Finishing and Polishing / orthodontic courses by Indian dental academy

CONTENTS

Introduction

Objectives of finishing and polishing

Finishing, cutting, grinding and polishing procedures

Finishing and polishing instruments

Hardness of abrasives

Abrasive instrument design

A) Abrasive grits

Type of abrasives

B) Bonded abrasives

Finishing burs

Diamond instruments

C) Coated abrasive disks and strips

D) Cloth and felt

Abrasive and erosive wear,

Other finishing procedures

Microabrasion and macroabrasion

Burnishing,

Finishing of different restorative materials

Amalgam

Composite

Glass ionomer cement

Direct gold restorations

Cast gold restorations

Porcelain

Health hazards of finishing and polishing

References

Conclusion.

Introduction :

The main objective of an operative dentist is to restore the individual

tooth to its form and functions along with imparting pleasing esthetics and

maintaining periodontal tissue in good esteem. It has been established that

rough or uneven surfaces initiate microbial flora to flourish and also light

reflected by these surfaces may not be even and uniform. Therefore a

restored tooth should be evenly smooth and reflect light uniformly. The

process of making the surface smooth is known as finishing and polishing.

Finishing is defined as the transformation of an object from a rough to

a refined form. The procedure involves removal of surface irregularities and

shaping the restoration according to functional occlusan polishing is defined

as the production of a shiny mirror like surface, which reflects light similar

to enamel.

Objective of Finishing and Polishing :

The objective of finishing and polishing of any restoration are

obtaining adequate adaptation and continuity of the restoration. Margins,

with the tooth, optimum restoration contour, proper occlusal contacts and a

surface free of any scratches or irregularities to make it biologically

acceptable. All these objectives lay the foundation for optimum oral health

function and esthetics.

i) Oral health: a well contoured and polished restoration will have

reduction in total surface area and reduced roughness of the restoration

surface which promotes the oral health by resting the accumulation of

food debris and pathologic bacteria. Smoother surfaces are easier to

maintain in a hygiene state when preventive oral home care is practiced.

With some restorations tarnish and corrosion activity can be

significantly reduced if the entire restoration is highly polished, which is

very important for the biocompatibilite property of a material.

ii) Oral function: Oral function is enhanced with a well polished

restoration because food glides more freely over occlusal and embrasure

surfaces during mastication.

Smooth restoration contacts, minimize wear rates on opposing and

adjacent teeth, which is particularly true for restorative materials such as

ceramics that contain phases that are harder than enamel and dentin.

Friction is the resistance to motion of one material body over another.

If an attempt is made to more one body over the other a restraining force to

resist motion is produced. The co-efficient of friction is reduced if the

surfaces are smooth and in single plane. Reduction in friction results in

reduction in wear which interns helps in longevity of restoration.

Rough material surfaces lead to the development of high-contact

stresses that can causes the loss of functional and stabilizing contacts

between teeth.

iii) Esthetics : Aesthetic demands may require the dentist to handle

highly visible surfaces of restorations differently than those that are not

accessible, Because.

When white light shines on a solid, some of the light is directly

reflected from the surfaces and remains white. This light is mixed with the

light reflected from the body of the material and dilutes the color.

As a result an extremely rough surface appears lighter than the

smooth surface of the same material. This problem is associated with

unpolished or worn glass ionomers and composite restorations.

The opacity, translucency and transparency of a dental material is

affected by the surface characteristic of the material.

Opacity is a property of materials that prevents the passage of light.

An opaque material may absorb some of the light and reflect the remainder.

For example the core material of porcelain is opaque it reflects yellow light

so it appears yellow.

Translucency is a property of substrate that prevents the passage of

light but disperses the light, so objects can’t be seen through the material.

Some translucent materials used in dentistry are ceramics, resins,

composites etc.

Transparent material allow the passage of light in such a manner that

little distortion takes place and objects may be clearly seen through them.

Finishing, Cutting, Grinding and Polishing Procedures :

Finishing can also be described as a process where by substrate

particles are removed by the action of cutting and or grinding. The surface

of the substrate in made to come in to frictional contact with a

comparatively harder material. This contact generates enough tensile and

shear stresses to over come the forces of atomic bonds and there by release

particles from the substrate.

In a cutting operation the substrate particles are, removed by the use

of a bladed instrument or any instrument in a blade like fashion. A grinding

operation on the other hand removes small particles of the substrate through

the action of bonded or coated abrasive instruments. These instruments

contain randomly arranged abrasive particles. Both cutting and grinding

procedures produce unidirectional scratches.

