Apical extrusion of debris by supplementary files used for retreatment: An ex vivo comparative study.

AIM: This study evaluated whether using supplementary files for removing root canal filling residues after ProTaper Universal Retreatment files (RFs) increased the debris extrusion apically.
MATERIALS AND METHODS: Eighty mandibular premolars with single root and canal were instrumented with ProTaper Universal rotary system (SX-F3) and obturated. The samples were divided randomly into four groups (n = 20). Group 1 served as a control; only ProTaper Universal RFs D1-D3 were used, and the extruded debris was weighed. Groups 2, 3, and 4 were the experimental groups, receiving a twofold retreatment protocol: Removal of the bulk, followed by the use of supplementary files. The bulk was removed by RFs, followed by the use of ProTaper NEXT (PTN), WaveOne (WO), and Self-Adjusting File (SAF) for removal of the remaining root filling residues. Debris extruded apically were weighed and compared to the control group. Statistical analysis was performed using one-way analysis of variance (ANOVA) and post hoc Tukey's test.
RESULTS: All the three experimental groups presented significant difference (P < .01). The post hoc Tukey's test confirmed that Group 4 (SAF) exhibited significantly less (P < .01) debris extrusion between the three groups tested.
CONCLUSION: SAF results in less extrusion of debris when used as supplementary file to remove root-filling residues, compared to WO and PTN.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Nonsurgical endodontic retreatment is indicated as the primary choice to eliminate or substantially reduce the microbial content from endodontically failed teeth. Nevertheless, well-compacted root fillings offer resistance to the instruments used for retreatment, leaving root filling residues. This restricts access to the apical foramen and impairs root canal disinfection and complete reshaping.[1]

Various instrumentation techniques have been designed for effective removal of root fillings. These include hand files, engine-driven rotary retreatment files (RFs), ultrasonic tips/files, and heat-carrying instruments. The use of rotary files successfully facilitates an operative removal of the bulk of gutta-percha-based fillings from the root canal system.[2] However, many studies have reported that complete removal is not gained.[345]

Endodontic retreatment might result in pushing the irritants in the form of root canal filling materials, necrotic pulp tissues, bacteria, or root canal irrigants into the periapical region.[6] These extruded irritants are responsible for postoperative inflammation, flare-ups, and even impaired healing.[7] According to the literature, all instrumentation techniques exhibit some degree of apical extrusion of debris, the amount varying with different instrumentation techniques.[8] Recent studies have reported the inability of the universal ProTaper RFs (D1-D3) to entirely remove the root canal fillings and proposed the use of supplementary files to aid removal of the root filling residues.[9]

Hence, the current study was formulated to evaluate the extrusion of debris apically after the use of ProTaper Universal RFs and different finishing files for removing the residual root canal fillings. The finishing files used in the current study were ProTaper NEXT (PTN), WaveOne (WO), and Self-Adjusting File (SAF). The null hypothesis tested was that the three different supplementary files used would exhibit no significant differences in the amount of debris extruded.

MATERIALS AND METHODS

Eighty extracted mandibular premolars with single root and canal confirmed radiographically were acquired. Standard oval access was gained with access cavity burs (Endo Z Access Kit, Dentsply Tulsa, Oklahoma, USA). The canal patency was accomplished and working length (WL) was determined as 1 mm short of the length of a size 15 K-file that was visible beyond the apical foramen. The teeth were cleaned and shaped using ProTaper Universal rotary files (SX-F3; Dentsply Maillefer, Ballaigues, Switzerland). Irrigation was performed using a 27-gauge side-vented needle placed 2 mm short of the apex between each file with sodium hypochlorite (NaOCl; 5.25%). The shaping procedure was continued till size F3 reached WL, followed by a final irrigation with 1 mL NaOCl. Ethylenediaminetetraacetic acid (EDTA) Gel (RC Help, Prime Dental Products, Mumbai, India) served as a lubricant for the file with every reinsertion. The canals were then irrigated with 3 mL of 17% aqueous EDTA solution, which was followed by flushing the canal with distilled water and drying the canal with paper points.

