Abstract Background This in vitro investigation evaluated the effect of conditioning protocol and thermal aging on the shear bond strength (SBS) of composite repair to zirconia, a resin matrix CAD/CAM ceramic, and a PMMA-based CAD/CAM polymer. Methods A total of 120 specimens were fabricated from zirconia (Katana Zirconia HT), a resin matrix CAD/CAM ceramic (Grandio Disc), and a PMMA-based CAD/CAM polymer (Structur CAD). All specimens were standardized by airborne-particle abrasion using 50 μm Al₂O₃ (1 bar, 10 s). For zirconia and Grandio Disc, two conditioning protocols were applied: universal adhesive alone (Clearfil Universal Bond Quick) and ceramic primer combined with universal adhesive (Clearfil Ceramic Primer Plus). Structur CAD was treated with the universal adhesive only, in accordance with the manufacturer’s recommendation. Composite (Clearfil Majesty ES-2 Universal) was applied, and SBS (MPa) was measured after 24-hour storage and after thermocycling (5000 cycles, 5–55 °C). Failure modes were evaluated at 40× magnification. Statistical analysis was performed using a three-factor ANOVA with Type II sums of squares computed by model comparison, allowing estimation of the effects considered estimable within the incomplete factorial design. Post hoc pairwise comparisons were performed with Bonferroni correction (α = 0.05). Results Shear bond strength was significantly affected by material ( p < 0.001) and aging ( p < 0.001). For the subset of materials in which both conditioning protocols were available (zirconia and resin matrix CAD/CAM ceramic), conditioning protocol also showed a significant effect ( p = 0.013), with a significant material × conditioning interaction ( p = 0.042). A significant material × aging interaction was observed ( p < 0.001). For Grandio Disc, ceramic primer application did not significantly alter SBS. In zirconia, ceramic primer increased SBS prior to aging ( p = 0.004), whereas this increase in SBS was no longer observed after thermocycling ( p = 0.102). Thermocycling reduced SBS across all groups, most pronouncedly in Structur CAD. Failure modes were predominantly adhesive and mixed. Conclusion Repair bond strength is material-dependent and reduced by thermal aging. Additional ceramic primer application did not improve bond strength for the resin matrix CAD/CAM ceramic and showed no sustained benefit for zirconia after aging. The PMMA-based CAD/CAM polymer exhibited the greatest aging-related reduction, suggesting that material-specific conditioning strategies warrant further investigation.
Janson et al. (Thu,) studied this question.