Options for Dental Restorations
The way that we use and manufacture crowns and bridgework has changed dramatically over the years, and they remain important treatments, but modern bonded restorative materials, such as veneers, make it possible to avoid or reduce the amount of tooth preparation required, and the use of implants means that we rarely make extensive dental bridgework anymore.
Why Do We Crown Teeth?
The main reasons for restoring teeth with crowns are:
- To strengthen a badly broken down or weakened tooth,
- Worn or fractured teeth can be restored to their original contour.
- Spaces can be filled and a more regular appearance restored or created.
- To improve the appearance of a badly broken down or heavily filled tooth,
- Highly discoloured and stained teeth can be improved,
- Poorly positioned teeth can be built forward.
- To support the end/s of a bridge which is replacing other missing teeth.
Before a tooth can be restored with a crown a strong foundation is usually built on what is left of the tooth. This foundation helps to strengthen the tooth and make sure that the crown is well retained. The foundation or "Core" may either take the form of a large bonded 'filling' retained by adhesive techniques, or a glass-fibre post or laboratory-made cast gold post that is cemented into the prepared tooth. Posts are usually only used with root filled teeth, where very little tooth structure remains.
Teeth that need crowns are usually broken down and in a poor state of repair, and because of this, there may be pre-existing inflammation of the dental nerve. Although this happens infrequently, occasionally this inflammation may be too advanced to be reversed by the restoration. Under these circumstances further treatment such as root canal therapy may be required.
Once a sound foundation is in place, the tooth prepared for the crown. Impressions are then taken using either conventional impression materials or a digital intraoral scanner to creat a 3D scanned model of the prepared tooth.
Crowns come in many forms, the most common varieties are:
All Ceramic: These have the most natural appearance for some tooth types, but they are weaker than metal reinforced crowns. They are built up of many layers of tooth coloured porcelain and are translucent and very tooth-like indeed. Unfortunately the strength of this material usually limits its use to the front of the mouth.
Porcelain Bonded to Alloy or Zirconium: This type of crown consists of a thin gold alloy, cobalt chrome, or titanium coping, or milled zirconium coping which fits the tooth and reinforces a covering layer of porcelain, which gives the tooth a natural appearance. The majority of crowns for back teeth are made on gold copings, however the combination of metal and porcelain needs a lot of space to allow the porcelain to mask the gold casting. This can sometimes make using this type of crown difficult if there is not enough space available between the crowned teeth and the opposing teeth. Bonded Zirconium Crowns are less translucent, but much stronger than an All Ceramic Crowns. The zirconium coping is a dense white material which means the crowns may be a little more translucent and natural in appearance. The copings may be cast, milled or 3D printed, depending upon the demands of the treatment.
All Zirconium: These crowns are tooth coloured, and strong but lack translucency - but they are a good alternative to gold crowns where appearance and strength are both a concern at the back of the mouth. The crown is designed in 3D software and made milled from a block of material before firing at exceptionally high temperatures.
All Gold: These crowns are made of yellow or white dental golds, and have been in use for decades. They are very strong and resistant to biting forces, and can be made very thin. The preparation for this type of crown is conservative, and full gold crowns can be useful where there are strong biting forces and there is little space in the bite. These restorations are made using the 'lost wax' casting technique.
A porcelain veneer is a thin layer of custom-made porcelain which fits over the front of the tooth. As with traditional porcelain and gold restorations, it is made in the laboratory by the dental technician on models of the prepared teeth which are obtained by taking very accurate impressions in the mouth, or by 3D modelling with an Intraoral scanner. A strong bond between the veneer and the tooth is achieved by etching the tooth, and using a special bonding adhesive. The result is a strong 'sandwich' restoration.
Veneers do not replace crowns, as these are often still required for structural reasons. With a veneer, tooth shape may be altered with only minimal tooth preparation, making this a relatively conservative procedure, and with the potential for a dramatic improvement in appearance.
Sometimes the technique can also be used for side and back teeth.
Bridges are used to replace missing teeth. The teeth on either side of the "gap" are usually prepared as for crowns, to receive the bridgework which extends from tooth to tooth.
Bridges used to be considered the best way to replace missing teeth using a fixed reconstruction. However, as dental implant restorations have proved so reliable and feel more natural, we tend not to use this type of bridgework on a permanent basis, unless there is a good reason not to use the implant alternative.