Comparison of the Retention and Fit of Polyether Ether Ketone Clasps during Fatigue Circulation Tests.

Purpose: The purpose of this study was to evaluate the fit and retention of clasps made of polyether ether ketone (PEEK) or cobalt-chromium alloy (Co-Cr) at different tooth positions in experimental simulations of in vitro wear and removal for 5 years. Methods: Standard crowns of the right mandibular first premolar (44) and first molar (46) were selected, and a circular three-arm clasp was designed, scanned and fabricated. Ten PEEK clasps were used as the experimental group, and 10 Co-Cr clasps were used as the control group. The seating channel was parallel to the side of the abutment base in both groups. The oral environment was simulated, and each clasp was tested in artificial saliva for 7200 cycles while the change in clasp retention force was recorded. The fit before and after the fatigue cycles was measured by the silicone rubber film copying method. Data were statistically analyzed using the independent samples t-test (α = 0.05). Results: Before circulation, the retention forces of the clasps at position 44 were 4.61 ± 0.91 N (PEEK) and 47.50 ± 10.59 N (Co-Cr), and the forces at position 46 were 3.38 ± 0.49 N (PEEK) and 28.79 ± 10.99 N (Co-Cr). After circulation, the retention forces of the clasps at position 44 were 4.15 ± 0.91 N (PEEK) and 13.90 ± 6.59 N (Co-Cr), and the forces at position 46 were 2.93 ± 0.25 N (PEEK) and 11.56 ± 3.93 N (Co-Cr). Before circulation, the fit of each clasp at the reference points (clasp tip, clasp arm, and occlusal rest) was between 41.70 µm and 170.29 µm, and after circulation, they were between 64.05 µm and 182.59 µm. The retention force and fit of the PEEK clasps did not undergo statistically significant changes from before to after circulation (P > 0.05). However, there were statistically significant (P < 0.05) decreases in the retention force of the Co-Cr clasps and the fit of the clasp tip during circulation. In addition, there was a sudden and large change in the retention force of the Co-Cr clasps after approximately 360 cycles. Conclusions: The retention force and suitability of the PEEK clasps met the requirements for clinical use during testing that simulated the in vitro wear and removal procedure for 5 years. Compared with the Co-Cr clasp, the PEEK clasp underwent less fatigue deformation, which makes it feasible for clinical applications.