ABSTRACT
STATEMENT OF PROBLEM: Long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused to metal (PFM) restoration could affect mechanical strength of dental porcelain if the restoration is refired. PURPOSE: This work was performed to verify the effect of water on the mechanical strength in aged dental porcelain. MATERIAL AND METHOD: 63 specimens(Vintage Metalbond opaque and opal powder) were distributed to three experimental groups; non-water immersed control, immersed and pedried, and immersed and non-predired groups. The changes in flexural strength and fracture toughness after specimen refiring related to Fourier Transform Infrared (FT-IR) spectroscopy. RESULTS: 1. The FT-IR reflectances assigned to molecular bonds of H2O were noted as significantly different between the first-fired group and three refired groups and between two water-immersed groups and control group after refiring( p<0.05). They were also significantly different between predried group and non-predried group after refiring( p<0.05). 2. For opal specimens, FT-IR absorbances for hydrogen bond of H2O and silanols were significantly higher in non-predried group than in predreid group( p<0.05). 3. Predried opal group showed the highest mean flexural strength( p<0.05). Non-predried group indicated higher mean flexural strength than control group( p<0.05). 4. The mean fracture toughness for predired group was higher than non-predried group( p<0.05). 5. The difference of leucite crystal size is noted between control group and water-immersed, predried group in scanning electron microscopic study(x10000).