Abrasives

Presented By : Arpit Viradiya Guided By : Dr Sandeep Metgud Dr Deepali Agrawal

Contents• Definition• Abrasive action• Types of abrasion• Principles : Cutting Grinding & Polishing• Desirable Characteristics Of An Abrasive• Factors affecting rate of abrasion• Abrasive instrument design• Classification of abrasive agents• Precautions• Biological hazards of abrasive agents• Recent Advances• Summary & Conclusion

• Craig has defined abrasion as:• "A process of wear whereby a hard rough

surface (like a sand paper disk) or hard irregular shaped practicles (like those in an abrasive slurry) plough grooves in a softer material and cause materials from these grooves to be removed from the surface".

Abrasive actionHarder material comes into frictional contact with the

substrate

Contact generates tensile and shear stresses

Break atomic bonds

Substrate particles are removed

Types of abrasion

1. Two-body abrasion • Abrasive bonded to instrument

Eg - diamond bur abrading a tooth.

Three-body abrasion

• Non bonded abrasives • Abrasive particles are free

Eg - dental prophylaxis paste

Erosion

• Wear caused by hard particles impacting a substrate surface, carried by a stream of liquid or stream of air. Eg. Sand blasting a surface

• Chemical erosion

Acid etching

Enhance bonding

Principles

Cutting

• Use of any instrument in a bladelike fashion

• Regularly arranged blades that remove

small shavings of the substrate

• Unidirectional cutting pattern

Grinding

• Removes small particles of a substrate

through the action of bonded or coated

abrasive instruments

• Predominantly unidirectional

• Innumerable unidirectional scratches

• Eg: a diamond coated rotary instrument

Polishing

• Most refined of the finishing processes

• Multidirectional in its course of action

• Acts on an extremely thin region of the substrate

surface

• Progress - fine polishing media

• Final stage produces fine scratches - not visible

unless greatly magnified

Desirable Characteristics Of An Abrasive

• It should be irregular in shape so that it presents a sharp edge.

• It should be harder than the surface it abrades.• Abrasive point should always fracture rather

than dull out so that always a sharp point or edge is available.

• Abrasive should possess attrition resistance so that it does not wear.

Factors affecting abrasion

• Hardness

• Shape

• Size

• Pressure

• Speed

• lubricants

Factors affecting rate of abrasion

Hardness

• Relates to durability of an abrasive

• Measure of a material’s ability to resist indentation

• Abrasive particle must be harder than the surface to be

abraded

• First ranking of hardness was published in 1820 by

Friedrich Mohs

• Knoop and Vickers hardness tests

Material Moh’s Brinell Knoop Material Moh’s Brinell Knoop

Talc 1 Alumnium oxide 9 1700 1900

Gypsum 2 Silicon carbide 9-10 3000 2500

Chalk 3 Boron carbide 9-10 2800

Rouge 5-6 Diamond 10 >3000 7000Pumice 6 450 560 SUBSTRATES

Tripoli 6-7 Acrylic 2-3 25Garnet 6.5-7 550 Pure gold 2.5-3 30Tin oxide 6-7 Porcelain 6-7 400Sand 7 650 800 Amalgam 4-5 90Cuttle 7 650 800 Dentin 3-4Tool steel 800 Enamel 5-6 270Zirconium silicate

7-7.5 Glass 5-6

Tungsten carbide

9 1200 2100 Resin composite 5-7 200

Shape

• Sharp, irregular particle produces deeper abrasion than

rounder particle under equal applied force

• Numerous sharp edges - enhanced cutting efficiency

• Abrasion rate of an abrasive decreases with use

Size• Larger particles size, abrade a surface more rapidly

• Particles based on their size:

1. Coarse -53 µm to 142 µm,

2. Medium -

15 µm to 52 µm,

3. Fine - 7 to 14 µm.

4. Superfine – 2 to 6 um.

Pressure

Greater force during finishing

Abrasive cut deeper into the surface

More rapid removal of material

Raise in temperature within the substrate

Distortion or physical changes within the substrate

• Deeper and wider scratches are produced by increasing

the applied force from F1and F

2

Speed

Faster speed

Faster cutting rates

Temperature increases

Greater danger of overcutting

Lubrication

• Minimize the heat buildup

• Facilitates removal of debris

• Cooling action and removal of debris enhances

the abrasion process.

• Water is the most common lubricant

• Eg. Water, glycerin or silicone

• Excess lubrication – prevent abrasive contact

Abrasive Instrument Design

• Abrasive Grits.

• Bonded Abrasives.

