by the skin of one's teeth肯定不是字面意思“靠牙齿的皮肤”，它是一个习惯用语，可以意为“侥幸，勉强”。

【例句】
I made the 5 o'clock train by the skin of my teeth.
我勉强赶上了5点的火车。

We managed to complete the project on time by the skin of our teeth.
我们勉强按时完成了这个项目。