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.

Objective: The aim of the proposed study is to determine whether photobiomodulation combined with a new self-cure resin improves hypersensitivity in molars with MIH and caries (primary outcome). Secondary outcomes include assessing the clinical performance of the self-cure composite resin in terms of restoration longevity and comparing the effectiveness of three interventions-photobiomodulation combined with self-cure resin, self-cure resin alone, and photobiomodulation combined with bulkfill photopolymerizable resin-in controlling hypersensitivity over time.

Methods and analysis: Permanent molars with MIH in patients eight to 12 years of age will be allocated to three groups. Group 1: photobiomodulation + self-cure composite resin restoration; Group 2: self-cure composite resin restoration; Group 3: photobiomodulation + restoration in bulk-fill photopolymerizable composite resin. Photobiomodulation will be performed in a single session involving low-level laser administered to four different points. The laser will be used at a wavelength of 808 nm, power of 100 mW and energy of 1 J per points; irradiance will be 3571 mW/cm², with a total radiant exposure of 35.7 J/cm². Data normality will be checked using the Shapiro-Wilk test, and variance homogeneity will be assessed with the Levene test. Descriptive statistics will be used to present the data, with continuous variables expressed as mean and standard deviation, and categorical variables by relative frequency. To compare the VAS and SCASS scales, repeated measures ANOVA will be employed, considering the 3 groups and 5 time points. Bonferroni adjustment will be applied for post-hoc comparisons. Sphericity will be tested with Mauchly's test, and if violated, Greenhouse-Geisser correction will be applied. A significance level of 0.05 will be adopted. Ethics and dissemination: This protocol received approval from the Human Research Ethics Committee of Nove de Julho University (certificate number: xxxxxxx). The legal guardians of the children will agree to participation by signing a statement of informed consent. The results will be published in a peer-review journal and the data will be made available upon request.

Inclusion Criteria:

• Male and female children;
• Eight to 12 years of age;
• At least one permanent first molar with MIH (codes 5 and 6 of molar-incisor hypomineralization severity scoring system [MIH-SSS])
• Presence of hypersensitivity
• Direct viewing and access.

Exclusion Criteria:

• Clinically: signs or symptoms of pulp involvement;
• Radiographically: evidence of pulp involvement (initial periapical radiograph);
• Teeth with MIH with no indication for direct restorative treatment (multiple surfaces associated with large extensions);
• Partially erupted teeth;
• Previous restorative treatment.

Clinical assessments after 48 horas as well as four, eight and twelve months after treatment (follow-up) will be performed by an examiner blinded to allocation (single-blind study).