It's just the sky . . When I was a child, a classmate often bit his lower lip with his upper two front teeth, and later found that his lower lip obviously went in. . .

In fact, many bad mouth shapes are related to teeth. . The landlord can see if the teeth need to be corrected, which may be helpful to the mouth shape.

As for daily life, maybe you can try this method I mentioned. Bite your lower lip with your two front teeth.