Available online 5 December 2023

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The purpose of this in vitro study was to assess the retentive force and deformation of PEEK and PEKK Akers clasps with different designs and undercut depths.

Material and methods

A master model containing the first and second molar abutments was used to design Akers clasps of different cross-sectional dimensions, undercut depths (0.5 and 0.75 mm), and materials. The components of the removable partial denture framework also included an occlusal rest and were manufactured using a milling machine (n=5). The fatigue resistance of the Akers clasps was measured before and after deformation regarding the retentive forces.

Results

The PEEK2-U50 clasp had the largest retentive force with no significant difference among all groups before and after the insertion and removal cycle. In addition, the increased cross-sectional dimensions of the design resulted in significant differences in retentive forces between the PEEK1 and PEEK2 groups and between the PEEK and PEKK materials.

Conclusions

Increasing the clasp's cross-sectional dimensions significantly impacted retentive forces, especially between different PEEK groups and between PEEK and PEKK materials.

Section snippetsMATERIAL AND METHODS

The mechanical properties of PEEK and PEKK were assessed by using a 3-point bend test following the International Organization for Standardization (ISO) 6872:2015 standard. Bar-shaped specimens (2×2×25 mm) were prepared using a low-speed diamond cutting machine (CL-4; SANPANY INSTRUMENTS CO LTD) with running water, followed by wet grinding using #1500 SiC abrasive paper (Waterproof Silicon Carbide Abrasive Paper; Kingdom Abrasive Co Ltd). The specimens (n=5) were positioned on supporting points

RESULTS

The stress-strain curves indicated that all PEKK specimens experienced brittle fracture after the bend test, while PEEK specimens only experienced plastic deformation (Fig. 2A, B). The flexural modulus and flexural strength of PEKK and PEEK are presented in Figure 2C, D. The PEKK specimens have statistically similar flexural strength to that of the PEEK specimens (P=.056). However, PEKK showed a significantly higher modulus than PEEK (P=.008).

Figure 3 shows SEM micrographs of PEKK and PEEK

DISCUSSION

The present study assessed the retentive forces and deformation changes of clasps with varying designs and undercut depths using PEEK and PEKK materials. Results revealed that all subgroups of the Design I groups exhibited no significant differences in materials or undercut amounts before and after the insertion and removal cycles. In Design II groups, although PEEK2 clasps slightly increased at the end of the cycle in the present study, no significant difference among subgroups were found in

CONCLUSIONS

Based on the findings of this in vitro study, the following conclusions were drawn.

1.

Significant differences in retentive forces were observed among Akers clasps with different cross-sectional dimensions, including width and thickness.

2.

No significant difference in retentive forces was found between Akers clasps with varying amounts of undercut.

3.

The retentive forces of PEEK and PEKK clasps did not show significant differences before and after simulating 10 years of clinical use through cyclic

Consent for publication

Not applicable.

CRediT authorship contribution statement

We-Fang Lee: Methodology, Validation, Investigation, Writing - original draft, Visualization. May-Show Chen & Tzu-Yu Peng: Validation, Resources, Writing - review and editing. Peng-Chien Huang: Methodology, Validation, Resources. Hiroki Nikawa: Validation, Resources. Pei-Wen Peng: Methodology, Investigation, Formal analysis, Data curation, Writing - review and editing, Visualization.

Acknowledgements

This study was supported by grants from the Ministry of Science and Technology, grant# 109-2314-B-038-028.

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