A crown (or “cap”) is the prosthetic replacement of the natural tooth that does all the work.
Once a tooth has developed a cavity and is restored with a filling, it is weakened. Over time the forces of chewing often lead to cracks and fractures.
It is most important at this point to restore the tooth with a crown. Otherwise future breakage is inevitable and sometimes results in the need of a root canal, or worse – the extraction of the tooth.