Polishing is the most refined process and acts on an extremely thin

region of the substrate surface. It procedures very fine scratches that can be

visible only under very high magnification.

Basically polishing is the process in which the polishing material

dos’t cut or grind, but fills fine scratches and procedures a perfectly smooth

surface. During the polishing of metals a highly stressed microcrystalline

layer is formed on the surface called the “Beilby layer”. It is believed that

because of the rapid movement of the polishing agent, top layer of the

material gets heated up causing it to flow and fill the scratches.

During these procedures :

i) Surface blemished and imperfections are removed

ii) The material is shaped to an ideal form and

iii) The outermost surface of the material is developed to a desired

state.

Finishing and Polishing Instruments :

Hardness of abrasives: One of the most important characteristics of

abrasive particles on dental instruments is, it must be great enough to

remove particles of substrate material without becoming dull or fracturing

too rapidly. The hardness of a material can be measured by using MOHS,

KNOOP or VICKERS hardness tests.

Abrasive Instrument Design :

A) Abrasive Grits :

Abrasive grits are derived from materials that have been crushed and

passed through a series of mesh screens to obtain different particle size

ranges. Dental abrasive grits are classified as coarse, medium fine and super

fine, according to particle size. Along with this the shape of particle also

plays a major role in its selection.

Many types of abrasive materials are available they can be classified

mainly in to two types.

i) Natural abrasives : Arkansas stone, Chalk, Sand

Corundum stone, Diamond, Tripoli

Emery stone, garnet, zirconium silicate

Pumice stone, quartz

ii) Manufactured or synthesized materials.

They are generally preferred because of their more predictable

physical properties.

Silicon Carbide, Aluminium Oxide

Synthetic Diamond, Rough, Tin Oxide

B) Bonded abrasives :

Bonded abrasives consists of abrasive particles which are

incorporated through a binder to form grinding tools such as points, wheels,

separating disks and a wide variety of other abrasive shaper. Particles are

bonded by four general methods.

a) Sintering

b) Vitreous bonding (Glass or ceramic)

c) Resinoid bonding

d) Rubber bonding

Sintered abrasives are strongest type because the abrasive particles

are fused together

Vitreous bonded abrasive are mixed with a glassy or ceramic matrix

material, then cold presses to the instrument shape and finally fired to fuse

the binder.

Resin bonded abrasives are cold pressed or hot pressed and then are

heated to cure the resin. Rubber bonded abrasives are made similarly.

The type of bonding method employed for the abrasive greatly affects

the grinding behaviour of the tool on the substrate. An ideal binder holds the

abrasive particle is the tool sufficiently long enough to cut, grind or polish

the substrate, yet release the particles either before its cutting efficiency is

lost or before heat built-up causes thermal damage to the substrate.

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 the harder abrasive block until the abrasive instrument rotates in the

hand piece without eccentrically or runout when placed on a substrate.

The dressing procedure like truing is used to shape the instrument but

accomplishes two different purposes. 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.

The clogging of abrasive instrument with debris is called abrasive

blinding, which results in reduction in abrasive efficiency and more heat

generation. So frequent dressing of the abrasive instrument during the

finishing operation on a truing instrument, maintains the efficiency of the

abrasive.

Diamond instruments are pre-shaped and trued so are not treated like

the bonded abrasives. Diamond clearing stones are used on the super coarse

through fine grades to remove debris build up and to maintain grinding

efficiency.

C) Coated abrasive disks and strips :

Coated abrasives are fabricated by securing abrasive particles to a

flexible backing material (heavy weight paper or Mylar) with a suitable

abrasive material. These abrasives typically are supplied as disks and

finishing strips.

D) Cloth :

Cloth carried on a metal wheel may be used for final polishing with

or without a polishing medium.

E) Rotary rubber instruments :

Rubber ended rotary tools are commonly used for polishing

procedures. They can be obtained in various shapes of cups, wheels, cones

etc. and are commonly used with other abrasives or polishing pastes.

ABRASIVE AND EROSIVE WEAR :

Wear is a material removal process that can occur whenever surfaces

slide against each other. In dentistry the process of finishing a restoration

involves abrasive wear through the use of hard particles. In case of a

diamond bur abrading a tooth surface, the diamond particles bonded to the

bur represent the abrasive and the tooth is the substrate.

It is important to observe the rotational direction of a rotary abrasive

instruments to control its 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, these by producing a more in controlled grinding action

and rougher surface.

Abrasive wear is further divided in to the processes of two body and

three body wear.

a) Two body wear: This occurs when abrasive particles are free to the

surface of the abrasive instrument and no other abrasive particles are

used.

