DentMat - Dental Abrasives

Dental Abrasives

Before any restoration or appliance is placed permanently in the mouth it should be highly polished.

Benefits of finished and polished restorations:

✓ Better gingival health

✓ Chewing efficiency

✓ Patient comfort

✓ esthetics

A rough or unpolished surface may:

✓ Be uncomfortable to the patient

✓ Cause food and other debris cling to it and makes it unhygienic

✓ Lead to tarnish and corrosion.

Abrasion

- wearing away of a substance or structure through a mechanical process, such as grinding, rubbing or scraping. It occurs when a hard, rough surface slides along a softer surface and cuts a series of grooves. Also referred to as GRINDING.

Abrasives

– material of sufficient hardness and sharpness to cut, or scratch a softer material (Ex. disks, stones, wheels or strips).

Finishing

– Process of producing the final shape and contour of a restoration. Removes surface blemishes and produce a smooth surface

Polishing

– abrasion of the surfaces to reduce the size of scratch until the surface appears shiny.

Abrasive can be Supplied as:

1. Paper/plastic coated

• particles may be glued on to a paper or plastic disc that can be attached to a handpiece. Ex. Sand paper

2. Coated strips

• abrasive may be attached to stainless steel or plastic strips (used for proximalstripping of teeth).

3. Electroplating bonding

• diamond chips are attached to steel wheels, discs and cylinders by electroplating with nickel based matrix (diamond burs)

4. Bonded stones

• the abrasive particles are mixed with a bonding agent that holds the particles together (grinding wheels and dentalstones)

5. Powder form

• abrasive may also be mixed with water or glycerine to form a paste or slurry. It is applied with felt cone, rubber cup or brush and used for smoothening irregularities (pumice powder)

6. Cake form

• abrasives are also available in the form of cakes

7. Rubber impregnated

• abrasives can be incorporated into rubber or shellac discs or cups for ‘soft grade’ abrasion

8. Paste form

• abrasive is made into a paste and supplied in a tube (polishing paste, tooth paste)

Classification of Abrasives

A. Finishing abrasives

• Finishing abrasives are hard, coarse abrasives which are used initially to develop contour and remove gross irregularities, e.g., coarse stones.

B. Polishing abrasives

• Polishing abrasives have finer particle size and are less hard than abrasives used for finishing. They are used for smoothening surfaces that have been roughened by finishing abrasives, e.g., polishing cakes, pumice, etc.

C. Cleansing abrasives

• Cleansing abrasives are soft materials with small particle sizes and are intended to remove soft deposits that adhere to enamel or a restorative material.

Desirable characteristics of an Abrasive

1. Irregular in shape

2. Harder than the surface

3. high impact strength

4. attrition resistance

Methods of Abrasion

1. Manually

• e.g., proximal stripping of enamel using abrasive strips.

2. Rotary instruments

• e.g., burs, wheels, cups, discs, cones, etc.

3. Blasting

• The object is blasted with a steady stream of abrasive, e.g., prophyjet polishing of enamel, sandblasting to remove investment of castings, etc.

Arkansas Stone

➢ Semi translucent, light gray, siliceous sedimentary rock mined in

Arkansas

➢ Contains microcrystalline quartz

➢ Grinding of tooth enamel and metal alloys

Chalk

➢ mineral forms of calcite

➢ mild abrasive substance to polish enamel, gold foil, amalgam, plastic materials and sometimes used in dentifrices

Pumice

➢ Silica like volcanic glass used as polishing agent on enamel, gold foil and dental amalgam and for FINISHING THE ACRYLIC DENTURE BASES IN LABORATORY.

Sand

➢ mixture of small mineral particles predominantly composed of silica

➢ Rounded to angular in shape

➢ Applied under air pressure to remove investment material from metal alloy casting (sandblasting)

➢ Coated on paper disk for metal alloy and plastic

Garnet

➢ Silicates of aluminum, cobalt, iron, magnesium and manganese

➢ Dark red, very hard

➢ Coated disk

➢ Grinding metal alloys and plastic

Corundum

➢ Mineral form of aluminum oxide, white in color “White stone”

➢ Grinding metal alloys.

