Comparative Evaluation of Bactericidal Effect of 810 nm Diode Laser and Sodium Hypochlorite on Enterococcus faecalis in Infected Root Canals of Primary Teeth- An in vitro Study

Introduction

A biofilm is a microbial sessile community characterized by cells attached to a substratum, embedded in a matrix of extracellular polysaccharide, exhibiting modified phenotype, growth and gene expression. Periapical pathosis seen following root canal treatment is due to the presence of E. faecalis in the biofilm. This microorganism has the capacity to live in environments low in nutrients and commensality of bacteria. Thus, removal of microbes results in successful root canal treatment. Because of complexities in the anatomy of the primary teeth roots, elimination of the microbes from the dentinal tubules can be challenging. In order to achieve this objective, multiple irrigants should be utilized during the biomechanical preparation.¹ 

Irrigation dynamics has always been the key to success in the root canal treatment. The irrigants should have the ability to contact the microbes present in the root canal and the working mechanism of the irrigants play a major role in the elimination of debris and microorganisms present in the tortuous primary root canals. The American Association of Endodontics recommend using lower concentrations of NaOCl (1.5% for 5 minutes) to minimize cytotoxicity to stem cells. Due to the excellent antimicrobial property, NaOCl is known as a long accepted endodontic irrigant. The mechanism comprises of oxidative action with bacterial enzymatic inactivation, biosynthetic alteration in phospholipid destruction and cellular metabolism, degradation of fatty acids and formation of chloramines.²

Shaping and cleaning helps in the elimination of microbial infection from the dentinal tubules and root canals. Endodontic irrigants help in removal of debris, smear layer and organic debris, hence play a significant role in irrigation mechanisms of root canal. Root canal smear layer is comprised of remnants of odontoblastic processes, dentin, necrotic and viable tissues, pulp tissue and bacteria. Dentinal tubules in primary teeth have greater density compared to permanent teeth. Because of these structural differences, primary teeth dentin is more reactive to chemical substances and smear layer in primary teeth can be easily removed compared to permanent teeth.³

Due to the shortcomings of commonly used irrigants in root canal treatment, newer methods with the help of lasers have been initiated to irradiate the root canals effectively, in recent years. It was first introduced in 1959 by Gordon Gould, a Columbia University graduate student. The first working laser was developed by Theodore Maiman at Hughes Research Laboratories in 1960. In 1987, neodymium-yttrium aluminum garnet (Nd-YAG) laser was specifically developed for dental procedure. With the invent of newer generation laser, it has been widely used on dental hard tissues as well. Hard tissue laser provides an effective alternative to conventional drilling with a better working field for the clinician that facilitates good results and better treatment outcome.

The efficacy of laser energy in removing smear layer and its ancillary antimicrobial effect on highly resistant species has been demonstrated by different laser systems such as erbium:yttrium–aluminium–garnet (Er:YAG), neodymium:yttrium–aluminium–garnet (Nd:YAG) and diode. Lasers emit photonic energy that can be used to activate irrigant solutions, and therefore, have the potential to enhance irrigation efficacy by providing greater accessibility to formerly unreachable parts of the tubular network.⁴

Combined therapy with medicaments or irrigation solutions along with lasers was found to have enhanced the effectiveness of canal disinfection. To evaluate the effectiveness of irrigation solution, laser irradiation was combined with chemical methods. This technique is called laser-assisted endodontics. Diode laser is preferred due to antibacterial effect and elevated penetration depth of dentinal tubules. When laser light is applied on target tissues, it initiates photothermal reaction which causes heat generation and a rise in temperature within the tissues. When the temperature reaches above 60°C, it causes protein coagulation within the tissues. The present study evaluated the antimicrobial and irrigational efficacy of 1.5% Sodium hypochlorite against E. faecalis with use of 810 nm diode laser in infected root canals.⁵

Materials and Methods

The current study was undertaken in the Department of Paediatric and Preventive Dentistry, Krishnadevaraya College of Dental College, Bangalore and collaborated with Department of Microbiology. Twelve freshly removed human single-rooted primary teeth were sterilized and utilized as study samples. Single canal teeth were considered and teeth that showed root resorption, root fracture, root caries and any developmental anomalies were excluded from the study. The teeth were segregated into two experimental groups (n = 6).

E. faecalis (ATCC 29212) was acquired from Department of Microbiology and was subcultured on Brain Heart Infusion (BHI) Agar and incubated at 37degree Celsius overnight. Access opening was done in all the twelve samples (Figure 1). 0.01 mL strains of E. faecalis suspension was introduced into each root canal with the help of sterile insulin syringe. Then, under aerobic conditions, the samples were incubated for one day in plastic vials at 37°C. Cleaning and shaping was carried out with the help of 21 mm K file and 21 mm H file, respectively and canals were instrumented up to 35 size K and H file using crown down procedure (Figure 2). Copious irrigation with 1.5% sodium hypochlorite was done in Group I (Figure 3). For a long time, Hypochloric acid was utilized as the active moiety which is responsible for inactivation of bacteria with the help of chlorine-releasing agents, the OCl ion has a minimal effect when compared with undissolved HOCl. Second group was irrigated with 1.5% sodium hypochlorite and endovac suction was done for one minute to make sure of the effect of the laser. Laser irradiation was carried out with the help of diode laser at a wavelength of 810 nm utilizing oscillatory technique, with an approximate speed of 2 mm/s for 5 s at 1.5 W (Figure 4). The laser treatment was repeatedly carried out four times with an interval of 10 seconds for each sample. To assess the effectiveness of antimicrobial properties, twelve petri plates were developed, and microbiological evaluation was done for both the groups. The data were tabulated and statistical analysis was done.

