Clinical Relevance Contamination of enamel and dentin with repair surface conditioning measures should be avoided. SUMMARY Objectives: To analyze whether the contamination with different repair conditioning measures impairs the adhesive performance of a universal adhesive applied in etch-and-rinse mode (ER) or self-etch mode (SE). Methods and Materials: Bovine enamel and dentin surfaces (each subgroup n=16) were bonded with a universal adhesive in ER or SE after contamination with different repair conditioning measures (sandblasting, silica coating, hydrofluoric acid etching, self-etching ceramic primer). In half of the groups, sand-blasting, silica coating, and hydrofluoric acid etching was followed by the use of a universal primer. If the universal adhesive was applied in ER, contamination was performed either before or after phosphoric acid etching. If the universal adhesive was applied in SE, bonding was performed after contamination. In the control groups, no contamination was simulated. Shear bond strength (SBS) and failure modes of composite buildups were determined after thermal cycling (10,000 cycles, 5°C-55°C). Statistical analysis was performed using analyses of variance, Weibull statistics, and χ 2 tests ( p <0.05). Results: In ER, sandblasting and silica coating significantly reduced SBS (control: enamel =25.7±4.2 MPa; dentin = 22.0±5.3 MPa) only when performed after phosphoric acid etching. Contamination with hydrofluoric acid impaired SBS on enamel but not on dentin. The self-etching ceramic primer reduced SBS, but not significantly. The contamination with the universal primer had no significant effect. In SE, all repair conditioning measures except the universal primer reduced SBS (control: enamel = 20.3±5.5 MPa; dentin = 23.0±4.0 MPa). Conclusion: Contamination of enamel and dentin by repair conditioning measures potentially affects bond strength.