You: Being Beautiful: The Owner’s Manual to Inner and Outer Beauty. Michael Roizen F.

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      Elephants displace teeth from the back; they’re grinders. But most animals are like us and have a single series of adult teeth, since we need to develop perfect occlusion and would lose this with continual change. Crocodiles have “nails” for teeth, which are designed for grabbing rather than chewing. Our mandibles were fused about 40 million years ago. We lost the independence of selective chewing but gained the ability to spread the force of chewing to the entire jaw. We also have a two-post jaw joint, which allows our mandible to slide forward and then drop down. This enables the masseter muscle to develop increased force during chewing. Carnivores don’t have the mechanism since they must grab and tear their food.

      Your jawbone (docs call it the mandible): The only time we ever get to see jaws is in museums, and they’re usually of the shark or dinosaur variety. But the human jaw is a powerful little clamp of its own—exerting 50 to 250 pounds per square inch of pressure during chewing. It’s also extremely efficient: It’s the only joint in the body that purposely dislocates itself during a motion, using two points of attachment—one lever point in the back of the jaw and another two inches in front. Every time you chew, your jaw dislocates and relocates, allowing you to crush food so you can swallow and digest. But the muscles that move the jaw can also be a source of pain. If you chew too much or subconsciously clench your jaw during stressful times, your jaw muscles can spasm. Stress-induced clenching or grinding can cause slight misalignment of the jaw, leading to jaw, neck, or eye pain, as well as jackhammer-like headaches. By the way, if you lose your teeth—be it through decay or an errant baseball—your jawbone will eventually erode away as well (use it or lose it). The main purpose of your jawbone is to support teeth, and a very intricate and complicated set of muscles, ligaments, and skin holds your jaw in place.

      Your gums: We all know how well that peas-in-the-teeth look impresses first dates and job interviewers, and it doesn’t go over too well with the rest of your body either. Lest you think your gums aren’t important: The amount of tissue involved in a severe gum disease case is approximately the same as the surface of the skin on the back of the hand. What would you do if the back of your hand was bloodred and swollen and bled at the slightest touch? You would haul your buns to the doctor. But when the same thing happens in the mouth, you think it’s normal. When plaque—that sticky gunk made up of bacteria, saliva, and yesterday’s dinner—wedges between your teeth into your gums, it triggers a process of inflammation that leads to periodontal disease (gingivitis is infection of the gums, while periodontitis occurs when the disease progresses to the ligaments and bones around the teeth). Regular flossing and checkups can rid you of plaque and help save your teeth. Gum disease is linked to many other problems, likely because the same bacteria that can cause periodontal disease can also trigger an immune response that causes inflammation and hardening of the arteries. That plaque that’s found near your teeth contains a zoo of bacteria and proteins, sugars, and fat, as well as calcium and phosphorus. This tough stuff sticks to your teeth and causes gingivitis (gingivitis is an even better indicator of heart disease than levels of cholesterol).

      Your teeth. Wiggle your jaw around (go ahead, nobody’s looking). Your top teeth are fixed to your skull, while your lower jaw has the flexibility to move front to back and side to side. If the top and bottom are misaligned, your upper teeth can’t adjust, so you end up wearing down your teeth. How do you know if you’re a teeth grinder? One, by taking the flat-teeth test in Chapter 3, and two, because teeth grinders show less tooth when they smile, which makes them look older and less attractive.

      While acceptable on dance floors, grinding isn’t so great for your mouth. It causes premature aging as the wearing down of the front teeth inhibits the ability of the jaw to work efficiently, causing back teeth to wear down as well. Grinding can also injure your jawbone joint, called the TMJ (temporomandibular joint). If you’re a grinder (which can be caused by stress or misalignment), you’ll want early detection so your bite can be analyzed and you can be fitted for a night-guard mouthpiece that prevents you from grinding while you sleep. Left untreated, your teeth will eventually break and split from your gums. It depends on the break or the severity of the split if they can be saved or not. If it’s not too severe, crowns can cover them. Severely worn teeth may have to be replaced (and that can cost up to $2,000 per tooth).