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Polymers used in Dentistry - White Fillings - Polymer Composite.

Polymers are used in dentistry to make white fillings for teeth.

What are Teeth made from?

Teeth are mainly made from hydroxyapatite (sometimes
called hydroxylapatite), which is a type of  calcium phosphate
with the formula Ca10(PO4)6(OH)2. The outside layer
of teeth, called enamel, contains over 90% hydroxyapatite
Enamel is the hardest substance in the human body.

Why are Fillings needed?

Bacteria which live in the mouth produce acid in the presence
of starch and sugar. The acid can cause small holes to form in
the tooth's enamel. Eventually these holes become big enough
to reach the nerve inside the tooth and it becomes painful.
A dentist can fill these holes
before they reach the nerve to prevent further decay.

What is an Amalgam?

For many years teeth have been filled with a mixture of metals
called an amalgam. Amalgam means an alloy of mercury.
The amalgam used for fillings contains mercury, silver and
other metals. The amalgam is strong enough to
withstand the pressures put on the back teeth (called molars)
during crunching and chewing. It has the disadvantage
that it looks like dark silver and is a good conductor of
heat which can make eating hot or cold things unpleasant.

What is a Polymer Composite?

More recently dentists have used a white composite
for filling teeth. A composite is a substance made
by combining two or more materials. White fillings
are a composite of a polymer filled with glass.
The filling is put on the tooth in the form of a paste
and then a beam of ultraviolet (uv) light is shone
on it. The uv light initiates (starts) chemical reactions
in the paste which form a number of cross links
between the polymer chains. The polymer containing
the glass filler becomes a solid three dimensional
cross linked
network which fills the hole in the tooth.

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