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. 

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