Dr ROTARY CUTTING INSTRUMENTS OR DENTAL BURS Set

Dr. ROTARY CUTTING INSTRUMENTS OR DENTAL BURS

Set Induction: Discussing the definition, classification and types of rotary cutting instruments or dental burs used in dentistry.

SERIES OF PROCEDURAL STEPS § Following steps are involved in the finishing & polishing process in dentistry – 1. Bulk reduction 1. Cutting 2. Grinding 2. Finishing 3. Polishing

What is bulk reduction Is the removal of unwanted large portion or material of the tooth or appliances quickly. Done by cutting & grinding instruments like – diamond points (and discs), carbide burs (& stones), steel burs & bonded abrasives.

Bulk reduction by cutting CUTTING is a removal of unwanted material for shaping , is done by using regularly shaped instruments with sharp edged blades Instruments used are – tungsten carbide bur, steel bur or instrument in a blade like fashion Cutting is done by Hand cutting instruments Rotary cutting instruments

Hand cutting instruments These instruments are used to cut hard or soft tissue of the mouth. These have one, two or more regular shaped sharp cutting edges or points at one or both ends of stainless steel shafts Cutting blades have different shapes, sizes & fixed at different angles at the neck of the shafts (denoted by instrument numbering)

Hand cutting instruments are composed of three parts: handle, shank and blade

Instruments , E. g – Excavators, chisels, hoe, enamel hatches, gingival marginal trimmers, scalars to remove calculus deposits, Spoon excavator etc. These instruments are to be maintained , sterilized & properly sharpened conditions before use

Chisel: Chisels are used for cutting enamel and dentin A- Straight

Hoe: It has the same uses of the chisel.

Hatchet: Also called enamel hatchet. Used for cutting enamel and dentin and comes as right or left types for using on opposite sides of the cavity.

Gingival margin trimmer:

Spoon excavator: Spoon excavators (with corresponding instrument formulas) A-Binangle spoon (13 -7 -14) B- Triple-angle spoon (13 -7 -14) C- Spoon (15 -7 -14)

Uses of Hand cutting instruments For removing carious debris, damaged enamel, cutting & leveling enamel surfaces, producing cavosurfaces bevels etc during cavity preparations

Rotary cutting instruments These are known as dental burs , have small regular shaped sharp multiple cutting edges at the bur – head This is connected to through neck (shank) to the steel shaft of the bur The other end (shaft) is connected through latch or friction grip to air-rotar

Air –rotar handpiece

Definition • Bur is defined as a rotary cutting instrument, with cutting heads of various shapes & having two or more sharp edge blades, used as a rotary grinder. • E. G- Steel , carbide bur , diamond bur • ADA Specification No. 23 for dental excavating burs.

Parts of Rotary Cutting Instruments Three basic parts are Head: is the cutting, polishing, or finishing portion. Neck (shank) : Portion of the rotary instrument that connects the shaft to the head. Shaft: Portion that fits into the air rotar hand piece. Straight shaft Latch type shaft Friction grip shaft

Shank Neck Head

Burs classifications

Burs - classified according to Bur head material – diamond, tungsten carbide, silicon carbide, alumina, hardened steel. Bur –head designs –number of teeth , rake angle (+Ve, -ve, zero) Rotation speed – low, medium, high, ultra high according to the cutting material

Burs - classified according to Mode of attachment to the hand piece, straight, latch type or friction grip type. Rotating mechanism - electrical motor, compressed air –turbine system , with or without cooling water stream or air jets According to the length of their head long, short or regular. According to their shapes, - round, inverted cone, pear shaped, wheel shaped, tapering fissure, straight fissure, end cutting etc.

Burs - classified according to Clinical use – Finishing of restorations Surgical removal of bone Cavity preparation. Excavation of decay. Trimming & finishing acrylic dentures. Taking out old fillings (amalgam). Tooth preparation for crown & bridges. Separating crowns and bridges. Implant procedures

Dental burs Dental steel burs Tungsten Carbide burs Diamond bur

1. Dental steel burs

1. Dental steel burs Prepared by shaping & cutting a steel blank using fine diamond points Three basic parts – head , neck , & shank Bur head is small & has 6, 8, 10, 12 sharp blades (teeth) Bur head shapes, - round, fissure & inverted cone, flame , pear , wheel tapering fissure, straight fissure, cross cut fissure, end cutting etc.

2. Tungsten Carbide burs

2. Tungsten Carbides bur : Prepared by heating tungsten with carbon at high pressure & temp. 1500*C , the abrasive powders are sintered & hot pressed on the metal shaft, the head is cut & shaped

Uses of tungsten carbide bur Commonly used for cutting, & finishing Used for hard base metals & other alloy casting, reducing silver amalgam & composites restorations.

3. Diamond bur

Diamond burs - Resinoid bonding Abrasive particles like synthetic diamond chips are bonded through heat resistant polyamide resinoids, then cold pressed & cured. For better retention , the matrix are electroplated with nickel & titanium nitride. Diamond burs

Diamond bur uses Cut excellently & are used for brittle & hard material like enamel, base metal alloy , cutting & forming tungsten carbide bur , steel burs Diamond burs easily get clogged while cutting dentin

Assignment : Definition of dental bur. Classifications of dental burs. Discriminate hand cutting instruments and rotary cutting instruments used in dentistry. Types of dental burs used in dentistry.

Mcq The hardest cutting tool is of : (a) Martensified carbon steel, (b) Tungsten carbide, (c) Silicon carbide (d) Diamond points and discs…… Ans- (d) Diamond points and discs.

Mcq Bulk reduction of appliances is done by (a) Hand cutting or mechanical rotary instruments, (b) Abrasions, (c) Glazing, (d) Polishing. Ans-(a) Hand cutting or mechanical rotary instruments.

References: Phillips Science of Dental Materials - Kenneth J. Anusavice. 12 thedition. 2013. p-231 -253. Science of Dental Materials –V Shama Bhat, B. T Nandish. 2 nd edition. 2013. p 325 -327