# Root Canal Preparation of a Commercial Artificial Tooth versus Natural Tooth--A MicroCT Study
## 1 Introduction  
Bacteria are the main cause of pulpal and periapical pathologies. Therefore, all endodontic procedures aim to eliminate pulp tissue, as well as as many bacteria as possible [1]. Root canal mechanical preparation is an important step to achieve this goal while simultaneously increasing the root canal volume to facilitate the decontamination of the root canal system by irrigants and medicaments [2; 3]. To accomplish this, a variety of manual and rotary instruments have been proposed. The revolution in the manufacturing of root canal instruments has led to a great variety of these endodontic instruments when comparing the design, alloys, and type of movement. Many new systems are available on the market, and clinicians require an impartial evaluation of their characteristics to help them in selecting systems to use clinically [1; 2; 4]. ProTaper Gold(r) (Dentsply Sirona) (PTG) uses control memory wire, which has a lower percentage of nickel (by weight), and because of the thermic treatments used during the manufacturing process, it does not rebound to its original shape after being flexed; this characteristic reportedly increases its flexibility [1; 2; 3; 4]. Among the most-important basic topics under research concerning root canal preparation are: (1) the removal of dentin and the volume increase; (2) straightening and transportation; (3) unprepared root canal areas; and (4) working time [5; 6]. Traditionally, for ex vivo studies and pre-clinical courses, extracted human teeth have been the standard practice [7; 8; 9]. However, natural teeth (NTs) have several drawbacks, which have been discussed in recent years: they are difficult to collect, and there are ethical considerations, potential cross-infection risks, storage drawbacks, and standardization issues [7; 8; 10; 11]. When using NTs, the external and internal anatomy should be fairly balanced between the groups to avoid any anatomical bias [7; 8; 11; 12], or studies might demonstrate the effect of canal anatomy rather than the variable of interest [13]. In the teaching environment also, students normally comment that the anatomical variability does not allow a valid assessment of their individual performance [14]. The most-common method used in ex vivo studies is to create pair-matched tooth samples according to their anatomical features, such as the tooth type, root length, root anatomy, degree and angle of curvature, and root canal diameter, or even with paired contralateral teeth [7; 12]. Many methods are used for anatomy assessment, namely visual examination, radiographs, and micro-computed tomography (microCT). MicroCT allows a non-invasive, non-destructive, high-resolution, and 3D investigation [7]. [PERSON] et al. (2020) compared the randomized method, radiographic method, and microCT method and concluded that microCT was able to provide better control of the confounding effects of anatomical variance. Nonetheless, this study also demonstrated the difficulty, time consumption, and high costs of this method [12]. Additionally, it should be noted that other tooth parameters should be taken into count, which cannot be sufficiently standardized by these methods, such as the age and ethnicity of the donor and environmental factors. These factors have an impact on the mechanical properties of the dentin, so a total standardization is, with the actual methods, almost impossible to achieve [15]. Three-dimensionally printed teeth that reproduce the features of natural teeth may overcome all these limitations [10; 11; 16] and are also suitable for practicing access opening, canal instrumentation, radiographic length control, and canal filling [8; 16]. They are realistic and standardized, so the same level of difficulty is guaranteed for every single student, and consequently, they will be scored fairly [8; 9; 10]. Additionally, in ex vivo studies, this morphological standardization has a major impact on the results' credibility, since anatomical bias would not exist [12; 13]. In the study of [PERSON] et al.