## 4 Discussion  
The minimally invasive endodontics concept is spreading in all the phases of the root canal treatment, starting from the access cavity to shaping, 3D cleaning, and ultimately to three-dimensional obturation [10]. In general, the root canal mechanical preparation is a crucial phase on which the quality of the entire endodontic treatment depends. All vital and necrotic pulp tissue, bacteria, and toxins are removed from the main canal during this phase. The root canal dentin is also shaped to create a space to accommodate for the cleaning and filling phases also to eliminate bacteria deep in the dental tubules. Significantly, this step can be critical when treating necrotic teeth or in the case of endodontic retreatments. The proper shaping of the canal must respect the original anatomy without altering it and evade excessive dentin removal to avoid the risk of microcracks or stripping. Root canal shaping procedures and rotary instrumentation can potentially induce cracks. Accordingly, once the tooth is in function and rehabilitated, it can lead to complete fractures. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **N** & **Mean \(\pm\) SD** & \(p\)** \\ \hline \multirow{3}{*}{**Teeth**} & 1 st Premolars & 50 & 1 \(\pm\) 0.39 & \multirow{3}{*}{**0.008**} \\  & 2 nd Premolars & 50 & 1.12 \(\pm\) 0.3 & \\ \hline \multirow{3}{*}{**Roots**} & Buccal Roots & 104 & 0.98 \(\pm\) 0.39 & \multirow{3}{*}{0.09} \\  & Palatal Roots & 104 & 1 \(\pm\) 0.39 & \\ \hline \multirow{3}{*}{**Sections**} & M-D Sections & 152 & 1 \(\pm\) 0.35 & \multirow{3}{*}{0.14} \\  & B-P Sections & 152 & 1.1 \(\pm\) 0.39 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Frequency of measurements, means, and standard deviations of each measurement. Independent two sample \(t\)-tests were performed to compare measurements between teeth (1 st premolars vs. 2 nd premolars), roots of monorradicular premolars (buccal vs. palatal), and sections (mesio-distal vs. bucco-palatal). Statistically significant differences are in bold type. According to various authors, several factors regarding nickel-titanium tools can influence microcrack formation, such as heat treatments, design, cross-sectional shape, and kinematics [11, 12]. Advances in Ni-Ti instruments and their kinematics have made it possible to model root canals with single-file systems activated with rotational or reciprocating motion [13, 14]. Moreover, the shaping must maintain the foramen in its original anatomy without creating any modifications. [PERSON] et al., in a review of the literature, analyzed three-dimensionally the biomechanical preparation of root canals using micro-computed tomography as regards to the final diameter; the studies examined by the authors showed that the final diameter of the instruments used for the biomechanical preparation varied from a diameter of 25/100 mm to a diameter of 40/100 mm, with a diameter of 30/100 mm being the most used in these canals. The mesial canals of the mandibular molars were the most used specimen among the studies examined, and the diameter of these canals at 1 mm of the apical foramen ranged between 0.28-0.40 mm in the buccal direction and 0.21-0.28 mm in the mesio-distal direction [13]. An equally important aspect to avoid during the mechanical preparation is fracturing the rotating files. Separating a file inside the canals can complicate the treatment and alter the prognosis, as retrieving it can be unachievable. Hence, a fracture of an endodontic instrument can also lead to treatment failure. Nowadays, with the aid of powerful irrigant activation systems, it is feasible to perform conservative shaping and obtain outstanding results in cleaning the walls and the success rates. According to [PERSON] et al., satisfactory outcomes are obtained using the intracanal heating of sodium hypochlorite associated with ultrasonic activation when performed after conservative preparations using rotary files 20.05 [15, 16].