Introduction
The primary aim of root canal retreatment is the total elimination of the previous obturating materials1 which is to be followed with complete re-cleaning and re-shaping and finally a three dimensional obturation of the root canal system. In endodontic practice, gutta-percha is the frequently used obturation material. Gutta perch from the root canals can be removed by gutta percha solvents, h files, retreatment files, ultrasonic instruments, lasers, heated instruments etc.2
Rotary instruments are becoming popular and most dentists prefer them to hand instrumentation techniques as they are less time consuming.3 Mtwo R rotary files (Sweden & Martina) and the R-Endo(Micro Mega, France) are the novel file systems specifically designed for retreatment. Solvents such as chloroform ,xylene, oil of orange, benzene, etc are also used, which dissolves the gutta-percha cones and facilitates faster access to the working length and their application along with specific retreatment rotary systems might improve canal cleanliness. A fluid-impervious hermetic seal within the root canal system is important for the long-term success of a root canal therapy.4 Root canal sealers when used along with the materials for obtration helpto establish a good impervious seal of the root canals.5 AH plus is a resin based sealer containg a non toxic hardner,and was used in this study.
If the obturating material is compacted well then their removal using hand files can be quite a hazardous task. 6 Hence the use of Ni Ti rotary instruments is becoming popular which decreases patient and operator’s fatigue. Various retreatment rotary files are commercially available, Mtwo and R-Endo are the most popular for retreatment. In this study we are comparing the ability of two retreatment file systems in removing the guttapercha from the root canals with and without the help of gutta-percha solvent,using the help of scanning electron microscope.
Materials and Methods
Forty extracted mandibular premolar teeth, were collected and cleaned of any tissue remnants, plaque and calculus on the roots with periodontal scalers. Radiographs were taken using cone shift technique (20° mesial shift) to confirm the absence of variations in anatomy.7 Distilled water was used for storage until further use. Decoronation of all the teeth were done with diamond disc and remaining root length was standardized at 14 mm.
Specimen Preparation
ISO 10 K-file, was passively introduced into the root canal to record the working length(WL). The file was introduced until its tip was seen emerging from the major apical foramen. The length was noted and the working length was calculated by reducing 1mm from this value. Biomechanical preparation was done using Hyflex CM rotary files. Coronal enlargement was done with SX file followed by Hyflex files in sequential order and enlarged upto 6/25. During shaping and cleaning each canal was irrigated with 2.5% sodium hypochlorite(NaOCl) via 27 gauge needle during each instrumention. A final irrigation was done with EDTA and 2.5% sodium hypochlorite, which was followed by a flush with distilled water. 8 Then drying of the canals were done with paper points. Obturation was done with gutta percha by the lateral condensation technique. AH Plus was the sealer used. Heated plugger was used to carefully remove 2mm of gutta percha from the coronal portion and was condensed. Inorder to appreciate the quality and apical extent of the obturation, radiographs were taken. The samples were kept at a temperature of 37 degree Celsius and cent percent humidity for 24 hours for the complete setting of the sealer.
Retreatment procedure
The specimens were randomly divided into four groups with 10 samples in each group.
Group A (R-Endo retreatment files)
In accordance with the instructions of the manufacturer, R-Endo retreatment files were used in brushing and circumferential filing. The first file to be instrumented was the Rm stainless steel manual file (17 mm, 25/.04 taper) which was used to its full working length. The second instrument to be used was the nickel-titanium instrument Re (25/.12 taper) orifice opener, R1(25/.08 taper) till cervical third, R2(25/.06 taper) till middle third, and finally R3 (25/.04 taper) to full working length. Speed was 300 rpm for 1 minte for each file and a torque of 1.2 N cm.
Group B (R-Endo retreatment file with solvent)
R-Endo retreatment files were used in the above same manner in combination with 2-3 drops of the guttapercha solvent(Endosolv-R), before the insertion of R-Endo retreatment files.
Group C (Mtwo retreatment files)
The Mtwo retreatment files used in the root canals as per manufacturers instruction ,i.e.first fileupto the working length using MtwoM1 15/.05 taper Max. torque (0.3 Ncm) and next with M2 25/.05 taper Max. torque (1.2 Ncm).
Group D (Mtwo retreatment files with solvent)
The Mtwo retreatment files were used with EndoSolv-R solvent (2-3 drops) and was kept inside the canal for 5 minutes. The canals were then instrumented in a simultaneous manner upto the working length.
In all the groups the root canals were irrigated with 5.25% NaOCl after every instrumention. Retreatment was considered successful when gutta-percha was fully removed from the canal and the retreatment instruments came out clean and the same was confirmed radiographically.
Scanning Electron Microscopy evaluation
Longitudinally sectioning was done from buccal to lingual surface with the help of diamond disk, and roots were split into mesial and distal halves using chisel and a mallet.9 Each of the halves were observed for the remnants under scanning electron microscope with40X magnification. Photographs were taken with a digital camera and loaded to the AutoCAD 2016 software for evaluating remaing area of root canal filling material.
Results
In the present study, the mean area of remaining obturating material was observed. Ingroup A (REndo), it was 402.75±75.98, 370±93.48 and 96.65±5.88 in coronal, middle and apical third respectively. In group B(REndo with solvent), mean area of remaining obturating material in coronal, middle and apical third was 307±41.31, 284±47.39 and 74.4±6.9 respectively.
