Abrasion, Polishing- Dental Materials

What is abrasion?

Wear or material loss from a substrate as a result of scratching or other mechanical means.

What is two-body abrason?

Abrasive particles are tightly bonded to the abrasive instrument that is removing material from the substrate surface

Like sandpaper

What is three-body abrasion?

Involves the use of non-bonded abrasives

Abrasive particles are free to translate and rotate between two surfaces

What is airbone particle abrasion?

Abrasive particles are propelled against a substrate by air pressure to remove surface material

What factors affect the rate of abrasion?

Hardness between the abrasive and substrate

Particle size of abrasive

Particle shape of abrasive

Speed and pressure

Lubrication

What scale describes the resistance of scratching of one material by another?

Mohs Hardness Test

How is pumice create?

Super-heated, highly pressurized rock is violently ejected

from a volcano

Why are hard gold alloys used in dentistry in terms of hardness?

Equally hard as dentin, less hard than enamel

What does the indentation hardness test calculate?

The size or depth of the indentation and the amount of force are used to calculate a hardness value

Test names: Brinell, Knoop, Vickers

Particle Size of Abrasive

Superfine- <10 μm

Fine- 10 to 20 μm

Medium- 20 to 100 μm

Coarse- 100 to 500 μmF

What does lubrication help with in abrasion?

Reduce heat build-up

Wash away debris to prevent clogging

The most efficient abrasion occurs when the difference in hardness between the abrasive and the substrate is?

Larger

Low speed rpm?

<20000 rpm

Med speed rpm?

20,000-200,000 rpm

High speed rpm?

>200,000 rpm Air-driven

What is air turbine?

Balance between speed and torque. It is faster and consistent with cutting and grinding

Are electric handpieces or air-driven handpieces louder (high-pitched)?

Air-driven handpieces

Finishing vs polishing difference?

Finishing: Put a final surface on. The refinement procedure of substrate surface

Polishing: To make smooth and glossy surface by abrasion

What are the types of finishing and polishing instruments?

Carbide Burs

Diamond Burs

Dental Stones

Rubber Wheels

Disk & Strips

What are carbide burs composed of?

Bur Shank: Stainless steel

Cutting Blades: Tungsten Carbide

What are carbide burs used for?

Contouring and finishing

What are diamond burs made of?

Stainless steel shank

Powdered diamond abrasive

Metallic bonding material

Diamond burs should always be used with?

Water spray

What are types of dental stones?

Silicon carbide

Aluminum oxide

Diamond stone

What are rubber wheels used for?

Used for fine grinding to remove coarse scratched from rough grinding

made by molding aluminum oxide, (silicone carbide and chromium oxide) in a rubber matrix

What are disks made of?

Stiff plastic or paper backing coted with abrasive particles

What is commonly used to finish and polish interproximal areas?

Polishing strips

If a scratch is larger than 0.5 microns, the surface will look?

Dull, the light scatters

What # of microns does the tongue feel like the surface is smooth?

<2 microns

What are the three most common types of coolant?

Air, water, and air-water spray

What does the abrasivity index measure?

A measure of the amount of material abraded from a dentin surface in a given time period

What sequence of grit do you use for efficient abrasion?

Coarse-Medium-Fine-Superfine

Straight Carbide Bur Blade Design vs Spiral Carbide Blade Design

Straight: One blade on tooth

Spiral: Several blades on tooth

Carbide Blade Design 3 angles + 2 faces

Rake Angle: Cutting edge strength

Edge Angle: Blade strength

Clearance Angle: provide a stop and space

Carbide Positive Rake Angle

The radius lies outside the blade, the rake angle is positive.

For soft &weak materials

Carbide Negative Rake Angle

The radial line lies behind the rake face and entirely within the blade

For hard & Brittle materials

What does a large rake angle mean?

A large rake angle means lower strength of the cutting edge

What is the Carbide edge angle?

Internal angle at the edge formed by the two faces of the bur blade

Related to the resistance of the blade to fracture

What is the Carbide clearance angle?

The angle between the clearance face immediately behind the edge and a tangent to the path of rotation

Which bur is better for end-cutting to produce lower heat and have more blade edges for cutting?

Carbide burs

Which bur is more effective for tooth preparation beveling enamel margins and enameloplasty?

Diamond burs

What does dental stones consist of?

Consist of abrasive particles that have been sintered together or bound with an organic resin to form a cohesive mass

What are dental stones used for?

Contouring and finishing restorations, and where maximum abrasion is needed

What are rubber polishers used for?

Adjusting and polishing acrylic material

Don't apply heavy pressure as it can produce excessive friction heat

What are disks used for?

Used for gross reduction, contouring, finishing, & polishing restorations

What is the role of larger abrasive particles and small abrasive particles?

The larger abrasive particles remove large amounts of material from the substrate, and the smaller particles smooth out the roughness produced by the larger particles.

What is the process of polishing dental restorations?

Polishing of a surface relies on using sequentially smaller and smaller abrasives.

How does proper polishing affect peak-to valley heigh and active surface area of restoration?

Proper polishing reduces peak-to-valley height and active surface area of the restoration

What # of microns does the tongue feel like the surface is rough?

>20 microns

What is Dentifrice, toothpaste?

Dental Prophylaxis Paste; Used for removing debris and residual stains from the teeth and for polishing the tooth surface and restoration