Antibacterial Effects of Diode Laser and Chlorhixidine gluconate on Streptococcus mutans in Coronal Cavity

Background : The principal objective of caries removal is to eliminate the infected and necrotic tissues and microorganisms that may cause a persistent inflammation and treatment failure. The aim of this study was to compare the antibacterial activities of diode laser), commercially available chlorhexidine gluconate (CHX) and the prepared one as a cavity disinfectant. Methodology: 70 extracted sound human premolar teeth used. Crown of teeth was cut horizontally to obtain flat dentinal surfaces. One cylindrical cavity (2 mm in diameter, 1 mm in depth) prepared on the flat surface. Samples were divided into 7 groups, each consisted of 10 prepared teeth. The first twenty samples disinfected with (commercially available) Chlorhexidine (2% and 0.2%), the second twenty samples (prepared) chlorhexidine gluconate (2% and 0.2%), and the last twenty diode laser (1w and 1.30 w). Dentin chips from the cavity walls collected immediately after treatment and put into sterile tubes containing 0.5mm of sterile normal saline. A 200μm from this saline was dispensed over Petri-dish contain Mitis-Salivarios agar. Results: The results showed that the CHX solution, CHX powder and diode laser have a significant difference from the control group. Highest antibacterial effect on S. mutans achieved by CHX solution (2%) followed by CHX solution (0.2%). In the second order group, CHX powder (2%) followed by CHX powder (0.2%) showed comparably higher mean values of bacterial colonies than the first two groups mentioned above, and there is a difference between them but not significant. Conclusion: The antibacterial effect of CHX (solution, powder) at all concentrations (2% and 0.2%) and diode laser at all powers (1w and 1.30w) in the infected coronal cavities with S. mutans was significantly different from untreated control group. Introduction The principal objective of caries removal is to eliminate the infected and necrotic tissues and microorganisms that may cause a persistent inflammation and treatment failure. Thus, thorough removal of the infected dentin has a direct influence and impact on the clinical success of a restoration. However, the caries treatment procedures used presently not always assuredly eliminates all of the microorganisms in residual tissues. Bacterial sources which contribute to cavity infection come from: Invasion from the tooth surface via marginal gap formation between a tooth and the restorative material, bacteria present in the smear layer, bacteria present in the dentinal tubules, bacteria present at the dentinoenamel junction and bacterial recontamination of the surface prior to restoration placement. A number of studies have demonstrated that the bacteria left in the dentin of a cavity due to any of the above mentioned infection sources could maintain their activities for a long time [1]. Chlorhexidine gluconate-based solutions are the most popular cavity disinfectants. The chlorhexidine application reported a significant decrease in the number of bacteria in the dentinal tubules. The effectiveness of chlorhexidine lies in its chemical charge, as it is a compound which exhibits strong cationic properties. The posit ive charge of chlorhexidine accounts for its adherent ability and prolonged antimicrobial effect [1]. Using the antibacterial effect of laser depends on the effects produced by laser light in the target cell, tissue, or organism. These effects may be photochemical (the production of free radicals and other reactive species), photothermal, photoablative (the breaking of chemical bonds), or photomechanical (the shock waves produced by the dissipation of a plasma). In general, soft lasers induce only photochemical changes while hard lasers may produce any, or all, of the above mentioned effects depending on the laser type and the conditions under which it is operating [2]. A number of studies demonstrated that different types WebmedCentral > Research articles Page 2 of 10 WMC004179 Downloaded from http://www.webmedcentral.com on 23-Aug-2013, 10:57:24 AM of lasers have antibacterial effects on different microorganisms. In particular, diode and erbium lasers are able to produce an antibacterial effect on enamel, dentin, and carious tissue with a minimal amount of thermal disruption to the residual tooth [3]. To eliminate