Effect of instrument speed when used in reciprocating motion on root canal transportation and centering ability.

AIM: This study aims to evaluate the root canal transportation, centering ability, and instrumentation times after root canal preparation using reciprocating motion at 300 rotations per minute (rpm) and 600 rpm.
MATERIALS AND METHODS: Twenty mesial root canals of mandibular first molars with curvature angles of 35°-70° and radii of 2-6 mm were included in the study. Root canal instrumentation was performed using R25 according to the manufacturer's instructions at 300 rpm or 600 rpm (n = 10). Cone-beam computed tomography scanning was performed both pre- and post-instrumentation. Root canal transportation and the centering ratio were calculated for both the groups, and the data were analyzed using independent sample t-test for the instrumentation time, root canal transportation, and centering ratio at the 95% confidence level (P = 0.05).
RESULTS: At the three levels (3 mm, 5 mm, and 7 mm), there were no significant differences in centering ratio between the groups (P > 0.05). At 3 mm, 600 rpm resulted in more transportation than 300 rpm. However, there were no significant differences in the root canal transportation between the groups at 5 mm and 7 mm levels (P > 0.05).
CONCLUSION: At the 3 mm level, 600 rpm resulted in more transportation than 300 rpm. However, centering ratio was similar at both 600 rpm and 300 rpm.

INTRODUCTION

During root canal instrumentation, iatrogenic errors such as root canal transportation, perforation, and zips can occur in curved root canals.[1] Several studies demonstrated that nickel–titanium (NiTi) systems were produced to maintain the original canal shape.[23] Reciproc® (VDW, Munich, Germany) is a novel NiTi single-file system and is made from M-Wire technology. This instrument was designed to be used in reciprocating motion. In a recent study, the full-sequence reciprocating motion was found to be superior to rotary motion with the same instruments with respect to the straightening of the canal curvature.[4]

Another factor that may influence root canal transportation is speed (rotations per minute [rpm]). Yared et al.[5] demonstrated that the lower speed (150 rpm) did not result in any locked, deformed, or separated instrument. However, recently, Peters et al.[6] found that increased rotational speed was associated with increased cutting efficiency. In another study by Bardsley et al.[7], it was found that instruments at 400 rpm generated less torque and force compared with 200 rpm.

For rotational motion, Poulsen et al.[8] found that there was no significant difference among the instrumentation at various rotational speeds in the amount of dentin removed, canal transportation, or the ability of the instrument to remain centered in the canal. To the best of our knowledge, there are no data in the literature related to the effect of different speed settings for reciprocating motion on root canal transportation. Therefore, the aim of the present study was to evaluate the root canal transportation, centering ability, and instrumentation times after root canal preparation using reciprocating motion at 300 rpm and 600 rpm. The null hypothesis was that there would be no significant difference between the groups in terms of root canal transportation, centering ability, and instrumentation times.

MATERIALS AND METHODS

Mandibular first molars were selected from a collection of teeth that had been extracted for reasons unrelated to this study. The teeth were stored in distilled water until use. The initial inclusion criterion was a tooth having visible curvature in the mesial root. The teeth were decoronated, and the distal root was separated. The teeth were then fixed in a silicone impression material and numbered. The mesial roots were scanned with a cone-beam computed tomography (CBCT) scanner (NewTom FP QR-DVT 9000 Verona, Italy), and the images obtained were analyzed using image analyzing software (ImageJ; http://imagej.nih.gov/ij/) to determine the curvature and the radius. Straight lines, with the same lengths, beginning from the apical and coronal regions were drawn. The midpoints of the lines were marked, and a circle was drawn over the midpoints. The radii were measured, and the angle between the lines was recorded as the curvature angle. Roots with curvature angles of 35°–70° and radii of 2–6 mm were included in the study. According to these criteria, 20 specimens were selected for the study and assigned according to the curvature and radius to three root canal shaping procedures (n = 10). According to a one-way analysis of variance, there was no significant between-group difference in the canal curvatures and radii (P > 0.05).

