An article for tooth care and stain removing

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February 10, 2003

Volume 81, Number 06

CENEAR 81 06 p. 29

ISSN 0009-2347

 

 

TEETH WHITENERS

For those seeking a dazzling white smile, polishers and peroxide may

do the trick

AMANDA YARNELL

 

As far back as the Middle Ages, people have been willing to go to

great lengths for a bright-white smile. In those days, the

neighborhood barber-surgeon--the guy you went to for anything from

minor surgery to a haircut--would also file down your not-so-pearly

whites and soak them in a concentrated solution of nitric acid.

Patients did get the white teeth they were looking for. But the

concentrated acid destroyed their tooth enamel, causing massive tooth

decay later in life.

 

 

SMILE Most whitening products rely on hydrogen peroxide to

remove stains from teeth.

 

Today, people seeking dazzling white choppers, à la Julia Roberts,

can turn to less extreme methods. A vast array of pastes, gels, and

strips promises to give you a movie-star smile, and they work at home

or in the dentist's chair.

The outermost part of your teeth consists of a translucent layer of

highly ordered hydroxyapatite, a mineral made up of calcium

phosphate. This protective layer, known as enamel, is the hardest

tissue in the body. Underneath it lies dentin, an off-white matrix of

amorphous calcium phosphate and collagen that surrounds the blood

vessels and nerves that nourish your teeth. Light passing through the

enamel is reflected by the dentin, giving your teeth their pearly

white color.

The root cause of most tooth discoloration lies just at the surface

of your teeth's enamel. Drinking red wine, coffee, and tea can

discolor your teeth. Colored molecules found in these beverages,

including tannins and other polyphenols, adsorb to the enamel's

surface. Dark pigments in cigarettes, blueberries, and other foods

can also be deposited on your tooth enamel. Much of this superficial

staining can be combated by regular brushing. But over time, these

compounds can diffuse into the enamel, where they cannot be removed

by brushing alone.

Aging is another big culprit. As we get older, our dentin gradually

takes on a yellowish hue. " We don't yet know what chromophore or

chromophores cause this tooth yellowing, " says Paul A. Sagel,

principal engineer of Procter & Gamble's oral care product delivery.

His group is using ion mass spectrometry on teeth of varying ages to

try to answer this question.

In addition, the antibiotic tetracycline can gray children's teeth if

taken during their early years, when tooth enamel has yet to

completely harden. Tetracycline is incorporated into children's

enamel and dentin. Over time, it photooxidizes, giving teeth a

grayish-blue tint that's difficult to remove.

Whether the culprit is diet, age, or drugs, those who have visited

their dentist or drugstore seeking whiter teeth know that there are a

dizzying number of products available. But many of them work the same

way, by removing surface stains. Instead of actually altering your

teeth's natural color, most whitening toothpastes just remove the

surface stains that mask your teeth's intrinsic hue.

All toothpastes rely on abrasives to scrub stains from the tooth

surface. The first " toothpowder, " created in England in the late-18th

century, contained rather harsh abrasives, including brick dust and

ground-up cuttlefish. Today, toothpastes contain milder polishing

agents such as silica, aluminum oxide, calcium phosphates, or calcium

carbonate. Some toothpaste manufacturers also offer products that

rely on proteolytic enzymes and chelators to lift stains on the teeth.

To combat stains below the surface, you'll probably need to turn to

whitening gels containing hydrogen peroxide. The tooth-whitening

power of peroxide was first recognized in the early 1970s. Dentists

noticed that an oral antiseptic containing peroxide not only helped

heal lesions in their patients' mouths but also gave them whiter

teeth. Today, peroxide-based gels for tooth whitening at home and at

the dentist are a booming business.

Hydrogen peroxide works its magic by breaking down into water and

oxygen via radical intermediates. It's thought that these radical

intermediates react with polyphenols and other pigments that stain

teeth, at least in part by destroying the double-bond network that

lends such compounds their color.

H2O2 can diffuse through the enamel and into the dentin in about 15

minutes, Sagel says. So, with proper use, H2O2 bleaching can combat

stains both at and beneath the teeth's surface.

But close inspection of the labels of many of the whitening products

on the market shows that most contain carbamide peroxide--a 1-to-1

compound of urea and H2O2 that contains 33% H2O2 by weight--instead

of H2O2 itself. The reason is historical, Sagel says. Because the

earliest peroxide antiseptics had to be packed into oral wounds,

solid carbamide peroxide was used instead of liquid hydrogen

peroxide. Carbamide peroxide remains popular, despite being more

expensive and harder to formulate than H2O2.

Most peroxide-containing whiteners come in a gel that also contains

glycerin and carbopol as thickeners and, in some cases, flavoring

agents. Stannate and pyrophosphate salts are often added to scavenge

metals and prevent peroxide decomposition while the gel is still on

the store shelf.

Gels containing 10 or 20% carbamide peroxide can be brushed directly

onto teeth, delivered in a mouth-guard-like tray, or embedded in an

adhesive plastic strip that is stuck on the teeth. Several weeks of

use is often necessary to see whitening with these at-home products.

In professional procedures for teeth whitening, dentists use up to

35% H2O2. Because whitening gels can cause tooth sensitivity and gum

irritation, extra precautions are taken to apply the gel only to the

teeth. Lasers and other light sources are sometimes used in

combination with the gel; it's thought that these light sources

simply accelerate the rate of peroxide decomposition, thereby

speeding up the bleaching process. But whether lights add real

benefit remains controversial.

If none of these options works for you, there's still one left: tooth

veneers. Popular with movie stars and models, thin veneers made of

porcelain are bonded to the existing teeth. Porcelain veneers won't

last as long as your real teeth. But unlike your own teeth, these

pearly whites don't stain--leaving you to dazzle maintenance-free.

 

 

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