Rotary Instruments in Operative Dentistry

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Rotary Instruments in Operative DentistryDr. Nithin Mathew

CONTENTS

• Introduction• History of Rotary Instrumentation• Powered Rotary Instruments• Rotary cutting Instruments

• Common design characteristics• Bur Classification systems• Modifications in bur design• Factors influencing cutting

efficiency of burs

• Rotary Abrasive Instruments• Diamond abrasives• Factor affecting abrasive efficiency• Other abrasives:

• Molded• Coated

• Cutting Mechanisms• Evaluation of Cutting• Bladed Cutting• Abrasive Cutting• Cutting Recommendation

Rotary Instruments in Operative Dentistry - Dr. Nithin Mathew 3

• Hazards with rotary instruments• Pulpal Precautions• Soft tissue precautions• Eye precautions• Ear precautions• Inhalational precautions

• Infection Control & Sterilization• Recent Advances• Conclusion


Introduction

• Removal and shaping of tooth structure is an essential part of restorative dentistry.

• Initially this was a difficult process accomplished entirely by the use of hand instruments.

• In order to perform the intricate and detailed procedures associated with operativedentistry, the dentist must have a complete knowledge of the purpose, availability andapplication of the many instruments required.


History of Rotary Instrumentation

Year Development Speed300 BC Hippocrates described a drill driven by chord around the shaft1728 Hand rotated instruments 3001858 –1862

First rotary instrument was introduced by Dr. Jonathan Taft and called them “bur drills”. Drill - rotated in either direction to perform cutting action.

1871 Morrison - dental foot engine 7001874 Electrical dental engine 10001910 Belt driven handpiece1914 Electrical engine was incorporated into the dental unit 50001942 Diamond abrasive points were introduced 50001946 Old units upgraded speed 10,0001945 Tungsten carbide burs 12,0001949 Walsh and Symmons - removal tooth structure with diamond

points70,000



Year Development Speed1953 Ball bearing hand pieces 25,0001955 Water turbine hand piece 50,0001955 Belt driven contraangle handpiece (Page-Chayes) 1,50,0001957 Air- turbine angle handpiece 2,50,0001961 Air- turbine straight handpiece 25,0001962 Experimental air bearing handpiece 8,00,0001994 Contemporary air turbine handpiece 3,00,000

• Rotary instruments includes:

• Hand Pieces• Burs• Polishing instruments


Handpieces

• Classified according to their driving mechanism

• GEAR driven handpiece• Rotary power is transferred by a belt which runs from an electric

engine• Power is transfered from the straight handpiece by a shaft and gears

inside the angle section.• Capable of working at variable speeds though they work best at low

speeds


• WATER driven handpiece• Discovered in 1955• Operate at speeds of 1,00,000rpm• Water is transported at high pressure to rotate the turbines• Quite in nature and highest torque

• BELT driven handpiece• Introduced in 1955• Operate at speeds >1,00,000rpm• Excellent performance and great versatility

• AIR driven handpiece• Introduced in 1957• Operate at speeds of approx. 3,00,000rpm


Type of Handpiece

• STRAIGHT handpiece• Long axis of bur lies in same plane as long axis of handpiece• Used in oral surgery and lab procedures.

• CONTRA-ANGLED handpiece• Head of the handpiece is first angled away from and then back towards

the long axis of the handle

• Because of this design, bur head lies close to long axis of the handle ofhandpiece which improve accessibility, visibility and stability ofhandpiece while working.


• CONTRA-ANGLED handpiece

i. Air-Rotor Contra-angle handpiece• Gets power from compressed air supplied by the

compressed• Handpiece has high speed and low torque

ii. Micromotor handpiece• Gets power from electric motor or air-motor• Has high torque and low speed


Speed Ranges in Rotary Instruments

• Rotational speed of an instrument is measured in revolutions per minute

• According to Sturdevant:• Low speed : < 12,000 rpm• Medium/Intermediate speed : 12,000 – 2,00,000 rpm• High / Ultra high speed : > 2,00,000 rpm

• According to Charbenau:• Conventional/Low speed : < 10,000 rpm• Increased / high speed : 10,000 – 1,50,000 rpm• Ultra high speed : > 1,50,000


• According to Marzouk:• Ultra low : 300 – 3,000 rpm• Low : 3,000 – 6,000 rpm• Medium high : 20,000 – 45,000 rpm• High : 45,000 – 1,00,000 rpm• Ultra high : > 1,00,000 rpm

• According to Clearance L. Sock (DCNA 1971):• Low/ Conventional : < 6,000 rpm• High / Intermediate : 6,000 – 1,00,000 rpm• Ultra / super speed : > 1,00,000 rpm


• Speed is proportional to the rotational speed and the diameter of the instrument.

