Dead (devitalised) teeth are teeth that have had root canal treatment in the past, in which the nerve of the tooth had to be removed. They differ from the other teeth in the mouth in being greyer in colour, and they break more easily. Sometimes these teeth need to be ‘covered’ with a crown to protect them from breaking. Devitalising a tooth involves removing the nerve and cleaning and disinfecting the root canal. Sometimes this procedure is not entirely successful and bacteria remain in the canal, which can be seen on an X-ray even if the patient feels no pain or discomfort in that tooth. Moving teeth with this kind of ‘hidden’ inflammation can make the process flare up and cause symptoms – pain in the tooth. This needs to be distinguished from the normal discomfort that teeth with braces feel while they are moving.
This answer is for general information. Your own case needs an examination by an orthodontist.