Ex: A diamond bur abrading a tooth.

b) Three body wear: This occur when abrasive particles are bonded to

translate and rotate between two surfaces.

Dental prophylaxis which involves the use of a rotating rubber cup

and an abrasive paste on a tooth or a material surface is an example of a

three body wear.

Erosive wear :

Erosive wear is caused by hard particles impacting a substrate

surface, carried either by a steam of air or a steam of liquid. It is mainly

used in laboratories for grit blasting units that employ hard-particle erosion

to remove surface material.

A distinction must be made between this type of erosion and chemical

erosion, which involves chemicals such as acids and alkalies instead of hard

particles to remove substrate material, chemical erosion is commonly called

as acid etching.

Other Finishing Procedures :

i) Micro and macro abrasion

a) Micro abrasion: Earlier in this technique a paste made of 18%

hydrochloric acid, pumice and water was used. The paste was then

applied to the desired surface with a hand device like tongue blade or

a rotary driven rubber cup, which has a fluted edges, the rubber cup

should be rotated at a very slow speed to avoid removing any excess

tooth structure and prevent spatter.

Croll further modified the technique by reducing the concentration of

the acid to approximately 11% and increasing the abrasiveness by

using silicon carbide particles instead of pumice, is a water soluble

gel paste, this is more safer due to low acid content.

Recently EMS has introduced AIR-flow HANDY systems which uses

sodium bicarbonate as an abrasive agent. The powder is passed

through the narrow nozzle of specially designed hand piece with the

help of compressed air.

This technique is used to remove extrinsic stains on the tooth surface.

b) Macro abrasion: This is a also a technique for the treatment of

surface stains and defects but utilizes a 12-fluted carbide bur or a

micro diamond point revolving at high speed to remove the defect.

Adequate air/water spray should be used not only as a coolant, but

also to facilitate proper visibility of the defect.

ii) Burnishing :

Burnishing is defined as the process of rubbing a metal over the

restorative material to make it shiny or lusterous. Further it acids in

adaptation and compaction of material at margins.

The metal of the burnishing instrument should not combine easily

with the metal or alloy being burnished; otherwise some metal may be

transported either on to the restoration or restoration on to the instrument.

Stainless still or chromium plated instruments are commonly employed

either by hand or in the form of smooth rotating engine burnisher.

This technique is employed in,

Finishing amalgam

Finishing gold restoration

Finishing cast gold restorations

FINISHING OF DIFFERENT RESTORATIVE MATERIALS :

1) Dental amalgam restoration :

Although few authors say that polishing of high copper amalgam is

less important as it is resistant to tarnish and corrosion it is often necessary

to

i) Complete carving

ii) Refine the anatomy contours and marginal integrity

iii) Enhance surface texture of the restoration.

Additional finishing and polishing procedures of amalgam restoration

is not initiated until first 24 hrs as the crystallization process is not

complete.

Burnishing the restoration before and after carving

reduces the surface roughness by ten times.

After 24 hrs, the surface of the restoration is usually

rough due to the heterogenous structure of amalgam on setting.

Finishing is then begun with the use of steel finishing burs or stones.

This includes trimming any overextended and excess margins, creating

adequate contour and correcting any occlusal disharmonies that may have

been overlooked during carving process. A high point in an amalgam

restoration appears as a shiny area, which is reduced with carborundum

stones or sharp finishing burs.

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 present. These

overhangs are reduced by using rhein trimmers, bard parker knives,

periodontal files or gold foil knives. Finishing of cervical areas is done by

inserting fine water resistant strips cervical to the contact area through the

interdental space and moving them to and fro.

Removal of superficial scratches and irregularities is accomplished

simultaneously. It should be remembered that abrasives always should be

applied through a descending grade, i.e. coarse, medium, fine and ultrafine

to achieve the best, finish. Suitable polishing agent like tinoxide, zinc oxide,

chalk, pumice, extra fine silex etc. carried with a soft rotating brush or

rubber cup.

For polishing in this contact areas and gingival embrasures, the

abrasive is introduced through polishing strips and dental tape.

During polishing, the restoration should be kept moist and only low

rotational speeds with light intermittent pressure should be used, to avoid

any over heating.

Excessive heat production (600C) will permanently damage the pulp

tissue and the mercury present in the restoration reaches the surface which

leads to loss of material property of amalgam.

With the advent of high copper amalgams, it is now possible to finish

the restorations much earlier, i.e. 15-30 minutes after condensation.

