For a Gracey curette to effectively scale or root plane, how must the terminal shank be oriented?

For a Gracey curette to effectively scale or root plane, the terminal shank must be oriented parallel to the tooth surface. This positioning is crucial as it allows the cutting edge of the curette to be properly positioned against the tooth surface, ensuring optimal contact for effective plaque and calculus removal.

When the terminal shank is parallel, the instrument can engage the tooth surface more effectively, facilitating the removal of deposits while minimizing trauma to the surrounding tissue. Additionally, this alignment helps maximize the efficiency of the curette's design, which is specifically angled for use on particular surfaces of the teeth.

In contrast, if the terminal shank were positioned at a different angle—such as perpendicular or at a 45° angle—the cutting edge would not effectively adapt to the contour of the tooth, potentially hindering treatment outcomes and increasing the risk of tissue damage. Thus, maintaining the terminal shank parallel to the tooth surface is essential for achieving successful scaling and root planing results with a Gracey curette.