A TECHNIQUE FOR FINISHING GOLD CASTINGS
by Richard V. Tucker, D.D.S.

After all procedures necessary to produce a gold inlay, onlay, or other type of casting have been completed with care and understanding; the last step, the finishing of the gold, if done properly, will make the difference between a serviceable restoration and that of a fine, beautiful case.

The procedures described below are predicated on the fact that the casting fits the tooth cavity, because without a good casting no finishing Technique will produce a fine case, nor even a serviceable restoration.

The initial procedure of finishing involves the laboratory, as it is here that the difficult access areas on the occlusal portion of the restoration are refined and polished; and the final contours are placed on the casting. To avoid destruction of the detailed anatomy in the casting, the following procedures are suggested. All accessible surfaces, except contact areas and margins are smoothed with 1/2 inch medium garnet disc, and 1/2 inch fine sand discs in that order. Then 1/2 inch fine cuttle discs are used over all surfaces of the casting, including margins and interproximal contact points. All pits and fissures are smoothed lightly with a #2 carbide bur, contacts corrected, occlusion corrected, then all occlusal anatomy is polished with a #11 standard stiff brush wheel and tripoli. If needed, the endbrush mandrel may be used with tripoli in the deep areas of the casting. Finally the #11 soft brush wheel is used with a high polishing compound over all surfaces of the casting. All finishing of the casting should be done in the hand and not on the stone die. Since the restoration is finished except for the margins before cementation, the dentist confines all his time and effort in the operatory to finishing the margins only.

Following the administration of an anesthetic and proper isolation with a rubber dam, the cavity is cleaned and a thin layer of cavity varnish is applied to the dentinal walls, using care not to apply it on the margins. The casting is 'tried' in to ensure proper contact. Adjustment of the contact areas can be done at this time. It is not necessary to drive the casting to place as is done at the time of cementation. Usually if it can be left a half millimeter from being completely seated, we can be sure of proper expansion and fit, and avoid the difficult task of removing a snug fitting casting that could damage both the tooth and the casting.

A slow setting mix of zinc phosphate cement should be made on a cool glass slab. This is accomplished by a slow introduction of the powder to the liquid, and the powder is continued to be added in small increments to the point where the mixture will just drop freely from the spatula. This step is important, as the casting has not been finished on the tooth prior to cementation, and time is needed to reduce the gold and the tooth surface to the same plane with the most coarse of the three discs, prior to the hardening of the cement.

The interior surfaces of the casting are first covered with cement with the remainder being applied to the cavity in the tooth. After having placed the casting in the tooth, it is seated hard and firmly by applying considerable pressure on the casting with a pointed orange wood stick while the stick is being lightly malleted. The casting should be held with firm pressure for a short period of time to allow release of hydraulic pressure which could cause the casting to lift and the excess cement can be removed at this time.

With a slowly rotating mandrel in a straight handpiece, a medium garnet disc should be rolled over the margins from the casting toward the tooth surface, creating a single plane between the gold and the tooth. This also accomplishes slight burnishing of the gold at the margin. Margins of the gold can be operated with the straight handpiece except the mesiolingual margin and the gingival margins of all teeth in both the mandible and maxilla, with few exceptions. After all other margins have been smoothed with this type disc on the straight handpiece, the contra-angle is used to smooth the mesiolingual aspect. This is accomplished with the grit side facing 'in' toward the handpiece. Finishing to this point should be done before the cement is harden.

The next procedure requires little time because it is merely to polish the gold and the tooth at the margins, not to reduce them. The 1/2 inch fine sand disc is used with the same handpiece as discussed above to accomplish a reduction in the size of scratches left by the medium garnet discs.

Attention is next given to the gingival margins. The casting should fit accurately at the gingival with no excess gold over the margin. A narrow eighteen inch finishing strip, with medium garnet grit tapered at one end, is passed interproximally. This step is aided, as is the entire finishing of the gingival margins, by the assistant retracting the rubber dam both on the buccal and lingual aspects to gain access for the strip. A little Vaseline lubricant can also be used to avoid catching the rubber dam with the strip as it is passed over the margins. The use of the strip, reduces the gingival gold and tooth structure to the same plane, as well as the gingival third of the buccal and lingual cavosurface margins which cannot be reached with discs. Usually two or three swipes over the margin accomplishes this purpose, and care should be given to avoid over use of the strip on the relatively soft cementum. It is observed that if the gold is in excess at the gingival margin, it seldom can be finished properly on the tooth, since the strip seems to remove tooth structure faster than the gold.

After use of the medium garnet strip, a similar fine cuttle is used in the same manner. Again two or three passes of the strip should suffice for this step which is used only to remove the fine scratches and polish the gingival margin where it is not possible to use a disc.

If there are inaccessible areas such as grooves or fissures, a fine white stone may be used in those specific areas of the tooth.

A fine cuttle disc is then used to polish all accessible margins in the manner described above. This seems to make the final closure of the joint as well as polishing the surfaces.

Final polishing can be done, after the proper discing, with very little effort. A flour-of-pumice slurry in a soft rubber cup on a contrangle is used, to be followed by flushing and irrigating with water. After drying the field of operation, dry tin oxide or similar fine polishing agent is lightly used over all accessible surfaces.

It should be noted that air coolant must be used during all phases of discing, stripping as well as polishing - to avoid over heating the tooth. Also for this reason, the discs and strips should not be used too fast and with too much pressure.

As a final note, it is a great aid to the operator to have a slow handpiece with adequate torque, which allows the discs to be bent and rolled slowly over the margins in the finishing process. This Technique is not easily accomplished with high speed instruments without removing excess tooth structure.