TITLE: The self-adjusting file instrumentation results in less debris extrusion apically when compared to WaveOne and ProTaper NEXT

  ABSTRACT.AIM:
The present ex vivo study aimed to evaluate the debris extrusion after instrumenting the root canals by three different files systems.

ABSTRACT.MATERIALS AND METHODS:
Sixty extracted human mandibular premolars with single canals were selected and randomly divided into three groups (n = 20) for instrumentation with three different files. Group 1: WaveOne (primary) single reciprocating file (WO; Dentsply Maillefer, Ballaigues, Switzerland) (25/08), Group 2: Self-adjusting file (SAF; ReDent-Nova, Ra'anana, Israel) (1.5 mm), and Group 3: ProTaper NEXT X1 and X2 (PTN; Dentsply Tulsa Dental, Tulsa, OK) (25/06). Debris extruding by instrumentation were collected into pre-weighed Eppendorf tubes. These tubes were then stored in an incubator at 70°C for 5 days. The tubes were then weighed to obtain the final weight, with the extruded debris. Statistical analysis for the debris extruded apically was performed using one-way analysis of variance and post hoc Tukey's test.

ABSTRACT.RESULTS:
The statistical analysis showed a significant difference between all the three groups tested (P < 0.01). The following post hoc Tukey's test confirmed that Group 2 (SAF) exhibited significantly least (P < 0.01) debris extrusion between the three groups tested.

ABSTRACT.CONCLUSIONS:
The SAF resulted in significantly less extrusion of debris when compared to reciprocating WO and rotary PTN.

BODY.INTRODUCTION:
Biologically, all irritants must be removed from the root canal space (RCS), while at the same time mechanically create an adequate space and shape for flushing and debridement.[1] Complete debridement of the RCS using recently developed rotary/reciprocating files and newer irrigation systems can prove as an aide predicting endodontic success. However, the instrumentation, irrigation solutions, and the formed debris due to instrumentation containing necrotic tissue, micro-organisms, pulpal fragments, and dentin particles may be extruded from the RCS into the periapical region, resulting in post-operative inflammation and treatment failure.[2]  The extrusion of debris using different protocols for instrumentation and irrigation has been reported.[345678910] The amount of debris extruded differs according to the preparation techniques because of the various available designs of the file systems and irrigation devices.[3] All the instrumentation techniques used for biomechanical preparation result in apical extrusion of debris, even after the root canal preparation is maintained short of the apical terminus.  Most nickel-titanium (NiTi) instrument systems work in a crown-down manner with push-pull rotation filing movements. Various advances in instrument design and the use of different operational principles can successfully influence the amount of debris extrusion.  An evolved generation in NiTi instrumentation files is marked by the introduction of single files systems for shaping and cleaning. The WaveOne (WO; Dentsply Maillefer, Ballaigues, Switzerland) single reciprocating file system simulates a reversed balanced force and a linear motion. The Self-Adjusting File (SAF; ReDent-Nova, Ra'anana, Israel) is also a single file system, which is a hollow compressible design. The SAF is used with vibrating movement accompanied by continuous irrigation with any desired solution.[4]  The most recent generation of shaping files ProTaper NEXT (PTN; Dentsply Tulsa Dental, Tulsa, OK) presents uniqueness with the center of mass and the center of rotation offset design. These files produce a mechanical wave of motion that travels along the active length of the file. This unique design is advantageous in minimizing the engagement between the file and dentin, may also enhance removal of debris out of a canal and improves flexibility of the files.[4]  Less apical extrusion associated with SAF and higher extrusion with WO have been reported in previous studies.[56] To the best of our knowledge, no report has compared apical debris extrusion of debris by WO, SAF, and PTN files; hence, the present study was designed to compare the apically extruded debris when the root canals were instrumented with these files. The null hypothesis was that the three different files (WO, SAF, and PTN) that used different kinematic motions (reciprocating, vibratory, and rotary) would have no effect on the apically extruding debris during instrumentation.

BODY.MATERIALS AND METHODS:
Sixty extracted human mandibular premolars with single canals confirmed radiographically (buccal and proximal) were collected from random collection. The soft-tissue remnants and calculi on the external root surface were removed using ultrasonics. The buccal cusp edge of each tooth was flattened aiding as a reference point, and coronal access was prepared using an access cavity kit (Endo Z Access Kit, Dentsply Tulsa). The canal patency was achieved and controlled with a size 15 K-file. The working length (WL) of each canal was determined as 1 mm short of the length of a size 15 K-file that was visible at the major diameter of the apical foramen. The teeth were then randomly divided into three experimental groups for different instrumentation techniques. The present study used the experimental model described by Myers and Montgomery[7] for assessing the debris extruded periapically.  An analytical balance (Single Pan K-15, K Roy Instruments Pvt. Ltd., Varanasi, India) with an accuracy of 10-4 g was used to measure the initial weights of the tubes. Three consecutive weights were obtained for each tube, and the mean was calculated. Each tooth was inserted up to the cemento-enamel junction, and a 27-G needle was placed alongside the stopper for use as a drainage cannula and to balance the air pressure inside and outside the tubes. Then, each stopper with the tooth and the needle was attached to its Eppendorf tube, and the tubes were fitted into vials. The same operator trained to use all the file systems efficiently carried out the instrumentation. The Eppendorf tube was covered with a silver foil to blind the operator from seeing the apex during instrumentation.

