Summary
A crown is a single piece that is glued over the tooth, helping to hold it together. Some beautiful results can be achieved with modern crowns.
A bridge is used when there is a missing tooth and the teeth next to the gap are suitable for crowning. Bridges can provide a good outcome, but they do have limitations.
The big picture
When you think about it, the word ‘filling’ is an indication of its purpose. There is a hole in a structure and you fill it up. But sometimes so much tooth has been lost, by either a number of fillings or by a fracture, that the concept of ‘filling’ a hole is just not applicable. You could not patch a hole in a wall if the wall has been knocked down.
The established solution for a tooth that is badly broken down is to cover the whole tooth with a new outer layer. It is like putting a new shoe over a foot. The inside of the tooth is still intact, but the outer layer has been replaced.
Crowns are mainly made from gold, porcelain or a layered combination of both. Because the crown is made in a single piece that is then glued over the tooth, it acts as a ring around the tooth and helps to hold it all together. The tooth is also protected from decay in the areas of the crown, (but the margin still needs to be kept very clean to stop decay starting here, and then spreading under the crown). There have been a number of advances recently in crown technology, and some new ceramics and ceramic techniques, and some truly beautiful results can be achieved with modern crowns.
To put a crown over a tooth the outer layer of the tooth has to be removed, so we are reluctant to put a crown on a healthy tooth but they come into their own when a tooth has already been heavily filled. Teeth that have had their nerves die can also be more brittle, so it can be a good idea to put a crown over a tooth that has had a root canal treatment.
A bridge is used when there is a missing tooth and the teeth next to the gap are suitable for crowning. The crown preparations for the two teeth are made parallel to each other, and then a bridge can be made that is of the two end crowns, and a crown (but without a tooth root) in the middle. This is all made in one piece and then cemented on. In the right situation, bridges are a good result and for many years were the best solution for missing teeth.
There are limitations to bridges. Since they are made in one piece, if anything happens to any part of that bridge, then the whole bridge is compromised. As such, we do not like doing very long bridges. Also, we do not like to cut a crown on a perfectly healthy tooth. This is where implants have come to our rescue. We can place an implant and crown without touching the teeth on either side.
