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

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.