Indian Journal of Dental Research

: 2013  |  Volume : 24  |  Issue : 5  |  Page : 537--541

Antibacterial efficacy of sodium hypochlorite with a novel sonic agitation device

Amarnath Shenoy1, Pragna Mandava2, Nagesh Bolla2, Sarath Raj2, Jacob Kurien2, MS Prathap1,  
1 Department of Conservative Dentistry and Endodontics, Yenepoya Dental College, Mangalore, India
2 SIBAR Institute of Dental Sciences, Guntur, Andhra Pradesh, India

Correspondence Address:
Amarnath Shenoy
Department of Conservative Dentistry and Endodontics, Yenepoya Dental College, Mangalore


Objective : The aim of this study is to evaluate the antibacterial efficacy of 3% sodium hypochlorite (NaOCl) with sonic agitation devices. Materials and Methods: Fifty extracted human single-rooted teeth were collected. Canals were prepared up to Profile #35/0.06. Forty teeth were inoculated with Enterococcus faecalis and incubated for 24 hours. The teeth were then divided into five groups based on the agitation device used. Group 1- was agitated with EndoActivator . Group 2 was agitated with Waterpik Power Flosser. In Group 3, Waterpik flosser was used with a nickel-titanium file. Group 4 (positive control) was not subjected to any agitation, and Group 5 -was the negative control. Superficial and deep dentinal shavings were collected from coronal and apical halves and sowed in brain heart infusion (BHI) agar to evaluate colony-forming units (CFU/mL). Results: Krusal Wallis, analysis of variance (ANOVA) and Mann-Whitney U test showed that Group 3 showed a smaller number of CFUs/mL Group 2 showed a relatively greater number of CFU/mL. The deep apical dentin areas showed more number of CFUs relative to other sites. Conclusion: The nickel-titanium file attached to the Waterpik Power Flosser system was found to be as effective as the EndoActivator in antibacterial efficacy against E.faecalis.

How to cite this article:
Shenoy A, Mandava P, Bolla N, Raj S, Kurien J, Prathap M S. Antibacterial efficacy of sodium hypochlorite with a novel sonic agitation device.Indian J Dent Res 2013;24:537-541

How to cite this URL:
Shenoy A, Mandava P, Bolla N, Raj S, Kurien J, Prathap M S. Antibacterial efficacy of sodium hypochlorite with a novel sonic agitation device. Indian J Dent Res [serial online] 2013 [cited 2021 Jan 27 ];24:537-541
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Full Text


The main goal of endodontic therapy is complete elimination of the infectious agent as well as its products which are responsible for the development and perpetuation of the pulpal and periradicular diseases. There are numerous obligate anaerobic bacteria associated with the development of the pulpal diseases but a few facultative strains, such as Enterococcus faecalis, are found to be involved in persistent infections. Failure to eliminate these bacteria may lead to poor outcome of the treatment. As root canal is an area not easily accessed by the defense mechanism of the body, elimination of this infection should be achieved by mechanical procedures along with chemical adjuvants and endodontic irrigants. Numerous irrigants have been introduced and are still being innovated to achieve complete disinfection. Sodium hypochlorite (NaOCl) is not only a bleaching, deodorizing, and tissue-dissolving agent, but also an effective disinfectant. [1]

Normal anatomy of the root canal is very complex with morphological irregularities which provide a perfect niche for the microorganisms to colonize and perpetuate. In addition to these areas, the microorganisms also infiltrate into the dentinal tubules, making the procedure of complete disinfection a clinical mirage. [2] A study compared the microcomputed tomography scans before and after mechanical instrumentation and found that regardless of the instrumentation technique, 35% or more of the root canal surfaces remained uninstrumented. [3] Therefore, disinfection of the uninstrumented surfaces depends mainly on the use of irrigants.

