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About Teeth

What are teeth made of?

Teeth are the hardest, most highly mineral substance in the human body.

A human tooth, at least the top part or enamel, is mostly made of minerals (96%), with a little water and organic matter mixed in. The main mineral is a form of calcium called hydroxylapatite.

Beneath the enamel is a layer called dentin. It has a little different composition that makes it more flexible. Dentin acts like a shock absorber so the teeth and bones beneath them don't break too easily.

Under the dentin is the soft center of the tooth, called pulp.

Did you know that a seashell is also mostly made of calcium? The sea snail's body extracts the calcium from the surrounding seawater.

Why do we lose our baby teeth?

Adult teeth are too big to fit in a baby's mouth. Baby teeth act as placeholders and organizers for the adult teeth that will come later. And of course, babies and little kids need to chew, too!

Do other animals lose their baby teeth?

Yes. For example, puppies and kittens have baby teeth, sometimes called milk teeth or deciduous teeth. They lose these before their adult teeth come in, just like human babies do.

There are special science words to describe this business of losing teeth. They start with a prefix meaning a number, such as mono (one), diph (two), or poly (many). The rest of the word—phyodont—means "generations of teeth."

Rows of teeth in a nurse shark's jaws.
Monophyodonts—animals that only have one set of teeth in their lifetimes. There aren't as many monophyodonts as diphyodonts among mammals, but they include walruses, seals, and toothed whales such as dolphins, sperm whales, and killer whales. The tusks of walruses are long canine teeth, while the narwhal grows just one of its canines so long that it looks like a spear or a unicorn horn.

Diphyodonts—animals that only have two sets of teeth in their lifetimes. Most mammals, including humans, are diphyodonts.

Polyphyodonts—animals that have more than two sets of teeth in their lifetimes. Most fish with teeth are polyphyodonts. Sharks are a familiar example, as are crocodiles and other reptiles. Sharks replace their teeth every two weeks! The teeth come into place as if they were on a conveyor belt. The most surprising polyphyodonts are three mammals: elephants, kangaroos, and manatees.

What's so special about rodent teeth?

The teeth of most rodents grow continually. The rodents keep them worn down to a good length by gnawing on things. If they don't gnaw, their teeth get too long.

Why don't we have more big pointy teeth like dogs and cats?

Humans have only two pointy teeth (canines), and they're not particularly large. The shape and size of animal teeth varies depending on what the animals eat. We don't hunt and catch prey with our mouths, so we don't need big pointy teeth. Of course, these days your dog may be most likely to hunt and catch a dog biscuit!

What are the different kinds of teeth different animals have, and why?

Let's break this down into four basic types of teeth: incisors, canines, premolars, and molars.

Incisors are at the very front of an animal's mouth. They are often flat across but sharp on the bottom. They're for catching and also for cutting, like kitchen knives. Your 1st and 2nd teeth on each side (the front teeth) are incisors.

Canines or cuspids are next, and they are those famous fangs we see in the mouth of a tiger or wolf. They are sharp, and they are for grabbing and holding tightly, or sometimes for fighting, like daggers. Your 3rd tooth on each side is a canine, which is why it is pointy.

Premolars are a cross between canines and molars. They're partly pointy and partly flat. They help cut up food and pass it back to the molars. Your 4th and 5th teeth on each side are premolars—the 4th with 2 bumps or cusps and the 5th with 3 cusps.

Molars are for chewing and grinding food into smaller pieces. Your 6th and 7th teeth on each side are molars. At some point you will grow an 8th tooth on each side, the 3rd molar or wisdom tooth. Molars usually have 4 or 5 bumps, or cusps.

How are the groups of teeth different in different animals?

In different animals, different teeth in the four groups are larger or smaller, more or fewer.

Carnivores have bigger, sharper canines for catching and holding prey. Animals like wolves, dogs, and cats have special teeth after the canines called carnassial teeth that act like scissors (top and bottom) to help them cut meat. Their molars are used partly to crush bones.

Herbivores like cows and deer have more premolars and molars for grinding up branches, grasses, and seeds. They use their incisors to clip off leaves and stems. They may not have canine teeth at all—or their canine teeth aren't sharp.

Insectivores like rodents and some bats have sharp molars so they can tear through the exoskeletons of insects.

Omnivores like raccoons, bears, and humans have a mix of teeth for dealing with both plants and meat.

What are wisdom teeth, and why do they get taken out of people's mouths so often?

Wisdom teeth are the 8th tooth or 3rd molar on each side of your mouth. They come in much later than other permanent teeth, usually between the ages of 17 and 25. You are presumably wiser at that age than you were when you were a child, which is where they got the name. These teeth are vestigial, which means they are no longer really needed in humans. In fact, wisdom teeth often cause dental problems, starting with overcrowding the mouth. That's why dentists pull them out so often in our day.

