Er YAG laser debonding of zirconia restorations from titanium abutments depends on cement type water content and thickness

This study investigated the influence of cement type and water content on Er: YAG laser debonding efficiency and residual bond strength between zirconia restorations and titanium abutments with varying zirconia thicknesses. One hundred and sixty titanium-zirconia specimens were fabricated with zirconia thicknesses of 1 mm, 2 mm, and 3 mm. Specimens were divided into four groups (n = 40 per group) based on cement type: glass ionomer cement (Ketac Cem Easymix, KCE), modified glass ionomer (KCE with 35 µL water, KCEW), resin cement (Clearfil SA Luting, CSAL), and modified resin cement (CSAL with 35 µL water, CSALW). Each group was further subdivided by zirconia thickness (n = 10 per subgroup). After 48 h of storage at 100% relative humidity, Er: YAG laser irradiation (2940 nm) was applied for debonding, with the debonding time recorded. Specimens not debonded within 2 min underwent shear bond strength testing. A non laser irradiated 2 mm zirconia group served as the control. Statistical analysis employed Kruskal-Wallis and Wilcoxon tests with Bonferroni correction. Interfacial morphology was examined using scanning electron microscopy (SEM). The KCE and KCEW groups demonstrated significantly higher debonding rates at 1 mm and 2 mm thicknesses (> 50%), while the CSAL and CSALW groups showed minimal debonding(< 40%), particularly at 3 mm. The Kruskal-Wallis test indicated significant variations in both debonding time (χ² = 72.9, p < 0.001) and shear bond strength (χ² =107.8, p < 0.001) across groups. Debonding time varied significantly among groups, with the shortest times observed for KCE/KCEW at thinner thicknesses. Residual bond strength was comparable among KCE, KCEW, and CSALW groups; however, CSAL at 1 mm and 2 mm exhibited significantly lower strength versus 3 mm and control (p < 0.01). SEM analysis revealed microstructural alterations at zirconia-cement interfaces post-irradiation. Cement type, water content and restoration thickness significantly influence the debonding efficiency of zirconia crowns on titanium abutments using Er: YAG laser. Specifically, glass ionomer cements facilitate more efficient debonding, whereas for resin cements, water modification introduces a trade-off between bond strength and debonding performance. Debonding efficiency decreases substantially as restoration thickness increases. Clinically, these parameters are essential for optimizing the feasibility of laser-assisted crown retrieval.