Abrasives and polishing agents in dentistry

Abrasives and Polishing Agents

Vinay PavanKumar .K

1st year PG Student

Dept of Prosthodontics

AECS Maaruti dental college

Abrasives and polishing agents

Abrasion

Erosion

Classification

Factors affecting abrasion

Abrasive instrument design

Finishing and polishing procedures for different materials

Steps in finishing and polishing

Abrasion

Abrasion is the process of wear on the surface of one material by another material by scratching, gouging,

chiseling, tumbling, or other mechanical means

The wearing away of a substance or structure (such as the skin or the teeth) through some unusual or abnormal mechanical process

-GPT 8

Abrasive action- PrinciplesHarder 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

• Use of progressively fine polishing media

• Final stage produces fine scratches - not visible

unless greatly magnified

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 7000

Pumice 6 450 560 SUBSTRATES

Tripoli 6-7 Acrylic 2-3 25

Garnet 6.5-7 550 Pure gold 2.5-3 30

Tin oxide 6-7 Porcelain 6-7 400

Sand 7 650 800 Amalgam 4-5 90

Cuttle 7 650 800 Dentin 3-4

Tool steel 800 Enamel 5-6 270

Zirconium 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 -100 µm to 500 µm,

2.

Medium -10 µm to 100 µm,

3. Fine - 0 to 10

µm.

PressureGreater 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

• Used against a weak substrate • 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 appliances.

• Aluminium oxide and diamond

Classification of finishing and polishing devices

Based on surface removal

1. Cutting Instruments : Tungsten carbide

2. Bonded abrasive

• Diamonds

• Silicon carbide

• White stone

• Tripoli

• Rouge

3. Impregnated abrasives-• Aluminium oxide• Emery• Quartz• Silicon carbide• Garnet• Zirconium silicate• Cuttle

4. Loose abrasives• Aluminum oxide• Ultra fine diamond particles• Tin oxide• Pumice

According to Hardness• Diamond - 7500 KHN

• Silicon carbide - 2500 KHN

• Aluminum oxide - 2100 KHN

• Emery - 2000 KHN

• Corundum - 2000 KHN

• Tungsten carbide - 1900 KHN

• Garnet - 1350 KHN

• Quartz - 800 KHN

• Sand - 560 KHN

• Pumice - 560 KHN

• Chalk - 135 KHN

Natural abrasives

1. Arkansas Stone

2. Chalk

3. Corundum

4. Diamond

5. Emery

6. Garnet

7. Pumice

8. Quartz

9. Sand

10. Tripoli

11. Zirconium silicate

12. Cuttle

13. 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. 

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

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 ceramic and resin based composite materials

Diamond burs color coding and grit size

Bur type Color Grit size ISO no

Supercoarse Black ring 181μm 544

Coarse Green ring 151μm 534

Medium No ring 107-126μm 524

Fine Red ring 40μm 514

Superfine Yellow ring 20μm 504

Ultrafine White ring 15μm 494

Emery

• Natural form of an oxide of

aluminium

• Grayish- black corundum

• Coated abrasive disks

• Greater the content of alumina -

finer the grade of emery.

• 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.

• 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

Steps in finishing and polishing

Bulk reduction

• Removal of excess material

• Instruments - diamond, carbide and steel burs,

abrasive coated disks, or separating disks.

• 8 - 12 fluted carbide burs or abrasives with

particle size of 100µm or larger

Contouring

• Achieved during bulk reduction

• Finer instruments may be used

• Desired anatomy and margins must be

achieved.

• 12 - 16 fluted carbide burs or 30 - 100 µm sized

abrasive particles used

Finishing

• Introducing finer scratches to surface of substrate

• Provides a blemish free smooth surface.

• 18 - 30 flute carbide burs , fine and super fine

diamond burs, or abrasives between 8 and 20 µm

in size.

Polishing

• Provides enamel like luster.

• Smaller particles provide smoother and shinier

surfaces

• Abrasives of 20 µm provide luster

• Importance of polishing dental restorations and teeth

• Less bacterial colonization

• Metallic restoration - prevention of tarnish and

corrosion

• Comfortable for the patient

Benefits of finishing and polishing restorative materials

• To promote oral health and function

• Enhance strength of the restorative surface

• To improve esthetics

Goals of finishing and polishing

• Obtain the desired anatomy, proper occlusion

• Reduction of roughness, and scratches.

• Smooth surface

• Resist bacterial adhesion and excessive plaque accumulation.

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.

Polishing instruments

• Rubber abrasive points.

• Fine particle disks and strips.

• Fine particle polishing pastes – applied with

soft felt points, muslin wheels, prophy cups or

buffing wheels.

Non-abrasive polishing

• Composite glazing

• Ceramic glazing

• Electrolytic polishing

Composite glazing

• Layer of glaze – unfilled resin

• Smooth highly glossy surface

Glazing ceramics

• Subjected to high temperature• Glass like surface

Electrolytic polishing

• Electrochemical process

• Reverse of electroplating

• Excellent method for Co-Cr alloys

Finishing and polishing procedures

Resin based composite restorations

• Most difficult to polish and finish

• Depends on fillers, preparation design, curing

effectiveness and the post curing time.

• Finishing & Polishing - in one direction only

• Should continue in a direction perpendicular to

the previous one.

Gold alloys

• Slow speed hand piece should be used

• Contour with carbide burs, green stones, or heatless

stones.

