Impact of material combinations and removal and insertion cycles on the retention force of telescopic systems

A variety of dental materials are available for the fabrication of telescopic crowns. The aim was to investigate the impact of material combinations and removal and insertion cycles on their retention forces.

CAD/CAM-fabricated cobalt-chromium-molybdenum (CoCr) and zirconia (ZrO₂) primary crowns were combined with polyetheretherketone (PEEK), polyetherketoneketone (PEKK), CoCr, and ZrO₂ secondary crowns (four combinations included PEEK/PEKK secondary crowns in a thickness of 0.5 mm bonded to the CoCr tertiary construction), resulting in 12 different material combinations: CoCr-PEEK; CoCr-PEKK; CoCr-ZrO₂; CoCr-CoCr; CoCr-PEEK 0.5; CoCr-PEKK 0.5; ZrO₂-PEEK; ZrO₂-PEKK; ZrO₂-ZrO₂, ZrO₂-CoCr; ZrO₂-PEEK 0.5; and ZrO₂-PEKK 0.5 (n = 15 pairings per material combination). Pull-off tests were performed with a universal testing machine initially and after 500, 5000, and 10,000 removal and insertion cycles in a mastication simulator. Descriptive statistics with the Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were computed (α = 0.05).

The tested parameters, material combination, and removal and insertion cycles had significant impact on the retention force values (p < 0.001). An increase in removal and insertion cycles was associated with a decrease in retention forces within CoCr and ZrO₂ secondary crowns, regardless of the primary crown material. In contrast, PEEK and PEKK secondary crowns presented higher retention load values after 10,000 cycles than initially.

Different material combinations behaved differently after simulated removal and insertion regimens. This difference should be considered during treatment planning.

Telescopic crown systems should be made of materials with predictable retention forces that do not deteriorate with time. The implementation of new materials and technologies facilitates reproducibility and time-saving fabrication.