Introduction
Matrices for dental ceramic composites are usually based on sodalime glass due to the transluceny of the resulting composites. Such translucency is very important for aesthetic appeal. Dental ceramic composites can be classified into the following four groups, depending on the type of dispersed phase:
The fracture toughness of the following dental ceramics/composites will be investigated in this lab:
Toughening of Dental Ceramics/Composites
Dental ceramics and their composites typically have fracture toughness values between 0.5 and 3 MPaÖm. Such fracture toughness levels are due largely to the intrinsic toughness of the sodalime glass-based systems and toughening due to crack deflection and/or microcracking. Microcrack toughening of dental composites can be achieved via reinforcement of sodalime glass with leucite crystals which tend to form microcracks in the high stress regions in the vicinity of the crack-tip. Similarly, toughening due to crack deflection can be accomplished by reinforcement with alumina particles which promote deflection by the tilting or twisting of cracks. Toughening results from crack deflection due to the reduction in the mode I (crack opening) mode. Multiple toughening may also result from combinations of microcrack toughening and crack deflection, and their combined effects may be assessed using the principle of linear superposition. A brief description of toughening mechanisms in ceramic composites is given in Ref. 1.
References
1. J. J. Mecholsky, "Toughening in glass ceramics through microstructural design," Mechanics of Ceramics, E. Bradt et al., Editors, Plenum Press, Vol. 6, 1983, pp. 165-179.