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ORIGINAL ARTICLE
Year : 2019  |  Volume : 9  |  Issue : 3  |  Page : 210-215

Evaluation of root canal preparation using two nickel–titanium instrument systems via cone-beam computed tomography


1 Department of Operative Dentistry and Endodontics, Faculty of Odonto-Stomatology, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam
2 Faculty of Odonto-Stomatology, City Children's Hospital, Ho Chi Minh City, Vietnam

Date of Web Publication16-Aug-2019

Correspondence Address:
Dr. Khoa Van Pham
652 Nguyen Trai Street, Ward 11, District 5, Ho Chi Minh City
Vietnam
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_147_18

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  Abstract 

Aim: The aim of this study was to evaluate the root canal preparation abilities of two nickel–titanium (NiTi) instrument systems, namely WaveOne (WO) and ProTaper Next (PTN), using cone-beam computed tomography (CBCT), on human extracted teeth.
Materials and Methods: Eighty mesiobuccal root canals of the maxillary and mandibular first molars with a curvature of 10°–39° were chosen. CBCT images were captured before instrumentation using special silicone molds to ensure that the teeth are positioned at the same place before and after instrumentation. The root canals were divided into two groups, namely Group 1 and Group 2 (40 root canals in each group with similar root canal curvatures). Group 1 and Group 2 were prepared using WO and PTN, respectively. Teeth were inserted again into the previous silicone molds at the right positions. Postinstrumentation CBCT images were captured with the same parameters. Pre- and postinstrumentation CBCT images were analyzed using Invivo 5 software provided by the CBCT machine manufacturer.
Results: There was no difference between the two groups of root canals instrumented by two NiTi instrument systems in root canal transportation, centering ratio, straightening, and volume changes (P > 0.05).
Conclusions: Both NiTi instrument systems can be used effectively and safely in root canal instrumentation.

Keywords: Cone-beam computed tomography, extracted teeth, nickel–titanium, reciprocating, root canal preparation


How to cite this article:
Pham KV, Phan TN. Evaluation of root canal preparation using two nickel–titanium instrument systems via cone-beam computed tomography. Saudi Endod J 2019;9:210-5

How to cite this URL:
Pham KV, Phan TN. Evaluation of root canal preparation using two nickel–titanium instrument systems via cone-beam computed tomography. Saudi Endod J [serial online] 2019 [cited 2019 Sep 18];9:210-5. Available from: http://www.saudiendodj.com/text.asp?2019/9/3/210/264647


  Introduction Top


Root canal instrumentation is a crucial step in endodontic treatment and is important for the success of the filling procedure. Mechanically, instrumentation should conserve the original configuration of the root canal system, including the apical foramen and root canal pathway.[1] Instrumentation should maintain the root canal's original shape, forming a cone shape from the apical to coronal orifice without errors.[2] However, many shortcomings are encountered in preparation such as zips, ledges, transportation, and even perforations, especially when using hand instruments.[3]

Advancements in technology led to the birth of rotary nickel–titanium (NiTi) endodontic instruments using integrated techniques that provide easier and faster ways to prepare the root canal with better retention of the original shape and fewer iatrogenic mistakes.[4]

Besides the conventional continuous rotation of instruments, the new mode of reciprocation rotation was developed in almost all the single-file instrument systems to decrease the complexity of instrumentation. The WaveOne (WO, Dentsply, Maillefer, Ballaigues, Switzerland) system was one of the first reciprocating single-file systems. The WO instrument was constructed from a special NiTi alloy M-wire, which allows for a special premanufactured heat treatment procedure. With this heat treatment process, the manufacturer of WO claims that it has more flexibility and strength as compared to that of conventional NiTi instruments.[5] With reciprocating rotation mode, which turns the instrument in unequal bidirectional movements with less than a circle active movement, the WO instrument generates less stress than does a continuous rotary instrument and therefore has a longer fatigue life.[6] While the symmetrical cross-sectional design was the most common type for almost all of the NiTi instrument systems, the offset design was used for a few of the special systems such as ProTaper Next (PTN, Dentsply, Maillefer, Ballaigues, Switzerland). PTN, which is made by the M-Wire, like WO, has a special offset design and is considered a multiadvantage instrument system.[7],[8],[9] The offset design not only provides the instrument a good debris-collection ability but also creates larger envelope movements as compared to a conventional rotary NiTi instrument of the same size.[10]

The purpose of the present study was to evaluate the root canal preparation abilities of two rotary Ni-Ti instrument systems, namely WO and PTN, using cone-beam computed tomography (CBCT).


