Effect of post-processing washing duration on the optical, surface, and mechanical properties of additively manufactured resins at different printing layer thicknesses: an in vitro study.

This in vitro study evaluated the effect of post-processing washing duration and printing layer thicknesses on the optical, surface, and mechanical properties of additively manufactured (AM) resins across different resin types. Disc specimens (15-mm diameter × 2-mm thickness) of Saremco Print Crowntec (SC) and VarseoSmile TriniQ (VC) were printed at 50 μm and 100 μm (90° orientation; n = 10/group), ultrasonically washed in 99.9% isopropanol (IPA) for 5, 10, or 15 min, post-cured, and polished. Color coordinates (L*, a*, b*), translucency parameter (TP), surface roughness (Ra), and Vickers hardness (VHN) were measured. The effects of washing duration and layer thickness were analyzed within each resin type using two-way ANOVA and Tukey's post hoc test (α = 0.05). Washing duration significantly affected the color coordinates of the VC resin at both layer thicknesses (P < 0.001), and significantly reduced TP values (P < 0.001). In contrast, the SC resin showed no significant differences in color coordinates or TP across washing durations (P ≥ 0.178). Surface roughness increased with prolonged washing in VC at 50 μm (P < 0.001) and in SC at 100 μm (P < 0.001), while no significant differences were observed in VC at 100 μm (P = 0.649) or SC at 50 μm (P = 0.084). Washing duration also reduced Vickers hardness in VC (P = 0.004), particularly at 50 μm, whereas in SC, hardness was primarily influenced by layer thickness rather than washing duration. These findings indicate that the influence of post-processing washing duration on optical, surface, and mechanical properties is material- and thickness-dependent, highlighting the importance of optimizing washing protocols; however, clinical extrapolation of these results should be interpreted with caution.