An 8-year-old child complains about pain in the 21 tooth that is getting worse during biting down. A month ago a part of tooth crown broke off as a result of a fall. The child didn't consult a dentist. Objectively: in the region of medial angle of the 21 tooth there is a crown defect that makes up 1/3 of the crown's height. Tooth cavity is open, probing and thermal stimulus cause no pain. Percussion is acutely painful. Gum around the 21 tooth is edematic and hyperaemic. What is the provisional diagnosis?