Dental caries, the most common oral disease, is a multifactorial disease caused by interactions among bacteria within the dental plaque, food, and saliva, resulting in tooth destruction. Streptococcus mutans has been strongly implicated as the causative organism in dental caries and is frequently isolated from human dental plaque. Photodynamic therapy (PDT) is a technique that involves the activation of photosensitizer by light in the presence of tissue oxygen, resulting in the production of reactive radicals capable of inducing cell death. Postantibiotic effect (PAE) is defined as the duration of suppressed bacterial growth following brief exposure to an antibiotic. In this study, the in vitro PAE of PDT using erythrosine and light emitting diode on S. mutans ATCC 25175 was investigated. The PAE of PDT for 1 s irradiation and 3 s irradiation were 1.65 h and 2.1 h, respectively. The present study thus confirmed PAE of PDT using erythrosine on S. mutans.

Low level light therapy (LLLT) is known to accelerate the process of wound healing, bone and cartilage formation, and to decrease tissue necrosis and inflammation. It also can be applicable to acute and chronic injury or degenerative disease. Despite forty- plus years of accumulating exprerience of the clinical efficacy of LLLT, their molecular biologic evidence is not fully elucidated. The aim of this review is to explore the role of the ROS system and its molecular biologic mechanism in related with inflammatory response, anti-apoptosis and angiogenesis during LLLT. We suggest that activation of ROS system explains many (if not most) of the observed response of cells to LLLT in vitro, and is likely to play a pivotal role in the response of animals and patients to LLLT for both experimental and clinical indications and diseases.

PDT is an established cancer treatment modality. This can be attributed to the attractive basic concept of PDT; Combination of two therapeutic agents, a photosensitizing drug and light, which are relatively harmless by themselves but when combined, cause more or less selective tumor destruction. Hematoporphyrin-derived photosensitizers are known to be stable and highly efficient. In this study, we conducted a series of experiments to develop light-induced anticancer drugs against oral cancer cells. We tested the cytotoxicity of photodin by MTT assay and observed cell death pattern (apoptosis or necrosis) by hoechst 33342 and propidium iodide staining methods after PDT. IC50 value of photodin was 0.65 ug/ml. At higher doses of photodin ( > 7.8 ug/ml), cancer cells died exclusively from necrosis after PDT. By contrast, at IC50 value, photodin induced cancer cell to undergo apoptotic cell death. The induction begins approximately 6 hours after PDT. We investigated intracellular localization of photodin by oral cancer cell via confocal laser scanning microscopy. Oral cancer cells dual-stained with photodin and organelle-specific fluorescence probes (Mitotracker, Lysotracker, ER-Tracker) revealed that an intracellular fluorescence distribution was restricted to cytoplasmic compartments with no detectable fluorescence in the nucleus. Confocal images of cells containing photodin were overlapped with the mitochondria-specific fluorescence probe images of the same cells. These results demonstrated that photodin may play the role of a photosensitizer for oral squamous cancer cells without swelling and inflammation. Therefore, photodin-based PDT is a suitable treatment for oral cavity carcinoma patients.