Purpose: To compare marginal adaptation in enamel and dentin after different surface treatments before and after longterm simultaneous thermal and mechanical stresses in a mixed Class V restoration. Materials and Methods: Thirty-six V-shaped mixed Class V cavities were prepared in extracted human molars and treated as follows: group 1: 30 s ozone exposure (Heal Ozone, Kavo); group 2: 20 s air abrasion with 50 µm Al2O3 particles (Dento-prep, Rønvig); group 3: 20 s exposure to 27 µm SiOx powder (RONDOflex, Kavo with CoJet powder, 3M-ESPE); group 4: control (no treatment). Cavities were restored with a light-cured composite material (Tetric Ceram, shade A2, Ivoclar Vivadent) using a self-etching adhesive system (Syntac Clasic, Ivoclar Vivadent) with H3PO4 conditioning of the enamel. Each group was evaluated in respect to marginal adaptation before and after mechanical and thermal loading under simulated dentinal fluid. Results: Even if loading significantly influenced marginal quality in all groups (paired t-test, p 0.05), the percentages of "continuous margin" of all groups in enamel ranged between 93.2% and 92.3% before and 84.1% and 76.9% after loading and were not significantly different (ANOVA and Scheffe's post-hoc test, p > 0.05). Continuous margin in dentin ranged from 98.9% to 94.2% before and from 95.9% to 76.4% after loading, and significant differences were observed between groups treated with ozone vs control before and after loading and CoJet vs control group after loading (ANOVA and Scheffe's post-hoc test, p 0.05). Conclusion: Surface treatment with ozone and silica coating may significantly decrease marginal quality in dentin without negatively influencing marginal quality in enamel. Keywords: marginal adaptation, ozone, CoJet, Al2O3