A 28-year-old man came to a dentist with complaints of pain in his lower left tooth. The pain is provoked by sweet foods and stops immediately after the stimulus is removed. Objectively, the distal surface of tooth 34 has a deep carious cavity filled with soft pigmented dentin. Probing the of the cavity floor is painful. No communication can be detected between the cavity and the pulp chamber. Thermal stimulation results are positive, short-term. What diagnosis can be made in this case?