Influence of margin design and restorative material on the stress distribution of endocrowns: a 3D finite element analysis

Abstract

Background This study aimed to evaluate the stress distributions in endocrown restorations as applied to endodontically treated teeth (ETT), according to the factors of “margin design” (four levels) and “restorative material” (six levels). Methods Four 3D-finite elements models were constructed for endocrown restored molars considering different margin designs. Model A was prepared with a flat butt joint margin and received an endocrown with a 2.0-mm occlusal thickness. Model B was prepared with a 20° bevel margin and received an endocrown with a 2.0-mm occlusal thickness. Model C was prepared with an axial reduction and 1-mm shoulder margin and received an endocrown with a 2.0-mm occlusal thickness. Model D was prepared with an anatomic margin and received an endocrown with a 2.0-mm occlusal thickness. The following endocrown materials were used: In-Ceram Zirconia (Zr), Vita Suprinity (VS), IPS Empress (IE), Grandio blocs (GR), VisCalor bulk (VS), and CopraPeek Light (CP). The Load application (600 N) was performed at the food bolus and tooth surface during the closing phase of the chewing cycle. The results for the endocrown and tooth remnants were determined according to the von Mises stress. The failure risk of the cement layer was also calculated based on the normal stress criterion. Results Model D (with an anatomic margin) showed the greatest stress concentrations, especially in the irregular and sharp angles of the restoration and tooth remnants. The stress concentrated on the dentin was significantly lower in Model B with a 20° bevel margin (20.86 MPa), i.e., 1.3 times lower than the other three margin designs (27.80 MPa). Restorative materials with higher elastic moduli present higher stress concentrations inside the endocrown and transmit less stress to the cement layer, resulting in lower bonding failure risks. In contrast, materials with an elastic modulus similar to that of dentin presented with a more homogeneous stress distribution on the whole structure. Conclusions An endocrown with a 20° bevel margin design could be a favorable preparation option for ETT. Composite resins (GR and VC) exhibit a more even stress distribution, and seem to be more promising materials for endocrown molars.

Stress Analysis on Mesiolingual Cavity of Endodontically Treated Molar Restored Using Bidirectional Fiber-Reinforced Composite (Wallpapering Technique)

“…Restoration materials should have a modulus of elasticity similar to dentin (17.8 GPa) to create a homogeneous stress distribution and reduce the incidence of root fracture. 7,12,40,41 The results showed the stress concentration on polyethylene fiber-reinforced composite restorations did not exceed the strength of the materials. E-glass fiber has an elastic modulus of 8.87 GPa.…”

“…7,8,10,11 Stress analysis due to masticatory forces can be performed by using the finite element method (FEM) to identify highstress concentrations that result in restoration failure. 12 The advantages of FEM are reduced research time and costs, as well as provide an overview of a new scientific concept to clinical application, by carrying out the virtual test under measured and conceivable loading conditions. 13 This study aims to determine the stress distribution of fiber-reinforced composite by adding fiber bidirectional made of polyethylene and e-glass on ETT mandibular molar without mesial and lingual walls using the finite element method…”

Indications for the use of endocrowns, design and selection of materials: Literature review

“…Due to the location of the restoration within the chamber cavity, a possible irreparable fracture of the piece must also be taken into account in case of failure, for which an excessively Hard e can also pose a risk [21] . More solid materials with less flexibility will receive a greater stress load directly on the restoration itself [22] ; while those with a flexibility modulus similar to that of the tooth will distribute the forces in an equivalent way throughout the piece [23] . Although metallic materials can be used in this type of restoration, the predominant materials used are ceramics, in addition to current alternatives such as hybrid materials and CADCAM-machined composites.…”

Present status and future directions: The restoration of root filled teeth

“…Recommendations for the preparation design include a depth of 3 mm for the central retention cavity with a divergence angle of 6–12° for more homogenous stress distribution (Abtahi et al, 2022 ; Tribst et al, 2021 ). The cervical margin width should be at least 2 mm, and prepared flat or slightly bevelled (Zheng et al, 2022 ).…”