Evaluation of the effect of connector thickness on fracture strength in framework manufactured with poly-ether-ether-ketone (PEEK) and poly-ether-ketone-ketone (PEKK)

Introduction and Aim: PEEK and PEKK, which are high performance polymer materials, have recently been used in posterior implant supported restorations due to their excellent physical properties. However, the fracture strength of implant-supported frameworks made of PEEK and PEKK materials remains uncertain. The aim of this study is to compare the fracture strength of two implant-supported three-unit cobalt-chromium, PEEK and PEKK frameworks with different connector cross-sectional areas. Material and Methods: To evaluate the fracture strength, 126 standard titanium abutments were screwed to the analogs and embedded in the acrylic blocks in pairs to mimic a missing single mandibular premolar. The frameworks were designed with a CAD software program with connector surface areas of 6.25 mm2, 12 mm2 and 16 mm2. A total of 63 frameworks were fabricated, 7 in each group, in 3 connector cross-sectional areas out of 3 materials (co-cr, PEEK, PEKK). Afterwards, the frameworks were cemented to the abutments with zincphosphate cement. A universal testing machine was used for fracture strength analysis, and the failure mode was recorded. The obtained data were statistically evaluated by running the Kruskal Wallis Test and the Mann Whitney U test with Bonferroni correction. Results: PEEK frameworks showed both plastic deformation and fracture, while PEKK and cobalt-chromium frameworks showed complete fracture. The highest mean fracture strength was observed in the 16mm2 group, followed by 12mm2, and then 6.25mm2 in the connector cross-sectional area. The highest mean fracture strength values were observed in the cobalt-chromium frameworks (7326N ± 1071,6N), followed by PEEK (1485N ± 116,4N), and then in the PEKK frameworks (995 N ± 180,8N). The difference in fracture strength value that occurred by increasing the connector surface area from 12mm2 to 16mm2 in Co-Cr and PEKK frameworks was not found statistically significant. The mean fracture strength value of all groups was found to be capable of withstanding the physiological forces in the posterior region. Conclusions: Within the limitations of this in vitro study, PEEK and PEKK can be used as an alternative framework material for posterior implant-supported 3-unit fixed dental prostheses.