Bridges & Crowns
When a tooth is heavily decayed it is more likely to fracture and lose considerable tooth substance. The greater risk is that a fracture line may go below the margin of the gum which makes restoration more difficult or near impossible. 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.
A bridge allows the dentist to replace lost teeth without the use of a denture or dental implant. Basically a false tooth is held in place by being attached to a tooth next door. The disadvantage is that the teeth next to the space have to be prepared in a similar way to a crown in order to accept the bridge. If these teeth already have crowns or big restorations then this is not a problem, the major concern however is when these teeth have small or no restorations (fillings). One compromise is the 'acid etched bridge', with this type a fine ledge is placed on the back of the adjacent teeth One disadvantage of a bridge is that the patient should wait three months before placement as the 'gum' shrinks' after a tooth is extracted. If the bridge was fitted early a gap would appear underneath the pontic (the false tooth). At the back of the mouth this may not be a problem, at the front of the mouth however this may appear as a black line along the gum.