This randomized clinical trial compares Er:YAG laser-assisted and conventional rotary cavity preparation in children aged 6-12 years with molar-incisor hypomineralization. A total of 52 children are randomly assigned to one of the two preparation methods. The study evaluates pain, dental anxiety, sensory experiences, physiological responses, patient comfort, need for local anesthesia, and procedure duration. Postoperative discomfort and the clinical performance of restorations are also assessed during follow-up visits at 1, 3, and 6 months.