Objective: To study the influence of two-wall bone defect on periodontal ligament stresses under normal occlusal forces, and to analyze the influence of depth and width of bone defect to periodontal ligament stresses. Methods: Three-dimensional finite element models of teeth, periodontal ligament and alveolar bone were created based on cone beam CT images. Proximal two-wall bone defect with different depths (bone defect occupies one third, two thirds, and full length of root) and widths (bone defect occupies one fourth, two fourths, three fourths and full width of buccal lingual width) were simulated by modifying the elastic modulus of elements within defect areas. Occlusal forces with magnitudes of half of the maximum occlusal forces were applied to the model at an angle of 45° to the long axis of tooth, and equivalent stresses of periodontal ligament were analyzed. Results: In the model of no bone defect, the equivalent stresses of periodontal ligament of incisors, canines, premolars and molars were 2.88, 2.31, 8.67 and 7.53 MPa respectively. The equivalent stresses of periodontal ligament increased with the enlargement of depth and width of bone defect. The equivalent stresses of periodontal ligament with maximum bone defect in both depth and width for incisors, canines, premolars and molars were 4.47, 3.62, 11.66 and 8.72 MPa respectively. In the model of width of bone defect was consistent and bone defect develops vertically, the increments of equivalent stresses of periodontal ligament were significantly greater in the early stage bone defect model (from no defect to one third of root length bone defect) than that in the later stage bone defect model (from two thirds to full length of root length bone defect). In the model of bone defect depth was consistent and bone defect develops transversely, the increments of equivalent stresses of periodontal ligament in the early stage bone defect model (from no defect to one fourth of buccal lingual width bone defect) were significantly smaller than that in the later stage bone defect model (from three fourths to full width of buccal lingual width bone defect). Conclusions: Bone defect with shallow depth and that with large width would increase periodontal ligament stresses. Therefore, more attention should be paid to occlusion evaluation and adjustment for teeth with shallow and wide two-wall bone defect.
目的： 研究邻面二壁骨缺损对正常■力下下颌牙列牙周膜应力的影响，分析骨缺损深度及颊舌向宽度对牙周膜应力的影响，为临床提供参考。 方法： 用锥形束CT数据分别建立牙齿、牙周膜和牙槽骨三维模型。采用修改骨缺损区域单元弹性模量的方法模拟不同深度（占根长1/3、2/3和3/3）和颊舌向宽度（占牙根颊舌向宽度1/4、2/4、3/4和4/4）的骨缺损，对各骨缺损有限元模型上各牙位牙齿施加与牙体长轴呈45°的■力（大小为相应牙位最大■力的一半），分析牙周膜等效应力。 结果： 无骨缺损设置时切牙、尖牙、前磨牙和磨牙牙周膜等效应力分别为2.88、2.31、8.67和7.53 MPa。随着骨缺损深度和颊舌向宽度的增大，牙周膜等效应力随之增大。当骨缺损深度最大且颊舌向宽度最大时，切牙、尖牙、前磨牙和磨牙牙周膜等效应力分别为4.47、3.62、11.66和8.72 MPa。在骨缺损颊舌向宽度相同的情况下，骨缺损深度从无缺损发展至缺损占根长1/3阶段的应力增量明显大于缺损从占根长2/3发展至占根长3/3阶段。在骨缺损深度相同的情况下，骨缺损颊舌向宽度从无缺损发展至缺损占牙根颊舌向宽度1/4阶段的应力增量，明显小于缺损从占牙根颊舌向宽度3/4发展至占牙根颊舌向宽度4/4阶段。 结论： 深度较浅、宽度较宽的邻面二壁骨缺损，均可使牙周膜应力明显增加。临床对浅而宽的邻面二壁骨缺损患牙，需重视患者咬合的评估与调整。.
Keywords: Alveolar bone loss; Finite element analysis; Periodontal ligament.