Viability of bacteria associated with root caries after Nd:YAG laser application in combination with various antimicrobial agents: An in vitro study.

ABSTRACT

BACKGROUND: The neodymium-doped yttrium aluminum garnet (NdYAG) laser has various therapeutic applications in dentistry, including the treatment of dentin hypersensitivity and the bacterial reduction therapy in periodontology. The addition of antimicrobial agents may enhance the impact of the laser on bacterial viability. OBJECTIVES: This in vitro study aimed to assess the effect of NdYAG laser application in combination with various chemical antimicrobial agents, including hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), chlorhexidine (CHX), and sodium fluoride (NaF), on the viability of bacteria implicated in the etiology of root caries. MATERIAL AND METHODS: Three oral bacterial species were examined Streptococcus mutans (S. mutans); Streptococcus sanguinis (S. sanguinis); and Enterococcus faecalis (E. faecalis). The bacteria were grown in broth at 37°C, and then treated with the chemical agents and/or irradiated with an NdYAG laser for 30 s. Each treatment modality was repeated 3 times group 1 - no treatment; group 2 - 0.5% H2O2; group 3 - 0.5% NaOCl; group 4 - 0.12% CHX; group 5 - 2% NaF; group 6 - NdYAG laser irradiation; group 7 - laser and 0.5% H2O2; group 8 - laser and 0.5% NaOCl; group 9 - laser and 0.12% CHX; and group 10 - laser and 2% NaF. The viability of the bacteria was determined by plating them, counting viable colonies, converting the data into colony-forming units (CFUs)/mL, and transforming them into the log form. Statistical analysis was performed using the two-tailed paired t test. RESULTS: Irradiation with an NdYAG laser alone did not show a statistically significant effect against any of the bacterial species. The only effective antimicrobial used alone was CHX for S. mutans. Chlorhexidine with NdYAG resulted in a greater reduction in S. mutans and E. faecalis than either treatment alone. Meanwhile, H2O2 with NdYAG also showed an enhanced S. mutans reduction. Treatment with 0.5% NaOCl in conjunction with NdYAG brought the most significant reduction in viability for all bacteria in comparison with other treatment modalities. CONCLUSIONS: The NdYAG laser combined with 0.5% NaOCl resulted in the most substantial reduction in bacterial survival as compared to the antimicrobials or the NdYAG laser used alone.