When a tooth develops a cavity, the decayed tissue must be removed. The earliest devices for doing this were picks and enamel scissors. Then two-edged cutting instruments were designed; they were twirled in both directions between the fingers. The father of modern dentistry, the Frenchman Pierre Fauchard (1678-1761), described an improved drill in 1728. Its rotary movement was powered by catgut twisted around a cylinder, or by jewelers' bowstrings. A hand-cranked dental drill bit was patented by John Lewis in 1838. George Washington's dentist, John Greenwood (1760-1819), invented the first known "dental foot engine" in 1790 when he adapted his mother's foot-treadle spinning wheel to rotate a drill. Greenwood's dentist son continued to use the drill, but the idea went no further. The Scottish inventor James Nasmyth used a coiled wire spring to drive a drill in 1829. Charles Merry of St. Louis, Missouri, adapted Nasmyth's drill, adding a flexible cable, in 1858. The first "motor-driven" drill appeared in 1864, the design of Englishman George F. Harrington; hand-held, it was powered by the spring action of a clock movement. In 1868 the American George F.
Green introduced a pneumatic drill powered by a pedal bellows. Fellow American James B. Morrison patented a pedal bur drill in 1871. A further improvement of the Nasmyth-Merry design, it featured a flexible arm with a "hand" piece to hold the drill, plus a foot treadle and pulleys. Each of these advances increased the speed at which the drill operated. In 1874 Green added electricity to the dental drill; powered by electromagnetic motors, it worked well but was heavy and expensive. Plug-in electric drills became available in 1908; by then most dental offices were electrified. Once efficient, mechanically-driven drills became widely available, teeth could be properly and accurately prepared for well-fitting crowns and fillings, and American teeth blossomed with gold. Modern dental drills are turbine-powered, rotating at speeds of 300,000 to 400,000 revolutions per minute. The Morrison drill, by comparison, operated at 600 to 800 r.p.m.
Re-emerging on the scene is the air abrasion drill, first developed in the 1940s as an alternative to the slow-speed, belt driven handpieces used at the time but which fell from favor with the arrival of the Borden air rotor, the first air turbine handpiece. Air abrasion drills, which use a pressurized stream of microscopic abrasive powder to remove decay, enamel, and previous dental work, reduce the amount of heat, vibrations and bone-conducted noise typical with conventional drills. Patients find this technology less traumatic and rarely request anesthetics. In May, 1997, the Food and Drug Administration cleared for marketing in the United States the first erbium:yttrium-aluminum-garnet, or Er:YAG laser, for use in "hard tissue." Clinical studies proved its equivalence to the high-speed drill for making cavity preparations in enamel and removing caries, in most cases without the need for anesthetic. The laser is also used for cavity prevention and etching. This approval concludes a search begun by Dr. Leo Goldman in 1964 and many subsequent searches for an appropriate laser wavelength.
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