A 28-year-old woman came to a dentist with complaints of a cavity in her upper right tooth. Objectively, on the masticatory surface of tooth 16 there is a carious cavity with a wide opening. The cavity is located within the parapulpar dentin and filled with dense pigmented dentin. The carious cavity does not communicate with the dental cavity. Probing of the carious cavity walls and floor, cold stimulus, and percussion cause no pain. Electric pulp testing-12 microamperes. What is the most likely diagnosis?