Canal transportation and centering ability of root canals prepared using rotary and reciprocating systems with and without PathFiles in cone-beam computed tomography-based three-dimensional molar prototypes.

BACKGROUND: It is important to use instruments that cause minimal changes in the canal path for root canal preparation. There is inadequate literature comparing rotary and reciprocating systems and hand files. No study used three-dimensional printed models to compare rotary, reciprocating, and hand files. AIMS: We aimed to assess the canal transportation and centering ability of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file systems with and without glide path preparation.
MATERIAL AND METHODS: Forty-nine resin models were randomly divided into Group I A - WaveOne Gold with WaveOne Gold Glider and Group I B - WaveOne Gold without glide path; Group II A - ProTaper Gold with ProGlider and Group II B - ProTaper Gold without glide path; and Group III A - NiTi Flex K-files with no. 10 stainless steel K-file and Group III B - NiTi Flex K-files without glide path. Pre- and postinstrumentation cross-sectional images at levels 3, 5, 7, 9, and 11 mm were compared.
RESULTS: WaveOne Gold caused the least canal transportation and improved centering ability (P < 0.05). NiTi Flex K-files transported the canal more than others in the apical levels (3, 5 mm). Glide path creation reduced canal transportation and improved canal-centering ability.
CONCLUSIONS: WaveOne Gold system has better centering ability and lesser canal transportation than ProTaper Gold and NiTi Flex K-file. Glide path creation reduced canal transportation and improved canal-centering ability. Copyright:

INTRODUCTION

The elimination of microorganisms through chemomechanical preparation is essential for the success of endodontic treatment. Even with advanced instrumentation technology, effective cleaning of the entire root canal system remains a challenge.[1] The risk factors that may contribute to treatment failure are iatrogenic procedural errors in the preparation of curved root canals, such as instrument separation, ledge, zips, perforations, and apical transportation.[23]

Canal transportation is the removal of canal wall structure on the outside curve in the apical half of the canal due to the tendency of files to restore themselves to their original linear shape during canal preparation, leading to ledge formation and possible perforation. Canal centering is the capacity of the instrument to remain centered within the canal. This ability indicates whether or not the dentin removal over the prepared area is spread evenly by the instrument.[4]

Glide path is a smooth radicular tunnel from canal orifice to physiologic terminus (foraminal constriction).[5] Creation of glide path prior to the use of rotary and reciprocating systems helps to maintain original canal anatomy.[67] It can be created both with rotary and hand instruments. Hand files, however, are said to consume much time, especially in a tooth having obliterated canals or canals with severe curvature. WaveOne Gold Glider, reciprocating glide path file, and ProGlider rotary glide path files are claimed to reduce the chances of canal transportation and deviation.[89]

The earlier studies conducted on extracted teeth could not ensure uniformity because of variation in canal anatomy in these teeth. With cone-beam computed tomography (CBCT)-based three-dimensional (3D) printed prototypes, standardization of the models with the highest fabrication accuracy is possible. Superimposing pre- and postinstrumentation images are possible with transparent simulated root canal models.[1011] Measurements can be made at different root canal levels to calculate canal transportation and centering ability using a digital microscope.

Thus, the purpose of the current study is to evaluate and compare canal transportation and centering ability after using WaveOne Gold reciprocating system, ProTaper Gold rotary system, and NiTi Flex K-files (hand) with and without glide path preparation 3D printed resin models of molars with severe curvature of roots.

MATERIALS AND METHODS

A mandibular first molar with a mesiobuccal canal having curvatures of 35° in the mesial-distal direction was selected and decoronated at the cementoenamel junction (CEJ) with a diamond cutting disk to a standardized root length of 15 mm [Figure 1]. The curvature of the sample was measured with the help of Schneider's technique.[12] The apical patency was checked using the stainless steel no 10 K hand file. CBCT scan of the tooth was done. The acquired CBCT scan data were converted into stereolithography files to use the 3D printer. Forty-nine identical resin models were fabricated from that extracted human mandibular first molar tooth using Formlabs standard clear resin (Formlabs, Somerville, Massachusetts, USA) [Figure 2]. One model was used for getting preinstrumentation images. The model was sectioned using a diamond disc at levels 3, 5, 7, 9, and 11 mm from the root apex, and cross sectional images were captured by digital microscopy (polarizing microscope Lawrence & Mayo,Model: N400M, Mumbai, India) at a magnification of ×4. These images were saved and compared with their corresponding postinstrumentation ones.

