Crowns:Crowns may be made from several different materials, gold and porcelain being the most common types. Gold is usually used on the back teeth, as it has several advantages over porcelain teeth. - Gold is strong in thin section and less tooth needs to be drilled away before taking the impression and fitting the crown. - The lab technician finds it easier to use gold as it shrinks less when cast and is easier to polish. Crowns of porcelain shrink when cast and the technician has to estimate this when making the crown. Porcelain is usually always used for the front teeth but may be used for the back teeth. This material can be made to appear very natural though several factors affect this and are outlined below; Some porcelain crowns have metal inside which gives strength and support to the porcelain. This acts as a barrier for light and gives the crown a dull colour. On posterior teeth this won't be noticed but in the front of the mouth it can occasionally be a problem as the tooth looks duller than the natural teeth.