Dental How's

Dental “HOW’s” and “WHATNOTS”.  A small look in the eyes of the professionals to see how things in dentistry works, and what you need to know.

How do people pull large objects with their teeth?

You've probably seen the headline: "Man pulls 50,000-pound bus with teeth." It sounds pretty impressive, but let's see how hard it really is to move the bus.

Assuming the bus is on level ground, the main force that has to be overcome to move the bus is the rolling resistance of the tires. This force depends on two things, the weight of the bus and the coefficient of rolling resistance of the tires. We know the weight, but where does the rolling resistance come from?

The tires on any vehicle deform or squish as they move, and it takes force to make them deform. The less they deform, the less force it takes. For instance, a train wheel has less than one-tenth the resistance of a car tire because a steel wheel doesn't deform as much as it rolls.

A big bus has tires with a coefficient of rolling resistance of 0.006 - 0.01. Making sure that the pressure in the tires is correct, or even a little bit high, can minimize the resistance. So, we'll say that for this stunt that coefficient is 0.006.

This means that the force required to pull the bus is 0.006 multiplied by the weight of the bus, or 0.006 times 50,000 pounds. That is 300 pounds. There might be some extra force from brake drag or friction in the driveline, so we'll say it takes 400 pounds of force to move the bus.

This is a lot of force, but it is possible for a person to exert this much force with his legs (and hold it with his teeth). But the problem now becomes traction. Just like the coefficient of rolling resistance, there is a coefficient of friction between your shoes and the ground. This coefficient determines how much force you can apply in the horizontal direction before your feet slip. About the best coefficient you could hope for is 1.0. If your shoes did have a coefficient of 1.0, then you could apply a force equal to your weight in the horizontal direction. Most likely though, the coefficient of friction would be less than 1.0, so unless you weighed much more than 400 pounds, you would not be able to exert that much force against the ground.

So the second part of the bus-pulling trick is to increase your traction. Sometimes the pullers do this by anchoring a ladder to the road and using the steps of the ladder to push against. If a man is pulling a train, then he could push against the railroad ties. These methods make traction less important because now you are pushing against a vertical surface instead of a horizontal one, so the force you apply against the ladder is in the same direction as the force you apply against the bus. This makes pulling the bus more like lifting a 400-pound weight with your legs.

Your teeth have to be able to hold the rope with 400 pounds of force, but they don't do the lifting. You might be thinking that your neck is the weak link -- how can your neck muscles lift 400 pounds? The answer is, you don't really lift the whole weight with your neck muscles. Since you have to lean back a lot to push against the ladder for traction, most of that 400 pounds of force is transmitted down your spine. For instance, if you were lying flat on your back while you pulled the bus, all of the 400 pounds of force would be transmitted down your spine. So the closer you can get to the ground, the less force your neck muscles have to apply.

Pulling the bus is still an impressive feat, but lifting 400 pounds with your legs while holding it in your teeth sounds a little less impossible than pulling a 50,000-pound bus.

http://science.howstuffworks.com/question523.htm

Teeth Whitening Facts

Teeth whitening, also known as teeth bleaching, has become extremely popular over the last several years. It’s a great way to improve your appearance, it’s reasonably priced, non-surgical and non-invasive.

As with everything else, teeth whitening isn't perfect and it isn't for everyone. Before you decide to have your teeth whitened, you should talk with your dentist. Your dentist can determine if you are a good candidate for teeth whitening. Knowing the facts can help you with your decision also:

Teeth whitening procedures are not covered by most dental insurance plans.

Tooth coloured fillings, crowns, bridges and veneers will not lighten when your teeth are bleached.

Whitening toothpastes can make your teeth appear a little lighter by removing stains, but they do   not actually bleach your teeth.

Teeth whitening does not produce the same results on all types of teeth discoloration. Someone with yellow tinted teeth would probably have great results with bleaching, while someone with gray tinted teeth might be disappointed because gray tinted teeth don't bleach as well.

Tooth sensitivity and gum irritation are common side effects of teeth whitening treatments.

If you have any cavities, they should be filled before you have your teeth whitened.

Teeth whitening kits from the dentist produce faster results because they contain a stronger peroxide bleaching agent than whitening kits purchased over the counter.

Touch ups are usually needed to maintain your desired shade, depending upon habits such as smoking, drinking coffee and tea and eating certain foods, which will stain your teeth.

People with gum disease shouldn't get their teeth whitened.

It's a good idea to have a dental cleaning prior to having your teeth whitened to remove surface stains.

http://dentistry.about.com/od/cosmeticdentistry/a/factswhite.htm