3‐D Finite element analysis of all‐ceramic posterior crowns

Abstract

The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior all-ceramic crowns. A three-dimensional finite element model representing a lower first molar was constructed. Variations of the model had two types of single layer all-ceramic crowns (Dicor and Empress) and two types of double layer all-ceramic crowns (In-Ceram and Empress2) cemented. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45 degrees angle, and horizontally). In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.4-19.4 MPa) concentrated around the loading points. In the masticatory force simulation test, the specimens experienced maximum tensile stresses of 19.7-27.0 MPa under a horizontal load and 10.8-10.9 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of the single layer crowns, and of the cervical area of the inner core of the double layer crowns. Within the limitation of this study, it was found that the strength of occlusal contact points is important to the integrity of posterior all-ceramic crowns and that bite forces applied from the horizontal direction are a critical factor.

Biomechanical Models of Endodontic Restorations

“…However, DTS and FS are obtained in loading states that are not uniaxial and the results of these tests are not equivalent, as numerous previous works have shown for different dental materials (Ban & Anusavice, 1990;Probster et al, 1997;Xie et al, 2000). Despite this, DTS and FS have been used interchangeably in recent works as a reference to compare with computed maximal stresses in finite element models of dental restorations (De Jager et al, 2006;Imanishi et al, 2003). On analysing the stress state in both tests, FS seems preferable as a reference for the tensile strength of a ductile material because the stress state is uniaxial at the failure point, and this can only be said of a DTT if a plain stress state is assumed, which if far from being the actual situation in real tests.…”

“…Not all models in the literature include the bone. When included, sometimes it is modelled with uniform properties (Imanishi et al, 2003;Nakamura et al, 2006), although most of the models consider the cancellous bone and a layer of cortical bone near the bone surface Gonzalez-Lluch et al, 2009b). Thin structures, such as the PDL and cement are not always considered in the FE models.…”

“…During the experiment a piece of beef jerky was masticated and the resulting load was predominantly directed in the apicocoronal direction (164.3 N) with lower and similar components in the mesial-distal direction and bucco-palatal direction (-28.9 N and -23.9 N respectively). For molars, Imanishi (Imanishi et al, 2003) used three different forces of 225 N to simulate masticatory loads with angles of 0º, 45º and 90º with respect to the radicular axis, and applied it in outer incline of the buccal cusps. Restored teeth are also subject to thermomechanical loading, because of the transient changes in the temperature of the different components of the restoration when hot or cold foods or liquids are introduced into the mouth.…”

Fitting accuracy and fracture resistance of crowns using a hybrid zirconia frame made of both porous and dense zirconia

“…That is, hybrid zirconia frames for crowns or fixed partial dentures need to be fabricated using the CAD/CAM system in such a way that the dense zirconia portion of the hybrid block is located at the lower part of the frame. This is because great stress is applied at the cervical area 8,9) of crowns or at the lower part 11) of the connectors of fixed partial dentures.…”

“…It is reported that the largest stress is usually applied to the cervical area of the crown 9,10) or to the lower part of the connector of all-ceramic fixed partial dentures 11) . Therefore, we conceived of fabricating a hybrid zirconia frame made of both porous and dense zirconia (hereinafter called hybrid zirconia frame).…”