All-Porcelain Labial Margin for Ceramometal Crowns Lewis Harrison, D.M.D.* Terry HufSman, C.D.T. Marvin Goldfogel, D.D.S. '

The elimination of the labiogingival metal collar of a porcelain-fused-to-metal (PFM) restoration is an attempt to achieve an improved esthetic result. In their expectation of a more cosmetic tooth restoration, patients may influence dentists to use the all-porcelain labial margin to avoid metal showing in the final restoration. Success of this type of restoration depends upon proper tooth preparation. The all- porcelain margin requires a 1.2-mm wide labiogingival shoulder of approximately 70 or 90 degrees wrapping into the interproximal area. Much of the effectiveness of the restoration depends upon the design of the metal substructure. The following change is made in the design of this substructure for this modified PFM crown: the labiogingival portion of the metal is Rnished back to the gingival-pulpal line angle with the metal against the axial wall being from 0.3 mm to 0.5 mm thick. This allows for 0.2 to 0.3 mm of opaque and 0.7 to 1.0 mm of shoulder porcelain. The direct lift- off technique is a useful method of achieving clinically acceptable all-porcelain margins. Such restorations may give excellent results.

erceived deficiencies at the labiogingival collar P area of porcelain-fused-to-metal (PFM) crowns can usually be related to one of the following factors: Expo- sure of the metal margin: opaque show through in the cervical third: or overcontour of the cervical area of the crown (Figs. 1-3). Traditionally, a PFM restoration in- corporates a narrow metal collar in the cosmetically critical area of the labiogingival area. The elimination of the labiogjngival metal collar is an attempt to achieve an improved esthetic result, thus addressing cosmetic disappointment that sometimes occurs. l There have been several techniques2-10 proposed in an attempt to achieve this goal. These include various proposed finish lines, metal contlgurations, use of platinum or gold foil, refractory dies, direct lift-off, and various separating solutions.

One of the most important considerations is prepa- ration design. The preparation must meet the require- ments of adequate reduction of tooth structure at the gingival area to provide sufficient space for the metal or ceramic material, provide retention and resistance, and have a smooth margin design with which the ceramist

can work. The shoulder with a bevel preparation has the advantage of excellent marginal integrity for PFM restorations. l2

The platinum foil technique, the oldest of the tech- niques, uses the foil to support the porcelain as it is built up on the die and dried to maturity. Slumping of the porcelain and rolling of the porcelain edge is often the result of this technique. An additional disadvantage to this procedure is that the margin cannot be properly evaluated until the crown is completed and the foil removed.

*Assistant Professor: t Technician: $ Professor and Chairman: University of Colorado Health Sciences Center. School of Dentistry, Department of Restorative Dentistry. Denver, Colorado

Address reprint requests to: Lnvis Harrison. D.M.D.. University of Colo- rado School of Dentistry, Department of Restorative Dentistry. 4200 East Nlnth Ave.. C284. Denver, CO 80262-0284 6 1992 Decker Perlodicds Inc. PyeUre 1. PFM restoration with metal showing.

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All-Porcelain Margin for Ceramometal Crowns

Figure 2. PFMrestorationwith opaque discoloration at gingival third.

When porcelain manufacturers developed margin porcelains that fuse at temperatures 30 to 80°F lower than the parent porcelain, the foil-less direct lifl process became popular.l0 These newer margin porcelains re- sist pyroplastic flow and allow for direct lift-off from the die with minimal deformation. Though complete elimi- nation of sintering shrinkage is theoretically impossi- ble, a carefully controlled procedure can minimize shrinkage and yield clinically acceptable results (Fig. 4). This article shows the steps used to make this a successful treatment procedure.

INDICATIONS

Patients, in their expectation for a cosmetic tooth restoration, are influencing dentists to use the all- porcelain labial margin to avoid metal showing in the final restoration. Lip-line, the thickness and color of the gingival margin, and the location of the free gingival

Figure 3. An overcontoured PFM restoration.

Figure 4. A 10-year result for an all-porcelain labial margin restoration for the lateral incisor.

tissue are factors that influence the dentist in assessing the need for an all-porcelain labial margin. In addition, the patient's oral hygiene must be considered, since the tooth-crown junction of the all-porcelain labial margin is seldom as smooth as the metal-collar margin, and plaque accumulation may be a factor.I3

Advantages and Disadvantages The advantages of this technique include improved

esthetics for PFM crowns. With this, the preparation can be kept supragingival or just slightly apical to the free gingival margin in most cases. This small sulcular marginal depth is a periodontal advantage14 and per- mits a more gentle impression technique.

A major disadvantage and objection of this tech- nique is that the loss of the metal margin may give a less optimal margin closure. Also, it is possible that fracture of the facial porcelain caused by lack of metal support may be increased. The direct life-off technique presents another potential disadvantage because of possible displacement during the porcelain shoulder build-up and pyroplastic deformation during firing. These disad- vantages can be overcome with careful technique.

