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Crowns
A
crown is a tooth-shaped cover placed over a
tooth that is badly damaged or decayed. A
crown, which many people call a cap, is made
to look like your tooth.
Crowns may be placed for several reasons,
but generally the tooth has been extensively
damaged by decay or breakage and filling
material can't replace the missing tooth
structure and make the tooth strong enough.
A crown may hold together parts of a cracked
tooth and can be used to hold a bridge in
place. Crowns also are used for cosmetic
purposes to cover misshapen or badly
discolored teeth.
Crowns can be prefabricated or made in a
laboratory. Prefabricated crowns are made of
plastic or stainless steel and can be used
as a temporary restoration until a permanent
crown is manufactured. In some cases,
prefabricated crowns can be used as a
permanent restoration.
Crowns can be all metal, porcelain fused to
metal (PFM), or all ceramic. Metals include
gold alloy, other alloys (palladium) or a
base-metal alloy (nickel or chromium). The
all-metal or PFM crowns are stronger and are
better choices for back teeth. PFM and
all-ceramic crowns look just like normal
teeth.
Usually, crowns last at least 7 years, but
in many cases they last much longer, up to
40 years or so.
Preparing the Tooth
If you need a crown, you may also need
endodontic or root canal treatment on the
tooth, due to extensive decay or the risk of
infection or injury to the tooth's pulp. Not
everyone who needs a crown will also need a
root canal.
Besides the crown, your dentist may need to
build up a foundation to support the crown.
A foundation is needed if large areas of the
natural tooth structure are decayed, damaged
or missing. If you are receiving the crown
after root canal treatment, your dentist may
insert a post-and-core foundation.
To place a crown, your dentist must file
down the tooth to make room for it. If you
are receiving an all-metal crown, less tooth
structure will be removed because these
crowns are thinner than PFM or all-porcelain
ones.
After filing down the tooth, your dentist
will use a piece of thread or cord to push
the gum down around the tooth, and then make
an impression of the tooth. The impression
material sets in five or six minutes and is
removed. Your dentist will also take an
impression of the teeth above or below the
tooth that will receive the crown, to make
sure the crown will not affect your bite.
The impressions are sent to the lab, where
the crown is made. During that time, you
will have a temporary crown. These crowns
are usually made of plastic and are made in
your dentist's office on the day of your
visit. They are not meant to last. If a
temporary crown is left in the mouth, the
cement eventually washes out and the tooth
can decay.
At a second visit, your dentist will remove
the temporary crown and test the permanent
one. Sometimes crowns need additional
polishing or glaze or some other adjustment
before they are placed. Once the crown is
ready, it's cemented to your tooth.
After a Crown
You shouldn't feel any discomfort or
sensitivity after a crown is placed, though
if your tooth still has the nerve in it, you
may have some hot/cold sensitivity. If you
notice pain or sensitivity when you bite
down, you should contact your dentist.
Usually this means that the crown is too
high on the tooth. This can be fixed easily.
You may notice a dark line next to the
gumline on your crowned tooth, particularly
if you have a PFM crown. This dark line is
the metal of the crown showing through and
is normal. A crowned tooth is not protected
from decay or gum disease. You should
continue practicing good oral hygiene.
Crowns, especially all-porcelain ones, can
chip. This can sometimes be repaired in the
mouth. Your dentist will etch the porcelain
with acid and bond composite resin to it to
fix the chip. If the chipping is extensive,
you may need a replacement crown.
It's also possible that the cement could
wash out from under the crown, but the crown
does not fall out. Under these conditions,
bacteria can leak in and cause decay. If
your crown seems loose, contact your dental
office.
Your crown may fall out, due to a lack of
cement or an improper fit. If this happens,
clean the crown and the tooth. You can
replace the crown temporarily using denture
adhesive or temporary cement sold for this
purpose. Contact your dental office
immediately and try to schedule a visit for
the next day. If you are away from home,
seek a dentist in the area who can evaluate
the problem. You may need a new crown or it
may be possible to re-cement the old one on
the tooth.
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