• Finish with pink stones ( aluminum oxide) , or

medium grade abrasive impregnated rubber wheels

and points( brown and green)

• Apply fine abrasive- impregnated rubber wheels,

cups and points .

• Apply Tripoli or rouge with rag or leather wheels

Ceramometal restorations

• Critical area while polishing is the porcelain metal

junction

• Using an air water spray and maintaining

intermittent contact

• Several kits:Axis dental corp, Universal ceramic

polishers, Dialite

• Recommended polishing speed -10,000 rpm

• Polishing at 20,000 rpm reduces flexural strength of

ceramics

Acrylic resins for Denture Bases and Veneers

• Contour with tungsten carbide burs and sand

paper. Use a rubber point to remove the

scratches.

• Apply pumice with a rag wheel, felt wheel,

bristle brush or prophy cup.

• Apply Tripoli or a mixture of chalk and alcohol

with a rag wheel.

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

Biological hazards of the finishing procedure

• Aerosols – silica based materials (smaller than

5µm)

• Silicosis or grinders disease

• Precautions -adequate water spray, suction

-eyeware ,facemasks

-proper ventilation

Contraindications of Polishing

• Exposed root surfaces• Newly erupted teeth• Patient sensitivity• Inflamed or bleeding gingival tissue• Xerostomia• Respiratory problems• Caries• Hypomineralization• Allergic reaction to pastes

Review of literature

• The objective of this study was to compare both qualitatively and quantitatively the effects of 4 chairside polishing kits (Exa Technique, Acrylic Polisher HP blue, AcryPoint, Becht Polishing Cream) and conventional laboratory polishing (Universal Polishing Paste for Resins and Metals, Lesk Polishing Liquid) on 3 different types of acrylic resins: autopolymerizing, heat-polymerizing, and injected heat-polymerizing resin materials.

Kuhar M et al, Effects of polishing techniques on the surface roughness of acrylic denture base resins, J Prosthet Dent, 2005;93(1):76-85

• The aim was to study the effect of three polishing

agents : pumice, universal polishing agent and

brite-O on the surface finish and hardness of two

types of acrylic material

• Universal polishing paste produced smoothest

surface

• Irrespective of resin type and polishing methods it

showed equal surface hardness.

Srividya S etal. Effect of different polishing agents on surface finish and

hardness on denture based acrylic resin : A comparative study IJOPRD,

2011, 1(1) 7-11

• The purpose of this laboratory study was to evaluate three-body wear of three indirect laboratory composite resins, five chair side bis-acryl resin-based materials, and two chair side methacrylate-based materials used to fabricate provisional implant-supported restorations.

• The use of indirect composite resin is preferred over chair side methacrylate-based materials when the provisional implant supported restoration has to be in service for a long period of time

Santing, H. J., Occlusal Wear of Provisional Implant-Supported Restorations. Clinical Implant Dentistry and Related Research, April 2013

• To find out the correlation between the roughness of diamonds and roughness created on dentin after tooth preparation & to measure the surface roughness of dentin after tooth preparation with different grit sizes of diamond rotary instruments

• There is positive correlation (r = 0.93) between the roughness of diamonds and roughness created on the dentin

The effect of grit size of diamonds on the dentinal surface : Dr. Shivangi Sinha

• Selection of correct grit size and their correct sequence for tooth preparation has an influence on the surface characteristics

• So completion of the tooth preparation with a finishing bur appeared to be the method of choice if a smooth tooth preparation surface is preferred

The effect of grit size of diamonds on the dentinal surface : Dr. Shivangi Sinha

• This study determined the two-body wear and toothbrushing wear parameters, including gloss and roughness measurements and additionally Martens hardness, of nine aesthetic CAD/CAM materials, one direct resin-based nano composite plus that of human enamel as a control group.

• Zirconium dioxide ceramics showed no material wear and low wear of the enamel antagonist.

Mörmann.W.H etal Wear characteristics of current aesthetic dental restorative CAD/CAM materials: Two-body wear, gloss retention, roughness and Martens hardness. Journal of the Mechanical Behavior of Biomedical Materials ,2013, 20, 113–125

• Two-body wear of CAD/CAM-silicate and -lithium disilicate ceramics, -hybrid ceramics and nano composite as well as direct nano composite did not differ significantly from that of human enamel

• Gloss retention was highest with zirconium dioxide ceramics, silicate ceramics, hybrid ceramics and nanocomposites.

• Temporary polymers showed least gloss retention

Mörmann.W.H etal Wear characteristics of current aesthetic dental restorative CAD/CAM materials: Two-body wear, gloss retention, roughness and Martens hardness. Journal of the Mechanical Behavior of Biomedical Materials ,2013, 20, 113–125

CONCLUSION

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Kuhar M et al, Effects of polishing techniques on the

surface roughness of acrylic denture base resins, J

Prosthet Dent, 2005;93(1):76-85

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Clin N Am 51 (2007) 379–397

The effect of grit size of diamonds on the dentinal

surface : Dr. Shivangi Sinha

Srividya S etal. Effect of different polishing agents on surface

finish and hardness on denture based acrylic resin : A

comparative study IJOPRD, 2011, 1(1) 7-11

Mörmann.W.H etal Wear characteristics of current aesthetic

dental restorative CAD/CAM materials: Two-body wear, gloss

retention, roughness and Martens hardness. Journal of the

Mechanical Behavior of Biomedical Materials ,2013 April, 20,

113–125

Santing, H. J., Occlusal Wear of Provisional Implant-

Supported Restorations. Clinical Implant Dentistry and

Related Research, April 2013