Born in Boston, John Greenwood (1760–1819), served during the Revolutionary War as a fife-major and in other capacities. After the war, Greenwood established his place of business at no. 199 Water Street in New York City. There, he practiced several trades, including that of a maker of mathematical instruments. He soon predominantly practiced dentistry, at which he was a success. An advertisement printed in the 27 April 1786 issue of The Daily Advertiser; Political, Historical, and Commercial (New York) informed the public that Greenwood cleaned teeth, removed tartar from teeth and gums, cured "scurvy in the gums," and fastened teeth "by causing the gums to adhere to them". Greenwood manufactured and repaired dentures for GW during the latter's presidency and subsequent retirement. The false teeth Greenwood crafted for GW were made with ivory and human teeth. Despite Greenwood’s careful attention to GW’s case, GW's dentures were apparently often ill-fitting and uncomfortable. Greenwood was one of the leading dentists in New York City in the early nineteenth century.

GW's ledgers show occasional payments to Greenwood for his dental services (see Ledger C, 22, 50).