| Abstract|| |
Aim: The study was designed to investigate the sealing ability of two obturation systems (cold laterally compacted gutta percha and Obtura II) over different apically separated rotary nickel-titanium files (RACE and K3 system) using dye extraction method.
Materials and Methods: Sixty-two mandibular premolars were divided into 2 groups of 30 teeth each, and 2 teeth served as negative controls. In Groups A and B, roots were prepared using RACE and K3 system, respectively, and were further subdivided into 4 subgroups. In subgroups A1, B1 and A2, B2 (n = 10 each), files were separated at 3 mm from the tip in apical 3 rd of the canal. In subgroups A3, B3 and A4, B4 (n = 5), instruments were not separated. Subgroups A1, A3, B1, B3 and A2, A4, B2, B4 were obturated by lateral condensation method and Obtura II techniques, respectively. The sealing ability of the obturated specimens were tested using dye extraction method. The values for each group were recorded and analysis of variance (ANOVA), Student "t" test (two-tailed, independent), and Leven's test were performed.
Results: Group A1 showed significantly less leakage than B1. No statistical significant difference between Groups A2 and B2 and Groups A3 and B3, respectively, were observed. Group A4 showed significantly less leakage than B4.
Conclusion: Groups obturated with Obtura II showed less leakage than the lateral condensation technique irrespective of presence or absence of fractured NiTi rotary system.
Keywords: Dye extraction method; file separation; microleakage; nickel-titanium files; obturation
|How to cite this article:|
Hegde J, Bashetty K, Kumar KK, Chikkamallaiah C. Comparative evaluation of the sealing ability of different obturation systems used over apically separated rotary nickel-titanium files: An in vitro study. J Conserv Dent 2013;16:408-12
|How to cite this URL:|
Hegde J, Bashetty K, Kumar KK, Chikkamallaiah C. Comparative evaluation of the sealing ability of different obturation systems used over apically separated rotary nickel-titanium files: An in vitro study. J Conserv Dent [serial online] 2013 [cited 2019 Dec 15];16:408-12. Available from: http://www.jcd.org.in/text.asp?2013/16/5/408/117502
| Introduction|| |
One among the procedural accidents clinicians come across during root canal treatment is separation of the instrument, which could compromise the clinical outcome in terms of failure of the root canal treatment.
NiTi rotary files are preferred over stainless steel files due to their shape memory, super elasticity, biocompatibility, and corrosion résistance. The disadvantage of NiTi alloy is the low ultimate tensile and yield strength as compared to stainless steel, making it more susceptible to fracture at lower loads. The reason for fracture of rotary NiTi instruments is complex and multifactorial and mainly depends on operator's skill and experience, other factors that may be responsible for the instrument fracture are instrument design like instrument size, taper, flutes, and pitch length. 
Separation of root canal instrument is troublesome, if the fragment cannot be retrieved. A number of treatment protocols for removing separated instruments have been described in the literature.  Many authors have suggested to leave the separated fragment in the canal followed by the precise endodontic obturation to achieve a fluid tight seal using separated fragment as a part of obturation.  The separated fragment is incorporated into the obturation, which makes it imperative that clinician be offered more definitive, evidence-based information for predicting the potential consequences of this procedural complication. Therefore, the aim of this study was to investigate the sealing property of two obturation systems (cold laterally compacted gutta percha and Obtura II) over different apically separated rotary nickel-titanium files (RACE and K3 system) using dye extraction method.
| Materials and Methods|| |
Sixty-two freshly extracted mandibular premolars with straight and single root canals were selected for this study. All the teeth were decoronated at Cemento-enamel junction with a carborundum disc, maintaining the root length of approximately 18 mm and examined under stereomicroscope to eliminate any specimens with cracks. Working length was determined by subtracting 1 mm from the length of a # 10 k file after having its tip flush with the apex.
Sixty-two roots were divided into 2 groups, with 1 sample in each group serving as negative control. Negative controls were sealed with cyanoacrylate cement. In Groups A and B, roots were prepared using RACE (FKG Dentaire) and K3 (Sybron Endo) systems, respectively, in crown down technique using an Endo-motor X-smart (Dentsply, maillerfer) in the presence of Glyde File Prep (Dentsply-Maillefer). Root canal preparation was carried out until #25, 6% taper up to the working length. The specimens were then assigned into 4 subgroups namely A1 to A4 and B1 to B4 with respect to the presence/absence of the separated instrument and the final obturation method used. All the root canals were irrigated using 3% sodium hypochlorite and were neutralized by sodium thiosulfate solution,  followed by saline and then dried using paper points. AH plus (Dentsply) was used as a sealer in both the groups.
