A filling is needed when there is decay present in a tooth. The decay is removed by your dentist and then filled with a suitable filling material.
Composite fillings are the most popular filling material around due to the appearance, as you can get different shades of composite; the right shade can be matched to your tooth and is virtually impossible to see.
Amalgam fillings are one of the oldest filling materials around. They are silver in colour and used for their durability and strength.
Glass Ionomers are primarily used as a temporary or intermediate filling as they aren’t as durable as a composite or amalgam filling.