Stress-induced shape optimization of two-unit cantilever fiber-reinforced composite dental bridge

Objective: Because of its minimal invasion and low cost, adhesive fiber-reinforced composite fixed partial denture (FRCFPD) has become an ideal treatment option for single tooth replacement. However, the two-unit cantilever dental bridge, which only makes use of one abutment tooth, often fail by retainer’s debonding or fracture within the structure. The present study aimed to develop a stronger retainer design and fiber layout for a two-unit posterior cantilevered FRCFPD using shape optimization technique.

Method: A physical model was constructed using a human mandibular first molar, and a second premolar pontic made with composite resin was attached to the mesial surface of the molar. The model was scanned using micro-CT and the acquired images were reconstructed using CT Pro 3D (Nikon Metrology). The 3D volume was segmented using Avizo (VSG) and exported to Hypermesh (Altair Engineering) for finite element model construction. Shape optimization was carried out using ABAQUS (SIMULIA) in conjunction with a User-defined Material Subroutine. Stress-induced Material Transformation was first performed within the tooth tissues to obtain the optimal cavity preparation, and then within the restoration to seek optimal fiber layout. Finally, stress analyses of the shape-optimized and conventional designs were carried out to compare their mechanical performances.

Result: Compared with the conventional design, the shovel-shaped cavity preparation obtained from the optimization has 67% reduction in interfacial tensile stress. The optimization also indicated that the fibers should be placed at the top of the connector area where tensile stress was high. With the optimized design, the maximum principal stress in the veneering composite was reduced by ~50%.

Conclusion: With its lower interfacial and structural stresses, the new, optimized design is expected to perform better mechanically than the conventional design. An in vitro study has been planned for its validation.