 Abstract | | |
Aim: To compare and evaluate the cleaning ability of two reciprocating systems, that is, WaveOne (WO) and self-adjusting files (SAF) in terms of removal of smear layer using sodium hypochlorite (NaOCl) and chlorhexidine gluconate (CHX) at apical one-third of the root canal.
Materials and Methods: Forty-three human maxillary anterior teeth were selected. The canal was instrumented manually up to a number 25 K-file size. WO and SAF were used to prepare the root canals. The following groups were studied: Group 1 using WO:-Group 1a = 5% NaOCl + 17% ethylenediaminetetraacetic acid (EDTA), Group 1b = 2% CHX + 17% EDTA, Group 2 using SAF:-Group 2a = 5% NaOCl + 17% EDTA, Group 2b = 2% CHX + 17% EDTA. All roots were split longitudinally and subjected to scanning electron microscopic. The presence of smear layer apical thirds was evaluated using a 5-score evaluation system. Chi-square tests were used for statistical analysis.
Results: The results showed no significant difference in smear layer removal among both reciprocating system and among the irrigants. Group 2a exhibited the best results and was close to significant difference in score (P > 0.05). The NaOCl + EDTA solution used in Group 1a and Group 2a could effectively remove the smear layer in most of the specimens. However, SAF was more effective than WO in the apical third of the canal.
Conclusion: The results obtained from the present study suggest that using the SAF system and continuous irrigation action with NaOCl and EDTA solution could overcome the difficulty of removing smear layer even in hard-to-reach regions of the root canal.
Keywords: Chlorhexidine; ethylenediaminetetraacetic acid; scanning electron microscope; self-adjusting files; smear layer; sodium hypochlorite; WaveOne
How to cite this article:
Jimna M M, Ashwini T S, Sowmya H K. Comparison and evaluation of two reciprocating root canal instruments on removal of smear layer by using two irrigants at apical one-third of the root canal-an ex vivo-scanning electron microscopic study. J Conserv Dent 2017;20:451-8 |
How to cite this URL:
Jimna M M, Ashwini T S, Sowmya H K. Comparison and evaluation of two reciprocating root canal instruments on removal of smear layer by using two irrigants at apical one-third of the root canal-an ex vivo-scanning electron microscopic study. J Conserv Dent [serial online] 2017 [cited 2023 Apr 1];20:451-8. Available from: https://www.jcd.org.in/text.asp?2017/20/6/451/223199 |
| Introduction | |  |
The success of root canal therapy depends on the method and the quality of instrumentation, irrigation, disinfection, and three-dimensional obturation of the root canal. Among the procedures involved in the control of endodontic infection, irrigation procedure may play an important role in the elimination of microorganisms from the root canal.[1] As demonstrated by many investigators, root canal wall preparation, using either manual or mechanized techniques, always causes the formation of pulpal debris, smear layer, and smear plugs, which cover the whole root canal surface.[2]
The smear layer and plugs consist of an organic portion (pulp tissue debris, odontoblastic process, proteins, saliva, microorganisms, and blood cells) and an inorganic portion (minerals from the dentin structure).[3] McComb and Smith were the initial investigators who found the smear layer on the instrumented root canal walls. They found it irregular, amorphous, and granular when viewed under the scanning electron microscopic (SEM).[4] Some investigators believed that the presence of the smear layer helps in increasing the success rate of endodontic treatment because this layer blocks dentinal tubules and prevents bacterial exchange by reducing dentine permeability.[5],[6]
According to Torabinejad et al., the presence of the smear layer prevents the penetration of intracanal medication into the irregularities of the root canal system and the dentinal tubules and also prevents complete adaptation of obturating materials to the prepared root canal surface.[7] Therefore, endodontic treatment cannot be limited to the removal of pulp remnants and the widening of root canals, but should also focus on smear layer removal.[8]
