A crown is a cover or cap that permanently sits over a tooth. They are usually needed when a tooth is very heavily restored (has a large filling) and damaged/weakened or has a root canal treatment. A crown is used to strengthen a tooth or improve its appearance. 

Sometimes posts are needed to go into the root surface if a tooth is very broken down.

Crowns are tax deductible.  In order for you to be able to claim relief for non-routine dental expenses your dentist must complete a Med 2 Form. Further details are available from the Revenue website.