Influence of CO 2 laser surface-conditioning protocols on interfacial bond strength and optical stability of repaired zirconia ceramics

This in vitro study compared CO2 laser surface-conditioning protocols with airborne-particle abrasion in zirconia repaired using two complete repair systems. Eighty zirconia specimens were allocated according to repair system and surface-conditioning protocol. Conditioning consisted of airborne-particle abrasion with 50-µm Al2O3 or CO2 laser scanning protocols comprising 1, 2, or 3 passes with different scanning directions. Color measurements were obtained before and after 6000 thermocycles, and specimen-level color differences (ΔE*ab) were calculated using the CIELAB formula. Nominal shear bond strength (SBS) was evaluated using a universal testing machine, and surface morphology was qualitatively examined by SEM. Data were analyzed using factorial methods with multiplicity-adjusted comparisons (α = .05). Two-way ANOVA demonstrated significant differences in SBS according to repair systems and surface-conditioning protocols (p=.018). The highest SBS was observed in the airborne-particle abrasion group repaired with feldspathic glass-ceramic. Within this repair system, the 3-pass laser protocol showed significantly higher SBS than the 1- and 2-pass protocols (p<.05), whereas differences among laser-treated composite resin groups were not significant (p>.05). Composite resin repair-system groups demonstrated greater color change after thermocycling than feldspathic glass-ceramic groups. SEM revealed qualitative differences in surface morphology among protocols. Under the tested conditions, airborne-particle abrasion produced the highest SBS values. The laser groups represent distinct scanning protocols rather than an isolated test of repetition alone. Differences between repair approaches should be interpreted at the repair-system level because adhesive chemistry and resin-layer configuration differed. All ΔE*ab values exceeded the perceptibility threshold of 1.2, while composite repair-system means exceeded the acceptability threshold of 2.7.