6Your 65 year old patient has 18 teeth in their oral cavity….

6Your 65 year old patient has 18 teeth in their oral cavity.  The patient tells you their 3rd molars were extracted when they were 16 years of age.   The other teeth were extracted due to periodontitis.   The FMX you took shows horizontal and vertical bone loss that is equal to or greater than 50% of the root length.   According to the AAP guidelines what Stage is their Periodontitis?