Why do we have to brush and floss our teeth every day?

Teeth develop infected spots called caries or cavities if you don't take care of them. These can get worse and worse until the tooth hurts, even rots, and has to be pulled out. That part of your mouth can get infected and make you sick, too. Brushing and flossing help keep you from getting cavities. Although cavities can be filled in by dentists, traditionally with metal but today often by porcelain or composite resin, it is much better to prevent them in the first place by taking good care of your teeth. Since cavities form easily between teeth when bits of food get stuck there, flossing daily is at least as important as brushing.

How hard should I brush?

Actually, you're not supposed to brush your teeth super hard! You should have a toothbrush with soft bristles and should not scrub at your teeth. Tooth enamel and gums can both be damaged by hard brushing. Brush your teeth gently, but for a good two or three minutes. Don't forget hard-to-reach places like the backs of your last molars. You should also brush your tongue. It needs to be kept clean, and you'll be less likely to have bad breath.

What did dentistry used to be like?

There was some dentistry practiced, but not for most people. A lot of people didn't know about brushing their teeth, either. Basically, if you got a cavity, your tooth would rot and get infected and painful, so you would have to have it pulled. Many people had bad, rotting teeth at a young age. And when those sore, infected teeth were pulled, they didn't have any anesthesia. For hundreds of years people even used a mallet and chisel to just crack the tooth out. Big ouch!

Still, somebody was using drills way back in 7000 BC, when people in the Indus Valley used the same bow drills they used for woodwork to treat tooth troubles. The Greeks and Romans invented a type of forceps for pulling teeth, though they were not used widely in most places—more likely among the wealthy. In Europe back in the Middle Ages the person who commonly pulled teeth was either a doctor or a barber. You could get your hair cut and your teeth pulled in the same place!

Who invented the toothbrush and toothpaste?

Napoleon's Toothbrush

The earliest toothbrushes we know about were twigs that had been mashed at one end, or "chew sticks." These came about as early as 3000 BCE. Then in 1498 CE the Chinese invented a bristle brush using hairs from the backs of pigs' necks.

In the United States a man named H.N. Wadsworth patented a toothbrush in 1857, and toothbrushes began to be mass-produced and sold in 1885.

Toothpaste has been around for a long time, but it often had strange ingredients, some of which even damaged tooth enamel. Of course, some ingredients weren't too awful, like ground-up fruit or seashells, honey, or dried flowers. Others sound pretty bad: mice, earthworms, spiders' eggs, rabbits' heads, lizard livers, and even urine.

The kind of toothpaste we use today was first sold in a jar by Colgate in 1873. The first tube toothpaste was sold in 1892. Toothpaste in the 1800s had ingredients like soap and chalk—but no mice or worms.

Still, Americans didn't really brush their teeth regularly until after World War II, when soldiers brought back the habit because it had been required during their military service.

Why is there fluoride in our drinking water?

Fluoride is a chemical substance that keeps people from getting a common tooth problem once known as the Colorado Brown Stain. When fluoride began to be added to American drinking water during the 1950s after more than 20 years of scientific research, everyone's tooth health improved. We all owe a big thank you to leading researcher and fluoride proponent Dr. Frederick McKay!

What do George Washington and Paul Revere have to do with teeth?

People say George Washington had wooden teeth, but it's not true. He did have bad teeth from an early age, which explains why his mouth looks stiff and uncomfortable in so many of his portraits. He eventually had to have all but one of his real teeth pulled. Washington had more than one set of false teeth over the years. They were made of things like hippopotamus ivory, human teeth, gold wires, and lead.

You've probably heard of Paul Revere, the American Revolution Patriot who rode to warn the people of Lexington and Concord that the British were coming one night in 1775. He worked as a silversmith, but did you know he was also a dentist? He was trained by our country's first real dentist, a man named John Baker. Revere cleaned teeth and put in the occasional false tooth, although he did not make full dentures.

Here is an ad from Paul Revere's dental practice, published in 1770 in the Boston Gazette and Country Journal:

Paul Revere, Takes this Method 'of returning his most sincere Thanks to the Gentlemen and Ladies who have employed him in the care of their Teeth, he would now inform them and all others, who are so unfortunate as to lose their Teeth by accident or otherways, that he still continues the Business of a Dentist, and flatters himself that from the Experience he has had these Two Years (in which Time he has fixt some Hundreds of Teeth) that he can fix them as well as any Surgeon-Dentist who ever came from London, he fixes them in such a Manner that they are not only an Ornament, but of real Use in Speaking and Eating: He cleanses the Teeth and will wait on any Gentleman or Lady at their Lodgings, he may be spoke with at his Shop opposite Dr. Clark's at the North End, where the Gold and Silversmith's business is carried on in all its Branches.


Articles about teeth and the history of dentistry can be found at the following sites:

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