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

Abstract

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°C and (3) water for 8 weeks at 80°C. 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.