Optimal design of the retainer and connector for a lithium disilicate resin-bonded fixed partial denture: A finite element analysis study.

Background: How the connector shape, retainer type, and retainer placement affect the functional stresses in lithium disilicate cantilever resin-bonded fixed partial dentures (RBFPDs) is unclear.

Objective: The purpose of this finite element analysis (FEA) study was to evaluate the effects of the connector shape, retainer type, and retainer placement on the stress distribution and magnitude of stress in RBFPDs.

Methods: Cantilever RBFPDs of the maxillary anterior lateral incisor with a retainer on the canine were modeled to conduct a 3-dimensional FEA. These designs were divided into 2 groups based on connector shape: rectangular and trapezoidal. Each group included 4 different retainer configurations-either labial or palatal veneer RBFPDs (LV-RBFPD or PV-RBFPD) or labial or palatal contact-point RBFPDs (LC-RBFPD or PC-RBFPD). FEA was performed for each RBFPD to evaluate stresses during regional and 3-point loading, including maximal intercuspal, protrusive, and lateral mandibular positions. The results were evaluated via colorimetric stress maps of the equivalent von Mises stress, maximum principal stress, and minimum principal stress in the prosthesis.

Results: The connector shape, retainer type, and placement affected the RBFPD stress, and the lowest stress was observed in the rectangular group. The LC-RBFPD group presented the lowest maximum principal stress (348.2 MPa) and minimum principal stress (49.1 MPa) under regional loading and the lowest equivalent stress (273.4 MPa) and maximum principal stress (356.0 MPa) with the protrusion position. The LV-RBFPD group presented the lowest equivalent stress (52.0 MPa), the lowest maximum principal stress (47.5 MPa), and the minimum principal stress (1.04 MPa) at the maximal intercuspal position, the lowest minimum principal stress (1.04 MPa) at the protrusion position, and the lowest equivalent stress (46.7 MPa) at the lateral position. The PV-RBFPD group presented the lowest equivalent stress (268.5 MPa) under regional loading and the lowest maximum principal stress (37.7 MPa) and minimum principal stress (2.02 MPa) under lateral loading.

Conclusions: A rectangular cross-sectional connector design for all groups could help disperse occlusal force and improve the resistance of the restoration. Both the veneer and contact-point retainer in the rectangular group were clinically acceptable and could resist fracture.