Effects of Sintering Protocol and Er:YAG Laser Application Mode on the Bond Strength of Monolithic Zirconia

Objective: To evaluate the combined effects of slow and rapid sintering protocols and Er:YAG laser application modes (non-contact and slight-contact) at different power settings on the microshear bond strength (μSBS) of monolithic 5Y-TZP zirconia to resin cement. Materials and Methods: Eighty rectangular 5Y-TZP zirconia specimens were fabricated and randomly assigned to two sintering protocols: slow and rapid (n = 40 each). Specimens were further subdivided into five surface treatment groups (n = 8): control, 3 W non-contact, 5 W non-contact, 3 W slight-contact, and 5 W slight-contact Er:YAG laser irradiation. Following surface treatment, a 10-MDP-containing universal adhesive was applied, and composite resin cylinders were bonded. μSBS testing was performed using a universal testing machine. Data were analyzed using two-way ANOVA and Bonferroni post hoc tests (α = 0.05).Results: Both sintering protocol (p < 0.001) and surface treatment procedure (p < 0.001) significantly influenced bond strength, whereas their interaction was not significant (p = 0.758). Rapid sintering yielded significantly higher μSBS values than slow sintering. The highest bond strength was observed in the 5 W slight-contact laser group following rapid sintering (156.2 ± 10.5 MPa), whereas the lowest values were recorded in the 3 W non-contact laser group with slow sintering (85.42 ± 4.5 MPa). The 5 W slight-contact laser group showed the highest bond strength among surface-treatment groups (p < 0.05).Conclusion: Both sintering protocol and laser application mode significantly affect zirconia-resin bond strength. Slight-contact Er:YAG laser irradiation may improve bonding performance, particularly under rapid sintering conditions.