Molar Incisor Hypomineralization (MIH) is a change in the formation of dental enamel of systemic origin that affects at least one of the first four permanent molars and usually affects incisors. During the eruption, the affected surfaces tend to fracture, exposing the dentin, which causes excessive sensitivity in addition to making the region very susceptible to the appearance of carious lesions. The objective of this research will be to evaluate the clinical effect of antimicrobial photodynamic therapy (aPDT) in permanent teeth with severe and sensitive MIH. The methodology will be based on the selection of patients from 6 to 12 years of age with permanent molar teeth, randomly divided in two groups. The selected teeth should have MIH on the occlusal surface, indicated for clinical restorative treatment. In Group 1, aPDT will be applied for the treatment of infected dentin. Afterwards, the teeth will be restored with high viscosity glass ionomer cement. In Group 2, the removal of the softened dentin around the side walls of the cavity with sharp dentine curettes and posterior restoration with high viscosity glass ionomer cement will be carried out. All patients will have clinical and radiographic follow-up with a time interval of 6 and 12 months. The data obtained will be submitted to descriptive statistical analysis to evaluate the association of categorical variables. Chi-square test and Fisher's Exact test will be used, and to analyze the correlation between the continuous variables, Pearson correlation test will be applied. For the analysis of dentin density in the scanned radiographic images and the microbiological results for colony forming units, ANOVA and Kruskal-Wallis will be applied.

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 will be made by two blind examiners, who will not know to which group the participants belong.