Relationship between stress distribution and microleakage of cervical restorations under flexural load cycling

1.在牛牙唇面颈部制备楔形和U形浅洞，用与牙釉质和牙本质粘结强度相近的自酸蚀底涂剂粘结系统进行修复。在弯曲载荷下模拟磨牙症（偏心咬合力），研究这些洞的微渗漏。浅楔型洞仅在切壁处有微渗漏，U型洞主要在根尖壁处有微渗漏.应变，这是在切缘和根尖壁产生的相同的负载，在微渗漏测试，使用应变计测定。在浅楔状洞的情况下，切壁的应变明显大于顶壁。在U形洞的情况下，切壁和根尖壁的应变大小没有显著差异.采用二维有限元法对与微渗漏试验相同条件下的宫颈腔周围的应变和应力分布进行了数学分析。将所得数据与应变片数据进行了比较。结果证实，我们的分析模型是有用的，以研究应力分布的修复牙齿。在浅楔状洞的情况下，切壁的正应力明显大于根尖壁。在U形洞的情况下，切壁的正应力小于根尖壁。我们计划制作三维模型以尽可能精确地研究应力分布.结果表明，咬合力引起的应力分布对树脂充填体的微渗漏模式有影响。

1. Shallow wedge-shaped and U-shaped cavities were prepared at cervical region on labial surfaces of bovine teeth and restored with self-etching primer adhesive systems which showed similar bond strength to enamel and dentin. Microleakage of these cavities were investigated under flexural loading which simulate bruxism (eccentric occlusal force). In the case of the Shallow wedge-shaped cavities, microleakage occurred only at the incisal walls, while in the U-shaped cavities, it occurred mainly at the apical walls.2. The strain, which were generated both at the incisal and apical walls by the same load as in the microleakage test, were determined using strain gauges. In the case of the Shallow wedge-shaped cavity, the incisal wall had a markedly greater strain than the apical wall. In the case of the U-shaped cavity, there was no significant difference in the magnitude of strain between the incisal and apical walls.3. Strain and stress distribution (around the cervical cavities) on the same conditions as microleakage test were mathematically analyzed by two-dimensional finite element method. The obtained data was compared with the strain gauge data. The results corroborated that our analytical models were useful to study stress distribution within the restored teeth. In the case of the Shallow wedge-shaped cavity, the incisal wall had significantly greater normal stress than the apical wall. In the case of the U-shaped cavity, the incisal wall had less normal stress than the apical wall. We plan to make three-dimensional models to investigate stress distribution as accurately as possible.4. The overall findings suggest that stress distribution induce by occlusal forces has an effect on the microleakage patterns of cervical resin composite restorations.