• Low speed cutting is ineffective, time consuming and requires relatively heavy forceapplication.

• Results in heat production and vibration of low frequency and high amplitude.

• Heat and vibration are the main sources of patient discomfort.

• At low speeds, burs roll out of the tooth preparation.• Carbide burs are easily broken at low speeds due to their brittle nature of the blades.

• Low speed mainly used for cleaning teeth, occasional caries excavation, finishing andpolishing procedures.


• At high speeds, the surface speed needed for efficient cutting can be attained by use ofsmaller and more versatile cutting instruments.

• Advantages of high speed includes:

• Diamond/carbide instruments remove tooth structure faster with less pressure,vibration and heat generation.

• No. of rotating cutting instruments required is reduced because smaller sized aremore universal in application.

• Operator has better control and greater ease of operation

• Instruments last longer.• Patients are less apprehensive as the operating time is reduced.


• Color Coding for handpieces based on speed:

• Coding indicates the relative gear ratio of each component and are present inthe form of dots / rings :

• Blue : No change in speed• Green : Speed Reduction• Red : Speed increase


Rotary Cutting Instruments

• These are individual instruments intended for use with handpieces and are available invarious shapes and sizes.

• Common design characteristics• Bur classification systems• Modification in bur design


COMMON DESIGN CHARACTERISTICS

• Each instrument consists of 3 parts:• Head • Neck• Shank


SHANK DESIGN

• Part that fits into the hand piece, accepts the rotary motion from the handpiece

• Provides bearing surface to control the alignment and concentricity of the instrument.

• Shank design and dimensions vary with the hand piece for which it is intended for.

• ADA Specification No. 23 for dental excavating burs includes 5 classes


1. Straight hand piece shank

• Shank portion : cylindrical, held by a metal chuck that accepts arange of shank diameters.

• Straight handpiece are now used for finishing and polishingcompleted restorations.


2. Latch-type handpiece shank

• Complicated shape of this shank reflects the mechanism by which theseare held in the hand piece.

• Shorter overall dimensions – permits easy access to posterior regionsin mouth.

• Handpiece has a metal tube within which the instrument fits


• Posterior portion of shank is flattened on one side, end fits into aD-shaped socket at the bottom of the bur tube.

• Retained by a latch that slides into D-shaped socket

• Used in slow and medium speed.

• Small amount of wobble due to the clearance between instrumentand bur tube - controlled by the lateral pressure during cuttingprocedures.


3. Friction-grip shank design

• Developed for its use in high speeds.• Overall dimensions are smaller thus increasing access in posterior

teeth.

• Simple cylinder manufactured very close to dimensionaltolerances.

• Designed to be held in handpiece by friction between the metalchuck.


• Minor variations in shank diameter can cause substantial vibrationin the instrument performance and problems with insertion,retention and removal.


NECK DESIGN

• Portion that connects the head to the shank.

• Neck normally tapers from the shank to the head.

• Main function - transmit rotational and transitional force to head.

• Also provides visibility and ease of operation.

• For this reason neck diameter is a compromise between strength and improved accessand visibility.


HEAD DESIGN

• It is the working part of the instrument - cutting edges or points.

• Shape and material used in manufacture are closely related to its intended applicationand technique of use.

• Head design forms the basis of instrument classification, such as; bladed instrument orabrasive instrument.


MATERIALS used in Manufacture of burs

• Steel Burs

• First developed burs

• Designed for slow speed <5,000 rpm, dull rapidly at high speeds.

• They are cur from steel blanks parallel to the long axis of the bur.

• Bur is then hardened to VHN 800.

• Once they are dulled, cutting efficiency is reduced, increasing heat and vibration.


• Tungsten Carbide Burs

• Manufactured by metallurgical process, by alloying powder of tungsten carbide withpowder of cobalt-nickel under pressure and sintered in vaccum.

• A blank is then formed and a diamond cutter is used to form the head design.

• Has a VHN in the range of 1650 – 1700.

