Antibacterial erect of photodynamic therapy on prepared tooth structure contaminated with Streptococcus mutans

Several studies during the last few years have demonstrated the antibacterial potential of photodynamic therapy (PDT). The overall objective of ongoing studies in our laboratory is to assess the efficiency of antibacterial PDT on various oral pathogenic bacteria, as well as to determine the side-effects of PDT upon tooth structure. The aim of the present study was to evaluate the antibacterial effect of PDT on Streptococcus mutans (S. mutans) which was imported onto prepared tooth structure. An in vitro study was made of 33 single-root teeth removed for orthodontic reasons. The teeth were prepared according to the requirement of crown restorations and contaminated intentionally by S. mutans. Sterilization of teeth was performed with the following treatments: 75% alcohol alone, PDT alone, the combination of alcohol and PDT. 7 teeth were left untreated as control. All the teeth were then submitted to bacteria culture, and the survival fractions were calculated. On the other hand, surface temperature and hardness of prepared tooth structure were tested before and after PDT, to examine the side-effects of this treatment. The one-way ANOVA test showed no significant statistical difference (P > 0.05) between bacteria survival fractions of PDT group (0.96% +/- 0.49%) and combination treatment group (0.80% +/- 0.32%), while that of the alcohol group was significantly higher than the others (10.55% +/- 2.30%). Acceptable surface temperature increase of 5.8 +/- 0.9 degrees C after PDT was measured, as well as insignificant surface hardness change (P > 0.05). It was concluded that PDT based on a photochemical mechanism has a reliable antibacterial effect on S. mutans-contaminated prepared tooth structure, and it will result in neither lethal increase of surface temperature nor decrease of surface hardness.