Bactericidal Effects of Nd

Abstract

The purpose of this study was to investigate the effect of Nd: YAG laser irradiation on Streptococcus mutans.Roots of intact bovine incisors were used in this experiment. After cleaning and shaping of the root canal, they were acid-etched for 1 minute and ultrasonically irrigated. The root surface was coated with nail enamel and the samples were sterilized. Each root canal was filled with 50μl of culture medium where S. mutans was incubated at 37°C for 24 hours. One hundred roots were divided into 10 groups according to irradiation energy and addition of evans blue in the culture medium. Non-irradiated samples were used as control.The culture medium in the root canal was irradiated under up-and-down motion between the apical and cervical portion of the root canal with an optical fiber (∅=600, μm) for 30 seconds using Nd: YAG laser (100mJ or 200mJ and 10 or 30 pps). After the irradiation, bacterial samples of 10μl were taken from each root canal and incubated aerobically on Mitis Salivalius Agar at 37°C for 72 hours. The number of colonies on the medium was counted and colony-forming-units (CFUs) /ml were calculated.Thermal change caused by Nd: YAG laser irradiation in the root canal and culture medium was also monitored with a thermal camera. In addition, the irradiated dentin surface of the canal wall was observed with SEM.The results were as follows:1. In comparison with the control group, the CFUs in 100mJ 10pps, 200mJ 10pps, 100mJ 30pps and 200mJ 30pps irradiated groups without evans blue were reduced to 41%, 37%, 16% and 2%, respectively. Likewise, the CFUs in 100mJ 10pps, 200mJ 10pps, 100mJ 30pps and 200mJ 30pps irradiated groups with evans blue were reduced to 46%, 34%, 3% and 0%, respectively. The bactericidal effect in all experimental groups was statistically significant compared with the control group (t-test, P<0.01).2. No significant difference was found between the groups with and without evans blue when irradiation energy was the same.3. The maximum temperature rise in the culture medium was 40°C in accordance with the temperature rise on the root surface of about 5°C under the lasing condition of 200mJ 3Opps.4. In SEM observation, most part of the lased canal wall surface showed open dentinal tubles, partially closed in other part.