Burs are the term a dentists use for the small drill bits that fit in their drills. Dentists need to have a broad assortment of burs. Some are carbides and some are diamonds. Commonly, carbides are used for preparing fillings. They often are used only once and then thrown away. They have tiny fluted blades that are almost as sharp as razor blades. When new, they cut fast and true, with little hand pressure. After only a single use they can become dull and no longer cut efficiently.
Diamond coated burs also used for our preparations and can be purchased in several different 'grits' . I use diamond burs for my crown preparations and for shaping my bonded restorations. Diamonds are more expensive than most carbides, but can easily be sterilized and still retain most of their cutting ability.
Burs come in many different shapes and they can be used to shape teeth when a dentist is 'sculpting his preparations. Teeth come in many different shapes and sizes tand may require longer, shorter, thinner or wider burs in order for a dentist to achieve an excellent result.
While some dentists manage to provide their dentistry with only a small variety of burs, I prefer to select from a large variety, so that I can find just the right 'tool' for each situation. I believe that it helps me create predictably excellent restorations.