A 50-year-old patient complains about problems with mastication, tooth mobility, halitosis, gingival hemorrhages. Objectively: gums are hyperemic with cyanotic colouring, there is dental calculus. Parodontal pouches of the superior molars are 8 mm deep, the pouches of other teeth are 6 mm deep. X-ray picture shows resorption of bone tissue by 2/3-1/2 of root length. What is the most likely diagnosis?