Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Lebanese University, Beirut, Lebanon.
Department of Prostethic Dentistry, Faculty of Dentistry, Medical University of Tirana, Tirana, Albania.
J Contemp Dent Pract. 2021 Apr 1;22(4):427-434.
The aim of this systemic review is to investigate these parameters by analyzing the characteristics of fractured instruments to determine which is the most relevant mechanical stress that induces intracanal separation .
The fracture of nickel-titanium (Ni-Ti) instruments is a result of flexural fatigue and torsional fatigue. An electronic search was conducted in MEDLINE database, Web of Science, and Cochrane following preferred reporting items for systematic reviews and meta-analyses guidelines. Data were collected and the key features from the included studies were extracted. Overview quality assessment questionnaire scoring assessed the quality of the articles. A total of 12 articles were selected, where the lowest score was 13.
Considering Ni-Ti rotary instruments, this overall evaluation comprehends 939 broken instruments with an incidence of fracture of 5%. Out of the 12 selected articles, 10 studies revealed that flexural failure was the predominant mode (range of 62-92%). It appears that motion plays an important role when it comes to mechanisms of fracture. The majority of defects found in hand-operated instruments were in the form of torsional failure. Although the major cause of separation of rotary instruments is flexural fatigue, smaller instruments show more torsional fracture than the larger instruments. The average fragment length was found to be 2.5 mm and 3.35 mm, respectively, for torsional failure and flexural failure. The risk of bias depends on fractographic analysis.
Flexural fatigue is the predominant mode of fracture in rotary Ni-Ti instruments. The type of motion and size of the instrument seem to affect the mechanism of fracture. Fragment length may show a strong association with the type of fracture mechanism.
This systemic review found that flexural fatigue is the most relevant mechanical stress that induces intracanal separation . Moreover, in clinical practice, the fragment length might be an excellent indicator of the type of fracture.
本系统评价的目的是通过分析折断器械的特征来研究这些参数，以确定导致根管内分离的最相关的机械应力。
镍钛（Ni-Ti）器械的折断是弯曲疲劳和扭转疲劳的结果。根据系统评价和荟萃分析报告的首选项目，在 MEDLINE 数据库、Web of Science 和 Cochrane 中进行了电子检索。收集数据并提取纳入研究的关键特征。概述质量评估问卷评分评估了文章的质量。共选择了 12 篇文章，其中最低得分为 13 分。
考虑到 Ni-Ti 旋转器械，总体评估包括 939 根折断器械，折断发生率为 5%。在选择的 12 篇文章中，有 10 项研究表明弯曲失效是主要模式（范围为 62%-92%）。运动似乎在断裂机制中起着重要作用。在手动器械中发现的大多数缺陷形式为扭转失效。虽然旋转器械分离的主要原因是弯曲疲劳，但较小的器械比较大的器械更容易发生扭转断裂。扭转失效和弯曲失效的平均断片长度分别为 2.5mm 和 3.35mm。偏倚风险取决于断口分析。
弯曲疲劳是旋转 Ni-Ti 器械断裂的主要模式。运动类型和器械尺寸似乎会影响断裂机制。断片长度可能与断裂机制类型有很强的关联。
本系统评价发现弯曲疲劳是导致根管内分离的最相关的机械应力。此外，在临床实践中，断片长度可能是断裂类型的一个很好的指标。