The root canal obturation was done by standardized F3 master cones (Dentsply Maillefer) and AH-Plus Sealer (Dentsply-DeTrey, Konstanz, Germany) by warm lateral compaction, adding accessory cones. The excess gutta-percha was sheared by hot hand plugger and the access cavities were sealed using composite resin. The teeth were then kept for 30 days at 37°C and 100% humidity to allow complete setting of the sealer. Following this, these 80 samples were randomly divided into four experimental groups for retreatment.

The present study used the model described by Myers and Montgomery[10] for evaluating apical extrusion of debris. An analytical balance (Single Pan K-15, K Roy Instruments Pvt. Ltd., Varanasi, India) with an accuracy of 10-5 g was used to help determine the initial weights of the tubes. Three consecutive weights were obtained for each tube (pre- and postinstrumentation), and the mean was computed.

Group 1: ProTaper Retreatment files (RFs), control

The root fillings in this group were removed using ProTaper Universal RFs: D1, D2, and D3 at 2-ncm torque and 500-rpm speed using X-smart Plus endomotor (Dentsply Maillefer). The files were used in a brushing motion resting against the walls in a crown-down direction until it reached the WL. D1 was used only for the cervical third, D2 only for the middle third, and D3 through the entire WL. Each file was used till no debris was seen on the files.

Group 2: Retreatment Files (RFs) + ProTaper NEXT (PTN)

The RFs were used for removing the bulk of the root canal fillings as described in Group 1. Then, PTN files (X2, X3, and X4) were used to remove the root filling residues that remained. These files were used in an X-smart Plus endomotor (Dentsply Maillefer) at 300 rpm and 3-ncm torque. Whenever the file met resistance the file was withdrawn, the canal was irrigated, the canal was dried, and the procedure was continued. The above procedure was performed till no root filling material debris was seen on the files after the X4 reached the WL.

Group 3: Retreatment Files (RFs) + WaveOne (WO)

The initial retreatment protocol was performed in a similar way to that in Group 1. Following the removal of bulk, a WO large file was used. This file was used in a preprogrammed endomotor X-smart Plus (Dentsply Maillfer). After every three pecks the file was withdrawn, the canal was irrigated, and the file was reintroduced into the canal. The above procedure was performed till no root filling debris was seen on the file after the file reached the WL, as in Group 2.

Group 4: Retreatment Files (RFs) + Self-Adjusting File (SAF: 2.0 mm)

After the removal of the bulk of root canal filling by RFs, the residual filling was removed using SAF (2.0 mm) in this group. This file instrumentation was accompanied by continuous irrigation (bidistilled water) provided by a peristaltic in-built pump in the Endostation (Redent Nova, Ra’anana, Israel) for 1 min, removing the coarse root fillings. Following this, the pump was turned off, the canal was filled with Endosolv R (Septodont, Paris, France), and SAF was operated for 1 min. Again the canal was irrigated by bidistilled water, and dried and filled with drops of solvent; SAF was operated for additional 1 min. Next, the pump was turned on and the file was operated for the last 1 min. The file was used in the canal till it reached the WL.

Irrigation for the rotary/reciprocating files

After each instrument (rotary) or after three pecks (reciprocating), 2 mL of bidistilled water was used as irrigant. The irrigation needle was placed as deep as possible into the canal but not deeper as the predetermined WL minus 1 mm. For all the groups, Endosolv R was used as a gutta-percha solvent.

The debris extruded by groups 2, 3, and 4 were compared to the control group.

Debris collection

Following the completion of the retreatment procedure, 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 [Figure 1]. Three consecutive weight measurements were then taken for each collection assembly, with the mean value recorded.

Figure 1

Collected debris after retreatment procedure

Statistical analysis

The one-way analysis of variance (ANOVA) and post hoc test were used to determine the significant group (SPSS 20, SPSS Inc, Chicago, IL, USA) with the alpha-type error set at 0.05. The weights obtained after the use of three experimental supplementary files (PTN, WO, and SAF) were compared to the control group to find out the percentage (%) of the debris extruded.

