无托槽隐形矫治器腭侧边缘不同延伸长度在拔牙病例中力学特点的三维有限元分析

Biomechanical Effects of Clear Aligners with Different Palatal Edge Extension in Extraction Cases:A Three-dimensional Finite Element Study

目的:通过三维有限元分析探讨无托槽隐形矫治器不同腭侧边缘延伸长度在拔牙病例中内收前牙时的牙列移动特点。方法:构建无托槽隐形矫治器三维有限元模型,依据不同第二前磨牙区腭侧边缘延伸长度分为4组工况:龈上1 mm、齐龈、延长1 mm及延长2 mm,分析4组工况下牙齿移动特点及牙周膜应力。结果:所有工况中,均表现为切牙舌倾伸长、尖牙远中倾斜及后牙近中倾斜。随腭侧边缘长度的增加,中切牙矢状向倾斜程度在工况4时最小,侧切牙在工况2时最小;尖牙远中位移量依次增加,舌倾位移量依次减小,伸长位移量在工况1~3时增加,工况4时减小;第二前磨牙近中及压低位移量在工况1~3时少量增加,工况4时减小;第一磨牙近中压低位移量依次增加。牙周膜等效应力表现为尖牙根尖区应力峰值最大。结论:无托槽隐形矫治器在拔牙病例内收上前牙时会出现过山车现象,边缘长度增加有利于切牙整体移动,但尖牙远中倾斜趋势增加,当膜片延长超过1 mm时可防止尖牙舌倾伸长及第二前磨牙近中倾斜,同时对第一磨牙支抗要求更高。

Objective:To investigate the displacement of dentition during retraction of anterior teeth under different palatal edge extension of clear aligners in extraction cases.Methods:A finite element model was constructed to analyze the characteristics of tooth movement and periodontal membrane stresses of clear aligners.The model was based on different palatal edge extension and classified into four cases:working condition 1:supergingival 1 mm,working condition 2:flanking gingival,working condition 3:extended 1 mm,and working condition 4:extended 2 mm.Results:Clear aligners therapy caused lingual tipping and extrusion of incisors,distal tipping of canines,and mesial tipping of posterior teeth in each group.With increasing palatal edge length,the degree of sagittal inclination was gradually decreased in central incisors and the lateral incisors were minimized at work condition 2.The distal tipping of the canine increased gradually,lingual tipping gradually decreased,and extrusion displacement increased in working conditions 1 to 3 and decreased in working condition 4.The medial tipping and intrusion of the second premolar initially increased and tended to decrease in condition 4.The mesial tipping and intrusion of the first molar were gradually increased.The Mises stresses exhibited the highest peak stresses in the apical region of the cusps.Conclusion:Clear aligners can be a roller coaster when retracting upper anterior teeth in extraction cases,extending the palatal edge can facilitate the bodily movement of incisal,but the canine distal tipping displacement increased.If the edge length exceeds 1mm,it can effectively prevent the canine lingual inclination and extrusion,and the second premolar medial inclination.However,there is a need of greater anchorage to support the first molar.