Altered cast technique for distal extension RPD’s.
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Basic goals of very prothesis are the replacement of missing teeth, and the restoration of function, occlusion and aesthetics. The distal extension removable partial denture (RPD) is potentially capable of causing damage to the remaining dentition and edentulous ridges, and impairment of the health of the temporomandibular joints, mainly due to the disparity of support exhibited by the different supporting tissues. These are the abutment teeth (which are relatively rigid), and the oral mucosa (which isrelatively resilient).During functional loading, the mucosa is displaced faster and for longer time than the periodontal ligament of the abutment teeth. Thus, when a vertical load is applied to the denture base, a class I lever is created, the fulcrum of which lies on the occlusal rest nearest to the distead extension of the RPD. Thus, the denture, rotating around the distal abutment, induces heavy stress on the residual ridge and the abutment teeth.This paper describes the rationale and the procedure of the altered cast technique, which applies some of the principles of impressions for complete dentures, to the fabrication of the tissue surfaces of the RPD. The metal framework is constructed first, and while is firmly seated on the teeth, the soft tissues of the residual ridges are recorded, in the shape that they would take during functional loading. This is achieved by the viscosity of the impression material, and not by arbitary finger loading. This impression is used to alter the edentulous areas of the master cast. Subsequently, the resultant cast reproduces accurately the supporting tissues, in a form that provides the correct extension of the denture base and diminishes the tissue overload, when the denture is in its fully seated position. This technique results in an RPD which has very good stability, minute moving potential and reduced stresses on abutment teeth and residual bone.
Journal of Contemporary Dentistry