臼歯部用コンポジットレジンのクリープ特性と変形挙動

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The composite resins have been widely applied for posterior restorations in place of amalgam since their compressive strength and wear resistance were markedly improved. One of the problems with amalgam is its large creep rate associated with marginal fracture of the restoration. In this study, therefore, the posterior composite resins were compared with amalgam in terms of static and dynamic creeps up to 6 months aging, and deterioration caused by the repeated compressive loading. The 24-hour creep was determined by applying compressive load (100kg/cm^2) to the specimen for 24 hours in water at 23℃ and storing it for 3 hours more without loading to make it almost completely recover from the elastic part of deformation. The static creep values of posterior composite resins were 1/4-1/10 times as small as those of amalgams. Among the composites, the hybrid type resins containing larger size and amount of fillers showed lower creep than the microfilled resins. The chemicalcured resins also tended to show lower creep than the light-cured. The creep was markedly decreased with increase in aging of the specimen from 1 hour to 3 hours in the composites and from 1 hour to 1 day in the amalgams. Little or no decrease was found thereafter in both materials. These creep behaviors might well reflect the polymerization or setting rates of the materials. The dynamic creep caused by repeated compressive loading was significantly larger than the static creep. It was notable that the repeated loading appeared to severely affect the creep of the amalgams even after their setting was almost completed. The compressive strength of the specimens after the creep test was not significantly different from that of the specimens after being stored without loading for the same period as the creep test. When the center of the restoration filled in the extracted tooth was subjected to repeated loading with steel ball, a depression was observed in all the materials. Some protrusions were found just outside the depression in the amalgams and the microfilled resins having higher creep, but not in the hybrid type resins showing lower creep. Distinguishable fracturing aspects by repeated loading were recognized between the amalgams and the composite resins. Namely the fractures occurred at the margin apart from the loaded area in the amalgam restorations, while in the composite resin restorations cracks were initiated just at the depression by the direct compressive loading.
九州歯科学会の論文
1987-12-25

臼歯部用コンポジットレジンのクリープ特性と変形挙動

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