Abrasion, Finishing, and Polishing

Chapter 12

Finishing and PolishingThe process of finishing and polishing

involves using a series of abrasives on a surface to first contour, then smooth, and finally bring a luster to the surface.

Finishing uses abrasives to produce the final contour of a restoration.

Polishing is the process of abrading the surface of a restoration with a series of coarse to fine particles, producing scratches.

This produces a surface smooth enough to be esthetically pleasing that is well tolerated by soft tissues and resists biofilm adhesion.

Abrasion

The rate of abrasion is determined by the following: Size, irregularity, and hardness of the particles Number of particles contacting the surface Pressure and speed at which they are applied

The size, irregularity, and hardness of the abrasive particle determine the depth of the scratches in the material being abraded and therefore the amount of material being removed.

If the surface being abraded is harder than the abrasive, little or no effect is noted.

Abrasion (cont’d)The size and shape of the particles are

important considerations in manipulating the abrasive.

Particles that are large and irregular will cut more efficiently.

The sharpness, or efficiency, of the particle is usually lost with use, as the edges break down and the particle no longer grabs the surface.

Unlike the shape of the particle, the size of the particle does not always break down with use.

Abrasive particles are classified from coarse to fine.

Abrasion (cont’d)The more concentrated the particles that

contact the surface, the more quickly the surface will be abraded. If a lubricant is used to dilute the concentration of the particles, the abrasiveness of the material is reduced.

Water and saliva are common lubricants used to dilute the effects of abrasion.

Increasing the speed and pressure of an abrasive will increase the rate of abrasion, but will make it more difficult to control the handpiece and will build up heat in the tooth.

Design of AbrasivesDental abrasives are supplied in a

number of forms: Loose abrasive paste and powder abrasives

classified by grit Coated abrasives attached to disks or strips Bonded abrasives attached to a rotary

instrument

Materials Used in Abrasion

DiamondCarbide finishing

bursSilicone carbideAluminum oxideSand

Pumice RougeTin oxideSilicone dioxideCalcium

carbonate

Prophy Paste50% to 60% abrasive materialsMay be up to 20 times stronger on

dentin than over-the-counter (OTC) toothpaste

When a prophy paste is selected, the least abrasive paste possible should be selected for existing stains and soft deposits.

These abrasives should be applied as wet as possible with a light touch and at low speed.

Dentifrice and Denture Cleaners

OTC toothpaste also contains abrasive agents.

Therapeutic agents such as fluoride are also added.

Denture cleansers use mild cleansing agents to remove plaque and stain from the surface of dentures.

Finishing and Polishing

The benefits of a properly finished and polished restoration/prosthesis include the following: Decreased biofilm retention Resistance to tarnish/corrosion Increased longevity of the restoration Decreased attrition of natural tooth surfaces

during chewing Improved esthetics Improved health of surrounding tissue

Finishing and Polishing (cont’d)The finished and polished restoration

should have a smooth, continuous line, flush with the tooth surface.

When restorative margins end at or near the cementoenamel junction, instrumentation near or on this cavosurface margin may result in ditching or gouging of the softer cementum surfaces.

Contours of teeth must be re-created and should not be flattened or overly rounded.

FlashBefore finishing or polishing an amalgam or

composite restoration, the clinician should check the integrity of the cavosurface margins for extra material known as flash.

The process of removing excess restorative material to bring the restoration flush with the cavosurface tooth structure is called margination.

Careful evaluation of the restoration is necessary to determine whether margination is indicated.

Amalgam

Amalgam restorations should not be polished sooner than 24 hours after they are placed.

Rotary cutting diamonds and carbide burs are used to reduce excess material at the cavosurface margin.

Care must be taken whenever rotary instruments are used for the generation of excessive heat and aerosols.

Composite ResinComposite restorations are finished and

polished as part of the restorative procedure.

First, marginal and occlusal excesses are removed in initial finishing with diamonds or multi-fluted carbide burs.

Intermediate finishing is accomplished with flexible disks, cups, and strips.

Final polishing is accomplished with a submicron aluminum oxide–based polishing paste applied with soft cups or felt pads.

Gold and Porcelain

Precious and nonprecious crowns, inlays, and onlays are finished and polished in the dental laboratory before delivery to the dental office for final fitting and cementation.

Rubber polishing points and wheels designed for porcelain are used for finishing, and diamond polishing paste is used to polish the restoration to an enamel-like luster.

Coronal PolishAll restorative materials must be

identified before the coronal polish, to prevent undesired removal or scratching of the surface of the restoration by traditional commercially prepared prophy paste.

The clinician should consider polishing only those tooth surfaces where stain is present.

Cemented MarginsMargins on resin-bonded porcelain

restorations are more susceptible to staining because of the properties of the resin cements.

Stains accumulating at the resin cement interface must be carefully evaluated for actual staining or microleakage.

If it is determined that the stain is within the cement and is not the result of leakage, it may be removed in the same manner as in a composite restoration.

Air Polishing and Microabrasion

The use of air to propel very small microparticles as a replacement for rotary cutting and polishing instruments has gained much popularity.

Air polishing utilizes a combination of sodium bicarbonate, air, and water at a pressure of approximately 40 psi as an effective and efficient means of removing stains and soft deposits from enamel surfaces.

Microabrasion uses compressed air and a 27 or 50 μm aluminum oxide powder.

Infection ControlAerosols are created whenever a

rotary device and moisture are used. These aerosols carry bioburden that

can be transmitted if the operator does not use proper personal protective equipment (PPE).

Silica particles from restorations and mercury vapors pose potential health risks as well.

Patient EducationPatients must be educated on how to

care for their new restorations: Composites are stained by various

substances. Over-use of abrasive materials may cause the

surfaces of restorations to deteriorate.

SummaryAbrasive agents are used to contour,

finish, and polish the surfaces of restorations.

It is essential that dental personnel are knowledgeable about what materials should be used with specific restorative materials.

Using the wrong materials may cause irreparable damage to restorations, requiring replacement.