The altered cast technique Dr.shanai

The residual ridge may be said to have two forms: the anatomic form and the functional form . The anatomic form is the surface contour of the ridge when it is not supporting an occlusal load. The functional form of the residual ridge is the surface contour of the ridge when it is supporting a functional load. The anatomic form is recorded by a soft impression material, such as a metallic oxide impression paste anatomic form: It is the shape of the ridge before functional load is applied. functional form: It is the shape of the ridge after functional load is applied.

Impression materials cannot record anatomic form of the teeth and functional form of the soft tissue in a functional relationship all at the same time. To achieve these objectives, the altered cast technique can be used. This technique is a secondary impression system which utilizes the metal framework to hold customized impression trays for the edentulous area. A favorably extended base will provide stimulation to the underlying bone and distribute forces uniformly. The altered cast technique allows the ridge, recorded in functional form, to be related to the teeth so that when the prosthesis is seated, it derives support simultaneously from the teeth and the denture base. The objectives of the altered cast technique are to obtain the maximum possible support from the distal extension base of the RPD and to accurately relate the soft tissue surface of the denture base to the metal framework.

Distal extension removable partial dentures (RPD's) derive their support from the abutment teeth and the mucosal tissues overlaying the residual alveolar process. There are differing philosophies in the scientific literature regarding how much support should be provided by the abutment teeth and how much support should be provided by the soft tissues. However, there is consensus that: occlusal stress should be shared by both in such a manner that neither the abutment teeth nor the residual ridge is abused; accurate fit of the denture base is an important factor in minimizing stress on the abutment teeth; stability of the prosthesis is the most important requirement for proper function and patient comfort.

Important points to remember concerning removable partial dentures: In order to determine whether the alveolar bone is capable of withstanding occlusal forces of a removable partial denture, an x-ray should be taken of the abutment teeth and the bone level surrounding these teeth should be evaluated. Periodontal health of the abutment teeth and maintaining the health of the supporting tissues is best achieved by maintaining tissue support (preserving denture bone support) of the edentulous areas. The total occlusal load applied to an RPD is influenced by the occlusal surface area, occlusal efficiency and the number of existing teeth.

Step by step procedure of altered cast technique Stage 1 Maxillary and mandibular impressions were obtained using irreversible hydrocolloid and upper and lower study casts were obtained. Study casts were placed on stage of dental surveyor and surveying was carried out after which the design of the cast metal framework was finalized.

Stage 2 Mouth preparation was done intraorally and final impressions of both the arches were recorded using medium bodied addition cured silicone using custom made trays. Master casts were obtained and designed finalized. Investing and casting procedures were performed in the laboratory and the completed framework was checked to ensure that it fits the casts accurately.

Stage 3 The cast metal framework was tried intraorally for accuracy of fit and once this was done, an acrylic resin custom made trays were fabricated to the mandibular framework. Border molding was performed using green stick tracing compound. Tray adhesive was applied over the impression surface of the tray and the final impression was taken using light bodied silicone. During seating of the loaded tray, gentile finger pressure was applied over the framework which only come in contact with teeth and not to the tray it self. It was ensured that the framework remained stable and did not move until the impression material was set.

Stage4: This was the stage when cast was altered in the laboratory. Beading of the final impression was done and saw cuts on the cast were made perpendicular the saddle areas. Grooves were placed on the cut surface of the cast so that retention of the newly poured stone could be improved. The framework seated completely on the cast, fixed using sticky was and boxing procedure was performed The final impression was poured using die stone and the working altered cast was removed The usual remaining steps of denture fabrication were carried out, denture was delivered to the patient and post operative instructions were given