Different protocol bar designs made of polyether ether ketone (PEEK) and metal: an analysis of mechanical behavior

Objective: To assess the flexural strength (FS) of protocol bars on implants made of polyether ether ketone (PEEK) and metal. Methods: Thirty PEEK bars and thirty metal bars (control) were manufactured in three different cross-sectional designs (n = 10): rectangular solid bar (R); T-shaped bar (T); and inverted-T shaped bar (T-inv). The 30 cm bars were screwed onto Cone Morse implants measuring 3.75 x 11.0 mm and subjected to FS test on a universal testing machine (0.5 mm/min), with load applied to the pontic. Then, the counter-torque (CTorque) was measured on the screws following the test. Results: Both the PEEK and metal bars showed the highest FS values for the R-type design, followed by the T and T-inv designs. On average, FS values of PEEK bars for the T and T-inv designs were, respectively, 32.5% and 47.2% smaller than the R-shaped bars. On metal bars, the T and T-inv designs showed values 19.9% and 30.5% smaller than that found for the R design. However, regardless of design, the Ni-Cr bars showed consistently higher FS values. CTorque was not affected by material, but the R design showed higher values. Conclusion: The bar design influences FS. Regardless of design, metal bars show higher FS relative to PEEK. On the other hand, CTorque was not affected by material; in terms of design, the R-shaped bars showed lowest CTorque and T and T-inv showed no statistical difference.