BUILDING & KEEPING HUMAN TEETH
Like many of our animal friends, human beings have two sets of teeth: primary teeth (a.k.a. “deciduous teeth,” “milk teeth,” or “baby teeth”) and permanent teeth. Dogs have twenty-eight of the former and forty-two of the latter; cats, twenty-six and thirty. The human mouth normally produces twenty primary teeth and thirty-two permanent ones, although, some perfectly healthy humans are born without a complete set of teeth, some without four wisdom teeth, and some with one or two extra.
The first primary teeth begin to form about six weeks into our embryonic life. The process begins with the appearance of a ridge called the lip plate (labiodental lamina). Next come the dental laminas and after that “dental buds,” five on the top jaw and five on the bottom. The buds are a kind of mold in which teeth are grown. By the fourth month of pregnancy, each of us normally has hard “baby” teeth inside the buds inside the gums; one or more of these teeth may actually erupt before birth. In some cultures, children born with teeth are regarded as a sign of good fortune; in others, they are labeled monsters. Historically, the British decided that arriving with a tooth or two in your baby jaws was a very good thing, indeed. King Richard the First might have been the one with the lion heart, but as Will Shakespeare wrote of Richard the Third in Henry the VI Part 3, “Teeth hadst thou in thy head when thou wast born,/To signify thou camest to bite the world.”21
It is more likely that your first primary tooth will slice its way through your gum when you are about two months old, giving you pain and your parents many sleepless nights. Number One to break through is probably one of the incisors in your lower jaw, followed by the corresponding upper teeth, the canines, the cuspids, and the molars. By the time you are two or three years old, you will have all your primary teeth, which a few years later will be pushed out by your permanent teeth whose permanence, of course, may vary with your dental health. The interesting thing about your molars, including your wisdom teeth, is that they are not replacement teeth that erupt when you lose baby teeth. They are permanent teeth that show up later in life, just as a cat’s molars arrive when Fluffy is about six months old, a point roughly comparable to human teenager.
Our teeth, like those of our animal friends, are defined by the job they perform. Start at the front with the four front teeth on top and the similar but smaller ones right under on the lower jaw. These incisors, from the Latin incidere, to cut, are just the tools you need to slice off a piece of meat or cut though a carrot. The canines, sometimes called cuspids, are the relatively long and pointy teeth, one on either side of the incisors. We call them canines, of course, because they look like Fido the dog’s or Fluffy the cat’s teeth. They, we, and every other animal that has them use the incisors to hold food steady while the incisors slice. In dogs and cats, these teeth are larger and more ferocious, the better to serve as a sign of the animal’s mental state. “Baring your teeth” is not just a phrase. It’s what these many animals do to signify aggression (we humans are conflicted, we bare our teeth both to invite people closer with a smile and to warn them away with a grimace). Next in line: the short, flat bicuspids, from the Latin bi- meaning two and cuspis meaning point. These “pre-molars” move food farther back toward your flat, broad molars, from the Latin molaris meaning grinder. And grind away they do, most vigorously when handed hard grains, seeds, veggies, and fruit.
If you divide the dental arch into four parts, most mammals have two or three incisors, one canine, four premolars, and three molars per quadrant, a formula that is written as 2:1:2:3 for humans and for those others as 3:1:4:3. The shape of the teeth may vary by species because different animals eat different foods. Like us, dogs are omnivores, so their teeth are rounded, flat, or pointed as required. All cats, on the other hand, from kittens to lions and tigers, are meat eaters, so all their teeth are sharp and pointy. And herbivores such as horses have teeth that are broader and flatter than everyone else’s, the better to mash up grains.
Your Canine Teeth, Gray’s Anatomy, 20th edition (1918)
Your Canine Teeth, Gray’s Anatomy, 20th edition (1918)
Once you have your teeth, with or without those four third molars, the question is, can you keep them? And if not, how will you replace them?