  Materials and Methods Top


This study was approved by the Research Ethics Committee of the University of Medicine and Pharmacy at Ho Chi Minh City, Vietnam. Approval number of the present study was 2268/QƉ-ƉHYD-SƉH from the university. Extracted human molar teeth were used for this study. They were extracted for other reasons not related to this study. The mesial roots had to have completely formed, curved roots and minimum length of 10 mm from the cementoenamel junction to the apex. The teeth were stored in the 10% formalin solution. Teeth were then accessed using Martin and Endo-Z burs (Dentsply, Maillefer, Ballaigues, Switzerland), and the working lengths of the mesiobuccal canals were determined by inserting a size 10 K-type file to the root canal terminus and subtracting 1 mm from this distance. Teeth were inserted into a silicon-filled cylinder plastic tray to get the silicon socket molds for each tooth. The tray had two small slots which were parallel and far from the floor at 3 and 5 mm, respectively. These two slots were filled with three gutta-percha segments for each slot at different positions to mark the reference planes for exactly determining the same slice for each pre- and postinstrumentation canal at two levels of investigation.

CBCT images of all teeth were captured for the first time (I-Cat Viewer, GENDEX GXCB-500™, Gendex Dental Systems, USA) before instrumentation. Exposure parameters were same for pre- and post-instrumentation: field of view, 8 cm × 8 cm; scanning time, 23 s; and pixel, 0.125 mm. The CBCT images were analyzed using Invivo 5 software (Egg Viewer, Gendex Dental Systems, USA) and Simplant Pro 11.04 software (Materialise Dental LV, Leuven, Belgium) with the Dell Precision M6400 Workstation (Dell, Round Rock, TX, USA). Preinstrumentation CBCT images were analyzed to measure the canal curvature values. The CBCT data were imported into the Simplant Pro. The slices in panoramic window were chosen in such a way that very clear images of the root canals could be acquired. Images of the mesiobuccal root canals in panoramic window were used to measure the angle curvature of these canals following Schneider method.[11] The coordinates of these slices were recorded and helpful in determining the postinstrumentation root canal curvature values.

Eighty mesiobuccal root canals of the maxillary and mandibular first molars with a curvature of 10°–39° were chosen. Teeth were then removed from the tray and inserted into a special stainless steel articulator with brackets with the appropriate relationship of the maxillary and mandibular molars. Samples were divided into two groups (40 root canals in each group); Group 1 was prepared using WO and Group 2 was prepared using PTN. First, all root canals were created glide path using PathFile 1 and 2 with WO Endo-Motor (Dentsply, Maillefer, Ballaigues, Switzerland) at 250 rpm and 2 N.cm torque. Both groups were prepared with the instruments in the WO Endo-Motor, per the manufacturer's instructions. In Group 1, the WO Primary file was used with the WO All program of the motor until the file reached the working length. In Group 2, a torque of 2.5 N.cm and 300 rpm was used, and the process was finished when the PTN X2 reached the working length. Each instrument was used for four root canals for both groups. Teeth were reinserted into the previous silicon socket molds for scanning using CBCT to obtain the postinstrumentation images.

