I would say that modeling teeth with geometry is very easy. The material, lighting, and rendering is the challenge, especially when you consider all of the occlusion (and hard/soft body dynamics) from your lips that is inevitable with teeth.

Some form of subsurface scattering[1] is a must, and not easily done in games/apps because you can't really "bake" it like you do for most other textures to run performantly.

[1] https://en.wikipedia.org/wiki/Subsurface_scattering#:~:text=....