Mechanical and surface properties of PMMA denture base resins fabricated by compression molding, fluid resin, milling, and 3D printing techniques

Different fabrication techniques for polymethyl methacrylate (PMMA) denture base resins may influence their mechanical and surface properties as well as their resistance to thermal aging. However, studies comprehensively comparing the mechanical and surface properties of conventionally and digitally fabricated PMMA denture base resins before and after standardized thermocycling remain limited. Therefore, the aim of this in vitro study was to compare the flexural strength, elastic modulus, surface hardness, and surface roughness of PMMA denture base resins fabricated by compression molding, fluid resin processing, milling, and 3D printing before and after thermocycling. Eighty PMMA specimens were fabricated using compression molding, fluid resin, milling, and 3D printing. Flexural strength and elastic modulus were evaluated at baseline and after thermocycling using separate matched specimens because the three-point bending test was destructive, whereas surface hardness and surface roughness were measured repeatedly on the same specimens before and after thermocycling. Flexural strength and elastic modulus were assessed using a three-point bending test, while surface hardness and surface roughness were evaluated using Vickers microhardness testing and profilometry. Statistical analyses were performed at α = 0.05. Significant differences were observed among the material–processing combinations for all parameters both before and after thermocycling ( P < 0.001). The 3D-printed group showed the lowest flexural strength, elastic modulus, and surface hardness and the highest surface roughness. After thermocycling, flexural strength decreased significantly in the 3D-printed and fluid resin groups ( P < 0.05). Elastic modulus decreased significantly in the milled and 3D-printed groups ( P < 0.01). Surface hardness decreased significantly in the milled group but increased significantly in the fluid resin group ( P < 0.01). Surface roughness increased significantly in the compression-molded, milled, and 3D-printed groups ( P < 0.05). Under the tested conditions, the compression-molded material showed no significant changes in flexural strength, elastic modulus, or surface hardness after thermocycling, although surface roughness increased significantly. The fluid resin material showed a significant decrease in flexural strength and a significant increase in surface hardness, while elastic modulus and surface roughness remained statistically unchanged. The milled material showed significant reductions in elastic modulus and surface hardness, together with an increase in surface roughness, whereas the change in flexural strength was not significant. The 3D-printed material exhibited the lowest initial mechanical properties and showed significant reductions in flexural strength and elastic modulus and a significant increase in surface roughness after thermocycling.