Effect of ion exchange on hardness and fracture toughness of dental porcelains

The objective of this study was to evaluate the effect of ion exchange, IE, on fracture toughness K-1c, and hardness H of five dental porcelains with different microstructures: B, Ceramco II/Dentstply; C, Finesse/Dentsply; Cb, Cerabien/Noritake; D, d.Sign/Ivoclar; V, Vitadur Alpha/Vita. Specimens were sintered according to manufacturers' instructions, n = 10. Vickers indentations were made on specimens' surfaces before and after IE to calculate H and K-1c. IE treatment consisted in coating the surface of the specimen with slurry of KNO3 and distilled water, with subsequent drying for 20 min at 150 degrees C and heating for 30 min at 450 degrees C. Microstructural analysis was also performed. The measured leucite contents were 22, 15, 6, 0, and 0% for porcelains B, D, C, Cb, and V, respectively. Porcelains C, Cb, D, and V showed a significant increase in hardness after IE. Hardness of porcelain B was not affected by IE. Materials with lower leucite content tended to present higher increases in hardness after ion exchange. Ion exchange significantly increased K-1c, between 64 and 156% of 4 out of 5 porcelains studied. Porcelain B was the only one to present a decrease in fracture toughness after ion exchange. (C) 2007 Wiley Periodicals. Inc.