The most common irrigation regiments for the removal of the smear layer includes NaOCl at various concentrations to remove the organic component of the smear layer and complementing its action by means of chelating agents such as 17% ethylenediaminetetraacetic acid (EDTA) to remove the inorganic components.[9] NaOCl has very good tissue dissolving properties and antibacterial activity, which make it the irrigant of choice for the root canal treatment of necrotic teeth; however, it will have widespread cytotoxicity if it enters the periapical tissues through the apical foramen, resulting in the necrosis and inflammation of periapical tissues, especially when used in high concentration and also pungent odor to the patient, and discoloration of teeth and corrosion of dental equipment's. For these reason, another irrigant, which has the potential to counteract these adverse effects, are desirable and CHX serves these purposes.[10]
CHX solution has been gaining popularity as an efficient root canal irrigant. It has broad-spectrum antimicrobial activity similar to sodium hypochlorite (NaOCl) along with a substantive antimicrobial activity. Irrigation with 2% CHX has been shown to prevent microbial activity with residual effects for 48 h. CHX is an excellent root canal irrigant for patients who are allergic to NaOCl. However, its capacity to clean root canal walls requires further investigation.[11]
Currently, the eradication of the microbial infection is accomplished mainly through mechanical instrumentation and chemical irrigation.[12] While mechanical preparation of the infected root canal has been shown to be most effective in reducing the number of bacteria, it alone is unreliable in achieving adequate disinfection. Irrigation allows for cleaning beyond what might be achievable through instrumentation as it enhances further bacterial elimination, facilitates necrotic tissue removal, and prevents packing of infected debris apically.[13]
Recently, new rotary nickel-titanium (NiTi) single-file system with different configuration design has been marketed as WO and self-adjusting files (SAF). Although both system consists of a single file with reciprocating motion, they have different alloy properties and working principles.[14],[15]
Since 2011, reciprocating NiTi WO set a new standard in root canal shaping from start to finish. Shaping the root canal to a continuously tapering funnel not only fulfills the biological requirements for adequate irrigation but also to clean the root canal system of all bacteria, bacterial by-products and pulp tissue, and also provides the perfect shape for three-dimensional obturation. The specially designed NiTi files work in a “balanced force” action using a preprogrammed motor to move the files in a back and forth “reciprocal motion.” The files are manufactured using M-Wire technology, improving strength and resistance to cyclic fatigue by up to nearly four times in comparison with other brands of rotary NiTi files.[16]
The SAF system, was introduced by ReDent-Nova. Different from the traditional NiTi rotary files, the SAF system uses a hollow reciprocating instrument which allows for simultaneous irrigation throughout the mechanical preparation. When inserted into the root canal, the manufacturer claims that the SAF is capable of adapting itself to the canal shape three-dimensionally. The instrument is used in a transline (in-and-out) motion and the abrasive surface of the lattice threads promotes a uniform removal of dentin.[17]
Hence, this ex vivo study concentrates on evaluating the cleaning ability of two reciprocating systems, that is, WO and SAF in terms of removal of smear layer using NaOCl and CHX at apical one third of the root canal.
| Materials and Methods | | |
Selection of samples
Forty intact human maxillary anterior teeth with single canals where selected for the study, disinfected in thymol, cleaned of debris and stored in saline.
Root canal preparation
- The teeth were decoronated at the cementoenamel junction to obtain a standardized length of 13 mm, with a diamond disc under water coolant which provide direct access to the root canal. The roots were randomly assigned into four experimental groups with 10 teeth in each group. The root canals were instrumented using respective techniques.
Initial preparation of root canals
Number 15 K-file were introduced into the root canals, until it was visible at the apical foramen of each root canal subsequently by subtracting 1 mm from this point. The canals were instrumented manually up to number 25 K-file using saline as an irrigant.
Canal preparation
Group-1: WaveOne reciprocating system
- 20 root canals was prepared using WaveOne (WO) instrument according to manufacturer's instructions. WO Primary file which has a tip size of 0.25 and a 0.08 taper in apical 3 mm was used in X-Smart Plus motor in “Waveone” mode. The samples was irrigated using 30-gauge closed end needle with plastic syringe keeping it 2 mm short of the working length for 6 min following below mentioned protocol.
