An investigation into the crack propagation behaviour of tooth-coloured particulate-filled dental restorative materials

Abstract

Particulate-filled resins, or dental composites, are being increasingly used to restore the load-bearing surfaces of teeth. If these restorations are not to fracture in service, and if improvements are to be made, an understanding of the fracture behaviour of these materials is essential. The fracture parameter used is the stress intensity factor at crack instability (K _IC). This has been calculated using the double torsion test in an Instron universal testing machine. The fracture behaviour was studied by varying the amount of filler (7, 15, 26 and 41 vol %); the surface treatment of the filler (coated or uncoated); the environment (air or water); and the crosshead rate (0.05, 0.5, 5 and 50 mm min⁻¹). Fracture was found to occur in either a continuous or stick-slip manner. The stick-slip behaviour was due to blunting of the crack tip, which was controlled by the yield behaviour. If there was no significant blunting, continuous crack growth occurred. A unique fracture criterion was shown to apply, which was that a critical stress of approximately three and a half times the yield stress must be obtained at a critical distance ahead of the crack tip.[/p]