冠外固位体义齿基牙牙周组织应力分布的三维有限元分析

目的研究下颌第一磨牙缺失、第二磨牙近中倾斜30°或45°时,用栓道附着体义齿或套筒冠义齿2种冠外固位体(extra-coronal retainer,ECR)义齿修复的基牙牙周组织应力分布。方法采用CT扫描技术和Mimics、Freeform、ANSYS软件,建立下颌第一磨牙缺失、第二磨牙近中倾斜30°或45°及ECR义齿修复后的三维有限元模型,模拟加载并计算分析基牙牙周组织应力的分布情况。结果下颌第二磨牙近中倾斜30°、45°模型,修复前第二前磨牙Von Mises应力分别是2.80 MPa、3.47 MPa,栓道附着体义齿修复后分别是19.26 MPa、25.18 MPa,套筒冠义齿修复后分别是19.47 MPa、24.48 MPa,ECR义齿修复后下颌第二前磨牙牙周组织应力明显增大;修复前第二磨牙Von Mises应力分别是20.45 MPa、20.50 MPa,栓道附着体义齿修复后分别是15.02 MPa、11.84 MPa,套筒冠义齿修复后分别是18.04 MPa、12.18 MPa,ECR义齿修复后下颌第二磨牙牙周组织应力明显减小。结论栓道附着体义齿和套筒冠义齿均能改善倾斜基牙牙周组织的应力分布,当下颌第二磨牙近中倾斜角度过大或下颌第二前磨牙牙周状况欠佳时,应该考虑增加近中端基牙数目。

Three-D finite element analysis of the stress distribution in periodontal tissue of abutments with or without extracoronal retainer

Objective To compare abutment＇s periodontal stress distribution of two types of extra-coronal retainer（ECR） restoration（key-key-way attachment denture and telescopic crown denture） in the case of the lower first molar missed along the lower second molar with 30 or 45 degree mesial tilting.Methods Threedimensional finite element models of lower first molar missed along lower second molar with 30 or 45 degree mesial tilt with or without ECR restoration were constructed by combination of the computed tomographic（CT） scanning and Mimics,Freeform and ANSYS softwares.Axial occlusal force and oblique occlusal force of 200 N were applied to the lower second molar on the central fossae in each case.The stress distributions in the surrounding tissues of the lower second premolar and lower second molar were compared.Results In the cases of lower second molar with 30,45 degree mesial tilting,without restoration the maximal Von Mises stress values of lower second premolar were 2.80 MPa and 3.47 MPa,with key-key-way attachment those were 19.26 MPa and 25.18 MPa,and with telescopic crown 19.47 MPa and 24.48 MPa respectively.Without restoration the maximal Von Mises stress values of lower second molar were 20.45 MPa and 20.50 MPa,with key-key-way attachment those were 15.02 MPa and 11.84 MPa,with telescopic crown 18.04 MPa and 12.18 MPa respectively.With ECR the stress of periodontal tissue of lower second premolar was significantly increased,and that of lower second molar was significantly decreased.Conclusion Both key-key-way attachment and telescopic crown ECR can ameliorate the stress distribution in the periodontal tissue of the tilted abutment.It is necessary to add mesial abutment when the degree of lower second molar mesial tilting is too large or the periodontal condition of lower second premolar is not in good condition.