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Stress analysis according to various retrograde cavity preparation designs for surgical endodontics in the mesial root of mandibular molar : Finite element analysis

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 하악 대구치 근심치근의 외과적 근관치료에서 역충전 와동형성 디자인에 따른 응력변화 연구 
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The aim of this study was to evaluate the effect of various designs of apical preparation for surgical endodontics in the mesial root of a mandibular molar, with or without the presence of alveolar bone, based on finite element analysis (FEA). Three-dimensional FEA models were created and adapted using computer software based on the mesial root canal anatomy of a mandibular first molar. To exclude the interference of variation in the tooth coronal portion, the tooth model was bisected at the cementoenamel junction (CEJ), the coronal part was removed, and only the mesial root was used. The experimental designs were classified depending on apical preparation size, with or without isthmus, at a level of 3 mm from the apex; a 150-N load was applied vertically, and von Mises stress and maximum principle stress were plotted. The results were as follows: 1. As the amount of apical preparation increased in tested sub-groups, von Mises stress and maximum principle stress were gradually reduced. This tendency was the same in experimental conditions with or without the presence of the alveolar bone. 2. In the isthmus preparation group (Group III and IV), where little root dentin remained (sub-group 4), the situation was reversed, i.e., both von Mises stress and maximum principle stress increased, especially in the distal concave area. 3. As the maximum principal stress had a positive value in the distal concave area, root fracture initiation or detachment of the filling material (MTA) could occur at this site. 4. As the amount of apical preparation increased, von Mises stress increased in roots without MTA retrograde filling. 5. In the experimental condition without alveolar bone present, the vertical force was transmitted directly to the tooth, concentrating stress mainly on the bucco-lingual side, regardless of the experimental group. 6. The apical preparation of sub-group 4 in Group III was modified. Following the outline of the root, the cavity was prepared more mesially than the original design, and an effort was made to retain the same root dentin thickness on both the mesial and distal sides if possible. Stress values were lower than those in the original preparation, especially the maximum principle stress, which reduced drastically in the distal concave area. 7. A low stress field was formed on the mesial side of the mandibular molar mesial root, and is thought to be due to the increased concavity of the distal side compared to that of the mesial side.
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