A 28-year-old woman complains about acute pain on the left of her upper jaw during eating. 6 days ago the 28 tooth was extracted, after that the pain came. The patient considers that extraction of the 28 tooth caused "damaging"of the next tooth. Objectively: alveolus of the 28 tooth is at a stage of healing. On the distal surface of the 27 tooth there is a carious cavity in the precervical area that doesn’t communicate with the tooth cavity. Cold stimulus causes short attack of pain. Dentin of walls and floor is light and softened. Probing of the floor is painful. What is the most probable diagnosis?