Finishing and Polishing of Composite Restorations :

Composite reins have been widely used as an anterior restorative

material and are now being used in posterior teeth also. The surface

smoothness varies with the type of composite resin, owing to the nature of

the filler particles.

i) Conventional composites: These pose greatest difference in

hardness of organic and inorganic phases. The resin matrix is soft and

filler particles are hard if fine grit polishing methods are used, the foster

rein matrix abrades away easily leaving behind the harder filler particles,

which gives it a rough surface. If coarse abrasions are used on the other

hand, the organic and inorganic phases are removed equally but the

abrasives have behind rough marks.

ii) Hybrid composites can be polished to a semi-gloss but the surface

is somewhat hydrophobic which makes it quite unpleasant for the

patient.

iii) 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 micorfilled

composites is a glossy one where that obtained on conventional

composites is a satin finish.

A surface finish attained with the use of a plastic matrix bond 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.

a) Finishing of direct composite restorations :

Excess composite at the cavosurface margins is scraped away using a

scalpal or a sharp gold knife. The use of stainless steel instrument should be

avoided, as these tend to leave grey marks on the restoration. For gross

contouring the finishing of the concave and comparatively non-accessible

areas on the occlusal surface, the alpine stone, 12-30 fluted carbide burs and

diamond points are recommended. Rotary instruments should always be

used in slow speed and with a stream of water and little pressure. High

pressure tends to loosen and dislodge the filler particles. In the accessible

and convex areas of the occlusal surface agents such as aluminium oxide,

cuttle fish or silicon dioxide coated disks and strips are used in a descending

grade of their abrasiveness. Vaseline or petroleum jelly should be used by

used as lubricant with these disks and strips. These disks should be used in

to and fro motion. Strips are used to polish the proximal surface with short

strokes rather than rapid lengthy strokes in the embrasure.

In class-V restorations care must be taken to avoid gingival damage

in class-V restorations.

The final luster is obtained with polishing pastes that may contain

pumice, silica, alumina, tin oxide etc.

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.

Studies have shown that the soflex disks which has aluminium oxide

polishing are superior to finish and polish composite restorations.

Indirect composite restorations :

The cured inlays / onlays is primarily trimmed and finished on the

die, using the armamentarium as in a direct composite restoration.

Chair side procedure : at the stage of the restoration, excessive pressure

should not be applied while seating, because of high fragility of composite

material. If the restoration dos’t fit in to the cavity, it should be reduced

using disks.

Once the marginal integrity has been established, the occlusion is

then checked and adjusted, occlusal adjustments are made using fine grit

diamond instruments followed by 30 fluted carbide burs. Final adjustments

are made with same instruments and materials as used for direct composite

restorations.

Finishing and polishing of glass ionomer restorations :

The finishing of glass ionomer cement has been described as an

exercise in damage. 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.

The surface of glass ionomer cement is sensitive to both dehydration

and water contamination during 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. Water

contamination on the other hand dissolves the matrix forming ions, resulting

in weak and more soluble restoration. Damage should be avoided by

checking against both these conditions. It is therefore preferable to delay

finishing and polishing of the restoration for at least 24 hrs after insertion so

that setting is complete in case of fast cements and light cure glass ionomer

cement, finishing can be started as early as 10 mins after insertion.

Rotary cutting instruments are preferred than hand cutting

instruments to prevent the tear of the material at the margins. 12 fluted

carbide-finishing burs or fine diamond burs are preferred. Woolford

observed that softex disks with Vaseline produced the smoothest surface. A

lubricant such as coca butter or petroleum jelly should be used along with

finishing and polishing instruments.

Finishing and polishing of direct gold restorations :

Burnishing is the first step in finishing a gold restoration. For occlusal

surfaces, a spratley burnisher or ball burnisher is moved with condensable

pressure from the metal to the tooth surface. A spratley blade carver is used

in the embrasure for proximal restorations.

The next step is giving an optimum contour to the restoration.

Instruments used for this purpose include Morse scaler, Jones knife or

cleoid descoid carver. On the occlusal surface, sued from the centre to

margins. In the proximal portions there is a need to remove any excess, if it

exists which is facilitated by tooth separation. Abrasive disks and strips are

used, the disks should be small in diameter to prevent gingival damage.

After the surface has been smoothed, burnishing is repeated once

again on all the margins. Polishing with tin oxide or extra fine silex applied

with a rubber cup gives the restoration a high metallic lustore and satin

finish.

Shofer brown and green cups have also been shown to be very

effective. These rubber cups have an abrasive impregnated in the rubber.

However they should be used only at slow speeds.

Finishing and polishing of cast gold restorations :

An obvious extension of the casting beyond the margins removed

upto the finish line with a small cylindrical point rotating away from the

operator. The remaining thick margin is carefully thinned with fine disks.

