I think V4's biggest (or most noticeable) flaw for open mouth is shading rather than geometry. There are some people who have done excellent work on shaders for some pretty convincing teeth, gums, tongues etc. On my computer I have some material room screenshots from stuff Vestmann was doing, in particular. I think he was working from something bagginsbill had started, but IMO took it further.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3