Which bridge type is similar to a saddle bridge but found on metal frames?

The correct answer is the Unfit bridge. A saddle bridge is a type of bridge often used in the design of ear and total contact prostheses, characterized by its curved shape that conforms to the contours of the body. Similarly, the Unfit bridge, found on metal frames, maintains a design that accommodates the anatomy it is applied to while providing stability and support.

In contrast, the other options do not typically share this similarity with the saddle bridge. The Adjustable bridge is generally designed to allow for modifications in fit or function but does not specifically resemble a saddle bridge. The Comfort bridge focuses on user comfort, which could lead to different design choices that do not emulate the saddle shape or structural characteristics. The Plastic bridge would imply a material choice that diverges from the metal frame aspect referenced in the question.

Thus, the Unfit bridge stands out as the best match to the characteristics of a saddle bridge while also being suited for use with metal frames.