**3. Results**

Table 1 and Figure 2 show the mean and standard deviation values for the volume of root canal system (mm3) between EDG and RB NiTi endodontic files at coronal, middle and apical root canal third.


**Table 1.** Descriptive analysis of the volume of root canal system (mm3) between EDG and RB NiTi endodontic files at coronal, middle and apical root canal third.

EDG: Endogal; RB: Reciproc Blue; a,b: statistical significance.

The paired *t*-test found no statistically significant differences (*p* = 0.0767) in the volume of root canal dentin removed between the EDG (4.30 ± 2.58 mm3) and RB (2.32 ± 1.07 mm3) study groups. However, the paired *t*-test found statistically significant differences (*p* = 0.0066) between the EDG (2.89 ± 1.26 mm3) and RB (1.22 ± 0.58 mm3) study groups in the volume of root canal dentin removed at the coronal root canal third (Figure 3).

**Figure 3.** Box plot of the difference in dentin volume pre- and post-root canal procedure between the EDG and RB study groups at the coronal level.

However, the paired *t*-test did not find any statistically significant differences (*p* = 0.4864) in the volume of root canal dentin removed between the EDG (1.20 ± 1.27 mm3) and RB (0.85 ± 0.47 mm3) study groups at the middle root canal third (Figure 4).

**Figure 4.** Box plot of the difference in dentin volume pre- and post-root canal procedure between the EDG and RB study groups at the middle level.

Moreover, the paired *t*-test did not reveal any statistically significant differences (*p* = 0.6276) in the volume of root canal dentin removed between the EDG (0.20 ± 0.25 mm3) and RB (0.26 ± 0.17 mm3) study groups at the apical root canal third (Figure 5).

**Figure 5.** Box plot of the difference in dentin volume pre- and post-root canal procedure between the EDG and RB study groups at the apical level.

## **4. Discussion**

The results of the present study refute the null hypothesis (H0) that there is no difference in root dentin removal capacity between the Endogal Kids and Reciproc Blue NiTi endodontic reciprocating systems for the root canal treatment of primary molar teeth.

Various methods have previously been used to evaluate root canal instrumentation, including plastic models, serial sectioning, scanning electron microscopic studies, and radiographic comparisons [18]. More recently, noninvasive 3D techniques, such as CBCT or micro-CT scans, have been used to assess the efficiency of cleaning and dentin removal after root canal treatment procedures [19]. In addition, high-resolution 3D micro-CT images are the gold standard for evaluating the root canal system anatomy and root canal instrumentation [20,21]. In the present study, micro-CT scans were used to examine the internal anatomy of the root canal system and evaluate the effectiveness of root canal instrumentation on the root canal system of primary second molar teeth. The authors selected the primary second molars because the anatomy of this tooth is very similar to that of the permanent first molar, which allows a comparison to be made between them. In addition, the eruption chronology of the second premolars is usually later than that of the first premolars, which leads to less root resorption of the primary second molars compared to the primary first molars [22].

Micro-CT scan measurement techniques have previously been used to analyze the amount of root canal dentin removed from permanent teeth after root canal treatment. Yilmaz et al. reported no statistically significant differences between the amount of dentin removed by ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland), OneShape (MicroMega, Besançon, France), and EdgeFile (Edge Endo, Albuquerque, NM) NiTi alloy endodontic rotary files for the whole canal length (*p* > 0.05) [23]. Moreover, de Albuquerque et al. reported that the Protaper Next, Wave One Gold, Predesign Logic, and Vortex Blue NiTi alloy endodontic systems caused a greater dentin removal at the coronal third (9 mm), decreasing at the apical one (3 mm) [24]. These findings are aligned with the results shown in the present study.

