Shear bond strength and characterization of interfaces between electroformed gold substrates and porcelain

This study aimed to determine the effects of two different sandblasting conditions on the shear bond strength between electroformed Au substrates and porcelain, and characterize the interface between the Au substrate and porcelain. Electroformed Au specimens, 0.3 mm thick with a cap-like shape were prepared. The prepared specimens were then divided into two different groups and each group was sandblasted with a different size of alumina grains (100 or 250 μm) prior to dental porcelain application. Bonded specimens from each group were subjected to shear testing. After debonding, the fracture mode was analyzed by optical microscopy and SEM-EDX. One intact bonded specimen from each group was metallographically prepared to characterize the interfacial bonding by SEM-EDX and area scan analysis. The shear bond strength values (MPa) and standard deviations were 8.2 ± 1.8 and 9.1 ± 2.7 for the samples blasted with 100 and 250 μm alumina particles, respectively. No statistically significant difference was found between the two groups. In addition, no differences in fracture mode were found between the two groups. Qualitative analysis showed that, surprisingly, the Au substrate contained O, N, and P which might be related to the Au–sulfite electrolyte used in electroforming. As expected, the retained porcelain comprised Si, O, Al, Ca, Na and K. Mutual diffusion of Au, P, Si, Na, K and O without concentration gradients was found at the interface. Mutual ionic diffusion at the interface between ceramics and electroformed Au substrates (as opposed to mechanical interlocking) seems to be the most possible factor contributing to Au–ceramic bonding.