A patient is missing teeth 17, 18, 19 and 30, 31, 32. For the resulting removable partial denture, where should the occlusal rests be placed?

Correct answer: B. On the mesial surfaces of teeth 20 and 29

• A. A DISTAL rest is the classic error in distal-extension design — it converts the abutment into a fulcrum and applies leverage that can loosen or damage it.
• B. CORRECT. This is a Kennedy CLASS I (bilateral distal extension) case. In distal-extension designs the rest is placed on the MESIAL surface of the terminal abutment. Under function the extension base sinks toward the ridge and the framework rotates; a MESIAL rest positions the rotation axis so that the clasp arm moves DOWN and AWAY from the undercut rather than being levered against the abutment. A distal rest would act as a fulcrum, torquing the abutment and transmitting destructive tipping forces to it.
• C. Canine cingulum rests function as INDIRECT retainers in this design, resisting rotation of the extension bases away from the ridge. They are not the primary occlusal rests on the terminal abutments.
• D. Teeth 20 and 29 are the second premolars adjacent to the edentulous areas, and they are the terminal abutments — not the first premolars.

Note: The RPI system (mesial Rest, distal Proximal plate, I-bar) exists precisely for this situation. Distal-extension rule: MESIAL rest on the terminal abutment; indirect retainers placed anteriorly, across the fulcrum line from the extension base.