RPD Review Questions
The plating must end exactly at the survey line (height of contour).
If the plating ends below the survey line, there will be a space between the superior edge of the plating and the tooth creating a food trap. In addition, the edge of the plating will stand away from the tooth and may be irritating to the tongue.
If the plating ends above the survey line, it will pre-empt the mesial rest. The axis of rotation will pass through the plating instead of the rest. The I-bar will contact the tooth in front of this "new" axis of rotation and will engage the tooth when the extension base moves toward the residual ridge. Also, since the plating will act like a rest on an inclined plane, there will be the tendency to push the tooth toward the facial during function.
The fact that the plating must end exactly on the survey line makes framework fabrication much more difficult for the laboratory technician. Therefore, whenever possible, avoid plating terminal abutments on distal extension RPDs.