Opaque Layer Firing Temperature and Aging Effect on the Flexural Strength of Ceramic Fused to Cobalt‐Chromium Alloy

Purpose: To evaluate the effect of the opaque layer firing temperature and mechanical and thermal cycling on the flexural strength of a ceramic fused to commercial cobalt‐chromium alloy (Co‐Cr). The hypotheses were that higher opaque layer temperatures increase the metal/ceramic bond strength and that aging reduces the bond strength. Materials and Methods: Metallic frameworks (25 × 3 × 0.5 mm³; ISO 9693) (N = 60) were cast in Co‐Cr and airborne‐particle abraded (Al₂O₃: 150 μm) at the central area of the frameworks (8 × 3 mm²) and divided into three groups (N = 20), according to the opaque layer firing temperature: Gr1 (control)—900°C; Gr2—950°C; Gr3—1000°C. The opaque ceramic (Opaque, Vita Zahnfabrick, Bad Säckingen, Germany) was applied, and the glass ceramic (Vita Omega 900, Vita Zahnfabrick) was fired onto it (thickness: 1 mm). While half the specimens from each group were randomly tested without aging (water storage: 37°C/24 hours), the other half were mechanically loaded (20,000 cycles; 50 N load; distilled water at 37°C) and thermocycled (3000 cycles; 5°C to 55°C, dwell time: 30 seconds). After the flexural strength test, failure types were noted. The data were analyzed using 2‐way ANOVA and Tukey's test (α= 0.05). Results: Gr2 (19.41 ± 5.5 N) and Gr3 (20.6 ± 5 N) presented higher values than Gr1 (13.3 ± 1.6 N) (p= 0.001). Mechanical and thermal cycling did not significantly influence the mean flexural strength values (p > 0.05). Increasing the opaque layer firing temperature improved the flexural bond strength values (p < 0.05). The hypotheses were partially accepted. Conclusion: Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co‐Cr alloy.