Evaluation of the Antibacterial Effect of Laser Diode and Zinc Oxide Nano Particles in Cavity Disinfection

This study will be carried out on adult patients attending to the department of conservative dentistry at The Faculty of Oral and Dental Medicine, Cairo University, Egypt. The procedures will be carried out by postgraduate student Sarah Atef Khattab (B.D.S. 2011) from Cairo university without an assistant. The researcher will bear ultimate responsibility for all activities associated with the conduct of a research project including recruitment of patients, explaining and performing the procedures to them.

A : Excavation protocol:

The teeth of the patients that meet inclusion criteria will be anaesthetized, isolated with a rubber dam. Cavity opened using conventional high-speed rotary instruments. The central cariogenic biomass and the superficial parts of the necrotic dentine will be removed with round burs. Caries lesion will be completely removed in the enamel/dentin junction. The excavation procedure will be terminated as soon as the soft and wet dentine was removed and the remaining tissue was leathery but not hard on exploring. A dentinal sample will then be collected from the base of the cavity using sterile spoon excavator as a baseline for bacteriological assessment. Then, after application of either interventions , another dentinal sample will be collected using a sterile excavator and transferred into sterile tubes and transferred to the laboratory for microbiological analysis.

1. Application of the interventions: b.1: laser diode Each cavity will be irradiated in contact mode with continuous wave of radiation. The laser light is transferred through a 600µm flexible fiber optic tip by a special hand piece. The fiber optic will be disinfected for each use by 70% ethyl alcohol and inserted inside the cavity to 1 millimeter 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 in the internal cavity surface. Irradiation time will be 15 seconds and repeated 5 times with 15 second intervals with contact, according to manufacture instructions. During this study the output power will be adjusted at 1.5 Watt. b.2: Zinc oxide nano-particles: The zinc oxide nano-powder will be mixed with ethanol and applied in the cavity, where the ethanol evaporates, while the zinc oxide nano-particles infiltrate into the carious floor of the cavity.

N.B: In both methods, a dentin sample will be taken before the application of the disinfectant, then the zinc oxide nano-particles are applied in the cavity and left for 5 minutes, then another sample will be taken. The second specimen will be compared to the first specimen taken before cavity disinfection, regarding the streptococcus mutans count.

c .Assessment of Outcome: Samples of carious dentin will be collected with sterile excavator before and after application of both interventions. The dentin samples will be transferred to sterile container containing a 1millilitre thioglycollate medium used as a carrier, then this sterile container will be kept in an ice box and taken to the microbiology laboratory for processing, within an hour, by another examiner who is blinded to the type of agent applied after partial caries removal. Samples will be vortexed for two minutes, decimally diluted and 0.1 ml will be plated on Mitis Salivarius Bacitracin agar plates, these plates will be incubated anaerobically for 48 hour at 37 degree celcius then aerobically for 24 hour at room temperature. The number of colonies will be expressed as colony-forming units (CFU/ml) compared before and after application of the antibacterial agent.