The root canals in primary teeth are not always easy to shape and obturate during treatments. In fact, many characteristics of the root canal anatomy make endodontic treatment difficult, potentially resulting in apical transportation, zipping, perforations, or gaps [18,21]. Esentürk et al. observed that 60% of the root canal system was left uninstrumented upon after root canal preparation due to the anatomical complexity of the primary molars, highlighting a need for NiTi alloy endodontic rotary instruments to be developed for use in primary teeth [25]. Prabhakar et al. found that the Wave One NiTi alloy endodontic reciprocal system enabled quicker and safer instrumentation compared with the One Shape NiTi alloy endodontic rotary system, because the former reduces levels of both torsional and flexural stress, as well as the number of instruments required for the sequence [11]. According to their findings, Katge et al. reported that the Wave One NiTi alloy endodontic reciprocal system had a statistically greater cleaning capability than the Protaper NiTi alloy endodontic rotary system at the coronal and middle third due to the benefits of reciprocating motion [12]. However, the risk of root perforation and root canal transportation is more correlated with a high taper value than a reciprocating or continuous motion, which means that the NiTi alloy endodontic system should be selected primarily based on the taper [21]. Ramazani et al. assessed the efficiency of Mtwo NiTi alloy endodontic rotary files and Reciproc NiTi alloy endodontic reciprocating files when cleaning, finding no statistically significant differences between the two study groups, although the Reciproc NiTi alloy endodontic reciprocating files required less preparation time [13]. Azar et al. found no statistically significant differences in cleaning capabilities between Mtwo NiTi alloy endodontic rotary files, Protaper NiTi alloy endodontic rotary files, and manual K files in the three root thirds of the root canal system, measuring the differences using ink and stereo microscopes [26]. These results were corroborated by the findings of Ramazani et al. for Mtwo NiTi alloy endodontic rotary files and K files [13]; Moghaddam et al. for Master NiTi alloy endodontic rotary files, Rotary Flex NiTi

alloy endodontic rotary files, and K files [8]; and Mehalawat et al. for Profile NiTi alloy endodontic rotary files and K files [27]. However, Madan et al. did observe statistically significant differences between Profile NiTi alloy endodontic rotary files and K files when using the same ink removal method, during which the Profile NiTi alloy endodontic rotary files were more efficient at cleaning the coronal root third, while the manual files were better at cleaning the apical root third [28].

Some studies have compared the cleaning capacity of both manual and NiTi alloy endodontic rotary files in permanent teeth [23], but not as many included primary teeth, and only a few of the studies used micro-CT scan assessments. The volume of dentin removed reveals the remaining dentin thickness, which is needed to provide enough resistance for root canal treatments. The force with which root canal instruments are used is in direct proportion to the amount of dentin removed [29]. Although manual instrumentation is commonly used in primary teeth, many studies have found that more dentin is removed using manual files than rotary instrumentation [19,20,29,30]. Selvakumar et al. used K3 NiTi alloy endodontic rotary files (with a 0.02 taper) and found significantly lower dentin removal when compared with manual K files and K3 NiTi alloy endodontic rotary files (with a 0.04 taper), which were shown to remove more dentin tissue in the coronal and apical root thirds in comparison with K files and K3 NiTi alloy endodontic rotary files (with a 0.02 taper) [19]. On the other hand, Zameer et al. observed no statically significant differences when using either the 2% or 4% taper rotary files to remove dentin, without damaging the dentinal walls and achieving an improved canal shape for root canal filling material [31]. In addition, Moghaddam found that a continuous rotation movement with up to a #30 apical diameter enabled better instrumentation and safer results when used with primary teeth without excessive dentin removal [8]. However, Zameer et al. observed a greater number of root perforations when dentin removal was performed using 4% taper NiTi alloy endodontic rotary files compared with 2% NiTi alloy endodontic rotary files and manual K files [31]. This result corroborates the findings of Kummer et al., who used rotary 6% taper NiTi alloy endodontic rotary files with a #30 apical diameter and found three root perforations, concluding that the mesial and distal roots of lower molars and mesiobuccal roots of upper molars had a higher risk of root perforation [30]. In addition, Barasuol et al. observed two perforations in the apical and middle root third, as well as root canal transportation, when using 8% taper Reciproc NiTi alloy endodontic reciprocating files [21]. Files with a larger taper can result in the reduced thickness of the dentinal wall, leading to greater fragility of the teeth and a higher risk of root perforation [20]. Madan et al. found that instrumentation failure was reduced when using 0.04 taper Profile NiTi alloy endodontic rotary files, which were also less damaging for primary teeth [28].

The strengths and innovation of the current study are that not many studies analyze the effect of specific pediatric instrumentation systems on primary teeth, even though pulpectomy is a widely performed dental treatment. Furthermore, the instrumentation systems compared are very novel; especially the Reciproc Blue system, which has not been released on the market. Finally, the micro-CT scan measurement technique for dentin removal analysis is very accurate and innovative.

The present findings are limited by the constraints of an in vitro study. The use of instrumentation with primary teeth is not subject to any universal guidelines, and clinical trials are needed to obtain clinical results. Additional studies should be carried out on a larger sample size, as well as using pediatric files.
