By the skin of your teeth (idioms #1)

To do something by the skin of your teeth is to barely achieve or accomplish something almost to the point of failure.

i.e. She may have passed the first midterm of organic chemistry by the skin of her teeth, but only divine intervention can save her butt on tomorrow's final!

Not surprisingly organic chemistry is an infamous right of passage for many a spirited or disenfranchised pre-dental and pre-med student, but even more (un)shockingly, human teeth don't actually have skin.

!!!

That's right folks! The tooth consists of FOUR major tissues, none of which is the epidermis.

Here they are:

1) Tooth enamel - the visible part of your tooth. Can range from brown to yellow to grayish-white in color. Also the hardest part of your body!
2) Dentin - found underneath the enamel but surrounds the pulp. Most of a tooth is composed of this stuff.
3) Pulp - the center part of the tooth. Consists of nerves and living connective tissue. A root canal removes this stuff.
4) Cementum - covers the root/non-visible part of your teeth.



Thanks to the NIH for the hot pic

Eric