Elsevier

Journal of Endodontics

Volume 46, Issue 4, April 2020, Pages 539-544
Journal of Endodontics

Basic Research
Stress Analyses of Retrograde Cavity Preparation Designs for Surgical Endodontics in the Mesial Root of the Mandibular Molar: A Finite Element Analysis—Part II

https://doi.org/10.1016/j.joen.2019.12.007Get rights and content

Abstract

Introduction

The aim of this study was to investigate the influence of apical filling material and the modification made to the apical preparation design in surgical endodontics on the areas of stress concentration in the mesial root of a mandibular molar using finite element analysis.

Methods

The filling material was injected under 2 conditions (ie, with or without mineral trioxide aggregate retrograde filling). The apical preparation design was modified by extending the preparation mesially while maintaining a similar prepared area. We contained the displacement of all the nodes at the base of the supporting bone and applied a force of 150 N to the vertical axis. We analyzed stress generation and concentrations numerically for all cavity design groups.

Results

In the presence of retrograde filling, the von Mises stress decreased gradually according to the enlargement of the prepared cavity in the subgroups. When the retrograde filling was absent, the von Mises stress increased as the prepared cavity enlarged. The modification of the apical preparation extending in the mesial direction showed a drastic decrease in stress concentration.

Conclusions

Within the limitations of this study, it was advantageous to perform mesial retrograde preparation within the mesial root dentin to maintain a balanced root dentin on both sides of the apical preparation and create a low-stress field. The surgeon should be careful not to wash out or dislodge the retrograde filling material during obturation to avoid failure of surgery.

Section snippets

Construction of a 3-dimensional Finite Element Root Model

The method of construction of a 3-dimensional (3D) finite element root model was presented in a previous article2. To summarize, 1 mandibular first molar was scanned at 2-μm intervals in a micro–computed tomographic system (HMX; X-Tek Group, Santa Clara, CA) to obtain the 3D geometric configuration of the root. The literature was searched to obtain the general size and dimension of the root5, 6, 7 and, based on this information, a standard 3D model of a mandibular first molar’s mesial root was

Results

The von Mises stress values from the experimental groups with or without retrograde filling are shown in Figure 2. In the condition with retrograde filling, the von Mises stress decreased gradually according to the enlargement of the prepared cavity in the subgroups (Fig. 2A, B, E and F). In the condition without retrograde filling, the von Mises stress increased as the preparation cavity enlarged (Fig. 2C, D, G and H). Subgroup 4 in group 2, which did not have retrograde filling (Fig. 2H),

Discussion

According to previous studies on the prognostic factors of endodontic microsurgery, the success rates of molars are lower than that of anterior teeth16,17. The low success rate of the molar may be caused by the difficult access to the surgical field and the complexity of the root canal anatomy18. One of the anatomic differences between the molar and the anterior tooth is the presence of 2 or more root canals in a single root. In particular, the mesial root of most mandibular molars has 2 root

Acknowledgments

Sunil Kim and Dongzi Chen contributed equally to this study.

Supported by the Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (grant no. 2018R1D1A1A09081906) and the Ministry of Science, ICT and Future Planning (grant no. NRF-2017R1C1B5018113).

The authors deny any conflicts of interest related to this study.

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