- Group 1a = 10 samples; 5% NaOCl was used for 3 min, and saline is used for 2 min then 17% EDTA was used for 1 min;
- Group 1b = 2% CHX was used for 3 min, and saline is used for 2 min then 17% EDTA was used for 1 min;
Group-2: Self-adjusting file system
- A self-adjusting file (SAF) was used to prepare the root canals according to the manufacturer's instructions, and irrigation was performed continuously during the instrumentation using a special irrigation apparatus (VATEA irrigation Device ReDent-Nova, Israel). This apparatus has two separate irrigation reservoir connected to a hollow SAF file. Continuous irrigation was done at a flow rate of 5 mL/min. The SAF file instrumentation with irrigation was performed for a total of 6 min in each root canal. Below mentioned protocol was followed.
- Group 2a = 5% NaOCl is used for 3 min, and saline is used for 2 min then 17% EDTA was used for 1 min;
- Group 2b = 2% CHX is used for 3 min, and saline is used for 2 min then 17% EDTA is used for 1 min;
Finally, all the root canals were irrigated with 5 ml of saline as a final rinse. The canals were dried with sterile paper points and left to dry at a room temperature for 24 h. In each sample, the teeth were grooved longitudinally with a diamond disc on the buccal and lingual surfaces to facilitate vertical splitting with chisel after instrumentation and to prevent further contamination. To avoid creating artificial debris, the disc was not allowed to penetrate the canal space. The roots were then split into two halves with a chisel. Roots were embedded into acrylic blocks. The half with the most visible part of the apex was used for SEM evaluation.
The smear layer was evaluated from images at ×3000 magnification based on the scale of Hülsmann et al.: Score 1, no smear layer and all dentinal tubules were open; Score 2, a small amount of smear layer and some dentinal tubules were open; Score 3, homogeneous smear layer covering the root canal wall and only a few dentinal tubules were open; Score 4, complete root canal wall covered by a homogeneous smear layer and no open dentinal tubules; and Score 5, heavy homogeneous smear layer covering the complete root canal. Scores 1 and 2 represent “clean canal wall.” Scores 3, 4, and 5 represent “smear layer present.” Chi-square tests were used for statistical analysis.
| Results | | |
[Table 1],[Table 2] and [Figure 1] show the comparison of score of each group. When comparing the smear layer removal of apical third of among the Group 2a [Figure 6], SAF operated with NaOCl + EDTA resulted in clear canals with Score 2 followed by Group 1a [Figure 6] were WO operated with NaOCl + EDTA. Group 1b and 2b [Figure 6] showed the highest presence of Score 3 and 4, which suggestive of Group 2a [Figure 6] being best. Statistical analysis using Fisher's exact Chi-square tests revealed that no significant difference among the canal irrigant and the system (P = 0.210).{Figure 6}
[Table 3],[Table 4] and [Figure 2] and [Figure 3] show the comparison of the agents in each group separately. No statistical significant difference was found in the smear layer removal on the dentinal wall among the irrigants. SAF with 5% NaOCl + 17% EDTA showed 70% of Score 2, resulted the maximum smear layer removal, followed by WO with 5% NaOCl + 17% EDTA showed 30% of Score 2; The least removal of smear layer was observed in the group with 2% CHX + 17% EDTA using WO system. When comparing both irrigating agents with WO and SAF, there was no statistical significant difference with P = 0.070 and P = 1.00, respectively. | Table 3: Comparison of the irrigating agents in each group separtely - cross tabulation
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 | Table 4: Comparison of the irrigating agents in each group separtely - Chi square test
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 | Figure 2: Comparison of the irrigating agents in each group separately - WaveOne
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 | Figure 3: Comparison of the irrigating agents in each group separately - self-adjusting files
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[Table 5],[Table 6] and [Figure 4] and [Figure 5] show the comparison of WO and SAF in each agent separately. However, there was no statistically significant difference between SAF and WO. Score 2 was higher in irrigation with NaOCl + EDTA using SAF representing a clean dentinal surface. The differences were again not significant. Therefore, both the WO and SAF were good in smear layer removal at apical one-third of the root canal wall. The Fisher's exact Chi-square tests revealed close to significant difference in score when using SAF system, (P = 0.179) and for WO (P = 1.00). | Table 5: Comparison of waveone and saf in each agent separtely - cross tabulation
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 | Table 6: Comparison of waveone and saf in each agent separtely - Chi square tests