• Perform better than steel burs at all speeds, superiority is greatest at high speeds.


• Harder than steel, so does not dull rapidly.

• Carbide is more brittle and more susceptible to fracture when subjected to sudden blow.

• Most carbide heads are welded or brazed to a steel shank and neck.


BUR CLASSIFICATION SYSTEMS

Classification systems developed by FDI & ISO to use separate designations forshape head and head diameter, measured in tenths of a mm.


SHAPES:Round:

• Spherical• Used for initial tooth entry, extension of preparation,

preparation of retention features and caries removal.


Inverted cone:• Portion of a rapidly tapered cone with apex towards the neck.• Head length is same as diameter.• For providing undercuts in tooth preparation.

Pear shaped:• Portion of a slightly tapered cone with small end of the cone

directed towards the bur shank.• Head length is same as diameter.• For providing undercuts in tooth preparation.• End of head may be continuously tapered or may be flat with

rounded corners.• Used in

• Normal length : Class I tooth preparation for gold foil• Long length : for amalgam preparations


Straight Fissure:• Elongated cylinder• Used for amalgam preparations.

Tapered Fissure:• Head tapered away from the shank• Used for indirect restorations

End Cutting Bur:• For carrying out preparations apically without

axial reduction

CLASSIFICATION

• According to Mode Of Attachment to handpiece• Latch type• Friction type

• According to Composition• Stainless steel• Tungsten carbide• Combination of both

• According to their Motion• Right bur : clockwise• Left bur : anti-clockwise


• According to their Length• Long• Short• Regular

• According to their Use• Cutting• Finishing• Polishing


• According to their Shape• Round• Inverted cone• Pear shaped• Wheel• Tapering fissure• Straight fissure• End cutting bur


SIZES:• Original numbering - 9 shapes and 11 sizes.• ¼ & ½ sizes were added later.


• Cross-cut burs: 500 was added

• End-cutting: 900 was added


BUR DESIGN

• Bur head consists of uniformly spaced blades with concave areas between them.• Normally a cutting bur has 6, 8 or 10 blades and a finishing bur has 12-40 blades.• Concave areas are called the chip/flute spaces.

• Actual cutting of the bur takes place at the edge of the blade.


Parts of a Bur head includes :

Bur Blade

• Blade is a projection on the bur head which forms a cutting edge.

• Each blade has 2 sides:• Rake face / blade face (surface of blade on leading edge)• Clearance face (surface of blade on trailing edge)

• 3 important angles:• Rake angle• Edge angle• Clearance angle

40Rotary Instruments in Operative Dentistry - Dr. Nithin Mathew

Rake Angle

• Most important design characteristic of a blade.• Angle between the rake face and the radial line.

• Positive rake angle: when rake face trails the radial line• Negative rake angle: when rake face is ahead of radial line• Zero rake angle: when rake face and radial line coincide

• For cutting hard, brittle materials, a negative rake angleminimizes fractures of the cutting edge, increasing the toollife.

• Carbide burs have blades with slight negative rake angleand edge angle of approx. 90°


Blade Angle / Edge Angle

• Angle between the rake face and the clearance face.

• Increasing the edge angle, reinforces the cutting edge andreduces the likelihood of the edge of the blade to fracture.


Clearance Angle

• Angle between the clearance face and the work.

• Primary Clearance angle: Angle the land makes with thework

• Secondary Clearance angle: Angle between the back of thebur tooth and the work

• Significance:• Clearance angle provides a stop to prevent the bur edge

from digging into the tooth and provides adequate chipspace for clearing the debris.

• 3 angles cannot be varied independently.• An increase in the clearance angle causes decrease in the

edge angle.Rotary Instruments in Operative Dentistry - Dr. Nithin Mathew 43

Concentricty

• Direct measurement of the symmetry of the bur

• Ie. It measures whether the blades are of equal length ornot.

Runout

• Measures the accuracy with which the tip of the blades passthrough a single point when bur is moving.

• Ie it measures the maximum displacement of the bur headfrom its center of rotation


Runout occurs if:• Bur head is off center on the axis of bur• Bur neck is bent• Bur bur is not held straight in handpiece chuck

Runout causes:• Increased vibration during cutting• Causes excessive removal of tooth structure.


ADDITIONAL FEATURES IN HEAD DESIGN

Head Length• Long to reach full depth of preparation

Taper Angle• Generate necessary occlusal divergence.

