A 12-year-old girl complains of periodic bleeding in the area of her lower right tooth. Objectively, the masticatory surface. of tooth 46 has a carious cavity filled with a soft red tissue. Superficial probing is mildly painful, while deeper probing causes pain and bleeding. The tooth is almost unresponsive to thermal stimuli, Percussion. of tooth 46 is painless. X-ray detects no pathological changes in the periodontal region of the tooth. What diagnosis can be made in this case?