Is Objectives And Procedures

The objectives and procedures for finishing are different for each part of the cast restoration. The following discussion is sequentially divided into corresponding phases; each are identified as zones (Fig. 29-1).

ZONE 1: INTERNAL MARGIN

Objective. To minimize any dissolution of the luting agent, a 1-mm-wide band of metal must be obtained that is closely adapted to the tooth surface.' A defect within this zone can significantly reduce a restoration's longevity. Good adaptation is obtained by carefully reflowing the wax pattern (Fig. 29-2). With careful standardization of technique, the dentist can achieve predictable and consistent results.

Procedure. If a defect occurs in the marginal area, the restoration will have to be remade. This may require an additional patient visit to make the new impression. Defects can be prevented or minimized by paying particular attention to reflowing the margins of the wax pattern and through careful investing (see Chapter 22).

Even small nodules can prevent a casting from seating completely. Careful examination under ample magnification will help identify interferences. Small nodules, if far enough away from the margin itself, can be removed under a binocular microscope with exceptionally cautious use of very small rotary instruments (e.g., a no. 1/4 round bur). However, great care is needed to avoid damage to the margin and annoying remakes.

Fig. 29-1. Recommended sequence for finishing of a cast restoration. All procedures for a zone should be completed before the next zone is started. Zone 1 is the internal margin; Zone 2, the internal surface; Zone 3, the sprue; Zone 4, the proximal contacts; Zone 5, the occlusal surface; Zone 6, the axial walls; and Zone 7,the external margins.

Fig. 29-1. Recommended sequence for finishing of a cast restoration. All procedures for a zone should be completed before the next zone is started. Zone 1 is the internal margin; Zone 2, the internal surface; Zone 3, the sprue; Zone 4, the proximal contacts; Zone 5, the occlusal surface; Zone 6, the axial walls; and Zone 7,the external margins.

Proximal Contact Wax Patterns
Fig. 29-3. Multiple nodules on a casting (arrows) have resulted from improper investing. To permit complete seating of the casting, even small ones such as these must be removed entirely.

Fig. 29-2. Reflowing the wax pattern. The objective is to create a well-adapted 1-mm zone to prevent cement dissolution. Proper reflowing before investing is a prerequisite to accomplish this.

ZONE 2: INTERNAL SURFACE (INTAGLIO)

Objective. No contact should exist between the die and the internal surface of the casting. A uniform space of 25 to 35 um is necessary for the luting agent to spread evenly. Any contact(s) must be identified and relieved by careful selective grinding of the internal surface.

Procedure. Under normal circumstances, a casting's internal surface does not require finishing. It should, however, be examined for nodules (Fig. 29-3) before the restoration is seated on the die. Nodules can be removed with a small round carbide bur, which can be time consuming because it may need to be repeated several times. If the internal surface needs to be adjusted more than occasionally, the investing procedure should be reexamined for flaws.

Even a very small nodule can result in significant increase of the marginal gap width (Fig. 29-4). A binocular microscope is especially helpful in identifying nodules. High-quality loupes are an acceptable alternative. Great care should be exercised when seating a casting on its die. Any significant force will abrade or chip the die so that the casting will seat on the die but will not seat fully on the prepared tooth. Overlooking this at the cementation appointment will result in a restoration with open margins and a poor prognosis. If a casting does not seat, a nodule may have been overlooked and may have scratched the die. A little stone may have been

NEVER force the casting onto the die; use great caution when fitting the casting.

Fig. 29-4. A relatively small nodule (arrow) will result in a substantial open margin.

picked up in the process. Close examination of the internal surface of the casting or the axial walls of the die (Fig. 29-5) will reveal this. Corrective action is often relatively simple, and the casting may be acceptable. Care must be taken not to seat a faulty casting repeatedly, thereby abrading the die. After a die has been abraded by a casting, it should not be used for rewaxing a restoration. If this is necessary, a new impression will be required.

When a nodule is removed from the internal aspect of a casting, deliberately removing a slightly greater amount of alloy in the area is recommended. Once the casting has been adjusted, determining the exact location of the nodule will no longer be

NEVER force the casting onto the die; use great caution when fitting the casting.

Fig. 29-5. A, Internal surface of a casting. Note the stone (arrow) adhering where the die has been abraded by the casting. B, A suitable marking agent (e.g., rouge and chloroform) can be used to detect areas that must be relieved to allow complete seating.

possible. Therefore, the nodule should be removed entirely in one step, rather than through sequential relief of the internal surface (Fig. 29-6).

Indiscriminately removing material from the internal aspect of any casting is not an acceptable alternative. This will result in excessive loss of retention and resistance form, and the restoration will need to be remade.

