Shin C S, Huang Y H, Chi C W, Lin C P
Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan.
Int Endod J. 2014 Sep;47(9):882-8. doi: 10.1111/iej.12233. Epub 2014 Feb 3.
To evaluate the effect of reciprocating amplitude and progressive angular increment on fatigue life enhancement of NiTi rotary endodontic instruments.
ProTaper F2 instruments were operated in steel artificial canals with both stationary reciprocating (SR) and progressive reciprocating (PR) motions. The SR motions involved symmetric to and fro reciprocation of ± 180(o) , ± 135(o) , ± 90(o) , ± 60(o) and ± 45(o) . The PR motions were ± 45(o) stationary motion superimposed with angular increments of 7(o) , 11(o) , 22.5(o) or 31(o) whenever an instrument completed 1, 10 or 30 reciprocating cycles (rc). The fatigue lives were compared with those under continuous rotation (CR) and a reciprocating operation with a forward 144(o) and backward 72(o) motion proposed by Yared (2008). The statistical significance of these operating modes on fatigue life was examined using one way anova and post hoc Tukey's tests at P = 0.05. Fractographic analysis was also applied to probe the fracture mechanisms of different rotation motions.
Fatigue life increased with decreasing reciprocating amplitude. Operating in the SR increased fatigue life by 355% over that in the CR. Except for the 22.5(o) increment, all PR motions yielded longer fatigue lives than the SR motion. A progressive reciprocating operation with a ± 45(o) reciprocating amplitude and a + 7(o) progressive angular increment every 10 reciprocating cycles (± 45(o) /10rc/+7(o) ) increased fatigue life by 990% over that in the CR motion. In terms of life enhancement over the CR motion, the larger the curvature the less are the differences between different movements. Single crack initiation sites were found in the CR and SR motions, while three crack initiation sites were typical in the ± 45(o) /10rc/+7(o) motion.
Fatigue life increased with decreasing reciprocating amplitude in stationary reciprocation. A progressive reciprocating operation with ± 45(o) /10rc/+7(o) motion led to significant fatigue life enhancement and multiple fatigue crack initiation in NiTi endodontic instruments.
评估往复振幅和渐进角增量对镍钛旋转根管器械疲劳寿命提升的影响。
使用ProTaper F2器械在钢制人工根管中进行操作，采用固定往复（SR）和渐进往复（PR）运动。SR运动包括±180°、±135°、±90°、±60°和±45°的对称来回往复运动。PR运动是±45°的固定运动，每当器械完成1、10或30个往复循环（rc）时，叠加7°、11°、22.5°或31°的角增量。将疲劳寿命与连续旋转（CR）以及Yared（2008）提出的向前144°和向后72°的往复操作下的疲劳寿命进行比较。使用单因素方差分析和P = 0.05时的事后Tukey检验来检验这些操作模式对疲劳寿命的统计学显著性。还应用了断口分析来探究不同旋转运动的断裂机制。
疲劳寿命随着往复振幅的减小而增加。与CR相比，SR操作使疲劳寿命提高了355%。除了22.5°增量外，所有PR运动产生的疲劳寿命都比SR运动长。每10个往复循环进行一次±45°往复振幅和+7°渐进角增量的渐进往复操作（±45°/10rc/+7°），与CR运动相比，疲劳寿命提高了990%。就相对于CR运动的寿命提升而言，曲率越大，不同运动之间的差异越小。在CR和SR运动中发现了单个裂纹起始点，而在±45°/10rc/+7°运动中典型地有三个裂纹起始点。
在固定往复中，疲劳寿命随着往复振幅的减小而增加。±45°/10rc/+7°运动的渐进往复操作导致镍钛根管器械的疲劳寿命显著提高和多个疲劳裂纹起始。
