Evaluating the efficacy of different techniques and irrigation solutions for removal of calcium hydroxide from the root canal system: A scanning electron microscope study.

AIM: The aim of this scanning electron microscope study was to compare the efficacy of two techniques (EndoVac and EndoActivator) and two irrigating solutions (5.25% NaOCl in combination with 17% ethylenediaminetetraacetic acid vs. Savlon™) for removal of calcium hydroxide (CH) from the root canal walls. SETTINGS AND
DESIGN: The study was carried out in the specialty of conservative dentistry and endodontics.
MATERIALS AND METHODS: Forty single-canal human teeth were used. The specimens were de-coronated to obtain a standardized root length of 15 mm using a diamond disk. The canals were instrumented till F3 ProTaper and CH intracanal medicament placed in the root canal. One week later, teeth were randomly divided into one control group and six experimental groups according to different irrigation protocols with different techniques. STATISTICAL ANALYSIS: Kruskal-Wallis test was conducted to analyze the effect of different treatment measures with respect to three regions of tooth.
RESULTS: The results indicated that there was no statistically significant difference between the two irrigation solutions and two techniques.
CONCLUSION: To achieve the best adaptation of filling material after root canal treatment, it is crucial to remove intracanal medication from the root canal walls. However, none of the irrigation regimens and different techniques were able to completely remove the CH from the root canal wall.

INTRODUCTION

Pulp–dentine complex is sterile and protected from the oral microbiota by the overlying enamel, dentine, and cementum. This pulp–dentine complex gets challenged by microorganisms present in carious lesions, attrition, abrasion, trauma-induced fractures, cracks, etc., Direct exposure of the dental pulp to the oral cavity is the most obvious route for endodontic infection.

The primary cause of endodontic diseases is the presence of bacteria and their toxins in the root canal systems. Hence, reduction of the bacterial populations and their by-products to levels compatible with peri-radicular tissue healing and prevention of apical periodontics are the primary goal of endodontic treatment. This is achieved with instrumentation and use of appropriate irrigation regimen. Instrumentation and irrigation procedures have improved noticeably over the years; however, none of the existing techniques can completely clean the root canal system owing to the complexity of the root canal systems.[12] Studies suggest that about 35% or more of the canal surface area remain unchanged, reducing the success rate to 68% of root canal treatment.[34] A study in 2017 by Siqueira et al. using three-dimensional micro-computed tomography (CT) revealed that approximately 10%–50% of the main root canal surface area remain untouched by instruments.[5] Hence, emphasis has been made on the importance of elimination of bacteria from the root canal system before obturation. Therefore, besides instrumentation, an approach for supplementing the disinfecting effects of conventional chemo-mechanical procedures with intracanal medication has been recommended.[2]

A wide range of chemicals have been used to disinfect the root canal system including formocresol, cresatin, phenolic compounds, aldehydes, antibiotics, steroids, and calcium hydroxide. Calcium hydroxide (CH) has been widely used as an intracanal medicament in endodontic therapies.[6] It is a universally accepted inter-appointment intracanal medicament because of its biocompatibility, antimicrobial properties, and tissue dissolution ability.[7] Sjögren et al. demonstrated that a 7-day application of a CH medicament could eliminate bacteria.[8]

However, removal of the CH is as crucial as removal of smear layer and debris from the root canal before obturation as it will help in better adaptation of the filling material to the canal walls. The residue of CH on root canal walls negatively affects the adaptation of the filling material to the root canal walls and influences the dentine bond strength. Further, literature intimates that residual CH on the root canal walls may increase apical leakage of gutta-percha root fillings when a zinc oxide–eugenol sealer was used.[6] In addition, such remnants change the physical properties of some sealers, reducing the flow and setting time and preventing the penetration of sealers into dentinal tubules.[9] Evidence also shows that the residual CH may react with zinc oxide and eugenol-based sealers, forming calcium eugenolate which is brittle in consistency and granular in structure that prevents the penetration into the dentinal tubules.[7] Therefore, the removal of residual CH holds importance before obturation in all endodontic therapies.

