What is a crown and when is it needed?
A crown is a “cap” that is placed around a tooth to restore it to its proper shape and to allow it to withstand biting forces. Crowns may needed when:
- A tooth is so badly decayed that a filling cannot be secured to the cavity
- A tooth is broken or fractured (e.g. due to accidents)
- After root canal treatment, if the remaining tooth structure has become too weak.
What is the process like?
The first step in making a crown is to remove any existing decay on the tooth. Your dentist may then fill up the cavity. Next, he will trim away the outer surface of the tooth to create space for the crown. He will then make an impression (or a mould) of your teeth to obtain models of your teeth. These models are sent to a dental laboratory where a customized crown will be fabricated. In the meantime, your dentist will cement a temporary crown on the tooth. At the second visit, the temporary crown will be removed and the definitive crown cemented on the tooth. You will usually need to wait a few days in between these two visits.
Some clinics are now able to fabricate the crown within the same day, using CAD-CAM technology. Thus you will be able to get your crown within one visit. Check with your GP if this service is available.
What material is the crown made of?
Crowns can be made of many different materials. These can be categorized into three groups:
- Full metal crowns – can be made of gold, precious alloys, semi-precious alloys or base metal. Full metal crowns can be very durable, but are only suitable for back teeth because the colour is so different from natural teeth
- Metal-fused to porcelain (PFM) crowns – these are crowns with an internal layer of metal, overlaid with a porcelain veneer. They offer good durability coupled with good aesthetics.
- Full ceramic crowns – these are the latest materials used for crowns. Only a few years ago, full ceramic crowns were used only for anterior teeth, because the materials gave excellent aesthetics but were somewhat weaker than the metal or PFM crowns. The latest ceramic materials, however, now offer both strength and great aesthetics. Ask your GP for more information.
Fig1. Process of making a crown. Clockwise from bottom right: after the tooth is prepared, an impression is made. A model is made from the impression. A crown is made based on the model. The crown shown is a full porcelain crown.
Veneers are similar to crowns, the difference being that only the front surface of the tooth is trimmed to accommodate a veneer, whereas the whole surface of the tooth is trimmed for a crown. (See diagram) Veneers are done mainly for front teeth.
Veneers can be done for the following situations:
- To improve the shape of front teeth that are worn down.
- To change the colour of front teeth that are severely stained and not correctable by whitening
- To improve minor irregularities in the position of the front teeth.
- To improve the shape of malformed teeth.
The process of making veneers is similar to that of crowns.
Fig2. Note the mal-alignment and irregularities.
Fig3. Crowns and veneers have been used to improve the general appearance.