Basic research on effect of root canal with Er,Cr:YSGG laser

Objective:To evaluate the efficiency in removing bacterial layer from the prepared root canal walls in vitro,we investigated temperature rises in root canals and morphological changes on root canal walls of extracted human teeth after irradiation by laser equipments. Materials and Methods: The laser equipments used in this study were CO2 laser(NewTec Co.), Er.Cr:YSGG laser(Biolase Co.)and ezlase 940(Biolase Co.). Streptococcus mutans 6715 was cultured in brain heart infusion broth at 37°C for 16h. A 50µl of bacteria suspension(108 cfu/ml)was added into root canal of extracted human maxillary anterior tooth and irradiated by laser. The irradiation was occurred in a time-dependant manne(0,15,30,90,180seconds). After irradiation, bacterial suspensions were serially diluted, plated on blood agar plates, and incubated anaerobically at 37°C for 7days. For scanning electron microscopy, tooth root specimens were fixed in a 2.5% glutaraldehyde solution in 0.2 M cacodylate buffer, pH7.2,for 1h. After rinsing and dehydration through a graded series of aqueous ethanol solutions, the cells were critical point dried, mounted on copper stubs. They were then coated with a thin layer of platinum and observed with a JEOL JSM-6301F scanning electron microscope.

Results: The bacteriological evaluation revealed a disinfecting effect in the root dentin samples that was dependent on the output power and irradiation time. SEM showed the removal of the smear layer from the root canal walls and the exposure of dentinal tubules. The temperature rise during irradiation was moderate when standardized power settings were used. The Er,Cr:YSGG laser was efficient to remove smear layer and debris without causing any carbonization and melting.

Conclusion: The results of this study suggest that the Er,Cr:YSGG laser with a flexible fiber tip has a significant antimicrobial effect on root canal infected with S. mutans. Moreover, the Er,Cr:YSGG laser treatment was effective even if the flexible fiber tip did not directly contact with bacteria.