Which instrument type is primarily used for detection rather than removal of calculus?

The explorer is primarily designed for detection, making it the correct choice in this context. This instrument has a thin, pointed end that allows dental hygienists to probe the surfaces of teeth to detect irregularities, such as caries, calculus, or other defects. The explorer's design enables it to navigate the contours of teeth and pockets, providing a tactile sensitivity that is essential for identifying issues that might not be visually apparent.

In contrast, instruments like sickle scalers are specifically designed for the removal of calculus and plaque from the tooth surfaces. Universal and Gracey curettes are also meant for scaling but have different applications. Universal curettes can access a variety of surfaces, while Gracey curettes are designed for specific areas based on their angle and design. Hence, their primary function is also to remove calculus rather than to detect it.