Influence of NiTi alloy on the root canal shaping capabilities of the ProTaper Universal and ProTaper Gold rotary instrument systems

Abstract Objective This study aimed to evaluate the influence of the NiTi wire in Conventional NiTi (ProTaper Universal PTU) and Controlled Memory NiTi (ProTaper Gold PTG) instrument systems on the quality of root canal preparation. Material and Methods Twelve mandibular molars with separate mesial canals were scanned using a high-definition microcomputed tomography system. The PTU and PTG instruments were used to shape twelve mesial canals each. The canals were scanned after preparation with F2 and F3 instruments of the PTU and PTG systems. The analyzed parameters included the remaining dentin thickness at the apical and cervical levels, root canal volume and untouched canal walls. Data was analyzed for statistical significance by the Friedman and Dunn’s tests. For the comparison of data between groups, the Mann-Whitney test was used. Results In the pre-operative analysis, there were no statistically significant differences between the groups in terms of the area and volume of root canals (P>.05). There was also no statistically significant difference between the systems with respect to root canal volume after use of the F2 and F3 instruments. There was no statistical difference in the dentin thickness at the first apical level between, before and after instrumentation for both systems. At the 3 cervical levels, the PTG maintained centralization of the preparation on the transition between the F2 and F3 instruments, which did not occur with the PTU. Conclusion The Conventional NiTi (PTU) and Controlled Memory NiTi (PTG) instruments displayed comparable capabilities for shaping the straight mesial root canals of mandibular molars, although the PTG was better than the PTU at maintaining the centralization of the shape in the cervical portion.


Introduction
Mechanical preparation of the root canal is an important step in endodontic treatment. The aim of this step is to remove vital or necrotic pulp tissue while simultaneously increasing the root canal volume to facilitate the decontamination of the root canal system by irrigants and medicaments 14 .
Several types of instruments and techniques for root canal preparations have been described 6,11,[16][17][18] . deviations in the root canal preparation and excessive have been widely used in endodontic practice due compared to hand-held instruments 24 and provide higher quality in the preparation of root 5 and higher fracture resistance to cyclic and torsional fatigue 25 .
in fabrication, including different types of thermic treatments that have been employed during the manufacturing process, which are designed to optimize physical characteristics that favor greater elasticity as 20 . Among highlighted in the present study.
According to the manufacturers, CM wire weight) than other NiTi instruments 10,22 . Additionally, because of the thermic treatments used during the manufacturing process, CM wire instruments do not bounce (rebound) to their original shape after being instrument fracture, and perforations 15 .
Among the NiTi systems, the PTU (Dentsply Maillefer, Ballaigues, Switzerland) is a rotary system of conventional NiTi wire that has been widely used and studied 1,6,11,24 . It has a variable taper along the length of the instrument, a convex triangular cross-section, and a sharp tip 7,13 . Another system, the PTG (Dentsply Maillefer, Ballaigues, Switzerland), was recently are generally similar to those of the PTU, except that the PTG uses CM wire, while the PTU uses conventional NiTi wire. Because of this distinction, the PTG exhibits than the PTU system 11,13 .  The remaining root canals (n=12) were instrumented using the PTG system in the same sequence as the one used for the PTU group.
Subsequently, the roots were scanned again as in the initial evaluation. After scanning, the root canals were prepared with the F3 (30/.09) instrument of each system. The X-Smart Plus motor (Dentsply Maillefer, Ballaigues, Switzerland) was used with a accordance with the manufacturer's instructions, and the instrumentation was performed with in-and-out procedure, a 2.5% sodium hypochlorite solution was used; the root canals were irrigated before, during, and after instrumentation. Two milliliters of solution irrigation was made with 3 mL of 17% EDTA for 3 minutes, and then with 3 mL of saline solution. Next, a new scan of the roots was performed using previously set parameters.

Results
In the pre-operative analysis, there were no volume of root canals between the PTU and PTG groups (P>0.05), indicating adequate pairing of the root canals.  surface area (mm²) before and after use of the F2 and F3 instruments. Also presented in Table 1 are the percentage of volume increase and the percentage of static voxel after use of the F2 and F3 instruments.
between the PTU and PTG systems with respect to the root canal volumes obtained after use of the F2 and F3 instruments (P>0.05). However, upon intra-group analysis of the PTU group, a statistically significant difference was observed between the pre-operative and post-operative volumes, but only after use of the F3 instrument (P<0.05). For the PTG between the volumes before and after use of the F2 and F3 instruments (P<0.05). Figure 1 depicts the three-dimensional reconstructions of mesial root  canals before instrumentation ( Figure 1A), and after instrumentation with F2 ( Figure 1B) and F3 ( Figure   1C) instruments. Table 2 shows the median, minimum and maximum values (presented as percentages) of dentin wear in the mesial and distal walls (mm) at the 3 apical and 3 cervical levels, before and after use of the F2 and F3 instruments for the PTU and PTG groups, respectively. There was no statistical difference apical level before and after instrumentation for both systems (P>0.05). At the 3 cervical levels, the PTG system maintained centralization of the preparation on transition between the F2 and F3 instruments, in contrast to the PTU system where this did not occur.
For all segments that were evaluated, a dentin of the instrument and system used ( Figure 2). Discussion that was targeted for analysis in the present study, the data supports the null hypothesis because there PTU and PTG instruments with respect to root canal enlargement or un-instrumented areas.
After a micro-CT evaluation, the mandibular molars to be examined were selected based on whether they: however, these methods compromise the integrity of the samples because they require the cutting of the specimens, which limits specimen use to a single analysis. By contrast, micro-CT is a nondestructive method that allows for the progressive evaluation and observation of the preparation instruments with 18 . The evaluations conducted in the present study were made after the use of the F2 and F3 instruments. 13   The CM wire is manufactured using a complex heat treatment, with variations in wire composition; i.e., it the most commonly used wire, which is composed of 21 . The PTU and PTG systems share a similar design, but they vary in the composition of the NiTi wire. One study assessed the shaping ability of these two systems, and found that the PTG produced less transportation and maintained more dentin than the PTU 11 .
Apical preparations with larger diameters have been suggested based on studies that showed that apical region 3 , better infection control and improved 9 . A previous report showed that, in the mesial roots of mandibular molars, the increase of apical preparation before use of the 18 . In the present study, the apical preparation was performed until use of the increase in the root canal volume. In both groups the preparation was centralized at the last apical millimeter; however, in the 3 cervical levels evaluated, the PTG system maintained centralized shaping on transition between the F2 and F3 instruments, which did not occur with the PTU. Nonetheless, both systems Another study by Gagliardi, et al. 11 (2015) showed that the PTG was associated with less deviation than the PTU, which could be explained by the curvature of the specimens, as that study used moderately curved (25°-35°) mesial canals of mandibular molars, in contrast to the present study that used straight root canals. Therefore, the degree of curvature of the performance of the NiTi CM wire.
For both groups, un-instrumented areas of the root canals were observed in all specimens, demonstrating that the PTU and the PTG instruments are not as capable of performing a complete mechanical cleaning of the dentin walls as other NiTi rotary instruments 11,12,26 . The post-preparation percentage of un-instrumented areas prior to use of the F2 instrument was comparable to that obtained in a previous study that employed similar instruments and methodologies 11 ; however, in the present study, the root canals were enlarged before reduction in un-instrumented areas. This increase in diameter after preparation may be associated with use of the F3 instrument in the PTU group, and the However, after use of the F3 instrument, the dentin was, on average, larger than 0.4 mm in both groups.