For 2 days a man has been suffering from spontaneous nocturnal pain attacks in his tooth 25. The pain irradiates along the branches of the trigeminal nerve and alternates with brief painless intervals. Objectively, on the medial surface of tooth 25 there is a deep carious cavity within the parapulpar dentin. Probing of the cavity floor and percussion are painful. Thermal stimulation of tooth 25 provokes a pain attack. What is the most likely diagnosis?