The influence of opaque application methods on the bond strength and final shade of PFM restorations

The aim of this study is to compare the influence of the opaque application method on the adhesion and final shade of porcelain-fused-to-metal restorations.

Four samples (n=12) were cast in a NiCrMo alloy and opaqued using three application methods: aerosol-spray (one application), aerosol-spray (two applications), paste and powder-liquid prior to veneering with dentine porcelain to a thickness of 1.0mm to mimic the clinical thickness of porcelain-fused-to-metal crowns. The porcelain to metal adhesion was determined by measuring the interfacial fracture toughness or strain energy release rate with a four-point bending configuration developed by Charalambides et al.,(13) at a loading rate of 0.05mm min(-1) in kerosene. The resultant porcelain shade was measured with a spectrophotometer under daylight. Values of L*, a* and b* were used to calculate the total color difference ΔE with different equations CIELAB, CMC(1:1), CIE94, and CIEDE2000. The resulting values were also compared with a reference unbonded sample made from the same dentine porcelain used to veneer the porcelain-fused-to-metal specimens.

The application technique of the opaque did not influence the adhesion between the porcelain and metal. All the application methods demonstrated brittle cracking behaviour through the opaque layer. No visible color differences were found between the applications methods in the final shade of the porcelain.

The application method in terms of bond strength and final porcelain shade is not a factor in choosing which method to use in the dental laboratory.