Assessment of mechanical characteristics of polyetheretherketone as orthodontic fixed lingual retainers

Pyi Phyo Win; Daniel De-Shing Chen; Bolormaa Sainbayar; Tzu-Yu Peng; Johnson Hsin-Chung Cheng

doi:10.1016/j.jds.2023.05.026

Assessment of mechanical characteristics of polyetheretherketone as orthodontic fixed lingual retainers

J Dent Sci. 2023 Oct;18(4):1804-1811. doi: 10.1016/j.jds.2023.05.026. Epub 2023 Jun 8.

Authors

Pyi Phyo Win^{1

2}, Daniel De-Shing Chen^{1

2}, Bolormaa Sainbayar³, Tzu-Yu Peng¹, Johnson Hsin-Chung Cheng^{1

2}

Affiliations

¹ School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan.
² Division of Orthodontics, Department of Dentistry, Taipei Medical University Hospital, Taipei, Taiwan.
³ School of Dentistry, Mongolian National University of Medical Sciences, Ulaanbaatar City, Mongolia.

Abstract

Background/purpose: Polyetheretherketone (PEEK) is known for its strength, flexibility, biocompatibility, and potential as a replacement for metals in dental appliances; however, uncertainty remains about the mechanical characteristics and dimensions of PEEK-made orthodontic fixed lingual retainers (FLRs). This study aimed to determine the optimal shape of PEEK-made orthodontic FLRs using the finite element method (FEM) and the three-point bending test (TPBT).

Materials and methods: Seventy-five three-dimensional PEEK rod-shaped models were created, which included five thicknesses (0.4, 0.6, 0.8, 1.0, and 1.2 mm), five widths (0.7, 0.9, 1.1, 1.3, and 1.5 mm), and three cross-sectional shapes (rectangular, oval, and hemielliptical). A 0.9-mm (0.036-inch) stainless steel wire (SSW) was used as a control and the FEM was used to determine six optimal dimensions among the PEEK models. The selected models were then fabricated and subjected, along with the SSW, to the experimental TPBT to assess their mechanical responses against lingual and biting pressures.

Results: The FEM analysis revealed that Von Mises stresses on the PEEK models decreased with an increase in width and thickness. Six optimal shapes of PEEK models were chosen based on acceptable lingual and biting stresses as well as patient comfort compared to the SSW. Furthermore, PEEK models showed significantly lower deformation during the 3.1-mm deflection test than did the SSW, while no notable differences were observed among different sizes of PEEK models. The hemielliptical PEEK model with a thickness of 1.0 mm and width of 1.5 mm was found to be mechanically robust enough to withstand lingual forces, while none of the PEEK models, including the SSW, were able to resist biting forces.

Conclusion: Within the limitations of this in vitro study, PEEK-made orthodontic FLRs with a hemielliptical cross-sectional shape and a thickness-to-width ratio of 1.0:1.5 would be suitable for use as orthodontic FLRs.

Keywords: Bending test; Fixed lingual retainer; Orthodontic; Polyetheretherketone; Shape optimization.