Bleaching page

  • Does bleaching the teeth really work?

In a word, YES!  It has been done in one form or another for the last 100 years, and it has proven itself to be safe and effective.  The current popularity of the bleaching process goes back only about 10 years, catching on with the public fairly quickly, and with dentists much more slowly over that time.  The reasons that dentists have been less quick to endorse the process are very interesting, and not what you would expect.  I will cover this aspect later in this piece, but first, you need to know a bit more about the process itself.

Exactly what gets bleached during the bleaching process?


The diagram to the right shows the internal structure of a natural tooth.  The layer you can see directly in the mouth is the enamel layer which is the only portion of the tooth that should lie above the gums.  The natural color of enamel is white, but it is translucent and the color of the other structures that underlie it tend to show through.  The material immediately under the enamel is called dentin.  It’s normal color is yellow, but its structure is porous, and materials from the nerve can permeate it causing it to darken to a brownish yellow as we get older.  The color we see when we look at a tooth in the mouth is a composite of the colors of the enamel which may permanently stain as we get older, and the underlying dentin which darkens over the years due to its close association with the underlying nerve.

This is the reason that simply brushing the teeth will not prevent the teeth from becoming  darker yellow as we get older.  You can brush all day, but you will not be able to brush away the natural internal color scheme.

Enter bleach!  Root canal treated teeth tend to be dark because the dead nerve which prompted the root canal treatment turns a chocolate brown and permeates the surrounding dentin before the dead material is removed during the root canal procedure.  It was discovered about 100 years ago that these teeth could be lightened up substantially by temporarily sealing up a cotton pellet soaked with oxalic acid inside the access hole in the crown of the root canal treated tooth.  The cotton pellet was removed after several days and the access was sealed with a filling. Hydrogen peroxide may have been used to lighten teeth as early as 1884.  In 1917, the process was speeded up using hydrogen peroxide and a heat lamp.  This is still the basic procedure used in some offices today.

Later, it was discovered that even dark vital teeth (teeth with live nerves) could be bleached by soaking the tooth in 30% hydrogen peroxide.  This stuff is 10 times more concentrated than the type you can buy in the drugstore, and in order to use it safely, the dentist had to isolate the dark tooth with a rubber dam.  The peroxide could penetrate through the enamel into the dentin and bleach out the dark color.

Finally, about 20 years ago, it was discovered that a 10-percent carbamide peroxide solution (also called urea peroxide) could be applied to the teeth safely without fear of burning or otherwise damaging the mouth, or poisoning the patient.  This dilute solution of peroxide, if kept in contact with the teeth long enough bleached the teeth to a brighter color.  The longer the contact, the brighter the teeth got (up to a point…..sooner or later, there’s no color left to bleach out.).

Is bleaching safe?

Most dentists now offer bleaching as an esthetic treatment for their patients. The American Dental Association has published the following statement:

“Dentist-prescribed, home-applied bleaching made by a reputable manufacturer and used under the supervision of a dentist in a relatively short-term treatment duration is safe and recognized as most effective in lightening the color of teeth. Bleaching materials that have received the ADA Seal of Acceptance are recommended.

Mild thermal sensitivity [sensitivity to cold] is a common side effect associated with most in-office and dentist-prescribed home bleaching methods. However, no long term irreversible tissue effects have been demonstrated in relevant clinical studies.”

Peer reviewed studies have found no irreversible side effects from bleaching with 10 % carbamide peroxide.

The dental profession has recently begun to recommend carbamide peroxide as a means of preventing periodontal disease and tooth decay in patients who are unable to carry out normal oral hygiene measures such as regular brushing and flossing.  For patients like these, rubber trays are fabricated to fit over both the teeth and the gingiva.  The tooth indents in the trays are filled with 10% carbamide peroxide and the patient wears the trays for two hours once a day, or overnight.  The carbamide peroxide breaks down into 3.5% hydrogen peroxide and 6.5% urea when it contacts plaque.  The urea further breaks down into ammonia and carbon dioxide under the action of bacteria.  The hydrogen peroxide kills the oral bacteria, and the ammonia raises the PH of the plaque neutralizing the acid that causes tooth decay.

Tooth Sensitivity

Bleaching solutions do cause your teeth to become temporarily sensitive.  In order to permanently bleach the teeth, the solution must penetrate through the enamel to reach the underlying dentin.  (Click here to see a schematic diagram of the anatomy inside a tooth.)  The dentin contains microscopic tubules which allow the flow of cellular fluids between the living nerve in the center of the tooth and the outer layer of enamel.  This is the reason that the teeth become sensitive.  It would be logical to assume that this process can’t be too good for the health of the nerve, however, over the course of the years that these bleaching products have been used, no ill effects have been reported.  The sensitivity goes away within a few days of terminating the bleaching treatments, and the nerves in the teeth suffer no permanent damage.  The sensitivity, while temporary, in rare cases may be severe and has been known to force some patients to terminate the bleaching treatment early.

What bleaching can’t do

Bleaching will not bleach out the black, brown or white color imparted to teeth due to decay.  Teeth should be repaired before bleaching is performed.

Bleaching will not bleach out darkness imparted to teeth by old amalgam fillings.  Removing the old metal filling and replacing it with a new composite will usually accomplish this, but if the tarnish has penetrated deeply into the tooth structure, the tooth may remain permanently discolored.

Bleaching will not generally improve the appearance of fluorosis if the patient grew up in a part of the country (before the 1960’s) that had a high concentration of fluoride in the drinking water.  This problem is also prevalent in patients who “ate” a lot of fluoride toothpaste when they were toddlers.

Bleaching is ineffective in reducing the irregular gray horizontal lines seen on patients with tetracycline stain in their tooth structure.  Tetracycline stain is seen primarily in older patients who received tetracycline to treat ear infections when they were infants and toddlers.  Physicians in those days did not know that this drug would incorporate itself into the developing teeth of children causing this deformity.

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