Structure–Chemistry–Tribology Coupling and Artificial-Intelligence-Assisted Performance Prediction of Cubic Boron Nitride-Reinforced Heat-Polymerized PMMA Denture Base Composites

Abstract

Heat-polymerized poly(methyl methacrylate) (PMMA) is widely used for denture bases but remains susceptible to surface deformation and sliding wear. This study evaluated the structure, chemistry, surface morphology, microhardness, and dry-sliding tribology of PMMA reinforced with 1, 3, and 5 wt.% cubic boron nitride (c-BN). Disk specimens (10 mm diameter × 2 mm thickness) were prepared; ten specimens per group were tested for Vickers microhardness and wear/coefficient of friction, while one representative specimen per group was examined by XRD, ATR-FTIR, and SEM/EDS before and after wear. The PMMA amorphous/semi-amorphous response and characteristic ester bands were retained, whereas c-BN-related diffraction features and B/N signals became more evident with reinforcement. Microhardness increased from 20.00 ± 0.70 to 45.00 ± 1.61 HV0.03. After 1000 m at 10 N and 1 m s−1, mass loss decreased from 32.4 to 9.8 mg and the overall coefficient of friction from 0.58 to 0.28. Post-wear SEM/EDS showed reduced grooving, smearing, and material detachment at higher c-BN contents. Statistical analysis confirmed large composition effects, and composition-window models reproduced the measured hardness and wear trends. Within the tested range, 5 wt.% c-BN provided the strongest surface-hardening and wear-suppression response under controlled dry-sliding conditions.