Introduction: Molar Incisor Hypomineralization (MIH) is a qualitative defect of enamel development that occurs in the mineralization phase. MIH affects one or more permanent molars and, occasionally, permanent incisors. The aim of the proposed study is to evaluate the clinical effect of antimicrobial photodynamic therapy (aPDT) on permanent teeth with MIH through decontamination and sensitivity control. The longevity of the restorations will also be evaluated after the deproteinization procedure. Methods and analysis: Patients 8 to 12 years of age with permanent molars will be randomly allocated to three groups. Group 1: selective chemical-mechanical removal of carious dentinal tissue around the walls of the cavity with Papacárie Duo and a curette followed by the application of aPDT and deproteinization with Papacárie Duo; Group 2: selective removal of carious dentinal tissue around the walls of the cavity with a curette, followed by the application of aPDT and deproteinization with a 5% sodium hypochlorite solution; Group 3: selective removal of carious dentinal tissue using a curette. The selected teeth must have a carious lesion in the dentin and post-eruptive enamel breakdown on one or more surfaces with an indication for clinical restorative treatment. The teeth will subsequently be restored using a mixed technique with resin-modified glass ionomer cement and bulk-fill composite resin. The data will be submitted to descriptive statistical analysis. Associations with age and sex will be tested using either the chi-squared test or Fisher's exact test. Pearson's correlation coefficients will be calculated to determine the strength of correlations between variables. Comparisons of the microbiological results (colony-forming units) will be performed using ANOVA and the Kruskal-Wallis test. Kaplan-Meier survival analysis will be performed to assess the performance of the restorations.

Inclusion Criteria:

• Healthy children with no adverse systemic conditions;
• At least one permanent first molar with MIH and active caries on the dentin with post-eruptive fracture on a single surface or multiple surfaces with an indication for restorative treatment; direct view and access; no clinical or radiographic signs or symptoms of pulpal involvement;
• Hypomineralized enamel with opacities near the margins of the cavities;
• Occurrence or non-occurrence of dentinal sensitivity.

Exclusion Criteria:

• Clinically: carious lesion only involving the enamel, deficient restorations, small carious lesions in dentin (without access to manual excavator), hidden caries, clinical sign or symptom of pulpal involvement, clinical impossibility of restoration;
• Radiographically: evidence of pulpal involvement;
• Teeth severely affected by MIH without indication for restorative treatment;
• Partially erupted teeth with MIH.

The information collected from the participants will be transcribed into a database replacing the individuals' names with the registration number of the evaluation form. The datasets (Excel spreadsheets) generated from this protocol will be available from the corresponding author (Sandra Kalil Bussadori - sandra.skb@gmail.com) upon any reasonable request. However, reuse of this data will not be permitted for anyone who is not an author of this paper.

The data will be available as soon as the article with the findings will be published in a peer-reviewed journal.

The datasets from this protocol will be available from the corresponding author (Sandra Kalil Bussadori -sandra.skb@gmail.com) upon any reasonable request.

An independent assessor blinded to the allocation to the different groups will perform evaluations after 48 hours and at three-month intervals for a follow-up period of 12 months.