Figure 1

Sample tooth for three-dimensional printing

Figure 2

Resin models divided into Groups 1, 2, and 3

The models were randomly divided into three equal groups (n = 16) based on the instrumentation system. Each group was then divided into two subgroups based on glide path preparation as follows:

Group I

Subgroup I A – WaveOne Gold reciprocating system (Dentsply Maillefer, Ballaigues, Switzerland) with glide path creation using WaveOne Gold Glider (Dentsply Maillefer, Ballaigues, Switzerland)

Subgroup I B – WaveOne Gold reciprocating system without glide path creation.

Group II

Subgroup II A – ProTaper Gold rotary system (Dentsply Maillefer, Ballaigues, Switzerland) with glide path creation using ProGlider (Dentsply Maillefer, Ballaigues, Switzerland)

Subgroup II B – ProTaper Gold rotary system without glide path creation.

Group III

Subgroup III A – NiTi Flex K-files (hand) system (Dentsply Maillefer, Ballaigues, Switzerland) with glide path creation

Subgroup III B – NiTi Flex K-files (hand) system without glide path creation.

A 6:1 low-speed, low-torque, endo motor X-Smart plus (Dentsply Maillefer, Ballaigues, Switzerland) was used to operate the various rotary systems as per the manufacturer's instructions. WaveOne Gold Glider was used at a speed of 350 rotations/min and torque 1.5 Ncm (0.15 tip size). ProGlider was used at a speed of 300 rotations/min, torque 2 Ncm (0.16 tip size). Glide path was performed with stainless steel 10 size K-file (10 #, 0.02) in the third group. All the pathfinders were instrumented up to the apex.

In Group I, canals were prepared using WaveOne Gold reciprocating primary file (25#, 0.08). In Group II, canals were prepared using ProTaper Gold files following a sequence of SX, S1, S2, F1, and F2. In Group III, NiTi K flex files were used up to size 25. All the instruments were used only for a single time.

Following instrumentation, the resin models were sectioned using a diamond disc at levels 3, 5, 7, 9, and 11 mm. Cross-sectional images at levels 3, 5, 7, 9, and 11 mm were captured by digital microscopy at a magnification of ×4. The preinstrumentation, the image of one model at levels 3, 5, 7, 9, and 11 mm that was used to compare with their corresponding postinstrumentation using ImageJ software (Image Proplus - version 4.1.0.0) for Windows 95/WT/98.

The canal transportation and centering ratio were measured with the help of the formula proposed by Gambill et al.[13]

Canal transportation = (a1 − a2) − (b1 − b2)

Centering ratio = (a1 − a2)/(b1 − b2)

where a1 is the shortest distance from the mesial edge of the root to the mesial edge of the uninstrumented canal, a2 is the shortest distance from the mesial edge of the root to the mesial edge of the instrumented canal, b1 is the shortest distance from the distal edge of the root to the distal edge of the uninstrumented canal, and b2 is the shortest distance from the distal edge of the root to the distal edge of the instrumented canal.

RESULTS

The data were subjected to statistical analysis using one-way ANOVA, independent sample t-test, and post hoc tests. In all the analyses, significance level was taken to be 0.05 (P < 0.05) and statistical analysis was carried out using the statistical package, SPSS Statistics (version 21.0).

Canal transportation

Group I caused the least canal transportation at all levels (Graph 1&2). In Group III, files were found to transport the canal significantly compared with Group I and Group II in the apical levels (3 and 5 mm), P < 0.05. There was no significant difference between Group III and Group II at 7-, 9-, and 11-mm levels.

Graph 1

Mean canal transportation values of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file with glide path preparation using WaveOne Gold Glider, ProGlider, and 10 size K-file, respectively

Graph 2

Mean canal transportation values of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file without glide path preparation

At all levels, subgroup B of all the three groups caused significant canal transportation (P < 0.05) except at level 9 mm (no significant difference between subgroups in Group I at level 9 mm).

Centering ability

Group I achieved the maximal value of canal centering ability at all levels, followed by Group II and Group III (Graph 3&4). There was a significant difference between all groups at all levels except at 3 mm (P < 0.05). At 3 mm, there was no significant difference between Groups II and III. At all levels, subgroup A of Group I achieved maximal value of centering ability and it was significant (P < 0.05) except at level 9 mm. At 3-, 5-, and 7-mm levels, there was no significant difference between subgroups in Group II.