Neck Diameter• Small neck : weakening of instruments against lateral forces• Long neck : hampers visibility during preparation.


Spiral Angle• Produces smooth wall.• In high speed, smaller angle is preferred to improve efficient

cutting.

Cross-cuts• Notches in the blade edges to improve cutting effectiveness at low

and medium speeds.

• Crosscuts effectively increase both cutting pressure resulting fromrotation and perpendicular pressure holding the blade edgeagainst the tooth.


• Each crosscut blade cuts, it leaves behind small ridges on thetooth surface.

• Since notches of two successive blades do not line up with eachother, these ridges formed from one blade are removed by thesuccessive blade.

• At high speeds, the contact of bur with the tooth is not continuous.

• Here, high cutting rate of crosscut is maintained but the ridges arenot removed. This leaves behind a rough cut surface.


FACTORS AFFECTING CUTTING EFFICIENCY OF BUR

1. Rake Angle, Clearance Angle, Blade Angle

• More positive rake angle, greater is the cutting efficiency.• However it has 2 major drawbacks:

i. Reduces the bulk of the blade – bur can easily curve, flatten or even fracture.ii. Positive rake angle produces chip, that is larger and tends to clog the flutes

• Negative rake angle has a smaller chip and moves away from the blade

• Clearance angle eliminates friction between the cutting edge and the work and preventsbur from digging into the tooth.


• Increase in clearance angle reduces the blade angle, thereby decreasing the bulk of theblade.

• Increasing the blade angle reinforces the cutting edge and reduces chance of the bladeedge to fracture.


2. Spiral Angle and Crosscuts

• Burs with small spiral angles are preferred at high speeds assmall angles produce more efficient cutting.

• Crosscuts tends to reduce the total length of the bur blade thatis cutting at any one time.

• This increases the force per unit area, and thereby reduces thepressure required to initiate cutting.


3. Concentricity and Runout

• It is the direct measurement of the symmetry of the bur head.• An indication of whether one blade is longer than the other.

• Runout is the maximum displacement of the bur head from theaxis of rotation.

• Average clinically accepted runout is 0.023mm


4. Heat treatment

• Used to harden a bur made of soft steel• This process preserves the cutting edge and hardens the bur to improve its life.

5. Influence of load

• Load signifies the force exerted by the dentist on the tool head and not thatpressure or stress induced in the bur during cutting.

• Load or force exerted is dependent on the speed of the handpiece.

• Slow Speed : 1000 – 1500 gm (1-2 pounds)• High Speed : 60 – 120 gm (2-4 ounces)


6. Influence of speed

• At a given load, rate of cutting increases with increase in speed, but this increaseis not directly proportional.

• There is also a minimum rotational speed for a given load below which the toolwill not cut.

7. Number of blades

• No. of blades are restricted to 6-8.

• Decreasing the no. of blades, increases the force on one blade and also increasesthe size of the chip removed.

• Also it tends to reduce the clogging tendency since the flute space is larger.


• Major drawback of lesser no. of blades:

• Tendency of bur tooth wear is more• Cutting life is reduced• Increased tendency for vibration

8. Design of Flute ends

• 2 types

• Star-Cut Design : Flutes come together at a commonpoint on the axis of the bur

• Revelation Design : Flutes come together at twojunctions near the diametrical cutting edge.

• Revelation design is more efficient in direct cutting


MODIFICATIONS IN BUR DESIGN

Modifications were seen with the introduction of high speed hand pieces.

• 3 major changes includes:

• Reduced use of crosscuts

• Extended heads on fissure burs

• Roundening of sharp tip angles


• Reduced use of crosscuts

• At high speeds, produce rough surface.• Newer burs have reduced no. of crosscuts.

• Extended heads on fissure burs• Carbide fissure burs with extended head lengths 2-3 times those of normal tapered

fissure burs of similar diameter have high efficiency at higher speed with light pressure.

• Roundening of sharp tip angles

• Proposed by Markley & Sockwell• Such burs will result in lower stress in restored teeth• Burs last longer


Diamond Abrasive Instruments

• They have a greater clinical impact due to long life and effectiveness in cutting enamel anddentin.

• Introduced in United States in 1942 and was used popularly as grinding and finishingagents.

