This study evaluated the effect of incorporating boric acid (BA) at different concentrations on the flexural strength, color stability, and microhardness of 3D-printed permanent crown resins. Disk-shaped specimens (15 × 2 mm) were fabricated for color stability and Vickers microhardness testing, and bar-shaped specimens (25 × 2 × 2 mm) were prepared for flexural strength evaluation using a masked stereolithography (MSLA) printer. BA was incorporated into the resin at 0% (control), 1%, 2%, and 3% (w/w). Flexural strength (n = 7 per group) was measured using a three-point bending test, microhardness (n = 7 per group) was assessed with the Vickers method, and color stability (n = 22 per group) was evaluated using ΔE₀₀ values at 3 time points: immediately after post-curing (T0), 30 min after post-curing (T1), and 60 min after post-curing (T2). Surface morphology was examined using field-emission scanning electron microscopy (FE-SEM). Data were analyzed using one-way and two-way ANOVA followed by Tukey’s HSD post hoc tests (α = 0.05). BA incorporation significantly affected flexural strength (p < 0.05), with the 3% BA group showing the highest mean value (177.92 ± 38.58 MPa), significantly higher than the control (p = 0.001), 1% (p = 0.002), and 2% (p = 0.011) groups. Microhardness showed an increasing trend with higher BA concentrations but did not reach statistical significance (p > 0.05). Color stability was adversely affected by BA addition (p < 0.001), as ΔE₀₀ values increased progressively from T0 to T2, with the 3% BA group consistently exceeding both perceptibility (ΔE₀₀ > 0.8) and clinical acceptability thresholds (ΔE₀₀ > 1.8) at all time points. BA incorporation enhanced flexural strength in a concentration-dependent manner, while microhardness improvements were not statistically significant, and color stability was compromised at higher concentrations. BA-modified resins may be suitable for posterior restorations where mechanical performance is prioritized.

Post-curing is a critical step in the fabrication of 3D-printed resin-based occlusal splints because it influences polymerization efficiency and final mate

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.

This in vitro study evaluated the effects of printing orientation and postpolymerization time on the color stability, gloss, surface roughness, and Vickers hardness of an occlusal splint material fabricated by additive manufacturing after artificial aging. Disc-shaped specimens were fabricated from a photopolymer occlusal splint resin at 0-degree, 45-degree, and 90-degree printing orientations and subjected to 10- or 20-minute postpolymerization. Separate specimen sets were used for optical, surface-roughness, and Vickers-hardness evaluations. Color stability and gloss specimens were thermocycled and then immersed in distilled water, coffee, or black tea. Surface roughness and Vickers hardness were measured before and after thermocycling. Color differences were calculated by using the CIEDE2000 formula. Data were analyzed by using Generalized Estimating Equations, effect-size estimates, and Bonferroni-adjusted multiple comparisons (α=.05). Printing orientation affected color stability after coffee (p=.016; ηp²=0.064) and black tea immersion (p=.009; ηp²=0.072), gloss (p<.001; ηp²=0.120), and Vickers hardness (p<.001; ηp²=0.115), but not surface roughness. Postpolymerization time affected coffee-related color change (p=.030; ηp²=0.038) and gloss (p=.017; ηp²=0.040). Aging condition showed the largest effects across outcomes, particularly for color stability, gloss, and Vickers hardness (ηp²=0.439 to 0.903). Staining media increased color change and reduced gloss, whereas thermocycling increased surface roughness and substantially reduced Vickers hardness. Within the limitations of this in vitro study and for the tested material-printer-postpolymerization workflow, printing orientation, postpolymerization time, and aging condition influenced the evaluated properties, although the magnitude and direction of these effects varied by outcome. Manufacturing parameters and aging conditions may affect the optical, surface, and mechanical behavior of occlusal splints fabricated by additive manufacturing. The selection of printing orientation and postpolymerization time should consider esthetic stability, surface quality, and mechanical performance.

Background: This in vitro study evaluated the effect of hydroxyapatite nanoparticle (nano-HAp) incorporation on surface roughness and Vickers hardness of a 3D-printed crown resin after thermocycling. Methods: Disk-shaped specimens (N = 84) were modified and fabricated with 0%, 1%, 2%, and 3% nano-HAp. Surface roughness (Ra) and Vickers hardness (VHN) were measured before and after thermocycling (5000 cycles). Surface morphology was qualitatively assessed using FE-SEM. Data were analyzed using two-way mixed-design ANOVA (α = 0.05). Results: Thermocycling increased surface roughness and reduced hardness in all groups. Ra values were highest in the 3% nano-HAp group after thermocycling (1.16 ± 0.47 µm). Baseline Vickers hardness differed significantly among nano-HAp concentrations, and hardness decreased after thermocycling in all groups; however, the 3% nano-HAp group exhibited the highest post-thermocycling hardness values (24.66 ± 1.51 VHN), which should be interpreted in the context of its higher baseline hardness. FE-SEM observations suggested increased surface irregularities with higher nano-HAp concentrations after thermocycling. Conclusions: Nano-HAp incorporation influenced both surface and mechanical properties, with 3% concentration showing higher hardness after aging but increased roughness.

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.