This project aims to evaluate the effect of antimicrobial photodynamic therapy (aPDT) in deep carious lesions. This study was approved by the Research Ethics Committee and was conducted on 53 patients between 3 and 12 years. Patients included in the study should have at least one primary molar or permanent with deep active caries and limited occlusal/proximal surfaces involving beyond the inner half of dentin. The investigators considered from exclusion criteria children whose parents refuse to sign the informed consent document; children who do not cooperate with the clinical examination/treatment; children with syndromes or chronic systemic diseases; teeth with painful symptoms consistent with irreversible pulpitis or mobility; periodontal changes; roots with pathological resorption; cases of primary teeth roots in an advanced stage of physiological resorption and patients that have made the use of any antibiotics during the study period or within three months prior to its beginning. The treatments were carried out after local anesthesia and isolation of the operative field with a rubber dam. The removal of carious dentin surface demineralized necrotic and not subject to remineralization was held with the drill at low rpm under cooling with sterile saline. The removal of decayed tissue will start with the side walls and later on the pulp wall. After this time the intervention with aPDT using 0.01% methylene blue as photosensitizer will be held. Finally, the cavity is restored with an adhesive and composite resin system. To collect data for the first outcome the dentin samples were collected from 23 participants with the help of spoon sterile dentine in two stages: C1 after digging and C2 after aPDT. The microbiological analyzes will be conducted by counting colony-forming units (CFU / mg of carious dentin), blindly from coded samples. The viability of microorganisms will be evaluated in the following culture media: Brain Heart Infusion agar for the feasibility of total microorganisms; CHROMagar candida to Candida genus; Mitis Salaviarius agar with the addition of bacitracin 0.2 U/mL, sucrose and glucose to Streptococcus mutans; Mitis Salivarius agar to total Streptococcus; Rogosa Agar to Lactobacillus spp. and enterococcosel for Enterococcus genus. The reproducibility of the counting method will be verified between triplicates. Microbiological data will be evaluated with appropriate statistical tests with a level of 5%. For the second outcome, a randomized clinical trial was designed. Primary molars of 30 patients (mean age 6.15 years) with deep caries lesions without signs and symptoms of pulpal involvement were selected. A total of 64 teeth were randomly divided into groups G1 (SCR, 32 teeth) and G2 (SCR + aPDT, 32 teeth) for treatment, restored with composite and evaluated after a week (T0), 6 months (T1), and 12 months (T2) according to the criteria of FDI. Groups were compared using the Rao-Scott chi-squared test and the logistic regression analysis for complex designs to ac- count for multiple observations per subject (alpha = 0.05). All participants answered a questionaire to detect the impact on Oral Health-related quality of life(OHRQoL) before and 3 months after the treatment. Based on this project we prove the clinical efficacy of aPDT using 0.01% methylene blue as an adjunct in reducing microorganisms from the interior of deep carious lesions and we contributed to demonstrate the clinical and radiographic success in a follow-up from 12 months providing additional support aPDT used as an adjunct to SCR on the longevity of composite resin restorations in primary molars. A low laser therapy (aPDT) with SCR did not influence negatively OHRQoL. In the practice of pediatric dentistry, this conservative dental treatment improved the OHRQoL after 3 months of follow up.

Inclusion Criteria:

• Patients included in the study should have at least one primary molar or permanent with deep active caries limited occlusal / proximal surfaces involving beyond the inner half of dentin.

Exclusion Criteria:

• Children whose parents refuse to sign the informed consent document
• Children who do not cooperate with the clinical examination/treatment
• Children with syndromes or chronic systemic diseases
• Teeth with painful symptoms consistent with irreversible pulpitis or mobility
• Periodontal changes
• Roots with pathological resorption
• Cases of primary teeth roots in advanced stage of physiological resorption and patients that have made the use of any antibiotics during the study period or within three months prior to its beginning