| Abstract|| |
Aims: The purpose of this study was to evaluate the efficacy of nickel-titanium rotary retreatment systems versus stainless steel hand retreatment system with or without solvent for gutta-percha removal during retreatment.
Materials and Methods: Sixty extracted human mandibular molar teeth with single canal in a distal root was prepared with ProTaper rotary nickel-titanium files and obturated with gutta-percha and sealer. The teeth were randomly divided into six groups of 10 specimens in each groups. The volume of filling material before and after retreatment were evaluated in cm 3 using the computed tomography (CT) scanner proprietary software.
Results: Maximum amount of filling material removed during retreatment with ProTaper retreatment system with solvent and minimum with hand retreatment system with solvent.
Conclusions: None of the technique was 100% effective in removing the filling materials, but the ProTaper retreatment system with solvent was better.
Keywords: Hand retreatment system; M-two retreatment system; ProTaper retreatment system; spiral computed tomography
|How to cite this article:|
Mittal N, Jain J. Spiral computed tomography assessment of the efficacy of different rotary versus hand retreatment system. J Conserv Dent 2014;17:8-12
|How to cite this URL:|
Mittal N, Jain J. Spiral computed tomography assessment of the efficacy of different rotary versus hand retreatment system. J Conserv Dent [serial online] 2014 [cited 2020 Jul 14];17:8-12. Available from: http://www.jcd.org.in/text.asp?2014/17/1/8/124089
| Introduction|| |
Endodontic retreatment is a procedure performed on a tooth that had received prior attempted definitive treatment resulting in a condition requiring further endodontic treatment to achieve a successful result. According to the literature, the success rate of orthograde retreatment ranges from 74 to 98%. 
According to Stabholz and Friedman the main success of endodontic retreatment relies on the complete removal of root canal filling material in order to regain access to the apical foramen so that it facilitates the sufficient cleaning and shaping of entire root canal system.  There are various techniques available for removing the gutta-percha from the root canal such as hand instrumentation technique, rotary technique, heat carrying instrumentation technique, ultrasonic devices, and solvent. ,,,, But there was no technique in the literature that adequately describes removal of gutta-percha and sealer from the root canal during retreatment.
Recently, a new NiTi rotary system, ProTaper Universal Tulsa (Dentsply Maillefer, Ballaigues, Switzerland), and Mtwo retreatment system (VDW) was introduced. ProTaper retreatment system has three instruments D1, D2, and D3. The tip diameter and taper of D1-30/.09, D2-25/.08, and D3-20/.07, which are used at 500 rpm. Lengths are 16 mm for D1, 18 mm for D2, 22 mm for D3. DI, D2, and D3 are used to remove the gutta-percha from the coronal third, middle third, and apical third, respectively. Mtwo retreatment system has two instruments, R1-15/.05 and R2-25/.05, both with 21 mm length, which are used at 250-300 rpm.
This study was designed to evaluate the efficacy of a NiTi rotary retreatment system (ProTaper retreatment system and Mtwo retreatment system) versus hand retreatment system with and without solvent group for endodontic filling removal in distal canal of mandibular molar assessed by spiral computed tomography (CT).
| Materials and Methods|| |
Sixty extracted mandibular molars were taken in the age group between 20 and 40 years. They were verified radiographically for patent distal canal and the selection of these teeth based on the following inclusion criteria; single canal in the distal root, fully formed apices, no calcifications, no internal resorption, no root fillings, or prosthesis. The external root surfaces of teeth were cleaned of tissue tags and debris with periodontal curette. Teeth were stored in normal saline solution before instrumentation.
Root canal preparation
Access preparation was done with no. 4 round bur, endoaccesss bur, and endo Z bur. After preparation of straight line access, coronal flaring into the distal canal of mandibular molar teeth was carried out by Gates-Glidden drill, and subsequently length was determined by introducing a size 10 K-file. When the tip of the instrument penetrated and fit the apical foramen, the real canal length was recorded and the working length (WL) was calculated. Distal canals were prepared with a size 20 K-type file (Dentsply/Maillefer) at the WL. After this ProTaper rotary NiTi files used up to F3. The root canals were irrigated at each change of instrument with 1 mL of 0.5% NaOCl using an irrigating needle placed 3 mm from the WL. In order to standardize the procedure, the files were replaced after being used five times. The instrumented root canals were filled with 17% trisodium Ethylene Diamine Tetra-acetic Acid (EDTA) for 3 min, flushed again with 1 mL of 0.5% NaOCl, and dried with absorbent paper points.
The root canals were obturated with corresponding ProTaper gutta-percha cones (Dentsply/Maillefer) and zinc oxide eugenol sealer. Access cavity sealed with a temporary filling material (Cavit; DeTrey Dentsply, Konstanz, Germany) and stored at 37°C in 100% humidity for 30 days. After the aging period, the teeth were numbered consecutively at random. Using a sheet of A4 paper, spaces corresponding to the teeth were demarcated and identified with the number of each tooth (1-60). The teeth were fixed on these locations with wax. The GE Light Speed Plus® multidetector CT scanner (General Electric Medical Systems, Milwaukee, WI, USA) was used for scanning. Three-dimensional image of the mandibular molars specimens were obtained using spiral CT. After obtaining CT scans from all specimens, the total volume of the root filling mass in each canal up to 12 mm from the root apex was measured in cm 3 using the CT scanner proprietary software (ADW-4.4 software; General Electric Medical Systems), which automatically calculated the volume of filling material previously outlined by radiologist.