Terminology:

• Diamond instruments consists of 3 parts:

• Metal blank• Powdered diamond abrasive• Metallic bonding material


• Metal blank resembles a bur without blades• 3 parts: Head, Neck & Shank

• Head of blank is slightly smaller than the final dimension ofthe instrument head to accommodate for the thickness ofabrasive layer.

• Neck gradually tapers from the shank to the head.• For large disk/abrasives, it may not be reduced below the

shank.

• Diamonds maybe either natural or synthetic; that are crushedto a powder of desired particles in size and shape.


HEAD

NECK

SHANK

• These are held against the blank while it is being electroplatedwith a metal.

• Done in multiple layers to provide a continuous regeneration ofcutting surface as wear occurs.

ClassificationClassified based on average particle size of the abrasive:

• Coarse grit : 125 – 150 μm• Medium grit : 88 – 125 μm• Fine grit : 60 – 74 μm• Very fine : 38 – 44 μm


• Larger particles – area for the particles is reduced and are widely placed.

• During cutting, only a few particles come in contact with the tooth surface which increasesthe pressure on each particle.

• Resulting in rough surface


Head shapes and sizes

• Available in wide variety of shapes and sizes.

• Because of their design which an abrasive layer over an underlying blank, the smallestdiamond instrument cannot be as small in diameter as the smallest of burs, but a widerange of sizes are available for each shape.


FACTORS INFLUENCING THE ABRASIVE EFFECIENCY AND EFFECTIVENESS

1. Size of the abrasive particle

• Larger the particle size, more deeper is the penetration on the surface of the work,hence rapid removal of the material occurs.

2. Shape of the particle

• Should be irregular in shape for greater efficiency.• Irregular particles – sharp edge• So cuts better than round smooth or cuboidal particles which have a flat edge.


3. Density of abrasive particles

• Refers to the no. of abrasive particles per unit area.• High density : closely spaced• Low density : widely spaced

• Therefore, greater force will be exerted on each particle with low density whenthe particles are widely spaced increasing grinding efficiency.

• Coarse grit have low density compared to fine grit.


4. Hardness of abrasive particles

• To be effective, hardness of abrasive particle should be greater than that of thework.

5. Clogging of the abrasive surface

• Clogging of debris between the spaces of the abrasive particles affects grindingbecause this partially blocks the penetration of the abrasive particles into thesurface.

• Clogging is enhanced when particles are close together.

• Use of coolant washes away the debris and prevent clogging.


4. Speed and Pressure

• Usual cause of failure of abrasive instruments is when excessive pressure isapplied onto them to increase cutting efficiency at inadequate speeds.

• This results in loss of diamonds decreasing their cutting efficiency.


Other Abrasives

Many types of abrasive were used in addition to diamond instruments. Nowthey are restricted to shaping, finishing and polishing restorations.

Classification

In these instruments, the head is composed of abrasive particles, held in a continuousmatrix of softer material.

Broadly divided as:• Molded instruments• Coated instruments


MOLDED ABRASIVE INSTRUMENTS

• Have heads that are manufactured by molding or pressing auniform mixture of abrasive around a roughened shank or bycementing a pre-molded head.

• Have much softer matrix and tends to wear with use thusexposing fresh abrasive particles.

• Rigid molded materials have rigid polymer or ceramic as theirmatrix.

• Mainly used for grinding and shaping procedures.


• Soft molded instruments use flexible matrix materials likerubber, which are used for finishing and polishing procedures.

• Mounted head are termed as points / stones.

• Unmounted discs / wheel stones are available which can beattached to a mandrel.


COATED ABRASIVE INSTRUMENTS

• Mostly discs that have a thin layer of abrasive cemented to aflexible base.

• Allows the instrument to conform to the surface contour ofthe tooth or restoration.

• Unlike molded instruments, coated instruments have to bediscarded when they wear off.

• Used in finishing certain enamel margins/walls for indirectrestorations.

• Most often for finishing procedures for restorations


Materials Used

• Matrix materials used are phenolic resins or rubber.• Some molded abrasives may be sintered or may be resin bonded.

• A rubber matrix is flexible and allows ease of polishing.• Non- flexible rubber matrix is used for molded SiC discs.

Silicon Carbide ( Carborundum)

• Molded in forms of rounds, bud-shapes, wheels and cylinders of various sizes.

• Gray-green in color suited for fast cutting except on enamel.• Produce moderately smooth surface.


