If you do something by the "skin of your teeth," you're barely managing to do it. One of the first recordings of this phrase is from the Bible.
如果你通過“牙齒的皮膚”（skin of your teeth）來做某件事，這說明你勉勉強(qiáng)強(qiáng)有能力做這件事。這個(gè)短語最早出現(xiàn)在《圣經(jīng)》中。

In Job 19:20, Job says, "My bone clings to my skin and to my flesh, / And I have escaped by the skin of my teeth."
在《約伯記》第19章第20節(jié)中，約伯說：“我的皮肉緊貼骨頭，我只剩牙皮逃脫了?！?/p>

Teeth don't have skin, so it was likely an allusion to something small or so thin that it was insubstantial.
然而牙齒并沒有皮膚，所以這一說法可能代指小、纖薄而不重要的東西。