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. 2022 Dec;8(6):1496-1504.
doi: 10.1002/cre2.645. Epub 2022 Aug 8.

Fatigue behavior of removable partial denture cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) clasp materials

Jenny Zheng  1 , John M Aarts  1 , Sunyoung Ma  1 , John N Waddell  1 , Joanne J E Choi  1
Affiliations

Fatigue behavior of removable partial denture cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) clasp materials

Jenny Zheng et al. Clin Exp Dent Res. 2022 Dec.

Abstract

Objective: To investigate the fatigue behavior of cast and laser-sintered cobalt-chromium (CoCr) and polyetheretherketone (PEEK) material for a removable partial denture (RPD) clasps.

Methods: Dumbbell-shaped specimens were digitally designed with the center part of the dumbbell being a half-round shape at the cross-sectional dimension of 1.25 mm to simulate a typical clasp design and dimensions. A fatigue machine with an offset axis rotation system simulated a typical undercut depth of 0.25, 0.50, and 0.75 mm. Each group was subjected to 30,000 fatigue cycles (simulating 21 years) or till specimen failure. Before testing, the stress value at each undercut depth for each specimen was established in a universal testing machine and SN curves were plotted for each group. Data were statistically analyzed using Kruskal-Wallis and post hoc tests. The fractured surfaces were analyzed using SEM.

Results: The average fatigue cycles with 0.25, 0.50, and 0.75 mm undercuts were 27,155 ± 6277, 9298 ± 4033, 5642 ± 8785 for cast CoCr and 26,765 ± 6150, 11,318 ± 7931, 2861 ± 4803, for laser-sintered CoCr, respectively. Apart from three specimens, the PEEK groups did not fail during the simulation period. Clasps with 0.25 mm deflection showed significantly higher fatigue resistance than other groups (p < .001). There was no significant difference in fatigue behavior between the cast and laser-sintered CoCr. Microporosities at the fractured site along with irregular crack propagation were observed for cast and laser-sintered CoCr specimens. Fatigue-induced broken polymer crosslinking chains were observed in PEEK specimens.

Conclusion: PEEK material exhibited the highest fatigue resistance and significantly lower deflection resistance. Cast and laser-sintered CoCr showed similar fatigue resistance and behavior.

Keywords: CAD/CAM; Cast CoCr; PEEK; denture clasps; fatigue; laser-sintered CoCr; removable partial denture.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Shape and dimensions of dumbbell test specimens. The diagram shows the dimension of a typical preformed wax pattern, which will be replicated in test specimens.
Figure 2
Figure 2
The cantilever test to establish the stress values for each specimen. The Blue arrow indicates the direction of the universal testing machine movement.
Figure 3
Figure 3
An SN curve graph for the three material groups, cast CoCr, laser‐sintered CoCr, and milled PEEK
Figure 4
Figure 4
Comparison between the number of fatigue cycles and stress (N) at the failure of different materials
Figure 5
Figure 5
Comparisons between deflections and stress for cast and laser‐sintered cobalt‐chromium specimens
Figure 6
Figure 6
SEM images of specimen surface before and after fatigue testing and fracture sites. (a) cast cobalt‐chromium (CoCr); (b) laser‐sintered CoCr; (c) polyetheretherketone
See this image and copyright information in PMC

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