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Mehuli´c K. 1, M. Lauˇs-ˇSoˇsi´c 2
1 Department of Prosthodontics University of Zagreb School of Dental Medicine, Zagreb, Croatia
2 Dental Clinic Zagreb, Zagreb, Croatia
Metal-ceramic restorations include the positive features of metal (strength, durability and stability) and ceramics (esthetics). The strong bond on the metal-ceramic interface is the basic prerequisite for the durability of the metal-ceramic restoration. The heating of metal construction results in the diffusion of certain atoms (tracers) on the surface. There they react with atmospheric oxygen creating in oxides which remain on the cast surface, because the reversible diffusion is prevented. Atoms of silica in ceramic are bound with these oxides as a result of which a metal-tracer-ceramic compound is formed and a chemical bond is realised. In addition to forming an oxide layer, the oxidation heat treatment (OHT) is applied for all alloys in order to remove the entrapped gas and eliminate surface contaminants. Surface metal preparation before porcelain application may also affect the bond strength of metal and ceramics. Roughened surface by sandblasting enables mechanical interlocking and an increased surface for bonding metal and ceramics. Applying a bonding agent may improve the quality of the bond of certain metal-ceramic restorations. Due to the continued oxidation of titanium and creation of a non-adherent oxide layer, the bond strength between titanium and ceramics is weak, which is attempted to be resolved by firing in an argon atmosphere.