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 | Figure 4: Comparison of WaveOne and self-adjusting files in each agent separately- sodium hypochlorite and ethylenediaminetetraacetic acid
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 | Figure 5: Comparison of WaveOne and self-adjusting files in each agent separately – chlorhexidine gluconate and ethylenediaminetetraacetic acid
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| Discussion | | |
Debridement of the root canal system is a major concern for endodontic success, and irrigation is an important part of root canal debridement. Certainly, many studies have reported that currently used methods of root canal preparation and irrigation do not effectively debride the entire root canal system. Ideally, root canal irrigants should flush out debris, dissolve organic tissue, destroy microbial by-products, and remove the smear layer. The past studies have shown that current canal preparation and irrigating methods may be effective at cleaning the coronal portion of root canals but much less effective in the apical portion of canals.[1] Although several studies indicate that achieving this goal in the apical third of the root canal may be difficult if not impossible, the use of the SAF in combination with a dual-irrigation regime of NaOCl and EDTA is reported to result in clean dentin surface in the apical portion of most root canals,[2] as confirmed by the present study.
The aim of this study was to compare the cleaning ability of two reciprocating systems that is WO and SAF in terms of removal of smear layer using NaOCl and CHX along with EDTA at apical one-third of the root canal. The results indicate that both the instruments could remove the smear layer. The SAF operated with NaOCl and EDTA resulted in clean canals. The least removal of smear layer covering root canal wall was observed following irrigation with CHX and EDTA. Root canal wall absolutely free of smear layer was not observed with any of the irrigation.
In this study, the SAF showed better performance than the WO; however, there was no statistically significant difference between them. The SAF file is composed of a hollow cylinder with a metal lattice, and its surface is treated to render it abrasive. The shape of the SAF file and its back and forth gridding motion allow it to expand into the canal and remove a layer of dentin.[3]
During instrumentation with the SAF, the SAF PRO irrigation device was used for 6 min, providing continuous irrigation at a rate of 5 mL/min, hence efficiently cleaning the root canal at the apical region.
The smear layer was successfully removed in the SAF group. This success can be attributed to the continuous irrigation and reciprocating action of the SAF system.[4] In the study of Metzger et al., the use of the SAF system and irrigation with EDTA and NaOCl resulted 65% of the specimens with canal free of smear layer. He claimed that the SAF file has a scrubbing action on the canals, which clearly results in a very clean surface even in the unreachable parts of the canal by activation of the irrigant in the apical third of the canal.[5]
The VATEA peristaltic pump used in the SAF system delivers a continuous flow of irrigant, which enters the canal through the hollow file. According to the manufacturer, the motion of the file agitates the irrigant to such an extent that it effectively reaches the apical part of the canal with sonic activation.[6] The continuous replacement of irrigant could also explain the excellent cleaning efficiency observed in this study.
In a recent study of MeloRiberio et al., SAF was used with continuous NaOCl irrigation on oval-shaped root canals. These researchers reported that the percentage of remaining debris and uninstrumented canal perimeter was significantly lower in the SAF group than in the rotary group.[7] Previously, this was supported by De-Deus et al. explained this result by the ability of SAF instrument to adapt itself to the cross-section of the canal and the mechanical debridement and efficacy of its continuous irrigation system.[8]
In recent years, numerous researchers studied SAF system using different evaluation methods and reported successful results as our study in shaping and irrigating root canals. However, as a result of a microbiological and SEM study, Paranjpe et al. found out insufficient apical preparation and irrigation when using the SAF system. This results could be explained by differences in the sample and the testing methods.[9]
The WO files are manufactured with the M-Wire NiTi alloy, using a heat procedure carried out at varying temperatures, which increases flexibility and resistance to cyclic fatigue.[10] The WO is used with a reciprocating motion that requires special automated devices. The counterclockwise engaging angle is five times the clockwise disengaging angle.
