A 48-year-old woman complains of low-grade fever and a gradually enlarging ulcer on her gingival mucosa near the molars; the teeth in the affected area are mobile. Objectively on the gingival mucosa between the lower left molars there are two superficial sharply painful ulcers with undermining margins. Floor of the ulcers is granulated and covered in yellow-gray coating. Small tubercles surround the ulcers. Tooth cervices are exposed, pathologic tooth mobility is observed. Regional lymph nodes are enlarged, painful, and matted together into dense clusters. Make the provisional diagnosis: