Effect of water exposure on the fracture toughness and flexure strength of a dental glass

Objectives: The low fusing dental glass (Duceram LFC) has been advertised as presenting a superior chemical resistance and augmented strength after 16 h exposure to water or 4% acetic acid. The purpose of this study was to evaluate the effect of prolonged exposure to water on two mechanical properties (fracture toughness and flexure strength) of LFC. Methods: Disks and bars were mirror polished and annealed prior to aging in: (1) air (control), (2) water for 24 h at 80 degreesC and (3) water for 8 weeks at 80 degreesC. Fracture toughness (K-Ic) was determined by indentation fracture (IF) and indentation strength (IS) using a 19.6 N Vickers indentation load. Flexure strength values were obtained from three-point bending at 0.1 mm/min. Statistical analysis was performed using the Weibull distribution, Tukey and Bartlett tests (P < 0.05). Results: Both techniques (IS and IF) showed a significant improvement in the K of Duceram LFC after 8 weeks in water (0.88 and 1.14 MPa m(0.5)) as opposed to the 24-h values both in water and air (0.77-0.78 MPa m(0.5)). However, for flexure strength the Weibull characteristic (S-0) and the m parameter did not change significantly with water storage (S-0 = 90-100 MPa, Weibull m = 7-8). Significance: The increase in toughness of Duceram LFC after aging in water is an interesting and favorable observation for a restorative material exposed to the oral environment. Nevertheless, in comparison with other contemporary ceramics, the toughness of this LFC remains in the range of soda-lime-glass or classic feldspar porcelains. (C) 2001 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.