Improved color matching of metal-ceramic restorations. Part III: Innovations in porcelain application

THE JOURNAL OF

PROSTHETIC DENTISTRY JANUARY

SAMUEL WILLIAM

VOLUME

59

NUMBER

1

. OPERATIVE DENTISTRY

FIXED PROSTHODONTICS SECTION

1988

EDITORS

E. GUYER

WILLIAM JOHN

F. MALONE

LEFKOWITZ E. RHOADS

ROBERT

C. SPROULL

Improved color matching of metal-ceramic restorations. Part III: Innovations in porcelain application John A. Sorensen, D.M.D.,* and Tony J. Tomes** University

of California,

Los Angeles, School of Dentistry,

Los Angeles, Calif.

lhe dentist systematically selects the individual opaque, body, and incisal porcelain shades as described in Part I.’ The shade numbers are recorded on the esthetics prescription form along with a detailed diagram indicating their pattern of application and desired surface texture as detailed in Part II.2 The selected shade and arrangement of porcelain is verified with the identification shade tab.* The stage is then set for the ceramist to use his artistic abilities to apply porcelain prescribed in the shade guidelines. Sophisticated techniques for layering porcelain colors to produce restorations that defy recognition have been developed by individuals such as W. Geller (Lecture at the Midwinter Dental Meeting, Chicago, Ill., 1984). Unfortunately, not all ceramists are as artistically gifted. Dentists and ceramists alike have had difficulty in consistently matching the color of natural teeth and achieving a lifelike appearance. A system of porcelain application is described that enables most ceramists, even those with little experience, to achieve improved color matching with greater predictability. The technique of layering of internal components superimposes individual color layers to create depth and vitality in ceramic restorations that will compensate for the limitations of existing metal-ceramic materials.

PROBLEM AREAS IN METAL-CERAMICS One of the greatest problem areas in metal-ceramics is the cervical region where opaque must be carried to the

*Assistant Professor, Assistant Director, Graduate Prosthodontics. **Research

Assistant,

Certified

Dental

Technician.

margin to mask out the metal. As the margin is approached, the thickness of ,overlying dentin porcelain decreases. The dentin thickness is inadequate to diffuse light and this results in high reflectivity of light from the opaque layer (high Value-low Chroma) (Fig. 1). The marginal area is frequently underreduced by the dentist. To compensate for this problem the dental technician often overcontours the porcelain at the margin in the attempt to decrease reflectance from the opaque. The probable result is gingival inflamation. Another problem area is at the junction of the incisal and middle third of the tooth. This area is often underprepared without two planes of reduction. The ceramist must make the dentin layer thin in this area to match the contour and form of the contralateral tooth. Again, the highly reflective, high Value opaque shows through the thin layer of dentin (Fig. 1). Regions of shadowing occur where there are excessive amounts of dentin without opaque backing such as interproximal regions or cervical regions of pontics (Fig. 1). These regions appear darker and have lower Chroma than other regions of the crown. The lingual aspect of the crown preparation is often intentionally underreduced to maximize the length of the lingual wall to reciprocate against the facial wall. Consequently, only a thin layer of dentin porcelain can be placed for proper occlusion. The result is an area of high reflectivity and high Value (Fig. 1).

INNOVATIONS APPLICATION

IN PORCELAIN

An approach to porcelain application that compensates for the inadequacies of current metal-ceramic materials is presented. The rationale for this method is to 1

SORENSEN

See opposite 2

AND

TORRES

paIge for legends. JANUARY

1988

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Table II. Opacous dentin ratios

Table I. Opaque modifier ratios Ratio

shade Ipp”P

It&i0

part 678.: 5 parts opaque part 678: 1 part 677: 5 parts opaque 1 part 675: 1 part 678: 5 parts opaque 1 part 676: 1 part 678: 5 parts opaque

A B C D

1 part 575,: 1 Part dentin 1 part 575: 1 part 576: 2 parts dentin 1 part 577: 1 part 578: 2 parts dentin 1 part 577: 1 part 579: 2 parts dentin

Shade group 1

A B

1

C

D

*Vita opaque modifiers, Vita Zahnfabrik.

*Vita VMK opacous dentins, Vita Zahnfabrik.

compensate for the regions of low Chroma, high Value, and shadowing at two levels. First, opaque modifiers are used to control areas that typically have low Chroma and high Value. Second, a combination of special porcelains and conventional porcelains are applied in patterns to eliminate shadow areas and design a crown that manipulates light similar to a natural tooth. To create lifelike ceramic restorations, the ceramist must apply porcelain in the appropriate proportion to create a balance of -light transmission, reflection, and scattering. The subtle balance of these light-modifying processesis difficult to achieve. Through the layering of internal components, ceramic restorations can be made that control light transmission and scatter in a fashion close to that of natural teeth.

for inadequate facial reduction at the junction of the middle and incisal thirds, opaque modifier is applied (Figs. 3 and 5). Either a violet or pink Hue is diluted with a white opaque to subtly modify the shade.

