Effect of ultraviolet surface treatment on color stability, surface water contact angle and bond strength of monolithic zirconia

This laboratory study investigated the impact of ultraviolet light exposure on the color, surface water contact angle, and resin cement–zirconia bond strength. Fourty-five zirconia specimens were randomly divided into three groups (n = 15): untreated (control), short exposure (15 min), and prolonged exposure (24 h)0.250 nm UV-C irradiation was used as the surface treatment method to evaluate its influence on zirconia’s color stability, surface water contact angle, and bonding behavior. Color measurements were recorded with a spectrophotometer, and contact angle measurements were obtained to assess surface water contact angle. Following UV irradiation, resin cement–zirconia bond strength was measured using a shear bond strength test. Statistical analysis was performed using one-way ANOVA and Tukey’s post hoc test (α = 0.05). Mean ΔE values were 3.77 ± 0.42 for the 15-min group and 6.77 ± 1.45 for the 24-h group, both exceeding the clinical perceptibility threshold. Short-term UV irradiation significantly reduced the surface water contact angle (p < 0.05), whereas no significant change was observed after 24 h. The mean SBS values were 4.2 ± 1.1 MPa for the control group, 4.9 ± 1.3 MPa for the 15-min group, and 3.8 ± 1.1 MPa for the 24-h group, with no statistically significant differences among the groups (p = 0.140). Weibull analysis showed higher bond-strength reliability after short-term UV exposure than after prolonged irradiation. Ultraviolet surface treatment improved zirconia surface wettability but did not result in a clinically meaningful enhancement of resin–zirconia bond strength. Prolonged UV exposure caused perceptible color changes, potentially limiting its use in esthetic areas. UV irradiation alone appears to offer limited clinical benefit unless combined with effective chemical bonding strategies.