A 13-year-old girl undergoes preventive examination. No complaints from the patient. Objectively: on the 36 masticatory surface there is a carious cavity within enamel with wide inlet. Enamel of the cavity floor and walls is dense and pigmented. Probing of the carious lesion is painless. No reaction to thermal stimuli. Tooth percussion is painless. The girl belongs to the I group according to her health status. Make the diagnosis: