What design feature of cavity preparation allows the remaining tooth structure and the restoration to withstand forces directed toward the long axis of the tooth?

• A. Retention form
• B. Resistance form
• C. Convenience form
• D. Finishing

Answer: (B)

Resistance form focuses on withstanding chewing forces that travel along the tooth’s long axis, so the remaining tooth structure and the restoration stay intact under axial loading. To achieve this, the cavity should preserve enough dentin and enamel around the preparation so walls aren’t too thin, provide sturdy walls and a solid floor that can share and distribute forces, and avoid sharp internal angles that concentrate stress. Rounded internal line angles help reduce crack initiation, and the walls should be shaped to resist fracturing rather than simply to fit the restoration. In short, this design approach strengthens how the tooth-restoration complex handles vertical, axial loads during biting.

Retention form, by contrast, is about preventing dislodgement of the restoration in directions other than along the long axis (using undercuts, grooves, or pins). Convenience form is about providing access and visibility, and finishing concerns shaping and smoothing the margins.