In that case, re-treatment (repeating the root canal treatment) is the preferred treatment. However, the tip of the root and the inflammation or cyst may sometimes have to be surgically removed too.
This is needed when the nerve canal is no longer accessible (e.g. because a false tooth has been placed) or when a cyst does not shrink after proper (re)denervation. The procedure takes place under local anaesthesia and takes only half an hour.
