A laboratory investigation of the role of guide planes in the retention of cast cobalt-chromium alloy partial denture frameworks

Objectives: This in vitro study examined the resistance to displacement offered by guide planes and the displacement mechanics of a bilateral bounded saddle cast cobalt chrome alloy removable partial denture framework under conditions simulating an average initial fit. Methods: A specially designed model mouth jig fitted with strain gauges to monitor the forces across the guiding plane/guiding surface interfaces was used. Guiding planes of enamel, silver tin amalgam and dental composite with seven combinations of guide planes and three angles of withdrawal were examined. Guiding plane size was also examined for dental enamel. Results: A statistically significant difference in retention was found for all factors examined. Retention increased with increasing angle of withdrawal. Size effects were found but considered unreliable. Conclusions: It was concluded that with a tight fit guiding plane retention may be readily predicted for any given material, combination of mesial, distal and lingual guiding planes and angulation conditions by the application of mechanical principles providing the basic parameters are known. Attention is drawn to the reasons for further work to fully understand the clinical situation.