10-22. Designs for Removable Partial

Denture Bases

a. Metal and Heat-Polymerized acrylic Resin.

(1) Indications. This type of base is used in cases with long spans, in recent extraction cases when it is anticipated that rebasing will be required in a relatively short time, in cases where acrylic resin will restore needed facial contours more satisfactorily than metal, and when there is ample interarch distance.

(2) Structural details.

(a) There must be adequate bulk and strength in the metal at the junction of the base and the major connector.

(b) Metal tissue stops must be used when the denture base has a distal extension. The tissue stop holds the end of the framework in position, preventing it from settling toward the ridge while the acrylic resin is being packed into the mold.

(c) The top horizontal bar of the retention mesh is designed lingual to the crest of the ridge in most instances. The top brace is never placed on the crest of the ridge because it would act as a wedge on the acrylic resin and fracture it.

(d) A preformed plastic screen mesh can be used, but with this material it is difficult to set the denture teeth in the edentulous space, to apply the separating material, and to pack acrylic resin if the framework is held in the lower-half flask during flasking operations (A, fig 10-30).

(e) A double bar retentive mesh made of 12-gage and 14-gage half-round wax shapes is stronger than the preformed plastic screen mesh (B, fig 10-30).

b. Metal and Autopolymerized Acrylic Resin.

(1) Indications. This type of denture base is used at the discretion of the dental officer when esthetics is a factor. It may also be used when small spaces between natural teeth create a replacement problem with a denture tooth.

(2) Types.

(a) Tooth acrylic butt (TAB). For this type a post is used to retain an anterior acrylic resin tooth. It should stand parallel with the long axes of the teeth adjacent to the space to insure adequate bulk of acrylic resin on facial and lingual sides of the post (A, fig 10-31).

(b) Hollow metal pontic. For this type a hollow metal pontic is used to retain the acrylic resin. Its margins should be kept as thin as possible (B, fig 10-31). The acrylic resin is contoured facially to keep the metal margins inconspicuous.

of medium hard pink baseplate wax together in a suitable container. The blockout attachment is mounted in the surveyor spindle and used to contour the wax and remove any excess (B, fig 10-33).

(a) The parallel blockout attachment is used to create parallelism in the desired areas.

(b) The tapered blockout attachments are used to obtain a tapered surface on each of the proximal surfaces of the teeth adjacent to an edentulous space, when there is an abutment at each end of the space. The degrees of taper vary from 2° to 6°. The 6° tapered blockout attachment is used on short teeth. The 2° attachment is used on medium and long abutment teeth.

(2) The blockout procedure must be performed with the cast properly mounted on the surveyor table in the same plane at which it was surveyed. None of the blockout wax is permitted to remain occlusal to the survey lines. The cast should not be moved or changed during this procedure.

(3) Ledging the abutment teeth is the next step. The purpose of ledging is to prepare the blockout wax on the abutment teeth so that there is a positive control of the amount of undercut that will be engaged by the clasp tips. Ledging involves the following steps.

(a) Blockout wax is placed in the undercuts of each abutment tooth (B, fig 10-34). It is then trimmed with a paralleling attachment (C, fig 10-34).

(b) A ledge is cut in the wax on each tooth on the exact position that the retentive clasp tip is to occupy (D, fig 10-34). The appropriate undercut gage is used to verify this position. The width of the ledge is an exact measurement of the amount that the clasp must flex as it slips over the bulge of the tooth when the prosthesis is inserted or removed from the mouth. After the master cast has been duplicated, the ledges will be reproduced in the investment cast and the clasps will be contoured to these guides.

10-24. Blockout and Relief for Maxillary

Major Connector

a. When the connector is to be designed to extend onto the lingual surfaces of the maxillary anterior teeth, it must not be placed in an undercut. A survey line is marked on each tooth to be contacted. Wax is added to the areas gingival to the line and trimmed with blockout attachment

A. ADDING WAX TO UNDESIRABLE UNDERCUTS.

B. BLOCKOUT WAX APPLIED AND
TRIMMED TO SURVEY LINES.

Figure 10-35. Blockout and relief for maxillary major

connector.

10-25. Blockout and Relief for Mandibular

Major Connector

a. The same general principles apply to the blockout and relief procedures for mandibular major connectors that apply to maxillary major connectors. Typical blockout and relief patterns

B. BLOCKOUT WAX APPLIED AND TRIMMED TO SURVEY LINES.

Figure 10-36. Blockout and relief for a mandibular major connector.

b. Soft tissue undercuts and mandibular tori require additional relief (A and B, fig 10-37).

10-26. Relief in Denture Base Areas

The acrylic resin denture base supporting the denture teeth will be attached to the metal framework overlying the edentulous area. These areas must be relieved on the master cast. This will raise the retentive mesh of the framework above the cast and allow the acrylic resin to flow under the framework during the processing step. Two thicknesses of 28-gage casting wax are placed in the desired areas. Twenty-four gage adhesive coated casting wax is sometimes used for this purpose. If the bases are of the distal extension