The principle behind LAD, so-called photodynamic therapy (PDT) has been known for over 100 years. StartFragment The concept behind the PDT has been thoroughly tested throughout the last 10 years, partly with lasers and partly with LED light. LAD is particularly interesting because the concept can be used for treatment of as many different micro organisms as there are cases. Dortbudak (2001) showed a significant reduction in the number of Actinomyces actinomycetemcomitans, P