Bond Strength of Composite-resin to Supercast-alloy: Effect of Thermocycling

Objectives:Intraoral repairs of fractured PFMs sometimes involve bonding composite to exposed metal substructure. 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 one of the mentioned systems using in repair procedures. Most studies observed significant differences between early and late bond-strength results especially as related to aging tests such as thermocycling. The purpose of this in-vitro study was to investigate the effect of thermocycling on the shear bond strength (sbs) of composite-resin to Supercast-alloy in conditions of three surface treatments including etching, sandblasting and combination of both.Methods:In this experimental study sixty Supercast-alloy blocks were prepared and randomly divided into three equal groups (n=20).Composite cylinders were bonded with ASMP to the 60 surfaces of alloy that were treated with etching(E), sandblasting(S) and combination of both(ES), following the manufacturer instructions, respectively. Subgroups of each groups were stored in distilled water or subjected to 1000 thermal cycles(T) respectively(n=10)(E,ET,S,ST,ES,EST). Shear bond strengths were measured and compared by loading each specimen in shear to failure occurred using an Instron testing machine. Data were analyzed using Two-way ANOVA and Duncanxs tests.

Results:The mean shear bond strengths in groups 1 to 6 were as follows: E:1.84 ± 0.49, ET: 1.08±0.62, S:4.77± 0.77, ST: 1.98±0.81, ES: 17.97±3.59, EST:12.77 ± 2.38(Mpa). There were significant differences between the study groups. (p<0.001) Thermocycling caused decrease in sbs for all the surface treatments.

Conclusion:According to the results of this study, reduction in sbs after thermocycling was remarkable for ASMP system. In addition, the bond strength of composite-resin to alloy increased when the combination of sandblasting and etching used.