Dental Crowns
A dental crown is a tooth-shaped "cap" that is placed over a tooth – covering the tooth to restore its shape and size,
strength, and/or to improve its appearance.
The crowns, when cemented into place, fully encase the entire visible portion of a tooth
that lies at and above the gum line.
Why is a Dental Crown Needed?
A dental crown may be needed when at least one of the following occurs:
What Types of Crown
Materials are Available?
Permanent crowns can be either all metal, porcelain-fused-to-metal, all resin, or all ceramic.
Metals used
in crowns include gold alloy, other alloys (for example, palladium) or a base-metal alloy (for example, nickel or chromium). Compared
with other crown types, less tooth structure needs to be removed with metal crowns, and tooth wear to opposing teeth is kept to a
minimum. Metal crowns withstand biting and chewing forces well and probably last the longest in terms of wear down. Also, they rarely
chip or break. The metallic colour is the main drawback. Metal crowns are a good choice for out-of-sight molars.
Porcelain-fused-to-metal dental
crowns can be colour matched to your adjacent teeth (unlike the metallic crowns). However, more wearing to the opposing teeth occurs
with this crown type compared with metal or resin crowns. The crown's porcelain portion can also chip or break off. Next to all-ceramic
crowns, porcelain-fused-to-metal crowns look most like normal teeth. However, sometimes the metal underlying the crown's porcelain
can show through as a dark line, especially at the gum line and even more so if your gums recede. These crowns can be a good choice
for front or back teeth.
All-ceramic or all-porcelain dental crowns
provide the best natural colour match than any other crown type and may be more suitable for people with metal allergies. However,
they are not as strong as porcelain-fused-to-metal crowns and they wear down opposing teeth a little more than metal or resin crowns.
All-ceramic crowns are a good choice for front teeth.
Temporary
versus permanent. Temporary crowns can be made in your dentist's office whereas permanent crowns are made in a dental laboratory.
Temporary crowns are made of acrylic or stainless steel and can be used as a temporary restoration until a permanent crown is constructed
by the dental laboratory.
What Steps are Involved in Preparing a Tooth for a Crown?
Preparing a tooth for a crown usually requires
two visits - the first step involves examining and preparing the tooth, the second visit involves placement of the permanent crown.
Before the process of making your crown is begun, your dentist will anaesthetise your tooth and
the gum tissue around the tooth. Next, the tooth receiving the crown is filed down along the chewing surface and sides to make room
for the crown. The amount removed depends on the type of crown used (for instance, all-metal crowns are thinner, requiring less tooth
structure removal than all-porcelain or porcelain-fused-to-metal ones). If, on the other hand, a large area of the tooth is missing
(due to decay or damage), your dentist will use filling material to "build up" the tooth enough to support the crown.
After reshaping
the tooth, your dentist will use impression paste or putty to make an impression of the tooth to receive the crown. Impressions of
the teeth above and below the tooth to receive the dental crown will also be made to make sure that the crown will not affect your
bite.
The impressions are sent to a dental laboratory where the crown will be manufactured. The crown is usually returned within 2
to 3 weeks. If your crown is made of porcelain, your dentist will also select the shade that most closely matches the colour of the
neighbouring teeth. During this first office visit your dentist will make a temporary crown to cover and protect the prepared tooth
while the crown is being made. Temporary crowns usually are made of acrylic and are held in place using a temporary cement.
How Should I Care for My Temporary Dental Crown?
Because
temporary dental crowns are just that – a temporary fix until a permanent crown is ready, most dentists suggest that a few precautions
be taken with your temporary crown. These include:
What Problems Could Develop With a Dental Crown?
Discomfort or sensitivity.
Your newly crowned tooth
may be sensitive immediately after the procedure as the anesthesia begins to wear off. If the tooth that has been crowned still has
a nerve in it, you may experience some hot and cold sensitivity. Your dentist may recommend that you brush your teeth with a toothpaste
designed for sensitive teeth. Pain or sensitivity that occurs when you bite down usually means that the crown is too high on the tooth.
If this is the case, call your dentist. He or she can easily fix this problem.
Chipped crown.
Crowns made of all porcelain
can sometimes chip. If the chip is small, a composite resin can be used to repair the chip with the crown remaining in your mouth.
If the chipping is extensive, the crown may need to be replaced.
Loose crown.
Sometimes the cement washes out from under
the crown. Not only does this allow the crown to become loose, it allows bacteria to leak in and cause decay to the tooth that remains.
If your crown feels loose, contact your dentist's office.
Crown that falls off.
Sometimes crowns fall off. Usually this
is due to an improper fit or a lack of cement. If this happens, clean the crown and the front of your tooth. You can replace the crown
temporarily using dental adhesive or temporary tooth cement that is sold in stores for this purpose. Contact your dentist's office
immediately. He or she will give you specific instructions on how to care for your tooth and crown for the day or so until you can
be seen for an evaluation. Your dentist may be able to re-cement your crown in place; if not, a new crown will need to be made.
Allergic
reaction.
Because the metals used to make crowns are usually a mixture of metals, an allergic reaction to the metals or porcelain
used in crowns is extremely rare.
Dark line on crowned tooth next to the gum line.
A dark line next to the gum line of
your crowned tooth is normal, particularly if you have a porcelain-fused-to-metal crown. This dark line is simply the metal of the
crown showing through.
What are "Onlays" and "3/4 Crowns?"
These are variations on the technique of dental crowns. The
difference between these crowns and the crowns discussed previously is their coverage of the underlying tooth - the "traditional"
crown covers the entire tooth; onlays and 3/4 crowns cover the underlying tooth to a lesser extent.
How Long Do Dental Crowns
Last?
On average, dental crowns last between 5 and 15 years. The life span of a crown depends on the amount of "wear and tear"
the crown is exposed to, how well you follow good oral hygiene practices, and your personal mouth-related habits (you should avoid
such habits as grinding or clenching your teeth, chewing ice, biting your fingernails and using your teeth to open packaging).
Does
a Crowned Tooth Require any Special Care?
While a crowned tooth does not require any special care, remember that simply because
a tooth is crowned does not mean the underlying tooth is protected from decay or gum disease. Therefore, continue to follow good oral
hygiene practices, including brushing your teeth at least twice a day and flossing once a day-especially around the crown area where
the gum meets the tooth.
