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...