Access burs through the crown:

   Carbide fissure burs : cut through metal ( amalgam alloy or cast metal ) or composite resin.

   Porcelain fused to metal :

-A round diamond is used to cut through the porcelain layer
-Transmetal bur to cut through metal
-transmetal bur has several blades to cut metal properly.
-Porcelain jacket crown :
-Diamond bur with copious coolant water spray to minimize micro fractures