There are many reasons for pain after filling, including dental nerve pain and periodontal pain. If the tooth is filled directly and is close to the nerve, the expansion of the filling material will put pressure on the nerve and cause irritation and pain, which can be left alone if it can be relieved in a day or two. If the pain persists, or if there is an exposed pulp hole that was not detected during filling, and the pain is difficult to sleep after filling, this is a symptom of pulpitis and requires root canal treatment of the tooth. Pain after filling may also be caused by overfilling material and pain due to occlusal trauma, in which case an adjustment of the bite is required. It is also possible that the filling material has an overhang that causes pain in the gums. If the filling is made of silver-mercury and the opposing tooth is a dissimilar metal, the contact with the saliva medium will cause an electric current that will cause pain. If the filling is a root canal treatment and not a one-time filling, the pain that occurs in this case may be caused by imperfect dental treatment, such as pulpitis that occurs when the tooth nerve is not completely removed. Therefore, the pain after filling may be caused by the residual nerve, or the filling material is too high, or the nerve is already exposed.