There are people out there who use urine to whiten their teeth. I can tell you how it works. Only you can decide whether you think it's worth it.
Life must have been tough back before there were any sanitized versions of necessities. There was a time when eating a pig meant going elbow deep in entrails, and when eating a vegetable meant plucking it from the soil made rich by the manure of many different kinds of animals, and when making a tooth whitener, anti-bacterial agent, or skin-conditioner, meant peeing in a jar and letting it condense. Thankfully, most people reading this aren't forcibly exposed to that anymore. Some people do expose themselves by choice.
Urine is extremely useful because it contains urea. Urea's chemical formula is (NH2)2CO, and with that alone, it gets a lot done. It's a popular skin softener. Outer layers of toughened dead skin are supported by a number of different molecules that were secreted by the cells themselves in happier times. Urea dissolves this support goop, known as extracellular matrix, to help people slough away hardened skin. Urea is also good at killing off bacteria. Urine high in urea can work as an antibacterial agent. The more urea, the less bacteria. In a study, a group of subjects given (human-made and sterile) urea to ingest excreted urine with strong antibacterial properties.
But it's when urea decomposes that urine goes heavy-duty. As urea breaks down, it drops its carbon and oxygen, and one of its nitrogens, to make NH3, or ammonia. Ammonia is in a lot of cleaning products, both as an antibacterial agent and a bleaching agent. Old urine, often boiled and bottled in jars, eventually develops a high ammonia content. Historically, people put it on their wounds to prevent infection. They would also put it on their teeth. Romans were famous for bleaching their teeth with urine but people throughout history have used urine to brighten their smile. (And then been confused when no one wanted to kiss them.)
And history is still happening. Go online, and you'll find any number of people planning to use their own urine to bleach their teeth. Today, whitening toothpastes use hydrogen peroxide as a whitening agent. Urine garglers feel this is unnatural. Which, of course, it is. That's what's great about it.