In subgroups A1, A2 [Figure 1] and B1, B2 (n = 10 each) [Figure 2], files were separated in the canal by previously nicking the file with a round diamond point at 3 mm from the tip to facilitate the separation in the apical 3 rd . In subgroups A3, A4 and B3, B4 (n = 5), instruments were not separated in the apical 3 rd .
In subgroups A1 and B1, the tip diameters of the separated instruments were measured using gutta-percha gauge (SybronEndo, Europe) and suitable-sized gutta-percha point was trimmed to the same tip diameter as that of separated instrument and was condensed using lateral condensation method. In subgroup A3 & B3 obturation was carried out using snugly fitting # 25, 0.06 taper gutta percha with lateral condensation method.
In subgroups A2, A4 and B2, B4 canals were obturated by setting the needle of the Obtura II to the length of 15 mm with a stopper, and the roots were obturated. After obturation, the coronal access was sealed with IRM (Dentsply). The sealing ability of the obturated specimens were tested using dye extraction method.  The specimens were coated with two layers of nail varnish, except for 3 mm around apical foramen. The apices were dipped for 24 h at 37°C in a neutral buffered 2% methylene blue solution (Spectrum, Cochin, India), under the normal atmospheric pressure. Thereafter, the roots were removed from the dye, washed for 30 min under tap water, and the nail varnish was removed with polishing disks. The roots were dried and placed in a test tube containing 6 ml of 65% nitric acid (Spectrum, Cochin, India) and left for 6 days. A dilution was made using 0.15 ml of acid solution from the specimens and 1.35 ml of distilled water. This solution was then centrifuged at 14,000 rpm for 3 min to separate gutta-percha debris from the extracted dye. From each test tube, 1 ml of the supernatant was taken and transferred into cuvette. The absorbance was determined using a spectrophotometer (Spectrophotometer-106, Systronic Ahmedabad, India) at 590 nm using 10 times diluted nitric acid as the blank.
Descriptive statistical analysis was carried out in the present study. Results on continuous measurements are presented on Mean ± SD (Min-Max) and results on categorical measurements are presented in Number (%). Significance was assessed at 5% level of significance. Analysis of variance (ANOVA) has been used to find the significance of study parameters between three or more groups of specimens, and Student t-test (two-tailed, independent) has been used to find the significance of study parameters on continuous scale between two groups (Inter group analysis) on metric parameters. Leven's test for homogeneity of variance has been performed to assess the homogeneity of variance.
The statistical software namely SAS 9.2, SPSS 15.0, Stata 10.1, MedCalc 9.0.1, Systat 12.0 and R environment ver. 2.11.1 were used for the analysis of the data and Microsoft Word and Excel were used to generate graphs and tables.
| Results|| |
Group A1 showed significantly less leakage than B1. Statistically no significant difference was observed between group A2 and B2 and Group A3 and B3, respectively. Group A4 showed significantly less leakage than B4 [Table 1].
In specimens prepared with the RACE and K3 system, the amount of leakage was significantly more with the separated instrument groups than the groups without separated instruments, irrespective of the method of obturation. Obtura II displayed (A2, A4 and B2, B4) significantly less leakage when compared to lateral condensation method (A1, A3 and B1, B3), irrespective of the presence or absence of separated instruments [Table 2] and [Table 3].
|Table 2: Pair-wise group comparison as per Post-hoc Tukey test in specimens prepared using RACE system|
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|Table 3: Pair-wise group comparison as per Post-hoc Tukey test in specimens prepared using K3 system|
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| Discussion|| |
Obturation of the root canal space will prevent the re-entry and growth of microorganisms and traps the traces of remnant pathogens inside the root canal system by a fluid tight seal. It also prevents the penetration of bacteria and their by products from oral cavity and periapical area into obturated root canals, failing which, it jeopardizes the endodontic treatment success. Therefore, evaluating the quality of root canal obturation as the final stage of root canal treatment is essential.
In the present study, two different rotary systems with different file design were chosen, namely K3 and RACE. K3 system has 3 radial lands, the constant core diameter and with asymmetrical cross section, whereas the RACE system has non-radial lands with alternating cutting edges, and the core is less as compared to K3 and with triangle cross-section.