RESULTS

The median and standard deviation of debris extrusion by the groups is shown in Table 1. The weights obtained after the supplementary use of PTN, WO, and SAF were subtracted from the control group, giving as the result the actual amount of debris extruded by the supplementary files used for retreatment [Table 2]. According to the statistical results of the twofold retreatment protocols, the WO file used after RFs extruded significantly more debris, followed by PTN and SAF (P < 0.01). SAF was associated with the least extrusion of debris among the three experimental groups (P < 0.01) [Graph 1]. When compared to the control group, WO was associated with 27% increase in the extrusion of debris, PTN with 19% increase, and SAF with 12% increase [Graph 2].

Table 1

Median and standard deviation of all the four groups. Control group — ProTaper Universal RFs. In addition, the debris extruded by twofold retreatment protocol using three investigational files after the RFs

Table 2

Median and standard deviation of debris extruded by the twofold retreatment procedure subtracted from the control group. All the groups were statistically significant (P < 0.01)

Graph 1

Meanwise distribution of the weights of apically extruded debris by the three experimental files (PTN, WO, and SAF) after the use of Universal ProTaper RFs. Statistically significant difference seen in all the three groups with WaveOne (*) exhibiting the highest and SAF (#) exhibiting the lowest extrusion of debris when used in retreatment

Graph 2

Percentage of increased debris extruded by the experimental files after subtracting from the weights obtained from the control group. WO was associated with 27%, PTN with 19%, and SAF with 12% increase in debris when used as supplementary files after using the PT RFs

DISCUSSION

The results of the current study exhibited that debris extruded apically regardless of the retreatment protocol. The current study aimed to conclude the debris extrusion using supplementary files after using ProTaper universal RFs. This twofold retreatment protocol was formulated, as previous studies stated that the RFs alone fail to render the canals free of root fillings.[9] Using WO after RFs resulted in more extrusion of the debris apically when compared to PTN and SAF (P < 0.01). Therefore, the null hypothesis was rejected.

In the current study, the debris extruded by RFs served as control. After the use of RFs, it is important to use supplementary files, in order refine the apical preparation because of the diameter of a D3 file being equal to size 20, impairing any reasonable cleaning of the apical portion. Using supplementary files for finishing provides a cleaner root canal, facilitating removal of the residual root fillings that cause periapical extrusion of debris.[11] Hence, the current study compared debris extrusion by supplementary files to the control group. The results obtained for the control group are in accordance with earlier studies;[121314] however, to the best of the authors’ knowledge, there is no report on apical extrusion of debris using supplementary files PTN, WO, or SAF. Additionally, in the present study bidistilled water was used as an irrigation solution to prevent possible crystallization of NaOCl.[10]

The SAF group was associated with the lowest percentage of debris extruded apically in the current study (12%). It is a single-file system, devoid of a central metal core and any cutting edge or flutes, and instead has an abrasive surface.[15] This hollow file adapts to the canal irregularities and the abrasive surface helps in creating fine dust while shaping, which is easily removed by associated, continuous irrigation. The continuous flow of irrigant does not build up any pressure in the canal as the metal meshwork allows free escape of the irrigant. In the narrowest apical part, the SAF leaves more than 38% of the canal cross section free for backflow of fluid and dentin debris.[16] De Melo Ribeiro et al.[17] stated that in the apical third, the SAF created cleaner canal walls when compared to the rotary system. The high amount of debris formed in the apical third may also cause its extrusion periapically.

Higher extrusion of debris by WO has been reported in the literature by various studies on primary endodontic in vitro studies, which can be attributed to the results of the present retreatment study as well. 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. The WO files also exhibit a larger taper of 0.08 at the apical 3 mm, which can be attributed to excessive debris formation apically, and extrusion periapically.[18]

The PTN file system has very rare reports on the apical extrusion of debris with its instrumentation. The PTN possesses 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).[1920] In addition, the swaggering motion of the file while in rotation may help the file to touch a greater root canal area. This may aid in better removal of the root canal filling residue and hence was used in one of the experimental groups in the current study. The samples in the group instrumented by PTN resulted in less extrusion of the debris when compared to the WO group.

CONCLUSION

The current study was an attempt to find the amount of debris extruded by the use of supplementary files after using ProTaper universal RFs. Under the experimental conditions of the present study, it can be possible to conclude that all retreatment systems caused apical debris extrusion. SAF instrumentation after the RFs results in less extrusion than PTN and WO.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.