摘要： This study evaluates the in vitro antibacterial effects of 5-ALA (photoactive dye) in regard to different disinfection methods (2% Chlorhexidine gluconate, 1% Sodium Hypochlorite) on cariogenic bacteria (Streptococcus mutans and Streptococcus sobrinus). After inoculation of dentin specimens with S. mutans and S. sobrinus separately, the reduction in bacterial count was evaluated by the colony counting method. A total of sixty specimens were assigned to six groups (Ten per each group, with five in each group inoculated with S. mutans and the other five inoculated with S.sobrinus); group one: positive control where no treatment was performed, group two: 1% NaOCl was applied, group three: 2% CHX was used, group four: 5-ALA with LED light (635nm) was applied, group five: 5-ALA was used without LED light activation, group six: LED light was used without dye application. There was a significant reduction in the number of S. mutans in the group treated with 5-ALA with LED light, followed by CHX and then NaOCl, whilst minimum bacterial reduction was detected in the groups that were treated with LED light alone and 5-ALA without LED. However, NaOCl exhibited a better effect regarding reduction of S. sobrinus, followed by 5-ALA and LED light and then CHX. All the disinfected groups showed a significant relation with the positive control non-treated group(p<0.05).