• Coated abrasive disks and strips

• Non bonded abrasives

Abrasive grits

• Derived from materials that have been crushed and passed through a series of mesh screens

• Dental abrasive grits based on particle size are

• Coarse• Medium coarse• Medium • Fine• Superfine

Bonded abrasives

• Abrasive particles are incorporated through

a binder to form grinding tool

• Particles are bonded by four general

methods:

• Sintering

• Vitreous bonding

• Resinous bonding

• Rubber bonding (latex or silicon based)

Type of bonding and grinding behaviour

1. Bonded abrasives that tend to disintegrate rapidly against substrate are weak

• Increased abrasive cost - Reduced instrument life

2. Abrasives that tend to degrade too slowly clog with grinding debris

• Loss of abrasive efficiency, increased heat generation, and increased finishing time

Maintenance of the efficiency of abrasive

• Truing : abrasive instrument is run against a

harder abrasive block until the abrasive

instrument rotates in the hand piece without

eccentricity or runout when placed on a

substrate.

• Dressing :

1)Reduces instrument to correct working

size, shape

2)Removes clogged debris (abrasive

blinding) - Restores grinding efficiency

Truing

Coated Abrasive Disks and Strips

• supplied as disks and finishing strips.

• Fabricated by securing abrasive particles to a flexible

backing material

• available in different diameters with thin and very thin

backings.

• Moisture – resistant backings are advantageous

Abrasive discs :

• Gross reduction, contouring, finishing, and

polishing of restoration surfaces

• Coated with aluminum oxide abrasive

Abrasive strips :

• With plastic or metal backing are available

for smoothening and polishing the

interproximal surfaces of direct and indirect

bonded restorations

Non bonded abrasives

• Polishing pastes - final polishing.

• Applied to substrate with a nonabrasive

device - synthetic foam , rubber, felt, or

chamois cloth.

• Dispersed in water soluble medium such as

glycerin for dental applications.

• Aluminium oxide and diamond

Classification :

Natural abrasives

1.Arkansas Stone

2.Chalk

3.Corundum

4.Diamond

5.Emery

6.Garnet

7. Pumice8. Quartz9. Sand10. Tripoli11. Zirconium silicate12. Cuttle13. Kieselguhr

1.Silicon carbide

2.Aluminium oxide

3.Synthetic diamond

4.Rouge

5.Tin oxide

Synthetic Abrasives

Arkansas stone

• Semi translucent , light gray, siliceous sedimentary rock.

• Contains microcrystalline quartz.

• Attached to metal shanks and trued to various shapes

• Fine grinding of tooth enamel and metal alloys

Chalk

• Mineral forms of calcite.

• White abrasive composed of

calcium carbonate.

• Used as a mild abrasive paste to

polish tooth enamel, gold foil,

amalgam and plastic materials. 

Natural Diamond• Transparent colorless mineral

composed of carbon• Superabrasive

• Supplied in several forms• Bonded abrasive rotary

instruments• Flexible metal backed abrasive

strips• Diamond polishing pastes.

• Used on tooth structure; ceramic and resin based composite materials

Diamond abrasive instruments

Introduced in the united states in 1942.Consists of 3 parts :

metal blank powdered diamond abrasive metallic bonding material.

•Blank resembles a bur without blades.•The diamonds are attached to the blank by electroplating a layer of metal on the blank while holding the diamonds in place against it.•Diamond instruments are available in variety of sizes & shapes.•More than 200 shapes & sizes are available.•Lack of uniform nomenclature for diamond instruments.

Various Shapes of Diamond abrasive instruments

Diamond particle factors

Particle size is categorized as:Coarse (125-150 um)medium (88-125 um)Fine (60-74 um)Very fine (38-44 um)

Diamond finishing instruments use even finer diamonds (10-38 um) Only cause of failure of diamond instruments is loss of diamonds from critical areas which results from the use of excess pressure in attempt to increase the cutting rate.

Corundum • Mineral form of aluminum

oxide

• Physical properties are inferior

to those of alpha aluminum

oxide.

• Grinding metal alloys

• A bonded abrasive in several

shapes.

• Used in instrument – White

stone

Emery

• Natural form of an oxide of aluminium

• Grayish- black corundum

• Coated abrasive disks

• Finishing metal alloys or acrylic resin

materials.

Garnet

• Dark red, very hard .

• Comprise - silicates of Al, Co, Mg,

Fe, Mn

• Garnet is coated on paper or cloth

with glue.

• Fractured during grinding sharp,

chisel-shaped plates

• Grinding metal alloys or acrylic

resin materials.

Pumice

• Highly siliceous material of

volcanic origin

• Powder-crushing pumice stone

• Abrasive action is not very high

• Polishing tooth enamel, gold foil,

dental amalgam and acrylic

resins

 

 

Quartz

• Very hard, colorless, and

transparent.

• Crystalline particles are

pulverized to form sharp,

angular particles - coated

abrasive discs.

• Grinding tooth enamel and

finishing metal alloys.

Sand

• Predominantly composed of silica.

• Particles represent a mixture of color.

Making it distinct in appearance.

• Rounded to angular shape.

• Applied under air pressure to remove

refractory investment materials

• Coated on to paper disks

Tripoli

• Derived from light weight, friable siliceous

sedimentary rock.

• Rock is ground and made into bars with soft binders

• Color- white/grey/pink/red/yellow.

• Grey and red types

• Polishing for metal alloys and some acrylic resins.

Zirconium silicate / Zircon

• Off -white mineral.

