Not only does a corpse reveal sex, age, race and other information critical for identification, but the cause of death, the probable weapon involved, and even something about the killer. For instance, in the Archambault case, the manner in which the victim had been mutilated suggested someone familiar with dismemberment. Sure enough, Archambault had worked as a butcher. Not only that, but the particular pattern of cuts left in bone by knives and saws can be analyzed to identify specific implements used in the murder. This is the preserve of the forensic dentist.
Teeth are the most durable part of the human body from which positive identifications are possible.
Useful as it is in individual deaths, forensic dentistry is an especially valuable tool in the case of mass disasters, such as plane crashes. But, as Dorion pointed out, he is the only forensic medical examiner who is also called upon to treat living victims. We can measure it to determine who might have inflicted a wound, say, in a child abuse case. And we can use it to identify the dentition when the assailant isn't human, but, for instance, a dog. Since even the relatively sanitary slides Reichs and Dorion presented had some in the audience flinching, the obvious question of why one chooses their profession came up.