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. The altered cast technique is employed to try and prevent this by taking an impression of the mucosa under controlled pressure. The metal framework is constructed on a cast produced by a mucostatic impression material, usually alginate. Baseplates are then constructed in self-cured acrylics on the framework in the saddle areas, these are close fitting. Impression paste or a medium viscosity silicone paste is then applied to the fitting surface of the self-cured acrylic. The denture is then inserted in place, held in place by the framework only, no finger pressure is applied as this would lead to over displacement of the mucosa. Border moulding is then carried out as the is impression material is setting.

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1) A cast has been sectioned prior to pouring up of the free end saddle on the right hand side of the mouth.

2) New free end saddle has been poured up in stone on the original cast

In the laboratory, the free end saddle areas on the master cast are sectioned off. The denture is then positioned on the model and the new saddle areas are poured. The resulting model represents the free end saddle areas under conditions, which mimic functional load. Denture construction then continues as normal. The distribution of loading of the free end saddles is improved and denture is more stable.

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3) Wax try-in constructed on the new free end saddle