The goal of this clinical trial is to examine the clinical success of different pre-treatments in resin infiltration therapy applied to the incisors of pediatric patients with Molar Incisor Hypomineralization (MIH) and to evaluate the impact of treatment on the quality of life of children. The main questions that this study aims to answer are:

• Does resin infiltration therapy improve the color and surface appearance of incisors affected by MIH?
• Is there a reduction in tooth sensitivity after treatment?
• Are patients and their parents satisfied with the treatment results?
• Is there an improvement in the quality of life of children after treatment?

Researchers will apply resin infiltration therapy to incisors affected by MIH and evaluate the results over a 12-month follow-up period. Participants will:

• Receive resin infiltration therapy on their MIH incisors.
• Attend follow-up appointments at 1, 3, 6, 9, and 12 months.
• At the follow-up appointments, the teeth will be evaluated with clinical examination and photographs.
• Participants will complete questionnaires regarding tooth sensitivity and quality of life related to oral health.

The results of this study are expected to contribute to the development of minimally invasive treatment options for children with MIH.

Children aged 6-14 years with molar incisor hypomineralization (MIH) will be evaluated for the presence of opaque lesions in their permanent incisors. Children with opaque lesions will be divided into two groups based on the classification published by Ghanim et al. in 2015: those with opaque areas limited to creamy-white to yellow-brown color. Teeth showing other developmental enamel defects (fluorosis, enamel hypoplasia, amelogenesis imperfecta, dental caries, etc.) will be excluded. The teeth in each of the two groups will be further subdivided into three subgroups, and treatments will be performed using Icon® (DMG, Hamburg, Germany) for resin infiltration, Opalustre (Ultradent Products, Cologne, Germany) for microabrasion, and Coxo CA-1 (Foshan Coxo Medical Instrument Co., Ltd., China) for air abrasion, either individually or in combination. The groups and procedures to be applied are planned as follows:

Group 1: Creamy-White opaque area, Icon Group 2: Creamy-White opaque area, Opalustre + Icon Group 3: Creamy-White opaque area, Coxo CA-1 + Icon Group 4: Yellow-Brown opaque area, Icon Group 5: Yellow-Brown opaque area, Opalustre + Icon Group 6: Yellow-Brown opaque area, Coxo CA-1 + Icon Informed consent forms will be signed by patients and their parents who wish to participate in the study.

The color stability and sensitivity of the opaque lesions after treatment will be checked at 1, 3, 6, 9, and 12 months. Standard photographs will be taken with a DSLR camera before treatment and at all control appointments.

A spectrophotometer will be used to evaluate color stability. The Schiff Cold Air Sensitivity Test (SCASS) and Visual Analog Scale (VAS) will be used to assess sensitivity. The validated COHIP-SF-19 questionnaire will be administered to children before treatment and 3-6 months after treatment to assess their quality of life. Parents will also be administered the P-CPQ questionnaire to assess their child's oral health and quality of life.

Inclusion Criteria:

• The child must be between 6 and 14 years old,
• Diagnosed with molar incisor hypomineralization (according to EAPD criteria) and have lesions in the incisors,
• The tooth to be treated must not be cavitated or must not require restoration,
• Having the reading and writing skills to answer the scale,
• Having no communication impairments (auditory, visual, cognitive),
• Having no systemic illnesses that would affect oral health,
• Not taking any medications that would affect oral health,
• Both the child and their parents must be willing to complete the scale,
• Agree to attend the 12-month follow-up appointments.

Exclusion Criteria:

• Presence of enamel defects other than MIH in the target tooth, such as dental fluorosis, amelogenesis imperfecta, or enamel hypoplasia;
• Presence of significant caries, extensive dentin caries, large restorations, fissure sealants, composite restorations, or any existing restoration that may interfere with lesion evaluation in the affected tooth;
• Presence of spontaneous pain, abscess/fistula, suspected pulpitis, or need for endodontic treatment in the affected tooth;
• Presence of orthodontic appliances (e.g., brackets or bands) on the tooth to be evaluated that may interfere with color measurement;
• Known allergy or hypersensitivity to the dental materials used in the study;
• History of recent microabrasion, bleaching, resin infiltration, or similar procedures performed on the affected tooth;
• Inability of the participant to read and write sufficiently to complete the questionnaire;
• Presence of any systemic disease that may affect oral health;
• Use of medications that may affect oral health;
• Presence of any communication barriers (hearing, visual, or cognitive impairment) that may interfere with study participation;
• Refusal or unwillingness of either the participant or the parent/guardian to complete the questionnaire.