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Finishing and Polishing
IntroductionBenefits of finishing and polishingBasic armamentariumPrinciples - Cutting, Grinding, Bulk reduction process, ContouringAir dispersed Hazards during finishing processWhat is Abrasive & Erosive wearAbrasive Instrument DesignsTypes of Abrasives - Natural abrasives & Manufactured abrasivesAbrasive motionFinishing of various restorations composite, amalgam, ceramic, GIC, and cast goldREFERENCESCONCLUSION
Introduction
The finishing process usually removes material such that :
Surface blemishes & imperfections are removedMaterial is shaped to an ideal form Outermost surface of the material is developed to a desired state
Benefits of Finishing and PolishingBenefits : (a) Health (b) Function (c) Aesthetics
CuttingCutting refers to use of a bladed instrument or the use of any instrument in a bladelike fashion.
Course of action predominantly unidirectionalCutting operation may divide substrate into large separate pieces / produce deep notches or groovesE.g. High speed tungsten carbide burs steel burs
There are distinct differences in function of cutting, grinding, finishing and polishing
GrindingIt is a process that removes small particle of a substrate through the action of bonded or coated abrasive instruments .Course of action predominantly unidirectional
Grinding instrument - contain many randomly arranged abrasive particle .
Each particle may contain several sharp points that run along the substrate surface and remove particles of materials . Eg Diamond coated rotary instrument disk & strips .
Bulk reduction processInstruments used Diamond, carbide and steel burs Abrasive coated disks or separating disks
Abrasive coated disks popular bulk reduction of resin based composite restorations
Clinician should choose 8 to 12 fluted carbide burs or abrasives with particle size of 100 micrometers or more with sufficient hardness.
ContouringThough it can be achieved during bulk reduction, in some cases it requires finer cutting instruments or abrasives to provide better control of contouring and surface details.
At the end of the process, desired anatomy and margins should be established.
Usually 12 to 16 fluted carbide burs or abrasives ranging in size from 30 to 100 micrometers provide the fine contouring action.
FINISHING AND POLISHING Provides blemish free & smooth surfacesRequires step wise approach 18-30 8-20 um particle size POLISHING : provide enamel like luster Speed of achieving polishing depend on 2 factor a) hardness & size of abrasive b) method of abrasion Polishing & luster can be judged by :1 , 2 , 3 methodsWhat is Abrasive Blinding ?
AIR DISPERSED HAZARDS OF FINISHING PROCESS
AEROSOL HEALTH HAZARD
95% of generated aerosol particles - < 5m in diameter can readily reach pulmonary alveoli during normal respiration
75% of aerosol particles potentially contaminated with infectious microorganisms
Aerosols can remain airborne for >24hours therefore capable of cross-contamination
If inhaled, swallowed or if it enters the eyes
Diseases of the lungs ,throat and eyes.
Silica based materials if inhaled
Silicosis or Grinders disease. (Fibrotic pulmonary disease)(major aerosol hazard)
AEROSOL - CONTROL3 ways :
Controlled at the source adequate infection control procedures High volume suction
Personal protection Safety glassesDisposable face masks
Adequate ventilation system To remove any residual particulates from air
WEARWear is a material removal process that can occur whenever surfaces slide against each other. 2 types a) Abrasive wear b) erosive wear
Abrasive wear is divided into: - Two Body Abrasion - Three Body AbrasionThe two processes are not mutually exclusiveThree body abrasion when abrasive particles are free to translate and rotate between two surfaces.Eg. Dental Prophylaxis Pastes.
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Two body abrasion occurs when the abrasive particles are firmly bonded to the surface of the abrasive instrument and no other abrasive particles are used.Eg. Diamond bur abrading a tooth.
How to prevent it ?....
ErosionErosive wear is caused by hard particles impacting a substrate surface, carried either by a stream of liquid or air.
Eg. Air-driven grit-blasting units - employ hard particle erosion to remove surface material
-important factor in controlling the instrument action on the substrate.
Bur in high speed handpiece rotates in clockwise direction.
Smoother grinding action when handpiece & bur are translated in a direction opposite to rotational direction of the bur.
Rougher surface when handpiece & bur are translated in the same direction as rotational direction of the bur.(Bur tends to runaway from the substrate)
The rotational direction of a rotary abrasive instrument
ABRASIVE INSTRUMENT DESIGNS
These are :Abrasive gritsBonded abrasivesCoated abrasive disks and stripsNon bonded abrasives
Abrasive Grits Derived from crushed materials passed through a series of mesh screens to obtain different particle size ranges.
