Part of the mouth interior. Specifically where the interior attaches to the tongue. Again, mudbox painting. You'll find it useful to have various body parts as seperate pieces while painting, masking and toggling visibility. Especially the eyes and various mouth parts. I won't bother describing the cross uv UDIM tile painting method I use, you've probably already come up against that in Blender. If you need help with that still I can describe how I do it in Mudbox, it's similar, I imagine, in Blender. Teeth dont really need much in the way of diffuse texturing, a flat off white fill with a very faint occlusion map works well. Teeth visual properties are handled mostly by SSS.