Colour Stability of Different Zirconia Generations Against Tobacco Smoke and Colouring Beverages: A Comparative Study on Glazing Vs. Polishing

Background. Long-term aesthetic success of all-ceramic restorations depends heavily on their resistance to surface discoloration under complex intraoral conditions. This study aimed to evaluate the impact of surface finishing methods on the colour stability of leucite-reinforced glass ceramic(LGC) and two generations of monolithic zirconia after chewing simulation and exposure to coffee, black tea, and tobacco smoke. Methods. One hundred sixty-two specimens prepared from LGC, 3mol% and 5mol% yttria-stabilized-zirconia(3Y-TZP/5Y-TZP) were divided into glazed and manually polished subgroups(N = 54/material,n = 27/surface treatment).All specimens were first subjected to mechanical wear and thermal aging in a chewing simulator(240.000 cycles,55 N,50–55 ^° C). Specimens were then subdivided(n = 9) and exposed to coffee, black tea(12 days), or tobacco smoke(105 cigarettes) in a custom-made smoke simulator. Colour coordinates(L*a*b*) were measured using a spectrophotometer before and after staining, and overall colour changes(ΔE) were calculated. Data were analyzed using robust three-way ANOVA and Yuen’s test with Bonferroni correction test( alpha =  0.05). Results. All experimental groups exceeded the clinical perceptibility threshold(ΔE > 3.7). Staining agent and surface treatment interactions were statistically significant( P <  0.05). Overall, coffee induced the highest mean discoloration(ΔE = 5.75 ± 0.26), followed by tobacco smoke(ΔE = 4.91 ± 0.27) and tea(ΔE = 4.68 ± 0.26). For 3Y-TZP, glazed specimens demonstrated significantly higher resistance to coffee discoloration than polished specimens( P <  0.05). For LGC, glazed specimens exhibited higher staining under tobacco smoke exposure compared to polished specimens. Conclusions. Mechanical wear followed by chromogenic exposure significantly alters ceramic colour stability. Coffee poses the highest overall staining risk across tested materials. While glazing provides protection against dietary staining for 3Y-TZP, surface finishing selection should be customized based on material composition and patient-specific habits. Clinical trial number: Not applicable