What makes Jaws so impressive isn’t just that he has all those big teeth; it’s that he is constantly growing new ones. An elephant, on the other hand, has what you might call “motor teeth.” The normal pachyderm has twenty-four teeth in his mouth, including those tusks, but he uses only about four at a time. As these wear out, the teeth behind them move forward to take their place, each tooth dropping out in turn as it reaches the front of the elephant’s mouth. An elephant’s first molars and second molars are in place at birth; the first falls out two years later, the second six years later. After that the third, fourth, fifth, and sixth molars make their appearance and fall out in turn. The last one, the sixth molar, goes when the elephant is around sixty-five years old and runs out of teeth and loses the ability to chew, a problem that among animals eventually contributes to his death.22
Once upon a time, says Louis Rafetto, chair of the Third Molar Task Force of the American Association of Oral Maxillofacial Surgeons, our wisdom teeth may have behaved something like the elephant’s moving molars. “Some say wisdom teeth are like spare tires,” he says, noting that before dentistry evolved suffiently to let us keep out teeth into old age, wisdom teeth were the extras that could fill out your mouth and keep you chewing happily along. Of course, human beings on the other hand have been losing teeth ever since the beginnings of human beings, a process accelerated by decay due to the introduction of processed sugary foods and smoking tobacco, which heat and loosen the supporting gums. Happily, we have been able to rig up more or less acceptable substitutes.
More than two thousand years ago, Etruscans wore dental bridges made of precious metals not necessarily to replace missing teeth, but to show off their wealth and status. The Egyptians were more practical; they tied carved replacement teeth with gold wire to whatever was left in the mouth. Things got serious in the 18th century when the French surgeon Pierre Fauchard, generally considered to be the “father or modern dentistry” and the man who invented wired dental braces to straighten crooked teeth, suggested that teeth carved from ivory or bone were good workable substitutes.23 Eventually, people agreed that real teeth were better. At first, dentists used teeth extracted from executed criminals or robbed graves to pull the teeth out of corpses, a practice that came with the possibility of transplanting unpleasant diseases such as syphilis along with the teeth. That led to a search for (relatively) healthy teeth. War provided an excellent supply. More than 50,000 soldiers died at the Battle of Waterloo, but their teeth lived on in the hands of scavengers who raced onto the field to yank out teeth, hopefully from truly dead mouths, in order to build dental bridges called “Waterloo Teeth.” They could also have been called “Civil War Teeth” because the same search-and-collect mission occurred across the ocean a century after the first President of the United States took the oath of office in 1789 at age 57 with only one tooth left in his mouth.24
In Natural History of Human Teeth (1778), the British surgeon John Hunter had begun to speculate about whether you could actually transplant living teeth from one person to another,25 but unfortunately for Washington, transplants did not become reality for another 165 years when, after the discovery of tissue compatibility and rejection, in December 1954, the first successful transplant of an organ, a kidney, from a living donor to a living recipient was performed by Joseph Murray and David Hume at Brigham Hospital in Boston.26
But how much better it would be to be able to simply grow replacements on our own, in our very own bodies. Regeneration (the ability to grow new body parts to replace the ones you lose) is relatively common in some parts of the animal kingdom. Lizards can regrow their tails. Spiders and starfish can regrow missing arms and legs, and lobsters and crabs, new claws. Cut a flat worm or a sponge into pieces and each
piece will become a whole new animal. As for teeth, sharks make new teeth all the time, and if you can manage to pull one from an alligator’s mouth without losing your nonregenerating arm, the alligator will regrow the tooth as many as fifty times.
Will we ever be able to do that?
They’re working on it.
