INVESTIGATION OF ANTIBACTERIAL ACTIVITY OF ND: YAG - LASER AND STANDARD ENDO-DONTIC TREATMENT

Introduction: The microbial infection is one of the main causes of the dental pulp and periodontal diseases. Previously used methods for its elimination are not fully effective, and often some microorganisms in root canals (RC) remain unaffected after treatment. Another modern method for disinfection of root canal system is laser disinfection. Different types of lasers are used - Nd: YAG, Er: YAG, Diode laser. Purpose: The purpose of our study is to compare the antibacterial activity of ND: YAG laser and conventional endodontic therapy in the treatment of infected root canals.


INTRODUCTION
The microbial infection is one of the main causes of the dental pulp and periodontal diseases. The most common methods (irrigation with 2.5% sodium hypochlorite solution and 17% EDTA ) used for its elimination are not fully effective, and often some microorganisms in root canals (RC) remain unaffected after treatment. [1,2].
Another modern method for disinfection of root canal system is laser disinfection. Different types of lasers are used -Nd: YAG, Er: YAG, Diode laser. They also have antibacterial action [3,4,5,6,7]. In endodontic treatment, photothermic and photomechanical effects of lasers of different wavelengths interact with the dental tissues (dentin, residual pulp), the polluting layer, and microorganisms. Using various capacities, all types of lasers can destroy the cell walls of microorganisms due to the photothermal effect [8,1,4].
The aim of our study was to compare the antibacterial activity of ND: YAG laser and conventional endodontic therapy in the treatment of infected root canals.

MATERIALS AND METHODS
The study involved 36 teeth of patients diagnosed with pulp gangrene or chronic periapical periodontitis, requiring endodontic treatment.

Case selection
Patients' complete medical history was taken. Those who have systemic diseases or have taken antibiotics for the last three months are excluded from the study. Each patient signs an informed consent. In each case (tooth), a preliminary X-ray is taken to detect the presence of periapical changes and get an idea of the morphology, length and number of root canals.
The teeth are isolated with a rubber dam. Then they are quenched with 2% chlorhexidine solution. Sterile burs are used for the preparation of the endodontic cavity and access. Old obturations and carious lesions are carefully removed. Microbiological samples are taken by placing a sterile paper point in the root canal for 60 seconds. After removing the paper point from the root, it is immediately placed in a sterile transport environment and then transported to a microbiological laboratory. This is the initial microbiological sample.
The treated teeth are divided into two groups depending on the method used for root canal disinfection:

RESULTS
In all compared pairs, there was no significantly different effect regarding the number of microorganisms (Table 1, 2, 3, 4).  NaOCl has the most pronounced antimicrobial activity in vivo. The remaining causative agents, after the impact of this disinfection method, are in a small amount -only 10%.
After in vivo therapy with Nd: YAG laser 34% of untreated etiological agents remain. Reduction of these microbial species again from KES, Enterobacter spp., Klebsiella spp. is about 2 log, but they remain at a microbial number of approximately 1000 cfu / ml. Unlike the other method, there is a lack of complete eradication in some other more sensitive bacterial species, as well. (Table 4)

DISCUSSION
From the two tasted groups are isolated predominantly polymicrobial associations and rarely mono-infection with a predominance of Gram-positive species It is noteworthy that the most pronounced antimicrobial activity in vivo has NaOCl (only 10% of the initially isolated microorganisms remain after the action of this disinfection method -the effect is 90%). Microorganisms remaining after treatment are Gram-positive cocci -oral streptococci that are likely to reinfect the dental canals despite the successful removal of the other causative agents from the original association from which they were isolated. Other microorganisms that remain after treatment are Enterobacteriaceae of the KES group, Enterobacter spp., Klebsiella spp. These species form extremely rigid biofilms due to the overproduction of substances in capsule form and many other adhesion molecules on their cell wall surface as outer membrane proteins, lipopolysaccharide, and adhesive piles. They are also polyresistant to many antimicrobial agents and are the cause of problematic in-hospital infections.
After Nd: YAG laser therapy, 34% of microorganisms stay unaffected -the effect is 66%. Microorganisms that are observed after treatment are again of KES group, Enterobacter spp., Klebsiella spp. Unlike the other two methods, there is a lack of complete eradication in some other more sensitive bacterial species -S. aureus and E. faecalis, several species of bacilli and associated with them corynebacteria. Similar results were also established by other authors who did not get a good antibacterial effect while using the Nd: YAG laser - Blum et al. (1997) [1], Jukic et al. (2004) [9]. The photothermal effect of the lasers for microorganism destruction is used in the endodontic treatment [10]. The lower response rate of E. faecalis can be due to the greater durability of this heat microorganism [2,11]. In con-trast, Gutknecht et al. (1996) [12] and Hardee et al. (1994) [4] received 99% bacterial reduction in their studies. This can be due to various parameters of the laser radiation or different exposure duration. The conducted clinical study allows for the reduction of microorganisms in RC after treatment applying the two methods. The used microbiological method permits reading the remaining microorganisms only in RC lumen, i.e., those microorganisms adhered to the paper pin while taking the second microbiological sample.
It does not give an idea of the microorganisms that have stuck to the canal walls and that have entered the dentinal tubules and micro-canals of the apical delta. They are the cause of root canal system re-infection after filling the canal and the appearance of periodontitis after the treatment of infected RC or the failure to treat existing periodontitis. However, the microbiological method used makes it possible to gain a comparative assessment of the two methods' effectiveness.
Nd: YAG laser disinfection at this stage can be used as a selection method, although it has the lowest antimicrobial effect. However, the power of the laser and the duration of procedures should be very carefully selected so that the limitations of heating the root canals and surrounding tissues are not exceeded.

CONCLUSION
The disinfection rinsing method with NaOCl has the strongest antimicrobial effect in clinical studies (90% against all microbial isolates).
The use of Nd: YAG laser independently is not always sufficient for root canal disinfection -the effect is about 66%.
We believe that the established antimicrobial effect of Nd: YAG laser makes the method appropriate both as complementary to routine one and as a method of choice in situations severely impeding the conventional method of rinsing with antiseptic solutions.
The microbiological studies were conducted at Bulgarian Academy of Sciences, Microbiology Institute "Stefan Angelov" (associated with the Institute "Pasteur" in Paris and the Department of Microbiology at the Medical Faculty of Medical University -Sofia). They were carried out by Assoc. Prof. R. Gergova (Department of Medical Microbiology, Medical Faculty, Medical University of Sofia).
In all two methods, significant differences in the amounts of microorganisms before and after treatment (p <0.001) have been observed (Table 3).