What would cause a person to be unable to open their mouth after having their wisdom teeth removed?

Trismus: Must go away soon or go back to the dentist. Check if you have numbness. It can take up to a month to be normal again. It is not uncommon.

Trismus: You may be experiencing a temporary condition called "trismus". Usually if you gently practice stretching your mouth open by placing your pointer on your lower front teeth and your thumb on your upper front tooth applying gentle pressure throughout the day, this helps to slowly allow your mouth opening ability to return to normal. Return to the treating dentist for a more definitive diagnosis.