Sometimes, a dead body will be so devestated (i.e. burned beyond recognition) that identifying the victim by the usual means of DNA testing, face recognition, and so on cannot be used. In such cases, investigators are left with no choice but to use the victim's dental records to find out their identity.
In fictional works, this scenario has become a kind of short hand for telling the audience that this death is even more gruesome than usual, and adds another layer of complexity to the plot (Was the body really correctly identified? What if the records are missing? etc.). Also Truth in Television
A common trope in police procedurals, medical mysteries, and forensic shows such as CSI