finishing and polishing in restorative dentistry
DESCRIPTION
restorative dentistryTRANSCRIPT
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FINISHING AND POLISHING IN RESTORATIVE DENTISTRY
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Contents
Introduction
Rationale and Objectives of Finishing and Polishing
Definitions
Principles of cutting, grinding, finishing and polishing
Phases in dental finishing procedure
Factors effecting a finishing and polishing device
Additional finishing procedures – Microabrasion and Macroabrasion
Burnishing – amalgam and gold
Health hazards during finishing and polishing
Abrasives
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Principles of tribiology related to dental abrasive science
Instruments for – Gross reduction, intermediate finishing and final polishing
Abrasive instrument design
Bonded abrasives
Methods to assess the finishing systems and devices
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Finishing and polishing of
amalgam restorations
composite restorations
direct filling gold
Cast gold
Glass ionomer
Porcelain
Recent new technology
Summary
Conclusion
References
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Oral cavity – constant contamination
Microorganisms – dental caries and periodontitis – survive adhering to non-shedding surfaces
Change in the surface – prevents dental caries and periodontitis
Introduction
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Main objective of an operative dentist?
Restore a tooth to normal form and function along with pleasing esthetics.
Rough or uneven surfaces invite microbial flora
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Why the interest in finishing and polishing
in dentistry?
Oral health
Function
Aesthetics
Rationale of finishing and polishing
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Objectives of Finishing and Polishing
To remove excess flash and refine the margins of the restoration.
To produce a smooth surface less likely to retain plaque.
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To reduce the risk of fracture since a rough surface is more likely to fracture.
To produce smooth restoration contacts, leading to less wear on opposing and adjacent teeth.
To produce a more esthetic, light reflectant restoration for the patient.
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What do we mean byFinishing and Polishing?
Finishing is the transformation of an object from a rough surface to a refined form.
Polishing is the production of shiny, mirror like surface to give the restoration an enamel like finish.
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Definitions
Finishing : the process that involves removing marginal irregularities, defining anatomic contours, and smoothing away surface roughness of a restoration.
Polishing : the process involving the removal of minute scratches from the surface of a restoration and obtain a smooth, light-reflective luster.
Dental clinics of North America, 2007, 51, 379-397
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Margination –
The specific step of the finishing process that involves the removal of excess restorative material at the junction of the tooth structure and the restorative material, and the application of various finishing techniques to establish a smooth, uniform, and well adapted cavosurface margin.
Dental clinics of North America, 2007, 51, 379-397
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According to Philips’ science of Dental Materials, Anusavice –
Finishing is a process of removing surface defects or scratches created during the contouring process through the use of cutting or grinding instruments/both.
Polishing is a process of providing luster or gloss on a material surface.
It is described as a process in which the polishing material does not cut/grind, but fills scratches and produces a perfectly smooth surface.
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Principles of Cutting, Grinding, Finishing and Polishing
Particles of a substrate material – removed by the action of a harder material that comes into contact with the substrate.
Contact – must generate sufficient tensile and shear stresses to break atomic bonds and release a particle from the substrate.
Anusavice, Phillip’s Science of Dental Materials, eleventh edition
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Rotary instruments – tips of abrasive particle and blades of carbide burs – transfer force to the substrate tensile and shear stress
Instrument fails to cut, grind and polish – stress in grinding/cutting surface exceeds in strength compared to strength of substrate
Blade edges become dull and abrasive particles fracture away from their binder.
Bryant RW, Collins CJ. Finishing techniques for amalgam restorations: clinical assessment at three years. Aust Dent J 1992 oct; 37(5): 333-9
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Cutting refers to the use of a bladed instrument or use of any instrument in a blade like fashion.
Substrates may be divided into large separate segments or sustain deep notches or grooves by cutting action.
Anusavice, Phillip’s Science of Dental Materials, eleventh edition
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When a 30 fluted finishing burs are used on a surface, the regular pattern of the cutting blades is discernible if the surface is magnified for inspection.
Separating wheel – cuts in bladelike fashion
Thin blade design allows it to be used in a rotating manner to slice through
Anusavice, Phillip’s Science of Dental Materials, eleventh edition
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Grinding refers to removal of small particles of a substrate through the action of bonded or coated abrasive instrument.
Grinding instruments - randomly arranged abrasive particles.
Each particle has several sharp points that run along the substrate surface and remove small particles of material.
Cutting and grinding are unidirectional in their course of action.
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Anusavice, Phillip’s Science of Dental Materials, eleventh edition
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Different types of burs have unique effects on surfaces
16 fluted carbide bur produces smoother surface than an 8 fluted carbide bur but it removes material from substrate slowly.
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Bulk reduction process – achieved through use of instruments such as diamond, carbide and steel burs, abrasive coated disks.
Diamond burs and abrasive coated disks – grinding
Steel and carbide burs - cutting
Anusavice, Phillip’s Science of Dental Materials, eleventh edition
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Contouring – mostly achieved during bulk reduction process
Some cases require finer cutting instruments or abrasive to provide better control of contouring and surface details.
12-16 fluted contouring burs/abrasives ranging in size from 80-100µm provide contouring
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Finishing provides a relatively blemish free – smooth surface
Done with 18-30 fluted carbide burs, fine and superfine diamond burs and abrasives between 8-20 µm size.
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Polishing - refers to removal of finest surface particles.
Each type of polishing abrasive acts at an extremely thin region of the substrate surface.
Begins from finest abrasive that can remove scratches and completes when desired level of smoothness is achieved.
Polishing is multidirectional – final surface scratches are oriented in many directions.
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During the polishing of metals, a highly stressed microcrystalline layer is formed on the surface called the “Beilby layer”.
Sir George Beilby discovered that during polishing the surface of gemstones actually melted and flowed as a “glassy” layer over very fine scratches.
He proved it by noting a certain scratch pattern, polishing the surface, and then recovering the scratch pattern by etching away the polished surface with acids.
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Pseudo liquid layer – composed of non-oriented crystals on the restoration – 20-40A° thick
Rapid movement of the polishing agent – top layer of material gets heated up – flows and fills the scratches.
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Buffing - polishing process in which abrasives are applied via bristle brushes, treated leather and cloth material.
Porous texture allows finer abrasive particles to be retained during buffing
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Abrasion
Is a material-removal process that can occur whenever surfaces slide against each other.
The process of finishing a restoration involves abrasive wear through the use of hard particles.
In dentistry, the outermost particles or surface material of an abrading instrument is referred to as the abrasive. The material being finished is called the substrate.
Anusavice, Phillip’s Science of Dental Materials, 11th edition
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PRINCIPLES OF TRIBIOLOGY RELATIVE TO DENTAL ABRASIVE SCIENCE
Discipline associated with material science, physics, chemistry, and surface contact engineering.
Experimental parameters – applied load, velocity, and duration of motion
System structure – the two bodies in contact, the interfacial media, and the surrounding media.
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Finishing and polishing devices are intended to produce intentional, selective, and controlled wear of dental restorative-material interfaces.
