If a tooth has been badly broken or very heavily filled, it may be advisable to crown the tooth.  To crown a tooth, it is necessary to shape the tooth very precisely, and the crown is then cemented in place so that it encompasses the remaining tooth/filling preventing the tooth from breaking any further.  The type of crown required and hence the cost of the crown depends on where it is to be placed in the mouth.  Most crowns have a gold substructure with porcelain fused on to mimic a natural tooth.  On very back teeth where durability is most important, the crown is often made entirely of a gold alloy.  However, on front teeth, we commonly use a crown made of entirely porcelain which costs a little more but provides a superior cosmetic result.