ABRASIVES

PRESENTED BY:

DR. HASHMAT GUL

DEMONSTRATOR ,

DENTAL MATERIALS ,

AMC, NUST.

SOME IMPORTANT DEFINITIONSABRASIVE A hard substance used for grinding, finishing, or polishing a less-hard surface.

CUTTING Process of removing material from the substrate by use of a bladed bur or an abrasive embedded

in a binding matrix on a bur or disk.

GRINDING Process of removing material from a substrate by abrasion with relatively coarse Particles.

CONTOURING Process of producing a desired anatomical form by cutting or grinding away excess material.

FINISHING Process of removing surface defects or scratches created during the contouring process through the

use of cutting or grinding instruments or both.

POLISHING Process of providing luster or gloss on a material surface.

BENEFITS OF FINISHING AND POLISHING RESTORATIVE MATERIALS

ORAL HEALTH

• By resisting the accumulation of food debris and pathogenic bacteria.

• Easier to maintain in a hygienic state when preventive home care is practiced.

ORAL FUNCTION

• Oral function is enhanced-food glides more freely over occlusal and embrasure surfaces during mastication.

• Lower contact stresses, so can improve the strength of the restoration, especially in areas that are under tension.

• Minimize wear rates on opposing and adjacent teeth ( Ceramics).

AESTHETICS

• Highly mirror-like restoration surfaces preferred for the invisible areas(posteriors) but is discouraged for anterior visible teeth to gain a more natural appearance.

• Tarnish and corrosion activity of some dental materials can be significantly reduced

ABRASIVE INSTRUMENTS

ARMENTARIUM FOR

FINISHING POLISHING

� Fluted carbide burs.�Diamond burs.�Stones. �Coated abrasive discs & strips.

�Polishing pastes.�Soft & hard polymeric cups, points &

wheels.�Polishing brushes. �Muslin (Woven Cotton Fabric) Wheels.

FLUTED CARBIDE BURS

DIAMOND BURS

STONES

COATED-ABRASIVE DISCS & STRIPS

�Paper-backed abrasive disc/strip.

�Myler backed abrasive disc/strip (moisture resistant)

TYPICAL BONDED ABRASIVE INSTRUMENTS

From left to right�Vitreous-bonded

abrasive wheel & points (1-3)

� Rubber-bonded abrasive bullets

POLISHING PASTES

POLYMERIC CUPS/POINTS/WHEELS

POLISHING BRUSHES

TYPES OF ABRASIVES

NATURAL ABRASIVES MANUFACTURED ABRASIVES� Ailzansas Stone� Chalk (paste)� Corundum (white stone) � Diamond

�Natural (super abrasive)�Synthetic

� Emery (Coated disks)� Garnet (Coated disks & arbor bands).� Pumice (rubber-bonded , flour)� Quartz ( Coated discs)� Sand� Tripoli � Zirconium Silicate (coated disks & strips) � Cuttle (coated abrasive) � Kieselguhr

� Silicon Carbide (coated disks & as vitreous-bonded & rubber-bonded instruments).

� Aluminium Oxide (bonded/coated abrasives & air-propelled grit abrasives)

� Synthetic Diamond,

� Rouge

� Tin Oxide

NATURAL ABRASIVES USES� Ailzansas Stone

� Chalk (paste)

� Corundum (white stone)

� Diamond� Natural (super abrasive)� Synthetic

� Emery (Coated abrasive disks)

� Garnet (Coated disks & arborbands.

� Pumice (rubber-bonded , flour)

� For fine grinding of tooth enamel and metal alloys.

� To polish tooth enamel, gold foil, amalgam & plastic materials.

� Grinding metal alloys.

� Mostly used on ceramic and resin-based composite materials. � Manufacture of diamond saws, wheels, burs, blocks & polishing pastes.

� May be used for finishing metal alloys or acrylic resin materials.

� Used in grinding metal alloys and acrylic resin materials.

� polishing tooth enamel, gold foil, dental amalgam, and acrylic resins.

NATURAL ABRASIVES USES� Quartz ( Coated discs)

� Sand

� Tripoli

� Zirconium Silicate (coated abrasive disks & strips)

� Cuttle (coated abrasive)

� Kieselguhr

� used primarily to finish metal alloys, and they may also be used to grind dental enamel.

