Chun Minna, Silvestrin Tory, Savignano Roberto, Roque-Torres Gina Delia
School of Dentistry, Loma Linda University, Loma Linda, California.
Endodontics Department, School of Dentistry, Loma Linda University, Loma Linda, California.
J Endod. 2023 May;49(5):575-582. doi: 10.1016/j.joen.2023.03.009. Epub 2023 Mar 23.
A finite element analysis (FEA) study was performed to determine whether the material of apical barrier used for root apexification and/or the use of canal reinforcement affect the stress distribution in an endodontically treated immature permanent tooth in order to infer in which clinical scenarios a fracture is more likely to occur based on the ultimate tensile strength threshold of dentin.
An extracted human immature mandibular premolar was selected as the reference model and scanned by micro-computed tomography (micro-CT). The digital model was segmented and converted to STL (Standard Tessellation Language) using Simpleware Scan-IP and exported in IGES (Initial Graphics Exchange Specification) to Ansys 19. Six experimental models were designed with different combinations of composite, mineral trioxide aggregate (MTA), and Biodentine (BIO). Using FEA, a static 300 N load at a 135 angle with respect to the axis of the tooth was applied to each model and von Mises stress values (MPa) were measured at the sagittal, apical 8-mm, 5-mm, 2-mm, and 1-mm levels.
In all regions examined, the control (NT model) had lower stress in the root compared WITH experimental models. At the mid-root level, models with composite, MTA, and BIO reinforcement exhibited lower stresses in the root dentin than those with pulp or gutta-percha. BIO models had equal or greater average von Mises stress values than those of MTA models in all regions. Both, MTA and BIO, caused increases in stress of surrounding root dentin, with BIO causing a greater increase than MTA.
Stress distribution in immature permanent teeth treated by apexification is affected by the types of materials used. Root dentin's stress was lower when the mid-root canal was reinforced by composite, MTA, or BIO, which provided similar stress reduction to the root dentin. MTA is a more favorable apical barrier material from a mechanical standpoint because it induces less stress on apical root dentin than BIO.
进行有限元分析（FEA）研究，以确定用于根尖诱导成形术的根尖屏障材料和/或根管增强的使用是否会影响根管治疗后的未成熟恒牙的应力分布，从而根据牙本质的极限抗拉强度阈值推断在哪些临床情况下更有可能发生骨折。
选取一颗拔除的人类未成熟下颌前磨牙作为参考模型，并用微型计算机断层扫描（micro-CT）进行扫描。使用Simpleware Scan-IP对数字模型进行分割并转换为STL（标准镶嵌语言），并以IGES（初始图形交换规范）格式导出到Ansys 19。设计了六个实验模型，采用复合材料、三氧化矿物凝聚体（MTA）和生物陶瓷（BIO）的不同组合。使用有限元分析，对每个模型施加相对于牙轴呈135°角的300 N静态载荷，并在矢状面、根尖8 mm、5 mm、2 mm和1 mm水平测量冯·米塞斯应力值（MPa）。
在所有检查区域中，对照组（NT模型）牙根中的应力低于实验模型。在牙根中部水平，使用复合材料、MTA和BIO增强的模型在牙根牙本质中的应力低于使用牙髓或牙胶的模型。在所有区域中，BIO模型的平均冯·米塞斯应力值等于或大于MTA模型。MTA和BIO都会导致周围牙根牙本质应力增加，BIO导致的增加幅度大于MTA。
根尖诱导成形术治疗的未成熟恒牙中的应力分布受所用材料类型的影响。当根管中部用复合材料、MTA或BIO增强时，牙根牙本质的应力较低，这为牙根牙本质提供了类似的应力降低效果。从力学角度来看，MTA是一种更有利的根尖屏障材料，因为它对根尖牙根牙本质的应力诱导小于BIO。
