An evaluation of four variables affecting the bond strength of porcelain to nonprecious alloy

Four variables that could possibly affect the bond strength of the porcelain to nonprecious alloy were investigated. The variables were directional variations of metal preparation using the Paasché Air Eraser with aluminum oxide fast-cut abrasive, atmosphere variations in the furnace from low to high temperature limits of the degassing cycle, time variations at normal atmosphere of 1,850 degrees F. (degassing upper-limit timing), and firing of the opaque layer of porcelain at different temperatures. A total of 162 Ticon alloy interfaces were prepared, from which 81 paired test samples were constructed. Porcelain was fused to the samples and tested under specified conditions of preparation utilizing an Instron Universal testing machine. It was determined that firing the opaque layer at 1,840 degrees F. at a rate of 75 degrees F. per minute more than doubled the mean bond strength of all samples. The time at the upper limit of the degassing cycle also had a significant effect on the bond. As the time increased, the bond strength decreased. Complete bonds between porcelain and nonprecious metals were demonstrated when the fracture occurred in the porcelain and not at the interface. It is recommended that the opaque firing and degassing be done in accordance with the foregoing findings.