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5. Prosthodontic Instruments


a. Appointments. Most complete denture techniques require five appointments. On the first appointment, the patient is examined and preliminary impressions are made. The purpose of this is to evaluate the patient and to plan treatment. Diagnostic casts are poured from the preliminary impressions. On the second appointment, final impressions are completed from which the master cast is poured. The purpose of this procedure is to fabricate accurate casts upon which the dentures will be made. On the third appointment, jaw relationship registrations are made for transferring from the patient to the articulator all the positions and information necessary to fabricate the dentures. On the fourth appointment, the trial denture is evaluated in the patient's mouth and on the articulator for esthetics, occlusion, and denture base contour. On the fifth appointment, the finished dentures are inserted into the patient's mouth. At this time, the dentures are adjusted for fit and occlusion and the patient is instructed in their use and maintenance and in oral health care. One or more subsequent appointments may be given for adjustment and evaluation of the dentures. Dental appointment systems vary from one clinic to another and can vary from one service to another service of the same clinic. Usually, the prosthodontic section has its own appointment system because the prosthodontist needs flexibility in determining the time needed for each appointment and a series of appointments works out well for prosthodontic procedures. The dental specialist must know the procedures and routines of the particular prosthodontist. A well-planned appointment schedule can increase the efficiency of the prosthodontic service.

b. Impressions. Impressions for complete dentures include all the teeth, alveolar ridges, and areas of muscle attachment in a single jaw. The type of impression material used will depend upon the purpose for which the impression is to be used, the impression technique to be employed, and the preference of the dental officer. The Subcourse MD0502, Dental Clinical Materials, discusses the properties, uses, and manipulation of impression materials. Examples of typical instruments and materials used and a description of the dental specialist's duties in impression procedures follow. Preliminary impressions are used to construct study models before fabricating complete dentures. Final impressions are used to construct the master cast upon which the denture is fabricated.

(1) Preliminary impressions. Irreversible hydrocolloid is the most commonly used material for making preliminary impressions. Figure 5-10 depicts instruments and materials used for irreversible hydrocolloid impressions.

(a) When irreversible hydrocolloid is used, the dental specialist prepares the impression material in strict accordance with the manufacturer's instructions. During its manipulation, the assistant should prevent the entrapment of air bubbles in the material by sifting the powder into the water, by using a stirring rather than a whipping motion, and by spreading the mix around the walls of the mixing bowl just before completion. Mixing should be done in the time specified by the manufacturer. After the material is mixed, the impression tray is filled, the excess material in the bowl is presented to the dental officer, and then the filled tray is passed to the dental officer who will make the impression.


Figure 5-10. Instruments and materials for irreversible hydrocolloid impressions.

(b) Modeling plastic may also be used for making preliminary impressions. Figure 5-11 depicts instruments and materials used for modeling plastic impressions. In using modeling plastic, the dental specialist should lubricate the edentulous tray (selected by the dental officer) with petrolatum. The compound beater is filled with enough water to cover the compound, and the heating element is adjusted to the proper temperature. After the modeling plastic has softened in the water bath, the lubricated tray is loaded. For maxillary impressions, the material is rolled into a ball and formed into the maxillary tray. For mandibular impressions, the material is rolled into a cylindrical shape and formed into the mandibular tray. After brush flaming and tempering of the material, the tray is passed to the dental officer who makes the impression. After the dental officer positions the tray in the mouth, the dental specialist may help speed the set of the modeling plastic by spraying cool water from the water syringe over the tray containing the material. If this is done, the saliva ejector is used to remove water as it collects in the patient's mouth.

Figure 5-11. Instruments and materials for modeling plastic impressions.

(2) Final impressions. The final impression is used to produce the master cast upon which the denture is fabricated. The tray used for final impressions is made of an acrylic resin material that is custom-made on the cast produced from the preliminary impressions. This tray is adjusted to the patient's mouth by selective grinding. The borders are molded with modeling plastic to clearly define the soft tissue border and other landmarks, such as muscle attachments, frenum, and posterior palatal seal area. The molded tray is used to carry the final impression material, a rubber-base (polysulfide base) material, or a zinc oxide and eugenol paste (metallic oxide impression) material, to place in the mouth. This impression should include the denture supporting area and the denture border area. Figure 5-12 depicts instruments and materials used for final impressions.

Figure 5-12. Instruments and materials for final impressions for complete dentures.

(3) Specific duties of the dental specialist. The dental specialist has specific duties in regard to the preparation of complete dentures. The dental specialist:

(a) Prepares the impression material according to the manufacturer's instructions.

(b) Coats the patient's lips and surrounding area with petrolatum before impressions are made to facilitate the removal of impression material.

(c) Cleans the instruments used to prepare the impression material before the material hardens on these instruments.

(d) Cleans any material from the patient's face and mouth after the impression has been removed. Oil of orange or oil of lemon is a good solvent for removing zinc oxide and eugenol impression pastes and rubber-base materials.

(e) Cares for the resulting impression by carefully handling the impression to avoid distortion or damage to tissue and peripheral areas of the impression.

(f) Washes the impression with cool water or cool slurry water (a solution of water and artificial stone or plaster of Paris) to remove saliva.

(g) Pours the master cast from which the complete denture is to be fabricated, if a dental laboratory specialist is not assigned to the clinic.

David L. Heiserman, Editor

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Revised: June 06, 2015