Comparison of surface properties, microhardness, and tensile bond strength of conventional, milled, and 3D-printed denture base materials: an in vitro study

This in vitro study compared the surface and mechanical properties of denture base materials fabricated using CAD/CAM milling (ML), heat polymerization (HP), and 3D printing (PR) and evaluated the tensile bond strength of two hard reline materials bonded to these denture bases. ML, HP, and PR specimens were prepared for surface roughness, contact angle, Vickers microhardness, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) analyses. For tensile bond strength testing, 120 bonded assemblies were prepared using two hard reline materials: Ufi Gel Hard (UG) and Tokuyama Rebase II (TR). Data were analyzed using one-way and two-way ANOVA with Bonferroni post hoc tests (α = 0.05). Surface roughness did not differ significantly among HP, ML, and PR (0.53 ± 0.12, 0.49 ± 0.07, and 0.51 ± 0.19 µm, respectively; p = 0.803). Carbon and oxygen were the predominant elements in all EDX spectra, whereas minor Na, Cl, Si, and Al signals varied among the analyzed materials and areas. Contact angle differed significantly among the groups ( p = 0.038), with PR showing a higher value than ML (88.64 ± 5.59° vs. 74.33 ± 7.68°; p = 0.039). Microhardness also differed significantly ( p = 0.016), with ML exhibiting the highest value (24.41 ± 3.79 VHN) and PR the lowest (16.32 ± 1.77 VHN; p = 0.024). Tensile bond strength was significantly influenced by denture base material ( p < .001), reline material ( p < .001), and their interaction ( p = 0.001). UG showed higher bond strength than TR for HP (7.11 ± 3.27 vs. 3.99 ± 1.72 MPa; p < 0.001) and PR (5.69 ± 2.94 vs. 3.30 ± 1.21 MPa; p = 0.001), whereas no significant difference was observed for ML ( p = 0.630). Mixed failure was the predominant failures (65.0%). Denture base materials significantly affected wettability, microhardness, and tensile bond strength to hard reline materials but did not influence surface roughness. ML exhibited the highest microhardness, whereas PR resin showed the lowest microhardness and the highest contact angle. Bonding performance depended on the denture base–reline material combination, with UG providing superior bond strength to TR for HP and PR denture bases.