A crown is a hollow cap that fits over a tooth,  giving it
strength and/or improving its appearance. The supporting
tooth has to be reduced in size to make room for the crown.
Crowns may be made from a variety of materials.
Crowns are indicated for teeth, which are too extensively
decayed, damaged or discoloured for treatment by other
means.
The tooth to be crowned may require root filling or rebuilding
with a "build-up core" material before the
dentist drills the tooth to a "peg" shape
for the crown. Tooth preparation for a crown is normally
done under a local anaesthetic and takes approximately
15 to 45 minutes per tooth. It should be painless.
The dentist then takes an impression of the prepared
tooth/teeth, which is sent to a laboratory where the
crown is made. A temporary crown is then fitted to
maintain the appearance, and keep the tooth comfortable
and in the correct position.
The quality of the final crown depends both on the skill
of the dentist and the technician. At the fitting visit,
the temporary crown is removed and the new crown tried
in, to assess that it has an adequate appearance, fit,
shape, and the occlusion is correct. The crown is finally
cemented with a dental cement.
A well made crown or bridge, in a situation where the
overall dental outlook is favourable, should last for
10 or more years.
Sometimes the supporting tooth under a crown decays – this
is more likely when the crown does not fit tightly to
the underlying tooth. Some crowns come off repeatedly,
even shortly after being fitt ed. In these circumstances
the reason for the failure may be a poorly fitting crown,
or a crown shape or bite which is not right for that
tooth. In those circumstances a replacement crown will
be required.
A bridges is a way of replacing a missing tooth with
a fixed solution. There are many different designs
of bridges, but the most common is a fixed bridge,
which is made by placing crowns on the teeth either
side of the space, and then joining the crowns together
by placing a solid crown in the space to replace the
missing tooth. Because this type of bridge uses joined
crowns, cleaning the teeth in the area will be more
difficult. A well-designed bridge should allow effective
daily cleaning.
Just like crowns, a bridge must fit the supporting teeth
tightly – if not, then cleaning the bridge will
be difficult and the teeth supporting the bridge may
decay or get gum disease. Sometimes a bridge will come
off repeatedly. This may be due to a variety of factors
but the size, shape, and relationship to opposing teeth
should be considered as possible problems as well as
the way the bridge fits on the supporting teeth.
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