A 28-year-old patient hadan appointment with a dental surgeon to prepare the oral cavity for a prosthesis. Examination revealed that the 11 tooth crown was decayed, the root was stable, its percussion was painless. The mucous membrane of the alveolar process was not changed. Ro-gram of the alveolar process shows widening of periodontal ligament space in the region of the 11 tooth. Alveolar process structure is not changed. The root canal was passable all through. What is the most likely diagnosis?