A 44-year-old man complains of indisposition, fever of 38°C, and a swelling under the lower jaw on the left. The patient's history states that throughout the last week he felt pain in the area of his tooth 36. Objectively, in the left submandibular area there is an enlarged painful nodule. The skin above the nodule is hyperemic, strained, and cannot be pinched. Tooth 36 is partially destroyed in the oral cavity. What diagnosis can be made in this case?