Semiprecision rest system for distal-extension removable partial dentures

The history of the nonlocking type of intracoronal semiprecision rest has been traced from its origins with Neurohr in 1930, up to its present use as the Thompson dowel rest. The advantages of the use of this deep rest design and the clasp arm design for primary retention have been discussed. The Blatterfein modification of the lingual clasp arm has been introduced to overcome the problems of breakage and lack of stabilization which are present with the Thompson, Van Dam, and Wands designs.