Effect of different surface treatment protocols on surface topography, biaxial flexural strength and compositional alteration of monolithic translucent multi-layered zirconia

This study aimed to compare the effects of different surface treatment protocols on surface topography, crystalline phase characteristics, biaxial flexural strength (BFS), and failure patterns of two contemporary monolithic zirconia systems after artificial aging. Ninety-six disc-shaped specimens were fabricated from two partially stabilized multilayered zirconia materials: Cercon xt ML and Katana STML. Specimens were randomly allocated into four groups ( n = 12) according to surface treatment: (1) untreated control, (2) Er, Cr: YSGG laser irradiation (6 W), (3) sandblasting with < 50 μm Al₂O₃, and (4) lithium silicate spray (LSS) followed by etching with 9.5% hydrofluoric acid for 100s. Surface morphology was examined using SEM. All specimens were thermocycled for 10,000 cycles prior to BFS testing and phase analysis. Data were analyzed using two-way and one-way ANOVA, with t-tests for intermaterial comparisons (α = 0.05). Fractographic analysis was performed on representative specimens. BFS trends were similar for both materials. LSS demonstrated the highest mean BFS values, whereas sandblasting yielded the lowest values and induced a pronounced tetragonal-to-monoclinic phase transformation. Laser treatment preserved surface integrity with minimal structural alteration. Surface treatment effects were material- dependent. Lithium silicate spray may represent a safer alternative to sandblasting for enhancing mechanical performance while preserving zirconia phase stability.