A dental crown is a tooth-shaped "cap" placed over a tooth to cover it to restore its shape, size, strength and to improve its appearance.

WHY IS A DENTAL CROWN NEEDED?

Dental crowns may be needed in case of any of the following Dental problems 

1. Protect a weak tooth (for instance, decayed) from breaking or to hold together parts of a cracked tooth
2. To restore an already broken or severely worn down tooth
3. To cover and support a tooth with a large filling when there isn't much of tooth left
4. To hold a dental bridge in place
5. To cover misshaped or severely discolored teeth
6. To cover a dental implant
7. To make a cosmetic modification

WHAT TYPES OF CROWNS ARE AVAILABLE?

Permanent crowns can be made from stainless steel, all metal (such as gold or another alloy), porcelain-fused-to-metal, all resin, or all ceramic while temporary crowns are made of acrylic or stainless steel and can be used as a temporary restoration until a permanent crown is made by   a dental lab.

HOW DENTAL CROWN IS DONE?

A dentist will normally be able to complete the procedure in 2 sittings. In the first sitting, the following things may be done:  

1. Dentist will take a few x-rays to check the roots of the tooth receiving the crown and surrounding bone. In case of  the tooth has extensive decay or if a risk of infection or injury to the tooth's pulp, a root canal treatment may be necessary.
2. Before starting on the process of making a crown, the dentist will anaesthetize the tooth and the gum tissue around the tooth. 
3. 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. 
4. After reshaping the tooth, the dentist will use a paste or putty to make an impression of the tooth to receive the crown. Sometimes impressions are made with a digital scanner.
5.  Impressions of the teeth above and below the tooth to receive the dental crown will also be made to ensure that the crown will not affect your bite.
6. Impressions or scans are sent to a dental lab where the crown will be manufactured. 

At the second visit, the dentist will remove the temporary crown and check the fit and colour of the permanent crown. If all turns out well, a local anaesthetic will be used to numb the tooth and the new crown  permanently cemented in place.

On average, dental crowns last between 5-15 years. Its life span of a crown depends on the amount of "wear and tear" the crown is exposed to and how well it is maintained.