Results

Data was analyzed using SPSS Version 22 software package (IBM Corporation, SPSS Inc., Chicago, IL, USA). Descriptive and inferential statistics were carried out. Statistical difference between the two different groups was assessed using Mann-Whitney U test and Wilcoxon Signed Rank test was used for within the group comparisons. p value below 0.05 was considered statistically significant. The results showed that Group II, with the use of endovac suction and 810 nm diode laser showed better efficacy (mean value: 561470) compared to Group I treated without using laser (Mean value: 773166). The group I showed a bacterial reduction of 78% and group II showed a reduction of 91% which was statistically significant. 1.5% sodium hypochlorite showed maximum antimicrobial activity at all the three intervals in Group II when treated with 810 nm diode and showed the best result in terms of decreased microbiological levels. The mean difference between group I and group II was 0.004, which was statistically significant. 

Discussion

In the present study, we compared the efficacy of 810 nm diode laser with 1.5% NaOCl in removing E. faecalis in the primary root canal system. The important factor to be considered for endodontic failure in primary teeth is the presence of complex network and anatomy of the root canals and dentinal tubules., Therefore, it is necessary to remove the bacterial toxins and debris from the root canals for the success of the treatment. Chemomechanical approach helps us to remove a part of infected dentin and the superficial layer of dentin in the process of root canal preparation. The effect of irrigants is high in the superficial layer of the dentin. Various antibacterial properties of 810 nm diode lasers were discussed and studied by several authors. E. feacalis is considered to be the commonly found bacterial species in the infected root canals. This coccus persists in the endodontic infections and is highly resistant to variety of disinfecting agents and thus results in endodontic failure. Our study showed the antibacterial efficacy of 810 nm diode laser and sodium hypochlorite in the reduction of E. faecalis in the primary root canals. The antimicrobial property of laser was exclusively heat dependent; it was recommended to evaluate heat independent antimicrobial effect of the laser since E. faecalis is basically a heat resistant species.⁶

In this study, the laser irradiation was carried out based on the factory setting and the samples were irradiated for about 5 seconds (irradiation was done four times for a duration of 5 seconds at an interval of 15 seconds), at 1.5 W output power, frequency of 50 Hz and in the continuous wave mode. Similar to the studies conducted by Ashofteh et al., and Kanumuru et al., in the present study, the optical fiber of the laser was introduced directly into the root canal. Thus, the fiber tip was directly in contact with the dentinal walls. Descriptive and inferential statistics were carried out. Statistical difference between the two different groups were assessed using Mann-Whitney U test and within the group using Wilcoxon Signed Rank test. p value below 0.05 was considered statistically significant.⁷ The result showed that Group II, with the use of endovac suction and diode laser showed better results (mean value: 561470) than Group I which was treated without using laser (Mean value: 773166). The group I showed a bacterial reduction of 78% and group II showed a reduction of 91% which was statistically significant. 1.5% Sodium hypochlorite showed maximum antimicrobial activity at all the three intervals in Group II treated with 810 nm diode and it showed the best result with decreased microbiological levels. The difference between group I and group II was 0.004.

Ashofteh and coworkers have concluded that diode laser can be utilized as an alternate technique for the irradiation of microorganisms and 97.56% reduction in bacteria was observed after using 810-nm diode laser with an output power of 1.5 W.⁷ A study conducted by Rahimi et al., reported that combined use of laser and NaOCl exhibited best results. De Souza et al., stated that laser irradiation followed by chemomechanical irrigation was highly effective than NaOCl irrigation which was also carried out for disinfection and elimination of E. faecalis in root canals.⁸

The major contrast of our study to other studies is that in our study, we utilized laser application method. The laser irradiation was combined with chemical methods to evaluate its efficacy and this technique is known as ‘laser-assisted endodontics’. In this study, however, the pure ability of 810 nm diode laser in E. faecalis removal was assessed. Gutknecht et al., concluded that strongest water absorption was found in 810-nm diode lasers when differentiated with other wavelength diode lasers and Nd:YAG laser. Majority of the laser energy was incorporated by superficial dentinal tubules enriched with water and this was seen in 810 nm diode laser. Consequently, the superficial dentinal layers receive major antibacterial effects, while the deeper dentinal layers receive only a minor effect. Since the deep dentinal layers are not being exposed to the laser, the disinfection ability of 810 nm laser gets reduced.⁹

Naik et al., conducted an in vivo study to evaluate the efficacy of 810 nm diode laser assisted disinfection in comparison to conventional sodium chloride based chemo-mechanical debridement in deciduous root canals. The study showed 100% reduction in the bacterial count after the diode laser application, and concluded that it can be utilized as an effective adjunct to conventional methods of deciduous root canal disinfection.¹⁰ Application of laser in endodontics have benefits other than its antimicrobial effect. A study by Parirokh et al., found that dentinal tubules successfully occluded after using diode laser for eliminating smear layer.¹¹

However, increase in the laser temperature can result in damage of adjoining tissues and the adjacent anatomic regions. So, laser application should be carried out carefully.¹²

In this study, pure antibacterial ability of 810 nm diode laser was assessed. To assess antibacterial effect of 810 nm diode laser, laser-assisted endodontics should be used in further studies. To improve the efficacy of 810 nm diode laser, it is also recommended to use higher output power and longer irradiation duration.¹³

Conclusion

Laser assisted endodontics is a boon to paediatric dentistry if practiced with adequate care and precaution in children. The introduction of diode laser in deciduous teeth has shown 95% bacterial reduction in this study. Furthermore, multicentric inputs and research is required to make the art and science of laser assisted pediatric endodontics a predictable one.

Financial assistance

Nil

Conflict of Interest

None