Crowns have been used in dentistry since the 1920’s although materials have changed significantly since then. Originally, crowns were made from gold but in the 1950’s it became possible to overlay gold with porcelain
Crowns (or caps) are where the whole tooth is completely covered, as compared to a veneer where only the front surface is covered. Crowns have been used in dentistry since the 1920’s although materials have changed significantly since then. Originally, crowns were made from gold but in the 1950’s it became possible to overlay gold with porcelain and so tooth coloured crowns were made with a gold base. Most crowns have been made this way over the last few decades.
What are crowns used for?
Crowns have a variety of uses from restoring badly damaged or broken teeth, heavily filled teeth, re-shaping teeth and strengthening root canal filled teeth. The patient below had all of his upper teeth heavily filled, some teeth had two or more separate fillings in them. To strengthen them and prevent teeth from breaking, improve the appearance and eliminate the need for more fillings, all ceramic crowns were used.
(The whole process was completed in a single appointment using CEREC CAD/CAM and the crowns were made from Empress ceramic. The lower teeth will be restored the same way.)
What is the procedure?
As crowns cover the whole tooth, it is necessary for the dentist to trim the tooth down in size. This will usually mean about 1mm+ trimmed off the outer sides all the way around the tooth and 1-2mm off the whole of the biting surface. An impression (mould) is taken and a temporary tooth fitted. If the dentist uses the CEREC CAD/CAM system, no impression moulds are needed as a digital picture is taken of the tooth instead. Also, it is often unnecessary to trim away healthy tooth substance when using CEREC CAD/CAM thus preserving far more natural tooth than with full crowns.
The impression of the prepared tooth and of the opposite biting teeth are sent to a dental laboratory for the crown to be made. This usually takes 10-14 days, during which time the patient wears a temporary crown.
At the second appointment the temporary crown is removed and the permanent crown tried in to make sure the fit and colour is correct. The crown is then cemented over the prepared tooth and the bite checked and adjusted as necessary.
If the dentist uses the CEREC system, the whole crown can be made and fitted in just one appointment, without the need for impression moulds or temporary crowns. More information on CEREC CAD/CAM dentistry can be found on our CEREC page.
Different types of crown.
There are a variety of materials that crowns can be made from. Gold has in the past been the ‘gold standard’ for dental crowns. Often for back teeth the whole crown would be made from a gold alloy, either white or yellow. Gold has been an excellent material for crowning teeth with as it doesn’t corrode, is strong, lasts years and years and can be made to fit very accurately. The disadvantage is in the aesthetics – it looks like a gold or silver coloured tooth.
Modern dental materials are based on ceramics and there are a variety of ceramic materials available for making crowns.
Porcelain over gold.
This is where dental porcelain is fused over a gold alloy or other metal cap, called a Porcelain Fused to Metal (PFM) crown. This is to combine the strength of the metal with the better appearance of porcelain. These crowns can be made for back or front teeth and are probably the most commonly used type of dental crown.
Over the last decade or so stronger ceramic materials have been developed so that crowns can now be made entirely of ceramic, even for back teeth where the bite is stronger. There are a variety of different materials to make ceramic crowns and some laboratories have also named their own type of crown. The most common ceramic crowns are:-
Feldspathic – such as Vita Block MkII as used in the CEREC system and the most widely used ceramic for laboratory made crowns.
Empress – a leucite glass material developed by Ivoclar Vivadent used by laboratories and in the CEREC system.
e.Max – a high strength lithium di-silicate material also produced and developed by Ivoclar
Vivadent. Used by laboratories (e.Max Press) and with the CEREC system (e.Max CAD)
Zirconia – these are layered crowns, a high strength ceramic called Zirconia is overlaid with dental porcelain.
Lava – a Zirconia overlaid with porcelain crown made by 3M. The Zirconia is milled from a ceramic block so only a few specialist labs can make these.
Procera – another layered crown, this time from Nobel Biocare. As with Zirconia or Lava, a strong ceramic cap is made and overlaid with porcelain.
The advantages of ceramic crowns over the more traditional PFM is there is no metal required to make the crown. Some people are allergic to certain metals, eg. Nickel, which may be used in the metal alloy. Also, there can sometimes be a thin dark line visible where PFM crowns meet the gumline which is unaesthetic. In the photo below the dark line where the metal and porcelain join is clearly visible whereas there is no join visible with the ceramic crown (Vita MkII Feldspathic made using CEREC CAD/CAM).
Which crown is best for me?
This will depend on your own situation and your dentist should be able to guide you through any options.
How long will a crown last?
Properly done, crowns can easily last 10-15 years. Indeed, many patients have crowns that are many, many years older.