Effect of Reciprocating Systems and Working Lengths on Apical Microcrack Development: a micro-CT Study

Abstract The objective of this study was to evaluate the effect of root canal preparation with single-file reciprocating systems at different working lengths on the development of apical microcracks using micro-computed tomographic (micro-CT) imaging. Forty extracted human mandibular incisors were randomly assigned to 4 groups (n=10) according to the systems and working length used to prepare the root canals: Group A - WaveOne Gold at apical foramen (AF), Group B - WaveOne Gold 1 mm short of the AF (AF-1 mm), Group C - Unicone (AF) and Group D - Unicone (AF-1 mm). Micro-CT scanning was performed before and after root canal preparation at an isotropic resolution of 14 µm. Then, three examiners assessed the cross-sectional images generated to detect microcracks in the apical portion of the roots. Apical microcracks were visualized in 3, 1, 1, and 3 specimens in groups A, B, C, and D, respectively. All these microcracks observed after root canal preparation already existed prior to instrumentation, and no new apical microcrack was detected. For all groups, the number of slices presenting microcracks after root canal preparation was the same as before canal preparation. Root canal preparation with WaveOne Gold and Unicone, regardless of the working length, was not associated with apical microcrack formation.

摘要 本研究旨在通过显微计算机断层扫描（micro-CT）成像，评估采用不同工作长度的单锉往复式根管预备系统进行根管预备时，对根尖微裂纹形成的影响。选取40颗拔除的人下颌切牙，根据所用根管预备系统及工作长度随机分为4组（每组n=10）：A组——WaveOne Gold系统预备至根尖孔（apical foramen, AF）；B组——WaveOne Gold系统预备至距根尖孔1 mm处（AF-1 mm）；C组——Unicone系统预备至根尖孔（AF）；D组——Unicone系统预备至距根尖孔1 mm处（AF-1 mm）。分别于根管预备前后以14 μm的各向同性分辨率开展micro-CT扫描。随后由3名检查者对生成的牙根根尖部横断面图像进行评估，以检测微裂纹。结果显示，A、B、C、D组分别有3、1、1、3个样本观察到根尖微裂纹。所有根管预备后发现的微裂纹均在预备前已存在，未检测到新的根尖微裂纹。所有组别中，根管预备后出现微裂纹的断层切片数量与预备前保持一致。综上，无论采用何种工作长度，WaveOne Gold与Unicone系统实施根管预备均不会导致根尖微裂纹的形成。