After having a look at it, it seems like it is the teeth meshes clipping through the face. They extend a lot further beyond the edges of the vanilla teeth meshes. Since they aren't skinned, there's nothing preventing them from clipping during extreme facial deformation. I made some adjustments and it seems to have cured it, based on some quick tests. Try the attached and see how it goes.
K1_Kira_Teeth_Fix_Beta.7z