Creating Esthetic Results in Minimal Space
Understanding the optical properties of materials is crucial
By Peter Pizzi, CDT, MDT, FNGS
The evolutionary advancement of restorative materials offers today’s dental technicians more options than ever. However, with that evolution comes the challenge of layering ceramic onto these substructure materials and understanding the materials’ optical properties with respect to opacity, translucency, depth, density, and space. The challenge also extends to understanding the proper use of the new substructure materials for supporting the ceramic layering material. Although ceramic-to-metal is still a very viable restorative material combination, especially when used in implant structures, the use of lithium disilicate and zirconium dioxide has evolved much more quickly than the porcelain-to-metal process has. Like all evolutionary processes, the work that went into mastering porcelain-to-metal has helped push the boundaries with these newer materials. Adding to the equation, these new substructure materials have many different degrees of opacity, value, and translucency. The technician’s knowledge of the optical properties of these materials is key when choosing restorative options that best fit the esthetic and functional parameters of the patient’s needs.
The Issue of Space
Regardless of which material is chosen for the restorative case, space and the technician’s use of it are still the most critical factors in achieving esthetic goals. When dealing with restoring the small natural size of the lower anterior teeth, we are always fighting for material space because these teeth most often are under-prepared and offer the smallest amount of space in which to restore them. One of the many positive advantages of the newer all-ceramic substructure materials is the ability to work in less than the “normal” 1.2- to 1.5-mm working space because it is no longer necessary to mask the metal substructure with opaque. It is now possible to use either opacified pre-colored or translucent-shaded materials as the base for the ceramic, or more translucent materials as a base for layering, depending on the existing stump shade of the natural teeth. Either choice allows treating the substructure as part of the layering space.
To understand this concept, it is necessary to break down the space by defining the ceramic proportions (Figure 1). Most ceramic materials have been formulated to work best in a working space of 1.2 to 1.5 mm. The space is divided as follows: .2 to .4 mm for the substructure; .8 to 1 mm for “dentin” type materials; and .2 to .5 mm for “translucent” type materials. Although it is never recommended to use only two powders to achieve the desired esthetic results, if the thickness of the substructure is .4 to .5 mm, then our knowledge of the optical properties of materials comes into play. How the powder choices are manipulated in the working area is critical (Figure 2).
The use of opacious, fluorescent, or translucent materials will define the esthetic results. Also, the ability to utilize the substructure as part of the layering space will aid in the use of fewer layering materials. This makes it possible to work in slightly less space than usual in cases with minimally prepared teeth or lower anterior teeth. The ability to choose the opacity level of the substructure material is critical to the final result, and the decision on material choice should be made based on patient information, the desired esthetic parameters, and an understanding of the material being used. Masking the prepared tooth based on the darkness of the stump color or exposed restorative will require opacified materials, while more translucent materials can be used when the underlying prepared tooth structure has adequate coloration. Using shaded translucent materials also makes it possible to treat the substructure as the first few tenths of a millimeter of the dental buildup, which in turn saves ceramic layering space.
Although the purpose of the choice of substructure material is to provide ceramic support, setting the base color by the choice of substructure material is just as critical. For the purpose of this case (Figure 3) an opacified zirconia was selected as the substructure material because the shade of the prepared teeth was considerably darker than the desired color of the final restoration. The author digitally designed three single substructures and a 3-unit bridge framework. For this particular case the substructure was designed as a simple coping because the lack of space dictated the substructure size. However, it is always recommended to use a more extended coping design to support the ceramic and to assist in the final esthetics.
Even though using zirconia as the substructure material eliminates the need for an opaque-type masking layer, it is recommended that a bonding layer be applied to the zirconia substrate (Figure 4). Several bonding layer material options are available, and each manufacturer offers guidelines to help facilitate the proper use. For this case, the author used Imagine InSync Zr Layering Ceramic (Jensen Dental, jensendental.com) (Figure 5). The use of the Imagine InSync FC Stain & Glaze liner system (Jensen Dental) was a critical step in balancing the proper coefficiency of the layering material because the InSync ceramic system can be layered on several types of substructure materials, including foil, refractory, zirconia, lithium disilicate, and titanium. In addition to aiding with bonding, most liner material options also create fluorescence in the substructure, which is critical for light transmission in the final esthetics. For this case, the author applied ZR Liner neutral (Figure 6) and used several stains from the same ceramic kit to create the canvas to support the final color.
Each ceramic material plays an important role in the final esthetic outcome. Opacious dentin material is often one of the most misunderstood materials that we use. It is important to understand that each powder, ie, dentin, opacious dentin, and enamels, has different amounts of opacified particles and reacts differently to absorption or reflection of light based on the particle amounts and the thickness of the material application. Obviously, opacious dentins exhibit higher opacity than dentine materials. If used in very thin amounts such as .2 to .3 mm, they do not possess the opacity needed for their general purpose. However, understanding the properties of the materials is key, and the powder can be modified to achieve the desired results in critical areas (Figure 7).
Using opacious dentin as a material to add chroma or to support the value of dentin material is optimal. Using a more intense shade interproximally will help create the depth needed, while on the facial surface it is possible to increase value or support the needed value of our dentin materials. Marginally, where the material will be at its thinnest, it will be necessary to modify the opacious dentin with the use of fluorescent, chroma stain materials.
The Dentin Enamel Canvas
Depending on the choice of substructure material, building the dentin enamel canvas will be based on the previous placement for the value and color scheme (Figure 8 and Figure 9). In this case, a higher chroma dentin was applied cervical and interproximal with higher-value dentins placed in the mid-third. Gradually the dentin will become more translucent either through the thickness of the layer applied or by mixing it with the enamel materials toward the incisal edge.
The transition between the end of the substructure and the translucent dentins is most challenging for many reasons (Figure 10). This is the most critical area with the least amount of space, and it is necessary to use a material that can provide both depth and opacity in thin areas. Mamelon materials are highly opacified and usually possess high fluorescence. This allows them to be very useful in small areas and perfect for creating an effective mask to hide the transition between the end of the substructure and the incisal frame (Figure 11).
Enamel and Translucent Materials
Enamel and translucent materials are chosen with two primary considerations. First, the choice of enamels is based on the final value desired for the restoration. Whiter, brighter enamel materials block the penetration of light while more translucent materials allow the internal canvas to show through and lower the overall value. Second, the choice of enamel and translucent materials should follow the patterns set by the previous layers placed from the choice of substructure material to the placement of opacious dentins and the dentin enamel canvas (Figure 12 and Figure 13).
Figure 14 through Figure 17 show the restorations on the model before and after polishing as well as right and left texture views. Figure 18 and Figure 20 show the definitive restorations seated in the mouth.
Restoring areas that offer limited space can inhibit the ability to create depth in the final outcome. However, knowledge of the materials being used will help manipulate light and allow the restorations to appear more natural even in these difficult spaces. Understanding powders is the key to creating successful restorations and a must for the future of our viability as technicians.
The author had no disclosures to report.
About the Author
Peter Pizzi, CDT, MDT, FNGS
Owner and Manager
Pizzi Dental Studio Inc.
Staten Island, NY