abrasive agents in dentistry
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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
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