Performance of PEEK based telescopic crowns, a comparative study

Abstract

Objective: Telescopic crowns are suitable components of partial dentures to efficiently anchor dental supra-structures to teeth or dental implants and achieve high chewing performance and wear comfort. Usually alloy- or metal-based structures are used for the primary and the secondary crowns. The advantage is the possibility to produce precise structures with a high perfection and sufficient friction force, but the disadvantage is the corrosion instability. The recent introduction of zirconia ceramics has enabled the fabrication of ceramic primary crowns, thus reducing corrodibility. The novel application of the high-performance polymer polyetheretherketone (PEEK) as another metal-free alternative material offers a new perspective for such applications. Therefore, the aim of this work was to assess the performance of telescopic crowns of PEEK by comparing telescopic crowns based on the combination of PEEK (prim. crown) + PEEK (sec. crown) with the pairings ZrO₂ (prim. crown) + PEEK (sec. crown) and CoCr-alloy (prim. crown) + PEEK (sec. crown).

Methods: All specimens were CAD/CAM planned and manufactured based on a model of a tooth 26. One master dental technician performed the post-treatment. For each group of material pairing, n = 9 telescopic crown pairs were manufactured and tested. Herein not only the maximum retention force was measured but also the retention force vs. pull-off distance were analyzed. As there is no commonly accepted test protocol available, the influence of various pull off speeds were tested as well. All measurements were first made with three blocks of three crowns (3C), subsequently with three blocks of two crowns (2C) and finally with nine single crowns (1C). The long-term behavior was estimated by performing 10.000 cycles, which is related to a life-time of more than 10 years.

Results: The maximum retention force in case of PEEK + PEEK was higher in comparison to the other tested material pairings. In the range between 1 and 10 mm/ min pull off speed there was no significant influence by the pull off speed. More influence on the friction force would be expected by changes of the number of the crowns acting simultaneously. The friction force was decreasing with decreasing number of crowns but not linearly in any tested case. The long-term test has shown that the friction force remained constant.

Significance: The performance of PEEK + PEEK telescopes is comparable with the usually applied material pairings. Over long time no loss in retention force could be observed. The retention force - distance progression in the PEEK + PEEK pairing offers more security against a possible loss of retention during repair or relining. For further tests of the performance of telescopic crowns or to estimate of friction force limits, a setup with at least two, but preferably three, crowns tested in parallel is suggested.

Keywords: Cobalt-chromium alloy; PEEK; Telescopic crowns; Zirconium dioxide.