Evaluation of canal transportation after preparation with Reciproc single-file systems with or without glide path files.

BACKGROUND: Canal transportation is a common sequel caused by rotary instruments. AIMS: The purpose of the present study is to evaluate the degree of transportation after the use of Reciproc single-file instruments with or without glide path files.
METHODS: Thirty resin blocks with L-shaped canals were divided into three groups (n = 10). Group 1 - canals were prepared with Reciproc-25 file. Group 2 - glide path file-G1 was used before Reciproc. Group 3 - glide path files-G1 and G2 were used before Reciproc. Pre- and post-instrumentation images were superimposed under microscope, and resin removed from the inner and outer surfaces of the root canal was calculated throughout 10 points.
RESULTS: Statistical analysis was performed with Kruskal-Wallis test and post hoc Dunn test. For coronal and middle one-thirds, there was no significant difference among groups (P > 0.05). For apical section, transportation of Group 1 was significantly higher than other groups (P < 0.05).
CONCLUSION: Using glide path files before Reciproc single-file system reduced the degree of apical canal transportation.

INTRODUCTION

Removal of microorganisms and infected tissue remnants is the main goal of root canal treatment. This task can be achieved with chemomechanical preparation.[1] For many years, root canal preparation was performed with hand files which carry the risk of straightening root canals and resulting in complications including ledging, zipping, and canal transportation.[2] Especially, in curved canals, preserving original canal morphology and avoiding procedural errors are important projections of root canal preparation.[3]

In our day, nickel-titanium (NiTi) systems raised the quality of root canal preparation by reducing the ratio of procedural errors mentioned above.[4] The flexibility of NiTi files provides the maintenance of root canal shape and declines in the complications related to canal preparation.[5] Following the advances in NiTi technology, single-file systems were introduced to save time and to reduce treatment cost.[67] These single-file systems work with either continuous rotation or reciprocation. Reciproc (VDW, Munich, Germany) is one of these single-file instruments working with reciprocating motion and manufactured with M-wire technology, leading to increased flexibility and resistance.[89] The manufacturer claims that this single-file system is reliable even in complex root canals. However, complications such as canal transportation related to Reciproc have been an issue of interest and were evaluated with different studies.[361011] While a group of studies revealed that the degree of canal transportation related to Reciproc is less than or similar to other rotary and/or reciprocating instruments,[71011] the others found greater degree of canal transportation with Reciproc.[3612]

The present study aimed to evaluate the degree of canal transportation related to the Reciproc files with and without glide path files using resin blocks. We hypothesized that the use 1 or 2 glide path instruments may provide to better maintain the original root canal morphology and reduce the degree of canal transportation.

METHODS

A total of 30 L-shaped resin blocks (VDW GmbH, Munich, Germany) with sizes of 10 mm × 10 mm × 30 mm were included. For each block, canal length was 19 mm, canal taper was 0.02, apical diameter was 0.15 mm, and radius of curvature was 45°. Blocks were divided into three groups (n = 10).

Canal preparation

Group 1: Canal preparation was performed with a Reciproc-25 file with in-and-out pecking motion using special settings of electronic motor (VDW Silver Reciproc).

Group 2:First, canals were prepared with glide path file 1 (G1, N°12, 0.03 taper, Micro Mega, France) with a continuous rotation motion (400 rpm; 1.2 Ncm) and then with a Reciproc-25 file as in Group 1.

Group 3:First, canals were prepared with glide path file 1 with a continuous rotation motion (400 rpm; 1.2 Ncm) and then with glide path file 2 (G2, N°17, 0.03 taper, Micro Mega, France) with a continuous rotation motion (400 rpm; 1.2 Ncm). Final preparation was performed as in Group 1.

All instruments were used only once with a lubricant gel (Glyde; Dentsply, Maillefer) until the working length was reached by the same operator. After each instrument, canals were rinsed with 2 ml of distilled water with 27-gauge irrigation needle that was inserted as deep as possible without binding.

Before and after preparation, all blocks were imaged under a stereomicroscope (Leica MZ 12.5, Heerbrugg, Germany) [Figures 1 and 2] in the same way with a magnification of ×10. Then, images were saved as tiff format files. Pre- and post-instrumentation images were superimposed with digital image software (Adobe Photoshop CS5 Extended, Adobe Systems, San Jose, CA, USA). After that, ten sequential circles, center of each is the apical point of canal and 1 mm away from each other, were placed over superimposed images [Figure 3]. The intersection points of circles with root canals were accepted as measuring points (Mps). The first 4 Mps from apices were considered as apical portion while Mps 5, 6, and 7 were middle portion. The last 3 Mps[8910] were calculated as coronal portion. At each Mp, the difference between the inner thickness of removed resin material (toward furcation) and outer thickness of removed resin material (outer side of curvature) was calculated (inner-outer) with a precision of ±0.01 mm using ImageJ (1.48 version, National Institutes of Health, USA) software and recorded as the value of that Mp. Positive values represented transportation toward the furcal area of root canals while negative values represented transportation toward outer side of root canals.

