Method: For Bond to Enamel: Human molar teeth were ground flat to remove superficial occlusal enamel. The cut enamel surface was polished using 600 Grits Silicon Carbide papers to produce standardized smear layer. Two adhesives were tested: Scotchbond Universal Adhesive (3M ESPE, USA) and Exp. Bond DC (Voco, Germany). The tested materials were applied to prepared surface then composite cylinders 0.8 in diameter and 2 mm length were fabricated using Tygon plastic tube. Twenty specimens were prepared for each adhesive and ten of them were subjected to 5000 thermal cycles between 50 and 550. For bond to dentin, the same procedures were done after cutting occlusal enamel to expose superficial dentin. Microshear bond strength measurement was performed using Instron testing machine at cross head speed 0.5/min. Data were analyzed using two-way ANOVA. Fracture surface was examined under SEM to determine the mode of failure
Result: For Scotchbond Universal Adhesive, the bond strength to enamel was: 36± 4.7 without thermocycling. The bond strength after thermal cycling was 25.1± 3.5 . For dentin the results were: 22.4±3.1 and 15.3±2.8 respectively. There was significant reduction in bond strength to enamel and dentin after thermal cycling.
For Exp Bond DC: The bond to enamel was 39.52±4.4 without thermal cycling. After thermal cycling it was 35.4±3.9. For dentin the bond strength was 32.8±2.7 and 29.5±4.3. Failure was mainly combined adhesive/cohesive failures with increasing percentage of adhesive failure in specimens tested by thermal cycling
Conclusion: The effect of thermal cycling on the bond strength of self etch adhesive is adhesive dependant.