# Bur Types and Selection > Dental bur types and selection for BDS Operative Dentistry — head, neck and shank, carbide shapes, diamond grits, finishing burs and speed pairing. - Canonical URL: https://prepelephant.com/topics/bds/operative-dentistry/bur-types-selection-operative - Exam / course: BDS · Subject: Operative Dentistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Bur Types and Selection", PrepElephant, https://prepelephant.com/topics/bds/operative-dentistry/bur-types-selection-operative ## Direct answer Every bur is described by three parts — head, neck and shank — and chosen by three questions: what shape does the cavity need, what material will it cut, and at what speed will it run. Tungsten carbide burs (the numbered shapes like 245, 330 and 557) cut efficiently at high speed with a smoother finish; diamond burs, graded by grit from coarse to superfine, abrade enamel and hard tooth structure best; and the shank type dictates the handpiece — friction-grip for the air rotor, latch-type (right-angle) for the micromotor. Matching these three answers to the task is the difference between controlled cavity preparation and a dragged, overheated one. ## What you must remember - **Bur anatomy:** head (the working part, sized in tenths of millimetres), neck (connects head to shank) and shank (fits the handpiece) — the diagram every viva starts with. - **Shank types:** straight or short shank for straight handpieces, latch-type right-angle (RA) for contra-angle slow-speed handpieces, and friction-grip (FG) for the air rotor — pairing errors are a standard mark-loser. - **Carbide shapes and uses:** round burs for caries and access, inverted cone for flattening floors, pear (330) for conservative Class I and occlusal access in children, tapered fissure (245) for Class II boxes and proximal walls, straight fissure (557) for walls and margins. - **Diamond logic:** abrasive rather than blade-cutting, graded by grit — coarse for gross reduction, medium for general preparation, fine and superfine (roughly 15-20 micrometre particles) for finishing — and paired with water at high speed. - **Finishing burs:** multi-bladed carbides, 12-bladed for gross finishing and 30-bladed for fine — the flute count, not the brand, decides the surface. - **Speed pairing (viva favourite):** high speed above 200,000 rpm cuts enamel with minimal pressure under water spray; slow speed up to about 40,000 rpm handles caries removal, finishing, and endodontic work with better control and torque. - **Wear and single-use thinking:** diamonds dull and carbides chip with autoclaving cycles; a dull bur heats the pulp faster than a fresh one ever would — a clinical point examiners increasingly stress. ## Selecting burs for a Class II amalgam on a lower molar Occlusal access begins with the 245 tapered fissure in the air rotor, entering the central fossa and sweeping mesiodistally under constant water spray — the same bur then drops into the proximal box, its taper giving the walls their divergence. Where caries is reached, the round bur on the micromotor takes over: slow speed lets the student feel the carious dentine part from sound, which is precisely the tactile control the air rotor never offers. The box floor is levelled with the inverted cone, and unsupported enamel is removed with a hand instrument rather than more rotary aggression. Finishing comes only at the end of restoration — 12-bladed carbide for excess amalgam, 30-bladed for the marginal ridge — never with the cutting burs of the preparation tray. The sequence teaches the deeper rule: preparation burs, excavation burs, and finishing burs are three different instruments answering three different questions, and mixing the trays is the commonest chairside disorganisation examiners notice first. ## Where students slip The classic error is shank-to-handpiece mismatch: forcing an FG bur into a latch chuck or running an RA bur in a turbine, which examiners treat as a basic-competency failure. The viva trap is diamond versus carbide rationale — diamonds abrade enamel cleanly but smear dentine and clog, while carbides cut dentine with cleaner chips; quoting that pairing earns the marks that naming brands never will. Students also quote bur numbers without shape context — "330" means nothing without "pear-shaped, conservative occlusal access" — and forget that grit size, not colour coding, defines a diamond's duty, the colour band being only a manufacturer's reminder. ## Frequently asked questions ### What are the parts of a dental bur? Head, neck and shank — the head does the cutting, the neck transmits torque, and the shank fits the handpiece as straight, latch-type or friction-grip. ### Which bur and speed combination suits caries removal? A round carbide bur on the slow-speed micromotor, where higher torque and lower speed give tactile control between carious and sound dentine. ### Why are diamond burs preferred for enamel reduction? Their abrasive grit planes hard enamel smoothly at high speed under water spray, where carbide blades would chip marginal ridges and dull quickly. ### What distinguishes finishing burs from cutting burs? Finishing burs carry many fine blades (12 or more, up to 30-40) that shave rather than gouge, producing controlled surface reduction and smooth margins. ### How does grit size govern diamond bur selection? Coarse grit removes bulk fastest but leaves rough surfaces; fine and superfine grits (around 15-20 micrometres) polish the preparation surface — grit size, not colour, defines the duty.