Abstract: Objective: To compare the retention force and wear of PEEK inner crown with PEEK, titanium, and cobalt-chromium alloy outer crown after long-term use. Methods: A total of 32 low-alloy steel-based dental crowns, including 27 PEEK inner crowns, 9 cobalt-chromium alloy inner crowns, 8 PEEK outer crowns, 8 pure titanium outer crowns, and 16 cobalt-chromium alloy outer crowns, were randomly divided into four groups. The inner and outer crowns of group A were PEEK. Group B was PEEK for the inner crown and pure titanium for the outer crown. Group C was PEEK for the inner crown and cobalt-chromium alloy for the outer crown. The inner and outer crowns of Group D were cobalt-chromium alloys. The inner crown was glued to the abutment type, the outer crown was completely placed and separately embedded. The simulated removal cycle test was carried out using an electronic universal testing machine, and the maximum dislocation force of the inner and outer crown separation before the start of the cycle, 1000 cycles, 2000 cycles, 3000 cycles, 4000 cycles, 5000 cycles, and 10,000 cycles was measured, and the analysis was recorded. The mass of the inner and outer crowns before and after the cycle experiment was weighed and recorded, the relative mass loss was calculated, and the outer surface morphology of the inner crowns before and after the cycle was observed by scanning electron microscopy. Results: The retention force values of groups A, B, C, and D under different cycles had statistical significance (P<0.05), and the retention force values of each group after multiple cycles had statistical significance (P<0.05). The retaining force of group A, B, and C increased first and then decreased with the increase of the number of cycles, and the retaining force of group D showed a downward trend. After 10,000 cycles of removal and wearing, the relative mass loss of internal and external crowns in the four groups was statistically different (P<0.05). Roughness of Group A was increased, but no obvious damage. However, the surface of group B and Group C was obviously damaged. The surface of group D was smoother than that of group A, B, and C. Conclusion: After simulating 10,000 cycles of insertion and removal, the combination of PEEK inner crowns with metal outer crowns can achieve retention force that is not lower than that of cobalt-chromium alloy for both internal and outer crowns. When choosing PEEK for the inner crowns, using titanium for the outer crowns can result in lower wear on the inner crowns and higher retention force.

Key words: telescope crown, retention force, wear performance, PEEK