Your 65-year-old patient presents with 18 teeth remaining. T…

Your 65-year-old patient presents with 18 teeth remaining. They report that their third molars were extracted at age 17, and the remaining missing teeth were lost due to periodontitis. A full-mouth series (FMX) reveals horizontal and vertical bone loss equal to or exceeding 50% of the root length. According to the AAP 2017 classification guidelines, what is the appropriate Periodontitis Stage for this patient?