title: Effect of ion exchange on hardness and fracture toughness of dental porcelains.
abstract: The objective of this study was to evaluate the effect of ion exchange, IE, on fracture toughness K(Ic) 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(Ic). IE treatment consisted in coating the surface of the specimen with slurry of KNO(3) 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(Ic) 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.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, Brazil. paulofc@usp.br
authors.forename: Paulo Francisco
authors.initials: PF
authors.lastname: Cesar
authors.forename: Carla Castiglia
authors.initials: CC
authors.lastname: Gonzaga
authors.forename: Walter Gomes
authors.initials: WG
authors.lastname: Miranda
authors.forename: Humberto Naoyuki
authors.initials: HN
authors.lastname: Yoshimura
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D006244:Hardness; D006801:Humans; D007474:Ion Exchange; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning
chemical_list: D000538:Aluminum Silicates; D003776:Dental Porcelain; C078519:leucite