The effect of die spacer on retention and fitting of complete cast crowns

Abstract

Purpose: The aim of this study was to determine the influence of multiple layers of die relief agent and different cement thickness on the retention of cast restorations using two different cements.
 Materials and Methods: 144 standard stainless steel dies were divided into two groups. Each of them includes 72 dies. These groups were divided into 12 equal subgroups as well. In both groups, die spacer was applied to dies in 0, 3, 4, 5, 6 and 7 layers (each layer=5µ). In the first group, crowns were cemented with Zinc Phosphate and in the second group, Polycarboxylate was used for cementing. After that, the strength required for separating the castings from the dies was measured.
 Results: The difference among 12 subgroups analyzed by one-way ANOVA regarding Polycar- boxylate cement did not reach statistical significance. (P=0.95). A similar result was obtained with zinc phosphate cement (P=0.616). Likewise, the two-way ANOVA was carried out between the zinc phosphate and polycarboxylate groups. There was a significant difference between the average of two groups (P<0.001).
 Conclusion: Range of cement layer thickness that used in this study didn’t statistically signifi- cantly affect the force required to remove cemented cast copings. Although the castings cemented with Zinc Phosphate needed higher force to be dislodged from dies.