Abrasives And Polishing Agents

Presented by;

Dr.Sumanth

Under the guidance of:Dr. Manoj Shetty.

1.Introduction

2.what is Abrasion, Finishing, Polishing 3. Desirable Characteristics Of An Abrasive

4. Design of abrasive instruments 5. Abrasive action 6. Factors affecting rate of abrasion 7. Factors influencing efficiency of the

abrasives 8. Types of abrasives

Contents;

ABRASIVES AND POLISHING AGENTS The finishing and polishing of

restorative dental materials are important steps in the fabrication of clinically successful restorations. The techniques employed for these procedures are meant not only for removal of excess material but also to smoothen rough surfaces.

The finishing of dental restorations prior to their placement in the oral cavity has therefore three benefits:

To promote oral hygiene. Enhance oral function. To improve esthetics

ABRASION 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.

Abrasion is further divided into the processes of two-body and three-body wear. Two-body abrasion occurs when abrasive particles are firmly bonded to the surface of the abrasive instrument and no other abrasive particles are used. A diamond bur abrading a tooth represents an example of two-body wear.

Three-body abrasion occurs when abrasive particles are free to translate and rotate between two surfaces. An example of three-body abrasion involves the use of nonbonded abrasives, such as exist in dental prophylaxis pastes. These nonbonded abrasives are placed in a rubber cup, which is rotated against a tooth or material surface

Finishing- Process of removing surface defects or scratches created during the contouring process through the use of cutting or grinding instruments or both.

Finishing action is usually accomplished using 18- to 30-flute carbide burs, fine and superfine diamond burs, or abrasives between 8 and 20 µm in size.

Polishing- Process of providing luster or gloss on a

material surface

The purpose of polishing is to provide an enamel-like luster to the restoration

abrasive particles ranging up to 20 µm provide luster at a low magnification

DESIRABLE CHARACTERISTICS OF AN ABRASIVE

It should be irregular in shape so that it presents a sharp edge.

It should be harder than the work it abrades..

Abrasive should posses a high impact strength or body strength.

Abrasive point should always fracture than dull out so that always, a sharp point or edge is available..

Abrasive should posses attrition resistance so that it does not wear.

DESIGN OF ABRASIVE INSTRUMENTS

The abrasives employed could be one of the three types,

Abrasive Grits. Bonded Abrasives. Coated Abrasive Disks and Strips.

A. Abrasive Grits

Abrasive grits are derived from (abrasive) materials that have been crushed and passed through series of mesh screens to obtain different particle size ranges. The grits are classified as COARSE, MEDIUM COARSE, MEDIUM, FINE and SUPER FINE according to the particle size ranges.

B. Bonded Abrasives These consist of

abrasive particles incorporated through a binder to form grinding tools.

The abrasive particles are bonded by 4 general methods:

Sintering. Vitreous bonding

(Glass/Ceramic) Resin bonding (usually

phenolic resin). Rubber bonding

(usually silicon rubber).

C. Coated Abrasive Disks and Strips

These abrasives are supplied as disks and finishing strips. They are fabricated by securing abrasive particles to a flexible backing material (heavy weight paper or Mylar).

The disks are available in different diameters with thin and very thin backings.

Abrasive action The mode of action of the abrasives is similar

to that of the dental burs, that is, it is merely a cutting action.

Abrasive MotionThe motion of abrasive instruments is

classified as rotary, planar, or reciprocal. In general, burs are considered rotary, disks are planar, and reciprocating handpieces provide a cyclic motion and are reciprocal in relationship to their direction of motion.

FACTORS AFFECTING RATE OF ABRASION

Size of the abrasive particle – larger the size – greater the abrasion.

Pressure of the work against the abrasive.

Speed at which the abrasive particles travels across the work. Greater the speed, greater would be the rate of abrasion

FACTORS INFLUENCING EFFICIENCY OF THE ABRASIVES

These factors are as follows:

The hardness of the abrasive particle (diamond is hardest; pumice and garnet etc. are relatively mild).

The shape of the abrasive particle (particles with sharp edge are more effective).

