A terminal abutment tooth for an RPD has a DISTAL rest and develops grade III mobility over time. What modification SHOULD HAVE BEEN made during initial design?

Correct answer: B. Use a mesial rest instead of a distal rest

• A. Extending the denture base increases mucosal support but does not correct the destructive force vector from a distal rest.
• B. For a distal extension RPD (Kennedy Class I or II), using a DISTAL rest on the terminal abutment directs rotational forces toward the distal of the tooth, leveraging the abutment and causing it to tip/become mobile over time. A MESIAL rest is biomechanically superior — it allows the denture base to sink slightly under load without torquing the abutment. This is a fundamental RPD biomechanics principle. ✓
• C. A wrought wire clasp provides flexible retention but does not change the rotational mechanics created by a distal rest on a terminal abutment.
• D. A precision attachment may help retention but still does not address the fundamental problem of force direction on the terminal abutment.