Effect of print orientation on sorption, solubility, and monomer elution of 3D printed resin restorative materials

Statement of problem
The long-term stability and clinical safety of 3 dimensional (3D) printed dental restorative resins in the oral cavity remains uncertain, despite their increased use.
Purpose
The purpose of this in vitro study was to evaluate the impact of different printing orientations on the sorption, solubility, and monomer elution of various 3D printed definitive and interim dental restorative resins compared with that of milled resin materials.
Material and methods
Two 3D printed materials for definitive restoration, VarseoSmile Crownplus (VCP) and Crowntec (CT) and 3 for interim restorations, C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC), were additively manufactured in 3 orientations (0, 45, and 90 degrees). A digital light processing (DLP) 3D printer (ASIGA MAX UV) was used with postprocessing parameters as per the manufacturers’ recommendations. Specimens for sorption and solubility (14×14×1 mm) were stored in artificial saliva at 37 °C and measured over a 90-day period (n=6). Specimens used for monomer elution (14×14×2 mm) were stored in a 75% ethanol and water (E/W) solution, and elution was assessed after 1 and 7 days using ultra-high performance liquid chromatography coupled with mass spectrometry (UHPLC/MS) (n=4). Milled materials, Lava Ultimate (LU) and Telio CAD (TC), were used as controls. Multiple way ANOVA, 1-way ANOVA, and Tukey HSD post hoc tests (α=.05) were used to analyze the data.
Results
Printing orientation significantly influenced the sorption and solubility of 3D printed resins (P=.008) but did not influence their monomer elution (P=.774). All materials met the recommended International Organization for Standardization (ISO) 4049 standards for sorption and solubility, except ND, which exceeded the maximum recommended sorption value (57.1 μg/mm3). The 3D printed interim materials ND, DT, and GC exhibited greater sorption (27.3-57.1 μg/mm3), solubility (2.6-3.6 μg/mm3), and monomer elution (53.2-87.4 μmol/L) compared with the definitive materials VCP (9.8-0.9 μg/mm3, 50.5 μmol/L) and CT (9.4-0.02 μg/mm3, 51.3 μmol/L). All 3D printed resins exhibited lower sorption (9.4-30.1 μg/mm3) but significantly higher monomer elution (50.5-87.4 μmol/L) compared with LU (36.1 μg/mm3, 7.6 μmol/L), except for ND, which had the highest sorption values (P<.001). TC exhibited sorption values (23.6 μg/mm3) that were intermediate between those of the definitive and interim 3D printed materials. Filler weight correlated negatively with sorption (r2=.739) and solubility (r2=.896) (P<.001) but did not correlate with monomer elution.
Conclusions
Sorption, solubility, and monomer elution were more influenced by the type of material than the printing orientation. Definitive 3D printed materials demonstrated less sorption, solubility, and monomer elution compared with the interim 3D printed materials. All 3D printed resins had greater amounts of eluted residual monomers compared with the milled resin block LU. The 3D printed resins primarily eluted bisphenol A ethoxylate dimethacrylate (bis-EMA) and urethane dimethacrylate (UDMA) monomers, with all concentrations remaining below the cytotoxic levels established in previous studies.