Comparison of the amount of apical debris extrusion associated with different retreatment systems and supplementary file application during retreatment process.

BACKGROUND: The type of instrument affects the amount of debris extruded. The aim of this study was to compare the effect of retreatment systems and supplementary file application on the amount of apical debris extrusion.
MATERIALS AND METHODS: Forty-eight extracted mandibular premolars with a single canal and similar length were selected. The root canals were prepared with the ProTaper Universal system with a torque-controlled engine. The root canals were dried and were obturated using Gutta-percha and sealer. The specimens were randomly divided into four equal groups according to the retreatment procedures (Group 1, Mtwo retreatment files; Group 2, Mtwo retreatment files + Mtwo rotary file #30 supplementary file; Group 3, ProTaper Universal retreatment (PTUR) files; and Group 4, PTUR files + ProTaper F3 supplementary file). The extruded debris during instrumentation were collected into preweighed Eppendorf tubes. The amount of apically extruded debris was calculated by subtracting the initial weight of the tube from the final weight. Three consecutive weights were obtained for each tube.
RESULTS: No statistically significant difference was found in the amount of apically extruded debris between Groups 1 and 3 (P = 0.590). A significant difference was observed between Groups 1 and 2 (P < 0.05), and between Groups 3 and 4 (P < 0.05).
CONCLUSIONS: The use of supplementary file significantly increased the amount of apically extruded debris.

INTRODUCTION

The retreatment of an endodontically treated tooth requires the removal of root canal filling material to achieve endodontic disinfection.[1] In the retreatment procedure, as much as possible of the bulk of Gutta-percha (GP) and the canal sealer should be removed. However, current available instruments and techniques are incapable of preparing root canals or removing root fillings without debris and irrigant extrusion.[2345] The host immune response against irrigation solutions, debris, or foreign body reactions to obturation materials such as GP may provoke postoperative pain and swelling during the retreatment.[6]

Various instrumentation methods have been introduced to remove the canal filling material such as; hand files,[7] Ni-Ti files in reciprocal motion,[8] Ni-Ti files in rotational motion,[7] and retreatment files.[9] The retreatment files were suggested to remove the root canal filling materials.[10] These instruments remove the GP more rapidly than hand files.[11] The ProTaper Universal retreatment system (PTUR) (Dentsply Maillefer, Ballaigues, Switzerland) consists of D1 (30/0.09), D2 (25/0.08), and D3 (20/0.07) files, which are designed with various tapers and the tip diameters. While the Mtwo retreatment system (Mtwo R) (VDW, Munich, Germany) has two files: R1 (25/0.05) and R2 (15/0.05).

To our knowledge, no report has evaluated the apical debris extrusion of supplementary file application during retreatment. Thus, the aim of this in vitro study was to compare the effect of supplementary file application on apical debris extrusion.

MATERIALS AND METHODS

Forty-eight extracted human mandibular premolars with a single canal and similar length were selected. All teeth were analyzed by digital radiography (Schick Tech Inc., Long Island City, NY, USA) in the buccal and proximal directions to confirm single straight root canals and mature root formation. The soft-tissue remnants and calculi on the external root surface were removed mechanically. The buccal cusp of the teeth was flattened to provide a flat reference point. The conventional coronal access cavity was prepared using a high-speed bur. A size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was used to control the canal patency, and the working length (WL) was determined as 1 mm short of the length of the file that was visible at the major diameter of the apical foramen. The root canals were prepared with the ProTaper Universal system (Dentsply Maillefer, Ballaigues, Switzerland) in a crown-down manner in combination with a torque-controlled engine (X-Smart, Dentsply Maillefer, Ballaigues, Switzerland) at 250 rpm according to the manufacturer's instructions. A Sx file was used at the root canal entrance as a guide for the other files. S1 and S2 files were used to prepare the coronal and middle thirds of the roots. Apical enlargement was performed using the F1 and F2 files. The root canals were irrigated using 2 mL of 2.5% NaOCl between instruments. The smear layer was removed by irrigation with 10 mL of 2.5% NaOCl, 10 mL of 17% ethylenediaminetetraacetic acid, and 10 mL of 2.5% NaOCl, respectively. This was followed by a final rinse with 10 mL of distilled water. The root canals were dried with sterile paper points and were obturated using GP and epoxy resin-based sealer (AH Plus, Dentsply DeTrey GmbH, Konstanz, Germany) by the lateral compaction technique. The access cavities were filled with resin filling material (Z250, 3M, St Paul, MN, USA). All specimens were stored in 100% humidity at 37°C for 2 months.

At the end of the storage period, the teeth were attached to Eppendorf tubes to create an experimental model which was previously described by Myers and Montgomery.[12] The model was as follows: The stoppers were separated from the Eppendorf tubes. An analytical balance (Radwag, Radom, Poland) with an accuracy of 10−5 g was used to measure the initial weights of the tubes. Three consecutive weights were obtained for each tube, and the mean value was calculated. A hole was created on each stopper. Each tooth was inserted up to the cementoenamel junction, and a 27-gauge 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. All retreatment procedures were completed by a single operator to avoid variation and eliminate biases. The operator was shielded from seeing the root apex during instrumentation by an aluminum leaf that covered the Eppendorf tube.

