Department of Endodontics, Faculdade de Medicina Dentária, Universidade de Lisboa, Lisboa, Portugal; Grupo de Investigação em Bioquimica e Biologia Oral, Unidade de Investigação em Ciências Orais e Biomédicas, Faculdade de Medicina Dentária, Universidade de Lisboa, Lisboa, Portugal; Centro de Estudo de Medicina Dentária Baseada na Evidência, Cochrane Portugal, Faculdade de Medicina Dentária, Universidade de Lisboa, Lisboa, Portugal.
UNIDEMI, Department of Mechanical and Industrial Engineering, NOVA School of Science and Technology, Universidade NOVA de Lisboa, Caparica, Portugal.
J Endod. 2022 Aug;48(8):985-1004. doi: 10.1016/j.joen.2022.05.007. Epub 2022 Jun 3.
Instruments' mechanical strength and flexibility are traditionally tested by running cyclic fatigue, torsional, bending, buckling, and microhardness tests. Several cyclic fatigue test models have been used in endodontics, all capable of providing a curved trajectory for the instrument to rotate. Cyclic fatigue testing allows the identification of conditions that may affect the fatigue strength outcomes, such as the canal radius and degree of curvature, handpiece static versus dynamic motions, test temperature, kinematics, instrument previously wear and sterilization cycles, or instrument's size and metal alloy features. Because of the international test specifications for both torsional and bending tests, the variations of their models are not as many as for cyclic fatigue. These tests have also identified conditions capable of affecting the outcomes, such as kinematics, instruments' preloading, cross-sectional diameters, or alloy heat treatments. Buckling and microhardness are less common, with the metal alloy being considered to have a major influence on the results. Instruments' mechanical testing, having all these individual conditions as independent variables, allowed the understanding of them and molded the way the technical procedures are performed clinically. Even though the artificiality and simplicity of these tests will hardly mimic real working situations, and independent of being capable of producing cornerstone knowledge, these tests are also associated with inconsistency, a lack of reproducibility, and low external validity. Several attempts have been made to increase the generalizability of the outcomes by adding test settings that intend to mimic the clinical condition. Although pertinent, these settings may also add variabilities inherent to their concepts and practical applications in the laboratory environment. Although the actual studies should be seen as laboratory mechanical tests that measure very specific parameters under very particular conditions and that by far do not mimic the clinical condition, the lower validity drawback seems to be possible to be minimized when achieving a comprehensive understanding of the instrument behavior. A finite element method and/or a multimethod research approach may lead to superior data collection, analysis, and interpretation of results, which when associated with a reliable confounding factor control and proper study designs may be helpful tools and strategies in order to increase the reliability of the outcomes.
器械的机械强度和柔韧性传统上通过进行循环疲劳、扭转、弯曲、屈曲和显微硬度测试来测试。在牙髓学中已经使用了几种循环疲劳测试模型，所有这些模型都能够为器械的旋转提供弯曲的轨迹。循环疲劳测试允许识别可能影响疲劳强度结果的条件，例如根管半径和曲率程度、机头静态与动态运动、测试温度、运动学、器械的先前磨损和消毒循环或器械的尺寸和金属合金特性。由于国际上对扭转和弯曲测试都有测试规范，因此它们的模型变化并不像循环疲劳测试那么多。这些测试还确定了能够影响结果的条件，例如运动学、器械的预加载、横截面直径或合金热处理。屈曲和显微硬度则不太常见，金属合金被认为对结果有重大影响。器械的机械测试将所有这些单独的条件作为自变量，使人们能够理解它们，并塑造了临床执行技术程序的方式。尽管这些测试的人为性和简单性几乎无法模拟真实的工作情况，并且尽管能够产生基石知识，但它们也与不一致性、可重复性差和外部有效性低有关。已经做出了一些尝试来通过添加旨在模拟临床情况的测试设置来提高结果的可推广性。尽管这些设置与临床相关，但它们也可能增加其概念和在实验室环境中的实际应用固有的变异性。尽管实际研究应被视为在非常特殊的条件下测量非常特定参数的实验室机械测试，并且远不能模拟临床情况，但当全面了解器械行为时，似乎可以最大限度地减少低有效性的缺点。有限元方法和/或多方法研究方法可能会导致更好的数据收集、分析和结果解释，当与可靠的混杂因素控制和适当的研究设计相结合时，这些方法可能是提高结果可靠性的有用工具和策略。
