A 35-year-old man has been hospitalized into a maxillofacial unit with complaints of mobility of the 38, 37, and 36 teeth and a fistulous tract in the socket of the extracted 35 tooth. The condition has been persisting for over 3 months. Insertion of a grooved probe into the fistulous tract palpated exposed coarse bone fragment that easily moved under pressure. X-ray of the lower jaw demonstrates a focus of bone tissue destruction, with a spot of dense bone tissue 0.5x0.3 cm in size. Make the diagnosis: