10 Smart Facts About Wisdom Teeth

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Like puberty and your first heartbreak, the painful process of getting your wisdom teeth removed is one of those cumbersome coming-of-age rituals that many people are forced to endure. But why do we have wisdom teeth when they seem to only cause problems? Read on to find out more about the humble third molar—the last tooth many of us get as adults.

1. THEY HAVEN’T SERVED ANY PURPOSE FOR HUNDREDS OF THOUSANDS OF YEARS.

Imagine, for a moment, that you’re a prehistoric man or woman. You subsist largely on raw meat, roots, and leaves. You’d need some pretty powerful chompers to cut up your food, right? That was where your third molars—also known as wisdom teeth—came in. Today, our palates are a little more refined, and we prefer softer foods (think avocado toast and smoothies). Plus, modern cooking tools have put our wisdom teeth out of business.

They’re not just pointless, though—they’re also problematic. Wisdom teeth are a “scar of human evolution,” according to Princeton University researcher Alan Mann. About 800,000 to 200,000 years ago, early humans’ brains started growing at a rapid pace—so much so that they ballooned to three times their original size. When that happened, it changed the shape of the braincase (the back part of the skull) and its position relative to the dental arcade (rows of teeth). The dental arcade shortened, and suddenly there was no longer enough room for third molars. And since the genes that determine the makeup of our teeth evolve separately from those that control brain development, humans were stuck dealing with the consequences of a crowded mouth, according to Live Science.

2. NATURE MAY EVENTUALLY SORT IT OUT, THOUGH.

On the bright side, scientists say evolution may eventually take care of the problem, meaning that people in the future would not develop wisdom teeth. It’s anyone’s guess as to when this will occur, though. “On the evolutionary scale, if I had to predict down the road—centuries probably—wisdom teeth are going to be one of the things that humans probably won’t have anymore,” Dr. William McCormick, assistant clinical professor at West Virginia University’s School of Dentistry, tells Mental Floss.

3. THE NUMBER OF WISDOM TEETH VARIES FROM PERSON TO PERSON ...

It’s possible that you have one, two, three, four, or none at all. Another possibility, although it’s rare, is to have more than four wisdom teeth, which are called supernumerary teeth. “In my career, I have seen two cases where patients have had fourth molars—or two sets of wisdom teeth,” McCormick says. (Comparatively, humans’ ancestors had quite the mouthful, with 12 wisdom teeth in total.)

According to McCormick, genetic factors like jaw size might determine the number of wisdom teeth that a person has. Your lineage may also have something to do with it. Practically no Aboriginal Tasmanians have third molars, but almost 100 percent of indigenous Mexicans have at least one wisdom tooth. African Americans and Asian Americans are also more likely than people of European descent to have fewer than four wisdom teeth. This variation can be attributed to a random genetic mutation that arose thousands of years ago, thereby preventing the formation of wisdom teeth. This mutation is more prevalent in certain populations.

4. ... AS DOES THE NUMBER OF ROOTS THAT EACH TOOTH HAS.

The roots are the part of the tooth that form first, and then push the bud (the part that's visible in your mouth) through your gums. While wisdom teeth typically have two or three roots, they can have more. McCormick says he personally removed his wife’s wisdom teeth in the ‘70s and was surprised to see that one of them had five roots. “It looked like a spider. It was not a pleasant extraction,” he says.

For that reason, if wisdom teeth need to be removed, it’s easier to do so before the roots start to take hold. “When the roots are totally formed, they’re anchored like a tree that’s been in your backyard for 100 years,” says Dr. Ron Good, an orthodontist in southwestern Pennsylvania who runs a family practice with his brother, Dr. Bob Good. On the other hand, surgeons want some roots to grab hold of, because removing a tiny tooth bud is “like extracting a marble,” Dr. Ron tells Mental Floss.

5. YOUR WISDOM TEETH CAN ERUPT AT ANY TIME.

According to Guinness World Records, the oldest person to ever grow a wisdom tooth was 94 years old. McCormick says there's a wide variation in ages when eruption occurs; he once had a 65-year-old patient with dentures whose wisdom tooth had started to erupt (poke through the gums). “They’re crazy little beasts. You never know what you’re going to see.”

Apparently, wisdom teeth have been acting erratically for thousands of years. Aristotle documented this phenomenon in his book The History of Animals: “Cases have been known in women upwards of 80 years old where at the very close of life the wisdom-teeth have come up, causing great pain in their coming; and cases have been known of the like phenomenon in men too.”

In most cases, though, wisdom teeth erupt when you’re in your late teens or early twenties.

6. THE FIRST IMPACTED TOOTH WAS RECORDED ABOUT 15,000 YEARS AGO.

When wisdom teeth don’t have enough room to grow normally, they get stuck in the jaw and fail to erupt. These are called impacted teeth. The oldest known case of an impacted tooth was found in the skeleton of a 25- to 35-year-old woman who died some 15,000 years ago. This case cast doubt on the theory that impacted teeth are a modern ailment, caused by recent changes in our dietary habits.

7. SOME PHYSICIANS SAY THAT IMPACTED WISDOM TEETH SHOULD BE SURGICALLY REMOVED ...

Many people get their wisdom teeth removed, even if there isn’t any pain or discernible problem aside from impacting. Known as prophylactic surgery, this preventative practice is common in the U.S., but in recent years there has been some debate as to whether it’s necessary. One popular theory holds that most people either have problems with their wisdom teeth or will at some point in the future. “It’s hard to get a percentage, but probably 75 to 80 percent of people do not meet the criteria of being able to successfully maintain their wisdom teeth,” Dr. Louis K. Rafetto, who headed a task force on wisdom teeth, told The New York Times in 2011.

