Evaluation of Marginal Leakage and Strength of Dental Resin Cement Based on Fracture Mechanics

本文采用断裂力学方法对牙科树脂水门汀的粘接强度、边缘渗漏等力学性能进行了研究。退化是在树脂本身和沿着粘合界面引起的。因此，我们首先通过使用树脂试样和使我们能够在热水浴中对试样施加拉伸力的夹具的实验来检查机械和环境因素对树脂的影响。无拉力的热水浸泡试样和有拉力的空气浸泡试样的粘接强度均未降低。另一方面，在热水中施加拉力的试样，其粘接强度随时间的延长而显著降低.在上述样本的断裂表面上，我们无法识别任何明显的图案。因此，力学和环境因素引起的退化被认为是在树脂基体本身中引起的.然后，我们研究了粘合界面的强度，通过使用DCB试样与恒定的开放力和WOL试样与恒定的位移。标本由不锈钢制成，树脂粘固剂为Panavia或Superbond，这两种材料在日本都是流行的牙科材料。对于DCB试样，用位移计和WOL传感器测力。我们观察到Superbond试件的裂纹开口随时间增加，表明裂纹扩展或树脂基体的伸长导致最终失效。另一方面，裂纹的张开几乎不可检测，裂纹扩展的开始立即导致最终失效.在试样的断口上，既有粘着断裂，也有内聚断裂。结果表明，材料的破坏主要发生在树脂基体和沿着界面，而树脂的力学性能决定了材料的破坏模式。

We study here the mechanical properties such as adhesive strength and marginal leakages of dental resin cements with the use of fracture mechanical approaches, and obtained the following results :1. The degenerations are induced both in the resins themselves and along the adhesive interfaces. So we first examined the effects of mechanical and environmental factors to the resins by the experiments utilizing the resin specimens and the holders which enable us to apply tensile forces to the specimens in hot water bath. The specimens immersed in hot water without tensile force and those in air with tensile force do not show decrease of adhesive strength. On the other hand, specimens in hot water with tensile force show the considerable decrease of adhesive strength with time.2. On the fracture surface of the above specimens, we could not identify any significant patterns. Hence the degenerations from mechanical and environmental factors are considered to be induced in resin matrix itself.3. Then we examined the strength of adhesive interfaces by the use of DCB specimens with constant opening force and WOL specimens with constant displacement. The specimens are made of stainless steel and the resin cements are either Panavia or Superbond, both of them are popular dental materials in japan. For DCB specimens are instrumented with displacement gauges and load cells for WOL specimens.4. We observed crack openings for Superbond specimens which increase with time, indicating the crack propagations or elongations of resin matrix proceeding the final failure. On the other hand, the crack opening are hardly detectable and the starting of crack propagation immediately succeeded by final failure.5. On the fracture surface of specimens, both of adhesive and cohesive fractures are observed. We conclude that the degenerations are induced in the resin matrix and along the interface, and the mechanical properties of resin cement determined the failure mode.