Surface engineering of zirconia to improve indirect composite bonding: an in vitro study

Porcelain-layered zirconia restorations are susceptible to chipping and delamination. This study evaluated the effect of different surface treatments on the shear bond strength (SBS) of indirect composite resin to zirconia. Fifty zirconia specimens were randomly assigned to five groups (n = 10): Control. 50-µm aluminum oxide (Al2O3) sandblasting (SB50). 110-µm Al2O3 sandblasting (SB110). Glaze + hydrofluoric etching (Gl + HF). SB50 followed by glaze + hydrofluoric etching (SB50 + Gl + HF). After composite bonding and thermocycling (5,000 cycles), SBS was tested and failure modes were assessed. Data were analyzed with one-way ANOVA and Bonferroni post-hoc tests. SBS differed significantly among groups (p < 0.001). SB110 (11.134 ± 0.866 MPa) and SB50 + Gl + HF (12.229 ± 1.101 MPa) showed statistically equivalent bond strength (p = 0.133, effect size -1.1) and were significantly higher than other groups (p < 0.05, effect size 0.913). The Gl + HF group had the lowest strength (3.771 ± 0.905 MPa, p < 0.05, effect size 0.913). Indirect composite could be a viable alternative to porcelain for veneering zirconia restorations in the short term. Sandblasting with 110 µm alumina particles provided high bond strength equivalent to the more complex SB50 + Gl + HF protocol, offering a clinically simpler and safer surface treatment option.