Comparison of apical debris extrusion of two rotary systems and one reciprocating system.

BACKGROUND: Postoperative inflammation and endodontic failure occur due to apical extrusion of debris. AIM: To evaluate the amount of apically extruded debris after preparation of straight root canals in extracted human teeth using three rotary systems.
MATERIALS AND METHODS: Sixty single-rooted human teeth with single root canal and apical foramen were selected and randomly divided into three experimental groups (n = 20) according to the rotary system used: Group 1 - ProTaper, Group 2 - Revo-S, Group 3 - WaveOne. Apical enlargement was done up to size 40/0.06 for Groups 1 and 2 and 40/0.08 for Group 3. For debris collection, each tooth was held in a preweighed Eppendorf tube fixed inside a glass vial through rubber plug. After instrumentation, each tooth was separated from the Eppendorf tube and the debris adhering to the root surface was collected by washing the root with 1 mL of bi-distilled water and incubated at 70°C for 5 days. The dry weight of extruded debris was weighed in an electronic balance. STATISTICAL ANALYSIS: The mean weights of extruded debris were statistically analyzed using GraphPad prism version 6 and the intergroup comparison was done using unpaired t-test.
RESULTS: There was a statistically significant difference in the mean debris score among all the three groups - ProTaper (0.00065 g), Revo-S (0.00045 g) and WaveOne (0.00089 g).
CONCLUSION: Revo-S system was associated with significantly less debris extrusion compared with ProTaper or WaveOne.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

The success of endodontics is based on thorough debridement, disinfection, and a three dimensional obturation. A complete debridement of the root canal by instrumentation and irrigation solutions is the critical step in endodontic treatment. All instrumentation techniques cause some amount of extrusion of debris, even when the root canal preparation is maintained short of the apical terminus.[123] Extruded debris consists of irrigation solutions, necrotic tissue, microorganisms, pulpal fragments and dentin powder. This is responsible for postoperative inflammation and failure.[4] Vande Visse and Brilliant were the first to quantify the amount of debris extruded apically.[5] In spite of adequate chemomechanical preparation and obturation, endodontic flare up may be caused by extruded material referred as the “worm” of necrotic debris.

For more than a decade, various rotary systems are in use which differs in material property, cross-section, taper, symmetry, etc. Although modifications in instrument design are done to improve cutting efficiency, flexibility, fatigue resistance etc., it does not improve all the properties. Instruments with asymmetrical cross-section are considered to decrease the axial stress. Single-file systems based on M-wire technology namely the Reciproc (VDW, Munich, Germany) and WaveOne (Dentsply, Maillefer, Ballaigues, Switzerland) systems, shape the root canal in reciprocating motion[6] and are found to have greater fatigue resistance[78] and better centering ability.[9]

WaveOne files are available in three sizes - small (size 21, taper 06), primary (size 25, taper 08), large (size 40, taper 08). By relieving stress on the instrument by their reciprocating movement, i.e., counterclockwise (cutting action) and clockwise (release of the instrument) movements, cyclic fatigue is reduced. They work in a reverse “balanced force” action (reverse cutting action) using a preprogrammed motor to move the files in a back and forth “reciprocal motion.” It has a modified convex triangular cross-section at the tip end and a convex triangular cross-section at the coronal end that provides flexibility. The variable pitch flutes along the length of the instrument considerably improve safety.

ProTaper Universal (Dentsply, Maillefer, Ballaigues, Switzerland) is a multiple-file system with progressive taper. Each instrument has a changing taper over the length of its cutting blade. Its cross-sectional design mimics that of a reamer with three machined cutting edges and a convex core. ProTaper Shaping files have a convex triangular cross-section and are allowed to passively float into the canal and follow the glide path.

Revo-S rotary system (MicroMega, Besancon, France) has a unique and innovating sequence with only three instruments Shaper and Cleaner 1 (SC 1), SC 2, Shaper Universal (SU). The canal axis has three cutting edges located on three different radiuses. Smaller cross-section allows more flexibility and the asymmetrical cross-sectional design initiates a snake like movement inside the root canal that produces less stress on the instrument and increases the available volume for upward debris elimination.

To our knowledge, there is no previous study that has compared the apical debris extrusion of ProTaper Universal, WaveOne, and Revo-S, which are distinctly different in their working and design. Therefore, the aim of this investigation was to evaluate the amount of apically extruded debris after preparation of straight root canals in extracted human teeth using two rotary full-sequence, ProTaper and Revo-S which differ in symmetry and a reciprocating single-file system, WaveOne.

