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Zirconia: Taking Dental Restorations to the Next Level - biw226 - 09-28-2021
Since the introduction of porcelain-fused-to-metal (PFM) crowns in the 1960s, the dental industry has sought materials with both the esthetic value of porcelain, and the strength of noble metals to withstand the pressure of posterior occlusal forces.
Glass-ceramic materials that came along in the 1980s were confined to use on anterior teeth. In the early 2000s, researchers found that a toughened version of the metal zirconia met the strength requirements needed for posterior teeth, although the esthetics of the material left much to be desired.
Today, with improved technology, zirconia now rivals PFMs and all-ceramic restorations both for strength and beauty.
A member of the titanium family of metals, zirconia has multi-industry uses and is ideal for use in both anterior and posterior crowns where it fulfills functional requirements and can be custom shaded for quality esthetics.
Advantages
Zirconia is now the preferred material for crown and bridge fabrication, including implant-supported restorations. These are replacing metal-based restoration as the choice of most dentists, lab technicians, and patients. Because it can withstand occlusal forces without causing wear on opposing teeth, the material has quickly replaced full-metal and PFM’s as the material of choice.
Zirconia is more wear resistant than gold, retaining its shape and resisting the tendency to crack and erode by patients who brux. The flex strength value (MPa) of zirconia is more than twice that of traditional lithium disilicate (glass-ceramic) making it the ideal material for posterior crowns and bridges.
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While there is, as always with innovative technology, a learning curve for dentists new to working with zirconia, the techniques for tooth preparations is basically the same as for porcelain and glass ceramic materials. A more conservative preparation of the patient’s original tooth structure is a distinct advantage.
With zirconia, clearance may be as little as 1 mm, while lithium disilicate materials require 1.5 to 2mm and will not be as strong. A thicker chamfer is preferable to a feathered margin to provide for minimum thickness at the margin while retaining the ability to taper it to the prep.
Traditional impressions or digital impressions can be used with equal success.
Concerns
As with all new materials and technology, dental zirconia does have its drawbacks.
Many dentists are hesitant to use zirconia because there are fewer long-term research studies to assess its properties and compare the longevity of the material to gold, porcelain, and lithium disilicate. However, the studies completed thus far all reflect positively on the future of zirconia crowns.
There is also a lack of ability to bond the material to the preps. Though, that might be seen as an advantage by some, since only cement is needed to permanently seat the restoration. The hardness, while certainly considered one of zirconia’s advantages, might be a disadvantage when having to remove or access through them for endodontic treatment.
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Chairside adjustments, while usually minimal, must be made safely, using diamond burs at slow speed with copious amounts of water, polishing wheels, and cones specifically designed for use with zirconia.
Do not use carbide burs or diamonds at high-speed for adjustments due to microscopic fractures that can occur from the impact of the burs on the material.
Ready to Try?
The future of zirconia use in dentistry is unlimited.
Gold and other noble metals used for decades are slowly dying out due to not only prohibitive cost, but also lack of demand by consumers. Zirconia more than fills that gap.
Researchers continually improve the translucency of these restorations, making them legitimate rivals to all-ceramic for beauty and surpassing other dental materials for strength and durability.
Here are First Choice Dental Lab, we specialize in all types of zirconia restorations, including full-contour and esthetic anterior.
Ship us your case today by clicking HERE, or send digital scans HERE to give zirconia restorations a try!
Want to learn more? Complete the form below and let us help you plan your next restoration!
Pre shaded zirconia has become popular with dental laboratories due to the time-savings and shade consistency the base shade provides. With pre-shaded zirconia there is no need for laboratory technicians to shade each unit in the green stage, saving production time and freeing them up to produce more units. However, standard pre-shaded zirconia systems require the dental laboratory to stock an inventory of 16 shades, each in a large selection of disc thicknesses to cover all unit shades and sizes. Furthermore, you can mill only one shade at a time, thus tying up your mill.
The ArgenZ Anterior Value Shaded Disc System is a collection of pre-shaded super translucent zirconia that covers all 16 shades of the VITA Classic shade guide with just six value-shaded discs. Each disc covers 2-3 shades based on value and chroma, requiring much less inventory and mill time. No green stage shading is required. You simply design, mill, sinter, and stain and glaze.
The discs are as follows:
? Disc 1: Shades A1, B1
? Disc 2: Shades A2, B2, A3
? Disc 3: Shades C1, D2
? Disc 4: Shades C2, D3, D4
? Disc 5: Shades A3.5, B3, B4
? Disc 6: Shades A4, C3, C4
Hue and Chroma Shading
Similar to the 16-disc shade systems, each ArgenZ Anterior Value Shade Disc group will be approximately one-half shade lighter than the lightest shade in that group. This makes it easy for the technician to change hue, adjust chroma intensity, and create a good incisal transition zone with external chroma stains.