In this study, the specimens were randomly divided into four equal groups according to the retreatment procedures as follows:

Group 1 - Mtwo R files with sizes 15, 0.05 taper and 25, 0.05 taper were applied with a gentle in-and-out technique, along with a short stroking/brushing motion in a coronal direction to the original WL

Group 2 - The Mtwo R files were used in the same manner as in Group 1. After reaching the WL, the root canal was reshaped using Mtwo rotary file #30, 0.05 taper supplementary file

Group 3 - PTUR files - D1, D2, and D3-were used in the crown-down technique. The D1 (size 30, 0.09 taper) and D2 (size 25, 0.08 taper) files were used at a rotational speed of 550 rpm and 2 N cm−1 torque in the cervical and middle thirds of the root canal, respectively, and the D3 (size 20, 0.07 taper) file was used at a rotational speed of 250 rpm and 1.5 N cm−1 torque until the WL was reached

Group 4 - PTUR instruments used in the same manner as in Group 3. After reaching the WL, the root canal was reshaped using a ProTaper F3 supplementary file.

After the removal of the root canal filling was completed, the stopper, the needle, and the tooth were separated from the Eppendorf tube, and the debris and the root filling material remnants adhered to the root surface were collected by washing the root with 1 mL distilled water in the tube. The tubes were then stored in an incubator at 70°C for 5 days to evaporate the distilled water before weighing. The Eppendorf tubes were weighed using the same analytical balance to obtain the final weight of the tubes including the extruded debris and filling materials. Three consecutive weights were obtained for each tube. The weight was calculated by subtracting the weight of the empty tube from that of the tube containing the debris and filling materials.

Statistical analysis was performed using SPSS version 19.0 software (SPSS Inc, Chicago, IL, USA).

The Shapiro-Wilk test was used for testing of normality. The Kruskal–Wallis test was used for the independent group comparisons and the Bonferonni corrected the Mann–Whitney U-test for posthoc comparison. For all statistical comparisons with a P < 0.05, it was assumed as a significant difference.

RESULTS

All retreatment techniques caused extrusion of apical debris. The mean weight ± standard deviation of apically extruded debris in grams caused by each of the retreatment technique was as follows: Mtwo retreatment: 0.000492 ± 0.0002843; Mtwo retreatment + Mtwo #30 supplementary file: 0.001301 ± 0.0009371; ProTaper retreatment: 0.000608 ± 0.0002234; ProTaper retreatment + F3 supplementary file: 0.001208 ± 0.0005160. No statistically significant difference was found in the amount of apically extruded debris between Groups 1 and 3 (P = 0.590). A significant difference was observed between Groups 1 and 2 (P < 0.05), and between Groups 3 and 4 (P < 0.05).

DISCUSSION

The success rate of endodontically treated teeth was reported between 90.2% and 99.3%.[13] However, lower success rates varying between 77% and 83.0%[14] were reported for nonsurgical retreatment. The extrusion of the root filling material was related to the outcome of retreatment since most of the teeth requiring root canal retreatment have infected root canal systems and the GP itself is recognized as a foreign body.[15]

Various studies evaluated the apical debris extrusion during primary root canal treatment.[1617] However, limited data is available concerning the amount of debris extrusion during nonsurgical root canal retreatment. The mechanical irritation of apical periodontal tissue is caused by overinstrumentation of the root canal and filling material extrusion through the apical foramen.[18] According to this conclusion, retreatment of an endodontically treated tooth may involve additional destructive factors such as the extrusion of root canal filling material and the root canal sealer which may cause foreign body reactions. Ng et al.[19] reported that the extrusion of root filling material reduces tooth survival. In this study, the effects of both various retreatment files and supplementary file application on apical extrusion during nonsurgical retreatment were evaluated.

During preparation of root canals or removal root fillings, current available instruments produce apically extruded debris and irrigant.[345] The amount of debris extrusion was associated with the design and the working principle of files.[20] In the present study, both selected retreatment systems demonstrated similar amount of apical extrusion. In addition, regardless of the design of the selected supplementary file, both ProTaper and Mtwo files demonstrated similar results in debris extrusion.

The supplementary files were used to enhance the cleaning efficacy of retreatment files. However, additional instrumentation after the use of retreatment files may cause crack initiation and propagation in apical dentin.[9] A recent study reported that there were no differences in the outcomes of retreatment files with the use of additional instrumentation, and the use of instrumentation with supplementary files did not result in significant improvement in the removal of filling material.[21] The result of the present study demonstrated that using a supplementary rotary file following retreatment file, even though produced by the same manufacturer, significantly increased the amount of apically extruded debris in both groups. There may be several reasons for the observed difference. First, the increased amount of debris could be related to an enlarged apical diameter following the use of the supplementary file. The obtainment of a high percentage of clean area was justified by the fact that reinstrumentation of a root-filled tooth corresponds to instrumentation systems with increased diameter.[22] However, Hoskinson et al.[23] reported that the success rate for small apical preparations (85%) was higher than that for large apical preparations (56%). In the present study, the initial root canal preparations were completed to a tip diameter of #25. During the removal of root canal fillings, in both Groups 2 and 4, the root canals were reshaped using rotary files with tip diameters of #30. Thus, the increase in tip diameter may lead to a higher amount of extrusion.

The noncutting tip may push debris towards the apex.[24] According to this conclusion, the second reason could be associated with the noncutting tips of both the ProTaper Universal F3 and the Mtwo #30 supplementary files. On the contrary, the retreatment files used in this study have cutting tips (PTUR D1, Mtwo R15 and R25) which might permit the movement of the file into the filling material without a pushing motion.[25] Therefore, when the above-mentioned conclusions were considered, such as microcrack formation, inefficiency to improve the removal of filling material, and increased amount of debris extrusion, clinicians should be attentive when using a supplementary file following retreatment files.

CONCLUSION

Both retreatment files demonstrated similar amounts of apical debris extrusion. The use of supplementary file significantly increased the amount of apically extruded debris.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.