Which blade is crescent-shaped with one cutting edge on the inside?

The blade that is crescent-shaped with one cutting edge on the inside is indeed the #12 blade. This specific design allows for precise and controlled incisions, particularly in soft tissue procedures. The crescent shape makes it ideal for cutting areas that require greater maneuverability and access, such as in periodontal surgery or when removing lesions in delicate areas. The inner cutting edge facilitates effective tissue management, reducing the risk of trauma to adjacent structures.

In contrast, the #11 blade is typically a pointier scalpel used mainly for making incisions in tougher tissue, while the #15 blade is a smaller, more versatile blade suitable for a variety of cutting tasks but does not possess the crescent shape. The #20 blade, being larger, is predominantly used for larger incisional needs and is not designed with the inner cutting edge that characterizes the crescent blade. Therefore, the unique features of the #12 blade make it the appropriate choice for specific surgical applications in periodontology.