The erbium-doped yttrium aluminum garnet (Er:YAG) laser is used to treat periodontal disease; however, its effectiveness at killing oral bacteria is not well known. Furthermore, the compounding effect of the combination of a laser treatment and irrigation methods with antimicrobials on bacterial viability is yet to be determined. The purpose of this in vitro study was to evaluate the effect of the Er:YAG laser with irrigation using chlorhexidine (CHX), hydrogen peroxide (H₂O₂), or sodium hypochlorite (NaOCl) on the viability of oral bacteria. Three bacterial species were used in our study: Streptococcus gordonii, Fusobacterium nucleatum, and Porphyromonas gingivalis. Bacteria were grown in an anaerobic chamber in brain heart infusion broth and incubated at 37 °C. Bacterial samples with an OD of 0.5 were irradiated with the Er:YAG laser at 2940 nm using a 400-µm Varian tip. The experiment was repeated four times using these parameters: 40 mJ, 40 Hz, and 1.6 W for 20 seconds with the 300 µs short pulse duration in contact mode. Treatment groups consisted of the following: (1) no treatment, (2) 0.5% H₂O₂ alone, (3) 0.5% NaOCl alone, (4) 0.03% CHX alone, (5) Er:YAG irradiation alone, (6) Er:YAG irradiation with 0.5% H₂O₂, (7) Er:YAG irradiation with 0.5% NaOCl, and (8) Er:YAG irradiation with 0.03% CHX. Microbial viability was determined through plating and colony counts and calculated into CFU/ml. Statistical analysis was done using a two-tailed paired t-test. The use of the Er:YAG laser alone failed to show statistically significant antibacterial activity against any of bacteria. The most effective mono-treatment with irrigation solutions for all three bacteria were 0.5% H₂O₂ and 0.5% NaOCl (p < 0.001 for each solution). Irrigation with 0.03% CHX was most effective against F. nucleatum (p < 0.01) and less against P. gingivalis and S. gordonii and showed the least antibacterial action alone but improved significantly in combination therapy (p < 0.05). The combined treatment with the Er:YAG showed the greatest and most significant improvement in the reduction of bacterial viability compared to any other treatment group (p < 0.05 for each combined treatment). Irradiation with the Er:YAG laser with the addition of 0.5% H₂O₂, 0.5% NaOCl, or 0.03% CHX under a short working time (20 s) resulted in a significant reduction of bacterial viability for all three bacterial species compared with any single treatment option. The combination of irradiation with the Er:YAG laser with the addition of 0.5% H₂O₂, 0.5% NaOCl, or 0.03% CHX resulted in a larger reduction of bacterial survival when compared to monotherapies with antimicrobial solutions or laser. The combination of the Er:YAG laser with a low concentration irrigant solution of 0.5% H₂O₂, 0.5% NaOCl, or 0.03% CHX could be an effective treatment protocol for the reduction of periodontal pathogens and thus suitable treatment for non-surgical periodontal therapy.

Introduction: The purpose of this in vitro study was to evaluate the effect of erbium-doped yttrium aluminum garnet (Er:YAG) laser with irrigation using chlorhexidine (CHX), hydrogen peroxide or sodium hypochlorite on Streptococcus gordonii (Sg), Fusobacterium nucleatum (Fn) and Porphyromonas gingivalis (Pg). Material and Methods: Bacterial samples were grown in an anaerobic chamber in Brain Heart Infusion (BHI) broth and incubated at 37°C. An optical density (OD) at 660 nm was taken and a working solution was diluted to an OD of 0.5 which corresponded to a cell density of 106 cells/µl. The samples were irradiated with the Er:YAG laser at 2940nm using a 400 µm Varian tip. The experiment was repeated four times using these parameters: 40mJ; 40Hz; 1.6W for 20 seconds with the 300 µs short pulse duration in contact mode. Treatment groups consisted of: 1: no treatment, 2: 0.5% H₂O₂ alone, 3: 0.5% NaOCl alone, 4: 0.03% Chlorhexidine alone 5: Er:YAG alone, 6: Er:YAG irradiation with 0.5% H₂O₂, 7: Er:YAG irradiation with 0.5% NaOCl, 8: Er:YAG irradiation with 0.03% Chlorhexidine. Statistical analysis was done using a one-tailed independent t-test. Results: Er:YAG laser treatment plus the addition of 0.5% H₂O₂, 0.5% NaOCl, or 0.03% CHX resulted in a significant decrease in the survival of bacteria. Conclusions: The combination of the laser with 0.5% H₂O₂, 0.5% NaOCl, or 0.03% CHX could be an effective treatment protocol for periodontal pocket therapy.