Influence of proximal box preparation on fracture resistance of single-retainer resin-bonded fixed dental prostheses: In vitro and in silico biomechanical analysis

Statement of problem Tooth preparations with proximal boxes improve the fracture resistance of resin-bonded fixed dental prostheses (RBFDPs). However, the effect of box location on the fracture resistance of single-retainer RBFDPs remains unknown.Purpose The purpose of this in vitro and in silico biomechanical analysis was to evaluate the influence of proximal box location on the fracture resistance of single-retainer RBFDPs.Material and methods Load-displacement data from previously published 4-point flexural strength tests were used to evaluate the properties of 5 mol% yttria-stabilized zirconia (5YSZ). Static elastic modulus and fracture strain were evaluated by in vitro and in silico 4-point flexural strength tests. Computer-aided designs of abutments and RBFDPs were created with proximal box preparations in the incisal third design (PDPI), middle third design (PDPM), and cervical third design (PDPC) of the abutment teeth, along with a digital model without proximal box preparation design (PD). PDPM was subjected to in vitro compression tests (n=3). The fracture load and pre-fracture biomechanical behavior of all designs were evaluated in silico based on the maximum principal strain (MXEPS) distribution and Weibull failure probability.Results By inputting the density (6.04 g/cm3), static elastic modulus (101.85 GPa), and MXEPS (0.0055) data of 5YSZ, PDPM had an in silico fracture load of 343.25 N compared with 346.46 N in vitro. The in silico fracture loads for the other designs were 378.04 N (PDPI), 364.27 N (PDPC), and 335.08 N (PD). The MXEPS was highest in the incisal region of the connector, while PDPI had the lowest failure probability.Conclusions Missing lateral incisors can be replaced with 5YSZ RBFDPs. Proximal box preparation in the incisal third of the abutment may improve predicted fracture resistance and biomechanical behavior while preserving enamel for better bond strength.