Effect of thermocycling on the shear bond strength of composite-resin to Supercast alloy

Intraoral repairs often involve bonding composite to fractured PFM crowns. Newer adhesive systems currently referred to as multipurpose systems are capable of bonding to enamel, dentin, metal and porcelain. The Adper Scotchbond Multipurpose Plus system (ASMP) is as one of the systems using in repair procedures. Most studies observed significant differences between early and late bond-strength results. This study evaluated the effect of thermal stresses on shear bond strength of composite resin to Supercast alloy by using different surface treatments including etching, sandblasting and combination. Methods & Materials: In this invitro experimental study composite cylinders were bonded with ASMP to the 60 surfaces of alloy that were treated with etching (groups 184), sandblasting (groups 285) or combination of both (groups 386) following the manufacturer instructions. In each group, groups 4, 5 and 6 were thermocycled intermittently in 5 & 55 Cº. Groups 1, 2 & 3 were stored in 37 Cº distilled water. Shear bond strengths were measured and compared by loading each specimen in shear to failure in an Instron testing machine. Data were analyzed using two-way ANOVA and Duncan tests. The mean shear bond strengths in groups 1 to 6 were respectively: 1.84±0.49, 4.77±0.77, 17.97±3.59, 1.08±0.62, 1.98±0.81, 12.77±2.38 (MPa). There were significant differences between the study groups (p<0.001). Thermocycling significantly reduced the bond strength of composite resin and Supercast alloy. The bond strength of composite resin increased when the combination of sandblasting and etching used for surface treatment.