The mean area of remaining obturating material in group C(MTwo) was 236±37.34, 225±22.44 and 64.82±10.86 in coronal, middle and apical third respectively. In group D(MTwo+solvent), mean area of remaining obturating material in coronal, middle and apical third was 108.65±35.73, 129±19.22 and 50.93±7.33 respectively. On comparison of area of remaining guttapercha between group A, group B, group C and group D at coronal, middle and apical was found least in group D(MTwo+solvent) followed by MTwo and highest in group A(REndo) followed by group B(REndo+Solvent) in coronal, middle as well as apical. ANOVA test was applied to compare the mean area of remaining obturating material among all the four groups, it was found to be statistically significant as p<0.05. Tukey HSD post hoc test was also implicated to see whether any statistically difference exists among the groups with each other or not. It showed that when all the groups were compared with each other in relation to area of remaining filling material, it was found to be statistically significant and hence it can be concluded that with respect to the mean area of remaining guttapercha MTwo+solvent (group D) was the best followed by Mtwo (Group C), R-Endo+solven(Group B) and R-Endo (Group A).
Discussion
Nonsurgical endodontic retreatment is the initial choice of treatment for the management of endodontic failures. 10 Removal of maximum obturating material from inadequately treated root canal system is very crucial as it discloses the necrotic tissue remnants, microorganisms which may be reason for retreatment procedure. Eventhough the initial endodontic therapy has been shown to produce good prognosis due to various reasons, failures may occur. 11
According to Dadresanfar et al12 (2011) among the different retreatment file systems, Mtwo retreatment files are the most efficient in removing obturating material and according to C.Yadav et al 13(2016)R-Endo retreatment system had the best efficiency towards removing gutta-percha condensed by different obturating techniques, so in this study these two systems were compared along with additional softening ability of a solvent.
The novel endodontic concepts works with the aid of devices, which can significantly raise the quality of treatments, less procedure steps and reduced time to make treatment more endurable for the patient. Mtwo (VDW) is an efficient NiTi system for rotary endodontics. The three design features offers efficient dentin removal, effective shaping and safe prepration. There is one single sequence for all the canals. All the files are instrumented till the full working length. Mtwo files, during instrumentation, cuts automatically as it moves down apically and also in a lateral direction while employing a brushing file movement. There is no unnecessary loss of tooth material, because a glide path is created for the subsequent instrument.
R-ENDO files are specially designed with respect to taper, pitch and length. This enables a progressive access to every zone of the canal space. R-ENDO includes a stainless steel Rm hand file which breaks the hard layer of the obturating material and the four NiTi instruments in continuous rotating motion for flaring (Re) and then progressive shaping root canal areas (R1, R2 et R3).
The root canal sealer employed is the AH plus sealer. It is a resin based sealer and can penetrate deep into the tubules and exhibit minimal microleakage. Resin based sealers have an advantage in term of radiopacity and biocompatibility as compared to other sealers. AH plus is an epoxy resin containing a non toxichardner. Radioopacity is imparted by bismuth oxide and it has a strong adhesive property and contracts slightly while hardening.There is no release of toxic formaldehyde during setting. Cho et al mentioned that the bond strength of final restoration is least affected when resin- based sealers were used as compared to eugenol-based root canal sealers.14 Considering several advantages, AH-plus was used as the sealer material.
To facilitate an easy removal of the obturating material, a gutta percha solvent was used, supplemented by mechanical removal which allows for a proper cleansing of the apical third. n(Rosier et al., 2008).15 In this study the efficiency of two different retreatment file systems were evaluated with and without solvent. Solvent used in this study was as Endosolv R which contains formamide and Phenetylalchohol, designed for softening resin-based pastes is likely to result in better resin sealer removal. Endosolv facilitates the removal of zinc-oxide eugenol based and phenolic resin based root canal sealers. 16 It’s efficient solvent action enables better sealer removal and protects from the disadvantages associated with the use of power driven instruments for removal. Endosolv eliminated the need for the two previous septodont products (Endosolv E and Endosolv R) thereby a single product is needed for both resin sealer and eugenol based sealer removal. According to PR Shenoi, GBadole et.al17 Endosolv was more effective to remove resin based sealer (AH Plus) in a short time span.
Various methods are there to assess the root canal debridement after retreatment. Among these the most common method is the longitudinal sectioning of the roots and the remaing root canal filling material can be visualised in the split mesial and distal half. All of the used techniques had its limitations. Schirrmeister et al., reported that residual material might be lost by splitting the roots longitudinally. 18
In previous retreatment studies remaining guttapercha was assessed radio graphically but here a three dimensional visualization of the root canal system gives a more reliable understanding of the distribution of the gutta-percha after retreatment. Takahashi et al reported that a radiographic examination provides a two-dimensional image, which was proved to be less effective than cleavage method. 19
According to Eduardo et al, scanning electron microscope can analyse even the presence of filling material penetrated inside the dentinal tubules during condensation, hence the scanning electron microscope was preffered in the study. 20 Both 100x and 40x magnifications were taken but the latter was used for calculating the area of the remaining filling material. The AutoCAD 2016 software have been used for evaluating area of remaining obturating material . The outcome was a measure of the area of remaining obturating material, measured in square millimetre (mm2) and the objective was to compare the outcome measure (area of remaining obutaring material) among the these four groups.The group which had the least amount of guttapercha was considered to have the maximum efficiency in removing the obturating material.
According to mean area of remaining obturation material Group D had the least, followed by Group C, Group B and Group A (i.e.Group D<Group C<Group B<Group A).Therefore to conclude the efficancy of MTwo+solvent was the best in removing gutta-percha followed by Mtwo used alone, then REndo with solvent and REndo used alone.
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