Effect of modified glaze application protocols on color stability of 3D-printed permanent dental resins

PURPOSE: This study aimed to evaluate the effect of four different surface‑treatment protocols-including a novel Optiglaze before post‑curing approach on the surface morphology and color stability of two 3D‑printed permanent resin materials following thermocycling and staining procedures. METHODS: Two permanent crown materials were fabricated and then divided into four groups, each subjected to one of the following surface‑treatment protocols: mechanical polishing (MP), Optiglaze applied after post‑curing (OG‑Post), Optiglaze applied before post‑curing (OG‑Pre), or a combined pre‑/post‑curing Optiglaze protocol (OG‑Pre/Post). A total of 248 specimens (n = 10 per material × surface treatment × staining solution) were prepared. Color measurements were performed at baseline, after 10,000 thermocycles, and following 30‑day immersion in artificial saliva, coffee, or red wine using a spectrophotometer (VITA EasyShade V). Color changes were assessed using the CIEDE2000 (ΔE₀₀) formula in relation to perceptibility (PT₀₀ = 0.81) and acceptability (AT₀₀ = 1.81) thresholds. Data were analyzed using mixed‑design ANOVA and adjusted post‑hoc tests with statistical significance set at p < 0.05. Surface morphology and glaze layer characteristics were examined using field‑emission scanning electron microscopy (FE‑SEM) on representative specimens, including both surface and cross‑sectional analyses (n = 1). RESULTS: Thermocycling significantly increased ΔE₀₀ values in all groups (p < 0.05), with the greatest change observed in the VarseoSmile MP specimens, which exceeded AT₀₀. Staining solutions significantly affected color change (p < 0.001), and coffee and red wine caused ΔE₀₀ values above AT₀₀ across all groups. OG‑Pre demonstrated significantly lower ΔE₀₀ values than OG‑Post (p < 0.05), particularly in Crowntec specimens. MP groups exhibited significantly higher ΔE₀₀ values than all Optiglaze‑treated groups (p < 0.05). FE‑SEM analysis revealed smoother, more homogeneous, and better‑integrated glaze layers in OG‑Pre specimens, with fewer surface defects. CONCLUSION: Applying Optiglaze before post‑curing represents an effective surface treatment strategy that enhances glaze integration, improves surface morphology, and provides superior resistance to discoloration compared with conventional post‑cure glazing.