The removal of residual CH has been endeavored with the help of various irrigation solutions (saline, sodium hypochlorite, and ethylenediaminetetraacetic acid [EDTA]) used alone or in combination with different techniques (EndoVac, EndoActivator, Canal brush, Max-i-Probe needle, and Passive Ultrasonic Irrigation) in conjunction with hand instrumentation. However, there is no general consensus regarding which is the best method for the removal of CH.[10]

For the removal of residual CH, it has been well established that a solution with detergent properties is required. Cetrimide, which is a quaternary ammonium compound, acts as cationic surfactant with bactericidal activity. It can also decrease the biofilm's mechanical stability.[11] Its use with chlorhexidine exhibits higher antimicrobial activity against E. faecalis planktonic cultures.[1213] It is available as part of the ingredients in a solution with the trade name of Savlon™, popular for its antiseptic properties. The purpose of this scanning electron microscope (SEM) study was to compare the efficacy of two techniques (EndoVac and EndoActivator) and two irrigating solutions (NaOCl in combination with EDTA and Savlon™) for removal of CH from the root canal walls. The null hypothesis was that there is no difference between the two techniques and the irrigation solution for the removal of CH from the root canal walls.

MATERIALS AND METHODS

Forty single-canal human teeth extracted for periodontal reasons were used. The external root surfaces were scaled with ultrasonic instruments to remove any soft tissue or calculus from the root surface. Subsequently, the teeth were stored in saline solution until they were used. The methodology was based on the study conducted by Alturaiki et al. where the criteria for tooth selection included one single root canal; no visible root caries, fractures, or cracks; and a completely formed apex on visual examination. The specimens were de-coronated to 15 mm using a diamond disc for standardization of the root length.[10]

For root canal instrumentation, the patency of the canals was verified by passing a file size #K-15 (DENTSPLY-Maillefer, Ballaigues, Switzerland) through the apical foramina. The working length was determined 1 mm short of the length at which a #15 K file extruded apically. The root canals were prepared using hand ProTaper instruments (DENTSPLY-Maillefer, Ballaigues, Switzerland) up to master apical file F3. Between each instrument, the canals were conventionally irrigated with 5 ml of 5.25% sodium hypochlorite (NaOCl) and rinsed with 5 ml 17% EDTA, followed by a final rinse of 5 ml distilled water. During the irrigation, the needle was used in an up-down motion within the apical third. After drying the canals with paper points (DENTSPLY-Maillefer, Ballaigues, Switzerland), all the forty de-coronated teeth received a paste of CH mixed with saline solution to a creamy consistency, which was placed into the root canals with the help of a lentulo spiral. Complete placement was confirmed once the CH extruded from the apex. Cavit™ was used as a temporary filling material. The specimens were then stored in 37°C at 100% humidity for 1 week. After this period, the temporary restoration was removed and the specimens were allocated to one control group and six experimental groups (Groups 2–7,Figure 3).

Figure 3

Flow diagram of the study design

Experimental protocol

All the experimental groups were agitated with master apical file to loosen the CH in the root canal wall. The roots were split into two halves and one half of each tooth and were subjected to SEM evaluation [Figure 3].

The classification of the groups was as follows:

Group 1 (control group, n = 4): The CH was not removed from the canals and the roots were split

Group 2 (conventional irrigation using Savlon™, n = 6): The removal of CH was performed using 5 ml Savlon™ and a conventional irrigation needle. The needle was used in an up-down motion within the apical third with a constant flow for 60 s. The needle depth was standardized for each canal by placing the rubber stopper 1–2 mm short of the working length

Group 3 (conventional irrigation using 5.25% NaOCl and 17% EDTA, n = 6): The removal of CH was performed using a conventional irrigation needle with 5 ml of 5.25% NaOCl followed by a rinse with 5 ml of 17% EDTA using a similar technique as described in Group 2

Group 4 (EndoVac using 5.25% NaOCl and 17% EDTA, n = 6): The canals were irrigated with 5 ml of 5.25% NaOCl and 5 ml of 17% EDTA using the EndoVac system for 30 s for each solution

Group 5 (EndoVac using Savlon™, n = 6): Removal of CH from the canals was done with Savlon™ as an irrigation solution in conjunction with the EndoVac system for 60 s

Group 6 (EndoActivator using 5.25% NaOCl and 17% EDTA, n = 6): The removal of CH was performed with 5.25% NaOCl and 17% EDTA, using the EndoActivator device. Sequentially, the canals were first irrigated with 5 ml 5.25% NaOCl agitated sonically with the EndoActivator System for 30 s followed by rinsing with 5 ml 17% EDTA which was agitated sonically with the EndoActivator System for 30 s. Specifically, a polymer tip #30/02 was used with a pumping motion for 60 s at 10,000 cycles per minute

Group 7 (EndoActivator using Savlon™, n = 6): The removal of CH was performed with sonic irrigation using the EndoActivator device and Savlon™ as an irrigant. Sequentially, the canals were first irrigated with 5 mL Savlon™ agitated sonically with the EndoActivator system for 60 s using a similar method as described in Group 6. For the SEM evaluation, the specimens were split into two halves by placing grooves along the buccal and lingual surfaces using a diamond disc. The surfaces were separated along their long axis using a plastic instrument to prevent canal contamination. For SEM analysis, one-half of all the teeth was used [Figure 3]. The one-half of the teeth was individually dehydrated, fixed on aluminum stubs, and viewed with a SEM at apical middle and coronal levels. The central beam of the SEM was directed to the center of each third of the root canal by the SEM operator under the magnification of ×2000, and the area of the canal wall was captured on the screen of the SEM which was used for evaluating the remaining amount of CH on the root canal wall.

