| The post materials, as well as the post shape will influence the fracture resistance of endodontically treated tooth. Until recently, no consensus has existed on which materials and technique was best suited for use. The material of prefabricated post mainly includes metal, fiber composite, and ceramic. Generally, metal and ceramic posts are stronger than fiber ones, but fiber posts offer greater flexibility and have demonstrated fewer root fractures when compared to metal or ceramic ones. Unfortunately, there is no clear guidance as to where the balance should be struck between strength and flexibility.Various post materials will influence the stress distribution and peak values in root dentine, at the same time they will influence the retention and resistance of post. Traditionally, cast post and core systems are the preferred choice because of their superior mechanical strength. However, because the Young's modulus of metal is much higher than dentin, an excessive stress may concentrate on the end of the post, finally resulting in catastrophic vertical root fracture. When the case happens, it is difficult to re-restoration in clinic, leading to the extraction of teeth. For that reason, studies have advocated that a modulus of elasticity close to that of dentin is preferable.A new family ofβ-Ti alloys suitable for biomedical application, Ti–24Nb–4Zr–7.9Sn (wt.%), has been developed recently. Owing to TNZS alloy possesses lower elastic modulus (45 GPa) and higher tensile strength (850 MPa) , it can make complete the defect that strength and flexibility of endodontic post are difficult to achieve balance. The anatomy of the post was based on the form of the Flexi-Flange post (Essential Dental Systems, Inc., South Hackensack, N, J. USA).The feature of Flexi-Flange system is split post. Literatures have demonstrated that the retention and stress distribution of Flexi-Flange post is better than the other post systems.The aim of the present study was to analyze the influence of post material of Ti-24Nb-4Zr-7.9Sn (wt.%) alloy, with split shape, on stress distribution in endodontically treated, post-restored teeth by means of three-dimensional finite element analysis. This study is composed of the following three parts. 1. Construction of three-dimensional finite element model of post and core by parametric self-adaptive changeA 3D finite element model of maxillary central incisor post and core which can self-adaptive change with reverse engineering and parameterization of Pro/E was constructed. The method enhanced the accuracy, flexibility and efficiency in constructing a 3D finite element model, which provided the platform for the optimum design of post.2. Stress distribution in roots and post/dentin interface with various elastic modulus materials as well as various shapeThe purpose of this study was to evaluate the influence of various elastic modulus materials as prefabricated endodontic post material and various shapes on the stress distribution and peak values in roots, which provided the platform for the optimum design of post. The result of calculation showed:①Maximum von Mises stresses increased with decreasing elastic modulus of materials in the dentin portion adjacent to the alveolar bone crest.②Maximum von Mises stresses decreased with decreasing elastic modulus of materials at post/dentin interface.③When post material and loading condition were same, maximum von Mises stresses of split post was lower than non split post.④Maximum von Mises stresses with TNZS alloy distributed uniformly at post/dentin interface.⑤TNZS alloy caused the lowest stress distribution at the post-dentin interface, which reduced the risk of root fracture further.3. Optimization split height and width of TNZS split postThe split height and width were set as the goal of optimizing. The split height (H) ranged from 2.5mm to 6.5mm, and width (D) ranged from 0.1mm to 0.5mm. The result of calculation showed:①The effect of H and D on maximum von Mises stress in post was most significant, following by post/dentine interface and root dentine. They were more easily affected by oblique load.②H affected the maximum von Mises stress of dentin portion adjacent to the alveolar bone crest than did D under vertical load, which was reverse under oblique load. D affected the maximum von Mises stress of post/dentin interface than did H under two loading conditions. H affected the maximum von Mises stress of post than did D under two loading conditions.④H played more significant roles in post stability than D under two loading conditions.⑤When H was between 2.5mm and 4.65mm, D was between 0.25mm and 0.32mm, the most stable stress and minimal stress level in root dentin and post were found. |
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