Effect of different polishing procedures and coffee thermocycling on the surface properties of high performance polymers

This study aimed to evaluate the effects of different polishing protocols and coffee thermocycling on the surface roughness (Ra) and surface characteristics of high-performance polymers, including PEEK materials with various fillers (unfilled, nanoceramic-reinforced, titanium dioxide-reinforced, and glass fiber-reinforced) and titanium dioxide-reinforced PEKK. All PEEK and PEKK specimens were prepared using 400, 800, and 1200 grit silicon carbide papers and divided into five subgroups: control without polishing (C), pumice with water and a brush (PM), pumice followed by polishing paste (PMP), aluminum oxide–based discs (SS), and diamond-impregnated spiral discs (TW). Surface roughness (Ra) was measured using a profilometer, and the surface morphology was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). After 5000 cycles of coffee thermocycling, all measurements were repeated for each sample. Data were statistically analyzed using a three-way analysis of variance (ANOVA) within the general linear model (GLM) framework to evaluate the effects of the material type, polishing protocol, and aging, as well as their interactions. Multiple comparisons were performed using Tukey’s honestly significant difference (HSD) post hoc test. Material type, polishing protocol, and coffee thermocycling significantly influenced the surface roughness values ( p < 0.05). Additional polishing procedures improved the surface smoothness of most high-performance polymers, whereas aging procedures generally increased the surface roughness. Among the evaluated protocols, pumice followed by polishing paste (PMP) procedure provided the most favorable surface characteristics, whereas chairside polishing systems demonstrated favorable post-aging surface stability for most materials. In contrast, the glass fiber–reinforced PEEK exhibited less favorable surface characteristics than the other tested materials. Polishing procedures significantly improved the surface quality of high-performance polymers regardless of material composition. Among the evaluated protocols, PMP demonstrated the most favorable surface characteristics, whereas SS and TW provided favorable post-aging surface stability for most materials. In contrast, glass fiber–reinforced PEEK generally exhibited higher surface roughness and less favorable surface characteristics compared with the other tested materials. SEM and AFM analyses supported the profilometric findings regarding surface morphology alterations after polishing and aging procedures.