Self-adhesive cement adhesion to hight strength zirconia ceramic after thermocycles

Objective: The aim of this investigation was to assess the influence of several surface treatments on the shear bond strength of a self-adhesive resin cement to densely sintered zirconia ceramic after artificial thermal aging. Methods: 40 densely sintered zirconia samples were divided into four groups (n=10). Each of them received a different surface treatment: Group MDP - a liquid ceramic primer containing a phosphate functional monomer was applied; Group Sand_110 - ceramic blocks were air-abraded using 110µm Al2O3 particles; Group Sand_MDP - surfaces were sandblasted and conditioned with the primer; Group No_T - no treatment. Composite cylinders were bonded with a self-adhesive resin cement (iCem, Heraeus Kulzer) to ceramic surfaces. After fabrication, specimens were stored in deionized water for 90 days and thermocycled for 5.000 cycles (+5°/+55° C; dwell time: 30s). A fifth group, Sand_Dry (n=10), whose samples were only stored dry for 7 days was prepared by luting 10 composite cylinders to sandblasted (110 µm) zirconia blocks. All bonded specimens were placed in a jig for shear bond strength testing and loaded to failure. The data were analyzed by one-way ANOVA model with α = 0.05; surfaces were examined with a light microscope (x25) to assess the mode of failure. Results: Spontaneous debonding affected an high percentage (57,6%, 23/40) of the thermocycled specimens. Mean shear bond strengths (MPa) obtained from the remaining tested samples were: MDP 0.39 ± 0.00; Sand_110 0.81 ± 0.36; Sand_MDP 2.08 ± 0.73; Sand_Dry 16.23 ± 4.02. Conclusion: Altough immediate bonding values to sandblasted zirconia are high, the tested self-adhesive cement is susceptible to thermal aging. Combined surface treatment using sandblasting and primer application avoided spontaneous debonding and positively affected long-term bond strength.