ANALYSIS OF CHANGES IN TRIBOLOGICAL PROPERTIES OF PMMA DENTURES UNDER DRY FRICTION CONDITIONS DURING BRUXISM

<ns3:p>This study investigated the influence of frequency, load, and test duration on the wear behavior of polymethyl methacrylate (PMMA) friction pairs under dry sliding conditions. Tribological tests were conducted using an MFT-5000 tribotester in a reciprocating pin-on-disc configuration simulating back-and-forth motion typical of tooth-grinding activity. Surface roughness parameters were evaluated using a Mahr profilometer with MarSurf XT20 software. The experimental program consisted of two test series designed to separately assess the influence of sliding frequency and normal load. In the first series, friction frequency was varied (1, 2, and 4 Hz) at a constant load of 70 N. In the second series, normal load was modified (50, 70, and 100 N) at a fixed frequency of 2 Hz. Each test lasted 15 minutes. The results demonstrated a clear, non-linear intensification of wear with increasing mechanical stress. The highest arithmetic mean surface height was observed at 100 N (Sa = 11.778 m), whereas the lowest value occurred at 50 N (Sa = 0.288 m), confirming that normal load is the dominant parameter governing wear regime transitions. Increasing sliding frequency also accelerated surface degradation, though to a lesser extent than load. The wear mechanism evolved from mild adhesive smoothing at 50 N to intermediate adhesive–microfatigue interaction at 70 N, and finally to severe viscoelastic–plastic deformation and material displacement at 100 N. These findings provide a practical basis for controlled acceleration of tribological testing while preserving representative degradation mechanisms relevant to dental PMMA applications.</ns3:p>