Silva Emmanuel J N L, Martins Jorge N R, Alcalde Murilo Priori, Versiani Marco A
School of Dentistry, Grande Rio University (UNIGRANRIO), Rio de Janeiro, Brazil.
Department of Endodontics, Rio de Janeiro State University, Rio de Janeiro, Brazil.
Int Endod J. 2025 Aug;58(8):1267-1276. doi: 10.1111/iej.14257. Epub 2025 May 23.
This study aims to demonstrate that phase transformation analysis, assessed via differential scanning calorimetry (DSC), offers a more comprehensive understanding of NiTi instruments' mechanical behaviour than traditional fixed-temperature fatigue testing by evaluating phase transformation temperatures and their impact on cyclic fatigue strength of ProTaper Universal and ProTaper Gold at 20 and 35°C.
Fifty ProTaper Universal F2 (n = 25) and ProTaper Gold F2 (n = 25) NiTi instruments were compared for geometric design (blade length, helical spirals, spiral density, spiral geometry, tip design and surface quality) and metallurgical properties including elemental analysis (energy-dispersive X-ray spectroscopy) and phase transformation temperatures. Then, cyclic fatigue strength was tested at room (20 ± 1°C) and body (35 ± 1°C) temperatures using a standardized artificial canal and cyclic fatigue resistance test. Time to fracture (in seconds) was recorded, and data were statistically analysed using the independent Student's t-test for intergroup analysis and the paired Student's t-test for intragroup analysis (α = 5%).
Both instruments had a 17 mm blade with 10 spirals (0.59 spirals/mm), similar geometry and NiTi wires with near-equiatomic nickel-titanium ratios, differing only in metal alloy colour. DSC analysis showed distinct phase transformation temperatures, with ProTaper Universal exhibiting an R-phase start (Rs) at 16.2°C and finish (Rf) at -12.7°C, while ProTaper Gold had an Rs at 44.0°C and Rf at 28.6°C, though both transitions occurred gradually. Fracture time was significantly longer at 20°C than at 35°C for both instruments (p < 0.05), with ProTaper Gold showing a greater reduction (58%) but maintaining superior cyclic fatigue strength at both temperatures (p < 0.05).
The cyclic fatigue strength of NiTi instruments depends on temperature, highlighting the limits of assessing performance at a single predefined temperature. DSC offers key insights into phase transformation, enabling a better interpretation of mechanical properties beyond mechanical testing alone. Integrating metallurgical characterization with cyclic fatigue analysis improves the evaluation of NiTi instruments, ensuring a more accurate understanding of their mechanical performance.
本研究旨在证明，通过差示扫描量热法（DSC）进行的相变分析，通过评估相变温度及其对ProTaper Universal和ProTaper Gold在20℃和35℃下的循环疲劳强度的影响，比传统的固定温度疲劳测试能更全面地了解镍钛器械的力学行为。
比较了50支ProTaper Universal F2（n = 25）和ProTaper Gold F2（n = 25）镍钛器械的几何设计（刀片长度、螺旋线、螺旋密度、螺旋几何形状、尖端设计和表面质量）以及冶金性能，包括元素分析（能量色散X射线光谱法）和相变温度。然后，使用标准化人工根管和循环疲劳抗性测试，在室温（20±1℃）和体温（35±1℃）下测试循环疲劳强度。记录断裂时间（以秒为单位），并使用独立样本t检验进行组间分析，使用配对样本t检验进行组内分析对数据进行统计学分析（α = 5%）。
两种器械均有17毫米长的刀片，带有10个螺旋（0.59个螺旋/毫米），几何形状相似，镍钛丝的镍钛原子比接近等原子比，仅金属合金颜色不同。DSC分析显示出不同的相变温度，ProTaper Universal在16.2℃出现R相起始（Rs），在-12.7℃出现R相结束（Rf），而ProTaper Gold的Rs为44.0℃，Rf为28.6℃，尽管两种转变都是逐渐发生的。两种器械在20℃时的断裂时间均显著长于35℃时（p < 0.05），ProTaper Gold的降幅更大（58%），但在两个温度下均保持了优异的循环疲劳强度（p < 0.05）。
镍钛器械的循环疲劳强度取决于温度，突出了在单一预定义温度下评估性能的局限性。DSC为相变提供了关键见解，能够在仅进行力学测试之外更好地解释力学性能。将冶金表征与循环疲劳分析相结合可改善对镍钛器械的评估，确保更准确地了解其力学性能。