TECHNIQUE Opaque modifiers Controlling modification of light by the crown begins at the opaque application stage. Opaque modifiers are placed in regions where the overlying dentin porcelain will be thinner than is normally needed for diffusion of light. As discussed, these regions usually are located near the margin, on the facial surface at the junction of the middle and incisal thirds, and on the lingual aspect (Fig. 1). Table I presents guidelines for the application of Vita (Vita Zahnfabrik, Bad Sackingen, West Germany) opaque modifiers to control areas of high Value-low Chroma along the porcelain-metal junction near the margin. The opaque modifier shade is selected from the basic A through D Hue group and applied appropriately (Figs. 2 through 5). To enhance the appearance of translucency and vitality at the incisal third of the crown or to compensate

Opacous dentins A special porcelain that has greater opacity and Chroma than conventional dentin porcelain is needed. Geller,3 in collaboration with Vita Zahnfabrik, developed the VMK opacous dentins. The opacous dentins are similar to normal dentin except that they have greater opacity, higher Chroma, and are more reflective of light.4 Table II offers a guideline for the use of opacous dentins according to the A through D Hue groups. The opacous dentins can be blended according to the patient’s age and in older patients 100% opacous dentin is applied. In young patients a blend of 60% opacous dentin and 40% dentin is applied. Opacous dentins are layered in problem regions of low Chroma or shadowing (Fig. 1) to increase Chroma and diffuse incident light in patterns closer to those of natural teeth.

Layering internal components It is primarily in the incisal third that the ceramist can achieve the greatest interplay of light. The gingival two thirds of the crown is limited for porcelain thickness. The incisal third, with its greater porcelain thickness and lack of opaque backing, allows the ceramist to achieve interaction with light that behaves most closely to natural tooth structure. Similarity to tooth structure is achieved through the layering of internal components. Natural tooth structure is made up of inhoniogenous structures such as dentin and varying thickness of enamel. At the incisal edge where the enamel is thickest and has dissimilar areas, light behaves differently in

Fig. 1. Problem areas in metal-ceramic crowns. Fig. 2. Legend for opaque and porcelain shades. Fig. 3. Schematic of opaque application.

Fig. 4. Facial view of opaque fired on metal coping. Fig. 5. Lingual view of opaque fired on metal coping. Fig. 6. Shoulder porcelain fired for porcelain labial margin. Fig. 7. Schematic of opacous dentin application.

Fig. 8. Application THE JOURNAL

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of opacous dentin.

See opposite

p’ age for legends. JANUARY

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various regions. In the same way, several different blends of incisal porcelains can be applied in columns to create selective scattering and transmissions of light similar to that of the natural tooth structure. Three different blends of incisal porcelain are used. These include (1) the incisal shade selected according to the shade determination in the first section,’ (2) transparent porcelain, and (3) a combination of equal parts of incisal and transparent porcelains. After the buildup of body porcelain to full contour and cutback, the first level of layered internal components is applied. The first level is the lateral internal component, measuring approximately 1 mm incisogingivally and placed at the incisal edge in increments as narrow as possible. The vertical internal component, which fills in the void between the cutback and the first level of lateral internal component, is applied next. The longer columns are incrementally applied in an alternating sequence of the three incisal blends. Different incisal blends should be placed at the two levels in the column to facilitate better scattering of light. By applying two levels of internal layering with alternating incisal blends, maximum scattering of light is achieved to produce a prismatic effect similar to that of natural tooth structure.

Sequence for porcelain application By use of the principles of porcelain application described previously and porcelain shades as determined by the laboratory prescription form, a sequence of porcelain application is outlined. The metal substructure is prepared and conditioned. A thin slurry mix of the selected opaque is fired. Before the second opaque bake, the appropriate shades of opaque modifiers are applied at the cervical and incisal areas (Figs. 3 through 5). Table I offers information for the appropriate cervical opaque shade to control Value and increase Chroma. A violet with white or pink Hue is placed at the incisal third to increase vitality (Figs. 3 through 5). Multiple shoulder bakes are done until an acceptable marginal fidelity is attained for the porcelain labial margin (Fig. 6). The appropriate shade of opacous dentin is selected according to Table II and applied in a tapering layer at the cervical, facial, proximal, and lingual aspects (Figs. 7

