Abstract
Porcelain-fused-to-metal restorations are used extensively in restorative dentistry because of their strength, esthetics, and insolubility in oral fluids.The purpose of this study was to determine the favorable firing temperature of commercially available porcelain used in the porcelain-fused-to-metal system.The favorable firing temperature was evaluated using observation of surface texture and gloss, the tensile strength test, and observation of the interface between opaque porcelain and metal.The muffle of the porcelain furnace made in our laboratory was controlled by a computer to verify the working temperature.The following results were obtained:1.Opaque porcelain a)On Ceramco and Vita porcelains, surface gloss can be obtained by a firing temperature of 860℃, on the other hand, the Unibond porcelain, surface gloss cannot be obtained, but a slight color change does occur when a firing temperature of 900℃ is reached.b)By means of photomicroscopic observation of the interface between porcelain and metal, penetration of porcelain into the irregularities of the metal surface was observed at various firing temperature of 700℃, 750℃, 800℃, and 850℃.And from the E.P.M.A.analysis of the interface between Unibond porcelain and metal, the appearance of bonding between porcelain and metal at the interface was observed at a firing temperature of 850℃. c)From the tensile strength test, when the firing temperature was raised, a resultant increase in tensile strength was observed.2.Dentin and enamel porcelain a)In the case of Ceramco and Unibond porcelains, their surfaces had a granular texture, and a surface gloss was obtained by a firing temperature of 760℃;but the granular texture disappeared and smooth surface was obtained when a firing temperature of 790℃ was reached.On the other hand, the Vita porcelain surface had a granular texture, and surface gloss appeared at a firing temperature of 770℃;but the granular texture disappeared and a smooth surface was obtained by a firing temperature of 800℃.b)From the tensile strength test, when the firing temperature was raised, a resultant increase in tensile strength was observed.The results of this study indicate the most favorable firing temperature for opaque porcelain is 850℃;and for dentin and enamel porcelains, 760-780℃(Ceramco and Unibond)and 770-790℃(Vita).
