ISRPDs are an effective treatment for partially edentulous patients. ISRPDs improve patients’ satisfaction and oral function to a greater extent than RPDs by improving denture stability and enhancing support. The effect of a type of direct retainer remains unclear. This study was done to make a resin mandibular model of unilateral mandibular distal-extension partial edentulism for mechanical simulation and compared the dynamic behavior of the abutment teeth and the denture base among different tooth-borne retainers with various rigidities for RPDs and ISRPDs.

The displacement of the denture bases in the ISRPDs was significantly smaller than that in the RPDs. There was no significant difference in vertical displacement of the denture bases among direct retainers with various connecting rigidities in the ISRPDs. The horizontal displacement of the abutment teeth in both the RPDs and ISRPDs tended to be larger with the cone crown telescope, which has high rigidity, than with the cast cingulum rest and wire clasp, which have much lower rigidities.

This study concluded that cast cingulum rest and wire clasps as direct retainers are appropriate ISRPDs to minimize denture movement and suppress displacement of the remaining teeth in patients with unilateral mandibular distal-extension partial edentulism.