MSFinals-1218

MSFinals-1218

A 28-year-old man presents with a swelling under the left jaw that comes and goes but leaves a dull ache behind. The problem has been present for around 2 weeks and is getting worse. The pain is most noticeable at mealtimes. In the last day, the swelling has become fixed and he reports an unpleasant taste in his mouth. He smokes five cigarettes a day and drinks ten units of alcohol a week, usually on a Saturday night. On examination, there is a smooth, tender swelling in the superior part of the left anterior triangle and, on inspection of the oral cavity, there is poor dentition and pus present just behind the lower incisors.
Which of the following is the most likely diagnosis?