Microfracture mechanisms of dental resin composites containing spherically-shaped filler particles.

The effects of spherically-shaped filler particles on bending strength, bending elastic modulus, and fracture toughness of resin composites were studied. The filler content was changed by 0, 20, 40, 60, and 70 wt%. Bending properties and fracture toughnesses were determined on three-point bending specimens. Acoustic Emission (AE), i.e., the elastic wave released from a localized source in the material, was detected by sensors of a high-sensitivity and low-noise resonance type during the fracture toughness test. Detected acoustic emission signals were analyzed for parameters such as amplitude, events, and locations. The fractured surface was examined by a scanning electron microscope. The bending strength and the fracture toughness showed almost the same trend in their increasing rates by filler content, but the elastic modulus showed a much higher increasing rate. A microfracture mechanism of the dental resin composites containing spherically-shaped filler particles is proposed based on the results obtained from the AE-releasing pattern, two-dimensional AE location, and fracture surface findings. In addition to the toughening effects of crack pinning and crack branching, which are observed in the usual commercial resin composites, crack-deflecting effects are confirmed in this new type of dental resin composites.