Head diameter of a 245 bur is:

 # Head diameter of a 245 bur is:

A. 0.1 mm

B. 0.5 mm

C. 0.8 mm

D. 0.9 mm

The correct answer is C. 0.8 mm.

No. 245 bur has a head length of 3 mm and head diameter of 0.8 mm. This is an inverted cone carbide bur used for amalgam cavity preparations. 

Benefits of the bur: 

• For amalgam cavity preparations, the initial punch cut should have a depth of 1.5 mm, so it is half of this bur length, so it is very convenient to use the bur. 

• In class II the proximal ditch cut is established easily with the 0.8 mm diameter bur end cuts 0.5 mm into dentin and 0.3 mm into enamel.