In- vitro-activity of additive application of hydrogen peroxide in antimicrobial photodynamic therapy using LED in the blue spectrum against bacteria and biofilm associated with periodontal disease

Background: Although antimicrobial photodynamic therapy (aPDT) has been shown to be efficient in killing planktonic periodontopathogenic bacteria, its activity on established biofilms is very limited. The aim of the present in-vitro study was to evaluate the potential effect of hydrogen peroxide as a pretreatment for aPDT. Methods: aPDT consisting of riboflavin as photosensitizer and illumination by a LED lamp emitting in the blue spectrum for 30 s and 60 s (aPDT60) was combined with a pretreatment with 0.25% and 3% hydrogen peroxide. The antimicrobial activity of these treatments was determined against eight oral species (incl. Porphyromonas gingivalis and Tannerella forsythia) and against eight-species biofilms. Treatment of biofilms in an artificial pocket model included a mechanical removal of the biofllm. Results: Against planktonic bacteria, pretreatment with hydrogen peroxide increased killing of planktonic bacteria, after aPDT60 no viable bacteria were detected in 7 of 8 strains. In biofilms formed on well-plates, aPDT60 reduced bacterial counts only by 0.53 log10 cfu, whereas reduction was closed to 4 1og10 or higher when 3% hydrogen peroxide was used. When biofilms were treated in the periodontal-pocket model, reduction of cfu was less than 0.5 log10 after mechanical therapy or aPDT60 only, however no bacteria were detected after mechanical biofllm removal followed by the use 3% of hydrogen peroxide and aPDT60. Conclusions: aPDT using riboflavin and blue LED light applied after mechanical removal of biofllm and adjunctive 3% hydrogen peroxide solution appears to represent an alternative for antimicrobial periodontal therapy.