Evaluation the Effect of Base Metal Alloy Recasting on Porcelain-Alloy Bond Strength

Metal-ceramic restorations have been commonly used in dentistry. These restorations have both the esthetics of porcelain and the strength and durability of metal. Noble alloys and base-metal alloys are usually used for metal-ceramic restorations. Applications of base-metal alloys has been developed because of economic consider-ations, mechanical properties and low density. Remelting of used alloys is a common way in dental labs to reduce the costs of fixed prostheses. Few studies have been performed on the effect of recasting alloys on the metal-ceramic bond strength. The purpose of this study was to evaluate the effect of commond alloy recasting on metal- ceramic bond strength.
In this laboratory – experimental study, 23 waxed patterns in the size of 0.5 325 millimeter were cut with bisturi blade. Wax patterns were sprued, burned out and casted with commend alloy. The second group has the same method although they consisted of equal amount of fresh alloy and alloy remnants cast only once, the third and fourth group contained 50% fresh alloy and 50% used alloy of last group. After sandblasting, grinding and surface preparation, porcelain application was done with Noritake porcelain .samples fractured with 3-point bending test by Universal Testing machine at the speed of 0.5 mm per minute. Finally, the results were analyzed by ANOVA (p value = 0.007).
The results indicate that the highest mean values of fracture strength of porcelain to metal was in the first group (30.9 N) and then squencely in the group 3 (28.7 N), group 2 (26.8) and group 4 (24.3 N).There is a significant difference between group 1 and 2 (p value = 0.03), group 1 and 4 (p value = 0.001) and group 3 and 4 (p value = 0.02). There was no significant difference between group 1, 3 (p value = 0.26), group 2 and 3 (p value = 0.3) and group 2 and 4 (p value = 0.18).
Recasting of base metal alloys statistically decrease the bond strength of porcelain to metal.