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Clasp retention: the effects of five variables
1Department of Removable Prosthodontics, School of Dentistry, University of the Pacific, San Francisco, CA.
Summary
The RPA clasp offered the most retention for removable partial dentures on natural teeth, while the Akers clasp was most effective on gold abutments. Natural tooth structure provided superior retention compared to gold surfaces.
Area of Science:
- Dental Prosthetics
- Biomaterials Science
- Biomechanics
Background:
- Removable partial dentures (RPDs) are crucial for restoring function and aesthetics.
- Clasp assemblies are key components influencing RPD retention and stability.
- Understanding the relative retentive forces of different clasp designs is essential for optimal prosthetic outcomes.
Purpose of the Study:
- To compare the retentive forces of four common clasp assemblies: RPI, RPA, modified T, and Akers.
- To evaluate clasp retention on both natural teeth and gold abutments.
- To assess the influence of environmental factors (wet/dry) and indirect retainers on clasp effectiveness.
Main Methods:
- Fabricated a mandibular bilateral distal extension RPD test model using a Dentoform with natural teeth and gold crowns.
- Constructed eight RPDs with the four clasp types and processed them to frameworks.
- Utilized an Instron testing machine to measure retentive forces in vertical and mesio-occlusal directions.
Main Results:
- The RPA clasp demonstrated the highest retention on natural abutments in both pull directions.
- The Akers clasp exhibited the greatest retention against mesio-occlusal pull on gold abutments.
- Natural tooth structure provided slightly greater frictional resistance than gold crowns.
Conclusions:
- The RPA clasp is highly effective for retaining RPDs on natural teeth.
- Clasp selection should consider abutment material (natural tooth vs. gold) and direction of dislodging forces.
- Further research may explore long-term clinical performance and patient satisfaction with these clasp designs.