A tooth filling repairs a hole in a tooth caused by decay (see image above). The most common type of filling is an amalgam. An amalgam made from a mixture of metals including mercury, silver, tin, copper and zinc.
Your dentist will suggest the appropriate type of filling according to your needs. This includes white fillings, if appropriate. In this case the filling is made of composite resin that looks like natural teeth.
A crown is a type of cap that completely covers a real tooth. It's made from either metal, or porcelain and metal. It is fixed in your mouth.
Crowns can be fitted where a tooth has broken, decayed or been damaged. Sometimes a crown is fitted just to make a tooth look better.
To fit a crown, the old tooth will need to be drilled down so it's like a small peg the crown will be fixed on to.
It can take some time for a new crown to be prepared. Thus it is unusual for a crown fitted on the same day.
Fillings vs Crowns
In the case of a crown, no material is removed from inside the tooth as the crown sits over your existing tooth. If there's decay, the tooth is drilled down to form a peg with any decay completely removed.
With a filling, first the decayed tooth material is removed. Then the tooth is cleaned, and finally filled with the amalgam.
Another way to treat tooth decay is using root canal therapy.