3D statistical failure analysis of monolithic dental ceramic crowns

Abstract

For adhesively retained ceramic crown of various types, it has been clinically observed that the most catastrophic failures initiate from the cement interface as a result of radial crack formation as opposed to Hertzian contact stresses originating on the occlusal surface. In this work, a 3D failure prognosis model is developed for interface initiated failures of monolithic ceramic crowns. The surface flaw distribution parameters determined by biaxial flexural tests on ceramic plates and point-to-point variations of multi-axial stress state at the intaglio surface are obtained by finite element stress analysis. They are combined on the basis of fracture mechanics based statistical failure probability model to predict failure probability of a monolithic crown subjected to single-cycle indentation load. The proposed method is verified by prior 2D axisymmetric model and experimental data. Under conditions where the crowns are completely bonded to the tooth substrate, both high flexural stress and high interfacial shear stress are shown to occur in the wall region where the crown thickness is relatively thin while high interfacial normal tensile stress distribution is observed at the margin region. Significant impact of reduced cement modulus on these stress states is shown. While the analyses are limited to single-cycle load-to-failure tests, high interfacial normal tensile stress or high interfacial shear stress may contribute to degradation of the cement bond between ceramic and dentin. In addition, the crown failure probability is shown to be controlled by high flexural stress concentrations over a small area, and the proposed method might be of some value to detect initial crown design errors.

The effect of adhesive failure and defects on the stress distribution in all-ceramic crowns

“…Besides, since the axial wall does not directly carry the occlusal load, the thickness decreases towards the margin, moreover, the stress in the wall increases with debonding as it progresses from the margin, which may facilitate crack initiation and growth from defects in the ceramic, and eventually lead to fracture of the restoration. This prediction is in good agreement with the case studies for all-ceramic crowns that most failures did not initiate from the contact surface, but at the resin cement interface [61] or the margin areas of the crown [15].…”

Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics

“…These analyses have all been based on maximum principal stress distributions. In analyzing failure probability with respect to ceramic fractures, the maximum tensile stress tangential to the surface, rather than the maximum principal stress, has primary importance in the fracture process (Nasrin et al 2016). In this work, we propose methodology that predicts the fatigue survival probability and probable fracture origin for a thin-walled monolithic ceramic crown by combining 3D FE analysis with statistical fracture mechanics-based concepts.…”

Approximate relative fatigue life estimation methods for thin-walled monolithic ceramic crowns

“…How well this approximation method can be utilized for actual restoration geometries is not known and further work would be needed. However, based on our prior work [13, 36], the high stress region was found to be relatively small in both the simple trilayer restoration and in an actual crown geometry even if the wall thickness is quite thin. Despite the differences in geometry, the maximum stress (47.0 MPa) for 1 mm thick LD trilayer under 300N load was somewhat similar to the maximum stress (57.7 MPa) for an actual thin-walled crown restoration under 500N load [13].…”