The CBCT images of root canals before and after instrumentation at 3-mm and 5-mm levels from the apical end were used to calculate the transportation and centering ratio with Invivo 5 software. The transportation and centering ratio were analyzed as described in previous studies.[12],[13]

The extent and direction of canal transportation were determined by measuring the shortest distance from the edge of the preinstrumentation canal to the edge of the tooth in a mesial, distal, buccal, and lingual directions and then comparing this with the same measurements taken from the postinstrumentation images. The following formula was used for the transportation calculation: |(M1− M2)−(D1− D2)| (mesial-distal direction) and |(B1− B2)−(L1− L2)|(buccal-lingual direction). M1 represented the shortest distance from the mesial root surface to the periphery of the preinstrumentation canal, D1 represented the shortest distance from the distal root surface to the periphery of the preinstrumentation canal, M2 represented the shortest distance from the mesial root surface to the periphery of the postinstrumentation canal, and D2 represented the shortest distance from distal root surface to the periphery of the postinstrumentation canal. A result of 0 from the canal transportation formula indicates no canal transportation. The mean centering ratio is a measure of the ability of the instrument to stay centered in the canal. These ratios were calculated for each section using the following ratios: (M1− M2) to (D1− D2) (mesial-distal direction) and (B1− B2) to (L1− L2) (buccal-lingual direction). The numerators for the centering ratio formula were the smaller ones of the two pairs of numbers (M1− M2) or (D1− D2) and (B1− B2) or (L1− L2) if these numbers were unequal. Using this formula, a result of 1 for the centering ratio would indicate perfect centering [Figure 1] and [Figure 2].
Figure 1: Preinstrumentation cross-sectional image of mesiobuccal root at 3-mm level

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Figure 2: Postinstrumentation cross-sectional image of mesiobuccal root at 3-mm level

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The CBCT data were imported into the Simplant Pro in order to measure the postinstrumentation root canal curvature values according to the abovementioned method[11] using the predetermined plane coordinates. In the segment interface of the Simplant Pro, two points were chosen. The first point was apical end. The second point was from the first point of 10 mm of the coronal part of the canal [Figure 3] and [Figure 4]. The root canal volume measurement [Figure 5] was done between these two points.[14] This procedure was used to calculate the pre- and postinstrumentation root canal volumes, which in turn indicated the volumetric changes because of instrumentation.
Figure 3: Determination of the first point at apical end for canal volume calculation

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Figure 4: Determination of the second point that was far from the first point of 10 mm for canal volume calculation

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Figure 5: Calculation of the canal volume

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  Results Top


The mean transportation (mm) and centering ratios of the two experimental groups are presented in [Table 1].
Table 1: Mean transportation (mm) and centering ratios of the experimental groups

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At 3-mm level, in mesial-distal direction, there was no significant difference between the WO and PTN groups about the transportation and centering ratio values (P = 0.232 and P = 0.179, respectively). In buccal-lingual direction, there was also no significant difference between the WO and PTN groups about the transportation and centering ratio values (P = 0.483 and P = 0.607, respectively).

At 5-mm level, in mesial-distal direction, there was no significant difference between the WO and PTN groups about the transportation and centering ratio values (P = 0.101 and P = 0.58, respectively). In buccal-lingual direction, there was also no significant difference between the WO and PTN groups about the transportation and centering ratio values (P = 0.509 and P = 0.343, respectively).

The root canal curvatures (°) and volumes (mm3) of the two experimental groups are presented in [Table 2].
Table 2: Preinstrumentation root canal curvatures (°) and volumes (mm3) of the two experimental groups

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The means of root canal curvature for the WO and PTN were 21.01° and 22.93°, respectively. There was no significant difference between the WO and PTN groups about the preinstrumented root canal curvatures (P = 0.139).

The means of root canal volume for the WO and PTN were 2.64 and 2.48 mm3, respectively. There was no significant difference between the WO and PTN groups about the preinstrumented root canal volumes (P = 0.168).

The straightening of canal curvature (°) and removed dentin volume (mm3) of the two experimental groups are presented in [Table 3].
Table 3: Straightening of canal curvature (°), and removed dentin volume (mm3) of the two experimental groups

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Both WO and PTN instruments straightened root canal up to approximately 6°, and there was no significant difference between the WO and PTN groups about the canal straightening values (P = 0.876). Root canal volumes increased up to nearly double after instrumentation using WO and PTN; however, there was no significant difference between the WO and PTN groups about the root canal changes after instrumentation (P = 0.257).


