Abstract：
OBJECTIVE: This study used image-based finite element analysis (FEA) to assess the biomechanical changes in mandibular first molars resulting from alterations in the position of the root canal isthmus.
METHODS: A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient\'s mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth\'s longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading.
RESULTS: In Group A (without an isthmus), the maximum stress was 22.2 MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4 MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8 mm from the root tip, Group B: 13.6 MPa vs. Group A: 11.4 MPa; at 3 mm from the root tip, Group C: 14.2 MPa vs. Group A: 4.5 MPa; at 1 mm from the root tip, Group D: 25.1 MPa vs. Group A: 10.3 MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus.
CONCLUSIONS: A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.
METHODS: A healthy mandibular first molar, characterized by two intact root canals and a cavity-free surface, was selected as the subject. A three-dimensional model for the molar was established using scanned images of the patient\'s mandibular teeth. Subsequently, four distinct finite element models were created, each representing varied root canal morphologies: non-isthmus (Group A), isthmus located at the upper 1/3 of the root (Group B), middle 1/3 of the root (Group C), and lower 1/3 of the root (Group D). A static load of 200 N was applied along the tooth\'s longitudinal axis on the occlusal surface to simulate regular chewing forces. The biomechanical assessment was conducted regarding the mechanical stress profile within the root dentin. The equivalent stress (Von Mises stress) was used to assess the biomechanical features of mandibular teeth under mechanical loading.
RESULTS: In Group A (without an isthmus), the maximum stress was 22.2 MPa, while experimental groups with an isthmus exhibited higher stresses, reaching up to 29.4 MPa. All maximum stresses were concentrated near the apical foramen. The presence of the isthmus modified the stress distribution in the dentin wall of the tooth canal. Notably, dentin stresses at specific locations demonstrated differences: at 8 mm from the root tip, Group B: 13.6 MPa vs. Group A: 11.4 MPa; at 3 mm from the root tip, Group C: 14.2 MPa vs. Group A: 4.5 MPa; at 1 mm from the root tip, Group D: 25.1 MPa vs. Group A: 10.3 MPa. The maximum stress in the root canal dentin within the isthmus region was located either at the top or bottom of the isthmus.
CONCLUSIONS: A root canal isthmus modifies the stress profile within the dentin. The maximum stress occurs near the apical foramen and significantly increases when the isthmus is located closer to the apical foramina.
摘要：
目的：本研究使用基于图像的有限元分析（FEA）来评估由于根管峡部位置改变而导致的下颌第一磨牙的生物力学变化。
方法：健康的下颌第一磨牙，以两个完整的根管和一个无腔表面为特征，被选为主题。使用患者下颌牙齿的扫描图像建立了磨牙的三维模型。随后，创建了四个不同的有限元模型，每个代表不同的根管形态：非峡部（A组），地峡位于根部的上部1/3（B组），根的中间1/3（C组），和较低的1/3根（D组）。在咬合面上沿牙齿的纵轴施加200N的静载荷，以模拟规则的咀嚼力。对牙根牙本质内的机械应力分布进行了生物力学评估。等效应力（VonMises应力）用于评估机械载荷下下颌牙齿的生物力学特征。
结果：在A组（没有地峡）中，最大应力为22.2MPa,而具有峡部的实验组表现出更高的压力，达到29.4MPa。所有最大应力都集中在根尖孔附近。峡部的存在改变了牙管牙本质壁中的应力分布。值得注意的是,特定位置的牙本质应力表现出差异：在距根尖8毫米处，B组：13.6MPavs.A组：11.4MPa；在距根尖3mm处，C组：14.2MPavs.A组：4.5MPa；在距根尖1mm处，D组：25.1MPavs.A组:10.3MPa。峡部区域内根管牙本质中的最大应力位于峡部的顶部或底部。
结论：根管峡部改变牙本质内的应力分布。最大应力发生在根尖孔附近，当峡部靠近根尖孔时会显着增加。
方法：健康的下颌第一磨牙，以两个完整的根管和一个无腔表面为特征，被选为主题。使用患者下颌牙齿的扫描图像建立了磨牙的三维模型。随后，创建了四个不同的有限元模型，每个代表不同的根管形态：非峡部（A组），地峡位于根部的上部1/3（B组），根的中间1/3（C组），和较低的1/3根（D组）。在咬合面上沿牙齿的纵轴施加200N的静载荷，以模拟规则的咀嚼力。对牙根牙本质内的机械应力分布进行了生物力学评估。等效应力（VonMises应力）用于评估机械载荷下下颌牙齿的生物力学特征。
结果：在A组（没有地峡）中，最大应力为22.2MPa,而具有峡部的实验组表现出更高的压力，达到29.4MPa。所有最大应力都集中在根尖孔附近。峡部的存在改变了牙管牙本质壁中的应力分布。值得注意的是,特定位置的牙本质应力表现出差异：在距根尖8毫米处，B组：13.6MPavs.A组：11.4MPa；在距根尖3mm处，C组：14.2MPavs.A组：4.5MPa；在距根尖1mm处，D组：25.1MPavs.A组:10.3MPa。峡部区域内根管牙本质中的最大应力位于峡部的顶部或底部。
结论：根管峡部改变牙本质内的应力分布。最大应力发生在根尖孔附近，当峡部靠近根尖孔时会显着增加。
