Statement of the Problem: The clinical success of zirconia intra-oral repair depends on the strength of the bond between the zirconia core and veneering composite. Purpose: In the present study, the effect of aging on the shear bond strength of zirconia ceramic and nanohybrid composite resin as a repair material was evaluated using different bonding agents. Materials and Method: Fifty six plates of zirconia ceramic (10mm×2mm) were prepared by CAD/CAM. All discs were air-abraded using 50μm Al2O3 particles at 2 bar pressure for 10 s, then divided into two equal groups A and B (n= 28) according to exposure to thermocycling. Each group was subdivided into four equal subgroups (n=7) according to the used bonding agent, as follows: control subgroup I, treated with Z-prime plus; subgroup II, All- Bond Universal; subgroup III, optibond; and subgroup IV, Voco-Futura bond. Surface roughness of all specimens (n=56) were evaluated immediately after bonding application using contact surf-test (Mitutoyo SJ 201, Japan). The composite resin (Ceram X nanohybrid) were then bonded and cured to each zirconia plate. The shear bond strength test was performed to group A with a universal testing machine at a crosshead speed of 1mm/ min before thermocycling. Specimens of group B were thermocycled 1000 times in water between 5˚C and 55˚C, then the shear bond strength test was performed. Bond strength values (MPa) were calculated and analyzed with a two-way ANOVA. The failure mode of each specimen was evaluated under a stereomicroscope. Results: The mean shear bond strengths before thermocycling were 13.22, 13.03, 7.02, and 6.69 (MPa) in subgroups IA, IIA, IIIA and IVA, respectively. After exposure to thermocycling the mean shear bond strengths were 13.47, 11.48, 0.00 and 0.00 (MPa) in subgroups IB, IIB, IIIB and IVB, respectively. The results showed that the shear bond strength were significantly higher in subgroups I and II than subgroups III and IV (p< 0.05). Chemical pre-treatment of zirconia with Z- Prime Plus revealed significant higher bond strength than the Optibond (subgroup III) and Voco bond (subgroup IV) before and after aging conditions. Conclusion: Treatment with both Z-prime and All- Bond Universal resulted in higher bond strength values compared to the Optibond and Voco Futurabond. The use of Z-Prime Plus treatment in combination with air-abrasion procedure resulted in the highest bond strength value that is stable on aging
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