title: The strengthening mechanism of a magnesia core ceramic.
abstract: A high-expansion core material containing magnesia and forsterite may be used to make all-ceramic dental crowns with porcelain-fused-to-metal body porcelains. The purpose of this study was to investigate the strengthening mechanism for the magnesia core material. Six batches of the magnesia core material were made by reacting magnesia with a silica glass with holding times ranging from 17 to 120 min. The flexural strength was measured using three-point loading according to the ISO specification for dental ceramics. The forsterite content was measured using quantitative x-ray diffraction. A statistically significant correlation was found between the forsterite content and flexural strength. The proposed mechanism for strengthening is the precipitation of fine forsterite crystals in the glass matrix surrounding unreacted magnesia. Longer reaction times produced more dissolution of magnesia and subsequent precipitation of forsterite. This method results in a new strengthening mechanism for dental ceramics which have previously relied on the incorporation of alumina, leucite or ceramic whiskers.
authors.affiliation: Department of Biologic and Materials Science, School of Dentistry, University of Michigan, Ann Arbor.
authors.forename: W J
authors.initials: WJ
authors.lastname: O'Brien
authors.forename: C L
authors.initials: CL
authors.lastname: Groh
authors.forename: K M
authors.initials: KM
authors.lastname: Boenke
authors.forename: G P
authors.initials: GP
authors.lastname: Mora
authors.forename: T Y
authors.initials: TY
authors.lastname: Tien
mesh_terms: D000704:Analysis of Variance; D003442:Crowns; D003799:Dental Stress Analysis; D004548:Elasticity; D016014:Linear Models; D008277:Magnesium Oxide / Q000737:chemistry*; D017633:Magnesium Silicates / Q000737:chemistry*; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D017633:Magnesium Silicates; D016876:Metal Ceramic Alloys; D008277:Magnesium Oxide