The Effect of Multiple Firings on the Shear Bond Strength of Porcelain to a New Millable Alloy and a Conventional Casting Alloy

Abstract

This study compared the effect of multiple firings on the shear bond strength (SBS) of porcelain to the new millable alloy (Ceramill Sintron) and a conventional casting alloy (4-all). Thirty-six cylindrical cores (6.8 × 9 mm) were made of millable and castable alloy through CAD/CAM and casting techniques, respectively (n = 18). In the center of each bar, a 4 × 4 × 2-mm shot of porcelain was fused. Having divided each group into 3 subgroups based on the number of firing cycles (3, 5, 7), the specimens were fixed in a universal testing machine and underwent a shear force test (1.5 mm/min crosshead speed) until fractured. Then the SBS values (MPa) were calculated, and the failure patterns were microscopically characterized as adhesive, cohesive, or mixed. Two-way ANOVA statistical test revealed that the number of porcelain firings had no significant effect on the SBS of any of the metal groups (p = 0.1); however, it was statistically higher in the millable group than the castable group (p < 0.05). Moreover, detecting the mixed failure pattern in all the specimens implied that the multiple firings had no significant effect on the failure pattern. The multiple porcelain firings had no significant effect on the SBS of porcelain to neither the millable nor castable alloys.

Keywords: alloys; bond strength; multiple firing; porcelain.

Figure 1

Metal cylinders with porcelain fused to their cross-section.

Figure 2

Shear bond strength testing.

Figure 3

The mean and standard deviation of the shear bond strength (MPa). The shear bond strength values of Ceramill Sintron group in all numbers of firing cycles were significantly higher than the 4-all group (*: p-value < 0.05).

Figure 4

×30 and ×1000 magnification of mixed failure pattern of 4-all group after 3, 5 and 7 firings. (a) is the adhesive and (b) is the cohesive part of mixed failure patterns.

Figure 5

×30 and ×1000 magnification of mixed failure pattern of Ceramill Sintron group after 3, 5 and 7 firings. (a) is the adhesive and (b) is the cohesive part of mixed failure patterns.