It has been demonstrated that meticulous instrumentation with copious irrigation only reduces the bacterial load. [4] Ideally, the endodontic irrigants are delivered into the canal system to flush out loose debris, dissolve organic tissues, kill microbes, remove microbial byproducts, and remove the smear layer. [4]

Even with the usage of modern nickel titanium instruments, it was observed that more than 35% of the canal remained uninstrumented. [5] The bacteria load may adversely affect the outcome of treatment. Studies have demonstrated that almost 40-50% cases exhibited negative cultures after chemomechanical preparation with different instrumentation techniques and instruments and conventional irrigation with different irrigants. [6]

Hence in this regard, many different irrigation protocols, solutions, and delivery systems have been recently introduced in endodontics, with the promise of optimizing disinfection of the root canal. [5] The phenomenon of acoustic microstreaming and cavitation inside the irritant-filled root canals has been investigated. When cavitation bubbles are produced by acoustic waves, they eventually collapse, and the energy released is transferred to the root canal wall, liberating any debris found thereon. Microstreaming then carries the debris coronally, so that it can be removed from the canal. Acoustic cavitation has been shown to remove and destroy the biofilm. [7]

In the present study, two sonic agitation devices, namely EndoActivator (Advanced Endodontics, Santa Barbara, California) and Waterpik Power Flosser (Waterpik, Inc. Fort Collins, Colorado) have been selected to compare their antibacterial efficacy.

Waterpik Power Flosser is an activation device used for flossing the interdental areas. It has a mechanism of action very similar as that of the EndoActivator; moreover, the tips of the EndoActivator and those of the power flosser system are interchangeable. This has led us to the idea of comparing the antibacterial efficacy of the commercially available, costlier EndoActivator with that of the less costly Waterpik Power Flosser system used with nickel-titanium files attached to the activator tips.

The aim of this study was to evaluate the degree of disinfection in dentin caused by agitation of 3% NaOCl using the commercially available EndoActivator , Waterpik Power Flosser, and nickel-titanium files attached to Waterpik. The null hypothesis tested was that there is no difference in disinfection levels using different agitation protocols.

 Materials and Methods

Fifty recently extracted human single-rooted teeth with a straight single canal were selected for the study. Exclusion criteria were as follows: Teeth shorter than 20 mm; apex larger than #25 before instrumentation; and presence of caries, root fissures, or fractures. The teeth were then soaked in 5.25% NaOCl for 30 minutes to remove residual tissue and debris from the root surfaces. The teeth were decoronated to standardize the length to 16mm.

Canal preparation

The patency of the canals was checked with a 10 k file and the teeth with more than one canal were eliminated from the study. The canals were subsequently enlarged up to #35/0.06 Profile (DENTSPLY/Tulsa Dental; Tulsa, Oklahoma) to working length using saline and NaOCl as irrigant. All the teeth were then subjected to ultrasonic cleaning for a cycle of 12 minutes using ethylene di-amine tetra acetic acid (EDTA) as solvent to ensure complete debridement and to open up the dentinal tubules. Then, all the specimens were subjected to sterilization in autoclave at 121°C, 15 lbs pressure for 15 minutes to ascertain that all the specimens were completely sterile.

Bacterial inoculation

Pure culture of E. faecalis (MTCC 439), grown in brain-heart infusion broth (BHI) was used to contaminate the root canals. A suspension of E. faecalis cells was prepared in BHI. Optical density of the suspension was adjusted to approximately 1.5 × 0 [8] colony-forming units (CFU)/mL by comparing its turbidity to a McFarland 0.5 barium sulfate (BaSO 4 ) standard which is used as a reference to adjust the turbidity of bacterial suspensions so that the number of bacteria are within a given range.

Of 50 teeth, 40 teeth were inoculated with 10 μL of the E. faecalis suspension using sterile 1 mL tuberculin syringes. The remaining 10 teeth served as negative controls to determine that the teeth were completely sterilized. The test teeth were placed in Eppendorf tubes. The Eppendorf tubes were then placed inside the incubator and incubated at 37°C for 24 hours.