In this study, the WO file was equally good as SAF when NaOCl and EDTA used as an irrigant. Albrecht et al. evaluated various sizes and tapers of rotary files and reported that an increased file taper leads to better root canal debridement.[10] In this study, the equal performances of WO files compared to the SAF may have been due to the fact that WO shows the higher taper. In spite of the irrigating needle going as deep as 2 mm short of the WL, the solutions remained in the canal for 1 min. The removal of the smear layer was not as effective as SAF. It is possible a deeper introduction of the needle would permit better cleaning. Such introduction, however, in clinical practice would bring greater risk of injuring the periapical tissues on account of the possible extrusion of the irrigants.[13] Hence, safe-ended needle was used in this study.
NaOCl has the ability to dissolve organic debris and destroy microbial by-products. EDTA is a chelating agent used to remove the smear layer. This dual combination of irrigants has been shown to be effective in debriding and disinfecting root canals as well as other irrigants. Studies have shown an increased efficacy of canal debridement with increased apical size preparations and increased taper of instruments.[14] As reported recently by Peters et al., the resulting apical size is usually at least equivalent to a #40 file.[15] Several studies confirmed that larger apical preparation reduces the bacterial count and enhance the effectiveness of irrigation. Probably, apical preparation performed using SAF and vibrating motion of the file's delicate mesh and continuous flow had synergist effect for debridement and resulted with clean root canals almost free of smear layer on the critical apical region.[16]
In addition, the role of chlorine should not be overlooked. It is known that chlorine is responsible for the dissolution of organic tissue and the antimicrobial effect of NaOCl. However, chlorine is consumed rapidly during the first phase of tissue dissolution, probably within 2 min. Therefore, regular replenishment and large volumes of NaOCl are required for successful debridement. During SAF operation with continuous irrigation, one should consider that NaOCl is refreshed every second making it possible for sufficient free chlorine to be present in the root canal to dissolve the organic component of dentine debris. NaOCl entering the file through a free-rotating hub is continuously replaced during the procedure, thus providing a fresh and totally active irrigation solution. Because positive pressure is absent throughout the root canal system, the solution can easily escape through openings in the lattice of the file. The success in removing the smear layer in the apical third may be due to the vibrating motion of the file's delicate mesh within the fluid that is continuously replaced.[17]
SEM is one of the most commonly used techniques for evaluating smear layer removal, and hence, was used in the present study. Before using root canal irrigants on human beings, laboratory studies have to be conducted to determine the benefits and consequences. Hence, the efficiency of 5% NaOCl and 2% CHX was evaluated.[18]
The results of this study show that 5% NaOCl and 2% CHX with 17% EDTA did not promote a complete cleaning of the root canal as considerable quantity of smear layer adhered to the dentin walls. Studies have shown that 17% EDTA efficiently removes the smear layer from root canal walls. Similar results were noted from the present study. EDTA reacts with the calcium ions in dentine and forms soluble calcium chelates. It is known that the efficiency of a chelating agent depends on several factors including application time, pH, concentration, and amount of the solution. In addition, the relationship between the concentration of the chelating agent and the application time seems to be important since it was found that highly concentrated solutions applied for a long period cause roughness of dentin surface.[19]
CHX has been used in various concentrations (0.002%–2%) with different periods of contact time between the disinfectant and various microorganisms. [20] According to these results, 2% CHX solution was far more efficient in the shortest period of time than were all other concentrations tested.
