DANIEL H. GEHL
esthetics in porcelain-to-gold
COLOR OF CROWNS
Peter Vryonis* Melbourne, Australia
ood results are readily obtainable in matching colors of the incisal and mid-third of crowns, but often the gingival third taxes the ability of most ceramists. One of the reasons for the unesthetic appearance of the gingival surface often results from inadequate reduction of the tooth. However, more often it is because matching, one of the most basic aspects of the tooth color, is overlooked. Examination of natural teeth indicates that enamel covers the whole surface of the tooth down to the cemento-enamel junction (Fig. 1). However, when porcelain-to-metal crowns are made, enamel is usually brought down to the mid-third of the crown, resulting in a good incisal and mid-third color and usually a dense and very creamy gingival appearance (Fig. 2). To obtain better results, the make up of natural teeth must be followed. More work must be done to understand reproduction of color in ceramics. Although manufacturers provide ideas, these ideas do not completely fill the needs. Shade guides now in use do not simulate the finished crowns. Instead of the 5 mm thickness of porcelain that is found on most shade guides, the thickness should be reduced to 1 to 1% mm as found on most natural crowns. In addition, the guides should be backed by metal to give the true depth and color of the porcelain. The alternative to this is a custom-made shade guide (Fig. 3). A guide such as the one presented in Fig. 4, with many combinations including incisal edges, with different hues, is long overdue. For improved esthetics in a crown, two custom shade guides, as well as a guide for incisal edges, have been made (Figs. 3, A, and 4). Every button is 1.3 mm thick at the neck and 1% mm at the incisal edge.
1980 The C. V. Mosby Co.
Maximum depth of color is provided by a layer of clear (colorless) porcelain 0.3 mm thick on the top of the crowns. Young teeth require 0.2 mm, older teeth 0.25 mm. The problem of metamerism is not noticeable, as light is absorbed and diffused giving crowns a natural look in most lighting situations. However, when exposed to blue fluorescent light (ultra violet), such as that used in discos, all crowns appear black because natural teeth fluoresce under ultra violet lights and crowns do not. Crowns without proper thickness of enamel and a clear overlay of porcelain reflect too much light and look dense. As natural teeth age and the enamel seems to lose some of its white color with time, they become more translucent allowing the dentin to show through. To compensate, the amount of enamel applied to crowns for young persons must be thicker and whiter than in older teeth where the enamel is thinner and more translucent. To aid the ceramist, a record should be made of the amount of enamel overlaying the dentin at the time of tooth preparation. In the case of a middle-aged patient, less enamel is applied to the crown and is then overlayed with a thicker layer of clear porcelain to give a greater amount of overall translucency (Fig. 5). When crowns require a great amount of translucency with a strong hue coming through, the dentin/enamel is overlayed with 0.25 mm of clear porcelain which gives it a deep look. Intensive powders are utilized for special effects. For example, if the tooth has a strong hue of blue/gray or yellow, some blue or gray pigment is mixed with the clear porcelain. In Fig. 6, gray and clear porcelain was used; in Fig. 7, blue and clear porcelain was used. To evaluate the effectiveness of the technique of proper overlaying of porcelain, the use of modifiers, and the proper thickness of enamel and clear (color-
Figs. 1 through 10. For legend, see facing page. DECEMBER
NUM IBER 6
less) porcelain, two sets of crowns were fabricated for a patient. One of the sets was made with the technique previously described in this article (Fig. 8), and the other was made according to the conventional technique used by many ceramists (Fig. 9). At different stages, the crowns were interchanged and photographs made. The upper right central incisor was from set No. 1 (Fig. 8), and the upper left central incisor was from set No. 2 (Fig. 9). The color used was A2.* For set No. 2 (Fig. 9), the usual A2 opaque and body powders were used with the usual final cutback for the incisal edge (Fig. 2). No clear OVfXldy of porcelain was used. The other set (Fig. 8) was made with a number of modifications to the A2 basic color. The A2 appeared a little too bright, and a darker opaque, C2, was used with the A2 body *Vita V.M.K. many.
powder. The A2 incisal coloring was not as white as desired, and a little white modifier with incisal No. 558 was added producing a greater amount of translucency than the normal A2 coloring. To achieve this, the crown was covered with enamel to the margin, and clear (colorless) porcelain was added (Fig. 10). CONCLUSION Crowns made with proper layering of porcelain and a knowledge of patient’s age, thickness of enamel, and built-in hues will have a better esthetic appearance and will look more natural. Reprint requests lo:
MR. PETER VRYONIS 15 COLLINS ST. MELBOURNE 3000 AUSTRALIA
Fig. 1. Cross section of a natural tooth. Fig. 2. Enamel buildup on a porcelain crown is usually brought to the mid-third of the facial surface. Fig.. 3. Custom-made shade guide. Fig. 4. Custom-made shade guide for incisal edges. Fig. 5. Clear porcelain is overlaid on the porcelain crown to increase the translucency. Fig. 6. A combination of gray and clear porcelain was used to intensify the hue of these restorations. Fig. 7. A combination of blue and clear porcelain was used to intensify the hue of these restorations. Fig. 8. Finished restorations as described in the author’s technique. Fig. 9. Finished crowns as described in the conventional technique. Compare with Fig. 8. Fig. 10. To show the difference, crowns from both techniques were interchanged. Upper right central incisor is from Fig. 8 (author’s procedure), and upper left central incisor is from Fig. 9 (conventional procedure). THE JOURNAL