A patient smokes more than 10 cigarettes per day, presents with a collapsed bite, malocclusion with tooth migration, and 15% radiographic bone loss. According to the 2017 World Workshop classification, what is the periodontal staging and grading?

According to the 2018 classification system (from the 2017 World Workshop), Stage IV periodontitis is defined by the presence of masticatory dysfunction — including bite collapse, tooth drifting/migration, flaring, and secondary occlusal trauma — in addition to the severity criteria of Stage III (CAL ≥5 mm, bone loss extending to the middle or apical third of the root, tooth loss due to periodontitis). The patient's collapsed bite and malocclusion with tooth migration fulfill Stage IV complexity criteria. Grade C (rapid progression) is assigned when risk modifiers are present: smoking ≥10 cigarettes/day is a direct Grade C modifier. A 15% bone loss in isolation might suggest Stage II, but the functional impairment elevates this to Stage IV. Grade C reflects the patient's heavy smoking history.