� Applied under air pressure to remove refractory investment materials from base metal alloy castings. They are also coated onto paper disks for grinding of metal alloys and acrylic resin materials.

� Polishing metal alloys & some acrylic resin materials.

� Used as a component of dental prophylaxis pastes

� Polishing of metal margins and dental amalgam restorations.

� Coarser form is called Dialomaceous earth, used as a filler in many dental materials, such as the hydrocolloid impression materials.

MANUFACTURED ABRASIVES USES� Silicon Carbide (coated disks & as vitreous-bonded

& rubber-bonded instruments).

� Aluminium Oxide (bonded/coated abrasives & air-propelled grit abrasives)

� Synthetic Diamond,

� Rouge

� Tin Oxide

� for fine grinding of tooth enamel and metal alloys.

� white stones, popular for adjusting dental enamel & for finishing metal alloys, Resin-based composites &ceramic materials.

� to polish high noble metal alloys.

� Polishing teeth and metallic restorations in the mouth

CUTTING, GRINDING, FINISHING & POLISHING

�FACTORS AFFECTING THE RATE OF MATERIAL

REMOVAL

�The speed of the hand-piece.

�The Pressure applied.

� The concentration , size , type & shape of the abrasive particle used.

�The relative roughness of the abraded/cut surfaces.

�THE GOALS OF FINISHING & POLISHING

�To obtain the desired anatomy/proper occlusion.

�The reduction of roughness, gouges, and scratches that were produced by

the contouring and finishing instruments.

�The polished surface should be smooth enough

� to be well tolerated by oral soft tissues and

� to resist bacterial adhesion and excessive plaque accumulation.

PRINCIPLES OF CUTTING, GRINDING & FINISHING

�Particles of a substrate are removed by the action of a harder abrasive that comes into

frictional contact with it.

�With rotary instrumentation, the blades of a carbide bur or the tips of abrasive

particles transfer the force to the substrate.

�This contact must generate sufficient tensile and shear stresses to break atomic bonds

and release a particle from the substrate.

�These tensile and shear stresses are induced within both the substrate and the rotary

instrument.

�The instrument will fail to function if the stress that develops in any part of the cutting or

grinding surface exceeds its strength compared with the strength of the substrate. Blade

edges will become dull, and abrasive particles will fracture or tear away from their

binder.

BULK REDUCTION/CONTOURING

GRINDING CUTTING

� Instruments used

� Diamond burs� Abrasive-coated disks

� 8-12 fluted carbide burs used for cutting.

� 12-16 fluted carbide burs used for Contouring.

� Instruments used

�Steel burs�Tungsten Carbide burs

� Abrasives with a particle size of 100 um or larger with sufficient hardness (9-10 mohs hardness).

� Abrasives ranging in size from 30-100um, used for fine contouring.

• Tooth cut by a High-speed Tungstun Carbide bur, the regular pattern of removal of tooth structure corresponding to the regular arrangement of blades on the bur.

• Unidirectional cutting pattern (small shavings).

Carbide bur

• Tooth ground by diamond bur, the multiplex scratches formed by the random arrangement of abrasive particles on the diamond bur.

• Unidirectional grinding. Diamond bur

• Photomicrograph of the bonded diamond particles on a coarse diamond bur (x150 )

Bonded diamond particles

THE CUTTING/GRINDING OPERATION

Tungsten carbide finishing burs

16-fluted (left), smoother finish, Slow material removal.

8-fluted (right) , less smooth finish, Rapid material removal.

Fine diamond bur

Slow material removal.

Smooth surface finish.

Medium-grit diamond bur

Coarse-grit diamond bur

Rapid material removal.

Rougher surface finish.

A course diamond bur

A 12-flute Carbide bur

A 16-flute Carbide bur

An abrasive impregnated finishing disk

An abrasive impregnated polishing disk.

� SEM images of the surface of a resin-based composite after the grinding, finishing, and polishing processes using live instruments

POLISHING

�The purpose of polishing is to provide an enamel-like luster to the restoration.

�The speed of achieving a luster, depends on the hardness and size of the abrasive

particles & the method of abrasion (e.g., two-body abrasion or three-body abrasion).

