Inside Dental Technology
Layered Light Refraction and Reflection in Esthetics
Are we heading in the right direction?
As we take a brief look back on the past, it is amazing to think about how many changes have transformed this industry. As with any industry undergoing change, not all new developments are necessarily better. Remember the materials we used before esthetics played a key role in dentistry? Single-unit gold restorations were the product of choice (Figure 1), and the ability to fabricate bridges soon became a mainstay (Figure 2). Long-lasting in most cases, these full-cast restorations exhibited excellent wear characteristics on the opposing arch. The era before porcelain concentrated on function, with esthetics taking a back seat in intraoral rehabilitation.
Veneering materials came on the scene long before most of us can remember. Materials such as silicate and acrylic resins were veneered to gold substructures (Figure 3). Soon after, porcelain facings were cemented to gold with zinc-phosphate cement (Figure 4). Finally, in the 1960s porcelain-fused-to-metal (PFM) was introduced to our industry (Figure 5). Although all of these materials had a significantly higher esthetic value than full-cast gold, there was still room for improvement.
Today, we have a wide range of highly esthetic materials and techniques from which to fabricate our restorations. While the emphasis on esthetics and function remains, the focus in most laboratories is on increased production with efficiency playing a key factor in our day-to-day processes. Because the range of materials and fabrication processes are so varied, it is sometimes easy to forget the true mission of our industry. Our sole mission, as dental technicians and ceramists, is to re-create a part of the human body that is life-like and naturally functioning. The dentist and patient must be kept in the foreground when making decisions on what
materials and techniques should be applied. Intraoral esthetics, fit, and function are all still the key principles in determining a successful outcome.
Making the Case for Layered Ceramics
Contrary to common belief, high-end esthetics can be achieved with layered materials in a production setting and will demonstrate excellent results. When the author began his dental technology career in the early 1980s, the porcelains on the market were very monochromatic—Unitek, Vita (Vident, www.vident.com), and Will-Ceram® (Williams Dental company) offered quality porcelains with a variety of modifiers to work with. There were only a few courses available for teaching the techniques for high-end esthetics. Laboratories at that time competed primarily on the fit and contour of their restorations.
Restorations were typically fabricated using a very simplistic build-up technique. Most commonly, they were built to full contour with body porcelain, cut back, and then incisal porcelain was added. The thought of translucency and body modifiers was not part of the average restorative process (Figure 6). Ceramic-metal crowns were commonly highly reflective with minimal translucency. The term “chicklets” was widely used to describe the final result. New solutions needed to be invented to incorporate translucency into the industry to help create a more natural-looking restoration.
Even in the 1980s, technology was pushing forward, looking for the next best material. A metal-free castable ceramic (flourmica glass) was introduced on to the market. This was a full-contoured material that was then stained and glazed—a technique
similar to that used with pressable systems today.
Dental manufacturers began offering translucent incisals and body modifiers. Once these esthetic-based materials came onto the market, highly skilled technicians were needed to teach the techniques for using them. Two technicians and world-class artisans that the author most admired are Makato Yamamoto and Willi Geller. In their skilled hands, light reflection and refraction played a key role in layered ceramics. Restorations fabricated on metal substructures now had a true lifelike appearance. Today, the combination of metal and ceramics continues to be a proven success. It is the standard to which all other restorative products are compared.
Evaluation of Light Refracted Esthetics in Three Materials
The author chose to evaluate the visual esthetic differences between the three most widely used materials in our industry today—PFM, zirconia, and lithium disilicate—using the exact same build-up process. Using a clinical model from a case in the laboratory, the author began his PFM build-up. This simplified five-powder build-up takes approximately 5 to 7 minutes to complete. Starting with the opaqued coping (Figure 7), the author placed dentin material on the occlusal/buccal surfaces (Figure 8), maintaining a detailed configuration of the cusp tips. Next, the occlusal/lingual dentin aspect was placed (Figure 9). The buccal dentin porcelain was added (Figure 10), and then the substructure for the remaining porcelain was ready. Placing occlusal modifiers that corresponded to the prescription shade in the deepest pit areas helped to create a more natural appearance (Figure 11). Note: Occlusal orange modifier should be used for lighter shades and applied with a wet brush. Amber modifiers should be used for darker shades and applied with a drier brush for detail.
