Examination shows that tooth 47 touches a deep defect in the patient's buccal mucosa. The margins of the defect are dense and clear, the floor of the defect is gray. Microscopy of the biopsy material obtained from the wall of the defect detected a purulent exudate on the floor of the defect. Under the exudate there is an area of necrotized tissue with underlying granulation tissue that transforms into mature fibrous tissue. What pathology has developed in the patient's cheek?