[Chemical durability of composite resins]

To evaluate their chemical durability, samples of posterior composite resins were stored in NaOH (0.1 mol, 1 mol), HCl (0.1 mol, 1 mol), acetone (99%), and distilled water at 37 degrees C for a week and subjected to the direct tensile test, measurement of surface roughness and SEM observation. NaOH caused the degradation of composite resins, decrease of tensile strength and increase of surface roughness. The SEM photograph of fractured surface of tensile specimens revealed the degradation zone under the surface. It was considered that NaOH caused the hydrolysis of silan coupling of composite resins. HCl also caused the degradation of composite resins, but some resins showed the durability in this condition. More examination is needed to clarify the mechanism of degradation. Acetone caused the degradation of matrix resin and some composite resins. It was considered to dissolve the low degree of polymerized matrix resin of composite resins. Immersion in chemicals of composite resins was thought to be useful to evaluate the chemical durability and to accelerate the degradation in water.