Sunday, February 20, 2005

Human Dental Chaos Theory

This is a piece about one of our most dreaded encounters: the one with the dentist. But it is more than that. It is a personal story, but most of you have no idea who I am, so what is personal to me, is really just a wild, wacky story to you about someone you don't know. But why is my personal dental experience important? Well, maybe it isn't, but here it is anyway. While I was in the dentist's chair the other day, I was wondering why I was there at all with my mouth open, my neck lodged uncomfortably into those padded rests, and dental instruments strewn across my chest. It was the location of the tools that caused the new dentist, who I was seeing for the first time, to deftly leave his hand a moment too long on my left breast. Hey, I've been going to dentists all my life (in an ongoing battle to keep all my teeth in my mouth), and not once, as in NEVER has a dentist inadvertently touched my breasts. And not only did his hand stay a split second over accidental, he apologized. He actually called attention to it-- his hand, my breast. Jeebus. What a jerk. I am never going to see this guy again. But, while I was in the chair I was thinking, what is it with our human dentition, that we end up in these rather vulnerable positions with strangers who not only put their hands in our mouths, but sometimes use the occasion for other fun and frolic. I found this article at Of course, it's all about evolution and the food we cook and eat.

Human 'dental chaos' linked to evolution of cooking

Crooked and disordered teeth may be the result of people having evolved to eat relatively mushy cooked food, suggests new research.

The disarray may have developed because evolutionary pressures affecting the size and shape of both the front teeth and jaw conflict with those influencing the back teeth. This means that there is often not enough space in the human jaw to accommodate all our teeth.

By animal standards, human dentition is extraordinarily disordered, says anthropologist Peter Lucas of George Washington University in Washington DC, US.

"The only body parts requiring regular surgery are the teeth," says Lucas. "It is extraordinary that the normal development of human teeth routinely fails to produce 'ideal' dentition," he says - and no one has yet been able to offer an explanation for this phenomenon.

Mess of a mouth

Human teeth are often spatially disarrayed or "maloccluded", accounting for the huge number of people who seek treatment from orthodontists. This disarray can lead to periodontal and gum disease, because it becomes more difficult to clear food particles from the mouth.

Teeth can also be missing - wisdom teeth simply do not have enough space to fit into the jaw, and sometimes do not form at all. In contrast most other mammals - including our close relatives, the great apes - have very low frequencies of malocclusion, Lucas told New Scientist.

Lucas's theory is that human dentition began to go haywire soon after our early Homo ancestors learnt to chop and process food with simple tools and, later, to cook it. These processes greatly decrease the size and toughness of food. Lucas estimates, for example, that molars can be between 56% and 82% smaller when eating cooked potato rather than raw.

Out of sync

The front teeth and jaws are primarily occupied with reducing food to a small enough size to consume, whereas the molars and premolars at the back of the mouth are used to grind down tough particles.

Lucas, speaking at the American Association for the Advancement of Science meeting in Washington, DC, US, on Saturday, presented evidence that since the advent of cooking these two processes have fallen out of sync.

"The size of particles has reduced more rapidly than the rate at which the [toughness] of food has changed," he says. In response the human jaw may have shrunk beyond the point where it can hold all the molars required to successfully chew tough food.

For example, most leafy material, "beyond the youngest bit of lettuce," is now difficult for us to eat, Lucas told New Scientist, but would have presented no problem to more robust ancestors.

"We've evolved to eat mush," agrees paleoanthropologist Bernard Wood also of George Washington University, but not involved in this study.

"We're a pretty puny bunch, really, with small teeth and small jaws," he says. "If we couldn't get the foods we like, and we ever had to adapt quickly, we might be in a terrible mess because our teeth aren't equipped to cope with anything very substantial."

Anthropologists have not been able to agree on when our earliest ancestors started to prepare food. Current estimates place the advent of cooking anywhere between 2 million and 300,000 years ago.

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