The outcome was based on the evaluation of the specimens for cleanliness by two specialists in Endodontics. The specialists were both blinded on the groups being evaluated. In the evaluation procedure, the following 5-grade scoring scale was used [Figures 1 and 2].[10]

Figure 1

Scanning electron microscopic images at ×2000 representative of the score distribution

Figure 2

Scanning electron microscopic images at ×2000 representative of groups at the coronal, middle, and apical regions. Group 2: Conventional irrigation using Savlon™, Group 3: Conventional irrigation using 5.25% NaOCl and 17% EDTA, Group 4: EndoVac using 5.25% NaOCl and 17% EDTA, Group 5: EndoVac using Savlon™, Group 6: EndoActivator using 5.25% NaOCl and 17% EDTA, Group 7: EndoActivator using Savlon™. EDTA: Ethylenediaminetetraacetic acid

Score 1: 80%–100% removal of CH (total cleanliness)

Score 2: 60%–80% removal of CH (great cleanliness)

Score 3: 40%–60% removal of CH (partial cleanliness)

Score 4: 20%–40% removal of CH (light cleanliness)

Score 5: 0%–20% removal of CH (no cleanliness).

Statistical analysis

Forty specimens were randomly distributed into one control and six experimental groups. Kruskal–Wallis test was conducted to analyze the effect of different treatment measures with respect to three regions of tooth followed by multiple comparison using Dunn's test with Bonferroni correction [Table 1].

Table 1

Comparison at apical, middle, and coronal levels using Kruskal–Wallis test

RESULTS

Group 1 which is the control group showed complete coverage of the canals with CH as opposed to the other six experimental groups. The results suggested no difference of cleanliness of the canal at coronal, middle, and apical levels. The results also indicated that there was no significant difference between EndoVac and EndoActivator irrespective of which irrigation solution was used. No statistically significant difference was found in the CH removal with any of the irrigation solution regardless of the technique used (P > 0.05).

DISCUSSION

Intracanal medicaments have been recommended with the goal of eliminating bacteria from the root canal, preventing bacterial proliferation between appointments, and acting as a physiochemical barrier preventing root canal infection.[14] Root canal morphology and its complexities can affect the application and removal of CH. Hence, in the present study, the extracted single-canal human teeth were used as the experimental model to compare the efficacy of different irrigation agents as well as different techniques for the removal of CH from the root canal walls. Numerous literatures suggest attempts made to remove CH from the root canal walls.[101516] However, the current status on CH removal still remains uncertain as its removal has been difficult and is incompletely removed. In the present study, cetrimide was used in a solution available in the ingredient with the trade name of Savlon™. Many products contain cetrimide because its addition improves the efficacy of irrigating solutions and is reported to have bactericidal and fungicidal properties.[1217] In this SEM study, the main goal was to evaluate the effectiveness of 5.25% NaOCl with final rinse of 17% EDTA and Savlon™ irrigation solution used with EndoVac and EndoActivator for removing CH from the root canal walls. The results revealed that none of the methods used were efficient in removing the entire CH from the walls. Therefore, the null hypothesis of no difference between the two irrigation solutions and two techniques was acceptable. Different methods have been used to detect the cleanliness of the root canal surface. Kenee et al. used digital photographs to do a quantitative assessment of efficacy of various CH removal techniques.[1] Similarly, a digital camera was used to capture images of each half of the canal in the study to compare two techniques for the removal of CH from root canals.[18] A stereomicroscope at ×20 magnification was used to evaluate the efficacy of various irrigation protocols on the removal of triple antibiotic paste by Arslan et al.[19] Micro-CT has also been used to assess the removal of CH medicament from C-shaped root canals of mandibular second molars.[20] A recent study used cone beam CT to assess the efficacy of different irrigation devices for the removal of silicon oil-based CH from root canal system.[21] The use of SEM is considered a standard and the most reliable approach to examine and evaluate canal cleanliness after removal of CH using various recent technologies in adjunct to irrigation solutions.[102223]

