Suppression of subcritical crack growth in a leucite-reinforced dental glass by ion exchange

Glass-ceramic materials are frequently used in prosthetic dentistry because of their excellent esthetics. Problematic aspects of glass ceramics are their limited strength, the scatter in their strength data, and their time-dependent strength decrease due to subcritical crack growth effects. The short-term strength level can be significantly increased by an ion-exchange process in a potassium salt. A dual ion-exchange process in KNO3/NaNO3 can additionally improve the scatter-in-strength. The objective of the present study was to examine the effect of a single and a dual ion-exchange process on the characteristic time-dependent strength decrease of a leucite-reinforced dental glass. The parameters of subcritical crack growth were evaluated by using the constant stress rate flexural strength test. Both ion-exchange processes showed a pronounced effect on the subcritical crack growth of the glass-ceramic material. The exponential crack parameter n was increased from 25 to 52 by the single-exchange and to 107 by the dual-exchange process, respectively. We conclude that the time-dependent strength decrease of a dental glass-ceramic material can be significantly limited by the ion-exchange process. This could improve the clinical reliability of dental restorations made from this class of materials. (C) 2003 Wiley Periodicals, Inc.