Effects of postwashing with contaminated ethanol solutions on 3D printed materials: Mechanical properties, dimensional trueness, and biocompatibility

Abstract

Statement of problem. Whether postwashing treatment with a contaminated ethanol solution adversely affects the biomechanical properties of 3-dimensionally (3D) printed resin restorations is unclear. Purpose. The aim of this in vitro study was to determine the impact of postwashing treatment using contaminated ethanol solutions on the mechanical properties, degree of conversion (DC) of resin monomers, biocompatibility, 3D trueness of 3D printed products, and ethanol contamination levels. Material and methods. Specimens were fabricated from 3D models using 2 resins: NextDent C&B resin (C&B) and NextDent C&B MFH resin (MFH). The specimens were ultrasonically cleaned in an ethanol solution containing unpolymerized resin at various concentrations: 0%, 5%, 10%, 15%, 20%, and 30%. Postwashing treatment was conducted at 60 degrees C for 30 minutes in accordance with the manufacturer&apos;s recommendations. The following properties and outcomes were evaluated with their respective sample sizes using appropriate methods: scanning electron microscope (SEM, & times;1000, n=3), degree of conversion (DC, n=15), Vickers hardness (VH, n=15), flexural strength (FS, n=15), 3D trueness (n=15), cell viability (n=18), 5-ethynyl-2 &apos;-deoxyuridine (EdU) staining (n=3), and the turbidity of the contaminated ethanol solutions (n=15). Statistical analyses were performed using 1-way ANOVA after confirming the normality of the data, with comparisons restricted to contamination groups within the same resin type. Post hoc analysis was conducted using the Tukey HSD or the Games-Howell test, depending on the variance homogeneity (alpha=.05 or .001). Results. Surface impurities and particle adsorption were observed via SEM at contamination levels >= 10%. DC decreased significantly from 62.5% to 32.7% (C&B) and from 71.4% to 57.1% (MFH) at contamination >= 5% (P<.001). The Vickers hardness number (VHN) declined significantly at >= 5%for C &B (from 12.97 to 9.01) and at >= 10% for MFH (from 14.76 to 11.52) (P<.001). Flexural strength remained stable across all groups (P>.05). Morphological deviations increased with contamination, with root mean square deviations rising from 51.5 to 105.8 & micro;m (C&B) and from 64.1 to 82.6 & micro;m (MFH) (P<.001); C&B crowns showed expansion, whereas MFH crowns showed shrinkage. Cell viability decreased significantly at >= 10% (C&B) and >= 5% (MFH) contamination (P<.05) but remained above 80% in all groups. EdU-positive cell percentage declined from 23.6% to 16.8% (C&B) and 23.7% to 18.0% (MFH) with increasing contamination (P<.05). Turbidity rose sharply with contamination, exceeding 1000 NTU at 5% (C&B: 1079 NTU; MFH: 1221 NTU), indicating substantial resin-derived particle accumulation. Conclusions. Postwashing treatment using contaminated ethanol solutions containing unpolymerized resin negatively impacted the surface morphology of resin products, significantly reducing their DC, VH, 3D trueness, and biocompatibility while having no significant effect on FS. Despite the contaminated ethanol solutions exceeding the turbidimeter limit of 1000 NTU, the 5% groups remain near this threshold, yielding more-reliable data and serving as operational indicators for evaluating postwashing compliance.