From diagnostic wax-ups to final layered ceramics
Peter Pizzi, MDT, CDT
The evolution of materials in the dental field has created many new options for technicians today. Our understanding of how to utilize each material as either a monolithic or layered substructure indicates each material's unique esthetic potential. Although the development of these various materials has aided our ability to better restore nature, some of the basic principles of substructure design have also evolved and presented technicians with the opportunity for greater precision in our work.
For me, fully layered and micro-layered restorations are still our most esthetic options, but as we progress and become more efficient in our work, the design of the substructure can aid us in several ways. The purpose of basic substructure design was to mask the underlying structure, support the layered ceramic, and allow as much space for layering as possible. As materials such as zirconia and lithium disilicate advance in opacity, translucency, and coloration, they become more useful to us and can be utilized in the same way as our dentin or opacious dentin powders would be used. Creating a working canvas that allows light to be either reflected or absorbed from the substructure offers a very efficient means for micro-layering ceramic while still providing a highly esthetic result.
To create an esthetic substructure, an understanding of space is critical. First, a diagnostic wax-up is either digitally or manually created (Figure 1). Although the wax is not a great medium for light, we can see the areas where light is reflected or absorbed (Figure 2). An index of the full-contour wax-up is taken and used to dictate the cutback. The cutback design is based on the desired effect for the final restoration with limited use of layering powders (Figure 3). Each convexity or concavity plays an important role in allowing the manipulation of light (Figure 4) and the design can be achieved either manually or in three-dimensional space.
Once the design is complete, the three-dimensional CAD/CAM process can be completed with the precision detail of the final carving stage as the focus (Figure 5). After milling and sintering, the esthetic substructure is completed and the layering process can be achieved with fluorescent liner materials (Figure 6). Based on the convexities and concavities of the substructure, only a few powders will be needed to achieve a desired esthetic result, as the substructure helps in the reflection or absorption of light (Figure 7 through Figure 10).
As the dental field witnesses advancements in the principles of substructure design as well as the materials utilized, technicians have the opportunity to create more precise and esthetic work that better mimics nature's design.
Bench Essentials is a quarterly series in which IDT Editor-in-Chief, Peter Pizzi, MDT, CDT, presents educational lessons about the fundamentals of dental laboratory technology based on his decades of working at the bench and lecturing around the world.