Hydrolytic Stability and Optical Properties of 3D-Printed, Milled, and Conventional Interim Resins After Thermal Aging

This study evaluated the effects of thermocycling on surface roughness (Ra), gloss (GU), color stability (ΔE00), and water sorption of interim materials manufactured by three methods. Disc specimens (n = 20/group) were fabricated from a conventional bis-acryl (PreVISION® Temp), a computer-aided design/computer-aided manufacturing (CAD/CAM)-milled methacrylate-based composite (StructurCAD Disc®), and a 3D-printed resin composite (Alias Dental Temp C&B®). Two disc dimensions were used: 10 × 2 mm for Ra, GU, and color, and 15 × 1 mm for water sorption. Measurements were performed before and after thermocycling (10,000 cycles; 5–55 °C). Nonparametric tests were used (α = 0.05). After thermocycling, Ra increased in the conventional and 3D-printed groups, whereas the milled group demonstrated a decrease (p < 0.05). GU decreased across all groups (p < 0.001) and differed among materials (p = 0.021), with a significant difference only between milled and 3D-printed groups. Color stability differed among materials (p < 0.001): the milled group showed the lowest ΔE00 perceptibility threshold (below PT00 = 0.81), whereas conventional and 3D-printed groups exceeded the acceptability threshold (AT00 = 1.81). Water sorption differed among groups (p < 0.001), with a significant difference between the milled and 3D-printed groups (p < 0.001). The tested 3D-printed material exhibited less favorable post-thermocycling optical properties, whereas the evaluated CAD/CAM-milled material demonstrated more favorable overall surface and optical performance under the applied aging conditions.