When a tooth is heavily decayed it is more likely to fracture and lose considerable tooth substance and strength. The greater risk is that a fracture line may go below the margin of the gum, which makes restoration more difficult, or even impossible.
Crowns can provide the necessary strength to save the tooth. Crowns may be fabricated from different materials, porcelain being the most superior. When the top of a tooth is lost due to decay there may be very little for the crown to actually hold onto. To gain 'retention' as dentists call it, a post may be placed inside the tooth, which forms a peg on top of the tooth and acts as a seat for the crown.
If a decayed tooth is left untreated for too long, or a failing restoration (filling) is not replaced, the tooth may no longer be eligible for a crown and may require extraction.
A bridge is a treatment option for patients who are missing one or more teeth. A bridge is fixed in the mouth, attached to the existing teeth on either side of the space to be filled where a tooth or teeth use to be. Like crowns, bridges can be made from different types of materials including porcelain fused to metal or all porcelain. Fixed bridges are cemented in and are cleaned with the help of specialized hygiene products.