Irrigation and agitation devices

NaOCl 3%which is commercially available was used as the irrigant. The agitation devices used in this study were as follows:

The EndoActivator (Advanced Endodontics, Santa Barbara, California) uses sonic energy to irrigate root canal systems. This system has two components, a handpiece and activator tips. The battery-operated handpiece activates 2,000-10,000 cycles/minuteWaterpik Power Flosser system (Waterpik Inc. Fort Collins, Colorado) also works on the principle of sonic activation. It also has a battery-driven handpiece and disposable flosser tips.

The main emphasis of this study is on the activator tips used in Group 3 in which files were attached to the power flosser handpiece.

These activator tips were fabricated by attaching the nickel-titanium files Profile series #25/0.04 taper (DENTSPLY/Tulsa Dental,;- Tulsa, Oklahoma) using cyanoacrylate resin such that the medium tip of the EndoActivator system correspond to the Waterpik Power Flosser system tips. The Waterpik Power Flosser system has sonic mechanism of action similar to that of the EndoActivator and operates at a frequency of 1-6 kHz.

The diameter, tip, taper, and length of these activator tips were maintained such that they corresponded exactly with those of the medium tips (#25/0.04) of the EndoActivator system.

After incubation, the contaminated root canals were divided into four groups according to the irrigation regimen used:

Group 1:- 3% NaOCl agitated with EndoActivator for 3 minutesGroup 2:- 3% NaOCl agitated with Waterpik Power Flosser for 3 minutesGroup 3:- 3% NaOCl agitated with Profile attached to the power flosser systemGroup 4:-Not subjected to any irrigation or agitation;-used to determine whether the bacteria are properly inoculatedGroup 5:- Not inoculated with bacteria (negative control).

Agitation was done 2mm short of the working length that is 14 mm for all the groups.

Subsequent to irrigation, each root was sectioned horizontally into two halves, that is coronal half and apical half. The superficial dentin shavings were collected with number 3 Gates Glidden drill in a slow speed handpiece followed by deep dentinal shavings collection with number 5 Gates Glidden drills. These dentinal shavings were stored in phosphate buffer solution until used to inoculate the bacteria in the microbiology laboratory. Then the aliquots were sowed to count the CFUs.


Kruskal Wallis, analysis of variance (ANOVA) tests were used for comparison of the three groups with respect to CFU/mL in coronal or apical, and superficial or deep dentin. A pair-wise comparison of groups was done by the Mann-Whitney U test. [Figure 1] shows the comparison of the three groups with respect to CFU/mL in all four segments which showed that Group 3 showed less CFUs in all the parts of the tooth. [Table 1] clearly depicts that Group 3 showed a smaller number of CFUs in the coronal superficial and deep parts followed by Group 1 and then Group 2. However, there was no statistically significant difference between Group 1 and 3 pertaining to the CFUs in the coronal or apical and deep or superficial segments [Table 1] and [Table 2].In the apical deep part, the number of CFUs was greater than coronal deep and superficial parts but a comparatively smaller number of CFUs was found with Group 3 than the rest of the groups.{Figure 1}{Table 1}{Table 2}


This study was done using two components of the radicular dentin (circumpulpal dentin and deeper dentin) to test the ability of different agitation techniques to disinfect the dentin deeply. The Group 3 Profile tip with the power flosser showed better antibacterial efficacy than the other experimental groups.

NaOCl is a widely used endodontic irrigating solution in infected root canals. Even though its antibacterial effects are recognized, the exact mechanism of microbial killing is not well elucidated. When NaOCl is added to water, hypochlorous acid (HOCl) is formed, which contains active chlorine, a strong oxidizing agent. Substantial evidence suggests that chlorine exerts its antibacterial effect by the irreversible oxidation of -SH groups of essential enzymes, disrupting the metabolic functions of the bacterial cell. [8] Chlorine may also combine with cytoplasmic components to form N-chloro compounds, toxic complexes which destroy the microorganism. However, the first contact oxidation reactions of chlorine with bacteria may lead to the rapid killing of bacterial cells even prior to the formation of N-chloro compounds in the cytoplasm. It has been appreciated that the disinfecting action of NAOCl increases with a decrease in pH as the concentration of undissociated HOCl increases, but alkaline pH is necessary to maintain the stability of the solutions. [1]

