Oral mucosal irritation potential of antimicrobial chemotherapy involving hydrogen peroxide photolysis with high-power laser irradiation for the treatment of periodontitis

In the present study, we assessed the oral mucosal irritation potential of antimicrobial chemotherapy involving hydrogen peroxide (H₂O₂) photolysis with a 405-nm laser device at an output power of ≥100 mW in hamsters. Twenty-four cheek pouches from 12 male Syrian hamsters received 7-min treatment with pure water (PW), 3% H₂O₂, laser irradiation of PW at 100 mW, laser irradiation of 3% H₂O₂ at 100 mW, laser irradiation of PW at 200 mW, or laser irradiation of 3% H₂O₂ at 200 mW (n = 4 each). The diameter of the irradiation area was set at 3 mm; accordingly, the calculated irradiances (optical power densities) of the 100- and 200-mW laser lights were approximately 1400 and 2800 mW/cm², respectively. In addition, 12 cheek pouches from six animals received laser irradiation of 3% H₂O₂ at 100 mW for 1, 3, or 5 min (n = 4 each). Each treatment was repeated three times at 1-h intervals. Macroscopic and histological changes were evaluated 24 h after the last treatment. In addition, in vitro bactericidal activity of the treatment against periodontal pathogens was evaluated. We found that 405-nm laser irradiation of 3% H₂O₂ caused moderate to severe oral mucosal irritation when performed at powers of 100 and 200 mW for ≥3 min, while the same treatment performed at 100 mW for 1 min resulted in mild irritation. Moreover, 1-min H₂O₂ photolysis at 100 mW caused a >4-log decrease in viable bacterial counts. These findings suggest that 1-min H₂O₂ photolysis, which can effectively kill periodontal pathogens, may be acceptable when a 405-nm laser device is used at 100 mW. However, use of the laser at a lower power would be preferable for the prevention of unnecessary oral mucosal irritation.