A crown is used if a tooth has been broken or is too weak to hold a filling. It is also used if the tooth is cracking vertically and would otherwise have to be extracted.
They are custom made and are glued over the top of the damaged tooth following preparation and an impression of the tooth. Crowns can be either porcelain, porcelain fused to gold alloy or all gold. Crowns can be used to strengthen teeth or to change the appearance of teeth when other, less invasive techniques, are not possible.