At Boston University’s Henry M. Goldman School of Dental Medicine, endodontists George Huang and Mey Alhabib are trying to do just that. First, they are attempting to grow dental pulp (the inside of the tooth) and dentin (the softer layer just under the dental enamel) from stem cells extracted from baby teeth lost naturally and otherwise collected by the Tooth Fairy who would simply toss them out. The hope is that eventually stem cells can be extracted and frozen and stored for use later in life when a patient’s teeth need repairing. Huang and Alhabib are also harvesting dental stem cells from wisdom teeth and setting them on small sponges that are put into a human tooth, which is then placed into the body of a lab mouse to provide the blood supply needed to grow the cells. Three months later if the process works, the tooth is removed from the mouse complete with dental pulp and dentin. Next step: trying this in a larger animal such as a pig, and eventually, down the line into the future, in human beings. “Nowadays, dental implants are very successful,” Huang says. “You get a tooth pulled, you put in an implant. But it took 30 to 40 years to get to this stage. Perhaps in the future, we’ll be re-growing a whole tooth, and that may take 30 years, but once the technology is mature, it may replace dental implants.”27
Or several million years into the future, we could forget about teeth entirely and just follow the birds into beak-dom. “Unlike teeth, a beak would not rot, chip or fall out. This would make it more robust and practical,” said Sheffield University (England) biologist Gareth Fraser. Putting his research where his mouth is, Fraser has been studying the blowfish, a.k.a. the pufferfish. The spiny, highly poisonous fish begins life with teeth, but they quickly morph into a beak that is used to open shells and crush and cut fish. He (or she) also has cells that enable him (or her) to continuously produce tooth-like material to repair any damage to its beak. Fraser calls these “tooth fairy” cells, and because they are similar to cells in the human mouth, he thinks the blowfish may hold the secret to convincing our own bodies to go to work repairing our own teeth. Sheffield scientists have also isolated the cells a shark uses to produce new teeth almost forever. If they can apply their findings to us, forget about repair, we’ll just take new teeth, thank you very much. Despite the durability of a beak, Dr. Fraser would prefer to keep his teeth: “I am happy with the shape of the teeth I have—although I would like more of them.”28
THE LAST BITE
As many as one-third of us simply do not develop third molars. It’s not that they are there and for some reason don’t burst through the gum. It’s that they really aren’t there at all, which raises this question: Are we on the path to proving Darwin right by simply evolving past the 32-tooth human mouth?
Not necessarily.
It may be that some of those missing teeth are missing due not to evolution but to modern dentistry. Your teeth begin to develop while you are still in the womb, perhaps sucking your fetal thumb and setting the stage for later orthodontic work to correct your crooked bite. But your third molars don’t follow this rule. These teeth do not even start to grow in tooth buds at the back of your jaw until you are six or seven years old. As a result, some dental researchers speculate that we could use lasers or modern medical chemicals to interrupt this process and eliminate the teeth. And in 2013, Anthony R. Silvestri, Jr. and Gerald Swee of the Tufts University School of Dental Medicine published a paper in the Journal of the American Dental Association suggesting that the needle used to deliver the local anesthesia routinely in dentistry may accidentally penetrate the wisdom tooth bud, stopping the wisdom tooth dead in its tracks. X-raying more than two hundred young patients, Silvestri and Swee discovered that less than 99 percent of those who had never gotten local anesthesia still had their nascent wisdom teeth; nearly 8 percent of those who’d been injected didn’t.29
The good news is that neither the one-third of us born without wisdom teeth nor the 8 percent whose dental procedures prevent wisdom teeth from growing will ever need surgery to remove the third molars. The question is whether you should make the case, as some have, for eliminating the wisdom teeth entirely. Currently they seem to serve no purpose other than to require millions of extractions costing millions of dollars and pounds and francs and so on. And now that we more or less know more about how to protect our teeth against decay and have access to advanced technology such as dental implants when prevention fails, we don’t need our third molars as replacement for lost teeth.
But the real question is not financial or medical, well, dental. It’s biological. As Silvestri and Singh ask in their study, is there any advantage to having fewer teeth?
We are, after all, omnivores whose latest health advisories tell us that we should be eating lots of tough, high-fiber foods: vegetables, fruit, whole grains. These foods require chewing. Chewing requires molars, probably the more the merrier. So losing our wisdom teeth might contradict Charles Darwin’s belief that evolution made and makes us more not less powerful.
