A 20-year-old patient complains about gingival pain and hemorrhage she has been suffering from for a week. The pain is getting worse during eating, hemorrhage is usually induced by mechanical stimuli. Objectively: there are evident hyperemia and edema of gums in the area of inferior frontal teeth. Apices of gingival papillae are dome-shaped, enlarged. Gum palpation causes pain, slight hemorrhage. No roentgenological changes were revealed. What is the most probable diagnosis?