BMJ Group Medical Reference
Doctors call this operation a percutaneous glycerol rhizotomy. It is done under a short-acting general anaesthetic, so you'll be asleep during the operation. You probably won't need to stay in hospital afterwards.
The doctor puts a thin needle through your cheek and through an opening in your skull, to the point where the three nerve branches join. He or she then injects a small amount of a chemical called glycerol into the space around the nerve. This is to damage the nerve and block pain signals. 
This operation can be repeated if it doesn't work. You are likely to be left with some permanent numbness or tingling in your face afterwards. 
You may have a type of medicine called a general anaesthetic when you have surgery. It is given to make you unconscious so you don't feel pain when you have surgery.
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