E. faecalis is one among numerous floras which is a facultative Gram-positive anaerobe, associated with persistent root canal infections. [9],[10] It is associated with persistent apical periodontitis and also in cases of endodontic failure. It is easy to culture and has been successfully used to demonstrate the antibacterial efficacy of various endodontic products. [11]

The antibacterial efficacy of NaOCl against E. faecalis is satisfactory in coronal and middle third, but its efficacy in the apical third is questionable. Consequently, different irrigant agitation techniques have been proposed to increase the efficacy of the irrigant solutions. [12] It has been shown that although an irrigant can penetrate into the dentinal tubules, it does not mean that the concentration is sufficient to kill all types of bacteria present. [13] It has been previously shown that bacteria may remain viable in tubules at great distances from the pulp. [14] This study showed that although current techniques clearly reduce the bioburden within the canal space in vitro, the root canal system cannot be effectively disinfected. This study and previous investigations have shown that disinfection of root dentin is not achieved by chemomechanical preparations alone. [15] It has been suggested that micro-organisms may be eliminated or rendered harmless by entombing through obturation of the canal space after chemomechanical preparation of the root canal. [16] Although the consequences of microbes remaining in the dentinal tubules after root canal treatment are not clear, the main goal of root canal treatment is still the elimination of micro-organisms. Future research must also be concerned with the efficacy of disinfection of microbial aggregates and biofilms in the root canal. [17]

Recently, the EndoActivator has been recommended to enhance the cleaning efficacy of irrigation of root canal systems. Its proposed ability to create sonic waves in irrigating solutions deposited inside of the root canal might aid in the killing of bacteria and debridement of necrotic tissue. [7] Sonic energy only has the power to produce one node along the length of the instrument; so, any constraint of the instrument will significantly decrease, if not eliminate, the acoustic streaming necessary to dislodge and carry away necrotic debris. [18]

The EndoActivator might not be powerful enough to disrupt bacterial biofilms [7] but in contrast the tip used in Group 3, because of its flute configuration, may cause an increase in the irrigant agitation and may aid in the removal of the bacterial biofilms.However, the fluid dynamics of the irrigant with this tip is yet to be studied and no conclusion can be drawn as yet. The activator tip is moved along the canal walls in circumferential motion to allow the close adaptation of the tip to the walls so that the disruption of the biofilm is better. [19]

Irrigation by sonic agitation showed improved debridement of the root canal in the coronal, middle, and particularly the apical thirds of the root canal. [20] This is in contrast to the present study which showed relatively more number of CFUs in the apical deep portion than in other parts of the canal.This may be because of the contact of the instrument with the canal wall which causes the node in the immediate vicinity to be diminished. [7] Because it is inevitable that the tip will touch the canal wall, it is important to create several nodes along the instrument being activated. This could be facilitated by means of a custom activated tip. The taper of this tip is maintained such that it correlates to the taper of various sizes of the EndoActivator tips, that is, small (0.02), medium (0.04), and large (0.04), so that the tips can be used according to the diameter of the canal.

The group activated with the power flosser with its original tip showed greater number of CFUs at all the portions of the canal. This may be because of the fact that the end of this tip showed a 1 mm wide circular ball-like projection, which prevented complete placement into the canal.


Within the limitations of the present study, it could be concluded that the highly economical Profile activator tip in the Waterpik Power Flosser system is as effective as the EndoActivator system pertaining to antibacterial efficacy. Further studies are warranted regarding the removal of the smear layer and hydrodynamics of the irrigant during agitation with these tips, before direct extrapolations in clinical conditions.


Dr. Gopikrishna V, Professor, Department of Conservative Dentistry and Endodontics, Thai Mookambika Dental College, Chennai. Dr. Shruti D Nayak, Assistant Professor, Department of Oral Pathology, Yenepoya dental college, Mangalore.


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