The incisal porcelain was then added in the same manner as the dentin porcelain. Beginning with the occlusal/buccal cusps, the incisal porcelain was applied (Figure 12). Then the occlusal/lingual porcelain was added, maintaining morphology during the process (Figure 13). The buccal porcelain was then added for a full-contour build-up (Figure 14). This simplified technique results in creating a more natural appearance. Using modifiers rather than stain allows the light to pass through the ceramics much like natural dentition. Following the triangular ridges, the author placed a lighter shade (white opal) modifier in these areas (Figure 15). Highlighting the triangular ridges, as well as the marginal ridges, creates a very natural result. Lastly, translucent porcelain was applied around critical areas of the build-up to optimize the results (Figure 16). The PFM crown was finished and glazed (Figure 17). The total time for the build-up and finishing was approximately 15 minutes, not including the fire time (one bake as well as a single glaze). The Re-Creating Nature™ no cut-back technique was developed by the author in the early 1990s.
To create the full-contoured zirconia-milled restorations as well as the full-contoured lithium-disilicate pressed crown, the author took a putty matrix of the PFM crown (Figure 18). A wax pattern was fabricated for the full-contour zirconia scan and the pressed lithium-disilicate restoration (Figure 19).
To create the layered zirconia crown, the author used the same die and then scanned it (Figure 20). To ensure the success of a layered zirconia crown, the substructure must be built up accordingly (Figure 21). The no cut-back technique was used in porcelain build-up, and finishing was the same used in the PFM restoration. The end result shows the natural effects of a layered restoration (Figure 22).
The wax pattern was then scanned for the fabrication of the full-zirconia crown. Then the wax pattern was used in the pressing process of the lithium disilicate. The stain and glazing process for both crowns took two firing cycles for optimum results. The finished result (Figure 23) shows the lithium-disilicate crown. Figure 24 shows the result of the full-contour zirconia crown. The author had no prejudice in the fabrication of all the restorations. Each crown was fabricated with the intention of fulfilling the best possible esthetic result.
Photography was used to evaluate the esthetics of the four crowns. Each photograph was carried out using the same lighting. Figure 25 illustrates the final PFM, Figure 26 shows the zirconia build-up crown, Figure 27 is the full-contour lithium-disilicate pressed crown, and Figure 28 details the scanned and milled full-contour zirconia crown. Placing the four restorations in a single photograph (Figure 29) provides a visual aid in understanding the importance of light reflection and refraction. On the top left is the PFM restoration, and moving clockwise, the pressed lithium disilicate, the layered zirconia, and the full-contour zirconia at bottom left. The dentist makes the choice of what materials should be used for their patients based on esthetics, price, and long-term results. All must follow the growing need for restorations with minimum failure and pricing to compete with offshore laboratories. Working closely with our clients, we can help in determining the optimum results for each individual case.
Materials such as zirconia and lithium disilicate offer a very esthetic result when layered with porcelain. The key to full-contour restoration is that light needs to reflect and refract in different directions to create a natural appearance. The translucent nature of lithium disilicate works exceptionally well in the anterior region when the layering process is introduced. Zirconia also exhibits excellent results when layered, keeping in mind the importance of a properly supported substructure design.
The proper build-up of ceramic material and using various modifiers as well as translucent incisals is essential for achieving “high-end” esthetic results. The use of opalescent incisals also adds a very natural appearance to the final restoration.
The next few photographs illustrate how the use of color and translucency can depict a natural-looking result. These photographs are not of a clinical case, but rather a case created for a seminar given by the author. The first two cases show the results of layered ceramics (Figure 30 and Figure 31). Figure 32 is the postoperative photograph of a PFM restoration. Figure 33 is the postoperative photograph of a porcelain-fused-to-zirconia restoration, and the last intraoral photograph (Figure 34) is a stained monolithic lithium-disilicate restoration. The understanding of dental ceramics is ongoing. The desire to create natural-appearing restorations is in the hands of the ceramist (Figure 35).
Ceramists should have the desire to create a natural and functional prosthesis. The final product is being paid for by a consumer who may have had to save valuable money to afford the restoration. The author’s belief is to try and keep the cost down while providing the most natural results. Automated production definitely has a place in our industry. However, with the explosion of new materials for these machines continuing at a rapid pace, the author believes there is a need for more definitive studies on the long-term durability of external stains in the oral environment.
No one can predict, with any degree of certainty, the future of our chosen profession. Automated technology and full-contour stained crowns may be here to stay. Nonetheless, the author believes that there will always be a place for the esthetically oriented technician and ceramist. Not that long ago, technicians prided themselves on creating the best multi-layered ceramic restoration. This is an art our industry should never forget. Having a creative and artistic mind helps us as technicians to become even better in replicating nature.
About the Author
Douglas J. Frye, CDT
Functional Esthetics Dental Lab Inc.