The Stress Distribution and Deformation of Maxillary Bilateral Distal-Extension Removable Partial Dentures with U-Shaped Palatal Major Connectors Fabricated from Different Materials: A Finite Element Analysis

Background/Objectives: This study aims to investigate the stress distribution and deformation of cobalt–chromium (CoCr) and polyetheretherketone (PEEK) maxillary bilateral distal-extension removable partial dentures (RPDs) on the abutment, periodontal ligament (PDL), mucosa, and RPD framework. Methods: A three-dimensional maxilla model was obtained from the patient’s cone-beam computed tomography (CBCT) and master model scan, composed of six maxillary anterior teeth, and U-shaped palatal major connectors for both the CoCr and PEEK RPD designs were constructed with computer-aided design (CAD) using the software program SolidWorks 2017 (SolidWorks Corp., Waltham, (MA), USA). A total vertical force of 320 N was applied bilaterally to the posterior artificial teeth. Three-dimensional finite element analysis was applied to evaluate the von Mises stress (VMS) distributions of the CoCr and PEEK RPDs on the abutment, PDL, mucosa, and RPD framework, and the deformation of the RPD framework was analyzed using ANSYS Workbench software, version 2020 (ANSYS Workbench 2020; ANSYS Inc.). Results: The stress distribution originated from the RPD free-end and was distributed to the mucosa, abutment, and PDL. The maximum stress observed in the oral structures was highest at the abutment, followed by the mucosa and PDL. The VMS occurring at the abutment in the CoCr RPD (9.098 MPa) was higher than that at the PEEK RPD (7.515 MPa), while the VMSs occurring at the mucosa and PDL in the CoCr RPD and PEEK RPD were similar. RPD frameworks constructed from different materials generated different stress distribution patterns. The maximum VMS occurring in the CoCr RPD framework (107.99 MPa) was significantly greater than that at the PEEK RPD framework (11.7 MPa). Meanwhile, the maximum deformation in the vertical direction of the PEEK RPD framework (0.0128 mm) was higher than that of the CoCr RPD framework (0.0082 mm). Conclusions: The results suggested that the PEEK RPD may have a better protective effect on the abutment. Both the PEEK and CoCr RPDs were unlikely to cause severe mechanical damage to the mucosa and PDL. However, the thickness of the PEEK framework should be focused on to reduce the stress distribution to the residual ridge mucosa.