Evaluation of chemical and mechanical properties of dental composites

Composite materials were aged in distilled, deionized water and a solution by volume of 50% distilled, deionized water and 50% ethanol for three mon at 37 degrees C. Also investigated was the effect of aging dental glass filler powder in distilled, deionized water for one, three, six, and ten mon at 2 degrees C, 37 degrees C, and 72 degrees C. Atomic absorption analysis was performed on the aqueous media in which the samples were aged in order to determine the extent of leaching of silicon and strontium. From the leaching rates at various aging temperatures, the activation energies for silicon (10.3-16.4 j/mol) and strontium (57.0-58.4 j/mol) were determined. Aging in the 50% distilled, deionized water and 50% ethanol solution greatly increased the leaching rate of both silicon and strontium, as compared to aging in distilled, deionized water. Glass powder leached far more than the composite materials, due to an increase in exposed surface area, as well as a lack of chemical bonding to a resin matrix or a linked glass network. Temperature greatly increased the leaching rate of both silicon and strontium. Only after ten mon did strontium leach substantially more than silicon. For the dental composites investigated after 3 mon aging, Mode I fracture toughness decreased 57-68% in ethanol and 37-43% in water, and mode II fracture toughness decreased 41-49% in ethanol and 6-11% in water.