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5. Prosthodontic Instruments


a. Impression Tray. Impression trays (figure 5-1) are carriers for the material used in making impressions of the teeth, alveolar ridges, and adjacent structures. They are manufactured in various sizes and shapes to accommodate the size and shape of the arch, the type of impression material to be used, and the impression technique to be followed.

Figure 5-1. Impression trays.

(1) Edentulous impression trays. Two types of edentulous impression trays are available. One type is for use with modeling plastic or compound and is made of a pliable metal alloy, which can be shaped by bending and cutting to fit the individual patient. Mandibular tray sizes are Nos. 51, 53, and 46. Maxillary tray sizes are Nos. 41 and 45. The second type is for use with hydrocolloid impression material and is made with rimmed borders to retain the impressions] material. Sizes available are small, medium, medium large, and large. Both types of trays are used for impressions when no teeth remain in the arch.

(2) Dentulous impression trays. These trays are made with rimmed borders to retain the impression material in the tray when the impression is removed from the mouth. Trays can be bent, within limits, to accommodate either a wide arch or a narrow arch, but they should not be cut. They are available in small, medium, medium large, large, extra large, and extra-extra large sizes for both maxillary and mandibular impressions. They are used when teeth are present in the arch.

(3) Orthodontic impression trays. These trays have deeper flanges than the standard edentulous trays. They are provided in large, medium, medium-small, and small sizes for maxillary impressions and in large, medium, and small sizes for mandibular impressions.

(4) Partial impression trays. Partial impression trays are provided in three designs for making impressions of anterior portions of the dental arch. The designs are maxillary anterior medium, maxillary anterior small, and mandibular anterior.

(5) Crown and bridge tray. A single-size crown and bridge tray is adaptable for making impressions of a small segment in any location of either arch.

(6) Custom acrylic trays. Often the procedure performed requires impression trays constructed especially for the patient being treated. The custom-made trays are made from self-curing acrylic resin and constructed by a dental laboratory specialist. The custom acrylic trays obtain an accurate impression of edentulous and partially edentulous dental arches by maintaining a uniform thickness (I to 2 mm) of the impression material. Custom acrylic trays may be used during treatment requiring construction of complete dentures, removable partial dentures, or fixed partial dentures.

b. Alcohol Torch. The alcohol blowtorch (figure 5-2) is designed to be held and operated in one hand. It has a plunger which, when pushed in, ejects a stream of air to produce a pinpoint flame which is useful in applying heat to small, localized areas of wax, modeling plastic, or other material. Either ethyl or methyl alcohol may be used for fuel.

Figure 5-2. Alcohol blowtorch.

c. Compound Heater. The compound heater (figure 5-3) is an electrically operated water bath used to soften modeling plastic. Temperature of water is controlled thermostatically.

Figure 5-3. Dental impression compound water bath.

d. Spatulas. Spatulas are used for mixing impression material and artificial stone and heating and manipulating wax. Laboratory spatulas are made of hard rubber or of metal with wooden handles (figures 2-10 and 2-11).

e. Plaster Bowls. Plaster bowls are made of rubber and are used for mixing impression materials, plaster, stone, and investment materials. They are available in four sizes: extra large, large, medium, and small.

f. Mold and Shade Guides. Denture teeth and facings are made in a variety of sizes, forms, and shades by many tooth manufacturers. Size and form are identified by letter or number as are the shades. Mold and shade guides (figure 5-4) are available for denture teeth and facings as special purchase items.

Figure 5-4.Shade guide.

g. Millimeter Gauge. The millimeter (Boley) gauge (figure 5-5) is a measuring instrument calibrated in tenths of millimeters. It is used in prosthodontics for determining tooth dimensions and making other measurements.

Figure 5-5. Millimeter (Boley) gauge.

h. Articulators. An articulator is a mechanical device, which represents the temporomandibular joints and jaw members to which maxillary and mandibular casts may be attached. Articulators are classed as nonadjustable and adjustable.

(1) Nonadjustable. This articulator permits opening, closing, protrusive and lateral movements at a fixed, average inclination. Example: Stephan Model Plainline (figure 5-6).

Figure 5-6. Nonadjustable articulators.

(2) Adjustable. This articulator permits opening, closing movements and adjustment of condylar elements that can be set to accept a protrusive record. Example: Hanau Model H (figure 5-7).

Figure 5-7. Adjustable (Hanau) articulator.

i. Face Bow. The face bow (figure 5-8) is an instrument used to register and record the positional relationship of a patient's maxillae to his temporomandibular joints, and to mount a cast of his maxillary arch in the same relationship to the hinge axis of an articulator. The face bow is fitted with a bite fork that is used to attach the face bow to the upper occlusion rim.

Figure 5-8. Face bow with bite fork.

j. Needle Point Tracer. The needle point-tracer (figure 5-9) is a mechanical device used to indicate or record the direction and extent of movements of the mandible. It is also used to indicate the relative horizontal position of the mandible to the maxilla.

Figure 5-9. Needle point-tracer.

k. Compound Knife. The compound knife is useful in trimming modeling plastic, impression materials, and waxes. Its handle is designed to accept interchangeable blades.

l. Mounted and Unmounted Stones, Points and Abrasive Disks. These motor-driven rotary cutting and abrasive instruments are used in modifying natural teeth and adjusting and finishing dentures.

David L. Heiserman, Editor

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Revised: June 06, 2015