MATERIALS AND METHODS

Sixty freshly extracted human single-rooted teeth that were extracted for orthodontic and periodontal purpose were collected. Teeth with single root canal and apical foramen with root curvature between 0° and 20° (Schneider's method) which were confirmed with mesiodistal and buccolingual radiographs were used for this investigation. Teeth with internal resorption, root canal calcification, and curved root canals were excluded from the study.

Coronal access was achieved using diamond burs and initial apical diameter was assessed. Teeth with initial apical diameter more than K-file size 15 were excluded from the study. Working length (WL) was measured 1 mm short of the anatomical apex and glide path was established with 20 size K-file.

The debris collection apparatus was set up according to the study by Myers and Montgomery.[10] Empty Eppendorf tubes were weighed in an electronic microbalance (Sartorius Cubis, G€ottingen, Germany). Each tooth was attached to a preweighed Eppendorf tube which was fixed to a glass vial by a rubber plug. Care was taken to avoid contact between the tube and the glass vial. The tube was vented with a 25 gauge needle to equalize the pressure inside to the atmospheric pressure.

The teeth were then randomly divided into three experimental groups according to the rotary system used:

Group 1 (n = 20) - Protaper

Group 2 (n = 20) - Revo-S

Group 3 (n = 20) - WaveOne.

For Groups 1 and 2, apical enlargement was done till 40/0.06 and for Group 3 40/0.08 according to the manufacturer's instructions.

A total volume of 7 ml of distilled water was used as irrigant after each instrumentation with irrigation needle (NaviTip 31 gauge, Ultradent) placed at least 2 mm short of WL without contacting the root canal wall. All the instrumentations were done with a 16:1 gear reduction handpiece powered by a torque-controlled electric motor (X-Smart Plus motor, Dentsply, Maillefer, Switzerland; Europe). All root canal instrumentations were performed by a single operator whereas debris extrusion was assessed by another investigator who was blinded regarding the experimental groups. After instrumentation, each tooth was separated from the Eppendorf tube, and the debris adhering to the root surface was collected from the root surface by washing the root with 1 ml of bi-distilled water into the receptor tube. The Eppendorf tubes were then placed in an incubator at 70°C for 5 days for moisture to evaporate. The dry debris was weighed in an electronic balance with an accuracy of 0.00001 g. Three consecutive weights were obtained for each tube, and the mean value was calculated. The dry weight of extruded debris was calculated by subtracting the weight of the empty tube from the weight of the tube containing debris.

Statistical analysis

The mean of the dry weights of extruded debris were statistically analyzed using GraphPad prism version 6 GraphPad Software (La Jolla; California; USA) and the intergroup comparison was done using unpaired t-test.

RESULTS

The mean weight of extruded debris and standard deviation for each group are presented [Table 1]. The results indicated that apical extrusion of debris was observed with both rotary and reciprocating systems with statistically significant difference among all the three groups (P < 0.05). Intergroup comparison between ProTaper and Revo-S groups (P = 0.005) and ProTaper and the WaveOne groups (P = 0.0094) showed that they were very statistically significant and between Revo-S and WaveOne groups, they were extremely statistically significant (P = 0.0001) [Table 2].

Table 1

Mean values for the experimental groups

Table 2

P value-unpaired t-test

DISCUSSION

One of the principal cause of postoperative pain is extrusion of infected debris from root canal to the periradicular tissues.[11] Persistent periradicular inflammation created due to extruded irrigant, intracanal medication, virulent bacteria, host response and extrusion of debris apically during instrumentation of the root canal system often presents as a distressing situation to dental practitioners. The factors that affect the amount of apical extrusion includes the instrumentation technique, complexity of root canal system, diameter of apical patency, extent of apical enlargement and formation of dentin plug, instrument design and size, irrigant solution used, the amount of irrigant, irrigation delivery system, etc.[23121314] In spite of maintaining the WL 1 mm short of the apical foramen and restricting all instrumentation within the cemento-dentinal junction, all canal preparation techniques and instrumentation have reported to be associated with extrusion of infected debris.

In this study, apically extruded debris was collected based on widely accepted experimental setup of Myers and Montgomery.[10] To simulate clinical conditions access opening and root canal instrumentation were conducted without decoronation. Straight single-rooted teeth were used in this study to eliminate any possible variables and to prevent loss of WL which might damage the apical constriction and may allow more extrusion. Although this study cannot mimic the vital periapical tissues, the technique allows comparison of file systems. Distilled water was used as irrigant to avoid any possible increase in debris weight due to crystallization of sodium hypochlorite.

