3D Face Mesh with Blend Shape Bug

I wanted to test face deformation using a 3D Face mesh with adjusted blend shapes but I got this pixelated teeth bug. Does anyone know how to fix this? Maybe I do something wrong?

I got the mesh from this source:

When you create “Face Texure” try firstly uncheck “fill eyes” and " fill mouth" and then click on " Create Face Texure"

When I uncheck the mouth another bug occurs. I think I need to use alpha texture in the opacity option. But I haven’t succeed in it yet. Btw, thanks for your response)