title: Fracture toughness and durability of chemically or thermally tempered metal-ceramic porcelain.
abstract: Thermocycling and water storage effects on fracture toughness (KIC) of chemically or thermally tempered metal-ceramic disks were investigated to evaluate the durability of tempering effects with regard to oral aqueous environment. Metal-ceramic disks (phi 10 mm x 2.0 mm) consisting of opaque porcelain (0.2 mm thick), body porcelain (1.3 mm) and Ni-Cr-Be alloy (0.5 mm) were prepared and the porcelain surfaces were polished with 1-micron diamond paste. The disks were subjected to ion exchange (potassium or rubidium) or thermal tempering treatments, then with the as-polished or further annealed disks, thermocycled for 8000, 15,000, and 22,000 cycles between 5 degrees C and 60 degrees C or stored in water at 37 degrees C for 33 days. After aging, KIC values of disks were determined by a Vickers indentation technique. Statistical analyses indicated that the KIC values of ion-exchanged and annealed disks were not significantly affected by the limited number of cycles and water storage, while the thermally tempered and untreated disks revealed a significant decrease in mean KIC from even 8000 cycles and after storage. However, there was no significant difference between thermocycling and water-storage effects on mean KIC of all surface treatment groups. Results indicate that chemical tempering (ion exchange) produced more durable residual stresses than does thermal tempering for metal-ceramic restorations. A low-thermal load only was unlikely to affect the apparent fracture toughness of porcelain.
authors.affiliation: Department of Dental Engineering, School of Dentistry, University of Tokushima, Japan.
authors.forename: H H
authors.initials: HH
authors.lastname: Lee
authors.forename: M
authors.initials: M
authors.lastname: Kon
authors.forename: K
authors.initials: K
authors.lastname: Asaoka
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry; D003776:Dental Porcelain; D004868:Equipment Failure; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D007474:Ion Exchange; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D008962:Models, Theoretical; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D002858:Chromium Alloys; D016876:Metal Ceramic Alloys; D008670:Metals; C403005:nickel-chromium-beryllium alloy; D014867:Water; D003776:Dental Porcelain