A 38-year-old patient consulted a dentist about aching pain in the region of the 48 tooth that is getting worse when biting down on food. Body temperature rise up to 37,6°C and aggravation of general condition is present. Objectively: insignificant swelling of retromolar region as well as hyperaemia of mucous membrane. The 48 tooth is covered with occlusal pad. It is painful on palpation. Purulent discharges are present. What is the most likely diagnosis?