  Discussion Top


Several methods are used to investigate the root canal before and after instrumentation such as the liquid silicone technique,[15] utilization of the plastic endoblock,[3] Bramante's technique,[16] the periapical radiographic technique,[17] medical computed tomography,[18] or micro-computed tomography (μ-CT).[19] Bramante's technique was the most popular method used for evaluating the root canal before and after instrumentation in the 1980s. This method used a muffle system including a plaster block around a resin-index experimental root that was horizontally sectioned. The block could be custom-fabricated and sectioned in different planes to allow correct repositioning of the cross-sectioned parts of the root and complete block. All these horizontal cutting root surfaces could be photographed before and after instrumentation to analyze the instrumentation techniques.[16] However, this method only allowed to evaluate the instrumentation technique following the horizontal direction and was an invasive method. Alternatively, μ-CT was the new, high-resolution, noninvasive method for investigating the root canal morphology and root canal before and after instrumentation.[19] Because of the high resolution and the integrated multipurpose software, μ-CT was the gold standard for endodontic investigation. However, the two important limitations of μ-CT were time-consuming scanning and expensive equipment.[19] CBCT also created the three-dimensional images but was less expensive than μ-CT. Moreover, the scanning time and radiation dose for CBCT were much less than those for μ-CT. With proper resolution and integrated software of CBCT, the images can be used for endodontic investigations.[20] CBCT used in this study is similar to that used in the previous studies.[14],[21] In the present study, the reference plane was determined using gutta-percha in slots that were created on the wall of the plastic tray and paralleled with the bottom of the plastic tray. The other studies used different methods to determine the reference plane, such as using the largest dimensions of the slice images,[13] a composite of six slots on the root surface from the apex end (2, 4, 6, 8, 10, and 12 mm),[22] or four small gutta-percha segments on the buccal, lingual, mesial, and distal positions at the cementoenamel junction.[14] The present study also used a special stainless steel articulator with brackets at the positions of the maxillary and mandibular molars that simulated positions of these teeth on the jaw, simulated the preclinical situations, and assembled and reassembled the teeth easily for CBCT scanning.

Almost all other studies evaluated the centering ratios following the mesial-distal direction but not the buccal-lingual direction,[23],[24] whereas the present study evaluated the centering ratios in both directions, i.e., mesial-distal and buccal-lingual directions. The results showed that the centering ratios of the WO instrument were similar at 3-mm and 5-mm levels in both directions. These results were in line with those of a previous study.[23] In that study, the two levels of investigation were 2 mm and 5 mm, and the resolution of the CBCT images seemed to be higher than that of the present study (pixel size of 0.075 mm for the former vs. 0.125 mm for the latter). For the PTN, the centering ratios were similar at 3-mm and 5-mm levels in both directions. These results were in line with those of previous studies.[23],[24] In the previous study,[22] the resolution of the CBCT images was comparable to that of the present study (pixel size of 0.125 mm for both studies), and the levels of investigations were also 3 mm, 5 mm, and extra 7 mm.

Straightening of the root canal curvature changed the original canal configuration, increased the overinstrumented removed dentin amount, and therefore, weakened the root tissue.[2] Straightening of the root canal curvature and volumetric changes were two crucial factors in the evaluation of the instrument systems' capabilities. The results of the present study showed that the pre- and postinstrumentation root canal curvature differences were nearly 6° for both experimental instrument systems, and these values were different from those reported in previous studies,[23],[25] which were about a half of the values reported in the present study. This difference is likely because of the different methods of root canal curvature determination and different ways of investigation employed in these studies. The changes in root canal volumes in the present study were similar to those of previous studies.[23],[24] The result was also comparable to that of the previous study that used μ-CT for the WO instrument system.[26] Both instrument systems increased the root canal volumes nearly two times compared to the preinstrumentation values.


  Conclusions Top


In the conditions of the present study, both instrument systems, WO and PTN, had good centering abilities, straightened the root canal by about 6°, and increased the root canal volumes to nearly twice. Thus, both instrument systems can be used effectively and safely in root canal instrumentation.

Data Availability

Data used to support the findings of this study are available from the corresponding author upon request.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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