The Indus Valley Civilization has yielded evidence of dentistry being practiced as far back as 7000 BC. This earliest form of dentistry involved curing tooth-related disorders with bow drills operated, perhaps, by skilled bead craftsmen. The reconstruction of this ancient form of dentistry showed that the methods used were reliable and effective. The age of the teeth has been estimated at 9000 years.
In later times, mechanical hand drills were used. Like most hand drills, they were quite slow. In 1864, a British dentist invented a clockwork dental drill, much faster than earlier drills, but also very noisy. The first electric drill was patented this day in 1875, a development that revolutionized dentistry. In 1968, an American dentist came up with a pneumatic dental drill powered with pedal-operated bellows. (from Wikipedia and cute-calendar.com)