Zirconia CAD CAM Metal Free Dental Crown Material in Delhi India
Zirconia CAD CAM Metal Free Dental Crown Material in Delhi India
Zirconium ( Zirconia ) is rapidly becoming the material of choice for cosmetic dentist for fabricating dental crown & bridge in India. It is a remarkably very hard & robust material which is able to withstand the wear and tear of our day to day life use. These are called as zirconia metal free CAD CAM all porcelain full ceramic dental crown in India.
More importantly however, it has a translucency that is very similar to a natural tooth – light is reflected from a Zirconium crown in much the same way as it passes through the natural tooth, so it looks next to natural when used in front teeth or in posterior teeth.(Zirconia Dental Crowns Dentist Clinic India)
Thus, Zirconium produces the best aesthetic effects, which is important if your new crown is to be for the front teeth area. It is particularly the case when the crowns will be seen beside a natural tooth.
Zirconium is one of the most abundant elements in the earth’s crust. Zirconia is formed by the addition of oxygen to the pure, elemental zirconium metal. The addition of minor components to the zirconia, such as yttrium, can produce a crystal that is both strong and resistant to crack generation because of the unique “transformation toughening” that occurs when zirconia goes from a tetragonal phase to a monolithic phase.
It is this monolithic phase of zirconia that is so resistant to breakage when used in full-coverage restorations.
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Introduction
Zirconia or zirconium dioxide (ZrO2) is a highly attractive ceramic material in prosthodontics due to its excellent mechanical properties related to transformation toughening, which are the highest ever reported for any dental ceramic and enhanced natural appearance compared to metal-ceramics.
It is widely used to build prosthetic devices because of its good chemical properties, dimensional stability, high mechanical strength, toughness, and a Young’s modulus (210 GPa) similar to that of stainless-steel alloy (193 GPa).
The high initial strength and fracture toughness of zirconia results from a physical property of partially stabilized zirconia known as “transformation toughening”. Zirconia is a polymorphic material that has 3 crystal phases: monoclinic (m), tetragonal (t), and cubic (c). At room temperature, zirconia is in monoclinic phase and transforms into tetragonal phase at 1170°C, followed by a cubic structure at 2370°C. While cooling, the metastable tetragonal zirconia is transformed into stable monoclinic zirconia.
The tetragonal to monoclinic (t→m) phase transformation is associated with a large volume expansion (3-5%) that induces compressive stresses opposing crack opening and acts to increase resistance to crack propagation.
In vitro studies of zirconia specimens demonstrate a flexural strength of 900 to 1200 MPa and a fracture toughness of 9 to 10 MPa/m2. It is a bioinert, not soluble metal oxide that also exhibits a favourable radio opacity and a low corrosion potential.
Zirconia frameworks can be produced according to two different CAD/CAM techniques. In soft machining technique, CAD/CAM systems shape pre-sintered blocks, which involves machining enlarged frameworks in a so-called green state. The enlarged pre-sintered zirconia frameworks are then sintered in a sintering furnace to their full strength that is accompanied by shrinkage of the milled framework by 25% to the desired dimensions.
In hard machining technique, fully sintered blocks are shaped. The framework coloration is performed either adding metal oxides to the zirconia powder, or embedding the frameworks in metal salt solutions after machining. Glazing is created by firing a small coating of transparent glass onto the surface or by heating the framework up to glazing temperatures for 1 to 2 minutes to get shiny glass surfaces.
Although zirconia has superior mechanical properties, its opaque white color and insufficient translucency require glassy porcelain veneering on the framework to achieve a natural appearance and acceptable aesthetics. However, cracking or chipping of the porcelain veneer has been reported to be a major complication of these restorations. The possible causes of porcelain veneer cracking are; differences in coefficient of thermal expansion (CTE) between framework and porcelain, firing shrinkage of porcelain, porosities, poor wetting of veneering, flaws on veneering, inadequate framework design to support veneer porcelain, overloading and fatigue.
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Chemistry and Technical Aspects
Monolithic zirconia restorations begin their journey as chalky white blocks. They are milled to their designed shape and then are soaked in a dyeing liquid to approximate the requested VITA® shade.
The dyeing liquids have improved over the past 2 years and likely will continue to evolve. The final VITA shades of the MZ crowns now being shipped by laboratories seem to be more consistent than was imaginable only 2 years ago.
Recent changes in coloration protocol for MZ restorations have seen the introduction of a three-zone colouring system. First, the un-sintered restoration is brushed with the desired final colour around the cervical zone of the crown. Next, the body of the crown is brushed with the desired body shade. Finally, effect shades are used to characterize the occlusal area of the crown.
After the milled crown has been shade-adjusted in the colouring solution, it is sintered in an oven for 6.5 hours at 1,560ºC. Sintering drives the tetragonal zirconia to its monolithic phase and the gives the milled crown its great resistance to fracture and breakage. During the sintering process, the zirconia shrinks and becomes much denser. A computer program is used to increase the size of the crown during the milling process to compensate for the shrinkage that occurs during the sintering process.
Resistance to fracture and crack propagation makes full-contour MZ an ideal material to fabricate bridges for posterior teeth. To be sure the bridge will not fracture, each connector must have a calculated number of 27 or higher.
The number is determined by measuring the connector area. The height, width, and depth of the connector, when combined, must equal 27 or greater. The connector is measured in millimetres and the results are multiplied to obtain the final number.
With adequate connector size, three-, four-, and even six-unit bridges are very predictable using full-contour MZ. Using conventional PFM cementation techniques, these bridges are easily cemented and the clean-up is very simple.
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Video Testimonial
We welcome people searching for all porcelain, full ceramic, Zirconia metal free CAD CAM designed computer manufactured dental crown and bridge treatment procedures in East Delhi – India, by certified dental surgeon in India at a renowned dental clinic with all latest well-equipped Zirconia dental Lab and clinic in East Delhi, India.
Appointments – The appointment time is flexible and we work all 7 days a week and we will give you your preferred time slot as per your preference.
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Dr. Goswami – dental crown dentist in Delhi, founder & owner of dental crown & bridge clinic in East Delhi – India, welcome people to have a detailed consultation for their missing tooth replacement with different type of dental crown material and why to choose zirconia metal free CAD CAM designed computer manufactured all porcelain full ceramic dental crowns over conventional metal porcelain crown work.
Same Dental Crown Dentist in Delhi, Affordable cost, Same location since last 23+ yrs. (est. 2000).
That’s the real beauty of having Dental Crown Treatment in Delhi from Delhi Dental Center.
