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Section III. INVESTING, SOLDERING, AND FINISHING THE FRAMEWORK

11-11. Assembling the Components

If the metal parts are to be soldered with gas-air torch, they must be transferred to the investment cast. The artificial stone working cast cannot withstand the heat of the torch.

a. Adaptation of Platinum Foil. A small piece of platinum foil is adapted in the rest seat of each prepared abutment tooth on the investment cast. The foil should be slightly larger in area than the rest preparation and should extend onto the proximal surface of the tooth below the body of the clasp. The adaptation can be done easily by using a small burnisher or a sharpened pencil eraser (A, fig 11-6).

b. Placing the Clasps. When the clasps are placed on the teeth, care must be taken not to dislodge the platinum foil.

c. Placing the Lingual Bar. Since the lingual bar was contoured to fit the adhesive tape relief on the working cast, there will be a slight space between its ends and the posterior lingual segments of the investment cast. If it is braced against the anterior lingual section of the investment cast with one finger, it can be tacked to its proper position with a small amount of sticky wax and the slight relief space will be maintained (B, fig 11-6).

d. Placing the Minor Connectors. These parts are attached to the clasps and lingual bar with sticky wax. Additional sticky wax is applied to build up the occlusal rests but the edges of the platinum foil are left exposed. Bulk is added to the body of the clasp and wax is flowed under it wherever necessary to fill the space (C, fig 11-6). e. Checking the Assembly. The entire assembly is checked for stability and correct positioning of the components.

11-12. Investing the Assembly

The assembly is invested by the following steps: a. The cast is moistened, but not excessively. b. A small amount of investment is mixed to a soupy consistency.

c. The lingual bar, clasps, edges of the platinum foil, and minor connectors are covered with the investment material except in small areas where the parts are to be joined. Wax points are left exposed (fig 11-7).

11-13. Minor Connector to be Joined

Directly to Denture Base

If the clasp is to be processed directly to the denture base material and not soldered to a major

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Figure 11-7. Components covered with investment. connector, a plate or loop attachment may be used (A, fig 11-8). A hole in the plate or a loop in the wire will secure that end of the connector in the acrylic resin denture base material after the case has been processed. The clasp parts for soldering are assembled as follows:

a. A piece of platinum foil is burnished into the rest area of the working cast, extending it beyond the rest in all directions and down the proximal surface below the body of the clasp (B, fig 11-8).

b. The clasp and connectors are positioned over the foil and fixed with sticky wax (C, fig 11-8). They are then ready to be invested for soldering. The clasp assembly is very carefully teased off the cast and placed in a paddy of soldering investment. The edges of the foil are covered to hold it in position during soldering.

11-14. Soldering

Soldering is the process of joining two pieces of metal by means of a third piece of metal whose melting range is lower than those of the two being joined. Dental soldering is done with either a gas-air torch or an electric soldering machine.

11-15. Soldering with Gas-Air Torch

a. Rules. Five rules must be observed to solder successfully.

(1) Cleanliness. The metals to be joined must be absolutely clean of wax and free from oxides. Pickling in an acid or filing with a revolving stone in the handpiece or lathe will remove any surface contaminants.

(2) Contact. The parts to be joined should be in contact with each other. (Exceptions to this rule are that most soldering techniques used in

B. PLATINUM FOIL BURNISHED INTO THE OCCLUSAL REST AREA.

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