• Ground to various particle sizes - coated

abrasive disks and strips.

• Component of dental prophylaxis pastes

Cuttle

• Referred to as cuttle fish, cuttle bone, or cuttle.

• White calcareous powder

• Available as a coated abrasive

• Polishing of metal margins and amalgam

restorations.

Kieselguhr

• Siliceous remains of minute aquatic plants -

diatoms.

• Coarser form - diatomaceous earth

• Excellent mild abrasive

• Risk for respiratory silicosis caused by chronic

exposure

 

Synthetic Silicon Carbide• Extremely hard abrasive and 1st synthetic abrasive

• Highly effective cutting of metal alloys, ceramics and

acrylic resin materials.

• Abrasive in coated disks and as vitreous - bonded

and rubber instruments.

Aluminum oxide

• White powder

• used as bonded abrasives, coated abrasives and air

propelled abrasives.

• Finishing metal alloys, resin based composites and

ceramic materials.

• Pink and ruby variations- adding chromium compounds

Rouge• Consists of iron oxide, which is the fine red

abrasive component.

• Blended in to various soft binders in to a cake

form.

• Used to polish high noble metal alloys.

Tin Oxide

• Extremely fine abrasive.

• Less abrasive than quartz.

• Polishing teeth and metallic

restorations in the mouth.

• Produces excellent polish of

enamel.

• Mixed with water or glycerin -

abrasive paste.

Synthetic Diamond

• Controllable, consistent size and shape.

• Resin bonded diamonds have sharp edges

• Larger synthetic diamond particles – greenish

• Blocks with embedded diamond particles –

truing other bonded abrasives

• Used primarily on tooth structure, ceramics

and resin based composites.

Dentifrices

• Available as toothpaste, gels and powders.

• The abrasive concentrations in paste and gel

dentrifices are 50% to 75% lower than those

of powder dentrifices

• Function :

• Abrasive and detergent action

• Polish teeth

• Act as vehicles

Prophylaxis pastes

• removal of exogenous stains, pellicle, material alba,

and oral debris.

• contain moderately abrasive materials : pumice

• Silcon dioxide and zirconium silicate are used

• Applied to teeth through rubber cup on a slow speed

handpiece

 

Precautions

• Heat generation during cutting and

contouring , finishing and polishing

procedures is a major concern.

• To avoid adverse effects to the pulp, cool

the surface using air water spray and

intermittent contact.

Biological hazards

• Aerosols – silica based materials (smaller than

5µm)

• Silicosis or grinders disease

• Precautions -adequate water spray, suction

-eyeware ,facemasks

-proper ventilation

Recent Advances

Air abrasive Technology• Alternative to rotary instrument

cutting.

• High pressure stream of 25-

30µm Al2O3.

• ‘Air polishing’- controlled

delivery of air, water and Sodium

bicarbonate slurry.

Uses

 

• Cavity preparation

• Removal of defective restorations

• Endodontic access through porcelain crowns

• Minimal preparation to repair crown margins

• Superficial removal of stains

• Roughening of internal surfaces of indirect

porcelains or composite restorations

CVD diamond-coated burs

• Advantages such as less noise, less pain for the patient, precise cutting, conservative cavity, preparation, longer lifetime, less injury to the dental structures, no cutting of soft tissues and easier access of the carious lesion.

Gripped diamond Strips

Diamond-coated stainless steel metal strips

Features:used for smoothing, contouring, finishing and trimming proximal, incisal and interproximal areastwo, color-coded working areas with different grit sizeshandles help to pull through tight contact areas

Finishing and Polishing system

designed to finish and polish all types of resin restoratives By incorporating a superior abrasive into a special resin.System uses a one-piece disc and mandrel - with no metal boss. So that, the possibility of discolouring the restoration has been completely eliminated.It completes intermediate and final finishing without the need to change discs.

Perforated Diamond Strips

Designed for complete control during inter-proximal reduction, shaping, and contouring. The design assists in debris removal, provides improved visibility, control, and flexibility; made of stainless steel to resist breaking and stretching.

They are color coded for grit identification: blue for medium, red for fine and yellow for super-fine.

single-gel diamond polishing system

it can polish the surface of all restorative materials: composite, glass ionomer, compomer, amalgam, precious metal and enamel. Even porcelain achieves a lustrous surface in less time due to the optimal concentration of micron-sized diamond particles.

SUMMARY & CONCLUSION

• Though a varied range of abrasive and polishing agents have been described with relation to individual dental materials, an ideal abrasive or a polishing agent which would satisfy all polishing needs of the dental materials, one would say is yet to be developed.

• Sturdevant’s Art and Science of Operative Dentistry, 5th edition, Elsevier publications.

• Anusavice, Phillips Science of Dental Materials, 12th edition, Elsevier publications.

• Craig . Powers and Wataha, Dental Materials, Properties and manipulation, 8th edition, Elsevier publications.

• Contemporary fixed prosthodontics. 2nd Edition, Stephen F. Rosensteil.

References

Thank You