How can I smooth the ends of my mouth loops in zBrush? I want the ends of the lips to conform to some type of axis instead of just sticking out like this (messed up the mouth loops with Move Topological). Is this avoidable if I just extrude the mouth loop backwards so the mouth has an interior, which I can then use to…
Don't end the mesh at the lips, give your base mesh a mouth cavity of some kind. That will help to avoid the strange boundary issues you're seeing. Your mesh also looks incredibly dense around the lips compared to everything else. I'd try pulling out a few loops there.