Studies from previous literature have shown that the CHX solution can be an effective endodontic irrigant.[21] CHX could maintain the canal free of microorganisms, even after biomechanical preparation because of its adsorption capacity and slow liberation of active cations by the dental tissues. However, in the present study, the CHX showed least smear layer removal.[22] Ferraz et al. observed that CHX was not capable of dissolving pulp tissue, which is an essential property for instrumentation and preparation of teeth with pulp necrosis.[23]
Because CHX is active against a wide range of microorganisms, it can help in preventing reinfection of the root canal; hence, further long-term in vivo studies may be needed to conclude the efficiency of CHX as root canal irrigant.
According to this study, 2.0% CHX solution combined with 17% EDTA promoted an effective cleaning of the dentin walls, and hence, due to its excellent antimicrobial activity, can be used as an alternative irrigating solution. There is no consensus on the optimum contact time which an irrigant solution to be kept in root canals for smear layer removal. However, some of the studies suggested a duration for 1 min with EDTA is sufficient.[24]
The choice and use of the appropriate and most efficient irrigating agent, however, requires a better understanding of their action. Moreover, smear layer removal is controversial and certainly not the only factor affecting root canal because in vitro conditions may not reflect in vivo conditions accurately.[25]
The association of NaOCl and EDTA solutions has proved effective in removing smear layer formed during endodontic instrumentation. EDTA acts on the inorganic components of the smear layer, causes the decalcification of peri- and intertubular dentine, and leaves the collagen exposed. Subsequently, the use of NaOCl dissolves the collagen, leaving the entrances to the dentinal tubules more open and exposed.[26]
Garberoglio and Becce (1994), using EDTA for 30 s, reported good cleaning of the apical third, although they did notice the presence of smear plugs in some of the specimens. On irrigating the canals for 5 min, Lopes et al. (1996) reported that the mechanical stirring of EDTA for 2 min using a lentulo spiral allowed for the near complete removal of the dentinal smear layer from the apical third. The authors explained that, on account of the reduced dimension of the root canal, air bubbles frequently remain trapped and prevent total filling with the irrigant. Mechanical stirring with a lentulo spiral removes the air bubbles, favors improved contact of EDTA with the canal walls, and takes the solution to areas that are not reached by the irrigating needle.[27] This explains the irrigation of NaOCl and EDTA with SAF.
Specimens irrigated with 5% NaOCl followed by 17% EDTA solution proved effective in removing the smear layer in the apical third, which is in agreement with a previous study. Siqueira JF et al. observed that alternating the use of EDTA and NaOCl is an effective method for smear layer removal.[28]
The efficacy of the smear layer removal was decreased, particularly in Group 1b and 2b when CHX and EDTA were used. Studies have shown that the removal of smear layer promotes dentin permeability allowing and producing greater penetration of filling material into lateral canals and dentinal tubules. Certainly, no irrigating solution is capable of acting simultaneously on the organic and inorganic elements of the smear layer.[29]
This study compared smear layer removal using two reciprocating system. Although there was no statistical significance, the SAF tended to produce cleaner canals. It would seem that the standard irrigation with syringe does increase the efficiency of removing debris and smear layer from instrumented canals. Further studies are necessary to find methods of improving the cleanliness of instrumented canals at the apical third level as current methods produce the least desirable results at this level.
| Conclusion | | |
According to the finding and within the limitation of the present study, it can be concluded as follows:
Significant removal of smear layer was observed among the groups, Group 2a and Group 1a removed higher amount of smear layer when compared to Group 2b and Group 1b in the apical third of the root canal.
The association of NaOCl and EDTA solutions proved effective in removing the smear layer from the apical third of the root canal. The efficacy of the smear layer removal was decreased, particularly when CHX and EDTA were used.
The results obtained from the present study suggest that using the SAF system and continuous irrigation action with NaOCl and EDTA solution could overcome the difficulty of removing smear layer even in hard-to-reach regions of the root canal.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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Correspondence Address:
T S Ashwini
Department of Conservative Dentistry and Endodontics, JSS Dental College and Hospital, JSS University, Sri Shivarathreeshwara Nagara. Mysore - 570 015, Karnataka
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/JCD.JCD_374_16
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6] |
