Grande N M, Plotino G, Pecci R, Bedini R, Malagnino V A, Somma F
Department of Endodontics, Catholic University of Sacred Heart, Rome, Italy.
Int Endod J. 2006 Oct;39(10):755-63. doi: 10.1111/j.1365-2591.2006.01143.x.
To determine how instrument design affects the fatigue life of two nickel-titanium (Ni-Ti) rotary systems (Mtwo and ProTaper) under cyclic fatigue stress in simulated root canals.
Cyclic fatigue testing of instruments was performed in stainless steel artificial canals with radii of curvature of 2 or 5 mm and an angle of curvature of 60 degrees . A total of 260 instruments were rotated until fracture occurred and the number of cycles to failure were recorded. The morphology of Ni-Ti rotary instruments was investigated by measuring the volume of millimetre slices of each instrument size starting from the tip to the shank by means of microCT analysis. The fracture surface of three representative samples of each size was analysed by scanning electron microscopy (SEM). Data were analysed by one-way anova, Holm t-test, paired t-test and linear regression; the significance was determined at the 95% confidence level.
Cycles to failure significantly decreased as the instrument volume increased for both the radii of curvature tested (P < 0.01). The radius of curvature had a statistically significant influence on the fatigue life of the instruments (P < 0.05). Larger instruments underwent fracture in less time under cyclic stress than smaller ones. SEM evaluation showed typical features of fracture through fatigue failure.
The metal volume in the point of maximum stress during a cyclic fatigue test could affect the fatigue life of Ni-Ti rotary instruments. The larger the metal volume, the lower the fatigue resistance.
确定器械设计如何影响两种镍钛（Ni-Ti）旋转系统（Mtwo和ProTaper）在模拟根管内循环疲劳应力下的疲劳寿命。
在半径为2或5毫米、曲率角为60度的不锈钢人工根管中对器械进行循环疲劳测试。总共260根器械旋转直至发生断裂，并记录失效循环次数。通过微型计算机断层扫描（microCT）分析，从器械尖端到柄部测量每种器械尺寸的毫米切片体积，研究Ni-Ti旋转器械的形态。对每种尺寸的三个代表性样品的断裂表面进行扫描电子显微镜（SEM）分析。数据采用单因素方差分析、霍尔姆t检验、配对t检验和线性回归进行分析；显著性在95%置信水平下确定。
对于所测试的两种曲率半径，随着器械体积增加，失效循环次数显著减少（P < 0.01）。曲率半径对器械的疲劳寿命有统计学显著影响（P < 0.05）。在循环应力下，较大的器械比较小的器械更快发生断裂。SEM评估显示了疲劳失效断裂的典型特征。
循环疲劳测试中最大应力点处的金属体积可能影响Ni-Ti旋转器械的疲劳寿命。金属体积越大，抗疲劳能力越低。
