Division of Endodontics, Department of Oral Biological & Medical Sciences, Faculty of Dentistry, The University of British Columbia, Vancouver, BC, Canada.
Int Endod J. 2013 Aug;46(8):720-9. doi: 10.1111/iej.12049. Epub 2013 Jan 21.
To analyse the type and location of defects in HyFlex CM instruments after clinical use in a graduate endodontic programme and to examine the impact of clinical use on their metallurgical properties.
A total of 468 HyFlex CM instruments discarded from a graduate endodontic programme were collected after use in three teeth. The incidence and type of instrument defects were analysed. The lateral surfaces of the defect instruments were examined by scanning electron microscopy. New and clinically used instruments were examined by differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Vickers hardness was measured with a 200-g load near the flutes for new and clinically used axially sectioned instruments. Data were analysed using one-way anova or Tukey's multiple comparison test.
Of the 468 HyFlex instruments collected, no fractures were observed and 16 (3.4%) revealed deformation. Of all the unwound instruments, size 20, .04 taper unwound the most often (n = 5) followed by size 25, .08 taper (n = 4). The trend of DSC plots of new instruments and clinically used (with and without defects) instruments groups were very similar. The DSC analyses showed that HyFlex instruments had an austenite transformation completion or austenite-finish (Af ) temperature exceeding 37 °C. The Af temperatures of HyFlex instruments (with or without defects) after multiple clinical use were much lower than in new instruments (P < 0.05). The enthalpy values for the transformation from martensitic to austenitic on deformed instruments were smaller than in the new instruments at the tip region (P < 0.05). XRD results showed that NiTi instruments had austenite and martensite structure on both new and used HyFlex instruments at room temperature. No significant difference in microhardness was detected amongst new and used instruments (with and without defects).
The risk of HyFlex instruments fracture in the canal is very low when instruments are discarded after three cases of clinical use. New HyFlex instruments were a mixture of martensite and austenite structure at body temperature. Multiple clinical use caused significant changes in the microstructural properties of HyFlex instruments. Smaller instruments should be considered as single-use.
分析在研究生牙髓学课程中临床使用后 HyFlex CM 器械的类型和位置，并研究临床使用对其冶金性能的影响。
共收集了 468 根从研究生牙髓学课程中废弃的 HyFlex CM 器械，这些器械在 3 颗牙齿中使用后丢弃。分析器械缺陷的发生率和类型。用扫描电子显微镜检查有缺陷器械的侧面。用差示扫描量热法（DSC）和 X 射线衍射（XRD）检查新的和临床使用的器械。用 200 克载荷在靠近螺旋槽处测量新的和临床使用的轴向剖分器械的维氏硬度。使用单向方差分析或 Tukey 多重比较检验分析数据。
在收集的 468 根 HyFlex 器械中，没有观察到断裂，有 16 根（3.4%）发生变形。所有未展开的器械中，20 号、0.04 锥度的展开次数最多（n=5），其次是 25 号、0.08 锥度的展开次数（n=4）。新器械和临床使用（有缺陷和无缺陷）器械组的 DSC 曲线趋势非常相似。DSC 分析表明，HyFlex 器械的奥氏体相变完成或奥氏体结束（Af）温度超过 37°C。经过多次临床使用后，HyFlex 器械（有缺陷和无缺陷）的 Af 温度明显低于新器械（P<0.05）。在尖端区域，变形器械马氏体向奥氏体转变的焓值小于新器械（P<0.05）。XRD 结果表明，室温下新的和使用过的 HyFlex 器械均具有奥氏体和马氏体结构。新器械和使用过的器械（有缺陷和无缺陷）之间的显微硬度没有显著差异。
在临床使用三例后丢弃 HyFlex 器械时，器械在根管中发生断裂的风险非常低。新的 HyFlex 器械在体温下是马氏体和奥氏体结构的混合物。多次临床使用导致 HyFlex 器械的微观结构性能发生显著变化。较小的器械应考虑为一次性使用。