Wear is defined as a cumulative surface damage phenomenon in which material is removed from a body as small debris particles primarily by mechanical processes. (DCNA, April 2007, vol 51,number 2)
As per Skinner – Wear is a material removal that can occur whenever surfaces slide against each other.
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The Tribiology of Dental Finishing
and Polishing
3-BODY WEAR LOOSE ABRASIVE POLISHING:
1. Aluminum Oxide Polishing Paste
2. Diamond Polishing Pastes
2-BODY WEAR :1. Trimming and Abrading
Burs2. Bonded Abrasives
3. Coated Abrasives for Finishing and Polishing
Dental clinics of North America, April 2007, 51, 379-397
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Erosion
Caused by hard particles impacting a substrate surface – carried by either a stream of liquid or a stream of air - sandblasting
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Phases in dental finishing procedure
Final polishing
Intermediate Finishing and
Polishing
Gross Reduction, Coarse Finishing and Margination
Dental clinics of North America, April 2007, 51, 379-397
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Significantmaterialremoval
Originalrough
surface
CoarseFinished
New surfaceapproximatesabrasive size
Polished
Smearing andburnishing to
smoothen surface
FineFinished
Fine grooves
20 mm 2 mm 0.2 mm
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Fact
ors
aff
ect
ing
Fin
ish
ing a
nd
Po
lishin
g
Factors affecting
finishing and polishing
Structure and mechanical properties of
substrate
Difference between hardness of
abrasive and substrate
Physical properties of the backing or bonding material
Speed and pressure with which abrasive
is applied to substrate
Lubrication used during application
of abrasive
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Speed is defined as the number of revolutions per minute (RPM) or the number of times a rotating instrument, such as a bur, will make a full turn during a minute.
Higher the RPM – Higher the speed of the hand piece
Low/slow speed – below 12,000 rpm
Medium/intermediate speed – 12,000-2,00,000 rpm
High/ultra speed – above 2,00,000 rpm
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The rotational direction of a rotary abrasive instrument is an important factor in controlling the instrument's action on the substrate surface.
When a hand piece and bur are translated in a direction opposite to the rotational direction of the bur at the surface being abraded, a smoother grinding action is achieved.
However, when the hand piece and bur are translated in the same direction as the rotational direction of the bur at the surface, the bur tends to "run away" from the substrate, thereby producing a more uncontrolled grinding action and a rougher surface.
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Certain procedures additional to finishing and polishing used to achieve smooth and shiny surfaces are –
Micro abrasion
Macro abrasion
Burnishing
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What is Microabrasion?
Procedure - a microscopic layer of enamel is simultaneously eroded and abraded
Developed by Dr. Theodore Croll
Used to treat enamel dysmineralization (Croll 1999)
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Difference between microabrasion and bleaching
MICROABRASIONImproves tooth color
by eliminating superficial discolored
enamel
BLEACHINGIt lightens the tooth
color and preserves the intact fluoride rich layer
of enamel and tooth shape
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Micro abrasion
McClosky in 1984 – technique for removing brown stains of fluorosis limited to enamel by using cotton pellet application of 18% HCl
Cavanaugh 1986 – modified by using controlled hydro-chloric acid-pumice abrasion – micro abrasion
18% hydro-chloric acid, pumice and water
Applied with a tongue blade/fluted edge rotary driven rubber cup
Acid causes dissolution of enamel – abrasive causes superficial removal of stains and defects
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Croll – modified by reducing concentration of acid to 11% - increasing abrasiveness using silicon carbide.
Air flow handy system – hand piece utilizing sodium bicarbonate as abrasive agent with compressed air
Used to remove extrinsic stains on tooth surface
E.C. Combe “Notes on Dental Materials”
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Before After
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An in-vitro study was conducted for the comparison of surface roughness after micro abrasion of enamel with and without using CPP-ACP.(Casein Phosphopeptide-Amorphous Calcium Phosphate).
According to the results of this study, a combination of the micro abrasion procedure and CPP-ACP application reduced the enamel surface roughness significantly, when compared to micro abrasion done alone.
Journal of conservative dentistry
Year : 2009, Volume : 12, Issue : 1, Page : 22-25
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Enamel microabrasion has become accepted as a conservative, non restorative method of improving the appearance of teeth with superficial dysmineralization and decalcification defects.
J Am Dent Assoc
1997;128:45-50
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Macro abrasion
Technique for treatment of superficial stains using 12 fluted carbide bur or a diamond point at high speed
Adequate air/water spray should be used as a coolant and to facilitate proper visibility of the defect.
Certain defects are normally not visible when teeth are hydrated, but become visible on dehydration.
Light intermittent pressure is used
Polished with 30 fluted carbide bur and abrasive point.
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Burnishing
It is defined as the process of rubbing a metal over the restorative material to make it shiny and lustrous.
It has also been described as a procedure in which the surface of a metallic restoration is smoothened by rubbing it with another small, highly polished, hard metal surface.
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Stainless steel/chromium-plated instruments commonly used
Instrument nibs – various shapes – ball shaped, egg shaped, beaver tail shaped, conical, hour glass shaped.
Spratley burnisher – proximal gingival marginal burnishing
Engine driven burnisher in also available
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Health hazards during finishing and polishing
Production of aerosol-
Dispersion of fine solid or liquid particles in air
Silicosis
Minimized by –
Adequate ventilation
Self-protection
Use of rubber dam
High vaccum suction
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Production of vapours –
During cutting of amalgam high temperature forms mercury vapour
Thermal decomposition of polymeric materials like sealants, acrylic resins and composites produces monomeric vapours.
High speed and intermittent cutting minimizes vapours
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Pulpal reactions –
Temperature rise as much as 20°C – rotary finishing and polishing
Depends on remaining enamel and dentin thickness
Coolants, intermittent polishing reduce heat generated
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Surface material is removed
Subsurface layers are affected
Microcracks are generated – upto a depth of 50 um
Non-uniform stress distribution present – affect the susceptibility to resist wear
Anisotropic surface layer is created
Dental Materials at a glance, J. Anthony Von Fraunhofer
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Abrasives
Finishing Abrasive
Polishing Abrasive
Cleansing Abrasive
Classification by Craig
Abrasive-A hard substance used for grinding, finishing, or polishing a less-hard surface.
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Abrasives
Natural abrasives
Arkansas stoneChalk, corundumDiamond, tripoli, zirconium silicate
Emery,garnet, pumice, quartz,
sand, cuttle, Kieselguhr
Manufactured abrasives
Silicon carbide, aluminum
oxide, synthetic diamond
Rouge and tin oxide
Classification by Skinners
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Desirable qualities of an Abrasive
Should be irregular in shape so that it presents a sharp edge
Should be harder than the particle (substrate) it abrades
Should possess high impact strength
Abrasive point should always fracture rather than dull out
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Abrasive particle size determines the depth of the scratch produced on the substrate.