The working length of the canals was determined by inserting a #10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) into the root canal terminus and subtracting 1 mm from this measurement. Root canal instrumentation was performed using R25 instrument according to the manufacturer's instructions at either 300 rpm or 600 rpm (n = 10). The instrumentation times for the groups were also recorded. For all groups, instrumentation was performed using an electric motor (Satelec Endo Dual, Acteon, France) that allows the user to modify and set the reciprocating angles and speed. After completion of the root canal instrumentation, the roots were placed in a silicone impression material using the same setup as that used in the preinstrumentation. Scanning was performed, with images obtained at 3, 5, and 7 mm from the apical terminus of the root for both pre- and post-instrumentation. Root canal transportation was calculated for each level using the following formula, as described by Gambill et al.:[9] (x1−x2)−(y1−y2). x1 and x2 represent the shortest mesial distances from the outside of the curved root to the periphery of the uninstrumented and instrumented canal, respectively, and y1 and y2 represent the shortest distal distances from the outside of the curved root to the periphery of the uninstrumented and instrumented canal, respectively. The canal centering ratio at each level was calculated using the following formula:[9] (x1−x2)/(y1−y2) or (y1−y2)/(x1−x2).

Data were analyzed using independent sample t-test for the instrumentation time, root canal transportation, and centering ratio. Because there was only one comparison, the level of significance used was P < 0.05 without Bonferroni adjustment. The statistical analyses were performed using IBM® SPSS® Statistics 20 software (IBM SPSS Inc., Chicago, IL, USA) at the 95% confidence level (P = 0.05).

RESULTS

Table 1 summarizes the centering ratio values at the 3, 5, and 7 mm levels for the groups. At these three levels, there were no significant differences in the centering ratio between the groups (P > 0.05).

Table 1

Mean centering ratio values of the tested groups

Table 2 summarizes the root canal transportation values at the 3, 5, and 7 mm levels for the groups. At 3 mm, 600 rpm resulted in more transportation than 300 rpm. However, there were no significant differences in the root canal transportation between the groups at 5 mm and 7 mm levels (P > 0.05).

Table 2

Mean root canal transportation (mm) values of the tested groups

The mean ± standard deviation for the instrumentation times was 1.05 ± 0.43 min for 300 rpm and 0.40 ± 0.11 min for 600 rpm. The 600 rpm was significantly faster than 300 rpm in root canal preparation. No instrument fracture occurred during instrumentation in any of the groups.

DISCUSSION

The present study evaluated the root canal transportation, centering ability, and instrumentation times after root canal preparation using reciprocating motion at 300 rpm and 600 rpm. According to the results of the present study, the null hypothesis was partially rejected. There were significant between-group differences in the root canal transportation at 3 mm. However, there were no significant differences between the groups in terms of centering ability.

Karagöz-Küçükay et al.[10] evaluated the influence of Hero 642 rotary NiTi instruments driven at 300, 400, or 600 rpm on root canal straightening using digital intraoral radiography system. According to the results, using Hero 642 rotary NiTi system at different rotational speeds had no effect on canal curvature. NiTi engine-driven instrument at different rotational speeds had no effect on root canal morphology. A similar finding was found in the study by Poulsen et al.,[8] who found no significant differences among the 750, 1300, or 2000 rpm in the amount of canal transportation, or the ability of the instrument to remain centered in the canal. In the present study, the reciprocating motion was used and 600 rpm resulted in more root canal transportation than 300 rpm at the 3 mm level. Inconsistency in the results of different studies seems to be related to the differences in kinematics used as well as to the design of the instrument.

CBCT is a noninvasive and reliable method for evaluating root canal geometry.[11] Previous studies confirmed that CBCT was useful to assess the effectiveness of rotary systems with regard to root canal geometry.[1213]

CONCLUSION

At the 3 mm level, 600 rpm resulted in more transportation than 300 rpm. However, 600 rpm was similar to 300 rpm in centering ratio.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.