Graph 3

Mean canal-centering ratio values of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file with glide path preparation using WaveOne Gold Glider, ProGlider, and 10 size K-file, respectively

Graph 4

Mean canal-centering ratio values of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file without glide path preparation

DISCUSSION

Cleaning and shaping is the most important stage in root canal treatment.[14] Instrumentation of curved canals is still challenging with conventional stainless steel files leading to iatrogenic errors such as canal straightening, ledges, and transportation.[15] NiTi files are found to decrease the canal transportation and are said to have the ability to shape the canal into a desired conical form because of its superelastic property, but file breakage was its major problem, especially in curved canals.

Establishing a “glide path” is a step carried out to create a smooth tunnel-like preparation, from the orifice of the canal to the terminus of the root, prior to the introduction of shaping instruments and is said to be a critical step in preventing premature file fracture.[5]

Two important parameters that affect canal-centering ability are alloy used in manufacturing instruments and instrument design (cross-section, taper, and tip).[4] Studies have concluded that Ni-Ti instruments show better canal-centering ability than stainless steel instruments.[1617]

Various methods are available to study the efficiency of preparing a root canal and also to compare the shape of the canal before and after instrumentation. The methods used for comparative analysis were radiography, scanning electron microscopy, photographic assessment, and computer manipulation.[18192021]

Single mandibular first molar with mesiobuccal canal having a curvature of 35° in the mesiodistal direction was selected and decoronated at the CEJ, and 49 3D printed models were printed for this study. Curved canals were chosen as they present instrumentation with greater challenges. Five levels were chosen: 3, 5, 7, 9, and 11 mm from the root apex. These represent the apical, middle, and coronal thirds of root canals where there are usually curvatures with high vulnerability to iatrogenic mishaps. The mesiobuccal root of the mandibular first molar was used because they are most frequently curved.

The curvatures of the sample were measured with the help of Schneider's technique. According to this technique, canal curvatures are categorized as the straight canal (5° or less), the moderately curved canal (10°–20°), or the severely curved canal (>20°).[22]

Resin models are printed from a single mandibular first molar because they allow standardization of canal curvature in three dimensions.[23]

ProGlider and WaveOne Gold Glider were selected as the glide path files as both have a similar tip diameter (0.15 and 0.16).

In the present study, the WaveOne Gold file system achieved the least value of canal transportation at all levels, and it was maximum at all the levels for NiTi Flex K-files (hand) system followed by ProTaper Gold rotary file system except at 11 mm. At this level, ProTaper Gold rotary file system had a higher value, but there was no significant difference between ProTaper Gold rotary file system and the NiTi Flex K-file (hand) system. The manual instrumentation may be the cause of its highest degree of transportation and decreased centering ability of NiTi Flex hand files.[24] The transportation by ProTaper Gold can be attributed to the design of ProTaper, which includes progressive taper along its surface; convex core mass causes a reduction in instrument flexibility and increased tip stiffness of the file.[4] Yoo and Cho also reported that the reciprocating method preserves the original canal shape better than the continuous rotation system.[25]

The use of glide path files reduced the degree of canal transportation in the apical and middle one-third. Hartmann et al. concluded that preparing a glide path with engine-driven sequences is linked with equivalent or reduced apical transportation and/or loss of canal-centering ability compared to manual preparation.[26]

In this study, WaveOne Gold Glider caused the least canal transportation, followed by ProGlider and 10-K stainless steel file. This might be due to better flexibility and the reciprocating motion of the WaveOne Gold Glider.[8]

WaveOne Gold file system achieved maximal value of canal-centering ability at all levels, followed by ProTaper Gold rotary file system and NiTi Flex K-file system. At the apical 3 mm level, there was no significant difference between the ProTaper Gold file system and the NiTi Flex K-file system. One of the characteristic features of reciprocating motion, which was proposed specifically to reduce the risk of root canal deformity, is increased canal-centering ability.[27] The two different cross-sections along the length of the active portion of WaveOne is the reason for decreased core diameter leading to the increased flexibility of the file. These features might be the reasons for the better canal-centering ability of the WaveOne file system.

CONCLUSIONS

Within the limitations of this study, it was found that all three file systems caused canal transportation to some extent, but the use of glide path files reduced canal transportation and improved canal-centering ability for all file systems.

WaveOne Gold single-file reciprocation has better centering ability and lesser canal transportation than ProTaper Gold and NiTi Flex K-file at all levels when used with and without glide path preparation in root canals with severe curvature.

Glide path creation using WaveOne Gold Glider, ProGlider, and 10 size K-file prior to the use of WaveOne Gold, ProTaper Gold, and NiTi Flex K-file, respectively, reduced the canal transportation and improved canal-centering ability at all levels.

WaveOne Gold Glider followed by WaveOne Gold single-file reciprocation caused the least canal transportation and improved canal-centering ability.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.