ALEXANDRU SIMION OGODESCU, ALEXANDRU ATTILA MORVAY, ADRIANA BALAN, LAURA GAVRILA, ANA PETCU, CARMEN SAVIN COMPARATIVE STUDY ON THE EFFECT OF THREE DISINFECTION PROCEDURE ON THE STREPTOCOCCUS PYOGENES BIOFILM FORMED ON PLASTIC MATERIALS USED IN PAEDODONTICS AND ORTHODONTICS Plastic materials are widely used today in Paedodontics and Orthodontics for manufacturing preventive and therapeutic devices. Since these are worn for long times in the oral cavity biofilm forms on the smooth acrylic surfaces of those appliances. The biofilm must be removed not to destroy the oral microbiology. The aim of this study was to research the possibility of removing the microbial biofilm and disinfecting retainers using the photodynamic effect of toluidine blue O, Fotosan System (CMS Dental, Copenhagen, Denmark) in comparison to two products available on the market Corega Denture Cleanser Tablets (GlaxoSmithKline) and the Retainer Brite® Cleaning Tablets (DENTSPLY International Raintree Essix, FL, USA). The plastic material used in this experiment was the cold-cure acrylic Palapress® vario (Heraeus-Kulzer GmbH, Hanau, Germany). Images of the biofilm formed by Streptococcus pyogenes were obtained using a confocal laser scanning m icroscope. The images were analyzed using Comstat 2 software. The results showed that all the three investigated methods had a disinfectant effect. Corega Denture Cleanser Tablets reduced most of the biofilm formed on the plastic substrate.