Purpose: The objective of this study was to evaluate the effect of thermocycling (TC), self-adhesive resin cements and surface conditioning on the microtensile bond strength (μTBS) between feldspathic ceramic blocks and resin cements.
Materials and methods: Fifty-six feldspathic ceramic blocks (10 x 7 x 5 mm) (Vita Mark II) were divided into groups according to the factors "resin cement" (3 cements) and "surface conditioning" (no conditioning or conditioning [10% hydrofluoric acid etching for 5 min + silanization]) (n = 8): group 1: conditioning+Variolink II (control group); group 2: no conditioning+Biscem; group 3: no conditioning+RelyX U100; group 4: no conditioning+Maxcem Elite; group 5: conditioning+ Biscem; group 6: conditioning+RelyX U100; group 7: conditioning+Maxcem Elite. The ceramic-cement blocks were sectioned to produce non-trimmed bar specimens (adhered cross-sectional area: 1 ± 0.1 mm2), which were divided into two storage conditions: dry, μTBS immediately after cutting; TC (12,000x, 5°C/55°C). Statistical significance was determined using two-way ANOVA (7 strategies and 2 storage conditions) and the post-hoc Tukey test (p < 0.05).
Results: Resin cement and thermocycling affected the μTBS significantly (p = 0.001). In the dry condition, group 5 (18 ± 6.5 MPa) presented the lowest values of μTBS when compared to the other groups. TC decreased the mean μTBS values significantly (p < 0.05) for all resin cements tested (9.7 ± 2.3 to 22.1 ± 6.3 MPa), except for the resin cement RelyX U100 (22.1 ± 6.3 MPa). In groups 3 and 4, it was not possible to measure μTBS, since these groups had 100% pre-test failures during sectioning. Moreover, the same occurred in group 2 after TC, where 100% failure was observed during thermocycling (spontaneous failures).
Conclusion: Hydrofluoric acid etching and silanization of the feldspathic ceramic surface are essential for bonding self-adhesive resin cement to a feldspathic ceramic, regardless of the resin cement used. Non-etched ceramic is not recommended.