Having some clipping issues I'd like to fix, but so far, despite looking I haven't found a .nif with the vampire teeth. Solved: they are stored, in argonians case, in skyrim\Data\Meshes\actors\character\character assets\mouth\mouthargonianchargen.tri using the handy blender tri script, it was trivial to shorten them. I didn't think that it was a .tri morph, but now that I know it makes perfect sense.