Hydrolytic stability and surface roughness of additively and subtractively manufactured CAD/CAM and indirect restorative resin materials

Hydrolytic degradation and changes in surface roughness may compromise the long-term clinical performance of contemporary restorative resin materials, particularly when different manufacturing techniques are used. This study aimed to evaluate the hydrolytic stability and surface roughness of restorative resin materials manufactured using additive and subtractive techniques by assessing their behavior after water immersion. Disc-shaped specimens (10 mm × 1.5 mm) were prepared for the evaluation of water sorption (Wsp) and water solubility (Wsl) using the same specimens (n = 15 per group), and for surface roughness (Ra) analysis using separate specimens (n = 15 per group). Specimens were fabricated from one nanohybrid resin CAD/CAM block (Lava Ultimate, LU), two indirect laboratory composites (Signum, SI; SR Nexco, NX), and two 3D-printed permanent resins (Formlabs Permanent Crown, FL; Saremco print CROWNTEC, SC), according to the manufacturers’ instructions. All specimens were immersed in distilled water for 24 h, 7 days, 28 days, and 60 days. Water sorption and solubility values (µg/mm³) were calculated after recording mass changes to constant mass. Surface roughness was assessed at baseline and after 60 days of water storage using a white-light interferometric optical profilometer. Two-way ANOVA was used to analyze Wsp and Wsl according to material and storage time, Ra was analyzed using one-way ANOVA for baseline comparisons among materials or two-way robust ANOVA for material- and time-dependent analyses when assumptions of normality and homogeneity of variances were not met (α = 0.05). For water sorption, significant main effects of resin composite material and storage time were observed (p < 0.001), with the highest values recorded for the FL and the lowest values for the LU compared with the other materials. For water solubility, both resin composite material (p = 0.005) and storage time (p < 0.001) showed significant main effects, with the NX differing significantly from the LU and SI. Surface roughness differed significantly among resin composite materials (p < 0.001), whereas storage time did not significantly influence Ra (p = 0.145). The hydrolytic behavior of the investigated resin composite materials was material-dependent. Differences in filler system, resin matrix composition, and manufacturing method significantly affected water sorption and solubility, whereas surface roughness was primarily determined by the material and was not significantly influenced by water storage time under the conditions of this study. The selection of indirect restorative materials has a direct impact on hydrolytic stability. Therefore, for long-term restorations, materials and manufacturing methods associated with lower water sorption and solubility should be prioritized to enhance durability and maintain surface quality in the oral environment.