铸造三臂卡环在使用过程中基牙牙周膜的应力分析

目的：研究不同倒凹深度的铸造三臂卡环在使用过程中基牙牙周膜所受的应力大小。方法：通过CBCT扫描下颌牙列，利用Mimics、Abaqus软件建立下颌第一磨牙缺失，以第二前磨牙和第二磨牙为基牙的活动义齿修复的三维有限元模型。实验分为六组：各组铸造三臂卡环进入倒凹深度分别为0．25mm、0．30mm、0．35mm、0．40mm、0．45mm和0．50mm。在有限元模型中，于义齿桥体中部垂直向下和向上逐渐加载，分别测定在义齿就位和脱位时各基牙牙周膜的应力变化。结果：义齿就位时的载荷（3．60±0．77N）显著性地小于义齿脱位时的载荷（4．19±0．92N）（P〈0．05）；义齿就位和脱位时第二前磨牙基牙牙周膜承载的应力显著性大于第二磨牙（P〈0．05）；就位时基牙牙周膜应力较脱位时小（P〈0．05）。结论：义齿就位时的载荷小于脱位时的载荷；义齿使用过程中第二前磨牙基牙牙周膜受到的应力大于第二磨牙的应力。

Stress analysis of periodontal membrane of abutment teeth with three-arm casting clasp

Objective： To investigate the stress distribution of the periodontal membranes （PDM） of the abutment teeth when applying three-ann cast clasp on the different undercut depths of the teeth. Methods： A three-dimensional finite element model of a removable partial denture system was established by scanning the mandible with CBCT, and using Mimics and Abaqus software. In the removable partial denture system, the mandibular first molars were missing and the second premolars and second molars were used as abutment. The experiment included six groups based on the depth of undercuts for the threearm casting clasps： 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, and 0.50mm. Vertical load was gradually placed downward and upward on the middle part of the occlusal surface of the denture in the model, and the stress distribution of the periodontal membranes surrounding the abutment teeth were measured during placement and removal of the denture. Results： The vertical load during placement （3.60±0.77 N） was significantly less than that during removal （4.19± 0.92N） （P〈0.05）. The stress of the PDMs of the second molars was also less than that of the second premolars during placement and removal （P〈0.05）. The stress during placement was also less than that during removal （P〈0.05）. Conclusions： The load during placement of the denture was less than that during removal, and the stress on the PDMs of the second premolars was greater than that of the second molars during placement and removal.