# Root Canal Preparation of a Commercial Artificial Tooth versus Natural Tooth--A MicroCT Study
## 4 Discussion  
The first aim of this study was to evaluate the time and number of pecking movements needed to prepare NT canals versus AT canals. The mean time of preparation for ATs was one second less, and they needed fewer pecking movements for canal preparation. These findings indicate that, although being faster and needing fewer pecking movements to prepare the AT canals, perhaps due to the difference in the hardness between resin  
Figure 4: NT mesiobuccal root after instrumentation: (**A**) raw image from microCT dataset; (**B**) image with threshold applied; (**C**) binarized black and white image; (**D**) histogram with selected threshold values. Figure 3: NT mesiobuccal root before instrumentation: (**A**) raw image from microCT dataset; (**B**) image with threshold applied; (**C**) binarized black and white image; (**D**) histogram with selected threshold values. and human dentine [7; 10; 11], there were no statistically significant differences between them. Therefore, we accepted the null hypothesis. This result is in accordance with the results observed in the study of [PERSON] et al. (2015), which compared the difference of the time of preparation needed by students and specialists, using hand-files, between NTs and ATs. They concluded that the time needed to prepare ATs was lower than NTs, in both groups [23]. In this study, the mean value of the preparation time for NTs was 64.3 s with the PTG system, which is less compared to the study of [PERSON] et al. (2017), which showed a mean value of 78 s. Nonetheless, the authors did not make any reference to whether the glide path was performed manually or mechanically or even if it was performed, and this could explain the difference between the two values [24]. The literature shows that a mechanical glide path is faster than a manual glide path [25; 26]; furthermore, if a glide path is not performed, the root preparation time is longer [27]. In the study of [PERSON] et al. (2016), 43 students were divided in two groups; one group only trained on ATs (TrueTooth(r)), the test group, and the other on NTs, the control group. The students had to attend a training period, and after this period, both groups prepared an NT and an AT and were evaluated. It was concluded that students solely trained on ATs did not perform significantly different on NTs than those trained on NTs; nonetheless, in general, the performance of students tended to be better on ATs than NTs [9]. Furthermore, in the study of [PERSON] et al. (2020), students were asked to perform endodontic treatments on different commercial ATs, and then, their outcome was evaluated by three calibrated experienced endodontic educators. The ATs were compared from three perspectives: students' achievements, students' perceptions, and educators' perceptions. The educators considered that replicas obtained from microCT scans better reproduced the internal anatomy, and specifically, TrueTooth(r) was the best replica for the training of access cavity preparation and negotiation. On the other hand, students rated and performed on TrueTooth(r) less well due to the greater level of difficulty compared to ATs [5]. The results of these two studies, and the results of the present study, regarding preparation time and the number of pecking movements needed for root canal preparation support that TrueTooth(r) can potentially be used for endodontic training. However, future studies are needed using different preparation systems, with different geometries and movements of preparation. The second aim of this study was to evaluate if the root canal volume increase was similar between ATs and NTs. In fact, there was a significant statistical difference between ATs and NTs, the root canal volume increase being higher in NTs. However, as we stated before, after the canal preparation of ATs, some samples showed negative values; this would mean a loss of volume after preparation, and this situation seems absurd.