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.
Highlights
Dental casting alloys play a prominent role in fabrication of porcelain fused to metal (PFM)restorations
Ren et al showed that increasing the number of porcelain firing from 3 to 5 and 7 cycles had no significant effect on the bond strength of porcelain to two different base metal alloys used in their study [34]
In addition to the shear bond test, this study investigated the metal-ceramic bond strength through scanning electron microscopy (SEM) analyses as an additional evaluation
Summary
Dental casting alloys play a prominent role in fabrication of porcelain fused to metal (PFM)restorations. Compared with gold-base alloys, base metal alloys are stronger and harder, more resistant to distortion during porcelain firing, and have higher fusion temperature [2,3,4]. They have overoxidation, uncertain biocompatibility, and finishing and polishing problems as their disadvantages [4]. In fabrication of PFM restorations, Ni-Cr alloys are preferred over gold-base alloys since they are harder, more elastic, and have higher fusion temperatures [5]. Co-Cr alloys are used as the main structure of partial removable dental prostheses They have fewer potential side effects and are more resistant to corrosion compared with Ni-Cr alloys [10]. Co-Cr alloys are alternatively used for patients who are allergic to Ni [11]
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