The result of this study indicates that apical debris extrusion occurred independent of the type of instrument or the motion. The reciprocating single-file system, Wave one produced the highest amount of extrusion followed by ProTaper and the least extrusion with Revo-S. Though there was a statistically significant difference among groups, the difference between Revo-S and WaveOne was extremely significant (P < 0.0001). The triangular or modified triangular cross-section of ProTaper and WaveOne produces a lower cutting efficiency and smaller chip space.[15] The smaller chip space limits their ability to allow coronal removal of debris resulting in a piston-like action.[16] Moreover, instrumentation in reciprocal motion may enhance debris transportation toward the apex.[6] This is because a continuous rotary motion acts like a screw conveyor and improves the coronal transportation of dentin debris.[6] But because of limited flute space, ProTaper was probably unable to effectively transport the debris as much coronally as Revo-S. The smaller taper with the asymmetrical cross-sectional design of Revo-S also allows oscillation of the file, providing adequate space for upward debris elimination, facilitating coronal movement of debris.[17] The instrument works in a cyclic way (3C concept) - cutting, clearance (debris elimination) and cleaning. SC 1 and SC 2 facilitates effective cleaning and SU smoothen the root canal walls. The progressive pitch avoids screwing effects. Due to its asymmetrical section, it recapitulates the action of the first two instruments SC 1 and SC 2, thus respecting the tapered shape of the canal. It performs excellent upward removal of the dentine debris, improved cleaning, and minimizes debris packing in the apical region and beyond.

Revo-S resulted in less debris extrusion – the hypothesis is that continuous rotation movement during instrumentation when used with engine driven and balanced force concept – results in collection of debris into the flutes and acts like a screw conveyor producing transportation of debris, dentin chips, and its evacuation out of the root canal in a coronal direction.

The result obtained from this study was similar to another study, where single use reciprocating WaveOne and Reciproc extruded more debris compared to single use rotational sequence One Shape system. WaveOne file works in a 170° counter clockwise (large rotation angle in the cutting direction) and 50° clockwise reciprocating motion (smaller rotating angle in the disengaging direction) - this unequal reciprocal motion, in and out filing motion acts like a piston causes more debris extrusion apically. The file with aggressive cutting ability removes a substantial amount of radicular dentin in a relatively shorter period, but unable to displace debris coronally that enhances the apical extrusion in combination with reciprocating motion.[18]

The results obtained in this study differed from the results obtained by Ozsu et al. where ProTaper Universal produced maximum debris extrusion whereas WaveOne, ProTaper Next, self-adjusting file produced less debris extrusion. The variation may be due to the difference in the experimental setup; moreover, vital pulp tissue cannot be simulated in the vitro model, decreased width of apical constriction, etc., significantly reduce the amount of debris extrusion.[19]

Üstün et al. also reported results differing from the present study where WaveOne produced the least debris extrusion compared to twisted files and ProTaper next. This can be explained by the reciprocating action, which is a type of mechanized balanced force pressure less technique.[20]

In another study conducted by Xavier et al., the results were in contrast to the present study were Wave One extruded less debris compared to Reciproc (REC-R40; reciprocating single file system). The reason was that WaveOne (large file) size 40 (0.08 taper) had 20% smaller diameter at the tip (D0) than the measurement provided by the manufacturer. As before canal preparation, Xavier et al. had determined the actual tip diameter by scanning electron microscope (SEM) morphological analysis of instruments using SEM revealed no correlation between the diameter provided by the manufacturer and the measured diameter for the WaveOne large file. Moreover, system extruded less debris than Reciproc due to the following reasons - WaveOne single file is used at rotational angles of 130° counter clockwise and 50° clockwise, this system has a different cross-sectional design along its entire active part: The tip has a triangular cross-section modified with radial lands, and there is a change to a neutral rake angle with a convex triangular transverse cross-section in the middle and neck portions of the working part of the instrument, it has a decreasing taper along its entire length, this may have less cutting power and would produce less debris.[21]

There are a few limitations of this study. The results obtained cannot be generalized to teeth with multiple roots, severely curved canals, incomplete root development, open apices as teeth only with single root canals with <20° curvature was selected. In the present study, no attempt was made to determine the association of debris extrusion with various irrigation systems, reassessment of apical dentinal plug, simulation of vital/necrotic pulpal tissue and periapical tissue by floral foam that serves as natural barrier limiting apical debris extrusion, histopathological correlation of periapical inflammation with apical debris extrusion.

CONCLUSION

Under the limitations of this study, it can be concluded that all instrumentation systems, whether rotary or reciprocating caused apical debris extrusion

Revo-S system was associated with significantly less debris extrusion compared with ProTaper and WaveOne

There was no significant difference in debris extrusion between ProTaper and WaveOne rotary systems.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest