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Abstract from Håkon Valens lecture at symposium PDT-4. Human antimicrobial PDT. ESP-IUPB World Congress, Light & Life, Barcelona, Spain. August 25-30. 2019.

Bacteria in the oral cavity lives primarily in polymicrobial biofilms. Oral mature biofilms may contain several hundred different bacterial species, and over 600 different species have been shown to colonize the oral cavity.

Bacteria in biofilms have different properties compared to their planktonic, free-floating counterpart. Dental caries and periodontitis represent the most prevalent diseases globally. Bacteria are necessary etiological agents for dental caries and periodontitis, and develops after dysbiosis, change in the composition, of the microbiota.

Bacteria may also invade the pulpal space of teeth and cause endodontic infections. In addition, bacteria may colonize and form biofilm on materials introduced into the oral cavity to restore oral function and aesthetics. Bacteria may colonize dental implant surfaces and cause peri-implant diseases, or colonize denture surfaces, which may lead to denture stomatitis.

All these diseases are caused by microorganism growing in biofilms. The biofilm may be located in anatomical areas that are difficult to access, such as deep periodontal pockets or inside the root canal system inside a tooth. Living in a biofilm may facilitate nutritional cooperation, cell signaling and horizontal gene transfer.

Bacteria in biofilms are less sensitive to antibacterial compounds compared to their planktonic counterparts. This property of biofilms, challenge dentist in their daily work, and may explain why many agents show promising results in vitro, but are less efficacious in vivo.

In light of the high prevalence and cost related to prevention and treatment of oral biofilm-associated diseases, there is need to develop novel agents, technologies and methods to prevent and combat biofilms that comply with health, without adverse effects.

May antibacterial photodynamic therapy be an adjunctive treatment for oral biofilm associated diseases? This presentation will discuss opportunities and challenges for antibacterial photodynamic therapy treatment of oral biofilm associated diseases in dentistry.