Effects of Additional Ethanol Exposure and Post-Curing Time on Color Stability, Water Sorption, and Solubility of 3D-Printed Permanent Restorative Resins

Background: The aim of this study was to evaluate the effects of additional ethanol exposure and additional post-curing times, applied following the standard post-printing protocols recommended by the manufacturer, on the color stability, water sorption, and solubility of two 3D-printed permanent restorative resins. Methods: A total of 160 disk specimens were prepared using Crowntec and VarseoSmile TriniQ. For each material, two independent experimental arms were established: additional ethanol exposure and additional post-curing. Within each arm, separate specimens were assigned to 0 (control), 3, 10, or 30 min conditions following completion of the manufacturer-recommended standard post-processing protocol. Water sorption (Wsp) and solubility (Wsl) were evaluated first using a gravimetric approach, after which the same conditioned specimens were subjected to color evaluation using the CIEDE2000 (ΔE00) system during a 28-day continuous black tea immersion challenge. Results: Additional ethanol exposure resulted in lower ΔE00 values on Day 1 compared to the control groups for both materials; however, this difference did not persist over time. In Crowntec, 30 min of additional post-curing was associated with lower Wsp than the 3- and 10-min conditions and with lower ΔE00 at later color-evaluation time points. In VarseoSmile TriniQ, 30 min of additional ethanol exposure resulted in higher Wsp than the 10-min condition. In VarseoSmile TriniQ, however, extended post-curing did not provide a similar benefit. Additional processing durations did not significantly alter Wsl within either material in the independent-group analyses; however, factorial analysis identified a significant material × duration interaction in the post-curing arm, and VarseoSmile TriniQ exhibited higher Wsl values than Crowntec under their respective manufacturer-specific processing workflows. Conclusions: Extending post-processing beyond manufacturer-validated protocols did not consistently improve material performance and, under some conditions, was associated with less favorable outcomes. Accordingly, the additional ethanol exposures investigated here should be regarded as experimental over-processing challenges rather than as alternative clinically recommended washing protocols.