Preparation Design Success of this type of restoration depends upon

proper tooth preparation. The all-porcelain labial mar- gin requires a 1.2-mm wide labiogingival shoulder of approximately 70 or 90 degrees wrapping into the interproximal area. A chamfer margin or shoulder with abevelisusedforallothermarginareas. Thelabiogjngival margin will usually be placed near or slightly below the free gingival margin for most teeth. The shoulder should be even and smooth when viewed with magnifying loops.

Pigure 5. Shows a silver-plated die with die spacer applied.

Impressions and Dies An impression must accurately record all prepared

surfaces. The conventional method of impression mak- ing usually involves gingival retraction using chord packing into the sulcus. But, if the tissues are thin and friable, it is sometimes less traumatic to the gingival tissues to use the tube impression technique.15 Al- though conventional stone dies are adequate, it is the experience of some clinicians and technicians that silver plating the die will give a strong and accurate reproduction of the shoulder area with which the tech- nician can work. A die spacer is recommended for the die before wax up of the metal substructure (Fig. 5).16

Metal Coping Design Much of the effectiveness of the restoration depends

upon the design of the metal substructure. The follow- ing change is made in the design of this substructure for this modifled PFM crown: the labiogingival portion of the metal is flnished back to the gingivo-pulpal line angle with the metal against the axial wall being from 0.3 to 0.5 mrn thick (Fig. 6). This allows for 0.2 to 0.3 mm of opaque and 0.7 to 1 .O mm of shoulder porcelain.

TECHNIQUE FOR PORCELAIN APPLICATION

1. Complete the metal substructure, sandblast, and place in the ultrasonic cleaner (distilled water) for 6 minutes.

2. Degas the framework, sandblast a second time, and place in the ultrasonic cleaner (distilled water) for 6 minutes.

3. Apply opaque porcelain and fire at the manufac- turer’s recommended temperature (Fig. 7).

4. Apply a release agent (Modisol Insulating Penm

Figure 6. Shows completed metal copings ready for porcelain application.

Vita Zahnfabrik, Sackingen, Germany) to the shoulder area of the die.

5. Mix shoulder porcelain (Vita Shoulder Porcelain? Vita Zahnfabrik) with normal liquid medium.

6. Seat the framework on the die making sure the framework seats completely and begin the actual shoulder build-up by picking up a fluid mix of shoulder porcelain with a porcelain carver or brush. This mix of fluid porcelain is flowed onto the opaque base and directed first to the shoul- der area with the point of the instrument or brush. The porcelain is carried up onto the opaqued metal a short distance above the shoul- der so that the body porcelain will slightly over- lap the marginal porcelain for color blend (Fig. 8).

7. Overbuild the shoulder porcelain slightly to al- low for shrinkage when condensed. Condense the porcelain. Remove the framework from the die and fire at the manufacturer’s recommended temperature under vacuum.

Figure 7. Opaque porcelain applied to the coping.

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All-Porcelain Margin for Ceramometal Crowns

Figure 10. A completed restoration for the canine.

Figure 8. Shows application of the shoulder porcelain and the overbuilding of the shoulder porcelain.

8. Allow the porcelain to cool slowly and reseat carefully on the die.

9. Due to the small amount of shoulder porcelain shrinkage, a second application of porcelain at the margin area is usually necessary. Fire the porcelain again.

10. Refit the crown onto the die as before. 1 1. Follow the full contour buildup of the body and

incisal porcelain following recommended firing temperatures.

12. Shape porcelain and make additions if neces- sary.

13. Finish porcelain margin using high magnifka- tion. Clean in ultrasonic cleaner (distilled water) for 6 minutes.

Figure 9. Shows the h a l application of a thin wash of the shoulder porcelain.

14. Check the fit of the porcelain margin. If neces- sary, reapply release agent on the die and use a thin watery mix of shoulder porcelain to perfect the marginal fit (Fig. 9). Fire the porcelain again.

15. When completely satisfied with the porcelain, polish the exposed metal. Clean the internal surfaces of the metal with a 5 0 - ~ aluminous oxide abrasive unit. Disinfect the crown before seating.

Seating of Restoration At the seating appointment, the fit of the restoration

is checked with special attention given to the margin adaptation, contour, and occlusion. The quality of the restoration must provide a n environment promoting long-term maintenance of periodontal health. The pro- file of the restoration as it emerges from the gingival margin is particularly important toward this goal. Cus- tom staining is often required to give the best esthetic result” (Fig. 10).

CONCLUSION

The all-porcelain labial margin is one of the options available to improve the cosmetic value of PFM restora- tions. Several techniques have been recommended for fabrication of these restorations. The preparation is crucial and requires a 70 to 90 degree shoulder that is at least 1.2 mm in width. The shoulder must be smooth and even with no bevel. The direct MI-off technique is a useful method of achieving clinically acceptable all- porcelain labial margins. Such restorations give excel- lent results.

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