h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Once, a long long time ago, before people wore braces, the metal beasts would roam free across open plains in Africa. They were magnificent in motion, truly one of God's most stunning creatures, and perfectly docile ones as well. They were ate by filtering the air for pieces of food, like the mighty plankton of the sea. If a chaff of wheat, a mustard seed, a branch, or a hunka cheese sandwich was aimlessly wafting through the brisk African breeze, the stainless steel of the brace would catch it, and slowly take in it's goodness, the wiry mane of the beast creaking and billowing with every movement. It was a grand sight to behold, and their presence was welcome among the tribes of Africans that shared the land. A few families managed to domesticate the wild brace, and careful breeding created the retainer, a friendlier, and cuter variation of the original brace.
Knowledge of the domestication spread to Europe, where interest in the animal spread like toothpaste on a warm brush. The retainer soon became a very popular pet among Europe's richest aristocrats, and various families would tout their lineage of fine-fuzzed red #2, or the even rarer scented whiskered black #7, whose luxurious coat was legendary, particularly among the peasents in Switzerland, but that's

The remarkable strength of the braces intrigued one Ortho von Odelay of Austria. Wild braces could easily crush rocks and pull trees together with their wiry extensions. Ortho thought this could be applied to the realm of dental surgery. Ortho, unfortunately, had really horrible teeth, and he constantly mocked by many of the cynical Austrians he mingled with. Possibly, these wild braces could be somehow applied to the straightening of teeth.
Eagerly, he captured a wild brace that was grazing on the Serengeti. It seemed young, tense, and small enough to fit in the mouth. Ortho thought taming it would be a simple job, but it was truly a fiesty little piece of metal. Ortho would hammer it, and cruelly bend it out and back into shape, to break it's will completely. Eventually, it submitted, and allowed itself to be inserted into Ortho's mouth.
It worked wonderfully. The fangs of Ortho straightened to a presentable form. He presented his method to the civilized world, and created a sensation, as much of the civilized world had pretty bad teeth at the time. Tame, and wild braces were soon captured and put to use in gaping mouths. But, the braces were unhappy in the smelly caverns of people. They yearned to prance through the plains again. They wished to swing from branch to branch again. They wanted to be free again. But they could not. Soon, all wild braces were taken from their habitats, and grown in the breeding grounds of Orthodontists. Retainers were taken away too. The plains soon became very lonely.
But, the braces and retainers all knew how to make the humans feel their pain, literally. Push as hard, and awkwardly as they can on the jaws; jut out into the gums; and grab any food that comes through. Irritate the humans as much as possible! And so they did. And that's the story of how braces came to be, and why they hurt so much.