Influence of rigidity of retainers on dynamic behavior of implant-supported removable partial dentures

Abstract

Background: Implant-supported removable partial dentures (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. However, the effect of a type of direct retainer on displacement of the abutment teeth and dentures in ISRPDs remains unclear. Therefore, we made 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.

Methods: A resin mandibular model for mechanical simulation that had unilateral mandibular distal-extension edentulism and was missing the first molar, second molar, first premolar, and second premolar, and a denture fabricated from the patient's computed tomography images were used. Three types of direct retainers with different connecting rigidities were evaluated. The vertical displacement of the denture base and buccal and lingual sides and the mesial displacement of the abutment teeth were measured.

Results: Regardless of the rigidity of the direct retainers and loading positions, the displacement of the denture bases in the ISRPDs was significantly smaller than that in the RPDs (P < 0.001). There was no significant difference in vertical displacement of the denture bases among direct retainers with various connecting rigidities in the ISRPDs. Conversely, 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.

Conclusion: Our results suggested 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.

Keywords: Direct retainers; Dynamic behavior; Implant-supported partial dentures; Removable partial dentures; Rigidity of connection.

Fig. 1

Fabrication process of the resin mandibular model for mechanical simulation and denture

Fig. 2

Schematic illustration of a mandibular experimental distal-extension removable partial denture

Fig. 3

Schematic illustration of the three different types of direct retainers used to evaluate rigidity

Fig. 4

Schematic illustration of the resin mandibular model for mechanical simulation and denture

Fig. 5

Load displacement curve for the artificial periodontal ligament. Black circles indicate data from the preliminary examination of the artificial periodontal ligament in this study; white circles indicate data from Parfitt GJ (1960) [38]

Fig. 6

Load displacement curve for the simulated mucosa. Black circles indicate data for the preliminary examination of the simulated mucosa in this study; white circles indicate data from Kishi M (1972) [39]

Fig. 7

Amount of vertical displacement at the end of the denture base. Data are expressed as the mean displacement at the end of the denture base of each direct retainer, and error bars represent the standard deviation

Fig. 8

Displacement at the direct abutment teeth. Data are expressed as the mean displacement at the direct abutment teeth of each direct retainer, and error bars represent the standard deviation