The effects of the scratch extend significantly beyond the scratch itself – extended region is known as cold-worked.
Dental Materials at a glance, J. Anthony Von Fraunhofer
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Abrasive Particle Sizes – as per AnusaviceGrit/Mesh Aluminum
oxide, silicon carbide and garnet (µm)
Coated disc grade
Diamond µm Diamond bur grade and diamond polishing paste
120 142 Coarse 142 Supercoarse - coarse
150 122 122 Coarse – regular
180 70-86 86 Coarse – regular
240 54-63 60 Fine
320 29-32 Medium 52 Fine
400 20-23 40 Fine – superfine – coarse finishing
600 12-17 Fine 14 Superfine – medium finishing
800 9-12 8 Ultrafine – fine finishing
1200 2-5 Super fine 6 Milling pastes
1500 1-2 4 Polishing pastes (2-5 µm)
2000 1 2 Polishing pastes (2-5 µm)
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Classification Particle size -Grit size
Particle size - µm
Extra coarse 60-100 >125
Coarse 100-140 105-125
Medium 140-200 70-105
Fine 200-280 50-70
Superfine 280-800 30-50
Microfine 800-2000 10-30
Polishing Paste >14000 <1
Dental Materials at a glance, J. Anthony Von Fraunhofer
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Factors Influencing the Efficiency of Abrasive
Hardness –
Important consideration – difference between the hardness of the abrasive and the hardness of the substrate
Durability of abrasive – related to hardness of its particle of the surface material
Hardness is a surface measurement of the material to be plastically deformed by indenting/scratching another material.
Diamond has the maximum Moh’s rating of 10; tooth enamel 5-6; dentin 3-4.
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Shape –
An irregular object has a tendency to dig into a surface rather than roll across it – cutting efficiency enhanced by numerous sharp edges
Sharper the abrasive – more effective it is as a cutting instrument
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Size –
Abrasive particles are classified based on their particle size with –
Coarse – 100µm
Medium – 10-100µm
Fine – 0-10µm
Finishing and polishing – sequential reduction in the size of the abrasive particles
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Arkansas
A semi translucent, light gray, siliceous sedimentary rock mined in Arkansas.
It contains microcrystalline quartz and is dense, hard, and uniformly textured.
Small pieces of this mineral are attached to metal shanks and trued to various shapes for fine grinding of tooth enamel and metal alloys.
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Chalk –
White colored abrasive composed of calcium carbonate
Mild abrasive – used in dentifrices
Polishing tooth enamel, gold foil, amalgam
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Aluminum oxide – Al2O3 (Alumina)
Produced as particles bonded to paper or polymer disks and strips or impregnated into rubber wheels and points
Corundum – white form of aluminum oxide
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Pink and ruby variations of aluminum oxide abrasives are made by adding chromium compounds to the original melt.
These variations are sold in a vitreous bonded form as noncontaminating mounted stones for the preparation of metal ceramic alloys to receive porcelain.
Remnants of these abrasives and other debris should be removed from the surface of metals used for metal-ceramic bonding so as not to prevent optimal bonding of porcelain to the metal alloy.
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Diamond Abrasives –
Composed of carbon
Diamond dust or particles of various sizes can be coated on a rigid matrix impregnated with a bonded, elastomeric matrix
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Synthetic diamond abrasives
The advantages of synthetic diamonds over natural diamonds include their controllable, consistent size and shape, as well as their lower cost compared with natural diamonds. The shape of the diamonds determines the binder needed for its use.
The binders can be either resin or metal. Resin-bonded diamonds have sharp edges.
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During use, the sharp edges break down and expose new sharp edges and corners.
On the other hand, metal-bonded diamonds are regular and more consistent in size. They function as cutting points or edges primarily through the benefit of their hard ness rather than their shape.
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Emery –
Grayish black corundum
Mixture of aluminum oxide and iron
Abrasive coating on cloth/paper disk
Finishing metal alloys
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Garnet –
Consists of silica/aluminum, cobalt, iron, magnesium and manganese
Dark red in color and extremely hard
Grinding metal alloys
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Pumice –
Most common fine abrasive
Powder – crushing pumice stone – a porous volcanic rock
Enamel, amalgam, gold foil and acrylic resins
Water/glycerin is mixed with pumice
Slow speed
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Quartz –
hard and colorless
Sharp angular particles of quartz used for coating abrasive disks
Finish metal alloys
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Sand-
Silica
Irregularly shaped particles are obtained by crushing sand stone and boned to paper with glue/resin
Sand particles under air pressure(air-driven grit-blasting units) – remove investment material from base metal alloy castings
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Tripoli –
Derived from siliceous sedimentary rocks
Grey and red color available
Polish metal alloys
Rock is grounded to fine particles – formed with soft binders into bars
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Zirconium silicate –
A natural mineral
Polishing agent in strips, disks, and prophylactic pastes
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Cuttle fish bone –
White calcareous powder – crushing internal shell of Mediterranean marine mollusc
Coated disks and strips
Polishing metal margins and amalgam restorations
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Kieselguhr –
Shell like remains of small aquatic plants – diatoms
Coarser form – diatomaceous earth
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Carbide compounds –
Silicon carbide, boron carbide and tungsten carbide.
Multifluted finishing burs – tungsten carbide bits
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Rouge
Iron oxide is the fine, red abrasive component of rouge.
Like tripoli, rouge is blended with various soft binders into a cake form
It is used to polish high noble metal alloys.
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Silicon dioxide and Zirconium oxide –
Primarily used in rubber or elastomeric cups and points
Initial finisher points
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Instruments and techniques for gross reduction and contouring of dental restorations
Diamonds
Fluted Finishing burs
Abrasive Finishing Discs
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Diamonds – primary purpose – contour, adjust and smooth porcelain
Secondary use – contouring and finishing composite resin
Rely predominantly on abrasive rather than blade cutting action
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Particle size ranging from 7 to 50 μm
Coarser grit Finer grit
Available as bonded abrasive rotary instruments, metal backed abrasive strips and polishing pastes
Should be used with water spray and at lower speed
Clinical performance depends on size, spacing, uniformity, exposure, and bonding of the diamond particles
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Diamond particles are bonded to metal wheels and bur blanks with special heat-resistant resins such as polyamides.
The super-coarse through fine grades are then plated with a refractory metal film such as nickel. The nickel plating provides improved particle retention and acts as a heat sink during grinding.
Titanium nitride coatings are used as an additional layer on some of the recent diamond abrasive instruments to further extend their longevity.
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Diamond burs should always be used with water spray and at rotational speeds of less than 50,000 rpm.
Disposable diamond burs recently gained popularity because of three factors:
(1) optimal instrument efficiency,
(2) concerns over the reuse of disinfected abrasive devices, and
(3) minimal heat build-up.
