Materials and Processes for Cutting, Grinding, Finishing, and Polishing

What’s the goal of these procedures?

Produce the smoothest surface possible in a limited time. 

 Different abrasives are used for the three major classes of materials:

ceramics, metals, and resin-based composites.

Bulk reduction can be achieved through the use of instruments such as

• diamond burs

• tungsten carbide burs

• steel burs

• abrasive wheels

• separating discs

Provide a fine contouring action:

• 12- to 16-fluted carbide burs

• 30 - 100 μm

finishing action is usually accomplished using:

• 18- to 30-fluted carbide burs

• 8 and 20 μm

Abrasive grits

are derived from materials that have been crushed and passed through a series of mesh screens (sieves) to obtain different particle size ranges

Dental abrasive grits are classified as (according to particle size):

• coarse

• medium coarse

• medium fine

• superfine

Particles are bonded by four general methods

• sintering

• vitreous bonding

• resinous bonding

• rubber bonding 

Abrasive discs are used for:

1. bulk reduction

2. contouring

3. finishing

4. polishing of restoration surfaces

Sintered abrasives

are the strongest type because the abrasive particles are fused together!

The motion of abrasive instruments is classified as

• Rotary

• Planar

• Reciprocal

Most popular nonbonded abrasives.

• Aluminum oxide

• diamond 

Natural abrasives:

• Arkansas stone,

• chalk,

• corundum,

• diamond,

• emery,

• garnet,

• pumice,

• quartz,

• sand,

• tripoli,

• zirconium silicate

Manufactured abrasives are synthesized materials, which are generally preferred because of their ?

more predictable physical properties.

Aluminum Oxide

• Fused aluminum oxide was the second synthetic abrasive to

be developed.

• Synthetic aluminum oxide (alumina) is made as a white powder and can be somewhat harder than corundum (natural alumina) because of its purity.

• However, corundum has a Mohs hardness of approximately 9 (on a scale of 1 to 10.

• Alumina can be processed with different properties

ARKANSAS STONE

• This abrasive material is a semi-translucent light-gray sili ceous 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.

CHALK

• One of the mineral forms of calcite is chalk, a white abrasive composed of calcium carbonate.

• Chalk is used as a mild abrasive paste to polish tooth enamel, gold foil, amalgam, and plastic materials.

CUTTLE

• Commonly referred to as cuttlefish, cuttlebone, or cuttle, this abrasive is a white calcareous powder

• Mediterranean marine mollusk of the genus Sepia.

• Cuttle is available as a coated abrasive and is useful for delicate abrasion operations such as the polishing of metal margins and dental amalgam restorations.

CORUNDUM

• is used primarily for grinding metal alloys and is available as a bonded abrasive in several shapes. 

• It is most commonly used in an instrument known as a white stone.

NATURAL DIAMOND

A clear, carbon-based mineral and the hardest known substance; used as a superabrasive for cutting and polishing ceramics and resin composites.

SYNTHETIC DIAMOND ABRASIVES

Man-made diamonds with uniform size and lower cost; used for cutting tooth structure, ceramics, and resin composites in burs, wheels, and polishing pastes.

EMERY

A gray-black corundum abrasive used in coated discs for finishing metal alloys and acrylic resin.

GARNET

A very hard dark red mineral that fractures into sharp plates; used on coated discs and bands for grinding metal alloys and acrylic resin.

KIESELGUHR (DIATOMACEOUS EARTH)

A silica-based abrasive from diatom remains; used as a filler and mild abrasive, but requires caution due to silicosis risk.

PUMICE

A light, volcanic abrasive used mainly for acrylic resin; fine “flour of pumice” is used for polishing enamel, gold, amalgam, and acrylics.

QUARTZ

A hard, colorless silica mineral; ground into sharp particles for coated discs used to finish metal alloys and sometimes grind enamel.

SAND

Silica-based mineral particles used in sandblasting to remove investment material from metal castings, and in discs to grind metal and acrylic.

TRIPOLI

A fine siliceous rock powder formed into polishing bars; used for polishing metal alloys and some acrylic resin materials.

ROUGE

A fine red iron oxide abrasive blended into cakes; used for polishing high noble metal alloys, especially yellow gold.

SILICON CARBIDE

A very hard synthetic abrasive (green or blue-black) that fractures into new sharp edges; used for cutting metals, ceramics, and acrylics in discs and bonded instruments.

TIN OXIDE

A very fine polishing powder mixed with liquids to polish teeth and metallic restorations such as amalgams.

ZIRCONIUM SILICATE

An off-white mineral ground into abrasive particles used in coated discs and commonly in dental prophy pastes.

ABRASIVE PASTES

Polishing pastes containing alumina or diamond; used with rotary cups or brushes but may splatter, retain thickness, and generate heat if not properly cooled.

 Dentifrices have three important functions: 

1. Their abrasive and detergent action removes debris, plaque, and stains more effectively than brushing alone.

2. They polish teeth for better shine and appearance, and smoother surfaces resist stain and bacterial buildup.

3. They serve as carriers for therapeutic agents with proven benefits

Typical dentifrice components: 

• abrasive

• detergent

• colorants

• flavoring

• humectant

• water

• binder

• fluoride

• tartar control agents

• desensitization agents

What are the six main benefits of finishing and polishing the surfaces of restorative materials?

• Finishing and polishing restorative materials improve gingival health, chewing efficiency, patient comfort, esthetics, corrosion resistance, and reduce wear on opposing teeth.

• Smooth surfaces prevent plaque buildup, making restorations easier to clean and maintain.

• Polishing also enhances strength by eliminating stress concentration points, especially in ceramic restorations.

What are the goals of finishing and polishing?

The main goals are to achieve proper anatomy and occlusion while producing a smooth, durable, and hygienic surface.

What are the similarities of and differences between the mechanisms responsible for the cutting action of carbide burs and abrasive wheels?

• Both carbide burs and abrasive wheels remove material by using harder surfaces that scrape off parts of the tooth or restoration. 

• Carbide burs cut with sharp blades in a regular pattern, while abrasive wheels grind with many tiny, rough particles in random directions. In short, burs cut and abrasives grind, but both smooth or shape the surface.

How does a clinician know when the smoothest surface has been achieved?

• The smoothest surface is achieved when no visible scratches remain and the restoration shows a uniform shine.

• Polishing stops once the finest abrasive no longer improves the surface gloss.

What precautions should be taken to minimize the generation of aerosols? What precautions should be taken to minimize exposure to and inhalation of aerosols?

To minimize aerosol generation, use water spray, high-volume suction, and proper infection control during finishing procedures.

To reduce exposure and inhalation, wear PPE such as masks and safety glasses, and ensure the clinic has good ventilation to remove airborne particles.

How can the amount of lubricant either increase or decrease cutting efficiency?

A small amount of lubricant increases cutting efficiency by reducing heat and friction between the bur and the surface.

However, too much lubricant decreases efficiency by lessening contact between the abrasive and the material.