Classification according to particle size ranges:CoarseMedium coarseMedium fineSuper fine
Bonded Abrasives Consist of abrasive particles incorporated through a binder to form grinding tools such as points, wheels etc.
Particles are bonded by four methods:Sintering Vitreous bonding Resinoid bondingRubber bonding
Coated Abrasive Disks And StripsFabricated by securing abrasive particles to a flexible backing material with a suitable adhesive material.
Supplied as disks and finishing strips.
Non Bonded AbrasivesPolishing pastes are considered non bonded abrasives Primarily for final polishing
Need to be applied to the substrate with a non abrasive device like synthetic foam, rubber felt etc.Abrasive particles are dispersed in a water soluble medium such as glycerin.Most popular aluminium oxide and diamond
Types of AbrasivesNATURAL ABRASIVES:
Arkansas stone ChalkCorundumDiamond Emery Garnet PumiceQuartz SandTripoli Zirconium silicateCuttle Kieselguhr
MANUFACTURED ABRASIVES:
Synthesized material that are usually preferred more predictable physical properties Silicon carbide, Aluminium oxide Synthetic diamondRouge Tin oxide
ARKANSAS STONE: - Semi translucent, light gray, siliceous sedimentary rock, mined in Arkansas. - Contains micro crystalline quartz - Dense, hard and uniformly textured. - Can be made into various shapes. - Use : to grind tooth enamel & metal alloys
CHALK: - Mineral form of calcite. - White abrasive - Composed of calcium carbonate. - Use : polish tooth enamel, gold foil, amalgam & plastic materials.
CORUNDUM: - Mineral form of aluminium oxide - Usually white - Use : grinding metal alloys. - Most commonly used in instrument known as white stone
NATURAL DIAMOND:
- Transparent colorless mineral - Composed of carbon - Hardest substance. - various forms : Bonded rotary instruments Diamond polishing pastes Flexible metal-backed abrasive strips - Use : on ceramic & resin-based composite materials
Difference between natural & synthetic diamond
SYNTHETIC DIAMOND ABRASIVES:
- Advantage: controllable consistent size and shape lower cost - Resin bonded diamonds sharp edge the sharp edge breaks down; exposes new sharp edges, corners. - Metal bonded diamonds regular, more consistent in size. Use cutting points. - Large synthetic diamond particles greenish.
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EMERY:
- Grayish - black - Fine grain form - Used form of coated abrasive disks. - Use : Finishing metal alloys or plastic materials
GARNET:
- Includes number of different minerals that possess similar physical properties & crystalline forms- Usually dark red. - Extremely hard- Use : Grinding metal alloys and plastic materials
PUMICE:- Light - Gray - Highly siliceous material- 2 form:-Grit -Rubber bonded abrasives - Use :- polishing tooth enamel - gold foil - dental amalgam
QUARTZ:Most commonly used is very hard colourless and transparent.Use : - finish metal alloys, - grind dental enamel.
SAND:- Mixture of small mineral particles - Predominantly composed of silica. - Rounded to angular shape- Use : Grinding metal alloys & plastic materials
TRIPOLI:- Derived from a lightweight siliceous sedimentary rock. - grey and red coloured are the most commonly used- Use: Polishing metal alloys and some acrylic resins.
ZIRCONIUM SILICATE:- Supplied as an off white material - Use: - To make coated abrasive disks & strips - As component of dental prophylaxis pastes.
KIESELGUHR:- Composed of siliceous remains of minute aquatic plants known as diatoms.- Use : Mild abrasive- Significant risk of respiratory silicosis
SILICON CARBIDE: - First of synthetic abrasives - Two types; green and blue- They are extremely hard and brittle
ROUGE:- Iron oxide is a fine, red abrasive component of rouge.- Use : Polish high noble metal alloys
TIN OXIDE:- Extremely fine abrasive - Use : polishing agent for polishing teeth and metallic restorations
ALUMINIUM OXIDE:- Second synthetic abrasive developed - Use : To make bonded abrasives, coated abrasives and air propelled grit abrasives. - Sintered aluminium dioxide is used to make white stone (popular for adjusting dental enamel and finishing metal alloys & ceramic materials)
ABRASIVE MOTIONClassified asRotary BursPlanar DisksReciprocal Reciprocating hand pieces
Note :Reciprocating hand pieces provide benefit of accessing interproximal and subgingival areas to remove overhangs, to finish subgingival margins without creating ditches and to create embrasures
Finishing and Polishing of Different Restorations
CompositesArmamentarium :Fibro optic lighting and magnification (for visibility)Fine grit conventional diamonds (for gross reduction)Round tungsten carbide burs (finishing)Flame shaped fluted tungsten burs (finishing)Impregnated rubber wheels or points (finishing)Slurry of fine aluminium oxide (polishing)
Composite finishing kit Composite finishing pasteimpregnated rubber wheels or points
Initial finishing by a sharp knifeFinal Finishing
In DCNA 1998 study was done on finishing procedure ..