The temporary filling material was removed with a size 4 round burs. Subsequently, all specimens were randomly divided into six groups:
Hand retreatment files without solvent (Group A)
A 3 mm of filling material were removed from the cervical part of the distal canal using Gates-Glidden burs #2 and #3. A size 40 H-type file was used to penetrate the gutta-percha by using a crown down technique until the WL was reached with a size 20 H-type file.
Hand retreatment files with solvent (Group B)
A 3 mm of filling material were removed from the cervical part of the distal canal using Gates-Glidden burs #2 and #3 to create a reservoir for the solvent (tetrachloroethylene; Canal Solve, amdent). Solvent (0.2 ml) was introduced in distal canal to soften the filling material and left to act for 1 min. Further technique similar to hand retreatment files without solvent.
ProTaper retreatment files without solvent (Group C)
ProTaper Universal retreatment instruments were used to remove the filling material. D1, D2, and D3 were used sequentially, applying a crown-down technique, until the WL was reached. The instruments were used with an electric motor (X-Smart; Dentsply Maillefer) at a constant speed of 500 rpm for D1, D2, and D3, with a torque of 3 Ncm.
ProTaper retreatment files with solvent (Group D)
A 3 mm of filling material were removed from the cervical part of the distal canal using Gates-Glidden burs #2 and #3 to create a reservoir for the solvent (tetrachloroethylene; Canal Solve, amdent). Solvent (0.2 ml) was introduced in distal canal to soften the filling material and left to act for 1 min. Further technique similar to ProTaper retreatment files without solvent.
Mtwo retreatment files without solvent (Group E)
Mtwo retreatment instruments were used to remove the filling material. It consist of two instrument, R1-15/0.05 and R2-25/0.05 were used sequentially, applying a crown-down technique, until the WL was reached. The instruments were used with an electric motor (X-Smart; Dentsply Maillefer) at a constant speed of at 250-300 rpm.
Mtwo retreatment files with solvent (Group F)
A 3 mm of filling material were removed from the cervical part of the distal canal using Gates-Glidden burs #2 and #3 to create a reservoir for the solvent (tetrachloroethylene; Canal Solve, amdent). Solvent (0.2 ml) was introduced in distal canal to soften the filling material and left to act for 1 min. Further technique similar to Mtwo retreatment files without solvent.
In order to standardize the procedure, each file was discarded after being used five times. Only one instrument get fractured in Mtwo. Gutta-percha removal was considered completed when no filling debris was observed either on the instrument flutes or in the irrigating solution. The smoothness of canal walls was checked by tactile sensitivity using the last instrument.
After root filling removal, the specimens were placed back on the demarcated A4 paper sheet and fixed in the same positions as for the initial CT scanning. A new CT scanning of the roots was done. The volume of filling material remaining inside the canals up to 12 mm from the root apex was calculated in cm 3 and recorded on a spreadsheet as final volume. The volume of residual filling material within the canals was analyzed using the ADW-4.4 software with the help of experienced radiologist, who was blinded to the groups. Time for removal of root canal filling was calculated with stop watch from the beginning of procedure to until no filling debris was observed either on the instrument flutes or in the irrigating solution and also the smoothness of canal walls was checked by tactile sensitivity using the last instrument.
Mean volume of filling material removed from the root canals by the different techniques and time taken during retreatment procedure statistically analyzed by Mann-Whitney test using Statistical Package for Social Sciences (SPSS) software. Significance level was set at 5%.
| Results|| |
No techniques were able to completely remove the filling material from the root canals. The mean volume of filling material removed during retreatment and the mean time taken this retreatment procedure is shown in [Table 1].
|Table 1: Mean volume of filling material removed in percentage and mean working time in minutes for the filling material removal|
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When the mean volume of filling material removed during retreatment was statistically analyzed by Mann-Whitney test, there was only a statistically significant difference between hand versus ProTaper retreatment with solvent (P < 0.05). In without solvent group ProTaper retreatment file obtained better result than Mtwo retreatment file and hand retreatment file, but there was no statistically significant difference found between these groups.
