Crowns

Ceramic single crownCeramic single crownCeramic single crown

Crowns (tooth caps) are dental restorations which completely cover the portion of a tooth that sits above the gum line, so they cover that part of the tooth that is visible in the mouth.

Different materials are used to produce dental crowns that match or enhance the appearance of natural teeth. The materials most commonly used for crowns are various types of dental ceramics (porcelains), which provide excellent aesthetics and are particularly used for restoration of front teeth. Other types of crowns consist of a metal core covered with ceramic veneer.

These so called metal-ceramic crowns provide good aesthetics combined with the strength and durability necessary in areas of high stress concentration, such as the molar teeth. The metallic part of such crowns is not visible below the porcelain, giving the appearance of a natural tooth. The exclusive use of “noble” gold based alloys ensures better fitting and longer lasting crowns.

Occasionally crowns are made completely of gold alloy, predominantly for use on upper back teeth where they provide long lasting service without being visible.

Why do teeth need dental crowns?

A crown might be recommended for a variety of reasons, typically falling into one of the following categories:

  • To restore a tooth to its original shape.
  • To strengthen a tooth.
  • To improve the cosmetic appearance of a tooth.

The steps in making a crown

The tooth itself has to first be trimmed and sometimes built up to a shape that will allow fitting of a crown. The tooth trimming (preparation) might have to be preceded by complete removal of all existing fillings. This is done in order to assess the tooth structure and to make a decision on whether the remaining tooth is sufficiently strong to support the crown. Along the way any underlying decay or cracks would be exposed and remedied, so the crown will ultimately be placed on sound tooth tissue. In some cases where the tooth is deemed not to be strong enough or insufficient to hold a crown, it will be built up with a new filling that is both strong and well anchored to the tooth to act as a core for the future crown.

Following preparation of the tooth, a silicone impression or mould is taken of the prepared tooth for the dental laboratory. A temporary (provisional) crown is made and cemented onto the prepared tooth until the next appointment. Temporary crowns are strong enough to allow gentle chewing and match the other natural teeth, so that appearance is not compromised.

The impression taken of the prepared tooth is sent to the dental laboratory where dental technicians will use it to manufacture the final crown according to specific instructions.

At the next appointment the temporary crown is removed and the new crown is tried on the prepared tooth. Usually some small adjustments are required at this stage and most of the time they can be done during the same appointment. Once both patient and dentist are satisfied with appearance and fit of the crown it will be cemented onto the tooth with “permanent” cement. If any necessary adjustments cannot be done at this time the temporary crown is replaced on the tooth and the final crown is returned to the laboratory for adjustment, and fitted at a following appointment.


Selection of the crown colour

The colours of teeth are different for everyone. There are also some differences in colours between the teeth of the same person. As a rule, the teeth on the lower jaw are darker than the teeth on the upper jaw; the eye teeth are darker than their neighbours and so on. As well, each tooth is a combination of different colours changing from the neck to the edge. All this makes the exact colour match a very difficult and tricky process. While some simple colours could be matched in the office, in other cases the patient may be asked to visit the dental laboratory to allow the technicians themselves to select the right colour for the crown.


How long do crowns last?

Like most things, crowns do not last forever. The crowns work under very harsh conditions, in a wet environment where they are subjected to constant stress resulting from chewing and clenching of teeth. The dental literature suggests that the average lifespan of a crown is somewhere between 10 and 15 years. This of course varies greatly from one person to another and depends on many variables. If a crown is fractured or lost, in many cases a new crown can be made, provided that the supporting tooth remains in good condition.