Auniversal curette,has a blade that is perpendicular to its terminal shank. This orientation allows the blade to be used against either the mesial or distal surface of a tooth. Because this type of periodontal curette was developed at theColumbia University College of Dental Medicine, it is also known as aColumbia curette. TheGracey curette, invented by Dr Clayton Gracey with the help of Hugo Friedman of Hu-Friedy Manufacturing company in the early 1940s, has a blade that is laterally offset by 70 degrees relative to the shank. Consequently, a Gracey curette has a lower, cutting edge, and an upper, non-cutting edge, . Because only one side of each blade can cut, Gracey curettes are site-specific, and a posterior instrument used to clean, mesialsurfaces of teeth will not work on, distalsurfaces, and vice versa. Gracey blades used for mesial surfaces of, anteriorteeth from the, facialare only suitable for the distal surfaces of the same teeth when access is performed from thelingual.