Reference Guide
Black’s Formula is a system of universally accepted numbers designed by Dr. G.V. Black that describe the shape, size and angle of cavity preparation instruments. Both dentists and manufacturers use Black’s Formula to communicate about instrument design. Black’s Formula is based on the concept of instrument balance. Balance is established by keeping the blade of the instrument within 2mm of the long axis of the handle line. Proper balance is necessary to achieve optimal cutting with minimal effort.
OUT OF BALANCE INSTRUMENT
BALANCED INSTRUMENT
Black’s Instrument numbering Formula
About the fourth number
Some instruments, such as margin trimmers, are constructed with a cutting edge at an angle other than a right angle. In these cases, a fourth number (in degrees centigrade) is placed in the formula that indicates the degree of angle of the cutting edge to the long axis of the handle.
Example: Margin Trimmer 15-95-8-12.
The first number (15) represents the width of the blade in tenths of a millimeter. The second number (8) represents the length of the blade in whole millimeters. The third number (12) represents the angle the blade forms with the long axis of the handle expressed in degrees centigrade.
The fourth number is placed between the first and second numbers.
Black’s Formula uses a centigrade scale to measure instrument angles.
E8
Made with FlippingBook Annual report