About 3.5 million extraction surgeries are performed each year, and according to another estimate, that adds up to be 10 million individual wisdom teeth pulled annually. Dr. Ron and Dr. Bob, of Good Orthodontics, are both of the opinion that wisdom teeth are ticking time bombs. “In our mind, we feel that wisdom teeth, in general, are of no value and are only potential problems,” Dr. Bob says. He added that third molars can interfere with your bite and cause your teeth to wear down, and in some cases, can also cause cysts, tumors, nerve damage, periodontal disease (affecting the gums and other areas around the teeth) and TMJ disorders (affecting the jaw joint). Plus, if your teeth are too crowded and you aren’t able to brush and floss them normally, it can lead to additional issues, such as gum disease and cavities.

8. ... WHILE OTHERS SAY YOU SHOULD AVOID IT.

Dental practitioners in the UK put an end to routine wisdom tooth extractions in 1998, citing a study at the University of York that reportedly found no scientific evidence to support the practice, according to the The Miami Herald.

Opposition is building in the U.S., too. Retired dentist Dr. Jay Friedman told How Stuff Works that only about 12 percent of wisdom teeth eventually cause problems. He compared that rate to the 7 to 14 percent of people who experience appendicitis, yet appendixes aren’t removed until they become a medical issue. If this seems to contradict Raffeto's statistics, it’s because there isn’t a whole lot of concrete data on the subject, and much of it is conflicting—so it really comes down to the individual physician’s and patient's preferences. “Ask three dentists the same question, and you’re going to get four different answers,” McCormick says with a laugh.

Like Friedman, McCormick doesn't support wisdom tooth removal unless there’s an infection, abscess, or other problem. “You have to weigh the surgical risk with what you’re going to try to accomplish,” he says. Like any surgery, wisdom tooth extraction poses a risk, although more serious complications, like fractured jaws and death, are extremely rare. McCormick says some possible side effects include nerve damage, infection, and dry socket (an infection of the tooth socket).

Despite the differing opinions in the dental community, McCormick, Dr. Ron, and Dr. Bob agreed that there’s no prescriptive rule for wisdom tooth removal, and that each patient should be evaluated on a case-by-case basis.

9. THEY’RE CALLED LOVE TEETH IN KOREAN.

In English, the name wisdom tooth conveys the idea that third molars come in later than other teeth, at a time when you’re older and (hopefully) wiser. Other languages don’t follow the same convention. In Korean, for example, the poetic name for third molars translates to “love teeth,” because it's around this time (late teens and early 20s) that one typically experiences their first love. The Japanese language also has a creative word for it: oyashirazu, or “unknown to parents,” since most people have already moved away from home by the time their wisdom teeth come in.

10. THEY’RE USED IN STEM CELL RESEARCH.

It turns out wisdom teeth aren't all bad. Although some of the research is still in the experimental phase, scientists are studying dental stem cells—which were discovered in 2003—to see if they can potentially be used to repair and regenerate tissue.

One study on mice, at the University of Pittsburgh’s School of Medicine, found that stem cells taken from wisdom teeth could someday be used to repair corneas that have been scarred by infection or injury. Any clinical applications for humans would require more research, though.

"There are studies with dental pulp cells being used to treat neurological disorders and problems in the eye and other things,” Dr. Pamela Robey, of the National Institute of Dental and Craniofacial Research, told CNN. “The problem is, these studies have really not been that rigorous ... the science needs a lot more work.”

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

What Purpose Does the Belly Button Serve?

misuma/iStock via Getty Images
misuma/iStock via Getty Images

While your eyelashes are protecting your eyes, your lungs are letting you breathe, and virtually every other part of your body—inside and out—is performing its own relatively well-known task, your belly button is just sitting there collecting lint. And while it’s true that your navel served its most important purpose before you were born, it’s not totally useless now.

According to ZME Science, back when you were a fetus, your belly button was more of a belly portal: Your umbilical cord extended from it and connected you to the placenta on your mother’s uterine wall. That way, the placenta could channel nutrients and oxygen to you through the cord, and you could send back waste.

Your umbilical cord was cut when you were born, creating a tiny bulge that left behind some scar tissue after it healed. That scar tissue is your belly button, navel, or umbilicus. Though you may have heard that the shape of your belly button is a direct result of the scissor skills of the doctor who delivered you, that’s not true. Dr. Dan Polk, a neonatologist in the Chicago area, told the Chicago Tribune that a belly button's shape “has to do with how much baby skin leads onto the umbilical cord from the baby’s body. Less skin makes an innie; more skin makes an outie.” About 90 percent of people have innies.

Regardless of how your belly button looks, you probably don’t use it on a daily basis. However, if you’ve studied anatomy, medicine, or a related field, you might recognize it as the central point by which the abdomen is divided into the following quadrants: right upper, left upper, right lower, and left lower. Another way of classifying that area is into nine regions—including the hypochondriac, lumbar, iliac, epigastric, and hypogastric regions—with the umbilical region at the very center.

Abdominopelvic regions diagram
Blausen Medical, Wikimedia Commons // CC BY 3.0

Your belly button can also serve as the opening for laparoscopic surgery, which can save you from having a scar elsewhere on your abdomen.

The navel is a great central landmark outside of medicine, too. If you’ve taken yoga or Pilates classes, you may have heard it referred to as the center of balance or center of gravity. Because it sits right on top of your abdominal muscles, your belly button is an easy marker for your instructor to mention when they want you to access your core, which helps you balance.

And, of course, belly buttons are notorious for storing quite a bit of lint, which always seems to be blue (you can learn more about that here).

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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