The characteristics of superelasticity and shape-memory of the NiTi make endodontic rotary files suitably flexible and resistant while operating within curved canals. However, continuous rotation within accentuated curvatures causes stresses that can lead to intraoperative fracture by torsional shear or flexural cyclic fatigue. The aim of this paper is to design and build a rotary bending testing machine able to estimate reproducibly the fatigue life of endodontic instruments. The main innovation of this apparatus consists in ensuring that the file rotates freely, not being forced within a suitable shaped housing, and this provides both advantages of reducing the influence of the friction phenomena and maintaining unchanged geometric parameters. A further element of novelty is the real-time measurement of the bending force during the test up to the failure. Moreover, such a machine makes it possible to perform predictive thermographic tests of the file fatigue life and to monitor the energetic trend of the static and rotary bending while testing.

中文翻译：

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新型牙髓锉循环疲劳试验机

NiTi 的超弹性和形状记忆特性使牙髓旋转锉在弯曲的根管内操作时具有适当的灵活性和抵抗力。然而，在增强的曲率内连续旋转会产生应力，从而可能因扭转剪切或弯曲循环疲劳而导致术中骨折。本文的目的是设计和建造一种能够重复估计牙髓器械疲劳寿命的旋转弯曲试验机。该设备的主要创新在于确保锉刀自由旋转，而不是被迫在合适形状的外壳内，这提供了减少摩擦现象影响和保持几何参数不变的优点。另一个新颖的元素是在测试期间实时测量弯曲力直至失效。此外，这样的机器可以执行文件疲劳寿命的预测热成像测试，并在测试时监测静态和旋转弯曲的能量趋势。