A Three-Dimensional Finite Element Analysis to Evaluate and Compare Stress Levels and Distribution Patterns in Lithium Disilicate and Zirconia Crowns.

OBJECTIVE

This article aims to assess and compare the patterns of stress distribution and the biomechanical responses of monolithic zirconia and monolithic lithium disilicate crowns of different occlusal thicknesses using three-dimensional (3D) finite element analysis (FEA).

MATERIALS AND

METHODS

A 3D FEA model of a mandibular first molar with all supporting structures was constructed. Eight models were developed to simulate clinically recommended preparation thicknesses for each material, including monolithic zirconia (n = 4; occlusal reductions of 0.5, 1.0, 1.5, and 2.0 mm) and monolithic lithium disilicate (n = 4; nonfunctional/functional cusp reductions ranging from 1.0/1.5 to 2.5/3.0 mm). Two loading scenarios were applied: a 225-N masticatory load at three angulations (0-degree vertical, 45-degree oblique, and 90-degree horizontal) and a 600-N axial maximum bite force. The von Mises stress (VM, used as a scalar yield indicator) and the maximum principal stress (S, used as a tensile fracture predictor for brittle ceramics) were recorded in the crown and in the underlying dentin.

RESULTS

Across all thicknesses, zirconia crowns developed higher peak internal VM stress (maximum: 456.8 MPa) but transferred less tensile stress to the underlying dentin (maximum: S ≈ 127 MPa) than lithium disilicate crowns, which transferred greater stress to the dentin (maximum: S ≈ 145.7 MPa). For both materials, non-axial loads (45 and 90 degrees) generated markedly higher stress concentrations (maximum: VM ≈ 457 MPa) than vertical loads (maximum: VM ≈ 278 MPa). Stress distribution within the lithium disilicate crown became visibly more homogeneous with increasing occlusal thickness.

CONCLUSION

Within the limitations of this in silico model, monolithic zirconia exhibited a stress-shielding pattern in which more stress was retained within the crown and less was transmitted to the dentin, whereas lithium disilicate transmitted comparatively more stress to the dentin. Non-axial loading produced the highest stress peaks for both materials in this simulation. Because each material was modeled at the occlusal thickness clinically recommended for it, direct material-versus-material superiority cannot be inferred from these results, and clinical extrapolation should be made with caution.