Emery

➢ grayish black corundum in coated abrasive disks

➢ Finishing metal alloys or plastic materials

Silicone Carbide

➢ First synthetic abrasive to be made, extremely hard and brittle

➢ Green and blue-black

➢ Cutting for metal alloys, ceramics and plastic materials

➢ Abrasive coated disk and rubber bonded instrument

Aluminum Oxide

➢ Second synthetic abrasive to be developed after silicone carbide

➢ Essentially replaced Emery

➢ Harder than corundum, widely used in dentistry

➢ Bonded abrasive, coated abrasive, air- propelled grit abrasive

➢ Popular for adjusting enamel and finishing both metal alloys and ceramic materials

Diamond

➢ Transparent, colorless mineral composed of carbon

➢ Hardest substance known,

➢ “superabrasive”

➢ Ceramic and resin-bonded composite materials

Tin Oxide

➢ Extremely fine abrasive

➢ Polishing teeth and metallic restoration in the mouth

➢ Mixed with water, alcohol glycerin

Chromic Oxide

➢ A relatively hard abrasive capable of polishing a variety of metals.

➢ It is used as a polishing agent for stainless steel.

Tripoli

• derived from a lightweight, friable siliceous sedimentary rock that originates in North Africa near Tripoli.

• formed with soft binders into bars

• Used for polishing metal alloys and some acrylic resin materials.

Kieselguhr

• Consists of siliceous remains of minute aquatic plants known as diatoms.

• The coarser form (diatomaceous earth) is used as a filler in many dental materials.

• It is an excellent mild abrasive; however, the risk of respiratory silicosis caused by chronic exposure to airborne particles of this material is significant

Zirconium Silicate

• is supplied as an offwhite mineral.

• It is ground to various particle sizes and used to make coated abrasive discs and strips.

• It is frequently used as a component of dental prophylaxis pastes.

Steps in Finishing/Polishing

1. CONTOUR

• carbide/diamond burs, coarse abrasive-coated discs

2. FINISH

• carbide/diamond burs(fine/extra fine), white stone(aluminum oxide), medium and fine abrasive-coated discs

3. POLISH

• fine and extra fine polishing paste (aluminum oxide or diamond); extra-fine abrasive-coated discs; silicon carbide–impregnated brushes; or diamond impregnated rubber polishing discs, cups, or points.

Finishing and Polishing Techniques: Dental Amalgam

• After 24 hrs

• very fine prophylaxis paste applied with a cotton pellet or a nonribbed rubber prophy cup rotated at slow speed and light pressure

• green stones or diamond burs or brown and green rubber points

• Fine pumice or thin slurry of tin oxide, with a rotating soft brush

Finishing and Polishing Technique: Composites

• Diamond stones/ Carbide finishing burs

• Extra fine diamond burs/ White stone (Aluminum oxide) / abrasive disks

• fine and extrafine polishing paste (aluminum oxide or diamond) / silicon carbide–impregnated brushes/ extra-fine abrasive-coated discs

Finishing and Polishing Techniques: Acrylic Denture Base

• Acrylic finishing bur

• Rag wheel and pumice slurry

• Tripoli/ tin oxide paste – high polish

Infection Control

• separate polishing burs, rag wheels, and pumice pans should be used for prostheses

• Pumice can be mixed with a liquid disinfectant (5 parts sodium hypochlorite to 100 parts distilled water)

• Pumice should be changed daily

• Rag wheels can be sterilized in a steam autoclave or by ethylene oxide

Dentifrices

• Popularly known as toothpastes

• these are agents used with a toothbrush to cleanse and polish

natural teeth.

• They should have maximum cleansing efficiency with minimum

tooth abrasion.

• Highly abrasive dentifrices should not be used especially when dentin (abrades 25 times faster) or cementum (35 times faster) is

exposed

Function:

1. Assists the toothbrush to mechanically remove stains,

debris and soft deposits from the teeth.

2. To impart a polished surface to the tooth.