Effect of Firing Temperature at the Porcelain-Metal Alloy Interface in Porcelain-Fused-to-Metal Restorations. A SEM/EDS Study.

PURPOSE: To probe in greater detail the changes at the ceramometal interface induced by heat energy absorption, using energy diffraction X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) and correlate these changes with the shear bond strength of porcelain to nickel chromium alloy.

MATERIALS AND METHODS: Seventy-five strips of nickel-chromium alloy (20 mm long, 5 mm wide, 3 mm thick) were prepared and layered with porcelain, conforming to ANSI/ADA specification no. 38 (for Metal-Ceramic Dental Restorative Systems: 2010). These test specimens were divided equally into three groups. Specimens of each group (25) were fired to a specific temperature range, that is 700°C, 900°C, and 960°C. SEM and EDS were performed on all specimens, at the metal alloy/ceramic interface. Bonding of the ceramic layer to the metal alloy was evaluated by a shear bond strength test as per ANSI/ADA specification no. 38. The data were recorded and analyzed using one-way ANOVA and post hoc Tukey HSD test.

RESULTS: SEM images of the porcelain/metal alloy interface revealed roughness of the metal alloy surface adjacent to the ceramic layer. EDS study revealed that an oxygen depletion zone was formed at the interface region, facilitating the formation of intermetallic compounds. The mean shear bond strength showed an upward trend until 900°C and decreased thereafter.

CONCLUSION: Formation of intermetallic compounds at the interface, in the presence of an oxygen depletion zone, was the prime factor in bonding of porcelain to metal alloy. This provides a new concept of ceramometal bonding.