Using optical methods to monitor and administer photodynamic therapy to oral bacteria

Oral diseases such as periodontal disease and dental caries affect more than 75% of U.S. adults over age 35, and treatment is increasingly challenged by antibiotic‑resistant bacteria in biofilms. Photodynamic therapy (PDT), which uses light‑activated photosensitizers (PS) to kill bacteria, offers a promising alternative because it targets infected sites precisely and is unlikely to induce resistance. This study used optical methods, including reflectance spectroscopy and confocal microscopy, to characterize PS uptake and PDT dosimetry in planktonic and biofilm bacteria. The lethal PDT dose was similar in both states, but biofilms required ten‑fold higher light exposure due to limited PS penetration. A Monte Carlo tooth model was used to evaluate light delivery throughout dental structures. These findings provide essential tools and dose parameters for designing effective PDT protocols for oral biofilm infections.