In the present study, the groups prepared with RACE system showed less leakage as compared to K3 system, with or without separated fragments. This finding could be attributed to the different cross-sectional designs (K3 with 3 radial lands and RACE with 3 cutting edges) of the instrument. According to studies, NiTi instruments with active cutting blades showed better canal cleanliness than instruments with radial lands. , Contemporary methods of root canal instrumentation produced a layer of organic and inorganic material called the smear layer. The smear layer produced by the rotary instruments may play a role in the leakage. It may act as a barrier between filling materials and the canal wall and, therefore, compromise the formation of a satisfactory seal. SEM study for residual debris in root canal walls showed that instruments with radial land tend to burnish the cut dentine to the canal wall, whereas instruments with positive cutting angles cut and remove the dentin chips. This might be the reason why K3 showed more leakage as compared to RACE. This study corroborates with Javan et al., who reported that the canal cleaning efficiency of RACE showed higher cleanliness scores for smear layer in coronal, middle, and apical third of the canal, as compared to K3, but no statistical significant difference was detected. 
To seal root canal system, the filling must adapt to all portions of the canal. Incomplete obturation of the canal system may result in failure of the endodontic treatment. Therefore, anything that may influence the adaptation of the root filling to the canal wall is of great significance in determining the degree and the extent of leakage, and ultimately the prognosis of the endodontic therapy.
Gutta percha is the most commonly used obturating material, and cold lateral condensation of gutta percha is one of the most common obturating techniques used in endodontics. Its ability to replicate the internal surface of the root canal has been questioned because of the voids, spreader tracts, and incomplete fusion of the gutta percha cones and lack of surface adaptation. To overcome the drawback of lateral condensation, thermoplasticized injectable obturation technique was introduced to improve the homogenicity and surface adaptation of gutta percha.  Many studies have shown that despite the enhanced adaptation of thermoplasticized gutta percha to the dentine of root canal, the use of a root canal sealer is essential to achieve the optimal seal.  Hence, in the present study, both the techniques were compared for its sealing ability over separated instrument using AH plus as sealer.
In the present study, the groups with presence of fractured fragments obturated with lateral condensation showed more leakage when compared to the group with separated fragments obturated with Obtura II. This could be because the Obtura II might have penetrated between the separated fragment and the canal wall apically. In case of lateral condensation, the master cones have poor adaptation to the irregular coronal surface of the fracture fragments, leading to a gap and also more interphases between master cone with coronal fracture end, accessory cones, sealer, and the root canal surface, which will lead to the formation of voids.
Study by Rahimi et al.,  showed no statistical significance between the lateral condensation and Obtura II techniques, whereas, on the contrary, Tsukada et al.,  showed that the technique using melted gutta percha alone may not be favorable as compared with lateral condensation. The variations in results may be due to the fact that thermoplastic root canal filling methods like Obtura II is technique sensitive. 
The effectiveness of root canal filling materials and obturation techniques in providing an apical seal has been evaluated by various techniques like dye penetration,  electrochemical leakage tests,  fluid filtration,  dye extraction method,  bacterial leakage,  and salivary leakage. 
Estimation of sealing quality in in vitro studies is done by measuring microleakage that allows the tracer agent to penetrate the filled canal. A study concluded that, methylene blue can be used as a dye of choice, since it is inexpensive, easy to manipulate, has a high degree of staining and a molecular weight even lower than that of bacterial toxins. 
In the present study, dye extraction method has been used to check microleakage. In this method, the teeth are dissolved in acids that release all the dye from the interface and the optical density of the solution is measured by a spectrophotometer based on the principle of Beer's law.
According to Camps and Pashley,  both dye extraction method and fluid filtration method gave similar results, because both the techniques measure quantitatively the fluids passing through the interface between root and the obturating materials. The dye extraction method presents great advantage over fluid filtration method, as the time passes, the values in fluid filtration method tend to diminish as the water tends to penetrate all the irregularities before reaching a platuea.  Hence, in the present study, dye extraction method was followed.
Within the limitations of this study, apically separated instruments may play a significant role in leakage as teeth with separated K3 instrument groups showed higher leakage as compared to teeth with separated RACE system. Obtura II showed less leakage as compared to lateral condensation method. While application of the present data to in vivo conditions should be done cautiously, since, in case of a file separation, sealing quality is just one of the factors that might affect the outcome of treatment.
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Department of Conservative Dentistry and Endodontics, The Oxford Dental College, Bangalore, Karnataka
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]