The objective of this study is to investigate the effect of Antimicrobial Photodynamic Therapy mediated by Erythrosine and blue LED in the reduction of bacteria in dental biofilm. This clinical trial will be carried out with 30 patients who have biofilm, but without the presence of periodontal pockets, and who are being treated at the Dental Clinic of Universidade Metropolitana de Santos. A split-mouth model will be used (n = 30), with group I control - conventional treatment and group II - conventional treatment and antimicrobial photodynamic therapy (aPDT). The bicarbonate jet will be used to remove dental biofilm in both groups. The treatment will be carried out in 1 session. aPDT will be performed before cleaning/prophylaxis, only in group II. Participants will rinse with the photosensitizer erythrosine (diluted to 1mM) for 1 min of pre-irradiation time, so that the drug can stain all the bacterial biofilm. Then, the D-2000 LED (DMC) will be applied, emitting at a wavelength of ʎ = 430-490 nm and 900-1100 mW/cm2. Irradiation will be performed until the biofilm of the cervical region is illuminated for 2 min per point. Each irradiation point will be approximately 0.4 cm2. The microbiological examination will be performed from samples of supragingival biofilm collected from the gingival sulcus. Two collections will be performed in each experimental site before irradiation, and immediately after the irradiation procedure (group II) or prophylaxis (groups I and II). Biofilm samples will be collected before and after exposure, respectively, and sent to the microbiological laboratory for colony counting. After this period, the CFU's will be counted and the data will be submitted to statistical analysis for comparison of pre and post-treatment results and between groups (conventional X aPDT).

Inclusion Criteria:

• The participant must present between 25% and 50% of biofilm index;
• Have at least 20 teeth present, without clinical probing depths greater than 3 mm.

Exclusion Criteria:

• Smokers;
• Uncontrolled diabetics or hypertensives;
• Cancer or its treatment;
• Pregnant women;
• Use of antibiotics in the last 6 months;
• Coagulation disorders (use of anticoagulants, presence of liver diseases, thrombocytopenia and immunosuppression);
• Patients undergoing orthodontic treatment.

The data sets generated in the study will be available from the corresponding author at a reasonable request. Once the data is entered electronically, participants identification details will no longer be attached to their data, they will be reported only by numbers. After the analysis of the data, volunteers will be invited to a meeting and the results will be shared, in case they wish to attend it. The authors intend to publish the results in a peer-review jornal and present them in cientific events.