BODY.MATERIALS AND METHODS.INSTRUMENTATION:
The glide path for all the 60 samples was created till a # 20 K-file for all the groups and a new instrument/file (WO, SAF, and PTN) was used for every sample.

BODY.MATERIALS AND METHODS.GROUP 1 WAVEONE (WO):
Twenty teeth were instrumented by single reciprocating file WO (primary) instrument, used in a pecking motion. The root canal orifice was flared using Sx file from the universal ProTaper (Dentsply Tulsa Dental, Tulsa, OK). A pre-programmed reciprocating endomotor (X-Smart Plus, DentsplyMaillefer) possessing the program for WO (small, primary, and large) files instrumentation was used. The flutes of the instrument were cleaned after three pecks. On meeting obstruction, the file was removed, the canal was irrigated, recapitulated, and the file was re-introduced into the canal again. The instrumentation was done till the WO (primary) file reached the apex.

BODY.MATERIALS AND METHODS.GROUP 2 THE SELF-ADJUSTING FILE (SAF):
Twenty teeth were prepared with the SAF system. A prior glide path established accommodated the 1.5 mm SAF. The SAF file was operated by using in-and-out manual motion for 4 minutes in the canal, with continuous irrigation by using bi-distilled (0.4-mm amplitude and 5,000 vibrations per minute), using VATEA peristaltic pump (ReDent-Nova) at a rate of 4 mL/min. A total of 3 mL bi-distilled water was then used for 3 minutes as a final rinse.

BODY.MATERIALS AND METHODS.GROUP 3 PROTAPER NEXT (PTN):
Twenty teeth were instrumented by PTN instruments, used according to the manufacturer's instructions using a gentle in-and-out motion with a torque-controlled endodontic motor (X-Smart Plus, Dentsply Maillefer) at 300 rpm and a torque of 2.6 Ncm. The root canal orifice was flared using Sx file from the universal ProTaper (Dentsply Tulsa Dental, Tulsa, OK). This was followed by the use of X1 and X2 files. On meeting obstruction the file was removed, the canal was irrigated, recapitulated, and the file was re-introduced into the canal again. The instrumentation was continued till the X1 and X2 both reached the working length.

BODY.MATERIALS AND METHODS.IRRIGATION FOR THE ROTARY/RECIPROCATING FILES:
After each instrument (rotary) or after three pecks (reciprocating) 2 mL of bi-distilled water was used as irrigant. The irrigation needle (NaviTip 31ga; Ultradent, South Jordan, UT) was placed as deep as possible into the canal but not deeper as the predetermined WL minus 1 mm. Ethylenediaminetetraacetic acid (EDTA) gel was used as a lubricant throughout the instrumentation procedures for all the groups.

BODY.MATERIALS AND METHODS.DEBRIS COLLECTION:
Following instrumentation, the teeth were removed from the tube and the debris adhering to the root surface was collected by washing off the apical area of the tooth with 1 ml of distilled water into the centrifuge tube. The centrifuge tube was stored in an incubator at 70°C for 5 days, to allow the moisture to evaporate, before weighing the dry debris, using an electronic balance.

BODY.MATERIALS AND METHODS.STATISTICAL ANALYSIS:
Theraw pooled data of the weights were statistically analyzed using D'Agostino-Pearson test for normal distribution and test for homogeneity. This was followed by application of one-way analysis of variance (ANOVA) and post hoc test to determine the significant group (statistical package of social sciences (SPSS) 16, SPSS Inc, Chicago, IL). The alpha-type error was set at 0.05.

BODY.RESULTS:
The weights obtained were analyzed using D'Agostino-Pearson test for normal distribution, which was not significant (P > 0.05). Also, the test for homogeneity was satisfied (P > 0.05) aiding in successful application of parametric test one-way ANOVA to find out the significant difference.  Statistical analysis exhibited a significant difference between all the three groups (P < 0.001) (one-way ANOVA; SPSS software v16). Post hoc tukey's test revealed Group 1 (WO) resulted in higher debris extrusion (P < 0.001) and Group 2 (SAF) resulted in least debris extrusion (P < 0.001) in the three groups tested (SPSS software v16). Whereas, PTN group presented with an intermediate debris extrusion when compared to SAF it was higher (P < 0.01) and with WO it was lesser (P < 0.01). The mean, minimum, maximum, and standard deviation of the three experimental groups are shown in Table 1. The mean extrusion of debris extruded apically is plotted in Figure 1.   Table 1 Mean, minimum, maximum, and standard deviation of the debris extruded for all the three groups. (*Statistically significant differences between the three groups)   Figure 1Meanwise distribution of the apical extrusion of debris for all the three groups. (A Highest and B Least debris extrusion among the groups)

