Indications:

Contraindications:

Where maximum retention is required.
If edentulous areas do not exist allowing clasps to be hidden (i.e., single central or single lateral).

It is suggested that study models be sent to laboratory for pre-planning and computerized prosthesis design.
You will be provided with a duplicate model on which a survey and design has been outlined with rest preparation suggestions highlighted in a green colour. You can request that a custom tray be provided along with the survey and design recommendation.

A. Tooth Borne Designs

Place occlusal rests on the tooth surface of the anterior and posterior abutments adjacent to the saddle area, using an oval or football shaped diamond. Rest preparations should be spoon shaped.
Prepare a guide plane gingival to the occlusal rest on the proximal surface by flattening the occlusal 1/3 of the proximal wall without eliminating the necessary undercut (Figure 1).

B. Posterior Distal Free-End Saddle

Prepare a spoon shaped occlusal rest in the mesial fossa of the abutment tooth. This preparation should be “lingualized” (i.e., remove the lingual portion of the mesial marginal ridge adjacent to the prepared rest) so the minor connector will not contact the tooth immediately anterior to the abutment where the appliance is seated.
Prepare a guide plane on the mesial surface that connects with the prepared rest (Figure 2). The buccal extension of the guide plane should stop at the buccal extension of the occlusal rest. The mesial guide plane is prepared without breaking contact with the adjacent teeth. Buccal-lingual 1/3 contact is maintained.
On the distal surface, just over the marginal ridge, prepare a guide plane by slightly flattening the occlusal 1/3 of the distal proximal surface (Figure 2).
If resiliency is desired, it can be accomplished by eliminating the distal occlusal rest. The mesial rest remains.

Take a single phase vinyl polysiloxane impression (e.g., Panasil or 3M Imprint). A stock tray is satisfactory but use plenty of material. A light bodied wash of the prepared teeth is helpful in providing more detail.
Take and pour an alginate impression of the opposing arch. Provide an accurate interocclusal record (Futar Occlusion or Regisil).
Ensure impression extends into the retro-molar areas of distal extension cases. Before final impressions are recorded, minor tooth preparation is recommended. Slightly flatten the occlusal 1/3 of the proximal wall of abutments, adjacent to the edentulous saddle, to enhance guide planning. Also allows the technician to place the clasp further apically and closer to the rotational axis of abutment.

For Preparation

Oval or football shaped diamond for rest preparations, fine grit tapered diamond for guide preparation
556 Bur
Finishing Disks

For Impressions