Introduction
Abrasion is the wearing away of material by rubbing, cutting or scraping. The object that does this is the abrasive. Abrasives are harder than the tooth tissues and restorations they work on.
Finishing and polishing
- Finishing shapes a restoration, removes excess material and gives a smooth surface.
- Polishing follows it, with a final, minimal removal of material that leaves a very smooth, shiny surface.
Types of abrasives
- Natural: diamond, corundum, emery, garnet and quartz.
- Artificial: synthetic diamond, carborundum (silicon carbide) and electrocorundum. These have a constant composition and well-defined properties.
Abrasive instruments
Rotary instruments have a head, neck and shank. They include dental burs of steel, tungsten carbide and diamond, plus cutters, stones, separators and abrasive rubbers.
How polishing works
Polishing agents come as dry powders (flours), mixed with water or oil, or as ready-made pastes. Their particles include pumice, alumina, silicon carbide, silicon dioxide, garnet, feldspar and zirconium oxide.
Linear speed
The speed of a tool's cutting surface depends on its diameter (d) and revolutions per minute (n):
Makers state the recommended revolutions for each tool, according to its size and shape.