Considering Abutment Color in Zirconia Restoration
Step-by-step instructions for utilization of opacity control materials in zirconia restorations.
By Hiroyuki Kito, RDT
Mastering the complex art of esthetic dentistry is strongly based on knowledgeable material selection and understanding the characteristics of those materials. In the past decade, with the introduction of zirconia copings manufactured by the CAD/CAM method, zirconia has become one of the most essential materials, preferred by many clinicians over porcelain-fused-to-metal (PFM), which had previously been the leading choice. More recently, zirconia and lithium-disilicate were regarded as innovative all-ceramic materials in esthetic restorations. The lithium-disilicate restoration shade has even greater translucency than zirconia, and therefore cannot avoid being affected by the abutment shade.
As long as the required thickness of a zirconia restoration is maintained, the strength of a zirconia restoration is almost the same as that of a PFM restoration. From the viewpoint of esthetics, a zirconia restoration has a distinctive advantage over a PFM crown—the zirconia coping has translucency.
Just as PFM was not flawless, there has never been a textbook-perfect material. Each has its advantages and disadvantages. Dental technicians seek to understand these material characteristics and constantly search out the best solutions for clinical cases.
The higher the translucency of a coping, the easier it becomes to reflect the shade of the abutment. By the same token, the lower the translucency of a coping, the better it covers the shade of an abutment. The translucency of the Noritake KATANA coping (Figure 1) provides “middle to high translucency.”
The author will focus on esthetics for each of the clinical cases. When making all-ceramic crowns, it is important to consider all kinds of shade factors, including the abutment, resin cement for bonding, coping, porcelains, internal stains, and external stains to be applied on the coping.
Noritake manufactures three kinds of color in zirconia restoration (CZR) opacity control porcelains (Figure 2) that are not intended for covering the shade, CZR Shade Base, CZR PRESS Shade Base Stain, and CZR Opacious Body (for dentin color).
Case 1: Metal Core
The chief complaint by the patient was the displeasing appearance of the maxillary dentin—especially the PFM crowns on the right central incisor and two laterals (Figure 3).
The case began with shade-taking photographs to document the case (Figure 4). The shade would need to equal A3.5 (equivalent with KATANA KT 14). Noritake KATANA KT13 was recommended instead of KT14 to increase the value of the die, which was darkened by the metal core. Next, the coping was adjusted while set on the white model. The die needed to be colored gold to recreate the actual tooth condition (Figure 5). Next, the coping on the gold-colored die was set and examined. The color and chroma were then adjusted by applying a first application of CZR PRESS Shade Base Stain SSA3, one shade lighter than A3.5, then baked. To avoid the “white margin,” CZR Internal Stain A+ was applied and baked, then applied a second time and baked, thus masking the die color 80%; CZR Opacious Body Enamel covered the remaining 20%. The mixture of A3.5B + CCV-1 + CCV-2 (mixing ratio 2:1:1) was applied on the cervical area. The mixture of A3.5B + Opacious Body White (ratio 1:1) was selected instead of A3.5 + Opacious Body OBA3.5 to prevent possibly lowering the value due to the metal core. E2 and E3, then E3 + Luster “LT Natural” (2:1) were applied in the incisal area and Luster “LT Natural” in the center area of the crown, then baked and the shade color was adjusted. Additional build-up was required for an all-ceramic restoration. The “crack line” was characterized with internal stain, enamel with CZR Luster “Sun Bright,” and a mixture of E1 and E2 (1:1). CZR Luster “Incisal Aureola” was applied on the incisal edge and LT0 on the entire area. Care was taken to ensure that 0.7-mm thickness was at the thinnest position (Figure 6). Once this was finished, the process was complete. The composite resin restoration on the remaining incisor using the most esthetically effective method was planned for completion at a later date (Figure 7).
Case 2: Fiber Core
The patient expressed a desire for an esthetic improvement of the devitalized tooth on the maxillary right central incisor to match the natural left central incisor (Figure 8). Like Case 1, the following steps were implemented through completion and began with shade-taking photographs to document the case (Figure 9). After the photographs were taken, the coping on the model was set. The die was made with composite resin material (Kuraray Epricord™, www.kuraray-dental.eu) to recreate the natural abutment. The internal stain A+ was applied on the whole surface of the coping to adjust the chroma, and then baked. Internal stain gray was applied one third from the incisal edge to create a translucency (Figure 10), after which a mixture of A3.5B + Opacious Body White (ratio 1:1) was applied to prevent decreasing value through the use of layered enamel porcelain; it was then baked. Care was taken to make sure the die (abutment shade) was seen through the translucent material. Next the shape was outlined with Noritake Original Shade (NP1.5B), E1 and E2 was applied, followed by luster “Creamy Enamel” and “T Blue” on the necessary spots, and then baked. After baking, the enamel was characterized with a mixture of E1 and E2, and the luster “Incisal Aureola” was applied on the incisal edge and LT0 on the entire area, and then baked. After the morphological correction, the glazing and final polishing were applied until the process was complete (Figure 11).
The two clinical cases featured in this article conclude with the next crucial points. It is important to know whether the zirconia restoration shades are either seldom or frequently affected by abutment shades—fiber core or metal core. Unnecessary attempts to cover the abutment shade may result in losing the benefit of superior translucency of an all-ceramic restoration. If the targeted restoration shade is close enough to the abutment shade, it will lead to an excellent final color match with correct material selection.
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About the Author
Hiroyuki Kito, RDT has served as a Chief Ceramist for Cusp Dental Supply/Kanare Technical Center, Nagoya, Japan, since 2003. He serves as an official instructor for Noritake Dental Supply.