A patient has 5mm probing depths, 8-9mm clinical attachment loss, 5 missing teeth, and 40% generalized bone loss. The patient smokes and has diabetes. What is the periodontitis stage and grade?

Having lost 5 teeth due to periodontitis meets the specific criterion for Stage IV (≥5 teeth lost due to periodontitis), even though the attachment loss alone might otherwise suggest Stage III. The presence of both smoking and diabetes — established grade-modifying risk factors — shifts the grade up to Grade C (regardless of the calculated bone-loss/age progression rate), giving Stage IV, Grade C.