Evaluation of eggshell abrasives as a sustainable polishing alternative: surface roughness of provisional polymethyl methacrylate fabricated by different techniques

The aim of this study was to evaluate the effects of eggshell powder (40 µm and 60 µm) and pumice on the surface roughness of provisional polymethyl methacrylate (PMMA) materials fabricated using different techniques before and after thermal cycling. PMMA specimens were fabricated using conventional autopolymerizing, Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) milling, and three-dimensional (3D) printing techniques. For each fabrication method, specimens were divided according to abrasive type (40 µm eggshell, 60 µm eggshell, or pumice). Ten disc-shaped specimens were prepared per subgroup. Surface roughness (Ra, µm) was measured using a profilometer before and after thermal cycling. Representative specimens were also evaluated using scanning electron microscopy (SEM). Statistical analyses were performed to assess the effects of fabrication method, abrasive type, and thermal cycling on surface roughness. Surface roughness differences were consistently observed among fabrication methods, whereas the effect of abrasive type was limited and inconsistent across conditions. CAD/CAM-milled PMMA specimens exhibited significantly lower surface roughness compared with conventional and 3D-printed materials across all tested abrasive conditions before and after thermal cycling ( p < 0.001). Thermal cycling had a limited effect overall, with a significant increase in surface roughness observed only in CAD/CAM-milled specimens treated with 40 µm eggshell ( p = 0.042). CAD/CAM-milled PMMA specimens demonstrated the lowest surface roughness under all experimental conditions. Eggshell powder showed comparable performance to pumice with minor variations depending on fabrication method. These findings suggest that fabrication method is the main influencing factor on surface roughness in provisional PMMA materials.