Statistical analysis for mean working time by Mann-Whitney test showed that in without solvent group the differences between the hand retreatment vs ProTaper, hand retreatment vs Mtwo and ProTaper vs Mtwo was statistically significant (P < 0.05), while in with solvent group the difference between the hand retreatment vs ProTaper, hand retreatment vs Mtwo was statistically significant (P-value < 0.05), but the differences between ProTaper vs Mtwo was statistically insignificant.
| Discussion|| |
The main goal of endodontic retreatment is to achieve the decontamination of the root canal system in order to establish healthy periapical tissues and allow tissue repair. According to the literature, the success of endodontic retreatment ranges from 74 to 98%. The variable outcome is due to different factor such as age of the patient, type of teeth, instrument design, and technique used to remove the existing filling material and possibility of removing the coronal restoration to access the pulp chamber. ,
A unique feature of the ProTaper shaping files is their progressively tapered design which clinically serves to significantly improve flexibility, cutting efficiency and typically reduces the number of recapitulations needed to achieve length, especially in tight or more curved canals. Another feature of the ProTaper instruments relates to their convex triangular cross-section. This feature reduces the contact area between the blade of the file and dentin, and serves to enhance the cutting action and improve safety by decreasing the torsional load. ProTaper files have a continuously changing helical angle and pitch over their 14 mm of cutting blades. Balancing the pitch and helical angles of an instrument optimizes its cutting action, effectively allows its blades to auger debris out of the canal, and importantly prevents the instruments from inadvertently screwing into the canal. Another feature of the ProTaper files is each instrument has a modified guiding tip. This design feature allows each instrument to better follow the canal and enhances its ability to find its way through soft tissue and loose debris without damaging the root canal walls. On the other hand, the cross-section shape of MTwo is an "italic S" with two cutting blades. The rake angle of MTwo is one of the most effective measures in NiTi rotary instruments, enhancing the cutting efficiency of this instrument. The tip is non-cutting, and the variable helical angle reduces the tendency of the instrument to be sucked down into the canal.
Each brand of NiTi rotary files has a recommended speed to ensure optimal performance. When a NiTi rotary file is used at a speed slower than recommended the instrument tends to lose cutting efficiency and bogs down during use. Another potentially negative result of using a speed lower than recommended is increased friction which can lead to rotary file failure. On the contrary, when a NiTi file is used at a speed faster than recommended then the instrument tends to become more dangerous as it can grab and screw into the canal predisposing to breakage. The ProTaper retreatment files at 500 rpm and Mtwo retreatment file at 250-300 rpm should be run at this speed to gives optimal performance.
In earlier retreatment studies remaining gutta-percha was assessed radiographically  or roots were split longitudinally and residual gutta-percha and sealer were measured linearly  or using evaluation scales ,, with the limitation that residual obturation material may be lost by splitting the roots longitudinally. In this present study spiral CT scanning was used to outweigh the limitation of the methodologies previously applied in endodontic retreatment studies, such as displacement of the filling debris during cleavage ,,,, and two-dimensional imaging on a three-dimensional structure. ,,, Although CT scanning has been extensively employed in endodontic instrumentation research, , but its use in endodontic retreatment research is limited.  This was a noninvasive method that allows visualization of morphological features in detail and does not require the destruction of the teeth.  Moreover, CT scanning offers three-dimensional reproducible data and allows the assessment of endodontic retreatment by comparing the volume of filling material inside the root canals before and after removal procedures.
The present study determined the efficacy of two rotary retreatment system in comparison with hand retreatment system to remove gutta-percha in conjugation with zinc oxide root canal sealer because rotary techniques are time-saving and cause less fatigue to the dentist and less discomfort to the patient, while hand instrumentation technique was chosen as the control group because it is a well-known and widely used technique. This study also evaluates the effect of solvent in retreatment procedure. Distal root of mandibular molar specimen were selected because in this root canals are usually straight or minimally curved so there is less chances of variations in result while analyzing the efficacy of different rotary and reciprocating technique in removing gutta-percha.
Zinc oxide eugenol root canal sealer was selected for this study because good sealing potential and minimum dimensional change occur after setting and teeth were stored at 37°C in 100% humidity for 30 days because this was the time required for complete setting of zinc oxide eugenol root canal sealer.
[Table 1] represents the mean volume of filling material (in percentage) removed during retreatment and the result shows that maximum percentage of filling material removed by ProTaper retreatment file with solvent and minimum percentage of filling material removed by hand retreatment file with solvent, which is consistent with the finding of Gergi and Sabbagh. 
The present study showed that maximum time for retreatment procedure was taken by hand retreatment file without solvent and minimum time was taken by ProTaper retreatment file without solvent which was consistent with the finding of Giuliani et al.  It also signifies that presence of solvent shorten the time taken during retreatment procedure in the case of hand retreatment file. Conversely, the use of rotary files without solvent speeded up the removal of gutta-percha. This study also showed that it was difficult to remove the filling material when solvent was used because fine layer of softened gutta-percha adheres to the root canal wall.
The CT image analysis software did not offer a tool to assess the removal of filling material into segmented thirds, thereby, limiting the assessment of removal of filing material segmented into third. Hence, the volumes of initial and residual filling material were analyzed as a whole.
| Conclusion|| |
Within the parameters of this in vitro study it can be concluded that among all six instrumentation techniques used for the removal of filled material in endodontic retreatment, none of the technique was 100% effective in removing the filling materials, but the ProTaper retreatment file with solvent was maximum efficient in comparison to other groups.
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Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Institute of Medical Sciences, Banaras Hindu University, Varanasi - 221 005, Uttar Pradesh
Source of Support: None, Conflict of Interest: None