Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Seoul National University, Seoul, Korea.
J Endod. 2011 Sep;37(9):1283-6. doi: 10.1016/j.joen.2011.05.032. Epub 2011 Jul 16.
The aim of this study was to evaluate the theoretical effect from pitch and cross-sectional geometry on torsional stiffness of nickel-titanium (NiTi) instruments.
Finite element models of NiTi rotary instruments with different cross-sectional geometries and different number of threads were made for comparison of torsional stiffness. Four cross-sectional shapes were tested: triangle, slender rectangle, rectangle, and square. Taper and external peripheral radius were the same for all models, whereas cross-sectional area and/or center core area were varied. Three pitch values (5, 10, and 15 threads) were tested for each type of cross-sectional geometry. The torsional stiffness of the 12 resulting finite element models was calculated by twisting the file shanks 20 degrees while holding the file tip at apical 4 mm.
The file models with larger pitch (fewer threads) had lower torsional stiffness. The models with the rectangular cross section had higher torsional stiffness than models with the triangular cross section, even when the cross-sectional areas were the same or the center core area was smaller. File models with larger cross-sectional area had higher torsional stiffness.
Torsional deformation and/or fracture of NiTi rotary files might be reduced by reducing the pitch (increasing the number of threads) and increasing the cross-sectional areas rather than the center core area.
本研究旨在评估扭转刚度的理论效果，即从镍钛（NiTi）器械的节距和横截面几何形状上。
制作了不同横截面几何形状和不同螺纹数量的镍钛旋转器械的有限元模型，以比较扭转刚度。测试了四种横截面形状：三角形、细长矩形、矩形和正方形。所有模型的锥度和外周半径相同，而横截面积和/或中心芯面积则有所不同。每种类型的横截面几何形状都测试了三个螺距值（5、10 和 15 个螺纹）。通过将文件柄扭转 20 度，同时将文件尖端保持在根尖 4 毫米处，计算 12 个由此产生的有限元模型的扭转刚度。
螺距较大（螺纹较少）的文件模型扭转刚度较低。矩形横截面的模型比三角形横截面的模型具有更高的扭转刚度，即使横截面积相同或中心芯面积较小也是如此。具有较大横截面积的文件模型具有更高的扭转刚度。
通过减小螺距（增加螺纹数量）和增加横截面积而不是中心芯面积，可以减少 NiTi 旋转锉的扭转变形和/或断裂。