Figure 1

Preinstrumentation image

Figure 2

Postinstrumentation image

Figure 3

Measuring subsequental circles; superimposition of pre- and post-instrumentation images

Statistical analysis was performed with Kruskal–Wallis test and post hoc Dunn test using IBM SPSS 20 (SPSS for Windows SPSS Inc., Chicago, IL, USA) at a significance level of P < 0.05.

RESULTS

The mean amount of canal transportation of groups for apical, middle, and coronal in millimeters are represented with their standard deviations in Table 1.

Table 1

The degree of canal transportation in each portion for all groups

In coronal and middle portions, the degree of transportation is not statistically different among three groups (P = 0.98 for coronal P = 0.79 for middle).

In apical portion, the degree of transportation is higher for Group 1 compared to other groups (P = 0.004) while Group 2 and Group 3 are statistically similar (P = 0.81). Using glide path files reduced transportation in apical region.

The direction of transportation was toward inner side, except the middle of Group 2 and coronal of Group 1.

DISCUSSION

The aim of this study is to evaluate the degree of canal transportation which is important in terms of cleaning and sealing of root canals. This should be achieved for the success of treatment.[13] Reciproc is a single-file system working with reciprocal motion. It rotates 150° counterclockwise and 30° clockwise. The manufacturer does not recommend a glide path before its use.[7] However, studies report that 0.08 tapered structure of the apical 3 mm of Reciproc reduces its flexibility and result in transportation particularly in the apical portion.[36] The authors of the present study questioned whether a glide path preparation may reduce the risk of canal transportation, particularly in the apical one-third. In the study of Bürklein et al.,[3] it was reported that glide path files did not affect the degree of transportation. However, in the present study, using at least one glide path file reduced the degree of canal transportation in the apical one-third. The disparity in the results may be related to the taper of the glide path files. Bürklein et al. used 0.02 tapered glide path files (Dentsply, Maillefer), while in the present study, glide path preparation was performed with 0.03 tapered files. The more tapered glide path files used in the present study (0.03 tapered files) enlarged the canals more than 0.02 tapered files, and by this way, they might have provided an easier inlet of Reciproc files into canals leading to reduced enforcement and reduced transportation. However, it must be noted that if the degree of transportation exceeds 0.3 mm, it is accepted as a problem in terms of sealing.[14] In the present study, none of the mean transportation values was more than 0.1281 mm.

The present study included resin blocks to better achieve standardization, while in the previous study, extracted teeth were used. Although using resin blocks enables standardization and their transparency facilitates photographic measurements, the results of the present and similar studies must be verified with other in vitro studies including human teeth because of the different physical properties of human dentin and resin.[6]

Studies regarding the mechanical behaviors of rotary instrument found different outcomes as either the motion type[1015] or the taper of instruments may affect the degree of canal transportation.[3] Furthermore, canal morphology, cross-sectional geometry of instrument, and the alloy of the file[15] may also affect the degree of transportation.[16] In terms of motion type, continuous rotation - particularly with active files - may result in more transportation due to their screw-in effect.[17] On the other hand, instruments with greater tapers, especially over the apical portion, have tendency to cause more transportation resulting from decreased flexibility.[6] Thus, the previous studies could never give a certain decision whether which factor affect the shaping behaviors of the instruments. For these reasons, instead of comparing different systems, we preferred to evaluate Reciproc system - a contemporary system - which work with reciprocal motion and which can be considered as a progressive file with and without glide path files. Furthermore, in the present study, a size-25 instrument was selected because the manufacturer recommends this size for narrow and curved canals.[11] According to the results, using G-files decreased the degree of transportation. Especially, if differences in the skills of operators during daily use are considered,[18] using at least 1 glide path file seems to be beneficial to minimize transportation in curved canals.

Unlike the previous studies,[819] the direction of apical canal transportation was toward inner surface in the present study. In general, rigidity of Reciproc files due to 0.08 tapered structure of apical 3 mm may result in the straightening of root canal, and thus, transportation occurs toward outer side of the canal. However, different from the previous studies, in the present study, L-shaped resin blocks were used. The authors of the present study assume that the difference in the direction of transportation may be as a result of using L-shaped canals because the degree of pressure applied by the clinician might affect the direction of transportation as the tip of this instrument is noncutting and acts a guide.[19] In the present study, gentle pecking motion was used by the same operator, and thus, transportation did not occur toward the outside in apical portion. In the study of Franco et al.,[20] after shaping root canals with three FlexMaster files serially, rotational use of files resulted in transportation toward outer canal surface different from the reciprocal use of the same files. In the light of their study, it may be assumed that for the present study, reciprocal motion may be another reason for the inner apical transportation for Group 1. For Groups 2 and 3, using G-files before Reciproc may have provided the contact of inner canal wall with the instrument more than outer wall and may be a reason for the inner apical transportation.

CONCLUSION

Under the conditions of this in vitro study, it may be concluded that using 1 or 2 glide path files significantly reduced the degree of canal transportation in the apical portion related to Reciproc files. If the variances in the skills and procedural habits of different operators during daily use are considered, using at least 1 glide path rotary file with a taper of 0.03 may be beneficial to minimize the apical canal transportation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.