GDC 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 mesial surfaces of teeth will not work on distal surfaces, and vice versa.
Gracey blades used for mesial surfaces of anterior teeth from the facial are only suitable for the distal surfaces of the same teeth when access is performed from the lingual.
The Gracey 3/4 is designed for use on all aspects of anteriors, specially for the far back as the second bicuspids.