The objective of this research was to evaluate the clinical effect of photodynamic therapy on dentin infected by caries lesion in permanent teeth with Molar Incisor Hypomineralization (MIH). The study was composed of Groups (1 and 2). The methodology was based on the selection of patients from 6 to 12 years of age with permanent molar teeth, randomly divided. The selected teeth had deep dentin caries lesions on the occlusal surface, and sensitivity, indicated for clinical restorative treatment. Photodynamic therapy was applied with the use of low-intensity laser in permanent teeth selected for the treatment of infected dentin in G1. In this group, antimicrobial photodynamic therapy (aPDT) and atraumatic restorative treatment (ART) were made. In G2, only ART was performed. The teeth were restored with high viscosity glass ionomer cement. All patients had clinical and radiographic follow-up with a time interval of 6 and 12 months. Data were submitted to descriptive statistical analysis. For the evaluation of the association of categorical variables like age and gender, the Chi-square test and Fisher's exact test were used. To analyze the correlation between the continuous variables, the Pearson correlation test was applied. ANOVA and Kruskal-Wallis were applied for the analysis of dentin density in the radiographic images scanned and the microbiological results for colony forming units.

Inclusion Criteria:

• Healthy children, without systemic alterations;
• Collaborative children;
• Present at least one permanent molar with active and acute caries lesion in dentin, not exceeding 2/3 and involving only the occlusal, with direct vision and access, without clinical and radiographic signs and symptoms of pulp involvement.

Exclusion Criteria:

• Child with systemic impairment;
• Non-cooperative behavior;
• Carious lesion of Class II, III, IV or V type of Black;
• Clinically: carious lesion involving enamel, deficient restorations, small carious lesions in dentin (without access to hand excavators), occult caries lesions, clinical sign and/or symptom of pulp involvement, clinical impossibility of restoration;
• Radiographically: evidence of pulpal involvement, carious lesion extending beyond 2/3 of the dentin.

Clinical evaluations of complete removal of caries lesion, microbiological and radiographic analysis were made by two blind examiners, who did not know to which group the participants belonged.