� Smaller particles provide smoother and shinier surfaces. Ideally, 20um abrasive

particles provide luster at a low magnification with no visible scratches.

�The surface must be cleaned between steps, because an abrasive particle left on the

surface from the previous step can cause deep scratches.

�The quality of the surface finish and polish can be characterized by the

measurement of the surface roughness using a profilometer, an optical microscope, or a

scanning electron microscope (SEM).

�In clinical practice, the surface luster is usually judged without magnification.

POLISHING

�POLISHING PASTES

A non-abrasive material should be used as an applicator.

� Soft Felt Points,

� Muslin (Woven Cotton Fabric) Wheels,

� Prophylaxis Rubber Cups/points,

� Buffing Wheels.

�A common feature of some of these materials is their porous texture that allows fine

abrasive particles to be retained during the buffing procedure

POLISHING PROCEDURES

�STEPS

�Polishing progresses from the finest abrasive that can remove scratches from the

previous grinding procedure.

�Each step is followed by the use of progressively fine polishing media until no

further improvement in surface finish is observed.

�Polishing is considered to be multi-directional in its course of action.

THE MECHANICS OF HIGH-SPEED ROTARY INSTRUMENTATION

Black arrow: Direction of rotation of High-speed Diamond bur (clockwise when viewed by operator)Grey arrow: Direction of shaving movement of hand-piece (opposite to da rotation of bur).Incisal viewFB : Rotational forces of bur at tooth surfaceFo : Opposing force of the operator

TWO-BODY ABRASION occurs when abrasive particles are tightly bounded to the abrasive instrument.

THREE-BODY ABRASION occurs when the abrasive particles are free to translate & rotate between two surfaces.

HARD PARTICLE EROSION occurs when the abrasive particles are propelled against a substrate by air pressure.

ABRASIVE INSTRUMENT DESIGN

Abrasive grits Bonded abrasives Coated abrasive disks

& strips

Non-bonded

abrasives

� Dental abrasive grits are classified on basis of particle size as � coarse, � medium coarse, � medium, � fine, and � superfine

� Consist of abrasive particles that are incorporated through a binder to form grinding tools such as points, wheels, separating disks, coated thin disks etc.

� Particles are bonded by four general methods:(1) sintering, (2) vitreous bonding(3) resinoid bonding (4) rubber bonding

� Fabricated by securing abrasive particles to a flexible backing material (heavy weight paper, metal, or Mylar) with a suitable adhesive material.

� These abrasives typically are supplied as disks and finishing strips

� Polishing pastes (used forfinal polishing).

� Applied to the substrate with a non-abrasive device such as synthetic foam, rubber, felt, or chamois cloth.

� The abrasive particles are dispersed in a water-soluble medium such as glycerin for dental applications.

� E.g. Aluminium oxide and diamond.

CLEANING & DRESSING OF BONDED-ABRASIVE INSTRUMENTS

A rubber-bonded abrasive cylinder.

A diamond-coated abrasive dressing tool used to true, shape & clean the bonded abrasive instrument both before & during the finishing procedure.

Abrasive instrument with desired working shape after truing.

Instrument blinded with debris.

Lose cutting efficacy & generate more heat.

SEM of the same instrument , revealing debris clogging the surface.

SEM , Instrument coated with abrasive dressing.

SEM, After dressing, debris removed & abrasive surface restored.

Diamond bur in high-speed rotary hand-piece before cleaning.

Running the diamond bur against moistened diamond cleaning stone for 2-4 seconds.

Cleaned diamond bur with no debris between abrasive particles.

FACTORS AFFECTING DENTIFRICE ABRASIVENESS

EXTRA-ORAL FACTORS INTRA-ORAL FACTORS�Abrasive particle type, size & quantity in

dentifrice.�Amount of dentifrice used.� Toothbrush type� Tooth brushing method and force applied

during brushing� Tooth brushing frequency and duration�Patient's coordination and mental status

�Salivary consistency and quantity (normal variations)

�Xerostomia induced by drugs, salivary gland pathology, and radiation therapy

�Presence, quantity, and quality of existing dental deposits (pellicle, plaque, calculus)

� Exposure of dental root surfaces�Presence of restorative materials, dental

prostheses, and orthodontic appliances.