A 5,5-year-old child is undergoing preventive examination. No complaints from the patient. Objectively: in the precervical area of buccal surface of the 75 tooth there is an enamel patch with loss of natural glossiness. The enamel surface is coarse, painless on probing. Tooth percussion is painless. Thermodiagnosis is negative. Damaged enamel stains with 2% water solution of methylene blue. Make the diagnosis: