RELATIVE FRACTURE-TOUGHNESS AND HARDNESS OF NEW DENTAL CERAMICS

Dental ceramics can fail through growth of microscopic surface flaws t hat form during processing or from surface impact during service. New restorative dental ceramic materials have been developed to improve re sistance to crack propagation. Eleven of these improved materials with the common feature of a considerable amount of crystalline phase in t he glassy matrix were evaluated. The ceramic materials studied include d fluormica-, leucite-, alumina-, and zirconia-reinforced glasses. The relative hardness and fracture toughness were determined by indentati on technique. Alumina-reinforced materials resulted in the highest fra cture toughness values, whereas the fluormica and leucite-reinfoced ma terials showed more moderate but statistically significant greater val ues compared with those of control materials. The hardness values of c eramic materials with improved fracture toughness were both substantia lly higher or lower than those of the control groups and suggested a l ack of direct correlation between these two properties. Selection of a ppropriate restorative materials depends on clinical application and r equires consideration of several physical properties including fractur e toughness.