A micro-computed tomographic evaluation of dentinal microcrack alterations during root canal preparation using single‑file Ni‑Ti systems

Abstract

The aim of the present study was to evaluate the length of dentinal microcracks observed prior to and following root canal preparation with different single-file nickel-titanium (Ni-Ti) systems using micro-computed tomography (micro-CT) analysis. A total of 80 mesial roots of mandibular first molars presenting with type II Vertucci canal configurations were scanned at an isotropic resolution of 7.4 µm. The samples were randomly assigned into four groups (n=20 per group) according to the system used for root canal preparation, including the WaveOne (WO), OneShape (OS), Reciproc (RE) and control groups. A second micro-CT scan was conducted after the root canals were prepared with size 25 instruments. Pre- and postoperative cross-section images of the roots (n=237,760) were then screened to identify the lengths of the microcracks. The results indicated that the microcrack lengths were notably increased following root canal preparation (P<0.05). The alterations in microcrack length in the OS group were more significant compared with those in the WO, RE and control groups (P<0.05). In conclusion, the formation and development of dentinal microcracks may be associated with the movement caused by preparation rather than the taper of the files. Among the single-file Ni-Ti systems, WO and RE were not observed to cause notable microcracks, while the OS system resulted in evident microcracks.

Incidence of microcracks after preparation of straight and curved root canals with three different NiTi instrumentation techniques assessed by micro‐CT

“…This finding is in line with previous micro-CT studies demonstrating no influence of root canal preparation with single reciprocating and multiple file rotating NiTi systems on the formation of microcracks (4,15,28). However, root canal curvature did not affect the formation of microcracks and contradicts previous considerations that mechanical preparation of curved root canals may result in increased stress on the dentinal walls with a potential risk for microcracks (6). This is the first investigation on the incidence of microcracks after using different NiTi instrumentation techniques for the preparation of straight and curved root canals using micro-CT.…”

“…Information from previous micro-CT investigations on the incidence of dentinal cracks after root canal preparation with single-file systems is sparse (4,6,28). Root canal preparation of premolars and molars with single-file reciprocating systems (Reciproc, WaveOne) did not induce the formation of dentinal microcracks (4,28).…”

“…Investigations on dentinal microcracks using micro-CT imaging are performed in straight (5,9,15) as well as in curved root canals (4,6,7,14,16) demonstrating a percentage amount of microcracks created by NiTi instruments ranging from 0% to 42%. These conflicting findings reported in micro-CT studies can be due to different scanning resolutions and reconstruction parameters, incorrect interpretation of digital artefacts or differences in the number of cross-sectional images (15,17).…”

“…Moreover, NiTi instruments are stressed during the preparation of curved root canals due to cyclic fatigue caused by alternating compression and tension. Recently, a study using micro-CT imaging demonstrated a significant increase in microcrack length after root canal preparation of mandibular molars using single-file NiTi systems speculating that preparation movement may affect the development of microcracks due to increased stress on the dentinal surface (6). Recently, a study using micro-CT imaging demonstrated a significant increase in microcrack length after root canal preparation of mandibular molars using single-file NiTi systems speculating that preparation movement may affect the development of microcracks due to increased stress on the dentinal surface (6).…”

“…These NiTi file systems differ in cross-sectional shape, alloys, heat treatments and kinematics which may influence the incidence of microcrack formation (1)(2)(3). However, previous in vitro studies have reported inconsistent results with a varying incidence ranging from 0% to 90% new microcracks after root canal preparation with single or multiple file systems operated in rotary or reciprocating motion (4)(5)(6)(7)(8)(9).…”