The synergetic effect of pulp chamber extension depth and occlusal thickness on stress distribution of molar endocrowns: a 3-dimensional finite element analysis

Abstract

The aim of this study was to evaluate the effects of butt margin, occlusal thickness and pulp chamber extension depth on stress distributions on mandibular molar endodontically treated teeth (ETT) with EMAX endocrown restoration using 3-dimensional finite element analysis (FEA). The FEA models of endocrown with flat surface or curve surface of butt margin were firstly evaluated stress distributions, and then 9 FEA models of endocrown with 1-, 2- or 3-mm pulp chamber extension depth and 1-, 2- or 3-mm occlusal thickness were generated using curve surface of butt margin. In all of FEA models, a 200 N of vertical load or horizontal load was applied, and the von Mises stress (VMS) were evaluated. The results showed that curve surface of butt margin offered more adhesive area of enamel, though VMS on the prepared teeth was similar in flat surface and curve surface models. In 9 endocrown models, 2-mm occlusal thickness showed the lowest VMS on restorations, teeth tissue and root furcations, and 2-mm extension depth displayed the lowest VMS on root furcations under vertical load. Also, 2-mm extension depth exhibited the lowest VMS on restorations and teeth tissue under horizontal load. Within the limitations of this FEA study, the results of this study could be used as an aid for dentists to better devise endocrown restorations. Graphical abstract.

Graphical abstract

Fig. 1

Schematic illustration of mandibular molar with endocrown restorations. Two types of butt margin of endocrown with 2-mm occlusal thickness and 2-mm pulp chamber extension depth were devised: flat surface of butt margin (a) and curve surface of butt margin (b). Nine types of endocrown restoration with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness were devised by a finite element analysis software (FEA, ANSYS, v18.0; Swanson Analysis Inc) c

Fig. 2

The von Mises stress (MPa) distribution in teeth tissue in flat surface (a, c) and curve surface (b, d) butt margin models under vertical load (a, b) and horizontal load (c, d). The color scale with red to blue colors corresponds to high to low-stress areas

Fig. 3

The von Mises stress (MPa) distribution on endocrown restorations in 9 FEA models under vertical load. Stress distribution plots of nine endocrown restorations with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness (a). The color scale with red to blue color corresponds to high to low-stress areas. The maximum VMS presented on endocrown restorations with the different occlusal thickness and pulp chamber extension depth (b)

Fig. 4

The von Mises stress (MPa) distribution on teeth tissue in 9 FEA models under vertical load. Stress distribution plots of teeth tissue by endocrown restorations with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness (a). The color scale with red to blue color corresponds to high to low-stress areas. The maximum VMS presented on teeth tissue by endocrown restoration with the different occlusal thickness and pulp chamber extension depth (b)

Fig. 5

The von Mises stress (MPa) distribution in root furcations in 9 FEA models under vertical load. Stress distribution plots of root furcations of teeth by endocrown restorations with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness (a). The color scale with red to blue color corresponds to high to low-stress areas. The maximum VMS presented on root furcations with the different occlusal thickness and pulp chamber extension depth (b)

Fig. 6

The von Mises stress (MPa) distribution on endocrown restorations in 9 FEA models under horizontal load. Stress distribution plots of nine endocrown restorations with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness (a). The color scale with red to blue color corresponds to high to low-stress areas. The maximum VMS presented on endocrown restorations with the different occlusal thickness and pulp chamber extension depth (b)

Fig. 7

The von Mises stress (MPa) distribution on teeth tissue in 9 FEA models under horizontal load. Stress distribution plots of teeth tissue by endocrown restorations with 1-mm, 2-mm, or 3-mm pulp chamber extension depth in combination with 1-mm, 2-mm, or 3-mm occlusal thickness (a). The color scale with red to blue color corresponds to high to low-stress areas. The maximum VMS presented on teeth tissue by endocrown restoration with the different occlusal thickness and pulp chamber extension depth (b)