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

1.在牛牙颈部唇面制作浅楔形和U形洞，用自酸蚀底漆粘接系统修复，粘接强度与牙釉质和牙本质粘结强度相近。在模拟磨牙症(偏心咬合力)的弯曲载荷下，研究这些洞的微渗漏。结果：1.对于楔形浅洞，微渗漏仅发生在切牙壁，而在U形洞中，微渗漏主要发生在根尖壁处。使用应变计测定了与微渗漏试验中相同的载荷在切壁和根尖壁产生的应变。在浅楔形洞的情况下，切口壁的应变明显大于根尖壁。在U形洞的情况下，切壁和根尖壁之间的应变大小没有显著差异。采用二维有限元方法，对与微渗漏试验相同条件下颈腔周围的应变和应力分布进行了数值分析。将得到的数据与应变片数据进行了比较。结果证实了我们的分析模型对于研究修复牙内的应力分布是有用的。对于楔形浅洞，切面壁法向应力明显大于根尖壁法向应力。U形洞的切面壁法向应力小于根尖壁法向应力。我们计划制作三维模型，尽可能准确地研究应力分布。结果提示，咬合力引起的应力分布对颈椎树脂复合修复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.