Marking Agents. Several agents are commercially available to facilitate identification of the seating interference between the casting and the die. These include water-soluble dies (e.g., Liqua-Mark*), solvent-based dies (e.g., Accufilm IV), and powdered sprays (e.g., Occlude$). A suspension of rouge in chloroform or an elastomeric detection paste (e.g., Fit Checker)§ can also be used as an alternative . These agents should be applied as a thin film to the internal surface of the casting. High magnification of the casting after seating will reveal initial contact for grinding. Regardless of the method used, the internal surface of the casting should always be thoroughly cleaned before the luting procedure (see Chapter 31).

ZONE 3: THE SPRUE

Objective. To reestablish proper coronal morphology and function, the sprue must be sectioned, and the casting must be recontoured in the area of its attachment.

The Wilkinson Company: Post Falls, Idaho fParkell Products: Farmingdale, N.Y. {Pascal Co, Inc: Be I lev ue, Wash. §GC America, Inc: Chicago, 111.

Fig. 29-6. When removing a nodule, remove slightly more than the defect to ensure complete seating of the restoration.

Procedure. Once the fit of the casting has been verified on the die and it has been found to be acceptable, the sprue is sectioned, and the area of its attachment to the casting (Fig. 29-7) is reshaped.

A carborundum separating disk is used to cut through the sprue. Cutting should be performed cir-cumferentially, maintaining a small area in the center of the sprue. This last connection is broken by twisting and separating it from the casting. Wire cutters are not recommended, because they may lead to distortion of the casting. Any excess in the area of the sprue attachment is removed with the disk, and the area is refined with stones and sandpaper disks.

ZONE 4: PROXIMAL CONTACTS

Objective. The proximal contact areas are adj usted in the laboratory so that they will be correct (or slightly too tight) when the casting is evaluated in the mouth.

Procedure. Special care is needed to prevent the finishing procedures from producing an overre-duced and consequently inadequate proximal contact. Although this can be corrected with solder (see p. 747), it is a time-consuming and unnecessary procedure.

A slightly excessive contact, however, may be corrected easily during clinical evaluation. The proximal contacts on the stone cast can be minimally relieved by careful scraping with a scalpel (Fig. 29-8). The casting is then adjusted until it just seats. When adjacent castings are made, they should not be ad-

Fig. 29-7. A, The button is most effectively removed by cutting around the sprue and then twisting it off. B, With multiple castings made simultaneously, access is more difficult. When it is necessary to sever a sprue completely, care must be taken not to damage the margin inadvertently. C and D, Disks and stones are used for gross recontouring. E, The recontoured casting before finishing.

Fig. 29-7. A, The button is most effectively removed by cutting around the sprue and then twisting it off. B, With multiple castings made simultaneously, access is more difficult. When it is necessary to sever a sprue completely, care must be taken not to damage the margin inadvertently. C and D, Disks and stones are used for gross recontouring. E, The recontoured casting before finishing.

Fig. 29-8. Rather than risk a deficient proximal contact at evaluation, the technician may reduce the cast slightly by scraping the adjacent teeth with a blade.

j usted to seat on the working cast simultaneously. Under these circumstances, the proximal contacts should be left slightly too tight in the dental laboratory. For such multiple castings, clinical evaluation is done sequentially and on an individual basis. Adj ustments are made for each casting independently.

When adjusting proximal contacts, placing a thin Mylar articulating film between adjacent castings or between the casting and the adjacent tooth is helpful (Fig. 29-9). Doing this allows the areas where binding contact occurs to be adjusted through selective adjustment where markings result.

Connectors. When an FPD is being finished, the connectors require special attention. Unless they are properly contoured and highly polished, periodontal health will invariably be affected, even in the presence of the most meticulous oral hygiene. Ideally, a properly finished connector has a parabolic configuration (Fig. 29-10). Rotary instruments such as rubber wheels, which allow access to the cervical aspect of the connector for finishing while not jeopardizing the margin, are essential in these situations. In cases of root proximity between adjacent teeth, this can be quite problematic. After preliminary finishing with rubber wheels, a piece of twine can be used to impart the final polish to the cervical aspect of the connector (Fig. 29-11).

ZONE 5:OCCLUSAL SURFACE

Objective. Occlusal contacts are reestablished in static and dynamic relationships to the opposing arch. Obtaining accurate and stable contacts does not require highly polished metal occlusal surfaces. A satin finish is acceptable. Occlusal morphology must ensure positional stability and satisfy all functional requirements (see Chapter 4).

Procedure. The occlusal contacts are checked with thin Mylar articulating film (Fig. 29-12) to ensure that they match the design in the waxing stage. If they do not, the occlusion must be adjusted. Wax

Procedure Thin Blood Film Test
Fig. 29-9. A, Thin articulating film interposed between a metal-ceramic restoration and the adjacent tooth. B, The area of contact that prevents complete seating is readily apparent. C to E, Articulating film is used to detect the location of an excessive proximal contact on cast metal.
Teeth Cross Section
Fig. 29-10. Cross sections showing properly finished connectors.

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