de Carvalho Kleber Kildare Teodoro, Moriya Paulo Takeji, Kishen Anil, Martins Jorge N R, Silva Emmanuel João Nogueira Leal, Alcalde Murilo P, Fernandes Francisco Manuel Braz, Souza Erick Miranda, Versiani Marco Aurélio
Department of Endodontics, Núcleo de Estudos Odontológicos (NEO), São Paulo, Brazil.
Private Practice, São Bernardo do Campo, São Paulo, Brazil.
Clin Oral Investig. 2025 Feb 8;29(2):122. doi: 10.1007/s00784-025-06193-9.
This study aimed to compare the stress produced by three heat-treated flat-side prototype rotary instruments and a non-flat side instrument on the internal walls of simulated canals with three different curvature degrees using the photoelastic technique.
Thirty-six resin blocks with simulated canals, comprising three curvature types (45°, 60°, and double curvature), were used in the study, with 12 blocks allocated to each curvature type. These blocks were further divided into four experimental groups (n = 9 per group) based on the heat treatment of the instruments: gold, silver, blue, and a control group with non-flat-side gold instruments. The blocks were analyzed using a circular polariscope setup, with real-time birefringence patterns captured by a digital camera. Stress on canal walls was evaluated using a semi-quantitative scale. Supplementary tests (stereomicroscope, SEM, energy-dispersive X-ray spectroscopy, and DSC) were performed to interpret the results further. Data were analyzed using the Kruskal-Wallis test (α = 5%).
Inter- and intra-observer agreements were 0.91 and 1, respectively. All instruments exhibited high stress patterns on canal walls. The highest stress was observed in the 45° and 60° blocks (middle third) and the double curvature blocks (apical third). The flat-side gold instrument recorded the highest stress in the coronal third, and the flat-side blue in the apical third (p < 0.05). All instruments displayed some degree of distortion after use.
Instrument type and canal curvature significantly influenced stress distribution across root canal thirds. All flat-side instruments exhibited high stress patterns, warranting caution in curved canals due to potential distortion and performance impact.
This study recommended caution when using newly designed flat-side instruments in curved canals due to potential stress on canal walls and greater distortion, which may affect performance and durability.
本研究旨在使用光弹性技术，比较三种热处理后的平面原型旋转器械和一种非平面器械在具有三种不同弯曲度的模拟根管内壁上产生的应力。
本研究使用了36个带有模拟根管的树脂块，包括三种弯曲类型（45°、60°和双弯曲），每种弯曲类型有12个树脂块。根据器械的热处理情况，这些树脂块进一步分为四个实验组（每组n = 9）：金色、银色、蓝色，以及一个使用非平面金色器械的对照组。使用圆偏振光装置对树脂块进行分析，用数码相机实时捕捉双折射图案。使用半定量量表评估根管壁上的应力。进行补充测试（立体显微镜、扫描电子显微镜、能量色散X射线光谱和差示扫描量热法）以进一步解释结果。使用Kruskal-Wallis检验（α = 5%）分析数据。
观察者间和观察者内的一致性分别为0.91和1。所有器械在根管壁上均呈现出高应力模式。在45°和60°的树脂块（中三分之一）以及双弯曲树脂块（根尖三分之一）中观察到最高应力。平面金色器械在冠三分之一处记录到最高应力，平面蓝色器械在根尖三分之一处记录到最高应力（p < 0.05）。所有器械在使用后均表现出一定程度的变形。
器械类型和根管弯曲度显著影响根管各三分之一处的应力分布。所有平面器械均呈现出高应力模式，由于可能的变形和性能影响，在弯曲根管中使用时需谨慎。
本研究建议，由于可能对根管壁产生应力以及更大的变形，在弯曲根管中使用新设计的平面器械时应谨慎，这可能会影响器械的性能和耐用性。
