VALUE OF GUIDE PLANES IN PARTIAL DENTURE RETENTION

The retention of five nominally identical partial denture castings 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 < 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.