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Carbide Finishing Burs –
8 to 40 fluted blades, which can be straight or twisted
Less abrasive action – depends on number of flutes – more number of flutes – more aggressive cutting action
Various shapes and sizes
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Abrasive Finishing discs –
Coarse and medium grit used
Coarse – 100µ aluminum oxide
Medium - 40µ aluminum oxide
Advantage – access to incisal edges, embrasures and line angles
Disadvantage – flatten surface features and restoration contours
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Intermediate Finishing and Initial Polishing
Coated abrasive disc
Bonded abrasive devices
Fine diamonds and multifluted
finishing burs
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Coated abrasive finishing and polishing discs and strips –
Abrasive particles are bonded onto a thin polymer or plastic backing (heavy weight paper/metal)
Coarse grit(55 to 100 μm) to superfine grit (7 to 8 μm)
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Disks are available in different diameters and with thin and very thin backing thicknesses.
A further designation is made in regard to whether or not the disk or strip is moisture-resistant.
It is advantageous to use abrasive disks or strips with moisture resistant backings because their stiffness is not reduced by water degradation.
Moisture acts as a lubricant to improve cutting efficiency.
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Stones –
Sintered abrasive particles with an organic resin to form a cohesive mass
Color indication –
Silicon carbide - Green
Aluminum oxide – White
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Rubber wheels, cups and points –
Abrasive particles dispersed and held in a softer, elastic matrix.
These elastomeric, bonded abrasives are molded to a latch-type mandrel for slow hand pieces.
Particle size distribution – 40 µm to 6 µm
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Final Finishing and Polishing
Extra fine Coated
Abrasive
Loose abrasive polishing
paste
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Extra fine coated abrasive –
Useful for polishing composite restorative materials
E.g.: Sof-lex fine (3M) aluminum oxide for contouring 20-80µ
Extra fine - 8µ - polishing
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Nonbonded Abrasives (Loose abrasives)
Polishing pastes are considered as nonbonded abrasives and are primarily used for final polishing.
They need to be applied to the substrate with a nonabrasive 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.
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Variables involved in the use of loose abrasive polishing –
Mean particle size of abrasive used
Structure and fineness of the application device used to apply the loose abrasives
Composition of loose abrasive paste
Application technique and incremental use of water
Induce cutting at a micro- and nano-meter scale
Aluminum oxide, diamond polishing pastes
Soft foam and felt applicators + abrasive polishing pastes
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Aluminum oxide – two particle sizes – 1µ and 0.3µ
Commercially available 1µ aluminum oxide pastes –
Prisma gloss
Luster micro polishing paste
Enamelize
3µ - Prisma – Gloss extrafine
Luster paste
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Prisma®•Gloss™
Prisma®•Gloss™ is a water-soluble, aluminum oxide paste designed for final polishing.
It is commonly used with an Enhance® Rubberized finisher and improves the smoothness of the finished surface, providing a high luster.
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Abrasive pastes have several disadvantages.
Relatively thick and cannot gain access into embrasures.
Pastes tend to splatter off of the instruments.
Heat is generated when insufficient coolant is used or when an intermittent polishing technique is not used.
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Felt and cloth
Cloth carried on a metal wheel is used for final polishing
Felt is used to attain final luster for metallic restorations
Wheels, cones and cylinders are available in felt.
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Abrasive Instrument design
Abrasive grits –
Derived from materials that have been crushed and passed through a series to obtain different particle size ranges.
Coarse
Medium coarse
Medium fine
Super fine
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Silicon carbide – graded as 8,10,12,14,16,20,24
Finer abrasives – powder/flours
Graded as increasing fineness – F, FF, FFF
Impregnated papers – 0, 00, 000
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Rate of material removal and finish obtained by a particular abrasive – very important
Very hard abrasive/grain size too coarse – deep scratches result in substrate
If an abrasive doesn’t have proper particle shape or doesn’t break down in a manner that creates or exposes new-sharp edged particles, it will tend to gouge the substrate.
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Abrasive motion – rotary, planar, reciprocal
Burs – rotary
Discs – planar
Reciprocating hand pieces – cyclic motion – reciprocal in relationship to their direction of motion
Help in accessing interproximal and subgingival areas to remove overhangs – to prevent ditches subgingivally – to form embrasures
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Bonded Abrasives Abrasive particles incorporated through a
binder to form grinding tools such as points, wheels, disks.
Particles are bonded by four general methods: (1)sintering(2) vitreous bonding (glass or ceramic), (3) resinoid bonding : (usually phenolic resin), and (4) rubber bonding (latex-based or silicone-based
rubber).
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Sintered abrasives - the strongest type because the abrasive particles are fused together.
Vitreous-bonded abrasives - mixed with a glassy or ceramic matrix material, cold-pressed to the instrument shape, and fired to fuse the binder.
Resin-bonded abrasives - cold-pressed or hot-pressed and then heated to cure the resin. Hot pressing yields an abrasive binder with extremely low porosity.
Rubber-bonded abrasives - made in a manner similar to that for resin bonded abrasives.
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Diamond particles are bonded to metal wheels and bur blanks with polyamides which are heat resistant resins.
Super-coarse to super-fine grades are plated with a refractory metal film – nickel
Nickel provides increased retention and acts as heat shrink during grinding.
Finishing diamonds – not nickel plated – highly susceptible to debonding – light pressure should be used
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Most of the rubber wheels, cups and points contain latex, a known allergen – this residue must be removed from the polished surfaces.
A bonded abrasive instrument should always be trued and dressed before its use.
Truing is a procedure through which the 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 the substrate.
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The dressing procedure, like truing, is used to shape the instrument, but it accomplishes two different purposes as well.
First, the dressing procedure reduces the instrument to its correct working size and shape.
Second, it is used to remove clogged debris from the abrasive instrument to restore grinding efficiency during the finishing operation.
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The clogging of that abrasive instrument with debris is called abrasive blinding.
Abrasive blinding occurs when the debris generated from grinding or polishing occludes the small space between the abrasive particles on the tool and reduces the depth that particles car penetrate into the substrate.
As a result, abrasive efficiency is lost and greater heat is generated.
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Diamond cleaning stones are used on the super-coarse through fine grades to remove debris build-up and to maintain grinding efficiency.
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Abrasive discs
Gross reduction – contouring – finishing – polishing
Aluminum oxide abrasive – commonly coated
Flexibility of the disc – wiping action
Contouring of an irregular surface – produces an unmatched smooth flat/convex contour
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Discs – diameter ½”, 3/8”, ¼” – small
Small – useful intraorally as better accessibility is achieved
Larger discs – 5/8”, 7/8” - reduce bulk of material and for shaping acrylic in temporary crowns and bridges
Coarse, medium, fine - carborundum
Medium cuttle and fine cuttle119
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Pin hole disk – used with screw type mandrel
Disadvantage – rotation limited to forward motion only
Reverse direction unscrews the head
To overcome this – pop-on mandrels available
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Diamond, silicon carbide and aluminum oxide – commonly used
Aluminum oxide – tougher than silicon carbide
Silicon carbide and steel react – dulling of silicon carbide particles
Silicon carbide – porcelain – as alumina reacts with glass
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Abrasive Strips
Available with plastic/metal backing
Useful for polishing proximal surfaces of all direct and indirect bonded restorations
Metal strips – tight proximal contacts
Care – laceration of gingival tissue
Autoclavable – repeated usage possible – expensive
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Coated Abrasives
Finishing devices usually in the form of paper, mylar
Abrasive particles are retained on the surface of the disc material/matrix by adhesive polymeric surface coating/layer
Aluminum oxide and silicon carbide commonly employed
E.g. – SOF-Lex contouring finishing discs, Super-Snap finishing disc, Flexidisc, Moore-Flex polishing system
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Methods to assess the effectiveness of finishing systems and devices
Aided and unaided visual examination
Optical Microscope
Scanning Electron Microscopy (SEM)
Profilometer
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Profilometer – Device utilizing a diamond stylus of precise
dimensions to trace a fixed linear distance over the surface of a prepared sample.
