A 28-year-old man came to a dentist for the purpose of sanation. Objectively, on the masticatory surface of tooth 47 there is a deep carious cavity that communicates with the dental cavity. Probing of the cavity is painless, the tooth is non-responsive to thermal stimuli, its percussion is painless. Electric pulp testing -108 microamperes. X-ray shows traces of filling material in the root canals of tooth 47, the periodontal fissure is widened and deformed in the apical region. Make the diagnosis: