الفهرس 
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Abstract
To evaluate the influence of opaque layer firing temperature variations on the ceramo-metal bond. Materials and Methods: Thirty metallic frameworks (25 × 3 × 0.5 mm3) ISO 9693 were cast in Co-Cr alloy, airborne-particle abraded (Al2O3: 150 μm) at the central area of the frameworks (8 × 3 mm2) and randomly divided into three groups (N = 20) according to the opaque layer firing temperatures used: Group ”A” (control)—980°C; Group ”B” —930°C; Group ”C” —1030°C. After the opaque ceramic, the dentin (body) porcelain was applied to all specimens to reach the thickness of 1 mm. Then all specimens were incubated in distilled water for 24 hours at 37°C prior to flexural strength test. Flexural bond strength was determined in MegaPascal (MPa) at 1 mm/ minute crosshead speed and recorded by universal testing machine. The bond failure modes for all the tested specimens were analyzed under a stereomicroscope. Three extra specimens for each group were examined under Energy Dispersive X-ray analysis (EDX) at the interface between the metal and the opaque layer. Results: The mean and standard deviation values of flexural bond strength were 36.1 ± 5.5 MPa, 34.4 ± 7.8 MPa, and 38.7 ± 5.2 MPa for Groups A, B and C, respectively. There was no statistically significant difference between the three different groups. Groups A and B showed adhesive failures between oxide layer and Co-Cr alloys, while group C showed mixed type of failure adhesive and cohesive. from EDX analysis, group C showed statistically significantly highest mean weight % value of Oxygen, chromium-/ Cobalt oxide ratio, and Potassium/ Sodium ratio, while group B was the lowest. Conclusion: Increasing of the opaque layer firing temperature improved the flexural bond strength between ceramic fused to Co-Cr alloy and vice versa which confirmed our hypothesis; but this was not to the level to be statically significant.