Calculates the surface roughness value (Ra) by producing a tracing and by using a digital analogue hardware and software.
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Visual methods - prone to errors as a result of influencing of shading and influence of composition and structure of the specimen under evaluation.
Scanning Electron Microscope - should provide sufficient contrast to observe surface topography and with low-angle views to detect clearly variations in surface smoothness.
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Finishing And Polishing Of Amalgam Restorations
A surface free of superficial scratches and irregularities is created. This decreases the chances of fatigue failure under the cyclic loading of masticatory stresses.
A smooth surface without irregularities minimizes the risk of tarnish and corrosion and is also esthetically acceptable.
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Burnishing of amalgam restorations
Burnishing can be carried out by rubbing a smooth instrument over setting or set material
Round burnisher is often used
Strokes – from amalgam to the tooth surface
Caution – over pressure used
Burnishing increases residual alloy grains and reduces residual mercury and micropores
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Precarve burnishing Postcarve
burnishing
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Precarve burnishing is done before the carving is initiated and is continuation of the condensation process.
Large egg shaped/ball burnisher used
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Effective in reducing mercuric content compared to polishing
Burnishing during condensation improves marginal adaptation
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Postcarve burnishing – done after carving is completed
Small sized burnisher is used with light strokes
Satin/velvet finish should be the aim
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Helps in achieving –
increased surface hardness
decrease in the size and number of voids on the surface and marginal areas
slower rate of corrosion
denser amalgam at the margins
improvement in marginal seal
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Finishing is begun with the use of well worn or blunted finishing bur. Carborundum stones can also be used.
Includes trimming any overextended and excess margins, creating adequate contour and correcting any occlusal disharmonies that may have been overlooked during the carving process.
A high point in an amalgam restoration appears as a shiny area, which is reduced with carborundum stones or sharp finishing burs.
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A common error in the trimming of amalgam is that of leaving fins or flashes at the margins.
Since amalgam has a low tensile strength, thin sections of amalgam can easily get fractured resulting in marginal ditching.
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For the proximo-occlusal restorations, finishing begins with a careful appraisal of the cervical margins, buccal and lingual proximal and occlusal margins.
Despite the fact that matrix bands and wedges are used during restorations, gingival overhangs of varying degree may be created.
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These proximal margins can be marginated with light cuttle fish sandpaper disks. The proximal surface is then aligned with the occlusal outline, and the marginal ridge is rounded with the disk.
Finishing cervical areas is done by inserting water resistant strips/linen strips cervical to the contact area through the interdental space and moving them to and fro.
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E.V.A polishing system – dr.Per Axelsson - safe-sided and safe-ended diamond tip
Diamond tip has a reciprocal action and with a stroke of 1.5mm – results in a scrubbing effect
Reciprocating handpiece – 5000-6000 RPM – fixed to operate in two modes.
Fixed mode provides directional control of movement in one of six indexing positions and is utilized for better control and adaptability of interproximal regions.
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The alternative self-steering mode allows the selected tip to rotate on its free axis for prophylaxis and polishing procedures.
System is equipped with a set of color coded autoclavable tips with diamond particles of progressive grain size from gross finishing to fine polishing.
Opposite side of each tip is smooth to prevent damage to adjacent tooth and soft tissues.
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It should be remembered that abrasives always should be applied through a descending grade i.e. coarse, medium, fine and ultra fine to achieve the final finish.
The final polish or the metallic luster is obtained by the application of a suitable polishing agent like tin oxide, zinc oxide, chalk, pumice, extra fine silex etc. carried with a soft rotating brush or rubber cup.
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For the last 10 years, introduction of rubber polishing points and wheels has led to a modification in these procedures. These are available commercially as Shofu greenie and brownie rubber points.
Silicon abrasives impregnated with polishing ingredients.Provides fast, brilliant results without pumice or tin oxide
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Cups are for proximal and mini-points are for occlusal
Brownies for pre-polishing
Greenies for polishing
Supergenes for super-polishing
Contra-Angle and Friction-Grip kit
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It includes 3 each Brownie cups and mini points,
2 each Greenie cups and mini points
1 super green cup( yellow band) and mini point.
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Finishing and Polishing of Composite Restorations
Widely used as an anterior restorative material and are now being used in posterior teeth also.
Attentive use of finishing and polishing methods is mandatory for their surface quality and natural appearance of the final restoration.
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Conventional composites pose greatest difficulty in achieving a smooth surface because of the difference in hardness of organic and inorganic phases.
The resin matrix is soft and filler particles are hard.
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If fine grit polishing methods are used, the softer resin matrix abrades away easily leaving behind the harder filler particles, which gives it a rough surface.
If coarse abrasives are used on the other hand, the organic and inorganic phases are removed equally but the abrasive leaves behind rough marks. This rough surface is highly conducive to picking up extrinsic stains and plaque.
The unequal surfaces of conventional composites lead to unequal wear, which may further disturb the occlusal harmony thereby creating problems in the temporomandibular joint.
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Hybrid composites can be polished to a semi gloss but the surface is somewhat hydrophobic which makes it quite unpleasant for the patient.
Microfilled composite materials can undoubtedly be polished to the highest gloss and are considered to be esthetically best amongst all composites. The surface of these restorations is highly smooth and the chances of extrinsic staining are minimal.
Finish obtained on microfilled composites is a glossy one, whereas that obtained on conventional composites is a satin finish.
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Primary considerations for finishing the restoration are –
Instrument shape
Surface of the finishing instrument
Environment
Delayed versus immediate finish
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Instrument shape –
Correct shape – dependent on surface being finished
Anteriors -
Labial surfaces – long, tapered straight edge instrument is preferred
Cervical – smaller – tapered – confirms to the desired straight emergence profile of tooth
Lingual – foot-ball shaped instrument
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Posteriors –
small and thin 4mm tapered point to remove overhang
Occlusal anatomy – rounded football shaped instrument
Grooves and fissures – round end tapered diamond/carbide instruments
Polishing – series of impregnated points – beginning with no band, yellow and then white banded points
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Surface of the instruments –
Diamond or carbide?
