Lethal photosensitization of bacteria in subgingival plaque from patients with chronic periodontitis

Subgingival plaque samples from patients with chronic periodontitis were exposed to light from a 7.3 mW Helium/Neon laser for 30 s in the presence and absence of 50 μg /ml toluidine blue O as a photosensitizer. Viable counts of various groups and species of bacteria were carried out before and after irradiation. The median numbers of viable bacteria initially present in the 30-μl aliquots irradiated were 1.13 × 10⁵ cfu (aerobes), 4.08 × 10⁵ cfu (anaerobes), 4.92 × 10³ cfu (black-pigmented anaerobes), 4.75 × 10² cfu ( Porphyromonas gingivalis ), 6.15 × 10³ cfu ( Fusobacterium nucleatum ) and 1.7 × 10⁴ cfu (streptococci). The dye/laser combination achieved significant reductions in the viability of these organisms, the median reductions in the viable counts being 91.1% for aerobes, 96.6% for anaerobes, 100% for black-pigmented anaerobes, P. gingivalis and F. nucleatum and 94.2% for streptococci. Overall, the viability of bacteria in the 20 plaque samples was not significantly decreased by the dye alone. However, in a small minority of samples there were indications of light-independent, dye-induced toxicity. Low-power lasers, in conjunction with appropriate photosensitizers, may be a useful adjunct to mechanical debridement in the treatment of inflammatory periodontal diseases if a similar effectiveness against subgingival plaque bacteria can be achieved in vivo .