Effects of silica particle size on the mechanical, surface and printing-trueness properties of 3D-printing dental resin

This study investigated the effects of silicon dioxide (SiO₂, silica) particle size on the mechanical, surface, and printing-trueness properties of 3D-printed dental resin. Silica nanoparticles (5-20 nm) and microparticles (0.5-10 μm) were incorporated at 1 wt% and 2 wt% into a commercial 3D-printing resin. The specimens were printed and postprocessed under standard conditions. Particle size distribution was determined using a Particle Size Analyzer. Surface characteristics such as color difference and roughness were analyzed using a profilometer and spectrophotometer. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) assessed the microstructure and silica dispersion. Degree of conversion (DC), flexural strength and Vickers hardness were evaluated to demonstrate the polymerization efficiency and mechanical performance of the modified resins. Printing trueness was measured using digital superimposition analysis of customized crowns by RMS (root mean square) values. Biocompatibility was evaluated via WST-8 assay using HGF cells treated with 24 h and 72 h extracts of the specimens. Results showed that small silica particles at 2 wt% produced a whitening effect (ΔE = 27.15 ± 0.60), while also improving surface smoothness (55.60 ± 7.91 nm). In contrast, large silica particles at 2 wt% increased surface roughness (114.73 ± 8.19 nm). The highest degree of conversion (P < 0.01) was also observed in the small-particle 2 wt% group. Large particles at 2 wt% yielded the highest flexural strength (134.03 ± 4.65 MPa) and Vickers hardness (17.12 ± 0.19 HV). SEM and EDS images confirmed a uniform silica dispersion and distinct morphology depending on particle size. All silica-containing resins showed comparable HGF viability to controls at both 24 and 72 h, regardless of particle size or concentration. Trueness analyses of crowns indicated reduced accuracy for both small (108.94 ± 4.14 μm) and large (105.38 ± 7.27 μm) silica particles at 2 wt%. In conclusion, silica incorporation significantly alters resin properties but with satisfying biocompatibility. Large particles enhance mechanical strength but reduce smoothness and trueness. Small particles improve DC and surface smoothness with whitening effects. Optimizing silica size and concentration is crucial for dental resin applications.