Carbides tend to pluck out filler particles from composites – diamonds cause potential damage to enamel and cementumv
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Bognosian, Randolph and Jekkals – carbides should not be used at higher speeds when trimming and finishing microfilled composite resin as they tend to disrupt the surface.
Diamonds operated with low speeds do not damage microfilled composites.
High speed finishing with carbide burs on small particle composite produces a non-disrupted surface that was free from striations and grooves left by diamonds.
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Polishing wet or dry –
Some clinicians are of the view that finishing in a dry field with finishing equipment mounted on slow speed allows – better visualization of the restoration margins.
Under certain conditions excessive heat generated by the instrument rotation could cause marginal breakdown.
Leinfelder showed that fine margin of microfilled composite could pull away permitting dry slurry to be swept under the margins appearing as a white line.
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Delayed versus immediate polishing –
Some advocate delaying the finishing of composite restoration up to 24 hours because polymerization is incomplete at placement.
Some advocate to finish shortly after placement.
Studies have shown that delayed polishing can actually increase marginal leakage and has no effect on surface characteristics compared with immediate finishing.
Restorations should be finished and polished during the same appointment after 15min following curing.
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A surface finish attained with the use of a plastic matrix band is the most desirable finish for resin restorations, but this is rarely obtainable because of the need for contouring and removal of excess material, which is often required clinically.
Hence, it is advisable to contour the unpolymerized composite with hand instruments, so that the need for removal of large amounts of set resin leading to surface damage are minimized.
The composite resins may be filled directly into the cavity in the oral environment (direct restoration) or may be fabricated outside the oral cavity and cemented into place (indirect restoration).
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Direct composite restorations
Excess composite at the cavosurface margins in scraped away using a scalpel or a sharp knife in a direction parallel to the margin or toward the gingival tissue.
For gross contouring and finishing of the concave and comparatively non-accessible areas on the occlusal surface, the alpine stone, 12-30 fluted carbide burs and diamond points (15-45 um size) are recommended .
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A kit is designed for finishing and polishing all types of composite restorations
It includes 2 Dura-Green and 2 Dura- White stones for finishing , 6 composite disks for pre-polishing and polishing and 2 composite Fine (white band) polishers for super fine polishing.
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The final luster is obtained with polishing-pastes that may contain pumice, silica, alumina, tin oxide, silicon carbide, zirconium silicate etc (0.1-0.7 um ).
The commonly used abrasives on composites are pumice and silica.
The paste is made by mixing the abrasive with water or glycerin and carried to the restoration with brushes, rubber cups, linen strips or dental tapes.
White rubber cups are preferred to avoid discoloring the resin and should be rotated slowly with light pressure.
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Composite Finishing KitComposite Finishing and Polishing Kit
Sof-Lex TM Contouring and Polishing Discs
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Care should be taken when polishing gingival margin because here the cementum is soft and easily abraded resulting in sensitivity. If the cementum is nicked, it creates nidus for bacteria and development of secondary caries.
Hence, it is advisable to confine the rubber cup to the restoration. Some polishing pastes are now available that have the same ingredient as the reinforcing particles present in the composite resin.
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After the polishing is completed, air is used to blow away any remaining abrasive particles. An explorer may be used on the occlusal surface to remove any deeply seated debris in the grooves.
Dental floss is used to clean the proximal embrasures of any remaining paste and the restoration is finally inspected for any deficiency.
After the final polishing of the composite is completed, a thin layer of glaze may be applied to improve surface smoothness. Glaze is a film of unfilled polymers with a composition similar to the resin matrix.
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Recently, a new material (Fortify, Bisco) has shown promising results. Functionally, this material acts as a surface penetrating sealant.
finishing process creates microstructural defects or cracks that extend across and below the surface to about 20 um.
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This type of surface decreases the wear resistance appreciably. Because of its extremely low viscosity and wetting ability, the material readily flows across the surface and then penetrates into the micro structural defects.
After polymerizing for 20 seconds, it causes resolidification or refortification of the defective surface, thereby increasing the wear resistance of the composite resin appreciably and eliminating marginal defects.
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Enhance Finishing & Polishing SystemThe Enhance Finishing and Polishing System combines several products designed to finish and polish all types of resin restoratives.
The Enhance finishing disc, cups and points are abrasive, flexible devices which complete intermediate and final finishing without the need to change discs.
The Enhance foam polishing cups are foam polishing devices used to buff and polish the restoration in conjunction with a polishing paste.
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PoGo One Step Diamond Micro-Polishers from Dentsply/Caulk are used for polishing resin composite and compomer restorative materials.
Each is a diamond-impregnated, urethane dimethacrylate disc mounted on a plastic, latch-type, slow-speed hand piece mandrel.
The single-use discs are used with increasing light pressure to supposedly produce a highly polished surface. 40-60 seconds is needed.
Users should note that it is intended strictly for polishing and does not effectively remove gross amounts of resin.
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PoGo® one-step diamond micro-polishers
Enhance Finishing and Polishing
System
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Comparison of different finishing/polishing systems on surface roughness and gloss of resin composites
Objectives: the aim of this study was to compare four finishing/polishing systems (f/p) on surface roughness and gloss of different resin composites.
Methods: A total of 40 disc samples (15mm×3mm) were prepared from a nanofill - Filtek Supreme Plus (FS) and a micro-hybrid resin composite - Esthet-X (EX).
Following 24h storage in 37°C water, the top surfaces of each sample were roughened using 120-grit sandpaper. Baseline measurements of surface roughness (Ra, μm) and gloss were recorded.
J Dent. 2011 Jan 168
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Each composite group was divided into four F/P disk groups: Astropol[AP], Enhance/PoGo[EP], Sof-Lex[SL], and an experimental disk system, EXL-695[EXL] (n=5).
Results: The Sof-Lex F/P system provided the smoothest surface although there were no statistical significance differences between F/P systems (p>0.01).
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Effect of different finishing techniques for restorative materials on surface roughness and bacterial adhesion
Statement of problem: the formation of biofilm and bacterial accumulation on dental materials may lead to the development of gingival inflammation and secondary caries.
Purpose: the purpose of this study was to examine the effect of different surface finishing and polishing methods on surface roughness and the adhesion of S.mutans bacteria to 2 new-generation indirect composite resins, 1 direct composite resin, and 1 ceramic material
J Prosthet Dent. 2010 Apr;103(4):221-7
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Results: the highest surface roughness values were recorded in sr adoro and diamond rotary cutting instrument groups. The lowest vital s. Mutans adhesion was seen in the ceramic group and in sr adoro indirect composite resin (p<.05).
Conclusions: bacterial adhesion to indirect composite resin materials differed from that to ceramic material after surface treatments. A positive correlation was observed between surface roughness and the vital s. Mutans adhesion
J Prosthet Dent. 2010 Apr;103(4):221-7
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Indirect composite restorations
The use of an indirect composite inlay/onlay in restoring teeth is becoming increasingly popular because of the improved physical properties and their ability to achieve better contacts and contours compared to a direct composite restoration.
