Why kangaroos don't need braces

I'm convinced my orthodontist was at least partially insane. He had a manic grin permanently fixed on his face, consistently commented on the colour of my (then blueish-purple) glasses frames, and seemed to enjoy injuring the delicate tissues inside my mouth - I never left without a bleeding gum, a cut lip, an ulcer-in-progress.

If you have similar problems with your orthodontist - have you considered becoming a kangaroo?

Kangaroos never need to go to a dentist for a root canal or a clean. Primarily because they're animals and the majority of animals do not go to dentists. However, they have no real need for dental work, because when their teeth become worn down, they simply fall out and are replaced by another set of teeth. In a way, it's similar to how our 'baby teeth' fall out through our childhood to be replaced by 'adult teeth' - only for kangaroos, this happens up to four times in their life, and by a slightly different mechanism.

Kangaroos have four pairs of 'cheek teeth', or molars, but they only use the front pair for crushing up their food. When these front teeth become too worn down to function, they fall out, and the next pair of molars actually move forward in the jaw to take the place of the missing teeth. Sort of like a 'conveyor belt' of teeth. When these teeth, in turn, become worn down, they fall out as well, and are subsequently replaced by the next set moving forwards. And so on, until the kangaroo is about fifteen or twenty years old, and they have no more replacement teeth left. By that stage, though, it's nearly the end of their natural lifespan anyway.

Why do their teeth get worn out so quickly? The diet of kangaroos consists entirely of plant material, containing tough cellulose in the plant's cell walls. Over the years, many of these plants have evolved an extra defence mechanism in an attempt to avoid being eaten - an even tougher substance, silica, is also present in the cell walls (some grasses are up to 50% silica!). For the kangaroos, this is the equivalent of chewing sand...and their teeth wear down rather quickly as a result.

And so they just slide in new ones to replace the old ones. Awesome.