Symposium on semiprecision attachments in removable partial dentures. Laboratory procedures.

The fabrication of semiprecision rest systems will differ depending on whether a prefabricated rest system or milled-in rest system is indicated. In a prefabricated rest seat, a die-related model must be used and the rest seats must be waxed into the wax pattern. A means of fabricating both locking and nonlocking rests has been described. The instruments and tools necessary for the milled-in rest seat have been illustrated. The need for a stress-releasing attachment for distal-extension removable partial dentures is satisfied by the Thompson dowel rest. In fabricating the Thompson dowel rest prosthesis, both vertical parallelism and horizontal parallelism are essential for rotation. The use of a parallelometer and the parallel rule insures precise positioning of the Thompson dowel rest, which in turn, will enable the distal extension partial to rotate.