The cured composite inlay/onlay is primarily trimmed and finished on the die, using the same armamentarium as in a direct composite restoration.
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Chairside finishing procedure
At the try in stage of the restoration, excessive pressure should not be applied while seating, because of the high fragility of composite material.
In cases where the restoration fails to seat completely, the most probable cause is an excessive proximal contact. With the aid of a mouth mirror the embrasures are viewed facially, lingually and occlusally as well as using a dental floss, the contact is judged as to where it is tight and needs to be modified.
Abrasive disks in a descending order of their abrasiveness are used to adjust the proximal contour and contact relationships.
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Flame shaped diamonds are used in the interproximal region, while oval or cylindrical shapes are used occlusally.
Finishing with diamond instruments is followed by finishing with 30 fluted carbide burs to obtain a smooth finish.
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Finishing and Polishing of Glass Ionomer Restorations
The ideal surface finish for glass ionomer cements is produced by the matrix strip and any interference with hand or rotary instruments inevitably disrupts the surface.
However, clinically it is almost impossible to place a restoration that adequately fills the cavity, without requiring any excess to be trimmed. It is, therefore, essential to have satisfactory procedure for finishing.
Standardization of anyone procedure for finishing of glass ionomer cements is difficult since the handling characteristics as well as finishing procedures varies with each brand of glass ionomer cement.
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The surface of glass ionomer cement is sensitive to both dehydration and water contamination during the initial setting phase.
If the restoration is exposed to air during this period without any protective covering like varnish, it loses water and develops crazing and cracks.
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Water contamination on the other hand dissolves the matrix forming ions, resulting in weak and more soluble cement. Damage should be avoided by checking against both these conditions. A damaged restoration stains and dissolves very readily.
It is therefore preferable to delay finishing and polishing of the restoration for at least 24 hours after insertion so that the setting reaction is not disturbed. After 24 hours, the surface of the material reaches ionic equilibrium with the oral environment.
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With some faster setting cements and light cure glass ionomer cement, finishing can be started earlier, approximately within 10 minutes.
Pearson (1983) has recommended finishing to be delayed for at least 6 minutes after placement, to prevent excessive desiccation of the surface.
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Procedure
Accurate matrix technique combined with sharp carving instruments under good lighting & magnification can produce a glass ionomer restoration that is undamaged on the surface .
The gross finishing is done immediately after the strip or matrix is removed. The surface should be coated with a protective layer while the excess is being trimmed.
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A sharpened gold finishing knife is used to shape the surface where the excess cement exists.
The trimmed restoration is then again coated with cavity varnish or petroleum jelly to protect the cement from moisture during the initial setting phase (30 minutes).
Rotary instruments can also be used at slower speeds to remove excesses at the margins.
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The final contours and embrasures are produced with fine diamonds or with 12 fluted carbide-finishing burs. Margins are finished by using 1/2-3/8 inch fine cuttle disks.
Aluminum oxide coated disks have also shown to achieve a very smooth surface.
Woolford (1988) observed that soflex disks with Vaseline produced the smoothest surface free of any coarse grooves whereas the use of a tungsten carbide bur in the air turbine hand piece severely disrupted the surface of even mature glass ionomer cements.
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A lubricant such as cocoa butter , petroleum jelly or a bonding agent should be used along with finishing and polishing instruments to avoid excessive heat generation and desiccation.
Water spray appears to give a rough surface because of dissolution of the matrix and so is not desirable as a coolant (Knibbs and Pearson, 1984). Air coolants may be used.
Polyacrylic gel has also been used for polishing glass ionomer restorations.
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Finishing and Polishing of Direct Filling Gold
Following burnishing the next step is giving an optimum contour to the restoration.
Instruments used for this purpose include Morse Scaler, Jones Knife or Cleoid discoid carver on the occlusal surface, used from the centre to the margins.
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Finishing and super-polishing cast gold/precious alloys.
Brownies for pre-polishing
Greenies for polishing
Supergreenies for super-polishing
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Finishing And Polishing Of Cast Gold Restorations
Initial finishing of a gold inlay is carried out on the die and most of the finishing is completed within the laboratory.
Once satisfied with the accuracy of the casting, the sprue is separated as close to the surface as possible using a separating disk or cutting pliers.
The stub of the sprue is then smoothened back to the existing curvature on the casting.
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Procedure
Sprue is cut off and sprue pin attachment area is recontoured and rough surfaces are reduced with ¾” carborundum separating disc.
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All axial surfaces are smoothed from the tips of the cusps to within 1 mm of the margins with the no.2F Cratex rubber wheel.
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Finishing of the occlusal anatomy is then initiated by using a round steel bur. The side of the tip of the bur is placed into the grooves and the grooves are defined by creating v-shaped cuts.
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The 5/8” inch rubber and felt wheel is then used to polish the axial surfaces of the casting from the tips of the cusps to within 1mm.
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Finishing And Polishing Of Porcelain Restorations
The key features of dental ceramics are
excellent biocompatibility
stable color
life like translucency
high abrasion resistance
good mach inability
modulus of elasticity and thermal conductivity close to that of tooth structure.
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There are three methods of fabrication currently available for ceramic inlays and inlays
(i) conventional filling on a refractory die using firing porcelain,
(ii) milling from a preformed ceramic block using machinable ceramic and
(iii) casting by the lost wax technique using castable and pressable ceramic.
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Restoration formed by firing porcelain
The desired finish on the fired ceramic restoration is obtained preferably by glazing and to a smaller extent by polishing.
Any adjustment of the fabricated restoration needs to be done at the expense of the glaze layer; thus it is hoped that the restoration should be accurately processed and placed without adjustment.
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A glazed surface of porcelain is comparatively much stronger than the unglazed porcelain. Once the glaze layer is removed, transverse strength of the restoration almost reduces to one half.
This situation has a clinical significance since the restoration often requires occlusal adjustment after placement.
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Any adjustment makes the surface rough and may lead to loss of glaze layer, thereby reducing the strength of the restoration. However, some studies (Haywood et aI, 1988; Elkaraski et aI, 1993) have shown comparable strengths between highly glazed surfaces and those that are not glazed but only polished.
Hence, with the use of polishing systems like Soflex disks, Shofu Porcelain laminate polishing kit etc, it is now possible to minimize the damage caused by intraoral adjustment.
Glazing the surface is also known to reduce flaws and eliminate crack propogation.
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Glazing is of two types:
Autoglazing and Over glazing.
'Autoglazing' is a process in which a smooth surface is obtained without the use of an additional glaze. By careful control of the furnace temperature (955°C-l 065°C), a glaze is created.
At this temperature, the surface porcelain melts slightly, flows and glazes with a little roundening of the corners.
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The disadvantages with this technique are that any excessive glazing would completely destroy the shape of porcelain, increase porosity, reduce the strength and alter the colour.
This technique requires great precision but provides a more esthetic appearance.
