Ludwig angina

A 30-year-old man is brought to the emergency department for inability to open the mouth and pain and swelling on the lower jaw and upper neck that have been worsening over the past day. His temperature is 38.1˚C (100.6˚F), pulse is 102/min, respirations are 30/min, and blood pressure is 144/88 mm Hg. There is significant bilateral swelling of the floor of the mouth with involvement of the sublingual and submandibular salivary glands, and the right first and second molars are decayed and purulent. The skin of the upper neck and submandibular region is erythematous but the epidermis is intact. Which of the following is the most likely diagnosis?