Value
Traditional all ceramic systems are low in value, especially the light high value shades such as A1. The ArgenZ Anterior Value Shaded System is formulated to deliver a true value to match the guide.
Incisal Translucency and Appearance
The translucency of ArgenZ Anterior and the additional light refraction from the cubic ZR phase results in a natural incisal translucency requiring little to no incisal staining. Units with thicker incisals may require some minor incisal enhancement with incisal enhancement stains.
Stain and glaze system
Many companies make a low fusing fluorescent stain-and-glaze system designed primarily for all-ceramic systems. The most important stains in the kits are the A, B, C, and D chroma stains. These stains are essential to stain up to the next chroma or shade level in each shade group. Incisal stains or intensive blue stains can be customized with black, white, or violet to make any incisal enhancement color needed.
Firing Temperatures
Stains do not penetrate zirconia, so it is not necessary to fire above 800°C. The systems the author uses allow stains to be fired at 750°C (fully melting) and glazes to be fired at 730°C.
Die Shading System
Units must be seated on a die for final staining to match the shade guide. Due to the translucency of anterior zirconia, the final shade is slightly affected by light diffusion and the color of the underlying die and preparation. The anterior unit will appear to have a higher value and slightly more chroma when seated on a die.
Using a die color coating system to match preparation shades (stump shades) is recommended. Preparation coloring systems contain a variety of colors to match light to dark shades. If you do not have guidance on preparation colors (picture or preparation shade), match the die shade color to the prescribed base shade.
Glass Ceramic Materials
Glass ceramic materials have the same chemical compositions as glasses but differ from them in that they are typically 95-98% crystalline by volume, with only a small percentage vitreous. The crystals themselves are generally very small, less than 1μm and most often very uniform in size. Furthermore, due to their crystallinity and network of grain boundaries, they are no longer transparent.
Production of Glass Ceramic Materials
Glass ceramic components are formed using the same processes that are applicable to glass components. To convert them from a vitreous glass material into a crystalline glass ceramic material they must be heat treated or devitrified.
Devitrification can occur spontaneously during cooling or in service, but is most commonly incorporated to produce glass ceramics. It involves heating the formed glass product to a temperature high enough to stimulate crystals to nucleate throughout the glass. The temperature is then increased, which induces growth of the nuclei, crystallising the remaining glass.
Nucleation requires a critical number of atoms converging to form a nucleus. When the nucleus reaches critical size, nucleation occurs. In many glass compositions, nucleation is hampered by the fact the material is silica-based and highly viscous, making it difficult for the required atoms to come together. The crystal compositions can also be complex making nucleation difficult. These factors aid glass forming and cooling without crystallisation.
The devitrification heat treatment must be carefully controlled to ensure the maximum number of nuclei are formed and that these nuclei grow into a uniform fine crystal structure. In order to obtain a high concentration of nuclei throughout the structure, it is common to add a nucleating agent to the glass composition.
How are resin frameworks made? CAD design software is used to design the framework and then it is milled out using milling machines. The resin clasps engage the origin of the undercut rather than the terminal third to allow three to four times the retention of metal. In addition to a superior esthetic color, the resin clasps can be placed more gingival, further increasing its natural appearance.
Acetal dental can also be used for tooth shaded clasps on acrylic partials as well as a single and two tooth posterior unilateral partials. The latter situation is a great way to make an interim partial for a patient having implants placed.
For these reasons, we believe in recommending acetal resin to other dentists and our customers. It’s a strong, versatile material that has proven to be superior to using metal clasps and frameworks. We are committed to researching and finding the best products for our dentists.
Roland DGA Corporation’s three Diamond-Coated Dental Milling Burs, meant to be used with Roland’s DXW-50 zirconia milling machine, are specially engineered for precise performance, maximum durability, and longer life. Extensively tested for tolerances, Roland’s new milling burs are available in three different sizes – 2 mm, 1 mm and 0.8 mm – allowing dental professionals to choose an ideal tool for every milling strategy.
The proprietary design of every Roland Diamond-Coated Dental Milling Bur enables the user to produce up to 10 times the number of units that can be milled with a standard carbide model. Because they are fully compatible with Roland’s existing carbide tools, users can switch to the new tools without any changes in the CAM software, making the upgrade a true “plug-n-play” solution.