A dental crown, some people call it cap, is a tooth-shaped cover placed over a tooth that is badly damaged or decayed. 

Usually the tooth has broken or severely damaged by decay and a filling can't replace enough. Therefore, placing crowns is a better solution. Crowns can be used to improve appearance as well for they can be placed to cover misshapen or badly discolored teeth.

Crowns can be made of:

All ceramic – The crown is made of a porcelain-based material. These are used for restoring front teeth, and are popular in this area for their ability to blend with your natural tooth color. With all ceramic crown there is no need to mask an underlying metal coping, as the restoration is metal free. However, all ceramic crowns have a limitation in strength. Therefore, it is more suitable for front teeth restoration.

Porcelain-fused to metal (PFM) -This type of crown includes two materials, metal and porcelain. Both materials have markedly different physical and aesthetic properties.This crown provides a stronger bond than regular porcelain and it also extremely durable.

Gold alloys – This crown is a mix of gold, copper and other metals. In addition to providing a strong bond to the tooth, it doesn't fracture, nor does it wear away the tooth itself. Gold alloy crown has a good biocompatibility, chemical stability and corrosion resistance. 

Base metal alloys – This crown is made up of non-noble metals that are highly resistant to corrosion, and make for a very strong crown. It also requires the least amount of healthy tooth to be removed prior to fitting. Those patients who are allergic to metal are not suitable to have metal crown.

All crowns have advantages and disadvantages and which type is best for you will be determined in part by your occlusion and whether you grind your teeth. The final choice is up to you and your dentist.

Crowns usually last at least 7 years and they may last much longer, up to 40 years or so. In many cases the crown is fine, but the tooth underneath it has developed a cavity. Therefore, maintaining good oral hygiene, including brushing and flossing, will help your crown last longer.