Do you have a smooth transition between Head and Jaw root?





Bone names might be different, but only 2 bones should have an influence for the upper face/head mesh here.
Next in series are Neck bones which should have 0 influence above the chin.



So inspect your rig closely....

I fixed it by re-importing, re-rigging it, and re-painted the skin weights. 

I think the program broke. Once I reimported it, it worked.
However, when I play the facial animation Lipsync in the animator the teeth don't move. they are rigged. The Tongue moves but the bottom teeth don't not sure why not. Do I need to create Blend shapes for the teeth as well? If so what do I call them?