Shear bond strength between feldspathic CAD/CAM ceramic and human dentine for two adhesive cements

The purpose of this study was to evaluate the shear bond strength values between dentin substrate and a feldspathic ceramic material, based on computer-assisted design and manufacture (CAD/CAM) technology, bonded together with two adhesive systems coupled with two dual-polymerized luting agents. In addition, the effect of a silane coupling agent on bond strength was evaluated.

Forty cylinders (6 mm in diameter, 5 mm thick) obtained from feldspathic ceramic blocks were cemented to the dentin of 40 recently extracted human teeth stored in saline solution at room temperature until testing. The specimens were randomly divided into four groups of ten teeth each. All specimens were airborne-particle abraded and etched with hydrofluoric acid. In the first two groups (A1, A2) 20 ceramic cylinders were cemented using Excite DSC and Variolink II; in the A2 group the bonding surfaces were also treated with a silane coupling agent. In Groups B1 and B2, 20 ceramic cylinders were cemented using Scotchbond MPP and RelyX ARC; in the B2 group the bonding surfaces were also treated with a silane coupling agent as in Group A2. All cemented specimens were submitted to a shear bond strength test to check the strength of adhesion between the two substrates, dentin and ceramic. The data were analyzed with two-way analysis of variance (p < 0.05).

The mean values of the shear bond strength were (in MPa): 22 +/- 7 for Excite DSC/Variolink II without silanization (Group A1); 29 +/- 3 for Excite DSC/Variolink II with silanization (Group A2); 22 +/- 4 for Scotchbond MPP/RelyX ARC without silanization (Group B1); and 26 +/- 5 for Scotchbond MPP/RelyX ARC with silanization (Group B2). Two-way ANOVA revealed a significant effect of silanization (p < 0.01) and did not reveal any significant effect for either the bonding agents (p > 0.1) or the interaction between silanization and bonding agent (p > 0.05). Multinomial logit model did not show any statistical effects on the failure mode by the shear bond strength (p > 0.1). The hypotheses of independence between failure mode (cohesive vs. adhesive) and both the adhesive system (p < 0.05) and silanization (p < 0.05) were rejected by Pearson's chi-square test.

Within the assumptions and limitations of this study (including the small number of specimens) both bonding systems used achieved good shear bond strength values. The application of a silane coupling agent on the ceramic surface after etching with hydrofluoric acid increased the adhesion strength with both adhesive materials used.