BODY.DISCUSSION:
According to the results obtained from the current study, the resultant debris from instrumentation of root canals was extruded periapically regardless of the file design (convex triangular WO, hollow SAF, and rectangular PTN) and different kinematic motions (reciprocating, vibratory, and rotary) used. The reciprocating file WO resulted in maximum debris extrusion (P < 0.01), whereas the vibratory file SAF resulted in least debris extrusion in the three groups tested (P < 0.01). Thus, the null hypothesis was rejected. Previous studies have reported less debris extrusion associated with SAF and more with rotary (Protaper) and reciprocating files;[56] however to the best of authors' knowledge the apical extrusion of debris resulting from the recently evolved ProTaper NEXT rotary file is rarely reported.[8]  The present study used method of Myers and Montgomery;[7] to simulate clinical conditions, only the buccal cusp edge of each tooth was flattened aiding as a reference point and the shaping procedures were conducted without de-coronation. Distilled water was used as an irrigation solution to avoid any possible crystallization of sodium hypochlorite. The amount of periapically extruded debris being extremely low, the contact of moist or greasy fingertips alters the weight of the extruded debris. Another important issue is the absence of a physical backpressure provided by periapical tissues, an imminent shortcoming of in vitro studies.[79] Also, the residual pulp tissue, condition of the pulp, and normal or pathological periapical tissues may act as barriers and inhibit the apical extrusion in vivo conditions.[91011] Some suggestions to simulate the periodontal ligament have been made, by the use of floral foam,[11] but they lead to absorption of the irrigant as well as the debris.[12]  The present study compared three different instrumentation protocols, a reciprocating file (WO), a vibratory file (SAF), and a rotary file (PTN), a comparison yet to be reported in literature. The results obtained from the current study may be explained by differences in the instrument design and movement kinematics between the WO, SAF, and PTN systems.  The WO file was associated with the maximum debris extrusion apically in the present study, which is accordance with other studies.[61314] The WO files are characterized by a modified triangular cross-section, which results in decreased cutting efficacy and smaller chip space resulting in auguring the formed debris after instrumentation, periapically.[613] The WO files also exhibit a larger taper of 0.08 at the apical 3 mm, which can be attributed for excessive debris formation apically, and extrusion periapically.[8]  SAF a single-file system, devoid of a central metal core and any cutting edge or flutes, instead has an abrasive surface.[15] The SAF is operated with a transline in-and-out vibratory motion and associated continuous simultaneous irrigation. This continuous flow of irrigant does not build up any pressure in the canal as the metal meshwork allows the free escape of irrigant. In the narrowest apical part of a canal prepared up to a # 20 K-file, the SAF is effective, leaving more than 38% of the canal cross-section free for backflow of fluid and dentinal debris.[15] deMeloRibeiro et al.,[16] stated that in the apical third, the SAF system created cleaner inner canal walls when compared to rotary system.  The PTN is a novel rotary file system and very rare reports on apical extrusion of debris resulting from its instrumentation. Capar et al., reported less debris extrusion associated with PTN files when it was compared to the universal ProTaper file systems.[8] The PTN possess a unique design, an offset center of mass and rotation. This design provides more cross-sectional space for enhanced cutting, loading and successfully allowing the debris to travel out of a canal (coronally), compared to a file with a centered mass and axis of rotation. It may also decrease the chances for the file packing the debris laterally, aiding in reducing the chances of blockage of the root canal system.[4] This can be the main advantage of the file and may lead to least debris extrusion; hence, it was used as one of the instrumentation techniques for the present study. The samples in the group instrumented by PTN resulted in less extrusion of the debris when compared to the WO group.  With rotary and reciprocal systems a predictable and circularly standardized apical preparation can be expected but incase of the SAF group, the apical enlargement depends upon the apical anatomy of the samples. In the present study, SAF group resulted in less extrusion of debris when compared to the other two groups tested. In a study by Dietrich et al.,[17] comparing reciprocal movement to the SAF, reciprocal instrumentation resulted in more debris in the apical part of the root canal than the SAF or a rotary system. The amount of debris formed in the apical third may also cause its extrusion periapically.

BODY.CONCLUSION:
In the present ex vivo study, the extrusion of debris associated with three different files possessing different designs that used different kinematic motions was assessed. Within its limitations, it can be concluded that the three file systems used for instrumentation resulted in extrusion of debris even though the working length was maintained 1mm short of the apex. The SAF that used a vibratory motion with continuous irrigation resulted in significantly less debris extrusion when compared to PTN and WO files systems. The results of the current study are favorable to the SAF system, but further studies clinically evaluating the incidence of post-instrumentation pain with these instrumentation systems can provide a better understanding of these file systems.

Question: Compared to Group 2: Self-adjusting file (SAF; ReDent-Nova, Ra'anana, Israel) (1.5 mm)  what was the result of Group 3: ProTaper NEXT X1 and X2 (PTN; Dentsply Tulsa Dental, Tulsa, OK) (25/06) on debris extrusion?
Evidence: Post hoc tukey's test revealed Group 1 (WO) resulted in higher debris extrusion (P < 0.001)
Answer: significantly increased