨牙牙根间)植入种植体,模拟临床在种植体上加载前牵引力,不同部位和不同角度之间两两组合共形成12种工况,分析比较不同工况下上颌复合体发生的应力分布以及旋转、移位变化。结果不同部位不同角度的前牵引力对上颌复合体的影响表现为:①牵引力向前下与眶耳平面呈30°方向时,随着种植体部位的逐渐后移,除颧额缝处应力逐渐减小外,其余各骨缝处应力逐渐增大。当种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体各相关骨缝主应力值最接近。②牵引力向前下40°方向时,蝶颌缝变化较大。当种植体位于中切牙与侧切牙牙根间和尖牙与第一双尖牙牙根间时此处受到的是压应力;而当种植体位于第二双尖牙与第一磨牙牙根间前牵引时则变为拉应力。③牵引力向前下50°和60°方向时,鼻颌缝处应力在三个不同部位种植体牵引时虽发生较大变化,但均为拉应力。蝶颌缝处应力均为压应力。结论根据应力分析,随着种植体植入部位的逐渐后移,上颌复合体逆时针旋转趋势逐渐增大:①牵引角度30°,种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体可能发生近似整体前移;当种植体位于中切牙与侧切牙牙根间、尖牙与第一双尖牙牙根间时,上颌复合体均可能发生顺时针旋转。②牵引角度40°,种植体位于第二双尖牙与第一磨牙牙根间时,上颌复合体可能发生逆时针旋转,其余两部位前牵引时上颌复合体均可能发生顺时针的旋转;③牵引角度大于50°,三个不同种植体部位前牵引均可能导致上颌复合体顺时针旋转。

3-D finite element study of maxillary protraction under different implant position

Objective To analyse the impact of implant anchorage protraction at different parts on maxillary complex with three-dimensional finite element method and to provide objective theoretical basis for treating skeletal Class Ⅲ malocclusion through implant anchorage protraction.Methods Implant at three different parts（between the roots of maxillary central incisor and lateral incisor;between the roots of canine and the first premolar;between the roots of the second premolar and the first molar）at buccal side of maxilla with the established three-dimensional finite element model of maxillary complex and implant and apply protraction to the implant in clinic manner.Then,there will be combination in pairs among different parts and angles and 12 conditions will be formed in all.At last,analyse and compare the stress distribution and changes on rotation and displacement on maxillary complex under different conditions.Results The impacts of protraction at different parts and angles on maxillary complex were： ① when the traction was applied to the lower part forward to form a 30-degree angle with frankfort plane,with the gradual retroposition of the implant part,stress at all sutures increased gradually except that stress at sutura zygomaticofrontalis decreased gradually.The values of principle stress at all related sutures of maxillary complex were closest to each other when the implant was placed between the roots of the second premolar and the first molar.②A great change was witnessed on sutura sphenomaxillaris when the traction was applied to the lower part forward to form a 40-degree angle.The implant was under pressure stress when it was placed between the roots of central incisor and lateral incisor and between the roots of canine and the first premolar; however,when protraction was applied to the implant between the roots of the second premolar and the first molar,it was under tensile stress.③Although there were great changes on the stress during implant protraction at three different parts on sutura nasomaxillaris when the traction was applied to the lower part forward to form a 50-degree angle and a 60-degree angle,tensile stress was remained all the time.Besides,pressure stress at sutura sphenomaxillaris was remained all the time.Conclusion According to the stress analysis,with the gradual retroposition of implant location,the counterclockwise rotation tendency of maxillary complex increased gradually： ① at traction angle of 30°,when the implant was placed between the roots of the second premolar and the first molar,approximate overall antedisplacement may take place on maxillary complex;when the implant was placed between the roots of central incisor and lateral incisor and between the roots of canine and the first premolar,clockwise rotation may take place on maxillary complex in both cases.②At traction angle of 40°,when the implant was placed between the roots of the second premolar and the first molar,counterclockwise rotation may take place on maxillary complex and clockwise rotation may take place at both the rest parts upon protraction;③At traction angle above 50°,protraction applied to the three different parts where the implant were placed may lead to clockwise rotation of maxillary complex.