Particle size of the abrasive (longer particle size will cut deeper grooves).

Rate of movement of the abrasive particles (slower abrasion – deeper scratches).

Pressure applied to the abrasive

Properties of material that is being abraded.

TYPES OS ABRASIVES

According to Craig : The abrasives used can be classified and grouped as

Finishing Abrasives. Polishing Abrasives. Cleaning abrasives

Finishing Abrasives These are hard, coarse abrasives used

initially to develop desired contours and remove off gross irregularities.

Polishing Abrasives These have a smaller particle size and are

less hard than abrasives used for finishing. They are used for smoothening surfaces that are typically roughened by finishing abrasives.

Cleaning Abrasives These are soft abrasives with small particle

size and are intended to remove softer materials that adhere to enamel or a restoration.

2. Skinner has grouped the abrasives employed in dentistry as follows:

A. Natural Abrasives. B. Manufactured Abrasives.

Under Natural Abrasives we have:1. Arkansas stone- Semi translucent, light gray, siliceous

sedimentary rock, mined in Arkansas.- It contains microcrystalline quartz.- fine grinding of tooth enamel and metal alloys.2. Chalk- Mineral form of calcite.- Contains calcium carbonate.- Used as mild abrasive paste to polish teeth

enamel, gold foil, amalgam and plastic materials.

3. Corundum- Is largely replaced by alpha Aluminum oxide

due to its superior physical properties. However corundum is primarily used for grinding metal alloys and is available as a bonded abrasive.

4. Diamond is a transparent colorless mineral composed of carbon. called super abrasive because of its ability to abrade any other known substance. It is used on ceramic and resin based composite materials.

Supplied as:Bonded abrasive rotary instrument. Flexible metal backed abrasive strips.Diamond polishing pastes.

5. Emery-This abrasive is grayish black corundum that is prepared in a fine grain form.

- Supplied as coated abrasive disks.- Used for finishing metal alloys or plastic

materials.

6. Garnet – the term garnet includes several minerals which possess similar physical properties like Silicates of Al, Co, Fe, Mg and Mn.

- dark red, extremely hard - disks and Arbor box.- grinding metal alloys and plastic materials

7. Pumice- Is produced from volcanic activity.- pumice is an extremely fine grinded volcanic rock. - Used in polishing teeth enamel, gold foil, dental

amalgam and acrylic resins.

8. Quartz – the particles are pulverized to form sharp angular particles which are useful in making coated disks.

- Used to finish metal alloys and may be used to grind dental enamel.

9. Sand- Is a mixture of small mineral particles predominantly

silica.- Particles have rounded to angular shape.- Used to remove refractory investment material from

base metal castings..

10. Tripoli- Derived from a light weight, siliceous- sedimentary rock.- white, gray, pink, red or yellow.- Gray and red are most frequently used.- finishing metal alloys and some plastic

materials.11. Zirconium silicate- Off white mineral, ground to various sizes

used to make coated disks and strips.- Also used as a component of dental

prophylaxis pastes.

Under Manufactured Abrasives we have:

1. Silicon Carbide.- Two types were manufactured 1. Green

form and 2. Blue form. Both are having similar physical properties.

- the green variety is preferred- cutting efficiency is higher..- Used in cutting metal alloys, ceramics

and plastic materials.

2. Aluminium Oxide- This is the second synthetic abrasive

to be manufactured.- This form of alumina is much harder

than its natural counterpart (CORUNDUM) because of its purity.

- The forms usually prepared are: a. White stones b. pink and ruby colours

3. Synthetic Diamond – developed in 1955..

used for the manufacture of diamond saws, wheels and burs

Synthetic diamond abrasives are used primarily on tooth structure, ceramic materials and resin based components.

4. Rouge- Principle component is iron oxide blended

with various binders.- Used to polish high noble metal alloys.

5. Tin Oxide- Is composed of very fine abrasive particles.- May be employed in an abrasive paste

form along with water, alcohol or glycerin.- Used as a polishing agent for teeth and

metallic restorations.

Thank u