A 24-year-old patient complains of a growing tumour in the body of mandible on the right. The tumour growth has been observed for 5 months. Objectively: in the angle of mandible there is a swelling. Regional lymph nodes are not enlarged. Ro-gram shows a well-defined focus of bone destruction at the level of the 46, 47, and 48 teeth and in the ramus of mandible. The lesion is in form of individual cavities with osseous septa. The roots of the 46,47, 48 teeth are resorbed. What is the provisional diagnosis?