A 45-year-old woman complains of bleeding gums. The bleeding occurs when she brushes her teeth or eats hard food. Objectively, in the frontal area of her lower jaw the gums are hyperemic, edematous, and bleed when palpated. In the other areas, her oral mucosa is normal. The woman has a deep bite. Her teeth are stable, except for teeth 41 and 31 that have the I degree of mobility X-ray shows resorption of the interalveolar septa in the area of teeth 42, 41, 32, and 31 to 1/3 of the root length. What diagnosis can be made in this case?