Investigation of polyetheretherketone as secondary crown material with an occlusal gap in double crowns

The use of polyetheretherketone (PEEK) in double crowns has gained increasing attention but the effect of an occlusal gap on various double crown assemblies involving PEEK material has not been thoroughly investigated although it has a critical influence on the retention mechanism. The aim of this study was to evaluate the retention and surface properties of double crowns with PEEK secondary crowns with or without an occlusal gap. Five groups were investigated ( n = 10): 1-Zirconia primary crown-electroformed gold secondary crown, no occlusal gap (ZA), 2-Zirconia primary crown-PEEK secondary crown, no occlusal gap (ZP), 3-Zirconia primary crown-PEEK secondary crown, 100 μm occlusal gap (ZP100), 4-PEEK primary crown-PEEK secondary crown, no occlusal gap (PP), 5-PEEK primary crown-PEEK secondary crown, 100 μm occlusal gap (PP100). A conus angle of 2° was used. A preload of 50 N was applied. Retention forces were measured initially and after 100, 500, 1000, 5000, 10,000 insertion-separation cycles. One specimen from each group was examined by Scanning Electron Microscopy (SEM) to evaluate wear. The highest retention value was measured in the PP100 group, and the lowest value was measured in the ZA group. Formation of an occlusal gap between the primary and secondary crowns increased the retention force values after 10,000 cycles for PEEK material couple. After the experiments, wear was observed on PEEK primary and secondary crowns and gold secondary crowns. The PP material pair with a 100 μm occlusal gap exhibited the most stable and reliable retention performance.