Solutions such as physiologic saline, NaOCl, EDTA, and citric acid, stand alone and in combination have been used to remove CH.[19] To remove inorganic components from the root canal, citric acid at concentration ranging from 5% to 50% and apple vinegar and phosphoric acid at different concentrations have been suggested in previous studies.[24252627] Over centuries, NaOCl with different concentrations has been the primary irrigation solution used for disinfection of the root canals. NaOCl possesses a broad-spectrum antimicrobial activity against microorganisms and biofilms which are difficult to eradicate from root canals such as Enterococcus, Actinomyces, and Candida organisms. On the other hand, EDTA is the best endorsed chemical for removal of smear layer. It is the most widely accepted irrigation solution and is a recognized procedure in endodontic therapy for disinfection protocol. Alternating between solutions of NaOCl and EDTA during canal preparation procedures reduces the accumulation of debris and results in cleaner canals as indicated in numerous studies.[282930] However, a detergent action is required in order to envisage canal cleanliness which explain why NaOCl has not shown promising results in removing residual; CH from the root canal system. Cetrimide (cetyl tri-methyl ammonium bromide), being a cationic surfactant, produces little irritation and reduces the surface tension of liquids, thereby facilitating their entry into places with difficult access.[10] It is a detergent effective against Gram-negative and Gram-positive bacteria. Cetrimide is available in many products because its addition improves the efficacy of irrigating solutions as cationic surfactants have been reported to possess bactericidal and fungicidal properties. Chlorhexidine gluconate is also mixed with cetrimide to get stronger and broader antimicrobial effect (Savlon™).[31]

In the present study, irrigation with 5.25% NaOCl and final rinse with 17% EDTA in amalgamation with EndoVac and irrigation of Savlon™ with EndoVac showed no statistically significant cleanliness in the coronal, middle, as well as in the apical regions. EndoVac has a property of creating negative pressure. It is used safely to the working length without extrusion of irrigating solution beyond the apical constriction of the canal.[32] It uses a combination of a macro- or micro-cannula attached to the suction device. The cannula, which is connected to a high-speed suction, creates a negative pressure that pulls the irrigant to the tip of the cannula and evacuates the irrigation solution and debris through small holes.[33] The result of the current study though not statistically significant is supported by previous studies where the EndoVac system has been shown to leave behind significantly less debris compared to conventional irrigation methods.[3435] Results for EndoActivator with Savlon™ were not statistically significant when compared to irrigation with EndoActivator using 5.25% NaOCl and 17% EDTA, for coronal, middle, and the apical regions for removal of CH. Nevertheless, EndoActivator leads to vigorous intracanal fluid agitation through acoustic streaming and cavitation.[3637] This sonic system improves the penetration, circulation, and flow of irrigant into the more inaccessible sites of the root canal system.[38] Literature suggests a positive role of agitation system to increase the efficacy of the detergent action of any irrigation solution for removal of CH, which advocates more studies on Savlon™ in future with increased sample size to arrive at a definitive conclusion. The results of the present study showed no statistically significant difference between the systems being used, i.e., EndoActivator or EndoVac, and similar results were appreciated with the irrigation agents, i.e., 5.25% NaOCl and final rinse with 17% EDTA and Savlon™ in cleanliness of the root canals. Sufficient literature insinuates that, for removal of CH, using 5.25% NaOCl and 17% EDTA is considered the best irrigation protocol till date. However, Savlon™ was used in the present study which presented with no statistical difference between 5.25% NaOCl and 17% EDTA irrigation and Savlon™. It can be concluded that Savlon™ irrigation was not inferior to 5.25% NaOCl and 17% EDTA irrigation and thus can be explored with more studies and larger sample size for removal of CH residues from the root canal. The current study also emphasizes a positive role of the agitation system in enhancing the efficacy of the irrigation solution in the removal of CH irrespective of using 5.25% NaOCl and 17% EDTA and Savlon™. Therefore, the use of agitation system accelerates the action of the irrigation, thus achieving superior cleansing action.

CONCLUSION

It was found that neither of the irrigating solutions nor the two agitation techniques mentioned herein thoroughly removed CH from the root canal. Keeping in mind the limitations of this SEM study, we would like to reiterate that using newer agitation devises (such as EndoVac and EndoActivator) does not prove to be superior when compared to the conventional needle irrigation techniques with regard to removal of CH when used as an intracanal medicament. We propose that further in vivo studies be conducted to evaluate the findings.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.