The problem here, is that the teeth are separate models entirely, attached too a bone. But they are having some issues and seemingly not having tips too them? as it looks like vertices got deleted on importing.
Alongside of that issue, there are random little dark spots on the model. And im not quite sure what could be causing them.
It could be an issue with a modifier or more if you are using blender.
When you do an export, all modifiers are applied, so you could try applying the modifier one by one inside blender to see if the same issue came in.
It could be an issue with a smooth modifier that could explain the dark sport and lost of vertices.
Make sure your different model & armature have proper Transform set to default 0 or 1.
Could be a few issues maybe import/export settings maybe it’s normals. Can you post a photo of what the model originally looked like in your modeling program
Little difficult to tell as the original is unlit, but it almost seems like an issue with normals, maybe try recalculating those, or in unreal you could try the fix inconsistent normals function in modeling mode, there’s a few other settings there you could play around with as well to see if it fixes your issue
This is the wireframe of the model, I imagined its a bit much, so ive been doing retopology mostly on the model today, and trying to tone down the verts
Could it also be due that the model has a vary bland material, as this was just a test for now, and I brought it ingame to see how it would preform?
Looking at the vertices they do seem to be blunted here, this could be a number of reasons. Though I highly recommend re-topologizing before continuing if this is a game, as that will likely solve the issue. This was mentioned prior but high poly + normal issues can cause similar issues when it comes to very tight groupings like the teeth.
