FAQ(En)

Anders Sundh, decim digitalkamera

FAQ
Below you will find answers to commonly asked questions.
Anders Sundh is clinically responsible for Denzir and answers your questions.
If you can not find your question below please feel free to ask your questions directly to Anders by clicking here>>

 

How well documented is Zirconia?
Zirconia is very well documented in some areas, notably its biocompatibility. Over 200 studies are scientifically published in the field Zirconia biomaterials. However, the documentation of long-term studies of dental restorations is lacking.

 

What about aging of zirconia are there risks with it?
All ceramics aging in some degree , and the result is that the ceramic changes it’s phase and finally burst. This also applies to Zirconia and is the major risk of using zirconia in dental restorations.

Aging is accelerated by two main factors ; loading and water . Technically, the aging of zirconia is when the tetragonal crystal grains transforms to monoclinic phase. This is also called the Zirconians self-healing effect, ie the monoclinic grains is 3-4 % larger than the tetragonal and “clog” again the appearance of microscopic cracks. But over time and with the help of water and load , this phase change continue on through the whole or large parts of the material. When large parts of Zirconia goes back to the monoclinic structure it loses its advantageous material properties, especially the strength .

This aging problem is by far the main reason why Zirconia should be HIP’t , ie treated by ultra-high pressure and heat. HIP process makes the material denser and the grain size becomes smaller, so that the material take up a minimal amount of water.

 

Can you influence Zirconia by different treatments?
Zirconia can be affected by some of the commonly used treatments in the lab and clinic.

Blasting affects zirconia and provides a phase change on the surface. A good study in this area are: Strength influence vaiables on CAD/CAM zirconia frameworks , Hang Wang et al , Dental Materials , 2007. While the blasting produces a phase change on the surface it also takes away material and thus provide for the HIP Zirconia, having a “rough” machined surface, a smoother surface with less micro- mechanical retention. Blasting before porcelain firing gives no increased risk of continued phase change since the firing process temperature makes the most of the monoclinic grains regain its tetragonal structure.

Steaming zirconia can affect the material and should be avoided and should never be performed after the final porcelain firing of the restoration. Water is the factor that accelerates aging of zirconia. This process goes fastest with heat and water has smaller particles, ie hot water vapor accelerates the aging of zirconia. HIP Zirconia is significantly more resistant to this damage, but it should also be here, and especially after porcelain firing.

Temperatures for porcelain firing affects on zirconia produce a positive manner by transforming any monoclinic grains back to the tetragonal. However, there is a “gray zone” because the burn also means that the Zirconia surface is exposed to water, ie wet porcelain. There are no studies on this particular effect, but here stands the importance of using HIP Zirconia as elimentary. Note that zirconia has very poor thermal conductivity and therefore may influence the firing temperature of the porcelain furnace.

 

What is HIP?
HIP stands for Hot Isostatic Pressed and is a process of both high pressure and heat (2000 bar and 1400 C) used on the sintered Zirconia. This process optimizes the ceramic properties and help to increase the material’s bending strength by about 30%.

Above all, the process makes the material become more resistant over time, ie, a higher resistance to phase change. The following study describes well the benefits of HIP Zirconia: Am. Ceram. Soc. <Issues, 64 [2] 310-13 (1985).

 

Why do Denzir plaque adhesiveness stand out from other Zirconia
Denzir is HIP zirconia and has a higher density and smaller grain size than the so-called “Green” Zirconia. These characteristics makes it possible for the Denzir surface to be highly polished and thus strap small plaque adhesiveness. Since the Denzir surface is denser it doesn’t age by water and can therefore advantageously be left clean and polished. For non-HIP zirconia this is not the case.