Amalgam In the past a delay of 24 hrs had been suggested before finishing and polishing the newly inserted amalgam Armamentarium :Rhein trimmers (Discrepancies in gingival area )Bard parker knife number-12 (Bulky overhangs )Narrow water resistant strip (19)(Cervical areas )extra fine water proof disk (Buccal and lingual proximal margins )small carrot shaped stone (20) (Occlusal margins )plug finishing burs (21) (further adjustment )Rubber cup (finish accessible proximal surfaces as well as occlusal contours)Abrasive impregnated silicon rubber points and cupstin oxide slurry (complete the finishing and polishing procedures)soft cut brush (complete the finishing and polishing procedures)
Finishing and polishing cannot be started until a future visit when the amalgam will have set hard. Any sizeable reduction may be undertaken with a carborundum point.
CeramicsAdequate cooling is important in vivo when finishing and polishing ceramic restoration Using an air water spray and maintaining intermittent contact between restoration and rotary instruments are critical during operation
Continuous contact between restoration and rotary instruments should be avoided
Heat less stone like silicon carbide provide heat reduction and can be used as an alternative
TechniquesContour with flexible diamond disc, diamond burs, heatless or polymer stones or greenstones
Finish with white stones or abrasives impregnated rubber disc, cups and points
Apply over glaze or natural glaze on ceramic if necessary
Glass Ionomer Cement
Problem of water loss continues for a longer period for both fast and slow set types and precautions should be taken to prevent dehydration.Diagramatic representation of water balance in glass ionomer. Type ii and I restorative aesthetic restorations remain succeptible to water uptake for at least one day after placement.All the types are fast settig gic and so are resisting to water uptake within 5 to 6 mins from the beginning of mix.
The best surface attainable is that produced when the cement is allowed to set against the matrix.
Where access can be gained, carving the cement external to the cavity margins with sharp knives or scalers after initial set is the best process of finishing.
Whenever possible, margins should be smoothed with hand instruments.
Finishing with rotary instruments and final polishing can be undertaken at a subsequent visit.
Glass ionomer should never be finished under dry conditions; a petroleum lubricant may be used to prevent desiccation.
Finishing Of GIC Restoration Finishing with a bur Finished GIC Restoration
CAST GOLD RESTORATION Use a 1/2 inch medium garnet disc in a straight handpiece to reduce gold and tooth to the same plane on all surfaces (use contra-angle with grit in to reduce mesial-lingual, where necessary, for both maxillary and mandibular restorations). Air should be blown continuously on the tooth to prevent overheating during all disking, stripping and polishing procedures.
Finished cast gold restoration
Use fine and extra-fine narrow, extra-long cuttle strips to reduce the size of scratches.
Complete disking with fine cuttle discs until all scratches have been removed.
Polish with flour of pumice. Do not use coarse pumice as it will destroy the finish achieved with the fine cuttle disc.
Use dry tin oxide powder over casting for final polish. Blow off excess tin oxide while utilizing a ribbed cup (webbed cup will throw powder away from tooth) at low speed to avoid heating the tooth.
ReferencesPhillips Science of Dental Materials.Atlas of operative DentistryAtlas of G. J. MountAllen D. WilsonCharbenauDavid KorsonRatnadeep PatilJ.R. Grundy
CONCLUSION Fluted carbide finishing bur appear to be the optimal rotary contouring device FINISHING DIAMOND preferred for GROSS FINISHING COATED DISK & STRIPS provides access for interproximal & incisal area RUBBERIZED BONDED provide great range of FINISHING ALUMINIUM OXIDE & DIAMOND PASTE are highly effective against POLISHING
THANK YOU& HAVE A NICE DAY.