• Unmounted discs, popularly called as carborundum discs, are black or dark in colour.

• They have a soft matrix and wear easily.• They produce moderately rough surface.

Aluminium Oxide

• Used for the same instrument design as SiC.• Points are white, rigid, fine textured and less porous.

• They produce smoother surface than SiC.


Garnet (reddish) and Quartz (white)

• Used for coated discs• Available in a series of particle sizes ranging from coarse to medium-fine.

• Used for initial finishing.• Hard enough to cut tooth and other restorative materials except some porcelain.

Pumice

• Powdered abrasive produced by crushing foamed volcanic glass into thin glass flakes.• Cuts effectively but breaksdown rapidly.• Used for initial polishing procedure.


Cuttlebone

• Derived from cuttlefish• A soft white abrasive.• Used only in coated discs for final finishing and polishing.

• It is so soft that it reduces the potential for tooth damage due to its abrasive action.


Cutting Mechanisms

For cutting, it is necessary to apply some pressure so that the cutting tool will dig intothe surface.

The process of rotary cutting is complex and not completely understood.

1. Evaluation of Cutting

• Cutting can be measured in both effectiveness and efficiency.

• Cutting effectiveness is the rate of tooth structure removal (mm/min or mg/min).

• Cutting efficiency is the percentage of energy actually producing the cutting.• It is reduced when energy is wasted as noise or heat.


• It is possible to increase effectiveness while decreasing the efficiency.

• Ie. In general both effectiveness and efficiency can be increased by increasing the speed.


2. Bladed Cutting

• Tooth structure similar to other materials undergoesbrittle and ductile fracture.

• Brittle fracture is associated with crack propagation,usually by tensile loading.

• Ductile fracture involves plastic deformation of thematerial proceeding shear.

Speed

• Low speed – plastic deformation before tooth structure fracture• High speed – produces brittle fracture

Strain Rate

• Faster the rate of loading, greater will be the strength, hardness, modulus of elasticityand brittleness of the material.

• For the blade to initiate the cutting action, it must be sharp, harder with high modulus ofelasticity than the material being cut.

• This helps in exceeding the shear strength of the material being cut.


3. Abrasive Cutting

• Similar to bladed cutting in many ways, but key differences result from the properties,size and distribution of the abrasive.

• Hardness of diamond provides superior resistance to wear and these particles tend tohave a very high negative rake angle.


• When diamond particle cuts through aductile material, material will flowlaterally around the cutting point andbe left as a ridge of deformed materialon the surface.

• Repeated deformation work hardens the distorted material until irregular portion becomebrittle and breaks off.

• This is less efficient than bladed cutting; therefore bur are preferred to cut through ductilematerial like dentin.


• When diamond cuts through brittle material, most cutting results from tensile fracturesthat produces subsurface cracks.

• Hence they are most efficient to remove enamel than burs.

• Also preferred for use in tooth preparations for bonded restoration, since they increase thesurface area.


Cutting Recommendations

• Requirements for effective and efficient cutting include using• Contra-angle handpiece• High operating speed• Air water spray for cooling• Light pressure• Carbide or diamond instrument

• Carbide burs are better for end cutting, produce lower heat and have more blade edges perdiameter for cutting.

• Effective for punch cuts to enter tooth structure, intra-coronal tooth preparation, amalgamremoval, small preparations and secondary retentive features.


• Diamonds are more effective than burs for both intra and extra coronal tooth preparation,bevelling enamel margins and enameloplasty.


Hazards with Rotary Instruments

Pulpal Precautions

• Injury to the pulp caused by:• Mechanical vibration• Heat generation• Desiccation of the dentin• Transection of the odontoblastic process.

• The Pulpal sequelae, take 2 weeks to 6 months, depending on degree of trauma.• The remaining tissue is effective in protecting the pulp in proportion to the square of its

thickness.


• Heat is produced by:

• Steel burs than carbide burs• Tools plugged with debris• When used without a coolant, diamond abrasives > carbide burs.

• Air-water spray must be used as

• Acts as a coolant• Moisten the tissues, lubricates• Cleans and cools the cutting tool thus increasing tool life• Clear the operating site


Soft Tissue Precautions

• Injury to lips, tongue and cheek.• Rubber dam used to isolate soft tissues• Use good accessibility and visibility to the operative field• Patient instructed not to make sudden movements.• If accident occurs, control haemorrhage with pressure pack

• Chance of mechanical pulp involvement during caries excavation is more with handinstruments than with rotary instruments.

