The new year is upon us. That means resolution time. Millions of people will dive into the anxifying world of self-improvement—through diet, exercise and whatnot. One thing that's sure to be flying off drug store shelves: teeth whitening treatments.

Bleaching and scrubbing our pearly whites (so they become pearlier and whiter), has become an $11 billion-plus national obsession. Some of these off-the-shelf products, and even dental office procedures, have downsides. Before you beautify those canines, here are a few things to consider.

How did we get here?

Teeth whitening has been cultural compulsion going back to the Egyptians, who mixed wine vinegar with crushed pumice to polish their smiles. Even worse were the early Romans. (Skip this next part if you're squeamish): They used urine to whiten their teeth;