Abstract
This in vitro study aimed to assess the effects of Al₂O₃ sandblasting and laser treatment, applied individually or in combination, on surface roughness, surface characterization, and shear bond strength (SBS) to resin cement after thermal aging of zirconia with yttria content of 3 mol% and 5 mol%. A total of 192 disk-shaped specimens (Ø12 × 1.2 mm) were prepared from 3Y-TZP (VITA YZ HT) and 5Y-TZP (VITA YZ XT) zirconia. For each zirconia material, specimens were assigned to eight surface-treatment conditions: 50 µm Al₂O₃ sandblasting (50S), 110 µm Al₂O₃ sandblasting (110S), Er,Cr:YSGG laser treatment (ER), nanosecond fiber laser treatment (FL), 50S+ER, 50S+FL, 110S+ER, and 110S+FL, forming 16 material-by-surface-treatment subgroups. In each subgroup, 10 specimens were included in the quantitative Ra and SBS analyses (n=10). These specimens were first evaluated for surface roughness using a 3D optical profilometer, then bonded with a self-adhesive resin cement (Panavia SA Cement Universal), subjected to 5,000 thermal cycles, and tested for SBS. Two additional specimens were prepared separately for descriptive surface characterization in each subgroup: one for atomic force microscopy (AFM) and one for scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). These additional specimens were not included in the statistical sample size and were not subjected to the bonding procedure. Data were analyzed using two-way ANOVA, simple-effects analyses, Tukey HSD tests, and Bonferroni-adjusted material comparisons (α=.05). Surface treatment and the material × surface treatment interaction significantly affected both Ra and SBS (P.05). For 3Y-TZP, 50S+FL produced the highest mean SBS and yielded significantly higher values than ER, FL, 50S+ER, and 110S+FL (P<.05). For 5Y-TZP, ER produced significantly lower SBS than all other treatments (P<.05). Between-material comparisons showed higher SBS for 3Y-TZP in the ER group (P<.001) and higher SBS for 5Y-TZP in the 110S+FL group (P=.045). Sandblasted surfaces exhibited irregular pores, grooves, and abrasive marks, whereas laser-treated surfaces showed a shallower, more uniform topography. Crack-like defects and fissure-like separations were observed in both 110S+FL groups. The effects of surface treatment on Ra and SBS varied by zirconia material, and higher surface roughness did not consistently yield higher SBS. In 3Y-TZP, 50S+FL produced the highest mean SBS but did not differ significantly from 50S, 110S, or 110S+ER. In 5Y-TZP, ER yielded significantly lower SBS than all other treatments, whereas no significant differences were observed among the remaining seven protocols. Crack-like defects and fissure-like separations were observed in both 110S+FL groups; however, their mechanical consequences require further investigation. The bonding response to surface treatment was dependent on the zirconia material, and no single protocol demonstrated superior performance across both materials. Standalone Er,Cr:YSGG laser treatment produced an unfavorable SBS response in 5Y-TZP under the tested conditions. The 110S+FL protocol should be interpreted cautiously because crack-like surface defects and fissure-like separations were observed. Additional long-term studies incorporating fracture-strength testing, thermomechanical aging, and cyclic fatigue loading, together with prospective clinical investigations under intraoral conditions, are required before definitive clinical recommendations can be made.