<modsnip> we know that a partial skull was recovered. Presumably some teeth were intact in the skull fragment. Dental X-Rays record the position and shape of the teeth in relation to each other. The structure of the bones around the teeth. Even the roots are distinctive. And of course, any fillings or other work done.
It is unlikely a positive odontological ID would be done with just random scattered teeth.
They can, however, extract DNA from teeth and teeth fragments. So, as was posted upthread, this is a secondary way that an ID can also be confirmed. Since we know that the latter hasn't been done yet, we can assume (occam's razor) that the former technique was used instead.
Since it's possible no bone marrow was recoverable, it might be difficult to get a DNA match via the skull itself.
The FBI has confirmed Brian as deceased through his remains. They are confident enough to issue a statement to that effect. That should be the end of it. JMO, but I think that continuing speculation of a criminal conspiracy with the parents planting corpses or corpse body parts to fool LE and 'pretend' BL is deceased does this case a massive disservice. MOO