ABSTRACT
PURPOSE: The aim of this study was to compare the retentive properties of an attachment with a nylon insert and an attachment with a polyetherketoneketone (PEKK) insert on two-implant mandibular overdentures during simulated masticatory loadings and insertion/removal cycles. MATERIALS AND METHODS: Two attachment systems with nylon inserts or PEKK inserts were investigated, including nylon/low, nylon/medium, nylon/high, PEKK/x-low, PEKK/low, PEKK/medium, and PEKK/high. The canine region of edentulous mandibular overdenture models was retained with two implant analogs through two different stud attachments at interimplant angulations of 0 and 20 degrees. The simulated mastication and insertion/removal cycles were 400,000 cyclic loadings and 1,080 times of insertion/removal. Wear patterns and deformations on the attachment surface were analyzed with scanning electron microscopy. RESULTS: At 0 and 20 degrees, initial retentive force was highest in nylon/high and lowest in PEKK/x-low. Final retentive force was highest in PEKK/high and PEKK/medium at 0 and 20 degrees, respectively, and PEKK/x-low was lowest at both angulations. At 0 degrees, nylon/low, nylon/medium, PEKK/x-low, and PEKK/low displayed a significant increase in retention (P < .05), and nylon/high and PEKK/medium showed a significant decrease in retention (P < .05), except PEKK/high, which exhibited no significant decrease (P > .05). At 20 degrees, nylon/low and PEKK/x-low increased retention significantly (P < .05), and nylon/medium, nylon/high, PEKK/low, PEKK/medium, and PEKK/high decreased retention significantly (P < .05). Patrices of both attachment systems barely showed detectable abrasion, while matrices revealed severe wear and surface deformation. Nylon inserts particularly displayed more noticeable wear and deformation than PEKK inserts. CONCLUSION: Within the limitations of this investigation, the attachment system with a PEKK insert indicated less abrasion and retention change than the attachment system with a nylon insert on both paralleled implants and axially tilted implants under 400,000 cyclic loadings and 1,080 insertion/removal cycles for 1 year.
