What to do if i cannot open mouth wide enough for wisdom tooth extraction?

Difficult problem.: It depends if it is an acute or chronic problem. Many patient with infected wisdom teeth have restricted opening due to infection. If you take antibiotics, the opening should improve. If you have a permanent decrease in opening - could be a problem. See an oral surgeon who can tell you the reason for your restricted opening. Then first you would address the restricted opening. Then the teeth.

Very common, trismus: The most common complication after wisdom tooth extraction is trismus, also called tightness in the jaw muscles. See your surgeon for post-op examination and treatment.