The great Valentine's Day toothpaste debate.

Valentine's Day is just around the corner, and you want to look your best. Should you splurge on premium toothpaste? After all, Cupid loves a winning smile. But an $11.00 tube of toothpaste will leave you with precious little spending money for your Valentine's Day date. Maybe some of the less-expensive brands work just as well. Try these experiments to find out.

P.S.: Teeth are just the beginning. Turn to the activities on pages 12-14 for more on the science of keeping clean.

PLAQUE: THE ENEMY

Cavities, bad breath, and dingy teeth. They're all caused by plaque (above)--that gluey layer of bacteria that feeds off sugars on your teeth. When these microscopic critters digest the sweet stuff, they produce lactic acid. It's this acid--not the sugar--that corrodes your teeth.

Brushing scrubs away both plaque and sugar. Fluoride, a key paste ingredient, can actually repair some tooth damage before it gets too deep. To read more about toothpastes, see Consumer Reports, September 1992.

THE ABRASION TEST

To help you get rid of plaque, toothpastes contain abrasives--gritty substances that create friction between brush and tooth to scrub the bacteria away.

Are high-priced toothpastes more abrasive than cheaper brands? Do "natural" toothpastes work as well as the standard varieties? You can find out.

WHAT YOU NEED:

* several brands of toothpaste

* clean microscope slides * lens-cleaning tissue * magnifying glass or microscope

WHAT TO DO:

1. Squeeze a 1/2-centimeter-long sample of toothpaste onto a slide. Place another slide on top and gently rub the two slides together for 15 seconds.

2. Remove the top slide. Wash and dry it with lens-cleaning tissue.

3. Using a magnifying glass or microscope, examine the slide carefully for scratches. In your Data Table, record the abrasive action (the number of scratches) as "light," "moderate," or "heavy."

4. Repeat for all other test brands. Which brand was the most abrasive? The least?

DON'T STOP NOW!

What factors besides abrasiveness determine whether a toothpaste is worth buying?

THE ACID TEST

Why shell out for expensive toothpaste? Because these high-priced products contain baking soda, manufacturers say. And baking soda, they claim, neutralizes the acids that corrode your teeth. Should you buy the claim? How about the products? This test will help you decide.

WHAT YOU NEED:

* toothpastes (use one brand without baking soda as a control) * universal pH indicator paper * test tubes * various liquids

WHAT TO DO: Find a test solution

The decay-producing acid made by plaque bacteria has a pH of approximately 3.0. Use strips of pH indicator paper to find a liquid with the same pH. Try orange juice, vinegar, what else? (Hint: You can dilute any liquid you try with water.)

Acid neutralization test 

1. Pour ten milliliters of test solution into a test tube. Add a 1/2-centimeter-long sample of toothpaste. Stir for 20 seconds.

2. Measure the pH of the solution with an indicator strip. Record the pH in your Data Table.

3. Repeat Steps 1-2 for all other brands to be tested. Did baking soda toothpaste neutralize the acid? How about regular toothpaste?

DON'T STOP NOW!

Maybe you don't need toothpaste of any type to neutralize plaque acids. Your saliva, dentists say, is basic. Will it do the job alone? Devise a test to find out. What factors might determine saliva's effect on these acids in your mouth?

UNDERSTANDING THE pH SCALE

The pH scale measures how acidic or basic a substance is. Pure water, which is neutral, has a pH of 7.0. As you move down the scale from 7.0 to 0, you get stronger and stronger acids. (The acid produced by plaque--pH 3.0--is as strong as the acid in apples.) As you move up the scale from 7.0 to 14.0, you don't get weaker acids--you get stronger and stronger bases, which can be just as corrosive as acids. Combine an acid with a base, and you get a neutralization reaction, producing water and a salt.

MAKE YOUR OWN EMERGENCY TOOTHPASTE

Your date will be at the door in two minutes and you're out of toothpaste. What now?

1. Place two spoonfuls of crushed antacid tablets (calcium carbonate) in a cup. That's your abrasive.

2. Add one spoonful of baking soda (sodium bicarbonate)--your acid neutralizer.

3. Add drops of water with an eydropper until you have a paste. Stir the mixture with your toothbrush.

Presto! You have toothpaste (minus the all-important fluoride and minty taste). To find out if it works well enough for emergency use, put it to the tests on this and the preceding pages.

Could you improve your toothpaste's taste, texture, and so on while retaining, or even improving, its effectiveness? How?