Value of guide planes in partial denture retention.

The retention of five nominally identical partial denture casting fitted to a master model was measured on an Instron testing machine in the direction of the guide planes and also at angles inclined to them. It was found that: the maximum retention was considerably reduced when the clasps were removed; the guide planes offered some frictional resistance to displacement, the magnitude being critically dependent on the fit; for frameworks with or without clasps a significant increase (P less than 0.01) in retention occurred when the pull was at 22 degrees but not at 12 degrees to the guide planes, and that there was no statistically significant difference between the retention in the forward and backward directions for either a 12 degrees or a 22 degrees tilt of the dislodging force.