With most checkpoints, "o"-shaped (circular) mouth can be reproduced with prompt (:0), but its size may be larger or smaller than expected. With this LoRA, mouth size can be fixed to large size or small size.
Use with open mouth, (:0) prompt. If you want to make teeth visible, add prompt like upper teeth and so on. If it does not form a proper round shape, try increasing weight of (:0).
Mouth size can be adjusted by LoRA weight (approximately 0.25 to 1.5). Stronger weight makes smaller mouth. Minus weight is not tested for this LoRA.