Wear resistance of CAD-CAM-milled PEEK, PEKK, and cobalt-chromium removable partial denture frameworks for implant-assisted removable partial dentures against zirconia crowns during simulated insertion/removal cycling in a mandibular Kennedy Class I model.

PURPOSE: To compare the wear resistance of CAD-CAM-milled PEEK, PEKK, and cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks against zirconia crowns during simulated insertion/removal cycling in a mandibular Kennedy Class I model. MATERIALS AND METHODS: A Kennedy Class I acrylic model with two implant analogues supporting zirconia crowns was used. RPD frameworks (n = 6/group) were milled from PEEK (BioHPP), PEKK (Pekkton ivory), and Co-Cr (Scheftner Dental Alloys). Specimens underwent 2160 insertion/removal cycles (24 month simulation) under 50 N load in a chewing simulator with thermocycling (5 - 55℃) and artificial saliva. Wear at the proximal plate, occlusal rest, and retentive arm was assessed via optical profilometry for volume change (µm3) and maximum surface height (Rz, µm). Two-way repeated-measures ANOVA with Bonferroni correction (α = 0.05) was used. RESULTS: Co-Cr generally exhibited higher surface roughness than PEEK and PEKK (P < .05, partial η2 = 0.436 - 0.629), with no differences between PEEK and PEKK. Volume change was negligible for Co-Cr (≈10-5 µm3) and highly variable for PEEK/PEKK, with no statistically significant differences among the three materials or over time (P > .05). No within-group changes from baseline to 24 months were observed. CONCLUSION: Within the limitations of this in vitro study, no statistically significant differences in wear resistance were observed between PEEK and PEKK frameworks; however, this does not constitute evidence of equivalence. Cobalt-chromium exhibited higher surface roughness but negligible volume loss. Clinical validation is required before PAEK materials can be recommended as routine substitutes for conventional metal frameworks.