The labio-dental sounds are articulated by the lower lip against the upper teeth, eg. /f/.

唇齿音由下唇与上齿连接发出，例如 /f/。

youdao

Pull your partner close to you and while you kiss him/her gently bite on the lower lip.

把你的伴侣拉近，同时轻轻地夺取他/她的下唇。

youdao

She’s lived on a dock the size of two pool tables built into the lower lip of a bridge for 37 years.

她的栖身之地有两张台球桌大小，蜷缩在桥下一个凹陷之处，一住就是37年。

youdao

He had a misshapen lower lip and his head sometimes when he when he was talking would seem convulsed to the right.

他的下嘴唇存在畸形,当他说话的时候

耶鲁公开课 - 欧洲文明课程节选

The line of his jaw is symmetrical and his lips are full, the lower lip slightly thicker than the upper.

NEWYORKER: Labyrinth

His nose had been broken and his mouth was cut at one corner and the line of the scar across the upper lip and lower jaw showed through the growth of beard over his face.

NPR: Robert Jordan, Hemingway's Bipartisan Hero

The goatee, as you might expect, is reserved for intellectuals, while a longer moustache, drooping over the upper lip to touch the lower one, well, that's the sure sign of an old-fashioned leftist.

BBC: Moustaches under threat