Crowns and Bridges
In dentistry, crowns and bridges refers to the restoration of natural teeth that have been damaged, decayed or lost. A crown can be made to restore an individual tooth damaged by decay or fracture back
to it's original form and function, while a bridge is used to replace one
or more missing teeth. These restorations are cemented onto the teeth and are referred to
as "fixed" dentistry as opposed to a restoration of missing teeth with a removable appliance
or partial denture.
A crown is a restoration that covers, or "caps," a tooth to restore it to its normal shape and size, strengthening and improving the appearance of a tooth. Prosthetic crowns are made of metal, porcelain fused to metal substrates, or new all-white restorative materials. Crowns are necessary when a tooth is generally broken down and fillings won't solve the problem. If a tooth is cracked, a crown holds the tooth together to seal the cracks so the damage doesn't get worse. Crowns are also used to support a large filling when there isn't enough of the tooth remaining, attach a bridge, protect weak teeth from fracturing, restore fractured teeth, cover badly shaped or discoloured teeth or protect a root-canal filled tooth with compromised strength.
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 similiar 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
MATERIALS FOR CROWNS AND BRIDGES
The three predominant choices of restorative materials for the full coverage crowns are:
- Porcelain-fused-to-metal (PFM)
- All-ceramic (all-porcelain): Procera, Cercon, and IPS Empress System
The material selected is determined by the clinical demands at hand; esthetic demands, strength requirements, material durability and restorative space available.
Porcelain-fused-to-metal crowns provide for a strong, durable, and esthetic treatment option. One of the key factors for the esthetic and functional success of this type of crown is ensuring the preparation of the underlying tooth structure provides adequate space for the appropriate thickness of the material selected. Additionally, the artistic skill of the laboratory technologist creating the crown will determine its esthetic appeal.
One consideration in the porcelain-fused-to-metal crown is that these crowns may tend to show the underlying metal or gold margin at the gum line as gums recede over time. Some patients opt for this
type of crown, but replace the crown at a later date in order to maintain
a higher esthetic benefit. Porcelain-fused-to-metal crowns with an all porcelain collar can eliminate this vulnerability.
All-Ceramic Crowns (Procera, Cercon, and IPS Empress System)
The predominant material choice for all-ceramic crowns today is either zirconia, or aluminous materials. They provide a metal-free esthetic option with a number of benefits.
By eliminating the need for the supportive metal core, an esthetic all-ceramic crown can be created with a reduced thickness of material. This makes them a more favorable treatment choice in areas with limited space. Additionally, the elimination of the metal core allows for
light transmission through the porcelain for better optical, life-like properties and a higher
level of esthetics.
All-ceramic materials continue to evolve in strength and durability, but caution should still be exercised for areas of the mouth requiring heavy function. Continuing research is exploring
the significant vulnerabilities of the porcelain systems in such areas.