By Lee Ann Brady, DMD
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The world of materials has become so vast since I graduated from dental school in 1988. In those days, choosing the right material was uncomplicated. 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 we should use to optimize the outcome. We have many choices that provide both esthetic and functional success in varying degrees. Making this choice requires understanding of the material characteristics that impact final esthetics and strength, and then combining that with the clinical situation and hoped-for outcomes.
We have all-ceramic materials today that can be used as a monolith or solid bulk of one material, such as lithium disilicate (e-max by Ivolcar) 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 off under flexural or sheer loads.
Monolithic restorations eliminate this weaker outer layer and give us restorations with strengths between 380 and 1000 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 beginning to close. 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 am 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 answer is which of these materials does your technician prefer? Usually lab techs will produce better results with a material they like to work with, 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 opaquing 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. We want to use the material with properties that can get us as close to the natural tooth as possible. In the clinical situation where we are restoring all of the teeth in the esthetic zone with good prep color, we want to use a material that will get us the best match for the value, hue, and chroma we desire. Taking plenty of photos of the prepared teeth to send to your technician, along with stump shade information, will allow them 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 we 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 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.
Dr. Lee Ann Brady earned her DMD degree from the University of Florida College of Dentistry. Her practice experience has been rich and varied. For 17 years, she worked in a variety of practice models from small, fee-for-service offices to large, insurance-dependent practices as an associate and a practice owner. She was invited to join The Pankey Institute in January 2005 as its first female resident faculty member and was promoted to clinical director within a year. She was asked by Dr. Frank Spear to join him in the formation of Spear Education and the expansion of his curriculum in September 2008 as executive vice president of clinical education. This year, Dr. Brady launched her website, www.leeannbrady.com, to offer clinical and practice content daily. In addition to being a dedicated educator, she maintains a private practice in Glendale, Ariz.
Choosing the right all-ceramic material
By Lee Ann Brady, DMD