Dental Material Lecture 9: Abrasion and Polishing

Questions and Answers

What happens when a hard, rough surface slides along a softer surface?

Abrasion occurs

What is the type of abrasion where abrasive particles are bonded to the instrument?

Two-body process

What is the main reason why restorations and prostheses need further trimming, smoothing, and polishing?

To remove any imperfections from the processing stage

What is the primary factor that determines the rate of abrasion of a given material by a given abrasive?

Hardness of the abrasive Signup and view all the answers

What is the term for the material being abraded?

Substrate Signup and view all the answers

What is the process of material removal achieved by air-pressure propelled abrasives?

Air-particle abrasion Signup and view all the answers

What may happen if a restoration or appliance is not polished before being placed in the mouth?

Food and debris may cling to it, making it unhygienic Signup and view all the answers

What is the definition of abrasion?

The wearing away of a substance or structure through a mechanical process Signup and view all the answers

What is the primary difference between an abrasive agent and a polishing agent?

The particle size of the agent Signup and view all the answers

What is the maximum amount of material removed during polishing?

0.005mm Signup and view all the answers

Which of the following is a non-abrasive method of polishing?

Application of a glaze layer Signup and view all the answers

What is the optimal speed for polishing compared to abrading?

Faster Signup and view all the answers

What is the purpose of blasting in abrasion?

To remove investment from castings Signup and view all the answers

What is the primary purpose of proximal stripping in abrasion?

To remove enamel Signup and view all the answers

What is the main characteristic of polishing abrasives that distinguishes them from finishing abrasives?

They have finer particle sizes and are less hard. Signup and view all the answers

What is the primary use of cleansing abrasives?

To remove soft deposits from tooth enamel or restorative materials. Signup and view all the answers

Which type of abrasive is most commonly used in a white stone instrument?

Corundum Signup and view all the answers

What is the main advantage of synthetic diamond abrasives over natural diamond abrasives?

They have a consistent shape and size. Signup and view all the answers

What is the result of reducing the particle size of an abrasive sufficiently?

The scratches become extremely fine and may disappear entirely. Signup and view all the answers

Which type of abrasive is used for fine grinding of tooth enamel and metal alloys?

Arkansas stone Signup and view all the answers

What is the definition of polishing?

The production of a smooth mirror-like surface without much loss of any external form. Signup and view all the answers

Why are synthetic abrasives preferred over natural abrasives?

They have more predictable physical properties. Signup and view all the answers

What is the effect of larger, coarse abrasive particles on a surface?

They abrade a surface more readily and leave coarser scratches. Signup and view all the answers

Why do sharp, irregular shaped particles abrade a surface more rapidly?

Because they have a larger surface area Signup and view all the answers

What is the effect of increasing speed and pressure on the rate of abrasion?

It is directly proportional to the rate of abrasion. Signup and view all the answers

What is the primary purpose of lubricants during abrasion?

To reduce heat buildup and wash away debris Signup and view all the answers

What type of abrasive instrument design involves adding a paste or a water soluble medium to a non-abrasive instrument?

Non-bonded abrasives Signup and view all the answers

What is the characteristic of finishing abrasives?

They are hard and coarse Signup and view all the answers

Why do bonded abrasives tend to disintegrate rapidly?

Because the particles detach with time Signup and view all the answers

What determines the types of abrasive grits?

Particle size Signup and view all the answers

Study Notes

Importance of Polishing

A restoration or appliance should be highly polished before being placed permanently in the mouth to prevent discomfort, food accumulation, and tarnish and corrosion.

Abrasion

Defined as the wearing away of a substance or structure through a mechanical process, such as grinding, rubbing, or scraping.
Types of abrasion: two-body (e.g., diamond bur on enamel) and three-body (e.g., pumice with a bristle brush) processes.
Factors affecting the rate of abrasion: hardness, particle size, particle shape, speed, and pressure.

Abrasives

Defined as a hard substance used for grinding, finishing, or polishing a less hard surface.
Substrate: the material being abraded.
Types of abrasives: finishing, polishing, and cleansing abrasives.
Examples of abrasives: Arkansas stone, chalk, corundum, diamond, and synthetic alpha aluminum oxide.

Abrasive Instrument Design

Abrasive grits: coarse, medium, and fine particle sizes derived from crushed and filtered materials.
Bonded abrasives: abrasive particles bonded to a grinding tool, which tend to disintegrate rapidly.
Non-bonded abrasives: paste or water soluble medium added to a non-abrasive instrument.

Polishing

Defined as the production of a smooth, mirror-like surface without much loss of external form.
Difference between abrasion and polishing: particle size, speed, and material removal.
Methods of polishing: abrasive process, non-abrasive polishing (e.g., application of a glaze layer, electrolytic polishing, and burnishing).

Methods of Abrasion

Manual abrasion: proximal stripping of enamel using abrasive strips.
Rotary instruments: burs, wheels, cups, discs, cones, etc.
Blasting: using a steady stream of abrasive to remove investment of castings.

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Description

This quiz covers the importance of polishing restorations and prostheses before placing them in the mouth, and the process of trimming, smoothing, and polishing. It is part of a Prosthetic Dental Technology course.