Compressive Creep of Composite Resins in Water

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The objective of this study is to determine the creep properties and the effects of the filler content on the composite resins.The compressive creep of acommercially available composite resin under various stress levels in water for 500 h. Linear regressions were obtained between the creep strains and the compressive stress levels at various hours. It is possible to predict the creep strain of the composite from the regression when it reaches water absorbed equilibrium after 500 h. The stress of the hygroscopic expansion was calculated from the linear regressions. The maximum stress due to the hygroscopic expansion of acomposite was 0.7 kg/mm^2 at equilibrium of the water absorbed of a composite.The compressive creep of the composite resins with various filler contents were also conducted in water equilibrium water absorbed with several stress levels. The creep strain after 500 h in each composite with same filler content was in proportion to the applied compressive stress levels within the buckling stress level of the specimen. Linear regressions were also obtained between the creep strains and compressive stress levels at various hours. The maximum stress due to the hygro- scopic expansion was 0.4-0.5 kg/mm^2. The value is similar to the value of the com posite above mentioned.The water sorption of the composites decreased as the compressive stress level increased, because the volumetric strain of the specimen also was proportional to the increase of the compressive stress level. But in the composites with a high fillet content, the water sorption was almost constant in the range of the low stress level where the volumetric strain was small.