Improvements to dental drills made the possibility of filling teeth a practical alternative to extraction. Dentists initially prepared cavities by removing the decay with files, chisels and later rotating burs. Bow drills and the clockwork drill required the dentist to use two hands to operate the device. It took a great deal of skill and time to prepare a cavity. It was also difficult to remove all the decay. For the patient the noise and vibration were very uncomfortable.
The first clockwork drill, Erado, (from the Latin for: 'I scrape out') was invented by British dentist George Fellows Harrington in 1864. After winding, it ran when wound-up for two minutes; this was the first time continuous rotation was possible for a drill. The following year he introduced interchangeable heads and contra-angles. Made of silver and richly covered in engraving, this heavy, hand-held drill resembled a musical box in appearance. During application it was very noisy. Its popularity was limited with patients and dentists, who had awkward control of the instrument. Its already limited appeal was short lived as in 1872 the foot engine was developed, the forerunner of the modern electric drill.
Dentistry was revolutionised by American dentist James B. Morrison's (1829-1917) invention. His foot-operated machine worked on the same principle as the treadle sewing machine, and achieved 2,000 revolutions per minute (rpm), thus making efficient removal of decay possible.
The first electric dental drill was patented in 1875 by Dr Green and by 1914 electric dental drills could reach speeds of up to 3,000 rpm. A second wave of rapid development occurred in the 1950s and 1960s, including the development of the air turbine drill.