Mechanical behavior of conceptual posterior dental crowns with elastic modulus gradation

Objectives: The linear gradation between enamel and dentin has led to the concept of bioinspired materials. The purpose of this study was to evaluate the biomechanical behavior of monolithic ceramic crowns with functional elastic gradient and their effects on remaining tooth structure.
Methods: Using 3D/CAD software, a lower molar received a full-crown preparation (1.5mm occlusal and axial reduction). The monolithic crown was modeled with 0.1mm of resin cement layer. Four groups were distributed according to the full-crown elastic modulus (E): (a) Bioinspired crown with regressive elastic gradation (from 90 to 30 GPa); (b) Crown with progressive elastic gradation (from 30 to 90 GPa); (c) Rigid crown (90 GPa); and (d) Flexible crown (30 GPa). The model was exported to the finite element analysis software and meshed into 385.240 tetrahedral elements and 696.310 nodes. All materials were considered isotropic, linearly elastic, and homogeneous, with contacts perfectly bonded. The occlusal surface was 300 N loaded and the base of the model was constrained in all directions. The results were summarized in maximum principal stress, Von-Mises stress, and displacement to crown and remaining tooth.
Results: Stress peak, average stress, and stress concentration (peek/average) for crown and teeth were obtained. It was possible to identify similar stress concentration patterns to all groups. The bioinspired group presented less stress concentration in the remaining tooth, without necessarily using an extremely rigid crown in contrasting with the flexible crown, which presented higher stress concentration in the tooth. Both crowns with gradual arrangement of layers presented intermediate mechanical behavior among results generated by the rigid and flexible crowns.
Conclusions: The elastic modulus gradation in dental crowns modifies the stress distribution in the restoration, lowering stress concentration in the remaining tooth, with promising results for future bioinspired designs.