Optimum Design Analysis of Polyetheretherketone Clasp via Finite Element Method

Objectives: Recently, high-strength, aesthetic, and non-allergic thermoplastic resins were developed as frameworks for dentures and clinical applications. Polyetheretherketone (PEEK), a representative thermoplastic, is expected to replace conventional metal frameworks. However, obtaining PEEK with flexible properties and retention is a vital challenge in clinical applications. Therefore, in this study, the optimal design of clasps prepared with PEEK was evaluated to provide a sufficient retentive force for dentures.
Methods: Three-dimensional models were prepared in the form of half-oval-shaped clasp arms using PEEK (Evonik Industries AG), based on 12 cross-sectional dimensions and 6 taper ratios (Table.1). In all, 72 different kinds of models were created with CAD software (SolidWorks). Each model was assembled using linear finite element methods (Autodesk Nastran In-CAD). As approximate PEEK properties, a tensile modulus of 5.1GPa and yield stress of 110MPa were used. The models contained 21,652 to 59,358 nodes and 13,026 to 39,841 elements. All nodes in a fixed area were restrained, and a concentrated load was applied to the tip of the models. The load-displacement relations and stress distributions with different cross-sectional dimensions and taper ratios were recorded, and statistical analysis was performed via Pearson correlation analysis and one-way ANOVA (α=0.05).
Results: There was a significant difference in the retentive force among the different cross-sectional dimensions used (p<0.05), and the effect of the thickness was greater than that of the width. For the same dimension, the retentive force increased with an increase in the taper ratio (r>0.7). When the undercut was set at 0.25mm or 0.50mm, the retentive forces of #6 (0.9-taper), #9 (0.5-taper), #11 (0.7-taper), and #11 (0.8-taper) were within the required range (3-7.5N); moreover, the maximum stress was less than the proportional limit, implying that these designs would not undergo permanent deformation.
Conclusions: Considering comfort and functionality, PEEK clasps of width 2.50mm, thickness 2.19mm, and taper ratio 0.7 are optimal.