Photoelastic analysis and comparison of force-transmission characteristics of intracoronal attachments with clasp distal-extension removable partial dentures.

This investigation photoelastically compared the load-transfer characteristics of various bilateral distal-extension removable partial denture designs embodying intracoronal attachments and clasp assemblies. Six distal-extension designs that included the RPI clasp assembly, cast circumferential clasp, P.D. locking semiprecision, Thompson dowel nonlocking semiprecision, and McCollum and Stern G/L precision attachments were tested. Each prosthesis was subjected to various simulated occlusal loads. Evaluation of the load-transfer characteristics of the various designs was based on comparison of the recorded isochromatic fringe distributions. The RPI clasp assembly generated the most uniform stresses. In general, the four intracoronal retainer frameworks produced higher stresses than did the two clasp frameworks. The highest stresses were developed by the Stern G/L precision attachment.