A 14-year-old girl complains of bleeding gums and foul smell from her mouth. Objectively: gingival mucosa is hyperemic, pastose, hemorrhaging. Schiller-Pisarev test is positive. Papillary marginal alveolar index is 70%. Fedorov-Volodkina Hygiene Index equals 3. X-ray of the frontal area of jaws demonstrates retained cortical plate. Make the diagnosis: