A 34-year-old man complains of acute spasmodic pain in the region of his upper jaw on the left that is aggravating when affected by cold stimuli. Toothache irradiates to the ear and temple. He had acute toothache in the 27 tooth one year ago, but he did not consult a dentist. Pain recurred three days ago. Objectively: the 27 tooth has a carious cavity communicating with the dental cavity. Probing of the opened carious cavity is extremely painful. X-ray picture shows widening of periodontal fissure at the root apex of the 27 tooth. What is the most likely diagnosis?