Shear bond strength of porcelain veneer with fresh and recasting Ni-Cr alloy: a comparative in vitro study

Abstract

Introduction: Dental alloys are routinely subjected to multiple casting procedures. Repeated casting of the same alloys may cause loss of trace elements (such as Sn, Si, Mn, etc.) that are essential for the metal ceramic bond. A common practice is to include a proportion of new metal with the previously cast metal that is thought to replenish the lost elements. Objective: The study was done to evaluate the effect of variation in percentage of recasted Ni-Cr alloy used and to compare the effects with the shear bond strength of porcelain to the fresh ingot Ni-Cr alloy. Materials and methods: Uniform patterns were fabricated, invested and casting was done in five different combinations of fresh and recast alloy. A hundred percent fresh alloy; 25% recast with 75% fresh alloy; 50% recast and 50% fresh alloy; 75% recast and 25% fresh alloy; 100% recast alloys. After uniform porcelain application and firing, the specimens were subjected to shear bond test using a universal testing machine. Data were statistically analyzed using Duncans’s multiple comparison test. Results: The results showed that the mean shear bond strength of the 100% fresh alloy was maximum and 100% recast alloy was least among the groups tested. The mean shear bond strength of castings obtained from 100% fresh, 25% recast, and 50% recast alloy were similar to each other and showed statistically significant difference when compared to the 100% recast group. Seventy five percent recast group did not show statistically significant difference with 100% recast alloy. Arch Oral Res. 2011 May/Aug.;7(2)177-82 Rajalbandi SK, Kumar V, Sajjan S. 178 Introduction The Development of “Taggarts” technique of casting by lost wax process into the Dentistry gave an impetus to use alloyed metals as a restoration (1). Most of the dental laboratories commonly use the sprue and button from a previous casting as a part of the melt for the new casting (2, 3). This practice is especially detrimental with ceramometal alloys, which contain trace elements essential for bonding to porcelain. Repeated casting of these alloys may cause sufficient quantities of these elements to be lost so as to affect the bond between the metal and the porcelain (4-6). Studies have shown that recasting the used alloy up to 25% did not show any deleterious effects on the bond strength of porcelain (2). A combination of cast alloy with 50% new alloy produced the highest bond strength values. Further use of pooled alloy with an unknown casting history was not recommended since reduced bond strength were observed in their study (6). Among all the base metal alloys systems, the most popular are Ni-Cr Conclusion: It can be concluded that minimum of 50% fresh alloy for casting is a safe margin for recasting Ni-Cr alloy. s.