PHYSIOLOGICAL AGING OF AN ALL-CERAMIC RESTORATIVE MATERIAL

Ceramic materials exposed to a liquid environment may be subject to stress corrosion and/or time-delayed failure. The intent of this project was to evaluate the susceptibility of a magnesia alumina spinel (Cerestore (TM) to stress corrosion and degradation. Bars 2.5 x 2.5 x 30.0 mm were prepared according to manufacturer's instructions. Specimens were aged in distilled water or air at 37-degrees-C. The modulus of rapture was evaluated at zero, six, and 12 months in four-point loading at loading rate of 0.05, 0.5, and 5.0 mm/min. The modulus of rupture of each specimen was tested in its respective aging medium. The data wre analyzed by one-way analysis of variance with a multiple-means comparison test, linear regression analysis, and Weibull statistics. The pooled data sets of specimens aged in water vs. those aged in air showed a significant difference in the respective modulus of rupture (air, 108.50 +/- 16.11; water, 96.94 +/- 15.04 MPa). The one-way analysis of variance showed no significant difference between the aging times zero, six, and 12 months in each respective aging medium. The Weibull analysis also showed no difference between the Weibull constants, 7.66 air vs. 7.64 water, but a significant difference between the characteristic strengths, 115.22 air vs. 103.02 water. This study indicates that distilled water has a significant degradative effect on a magnesia alumina spinel, more likely affecting the mode of fracture rather than the stress corrosion characteristics.