Bond Strength to Dentine and Degree of Conversion of Adhesive Systems

Objectives: The study evaluated the bond strength, degree of conversion and fracture pattern of the hybrid layer in cement-dentin adhesion techniques. Materials and Methods: Bovine teeth dentin blocks were divided according to the cementation techniques: G1- Conventional three-step adhesive and dual-curing resin cement; G2- One-step self-etch adhesive and dual-curing resin cement; G3-Self-adhesive resin cement; and G4- Self-adhesive primer and dual-curing resin cement. Specimens were submitted to thermal cycling, chemical aging or water storage. Bond strength was evaluated by testing machine; fracture pattern observed by optical microscopy, and degree of conversion evaluated in micro-Raman spectrophotometer. Data were analyzed by two-way ANOVA and Tukey's test (α=0.05).  Results: G1 showed greatest bond strength (p<0.001) followed by the G2 with higher values compared to G3 and G4, and no difference between them. For G2, G3 and G4, the thermal cycling affected the bond strength. The greatest degree of conversion was for G2 with Single Bond Universal, significantly higher than Scotchbond and RelyX U200. G4 provided highest value for the cement layer, and statistically higher than G1. G1 showed the highest strength than G3 associated to resin cement or self-adhesive resin cement. Different fracture patterns were observed. Conclusions: Aging methods reduced the bond strength. Degree of conversion was highest in the adhesive layer photo activated and in the cement layer with dual activation. Different fracture patterns were observed. Clinical Relevance: Resin cements degree of conversion and fracture pattern of the hybrid layer are relevant factors in the different bond strength values obtained in adhesive protocols.