Our body is a trust from Allah. We must protect and preserve it. Therefore, it is not permissible for us to alter or tamper with our physical faculties unnecessarily. However, if there is a need to repair a damaged part of the body such as a fractured tooth, then there is nothing wrong with that, as the aim of Islam is to keep the Muslim away from all sources of harm, whether psychological or physical.
The Islamic Religious Council of Singapore states the following: Crowning the tooth is not forbidden in Islam, as it means repairing something that is broken.