When teeth have been heavily compromised and require a restoration to protect the remaining tooth tissue, crowns and onlays are an excellent solution. Both are constructed from high strength porcelain (although in certain situations a metal centre core is used) which will mimic the tooth substance that has been lost. Onlays are less destructive of remaining tooth tissue, and so provide an excellent minimal treatment, but can only be used in certain situations. A crown involves reduction of all the surfaces of the tooth, and the porcelain then covers the whole tooth providing protection.
Crowns can also be used as a cosmetic solution to problems, where more minimal treatment options are not possible.