When most people think of rats, they envision long, yellow teeth chewing away at everything in their path.
Rats are monophyodont, which means that they have one set of teeth during their lifetime.
In comparison, humans are polyphyodont, because we lose one set, then grow another. Rat molars are very similar to human molars. They begin to erupt around 16 days after birth, take about 125 days to completely develop, and are composed of a layer of enamel on the exterior. Enamel is the hardest substance in the body. Underneath the thin layer of enamel is dentin, which is a material very similar to bone.