• Residual caries can be removed using a bur at low speed and light intermittent forces.


Eye Precautions

• Use of protective eye wear• Eye damage from airborne particles• High volume evacuation is advised

Ear Precautions

• High pitched sound by some air-turbine handpieces at high speeds.• Potential damage to hearing depends on:

• Intensity or loudness (decibels- db)• Frequency (cps)• Duration of the noise• Susceptibility of the individual


• Increased age, existing ear damage disease and medications are other factors that canaccelerate hearing loss.

• Air turbine handpieces at 30 pounds : 70 – 94 db at high frequency.

• Noise levels > 75 db @ of 1000 – 8000 cps : hearing damage.

• Protective measures are recommended for 85 db @ 300 – 4800 cps.

• Protection is mandatory at 95 db.

• Earplugs, sound proof rooms with absorbing materials on walls and floor

• Anti-noise devices can be used to cancel the unwanted sounds as well.


Inhalational Precautions

• Aerosols are fine dispersion in air of water, tooth debris, micro-organisms and / orrestorative materials.

• Cutting amalgams or composite resin produce both sub-micron particles and vapours.

• Vapours from cutting amalgam - mercury & that from composite resins -monomers.

• Inhalation can produce alveolar irritation & tissue reactions.

• A face mask filters out bacteria and fine particulate matterbut not mercury or monomer vapours.


Infection Control

• Latch angles, burs and rotary stones must be cleaned & sterilized.

• Handpieces are semicritical instruments requiring sterilization

• Motor-end of micro-motor must be covered with a single used disposable plastic bag.

• Scrub and disinfection of the end may also be performed


Sterilization of Burs

• Presoak: burs placed in soap water to loosen debris

• Cleaning: Stainless brush under water or ultrasonic systems

• Sterilization by:• Dry-clave - 160°C for 30min• Autoclave – 121°C for 15min @ 15 lbs.

• Tendency of corrosion at the neck region, hence soak in 2% Sodium nitrite prior toautoclaving.

• Chemiclave – chemical vapour under pressure: 131°C @ 20 pounds pressure.• Best suited for corrosion prone instruments.


Sterilization of Handpiece

• With metal bearing:• Scrub the metal bearing with water and soap.• Lubricate and place in sterilization bag & autoclaved.

• Lube-free ceramic bearing• Must not be chemically sterilized – damage to internal parts.

• Chemical vapor pressure sterilization

• Ethylene oxide gas• Provides both internal & external sterilization due to penetrating capacity.• Takes long time for sterilization.

• Dry heat for handpiece is generally not recommended


Recent Advances

Single patient use burs:• Developed by CDC & ADA to minimise cross- contamination & prolonged sterilization

protocol

Turbo diamond:• Have diamond free zone or continual spiral of blank space.• The diamond free zone breaks surface contact with the tooth, thus allowing cooler &

cleaner cutting.• The continual spiral design leaves a smooth wall.


Fiber-optic handpieces:• Provide light at the working site.• Shut off delay – allows illumination even after release at foot control

Cellular optic handpiece:• Handpiece can be repeatedly sterilized without light degradation.

Lube free ceramic bearing handpiece:• Do not require lubrication• Care should be taken against chemicals


Fissureotomy burs (carbide):• Tip of the bur is smaller than no. ¼ round bur.• Helpful in conservative preparations

Smart Prep burs:• Aka Polymer bur / smart bur• Made from polymer• Self limiting• Effectively remove decayed dentin without affecting

the healthy dentin


Conclusion

• The introduction of rotary, powered cutting equipment was one of the truly major advancesin dentistry.

• These advances have enabled us to move from operative dentistry to conservative dentistry.

• Proper understanding of speed and its implication in clinical use will help in providing anexpertise treatment.


References

• Art & science of operative Dentistry – Sturdevant ( 4th Edition)

• Art & science of operative Dentistry – Sturdevant ( 5th Edition)

• Operative Dentistry – Marzouk

• Textbook of Operative Dentistry – Vimal Sikri

• Pickard’s Manual of Operative Dentistry (8th Edition)

• Textbook of Operative Dentistry – Nisha Garg



Education

Rotary Instruments in Operative Dentistry