Color stability of CAD/CAM and additively manufactured resin materials: influence of surface treatment and layer thickness - an in vitro study

The increasing establishment of digital workflows in dentistry has brought both subtractive CAD/CAM processes and additive manufacturing techniques for fixed dental restorations into focus. This in vitro study aimed to compare the color stability of a CAD/CAM nanohybrid composite with a ceramic-filled, additively manufactured resin and to investigate how surface treatment and layer thickness influence this stability. Each thirty rectangular specimens in two different thicknesses (0.5 and 1.0 mm) were fabricated from two materials: a CAD/CAM nanohybrid composite (Grandio blocs) and a ceramic-filled 3D-printing resin (Permanent Crown Resin). Specimens of each material were assigned to three surface conditions: untreated, polished, or glazed. To simulate clinically relevant discoloration, specimens were stored for 28 days with one half immersed in coffee. Spectrophotometric measurements were performed daily during the first week and on days 14, 21, and 28. Changes in color (ΔE) were calculated. One-way ANOVA followed by Tukey's post hoc test was performed. All experimental groups showed a time-dependent increase in color change relative to baseline during coffee storage, with the greatest increase occurring during the initial days. Within the limitations of this in vitro study, the CAD/CAM nanohybrid composite showed more favorable color stability than the additively manufactured resin. Surface treatment generally improved color stability, with more consistent effects in the additively manufactured material than in the CAD/CAM composite. In addition, specimens with reduced layer thickness showed greater color changes than thicker specimens.