Survival Predictions of Ceramic Crowns Using Statistical Fracture Mechanics

Abstract

This work establishes a survival probability methodology for interface-initiated fatigue failures of monolithic ceramic crowns under simulated masticatory loading. A complete 3-dimensional (3D) finite element analysis model of a minimally reduced molar crown was developed using commercially available hardware and software. Estimates of material surface flaw distributions and fatigue parameters for 3 reinforced glass-ceramics (fluormica [FM], leucite [LR], and lithium disilicate [LD]) and a dense sintered yttrium-stabilized zirconia (YZ) were obtained from the literature and incorporated into the model. Utilizing the proposed fracture mechanics-based model, crown survival probability as a function of loading cycles was obtained from simulations performed on the 4 ceramic materials utilizing identical crown geometries and loading conditions. The weaker ceramic materials (FM and LR) resulted in lower survival rates than the more recently developed higher-strength ceramic materials (LD and YZ). The simulated 10-y survival rate of crowns fabricated from YZ was only slightly better than those fabricated from LD. In addition, 2 of the model crown systems (FM and LD) were expanded to determine regional-dependent failure probabilities. This analysis predicted that the LD-based crowns were more likely to fail from fractures initiating from margin areas, whereas the FM-based crowns showed a slightly higher probability of failure from fractures initiating from the occlusal table below the contact areas. These 2 predicted fracture initiation locations have some agreement with reported fractographic analyses of failed crowns. In this model, we considered the maximum tensile stress tangential to the interfacial surface, as opposed to the more universally reported maximum principal stress, because it more directly impacts crack propagation. While the accuracy of these predictions needs to be experimentally verified, the model can provide a fundamental understanding of the importance that pre-existing flaws at the intaglio surface have on fatigue failures.

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].…”

“…The reliability of monolithic lithium disilicate crowns has also been confirmed by fatigue tests [13,14]. Of course, a monolithic crown structure is advantageous as it eliminates the potential for failure associated with porcelain layering [15]. However, the load bearing capacity of ceramic crowns can be influenced by many factors, such as the tooth preparation, processes involved in manufacturing the restoration, and the luting process [16].…”

“…Hernandez et al [39] reported that approximately 65% of failures of ceramic blocks bonded using resin cement to a flat dentin substrate were found debonded between ceramic and cement under conditions of either water storage or mechanical loading. Interestingly, Nasrin et al [15] found that lithium disilicate crowns subjected to fatigue loading were more likely to undergo early debonding at the wall area near the margin. Debonding is believed to originate at the margin of the shoulder due to the existence of marginal gaps [31,36].…”

3D finite element model based on CT images of tooth

“…To conduct a FEA, the start point is the construction of an accurate model, which is the key to the analysis outcome 9,10 . Several methods have been used to generate FE models of teeth, such as the use of standard anatomical data in the literature 11 , manual tracing of tooth sections from histological 12 or computer tomographic (CT) images of teeth [13][14][15][16] .…”

“CAD‐on” Interfaces – Fracture Mechanics Characterization

“…Translucency, biocompatibility, and ease of production through CAD/CAM are additional favourable properties . Nevertheless, restorative failures, such as chipping and framework fractures, continue to be an issue . Efforts to reduce failures through improved firing protocols, coping and framework modifications, and altered processing techniques have yielded mixed results.…”