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Home  Dentistry Articles Tooth bleaching
Tooth bleaching
Tooth bleaching, also known as tooth whitening,
is a common procedure in general dentistry but most especially
in the field of cosmetic dentistry. Many people consider white
teeth to be an attractive feature of a smile. A child's deciduous
teeth (milk teeth) are generally whiter than the adult teeth that
follow. As a person ages the adult teeth often increase in value,
that is to say they become darker. This darkening is due to changes
in the mineral structure of the tooth, as the enamel becomes less
porous. Teeth can also become stained by bacterial pigments, foodstuffs
and tobacco.
As white teeth are subconsciously associated
with youth, they have become desirable. This has been made more
apparent with the spread of American culture worldwide, where
an especially white smile is coined, a "Hollywood smile".
The procedure to bleach teeth uses oxidising agents such as hydrogen
peroxide to lighten the shade of the tooth. The oxidising agent
penetrates the porosities in the rod-like crystal structure of
enamel and oxidises interprismatic stain deposits, over a period
of time, the dentine layer, lying underneath the enamel, is also
bleached.
There are two main methods of bleaching. The
first involves applying a high concentration of oxidising agent
for a short period of time (the so called office bleach). This
produces quick results but risks chemical burns to the soft tissues.
The bleaching agent here is carbamide peroxide, which breaksdown
in the mouth forming hydrogen peroxide.
The alternative method involves using a thin
mouthguard to hold a low concentration of oxidising agent next
to the teeth for several hours a day for a period of some weeks.
This is known as the home or nightguard bleach. This is slower
but has lower risks to the soft tissues.
A typical course of bleaching can produce dramatic
improvements in the cosmetic appearance of most stained teeth,
however some stains do not respond to bleaching. Tetracycline
staining may require prolonged bleaching, as it takes longer for
the bleach to reach the dentine layer. White-spot decalcifications
may also be highlighted and become more noticeable.
Recently, efforts have been made to accelerate
the bleaching process by the use of light. Studies have shown
varying results as to the efficacy of light-activated bleaching.
Side effects of tooth bleaching are: Chemical
burns if high concentration oxidising agent contacts unprotected
tissues; sensitive teeth, and overbleaching to produce what are
known in the profession as "Fridge-door teeth". Rebound,
or teeth losing the bleached effect and darkening, is also an
issue, with few studies showing the rebound effect over 30 days.
A recent study by Kugel et al, has shown that as much as 4 shades
of lightness can be lost over 30 days with light-activated/office
bleaching.
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