WHAT IS A CROWN?
A crown (or cap) is a dental restoration that fully covers the tooth. It is cemented in place.
WHAT IS IT MADE OF?
A crown can be made of porcelain only, gold or metal only, or a combination of porcelain and metal.
WHY DO TEETH NEED A CROWN?
A dentist will recommend a crown
- Strengthen a tooth
- Restore the shape of a tooth
- Improve the appearance of a tooth.
FILLING VERSUS A CROWN
If a tooth has only a small hole due to decay or a small fracture it can be restored using a filling. There must be sufficient tooth structure to hold the filling in place. When a large part of the tooth is missing a filling can be placed but the strength of the tooth is compromised and there is a risk of the tooth fracturing.
The advantage of a crown is that it completely covers the remaining tooth, preventing further fracture and restoring the original shape of the tooth. The crown can act as a splint and bond the tooth together.
HOW IS A CROWN MADE?
Two appointments are required when crowning a tooth.
The first visit, usually about an hour, involves:
- Numbing the tooth with local anaesthetic if required.
- The tooth must then be reshaped to accommodate the thickness of the crown. Otherwise the new shape will be too large and your teeth won’t meet properly.
- An impression is then taken of the tooth. This is sent to the laboratory where the crown is fabricated.
- A temporary crown is then made and fitted over the tooth and cemented with temporary cement.
- A shade is selected for the porcelain so that it matches the colour of your own teeth to make it look natural.
A second visit some weeks later is needed to remove the temporary crown and cement the permanent crown. The fit and bite are checked.
LOSS OF TEMPORARY CROWN
The temporary crown is made of plastic and cemented using temporary cement. If it breaks or comes off it is advisable to return to the surgery as soon as possible to recement it or make a new one. Keeping hard, chewy or sticky food away from the temporary crown avoids this mishap.
HOW LONG DOES A CROWN LAST?
Studies show that 90% of well made crowns will last ten or more years.
A crown may need to be replaced due to:
- Crown fracture. This is more likely with an all-porcelain crown on the front teeth.
- Decay at crown margin. If plaque accumulates at the margin between the crown and the tooth due to poor oral hygiene, decay may start.
- Crown is worn. This does not occur often but if there is a grinding or clenching habit the crown can wear excessively.
- Dark colour at crown margin. This can develop due to natural gum recession caused by poor oral hygiene, gum recession due to the presence of a clenching or grinding habit or where the front teeth take most of the force of the patients bite due to a lack of back teeth. The margin of the crown, previously below the gum, is exposed and a grey appearance is visible.
ROOT FILLED TOOTH
When a tooth is root filled the pulp and nerve are removed as they are damaged. The nerve canal is then filled. This makes the tooth more susceptible to fracture. A root filled tooth usually has a large part of it missing due to decay or fracture. For this reason the dentist may recommend a crown be placed to prevent the possibility of root fracture and consequent loss of the tooth.
Teeth of poor appearance, especially at the front of the mouth, will benefit from custom fitted well made crowns. The teeth may be crowded, crooked, misshaped or discoloured. Porcelain crowns are suitable for these teeth. These cosmetic crowns are translucent and therefore allow the natural colour of the underlying tooth to shine through. The margins are metal-free and therefore the aesthetics are superior.