## 4 Discussion
Nevertheless, differences in the methodology in respect to the evaluation of the filling seal through radiographs and scores, as well as the use of naturally extracted teeth, might have influenced the results. It was also reported that systems using fewer files were less time-consuming. Instead, a previous study of our group did not find differences between single-file or multi-instrument systems, emphasizing that the creation of a glidepath, manual (10 KS-file) or mechanized (ProGlider), can influence the results, [11]. Furthermore, differences in methodology, such as considering manual (K-flex stainless steel files) and several machine-driven systems, such as ProTaper Universal, ProTaper Next and Wave One, may account for the differences [16]. Additionally, apart from reporting that the manufacturer's manual was followed, there is no mention of the creation of a glidepath or maintenance of patency during the root canal preparation, as stressed in the present work. The promising findings of this pilot study justify implementing the experience with a larger number of students, to evaluate the impact of several factors, such as teaching methodology and training levels, as well as different assessment criteria for evaluation. The existence of a short learning curve, using a reciprocating system, was evidenced in the present study, with significant time-reduction in instrumentation, after the preparation of 20 L-simulated root canals. In addition, a good filling quality was generally registered. This has been also corroborated by other investigations, either with experienced operators or students [32]. Other characteristics inherent to these systems, such as, being \"single-use\" systems, with a reduced risk of cross-infection and instrument fracture, improves the safety of the procedures [3; 4]. Moreover, students seem to prefer the \"single-file\" systems with a smaller number of instruments due to their ease of learning [4]. Despite the recommended \"single use\" of some instrumentation systems, mechanized files are generally used, in clinical settings, in more than one canal, such as in the case of multirooted teeth, being reported as very safe instruments [6; 34]. In the present investigation, the instruments, according to similar studies, were discarded after five uses, which means five simulated canals [2; 34], its use reported by some studies until five teeth [33]. In any case, the lack of variability between the simulated canals anatomy did not allow to infer other factors that could influence a potential wear that could impact the treatment quality [34]. Technological advances in materials and the greater predictability of endodontic nickel-titanium instruments compared to stainless steel instruments have reduced procedural errors and complications in endodontic treatments [2; 32; 35]. In the present work, no iatrogenic errors were detected. Other novel materials recently proposed for root canal filling, such as the hydraulic calcium silicate-based endodontic cements [36], represent a new challenge to search for the interaction of specific materials and proper clinical protocols. The need for standardization prevented its study in the present undergraduate setting. In the present pilot study, the emphasis on the short learning curve was directly correlated with an improvement in treatment (instrumentation and filling), concerning time. This aspect alone should not be the primary aim in the search for ET quality, even though improving any technical procedure implies training periods to acquire the needed skills. In this sense, the stabilization of the treatment time after 20 preparations supports the previous curricular guidelines for the undergraduate teaching of Endodontics [37], recommending a minimum of 20 root canal treatments before graduation, clinical or preclinical, to achieve the minimum competences in the ET of simple cases.