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.

This study examined the compatibility of 3D-printed artificial teeth and extracted teeth by combining oral cone-beam computed tomography (CBCT) and multi-jet printing technology to print the extracted teeth in vitro. The 3D-printed artificial teeth were then used to choose a master gutta-percha with an appropriate working length and taper to fill root canals. The quality of root canal-filling was evaluated via X-ray. Twenty orthodontically extracted premolars with a single root canal were collected and CBCT-scanned, and the scan data were extracted and converted to 3D models using MIMICS software, which in turn were used to 3D-print artificial teeth using multi-jet printing technology. The artificial teeth were re-scanned by CBCT to acquire 3D scan data, and the 3D deviation between the 3D-printed artificial teeth and extracted teeth was analyzed using Geomagic Studio software, in which the root canal cross-sections at 3 mm, 6 mm and 9 mm from the apex were measured and statistically analyzed. Clinically, three cases of adult anterior teeth with root canals were treated, and artificial teeth for root canal preparation were 3D-printed using multi-jet printing technology. A master gutta-percha with an appropriate working length and taper was matched and chosen to fill the root canal based on the root canal of the 3D-printed artificial tooth, and the quality of filling was evaluated by X-ray. An analysis of the 3D deviation between the 3D-printed artificial teeth prepared by combining oral CBCT and multi-jet printing technology and the original extracted teeth showed that the teeth were well-matched. There were no significant differences between the teeth regarding root canal cross-sections at 3 mm, 6 mm and 9 mm from the apex (P > 0.05). In the three clinical cases, postoperative X-ray examination showed that the root canal filling with the master gutta-percha prepared by in vitro matching based on the 3D-printed artificial teeth was good quality. The combination of CBCT and multi-jet printing technology generated accurate 3D-printed artificial teeth, which provided a master gutta-percha with a matching working length and taper for the in vivo root canal, thus providing a new approach to improve the rate of correct fill-ins in root canal fillings.