نبذة مختصرة : AIM: Composite resin repair is a conservative method for preserving the tooth structure. However achieving a suitable bond between the pre-existing composite and repair composite resin is difficult. The aim of this in vitro study was to assess the shear bond strength of two different repair composite materials and three different bonding procedures to the pre-existing composite. MATERIALS & METHODS: A total of 60 disc shaped specimens (5 mm in diameter and 2 mm thickness) from a mycrohybrid composite material Filtek Z250 were prepared and subjected to 5000 thermocycles (5- 55 °C). The specimens were embedded in acriylic resin blocks and the surfaces were treated with 37 % orthophosphoric acid than divided intotwo groups according to the repair material (Tetric Evo Ceram Bulk Fill (TB), Filtek Z250 (F)) and three subgroups according to the bonding procedures (Clearfil S3 Bond (S3), silan+Clearfil S3 Bond (SS3), Clearfil Universal Bond (CU)) (n=10). Samples were stored in distiled water for 24 hours at 37 °C after repair composite resins were applied. All samples were subjected to shear bond strength testing using universal testing machine at a crosshead speed of 1 mm/min. Data were analysed using two-way ANOVa and Tukey HSD test. Mode of failure was determined using stereomicroscope. RESULTS: No significant differance was observed between neither repair composite materials (p=0.628) nor adhesive procedures (p=0.277). The highest shear bond strength was observed in S3+TB(11.80 MPa) group and the lowest was observed in CU+TB (8.55 Mpa). CONCLUSION: Within the limitations of this in vitro study it can be concluded that there
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