Fracture toughness of dental composites determined using the short-rod fracture toughness test.

Plane strain fracture toughness (KIC) has been evaluated for a number of commercially-available dental composites. A modified Short-rod Fracture Toughness (SRFT) specimen design has been used, enabling small specimens to be tested conveniently. The effect on KIC of aging in water at 37 degrees C for seven days, one month, and six months has been determined for conventional, microfilled, and hybrid (coarse and fine filler particle-containing) composites. Our results suggest that aging for one month or more caused a reduction of KIC for the composites so aged. Comparison of the KIC values determined using the modified SRFT specimen with values obtained using more conventional specimen geometries gave good agreement, thereby suggesting the suitability of the small SRFT specimens for valid KIC determinations.