Maybe instead of even trying to breed our human wisdom teeth out of our human jaw, we might do better to follow the example of our chimpanzees and ape cousins whose diet, although it does include insects and an occasional small animal, is primarily vegetarian, which means they spend their days chewing through nuts and seeds and leaves and fruits and strengthening their jaws. Yes, Darwin said our wisdom teeth were vestigial. But in reality what’s disappearing isn’t the teeth, it’s the jawbone, whose continuing shrinkage may track back to the changes in our diet that had us chewing less vigorously. And not just on foodstuff. One wonders whether the appearance of soft leather goods affected the oral anatomy of Inuit women whose tradition of chewing leather to soften it produced jaws with plenty of room for extra teeth.
In short, going forward, our best bet may be to heed the pragmatic words of New England’s Peter Brown: “Because I am an anthropologist, I tell my children to chew their food.”
NAME THAT TOOTH
These people… Call the third molars Which means …
Ancient Greeks sophronisteres prudent (sophron) teeth
Romans (Latin) dentes sapientiae wisdom (sapien-) teeth
Arabs ders-al-a’qel teeth of the mind
Germans Weisheitszähne wisdom (Weisheit)
French dents de sagesse wisdom (sagesse) teeth
Indonesians gigi bungsu youngest child (i.e., newest tooth)
Japanese oyashirazu unknown to the parents (referring to an age when children leave home)
Koreans sa-rang-nee young love (sa-ran-gee) teeth
Spanish muelas del juicio teeth of judgment (juicio)
Thai fan-khut “huddling tooth” (teeth crowded in back)
Turks yirmi yas disleri 20-year teeth
[Source: “Wisdom Teeth—Word of the Week,” Kaplan International English, July 4, 2012, http://www.kaplaninternational.com/blog/wisdom-teeth-word-of-the-week/]
7
Dispensables
“Four be the things I’d been better without: Love, curiosity, freckles, and doubt.”
—Dorothy Parker (1893–1968)
Like every one of us, Charles Darwin was a child of his age. His generous intellect led his observations, but his attempt to assess the vestigiality of certain body parts was hampered by then-current science. Nearly two centuries later, we know that our tissues and organs divide more or less into six broad categories.
One is vital and irreplaceable.
Some are vital but replaceable.
Some are equally vital but happily redundant.
Some we use but can live without.
Four are examples of total uselessness with nothing to recommend them other than the fact that they are there because that’s the way Nature made us.
And
at least one is undisputedly vestigial.
THE ONE AND ONLY BRAIN
With a few rare exceptions such as the starfish, animals from ants to humans are bilaterally symmetrical, their bodies divided by a midline with pairs of parts on either side: eyes, ears, arms, legs, and so on. You might think this alone would be the perfect blueprint Charles Darwin needed to identify what’s needed and what’s not. It wasn’t then, and it still isn’t today, because not every pair is made of equal parts.
Consider the human brain, beginning with the idea that you only use 10 percent of what you have and that if you used the rest you’d be as smart as Einstein. This particular medical myth seems to have sprung from the writings of Harvard physician, psychiatrist, and philosopher William James (1842–1910), who once casually observed that we do not make all we might of our intelligence.1 The notion was expanded and popularized by mid-20th-century radio commentator Lowell Thomas, who added the 10 percent figure on his own and stuck it into his foreword to How to Win Friends and Influence People, the 1936 self-help book by the pioneering relationship guru Dale Carnegie.
Modern PET (positron emission tomography) scans produce images of your brain at work with first one section and then another lighting up like a “moving” sign in Times Square. That looks like only one section is working, but in fact the connections among cells in different parts of the brain are always active. The scan showing that one part of your brain lights up when you are solving math puzzles and another when you are listening to music simply demonstrates which area is working hardest. It does not show the multiple continuing interactions among the billions of neurons that turn on the lights.
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