Occlusal surface is then finished using abrasive stones and disks in an order

of descending abrasiveness.

The proximal surface is contoured lightly with a ½" to 5/6"

carborundum disk followed by smoothening with medium and fine cattle

paper disks.

The occlusion is checked with an articulating paper and premature

contacts, if any are refined with a selective grinding. The roughness created

is then polished with rubber polishing disks or points.

Finally after the insertion of the restoration it is burnished again.

Finishing and polishing of porcelain restorations :

The high esthetic quality of porcelain is attributed to surface texture,

which is characterized by reflection and absorption of light rays.

These are three methods of fabrication currently available for ceramic

inlay and onlays.

i) Conventional filling on a refracting die using firing porcelain,

ii) Milling from a preformed ceramic block using machenable

ceramic and

iii) Casting by the lost wax technique using castable and pressable

ceramic.

The second and third methods do not use the application of a glaze

layer to attain the final surface finish.

i) 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.

It is proven that 40-46% of the strength of the porcelain restoration

will be reduced if the glaze surface is removed. But the strength of a glazed

porcelain and one highly polished are comparable. Hence with the use of

polishing systems like, softex disks, shofu porcelain laminate polishing kit

etc. it is now possible to minimize the damage caused by intra oral

adjustment.

Glazing is of two types autoglazing and overglazing.

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 (9550C – 10650C), a glaze is created. At this temperature the

surface porcelain melts slightly, flows and glazes with a little roundening of

the corners.

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.

Chair side finishing procedures

i) Use fine grit diamonds.

ii) 30 fluted carbide finishing burs

iii) Rubber abrasive points and cups at slow speed with air water

spray.

iv) Diamond polishing pastes applied with bristle brush.

ii) Restoration formed by milling ceramic blocks :

These ceramic inlays and onlays are fabricated using CAD-CAM

technology (computer assisted designing and computer assisted

manufacturing).

Diamond finishing burs are used followed by soflex discs to polish

the restoration.

iii) Restorations formed by casting ceramic :

The fabricated restoration is finished and polished on the master die

similarly as described earlier for ceramic restorations.

Hazards of finishing and polishing :

1) High temperature may damage pulp during finishing and

polishing. This raise in temperature may also damage the properties

of restorative material, like bringing mercury to the surface in case of

amalgam restorations.

2) Microstructural defects or cracks can extend below the surface

during finishing and polishing.

3) As finishing proceeds, voids incorporated during the filling

process may be exposed, lodging unsightly stains.

4) The edges of the inflexible disks tend to scratch the surfaces

and the central metallic mounting hub of certain disks also have a

tendency to cut the surface.

5) Restorative materials may be lodged in the oral soft tissues

during finishing and shaping procedures, which can lead to persistent

chronic inflammation of those tissues.

6) Loss of external stains may occur during finishing of castable

ceramic restorations.

7) If attention is not given an excess of glazing could lead to

complete loss of anatomy.

8) And one of the most important complication is the aerosol

production.

i.e. dispersions of solid particles are generated and released into the

breathing space of laboratories and dental clinics whenever finishing and

polishing operations are performed. These airborne particles may contain

tooth structure, dental material and microorganisms. Such aerosols have

been identified as potential sources of infections and chronic diseases of the

eye and lungs and present a hazard to dental personnel and their patients

silicosis also called grinders disease is a major aerosol hazard is dentistry

because a number of silica based materials are used in the processing and

finishing of dental restorations.

Aerosol produced during finishing and polishing can be reduced by

three ways.

i) They can be controlled at the source through the use of adequate

infection control procedures, water spray, and high volume

suction.

ii) Personal protection like safety glasses, disposable face masks can

protect the eye and respiratory tract from aerosols.

iii) The entire facility should have a adequate ventilation system.

REFERENCES 1. Finishing techniques for high copper amalgam restoration. A laboratory

study.

Journal of dental research vol – 67, page – 633, 1988.

CONCLUSION

A beautiful statue, even if it is Beautifully sculptured, if left

unfinished will attract no spectators. Similarly a dental restoration without

finishing and polishing will be unesthetic, but this is not the only problem it

will face. The effects are cumulative which will finally lead to its failure. So

why not spend a few more minutes of out precious time finishing and

polishing the restoration rather than see all our hard work go in vain.

COLLEGE OF DENTAL SCIENCES

DEPARTMENT OF CONSERVATIVE DENTISTRY

AND ENDODONTICS

SEMINAR

ON

FINISHING AND POLISHING OF DENTAL

MATERIALS

PRESENTED BY :

Dr. SUDHIR BABU S.