Fig. Fig. Fig. Fig. Fig. Fig. Fig. Fig. THE JOURNAL

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and 8) to compensate for areas of shadowing and low Chroma. The crown is built to full contour with the proper shade of dentin (Figs. 9 and 10). The cutback for the incisal layer is accomplished with a blade, extending about halfway down the facial surface (Figs. 11 and 12). The lateral internal components are placed at the incisal edge 1 mm by starting with the transparent incisal blend at the proximal edge and applying alternating segments of the three incisal blends. The alternating sequence of the three incisal blends is carried across the entire incisal edge, with the increments kept as small as possible (Figs. 13 through 15). The vertical internal components are then applied sequentially with the three alternating incisal blends from proximal to proximal surface (Figs. 16 and 17). These columns should be made as narrow as possible to gain maximum scattering of light. For better scatter of light, the same shade of incisal blend should not be in the vertical column formed from the lateral and vertical internal components (Figs. 18 and 19). The crown is removed from the cast and the proximal contact surfaces are added. Transparent porcelain is placed on the incisal half of the contact and opacous dentin on the gingival half (Figs. 20 and 21). The addition of porcelain to the contact region compensates for firing shrinkage and provides for maximum esthetics with natural-appearing transmission of proximal light (Fig. 22). Fig. 23 demonstrates the completed restoration with matching surface texture.

DISCUSSION Despite the advent of the new all-ceramic systems such as castable ceramics, the layering of the internal components system facilitates achievement of superior esthetics. Natural teeth are formed in layers with the dental pulp at the center surrounded by yellow-orange dentin and covered with more translucent enamel. Each layer transmits and refracts different amounts of light because of the difference in ratios of mineral matter and organic matrix. The layering technique applies color and translucency in a three-dimensional pattern similar to that of natural tooth structure. The three dimensions of color are created intrinsically rather than by the heavy

9. Schematic of dentin porcelain built to full contour. 10. Dentin porcelain built to full contour. 11. Schematic of incisal cutback. 12. Cut back for incisal porcelain. 13. Schematic of lateral internal components. 14. Application of lateral internal components. 15. Incisal view of application of lateral internal components. 16. Schematic of vertical internal component application. DENTISTRY

SORENSEN

See opposite 6

AND

TORRES

page for legends. JANUARY

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extrinsic colorants of castable ceramics. Crowns with high Chroma may require many layers of shading porcelain and could result in obliteration of surface irregularities prepared on the restoration. The methods presented in this series can be applied to other ceramic systems such as porcelain jacket crowns and the Cerestore (Cerestore, Ceramco Inc., Johnson and Johnson Co., East Windsor, N.J.) crown system. The Cerestore crown has an opaque core that is highly reflective in the cervical area and requires opaque-type modifiers. CONCLUSION The principles and methods of porcelain application outlined compensate for some of the weaknesses of current metal-ceramic materials. Among these problems are regions of high Value and low Chroma in the cervical, facial, and lingual regions, and zones of shadowing in the proximal regions. The layering of the internal components system permits the ceramist to make restorations that transmit, reflect, and scatter light similar to natural teeth. The tables and guidelines will aid ceramists of varying skill levels in the pursuit of creating ceramics with lifelike vitality. Fabrication of ceramic restorations will continue to be more of an art form than a science. However, with the

system outlined in this series for shade determination, communication, and porcelain application, the dentistceramist team will produce ceramics with improved esthetics in a more systematic and predictable manner. We thank Mr. Willie Geller for his tremendous contribution and inspiration in dental ceramics. Special thanks to Ms. Irene Petrevicious of the University of California, Los Angeles, Illustration Department for preparation of the art work. Appreciation is extended to the U.C.L.A. Word Processing Center.

REFERENCES Sorensen JA, Torres TJ. Improved color matching of metalceramic restorations. Part I: A systematic method for shade determination. J PROSTHETDENT 1987;58: 133-9. Sorensen JA, Torres TJ. Improved color matching of metalceramic restorations. Part II: Procedures for visual communication. J PROSTHETDENT 1987;58:669-77. Geller W. Dark and shadowed zones: an important aspect of the Geller creative shading technique. Quintessence Dent Tech 1983. Vita Zahnfabrik. Vita VMK opacous dentin, manufacturer’s brochure. Reprint requests to: DR. JOHN A. SORENSEN UNIVERSITYOF CALIFORNIA SCHOLL OF DENTISTRY

CHS 33-041 Los ANGELES, CA 90024

Fig. 17. Application of vertical internal components. Fig. 18. Contouring and smoothing of porcelain buildup. Fig. 19. Excavation and placement of white internal characterization for appearance of

hypocalcification. Fig. 20. Schematic of addition of porcelain for proximal contact. Fig. 21. Application of porcelain for proximal contact. Fig. 22. Completed crown ready for firing. Fig. 23. Cemented metal-ceramic crown for left central incisor. THE JOURNAL

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DENTISTRY