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'Overglazing' on the other hand is the application of an external glaze layer over the surface of the completed body of porcelain. Such a glaze contains silica and low fusing fluxes and increases translucency.
The fabricated ceramic restoration is separated from the die and cleaned of any adherent investment with a coarse toothbrush or sandpaper.
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Metallic instruments should be avoided, as they tend to leave grey marks on the restoration. The restoration is then seated on the master die for any final adjustments and finishing.
Extensive care should be taken during their handling as ceramic is very much brittle and susceptible to fracture.
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Chairside finishing and polishing
Before the ceramic inlay/onlay is cemented into the cavity, the cavity side of the restoration is etched. After etching, the etched ceramic surface is treated with a silanating agent to improve its bond with the cementing medium.
A dual cure composite is preferred for luting so as to ensure complete polymerization in any area where light may not reach. The finishing methods and equipment used are similar to those described earlier for an indirect composite restoration.
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During the process, care should be taken to preserve the glazed surface as much as possible. After all adjustments have been made, repolishing is done in all those areas where the glaze has been damaged.
Haywood et al (1988) have recommended the following sequence to attain a smooth finish comparable to a glazed surface:
Use of fine grit diamonds.
30-fluted carbide finishing burs.
Rubber abrasive points and cups (Porcelain Laminate Polishing Kit) at slow speed with air water spray.
Diamond polishing pastes applied with a bristle brush.
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Restorations formed by milling ceramic blocks
Computers are widely used in the fabrication of high precision ceramic inlays and onlays. The commercially available system which utilizes the CAD-CAM technology (Computer Assisted Designing - Computer Assisted Manufacturing) is the CEREC(Ceramic Reconstruction)system (Siemens, Germany).
The milled restoration is adjusted on the occlusal surface using coarse to medium to fine diamond instruments with air - water spray as coolant.
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Since these systems mill the ceramics with diamond burs, a rough surface is produced on the casting initially.
The dentist needs to polish these surfaces to a high gloss with soflex disks impregnated with diamond particles.
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Steps
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Applying HF acid The fit of the inlay is verified
clear matrix strips are applied & wedged before etching and cementation
enamel & dentin are etched
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Dual cure resin is applied to the inlay
cement is applied to preparation
ceramic inlay is seated into the preparation
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Before curing, excess composite is removed with explorer
Cement is light cured
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Slender, fine grit,flame shaped ,diamond instruments used to remove the flash
30 fluted finishing burs are used to smooth the areas adjusted with diamonds
smoothing the interproximal area with abrasive finishing strip
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Rubber abrasive points & cups of successively finer grits are used at slow speed
final polish imparted by porcelain polish paste applied with bristle brush
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Restorations formed by casting ceramic
The fabricated restoration is finished and polished on the master die similarly as described earlier for other ceramic restorations.
Care should be taken during handling of any ceramic restoration because of its extreme fragility. After all the adjustments have been made, the colorant shades are applied on the exterior surfaces and baked.
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The disadvantage with castable ceramic is the loss of external stains and esthetics, when restoration is adjusted for occlusion and marginal fit during the try-in.
The restoration is cemented into the cavity and chairside finishing and polishing is carried out as described before.
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Finishing of Non-Precious alloys
Most commonly used non-precious alloys are cobalt chromium and nickel chromium alloys.
Have high resistance to corrosion owing to the presence of large percentage of chromium.
Have increased hardness compared to gold alloys – difficulties encountered during their finishing procedure
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Two reasons –
High hardness – resistant to abrasion
To combat this – high linear speed and rotational speed of 7000-20,000 rpm are advocated for small dental stones
Advantage – polished surface can be maintained for a longer time
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Second reason – coarse nature of the investment powder – produces rough surface on casting
To combat this a thin layer of fine powdered refractory material may be sprayed on to the wax pattern to improve metal surface
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Procedure –
Casting is separated from the investment – cleaned of the investment
Electrolyte polishing – reduces time and effort for mechanical finishing
Works on the principle of reverse electroplating in which restoration acts as anode
Electrolyte is a mixture of sulphuric acid and phosphoric acid, glycerine and water
Current density of 0.5-1.0 amps/mm2 ata voltage of 4 is passes for a few minutes.
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The anode – restoration ionizes and is depleted of a very small amount of alloy more readily on the rough surfaces than on the smooth surfaces.
Prominences are gradually dissolved and a smooth surface results.
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Recent new technology
Nanotechnology liquid polish -
-High wear resistance-High stain resistance-Marginal sealing
Composition – Nano-fillersAcetone ButanolPhotoinitiatorMethacrylate resinsAdditives
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Abrasive impregnated brushes and felt devices-
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Abrasive impregnated latch type polishing brushes were introduced in late 1990’s
Various shapes – various abrasives impregnated
Intended to reach grooves, fissures and interproximal areas
Precursor – diamond impregnated felt wheels for polishing hybrid composite
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Rotary resin-matrix stain, cement, composite removing devices-
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Based on polymer/composite resin binder/matrix with controlled abrasivity
Removal of orthodontic adhesive, periodontal root planing and stain removal
Structure of the rod bur is made up of fibers and optionally a load of particles embedded in a resinous matrix giving the working surface of the rod a continuous abrasive powder.
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Summary
• the process that involves removing marginal irregularities, defining anatomic contours, and smoothing away surface roughness of a restorationFinishing
• the process involving the removal of minute scratches from the surface of a restoration and obtain a smooth, light-reflective luster.Polishing
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Oral health
Function
Aesthetics
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Classification of abrasives
Natural abrasives
Arkansas stoneChalk, corundumDiamond, tripoli, zirconium silicate
Emery,garnet, pumice, quartz,
sand, cuttle, Kieselguhr
Manufactured abrasives
Silicon carbide, aluminum
oxide, synthetic diamond
Rouge and tin oxide
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Phases in dental finishing procedure
Final polishing
Intermediate Finishing and
Polishing
Gross Reduction, Coarse Finishing and Margination
Dental clinics of North America, April 2007, 51, 379-397
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Instruments for gross reduction
Diamonds
Fluted Finishing burs
Abrasive Finishing Discs
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Intermediate finishing and Polishing
Coated abrasive disc
Bonded abrasive devices
Fine diamonds and multifluted
finishing burs
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Final polishing
Extra fine Coated
Abrasive
Loose abrasive polishing
paste
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References -
Abrasive Finishing and Polishing in Restorative Dentistry: A State-of-the-Art Review, Dental Clinics of North America, April 2007, Volume 51, Number 2, 379-397
Anusavice – Phillip’s Science of Dental Materials
Dental Materials at a glance, J. Anthony Von Fraunhofer
Sturdevant’s Art and Science of Operative Dentistry, 5th Edition
Bryant RW, Collins CJ. Finishing techniques for amalgam restorations: clinical assessment at three years. Aust Dent J 1992 oct; 37(5): 333-9
The Efficiency Of a New Polishing Material: Nanotechnology Liquid Polish, Journal Of Operative Dentistry, 2010 May-June, 35(3):362-9.
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Thank You