Efficacy of gasiform ozone and photodynamic therapy on a multispecies oral biofilm in vitro

Ozone gas and photodynamic therapy (PDT) have been claimed to be antimicrobially effective. This study assessed their antimicrobial potential in vitro. Mature six-species oral biofilms were treated as follows (n = 9 per group): (i) a 60-s application of gasiform vacuum-ozone or vacuum alone (on wet or air-dried biofilm samples); (ii) PDT ( i. e. methylene blue in combination with or without a diode soft laser, and a soft laser alone); or (iii) antimicrobial solutions: immersion of biofilms for 60 s in 0.2 and 2% chlorhexidine or in 0.5 and 5% hypochlorite solution. Treatment with chlorhexidine or hypochlorite served as a positive control, whereas untreated samples served as negative controls. Colony-forming units on blood agar were counted. Only the 5% hypochlorite solution was able to totally eliminate the microorganisms in the biofilm. The observed reduction of viable counts by vacuum-ozone application and PDT was less than one log(10) step. Under the conditions of the current study, gasiform ozone and PDT had a minimal effect on the viability of microorganisms organized in a cariogenic biofilm.