1-to protect a weak tooth (for instance,from decay) from braking or to hold together partsof a cracked tooth .
2-to restore an already broken tooth or a tooth  that has been severely worn down 
3.to cover and support a tooth with a large fillinng when there  isn't a lot of tooht left
4.to cover misshaaped or severly discoloured teeth  
5.to make  acosmetic modification