By Lee Ann Brady, DMD
The world of materials has become so vast since I graduated from dental school in 1988. In those days, choosing the right material was not complicated. I had one choice when esthetics was my primary concern — a porcelain-fused-to-metal crown with metal margins. When I wanted strength and durability of esthetics, the patient and I opted for an all-gold restoration and could even save a cusp here and there. Today, each clinical situation presents a decision about what material to use to optimize the outcome. We have many choices that provide both esthetic and functional success in varying degrees. Making this choice requires understanding the material characteristics that impact final esthetics and strength, and combining that with the clinical situation and desired outcomes.
Today we have all-ceramic materials that can be used as a monolith or solid bulk of one material, such as lithium disilicate (e.max by Ivoclar) and zirconia (BruxZir by Glidewell). The advantage of using a monolithic restoration is strength. In all of our ceramic restorative options, it is the layering porcelain we apply over the core that is the weak link, usually having a flexural strength of between 90 and 140 Mpa. It is this outer layer of ceramic that fractures under flexural or shear loads.
Monolithic restorations eliminate this weak outer layer and give us restorations with strengths between 380 and 1,000 Mpa, ideal for posterior situations. The challenge with monolithic restorations is our ability to optimize the esthetic results. In the last few years, the esthetic choices in these materials have become broader. With new ingots and blocks with better color and light-reflective qualities, the esthetic gap is closing. In addition, the final result is influenced by the addition of stains and the skill of the technician (dentist or assistant) who applies the stain.
We now have a broad range of layered all-ceramic choices. The outer esthetic layer of porcelain can either be completed with a powder and liquid ceramic, or pressed over the ceramic coping. Pressing has become more prevalent due to the ease of fabrication and accuracy of the marginal fit. Traditionally, we discussed powder/liquid ceramics as having a broader esthetic range, but again, this is technician-dependent. Today, I'm often unable to tell the difference between a hand-stacked and a stained restoration.
The greatest difference in layered all-ceramic restorations is the ceramic used for the coping. Our choices include metal ceramics, Captek, zirconia, lithium disilicate, and alumina. An important question to address is which of these materials does your technician prefer? Lab techs will usually produce better results with a material they prefer, so this alone may guide your choice. The ultimate strength of the final restoration will be the same, as the layering glass will be where failure occurs, not the coping. Each of these core materials has different esthetic characteristics that, for me, are critical factors when paired with my technician's choice. When dealing with very discolored preparations or covering restorative materials (such as metal post cores), my first choice is metal ceramics coupled with adequate reduction and a skilled ceramist. Zirconia also has good opaque characteristics. Your technician may prefer the high reflectivity of the core to achieve certain final value and chroma combinations.
Lithium disilicate and alumina are available in a variety of opaque and translucent ingots and blocks that allow the technician to blend the color characteristics of the tooth, core, and layering ceramic to achieve the final result. When matching a single tooth, the difference in light characteristics of the core can be critical. Use the material with properties that can get as close to the natural tooth as possible. In the clinical situation where you are restoring all of the teeth in the esthetic zone with good prep color, use a material that will get the best match for the value, hue, and chroma desired. Taking plenty of photos of the prepared teeth to send to the technician, along with stump shade information, will allow the technician to guide you in this decision process.
In addition to the choices currently available, new materials are coming on the market as manufacturers strive to find the perfect combination of esthetics and strength. So how do you choose the "right” material? Spend time learning about the different materials, and use your technician as a resource. Invite him or her to be part of the process during treatment planning, sending your tech the preop photos and your plan for final tooth position and shade. The technician can add valuable information about materials and tooth preparation that will set you up for success.
Lee Ann Brady, DMD, is a nationally recognized educator, lecturer, and writer. She is the clinical director of the Pankey Institute. Dr. Brady is president of leeannbrady.com, which offers continuing education workshops, seminars, and online content. She maintains a private practice in Glendale, Arizona, is the clinical editor of the Seattle Study Club Journal, and is a guest faculty member for the Pankey Institute. Reach her at [email protected].
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