A 23-year-old young man complains of acute bleeding from the guys and bad breath that appeared 5 days ago. Objectively, the interdental papillae and the gingival margin are bright red, edematous painful, and bleed intensely when palpated. Gingival pockets are 2-3 mm deep. X-ray shows marked osteoporosis of the interalveolar septa and widening of the periodontal fissure around the apices of the interalveolar septa. The lamina dura is intact. What is the most likely diagnosis in this case?