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Ask Doctor Cory.

Dear Dr. Cory:

Does cracking your knuckles cause you to get arthritis? I crack my knuckles a lot. It's a habit I developed a while ago. I heard that it wears out the cartilage in your fingers. If it is bad, will you tell me how to stop it? Thank you.

Shane Carney

North Pole, Alaska

Dear Shane:

Cracking your knuckles isn't bad. In fact, several studies suggest that it does not lead; to such diseases as osteoarthritis. However, one study did find that adults who had cracked their knuckles for a long time were more likely to have swelling in their hands and less strength in their grip.

Instead of cracking your knuckles (which is bad manners even if it isn't unhealthy), try to think of something else you can do, such as squeezing a tennis ball. This will help you strengthen your hand and wrist muscles.

Dear Dr. Cory:

About how many teeth am I supposed to lose before I have all my permanent teeth? At what age am I supposed to lose all of my baby teeth?

Kelley Petit

Ojibway, Wisconsin

Dear Kelley:

Every child gets twenty baby, or primary, teeth that should all be present by two and a half years of age. The first permanent molars begin to come in between the ages of five and six. Usually the central incisor teeth arrive at about the same time. Then come the lateral incisors. The teeth will continue to erupt and shed in an orderly way until you are ten or twelve, when the last of the twenty primary teeth fall out.

Between the ages of eleven and thirteen the second permanent molars appear. Most of the other 32 permanent teeth should be in place by that time.-File last set, the third molars, or wisdom teeth, arrive between the ages of seventeen and twenty-one.

Dear Dr. Cory:

My dad says that we yawn because our brain needs oxygen. Is that true?

Jenna Register

Valdosta, Georgia

Dear Jenna:

Your dad is right! Yawning is a way for the body to get extra oxygen and to help wake us up. When we yawn we breathe in slowly and deeply, flooding the lungs with fresh oxygen.

Yawning also helps to open our eustachian (u-STAY-shun) tubes. These are the tubes that connect our middle ear to the back of the throat. We feel the need to open our eustachian tubes when there is a change in air pressure such as, when going up or down in an elevator or an airplane.

Dear Dr. Cory:

How come when you spin around you get dizzy? Is it nerves, or what?

Amber Lutz

Portland, Oregon

Dear Amber:

Yes, the feeling of dizziness does involve your nervous system. There are three semi-circular canals in your inner ear that help you keep your balance. These tubes are filled with a chalky fluid that is in contact with sensitive nerve cells. This fluid moves when you do, stimulating the nerve cells, which then let your brain know the position of your head.

The fluid in your inner ear canals keeps moving even after you have stopped spinning, which sends the message to your brain that you are still moving. Meanwhile, messages from your eyes; and muscles tell your brain that you have stopped. The brain gets confused by these conflicting signals, and you feel dizzy as a result.

See you next issue!

Your friend,

Cory SerVaas, M.D.

A Handful of Handy Hobbies

Here are some things you can do with your hands instead of cracking your knuckles.

* Write a poem

* Scratch your head while you figure out a fun puzzle

* Retie your shoes (mustn't trip!)

* Dial up a friend for a phone chat

* Type an essay

* Tickle your little brother or sister (gently)

* Do push-ups

Send your health questions to: "Ask Doctor Cory" Children's Digest, P.O. Box 567, Indianapolis, IN 46206. This column does not replace your doctor's advice.
COPYRIGHT 1999 Benjamin Franklin Literary & Medical Society, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1999 Gale, Cengage Learning. All rights reserved.

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Title Annotation:questions and answers on knuckle cracking; baby teeth; yawning; dizziness
Author:SerVaas, Cory
Publication:Children's Digest
Date:Sep 1, 1999
Next Article:WINTER LAMB.

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