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Altered Cast Technique

Free end saddles are liable to be displaced under occlusal pressure (anteroposterior rocking around the abutment tooth, which acts as a pivot). This is as a result of the displaceability of the mucosa of the free end saddle. The altered cast technique was a popular technique that was introduced in an attempt to overcome the problem. The metal framework is constructed and light or self cured acrylic material is placed on the framework in the saddle areas creating a close fitting customised tray over the saddle areas. Zinc oxide eugenol or low viscosity silicone is then placed in the customised tray and the framework is placed into the mouth and the impression taken with pressure only on the support elements of the framework resting on teeth. The laboratory then alter the cast (remove the free end saddle), place the metal framework on the cast, invert the cast and framework and pour dental stone to complete the cast.

A clinical trial by Frank et al (2004) showed that there was no difference in patient satisfaction, stablility or retention between partial dentures made by either technique.  Therefore this interesting clinical technique is now one for the prosthetic history books.

Frank RP, Brudvik JS, Noonan CJ. Clinical outcome of the altered cast impression procedure compared with use of a one-piece cast. J Prosthet Dent. 2004;91:468-76.

Lower cast sectioned as per the altered cast technique

Framework on the cast after the new impression has been cast
A cast has been sectioned prior to pouring up of the free end saddle on the left hand side of the mouth New free end saddle has been poured up in stone on the original cast

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