US No. 40 Bur – Busch Inverted Cone Steel, Made in Germany

The US No. 40 is the American number for a inverted cone bur with a 2.1 mm head (ISO size 021): a head that widens toward the tip, so it cuts undercuts and flat floors that a round or cylinder bur cannot. Busch & Co. manufactures it in Germany as Busch No. 2 021. Every US No. 40 on this page is a genuine Busch instrument and ships from our US warehouse.

Which US No. 40 Do You Need?

US No.	Busch No.	Material	Cut	Shank	Best for	Pack
40	2 021	Steel	Plain-cut	HP	Economical laboratory cutting of acrylics and plaster	6

HP (2.35 mm shank, straight handpiece). See the Busch Bur Size Chart for head and shank dimensions.

Clinical Uses of the US No. 40

Retention form: cutting undercuts at the base of a preparation so a restoration locks in place.
Flat floors: flattening the pulpal floor of Class I and Class II preparations.
Class V and access refinement: squaring the internal form of small preparations.
Laboratory work: the HP and steel versions cut retention channels and relief in acrylic and plaster.

At 2.1 mm the No. 40 is a large head for prosthetic and laboratory reduction.

Speed and Technique

Because the widest cutting edge is at the tip, work with the side of the head in short strokes rather than plunging; use water spray with the FG versions and laboratory speed for HP. Maximum recommended speeds for every Busch shape are in our Dental Bur Speed Chart, and reprocessing steps in the Bur Sterilization Guide.

Made in Germany by Busch & Co.

Busch & Co. has manufactured rotary instruments in Engelskirchen, Germany since 1905. Every instrument on this page is a genuine Busch product, precision-ground on a concentric shank under ISO-certified quality management and guaranteed to arrive free of manufacturing defects under our Busch arrival guarantee.

Dental Instruments, Tools, Burs, Diamonds and Polishers Made In Germany

FAQ

What is the Busch number for a US 40 bur? Busch No. 2 021 in steel (HP).

What size is a No. 40 bur? The No. 40 has a 2.1 mm head diameter (ISO size 021) on a inverted cone bur head, ISO shape 010 (inverted cone).

Are Busch No. 40 burs reusable? Yes. Carbide and steel burs are cleaned, disinfected and sterilized between patients and replaced when they dull; the Bur Sterilization Guide gives the validated steps.

Related resources: US Bur Number Finder · Bur Comparison Chart · Speed Chart · Bur Glossary · Nearby sizes: US No. 38, US No. 39, US No. 41