the residual caries thoroughly and efficiently, it is important to know the possible antibacterial effect of diode lasers on the microorganisms related to dental caries [4]. Materials and Methods Sample Preparation A total of 70 extracted sound human premolars were cleaned and scaled to remove the debris and calculus. The teeth were examined under a stereomicroscope (20x) to exclude the external root resorption, immature apex and vertical root fracture. Crowns of the teeth were cut horizontally with a water-cooled diamond disk to obtain flat dentinal surfaces under water coolant to expose the mid-coronal dentin. The teeth were embedded in a cylindrical polyvinyal tube, poured with autopolymerizing acrylic resin, then the specimens were attached to the survoyer and each specimen received a cylindrical cavity (2 mm in diameter, 1 mm in depth) and any specimen with pulp exposure was excluded. The specimens of all groups adapted in the stainless steel boxes which were covered with aluminum foil and placed in autoclave for 15 minutes at 121C° [5]. Sample Groups The total number of samples was 70, divided into 7 groups (n= 10). One served as control and the others were divided into 3 subgroups of 20 specimens according to the disinfective treatment (prepared chlorhexidine solution, commercially chlorhexidine solution and diode laser), each subgroup again was divided into two groups according to the CHX concentrations (2% and 0.2%) [6] and diode laser powers (1w and 1.30w) Preparation of Bacterial Suspension A single colony of S. mutans inoculated in 5ml Brain heart infusion broth (BHI-broth) in the screw capped vial and incubated at 37?C for 24 hrs. After that 0.5ml of bacterial suspension was added to 0.5ml BHI-broth in the screw capped vial giving a final concentration of 4×107CFU /ml [7]. Inoculation of coronal cavities with S. mutans Before inoculation, the coronal cavities were dried by sterile absorbent endodontic paper points. Then each cavity for each group inoculated with 10μl of a bacterial suspension containing 4x105 CFU by micropipette and incubated at 37?C for 24 hrs. Control groups divided into control positive (cavities infected with bacteria but not treated) and control negative (cavities not infected and not treated). Group 1 (n=5): Control group +ve. (n=5): Control group -ve. Groups Disinfected with CHX Each infected cavity was treated with 10 μl of CHX solution via micropipette for the selected time, then each cavity was dried with a sterilized absorbed endodontic paper point. Group 2 (n=10): 2% CHX (commercially available), 40 sec. Group 3 (n=10): 0.2% CHX (commercially available), 40 sec. Same procedure used for CHX (Freshly prepared from powder) Group 4 (n=10): 2% CHX (Freshly prepared), 40 sec Group 5 (n=10): 0.2% CHX (Freshly prepared), 40 sec Groups Disinfected with Laser Each cavity was irradiated in contact mode with continuous wave of radiation. The laser light was transferred through a 600μm flexible fiber optic tip by a special hand piece. The fiber optic was disinfected for each use by 70% ethyl alcohol and inserted inside the cavity to 1mm with a spiral continuous movement clockwise from the top to the floor and anti-clockwise in the reverse direction. This procedure improves the distribution of the laser light inside the cavity and to avoid excessive heat generation and carbonization in the internal cavity surface. Irradiation time was 15 seconds and repeated 5 times with 15 second intervals with contact, according to manufacture instructions. During this study the output power was adjusted at 1W and 1.30W. Group 6 (n=10): 1W, 15 sec, 5 cycles. Group 7 (n=10): 1.30W, 15 sec, 5 cycles. Antibacterial activity determination To evaluate the antibacterial effects of the CHX and Diode laser against S. mutans, a standardized amounts of dentin chips?25±5 mg ) was collected from the circumferential cavity walls using a new, sterile WebmedCentral > Research articles Page 3 of 10 WMC004179 Downloaded from http://www.webmedcentral.com on 23-Aug-2013, 10:57:24 AM carbide round bur mounted to a low-speed contra-angle headpiece. Collected dentine chips with bur was transferred into sterile tubes containing a 0.5ml normal saline. A 200μl from this saline was dispended onto the separate Petri dishes of MSA and incubated at37Co for 24hrs [7]. Colony Counting After 24hrs of incubation, the number of bacterial colonies was counted.