ROTARY CUTTING INSTRUMENTS

1ST

SHAMNAH C USMAN,BDS BATCH

IntroductionA group of instruments that turns on an axis

to perform cutting, abrading, burnishing, finishing or polishing tooth tissues or restoration

Speed rangesLow/ conventional speed Below 6000 rpm

High/intermediate speed

6000 100,000 rpm

Ultra/ super speed

Above 100,000 rpm

Low speed excavating caries with round

burs, refining cavity preparations, polishing procedures High speed cavity preparation, finishing procedure such as placement of retentive groves and bevels ; preferred when vision is poor, more positive sense of touch required or both Water coolant system Fiber optic lighting Friction grip locking system

Ultra speed bulk reduction, obtaining

outline form, remove metal restoration

Common design charecteristics1.Shank 2.Neck 3.Head Head working part of instrument, cutting edge

perform desired shaping of tooth structure. Instruments are bladed or abrasive Neck connects shank to head, transmit rotational and translational forces to head Tapers from shank diameter , dimension a compromise between need for large CS (provide strength) & small CS (improve access and visibility)

1.

Shank part that fits into the handpiece,

accepts rotary movement ,controls alignment and concentricity of instrument 1.Straight handpiece shanks 2.Latch type handpiece shank 3.Friction grip handpiece shank

Dental bursBurs all rotary instruments that have

bladed cutting heads Can be steel bur or tungsten carbide burs Steel burs cut human dentin at low speeds, but dulls rapidly at higher speeds or when cutting enamel Carbide burs (1947) performs better. Have heads of cemented carbide in which microscopic WC particles are held in a matrix of cobalt or nickel Modern burs combination of the two ; freedom in design and economical, but steel necks bends easily causing vibration

ClassificationMode of attachment latch type, friction

grip type Composition stainless steel, carbide burr or combination Length of head long, short, regular Use cutting , finishing , polishing Shape round, inverted cone ,pear shaped ,tapering fissure, straight fissure, end cutting

Round bur: caries removal, initial tooth

preparation, extension, placing retentive grooves Inverted cone: wall angulation, creating undercuts, smoothening floors Pear shaped bur: class I cavity for gold foil Straight fissure: amalgam preparation Tapering fissure: inlay and crown End cutting bur: preparation apically without axial reduction

Modifications In bur designReduced use of crosscuts Extended heads on fissure burs Rounding of sharp tip angles Markley &

Sockwell

Design of a dental bur

Blade - projection on bur head Flute/chip space depressed areas in

between the blades Rake angle angle between rake face and radial line Land plane surface immediately following cutting edge

Factors affecting cutting efficiency of burRake angle Spiral angle and cross cuts Concentricity and runout Neck diameter No of teeth/blades

Abrasive instrumentsHead consists of small angular particles of

hard substance embedded in a soft binder(ceramic, metal, shellac, rubber) 1.Diamond abrasive 2.Other abrasives boron carbide, pumice,Al2O3, garnet

Diamond abrasivesDeposited by Electroplating, sintering or

microbrazing Classification 1.Coarse grit(125 150u) 2.Medium grit(88- 125) 3.Fine grit(60 74u) 4.Very fine grit(38 44u)

Burs, Discs, Mandrel, Stones, and Wheels

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Copyright 2006 Thomson Delmar Learning. ALL RIGHTS RESERVED.

Other abrasive instrumentsMoulded abrasive instrument heads that

manufactured by pressing a uniform mixture of abrasive and matrix around roughened end of shank; points and stones; finishing &polishing Coated abrasive instrument disks that have a thin layer of abrasive cemented to a flexible backing ;surface contour, finishing

Different methods of cuttingCutting effectiveness rate of removal of

tooth structure in mm/min or mg/sec Cutting efficiency percentage of enegy producing cutting

HazardsPulpal precautions Soft tissue precautions Eye Ear Inhalation precaution

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