Finally, there’s the enamel. The enamel’s job is pure protection. It surrounds the dentin, protecting it from bacteria, chewing ,and changes in temperature when eating hot and cold foods. However, it’s not the enamel that is affected by whitening agents, but the dentin (via Tower Dental Associates). When a whitening agent is applied to the tooth, the agent crosses over the enamel, and lightens up the yellow tint that is naturally caused by dentin.

And while ancient Egyptians used pumice and vinegars to whiten their teeth, ancient Romans took to the swilling of urine to whiten theirs. During the height of the Roman Empire, it was discovered that urine would indeed whiten teeth. It wouldn’t be until 1908 when Fritz Haber would synthesize ammonia for the first time (via WIPO Magazine), that ammonia would actually be “discovered,” however, ancient Romans figured out that the ammonia in urine would whiten their teeth. In fact, according to Smithsonian Magazine, Roman poet Catullus threw some shade at Roman Senator Egnatius in what could be considered the ancient form of a poetry slam by saying of him: “…what each man pisses, he’s used to brushing his teeth and red gums with, every morning, so the fact that your teeth are so polished just shows you’re the more full of piss.” Sort of makes the stomach turn, but at least your teeth will be white.