الفهرس 
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Abstract
This study aimed to assess the micro tensile bond strength and flexural bond strength of two resin- matrix ceramic CAD/CAM blocks bonded to composite resin using different surface treatment protocols with and without mechanical aging. The reliability of the flexural bond strength test as a valid substitute for the microtensile bond strength test was evaluated.
Two resin-ceramic materials (Vita Enamic and Lava Ultimate) were divided into 4 groups according to the surface treatments: Bur grinding (control), Bur grinding with silane, 9.5% HF acid etching, and 9.5% HF acid etching with silane. The single bond universal adhesive was applied on all the samples after the surface treatments, followed by composite resin application. Each group was further divided into 2 main subgroups (without/with chewing simulation 500,000 cycles). Microtensile and flexural bond strength tests were performed for each group using universal testing machine. The modes of failure were analyzed using digital microscope. The surface treatments topography was examined using scanning electron microscope.
“Lava ultimate” groups showed higher mean microtensile and flexural bond strength compared to “Vita Enamic” groups, irrespective of the effect of chewing simulation. Except for the FBS value for the (B+S) group, there was no difference between the two materials without chewing simulation.
“Bur+ Silane “surface treatment enhanced the bond strength for the two materials irrespective of the effect of the material and aging.
“Without chewing simulation” groups showed higher mean bond strength compared to “with chewing simulation” groups irrespective of the effect of material, different surface treatments, and the testing methodologies.
The flexural bond Strength test had a higher Weibull modulus than the microtensile bond strength test, indicating its higher reliability.
The adhesive mode of failure was more encountered with the flexural bond strength test than with the microtensile bond strength test.
Conclusion
Within the limitations of this study, it could be concluded that:
1- The surface roughness induced by the bur grinding coupled with the separate silane coupling agent application was the most efficient, durable repair protocol for both materials. Thus, it can be used instead of HF acid, which is hazardous and should be used with extreme caution intraorally.
2- Flexural bond strength test (4-point bending test) can be a reliable alternative to the microtensile bond strength test to evaluate the bond strength between resin-matrix ceramics and dental resin composite.
Recommendations:
It is recommended to perform finite element analysis to analyze stress distribution in the flexural bond strength test.
A combination of different aging methods (thermocycling and chewing simulation) and longer aging intervals are recommended.