Porcelain to Zirconia
Posted on 09/07/2011
The first category of All Ceramics that was outlined yesterday are the Zirconia based restorations - also known as Porcelain Fused to Zirconia or PFZ for short. These restorations are similar to the PFM in that they have a coping with a porcelain overlay. The zirconia substructure is fabricated through a CAD/CAM process whereby the lab mills the zirconia (composed of zirconium oxide) in a machine and then sinters it to give it strength.
Zirconia based restorations, like the PFM, have an opaque quality that easily masks dark stumps or post/cores. The tooth shade is created using a standard porcelain build up technique. As such, zirconia is less translucent than other all ceramics such as IPS Empress, IPS E.Max or Procera Alumina. However, it does allow for incisal translucency and is prescribed quite often for anterior teeth.
The real advantage to the Zirconia based All Ceramics is strength. Zirconia, after sintering, can reach flexural strengths of 900-1300 MPa - depending on the process and manufacturer. Compared to the Empress Press (180 MPa) or E.Max Press (400 MPa), zirconia is quite a bit stronger. This allows for the use of zirconia in the both posterior and anterior regions of the mouth, and allows for large bridges spanning even 3 pontics. One important note to understand about zirconia is that it is a material - not a brand. As such, each lab may purchase the material from a different supplier which results in different strengths and shades of the coping.
Preparation style requires a chamfer or shoulder finish. Knife edge or chamfer bevels are not recommended.
However, like the PFM, zirconia actual strength is dependent on the porcelain overlay. So even a quoted strength of 1000 MPa, may refer only to the understructure. Once porcelain is added, the strength may reduce to 600 MPa or less - which is why porcelain can fracture off of zirconia. The use of All Zirconia (popularized by Glidewell Dental Labs as the Bruxzir crown) allows zirconia to exhibit its actual flexural strength. However, aesthetics are compromised as there is no porcelain added. We will discuss the the All Zirconia restorations in an upcoming blog post.
Zirconia based restorations, like the PFM, have an opaque quality that easily masks dark stumps or post/cores. The tooth shade is created using a standard porcelain build up technique. As such, zirconia is less translucent than other all ceramics such as IPS Empress, IPS E.Max or Procera Alumina. However, it does allow for incisal translucency and is prescribed quite often for anterior teeth.
The real advantage to the Zirconia based All Ceramics is strength. Zirconia, after sintering, can reach flexural strengths of 900-1300 MPa - depending on the process and manufacturer. Compared to the Empress Press (180 MPa) or E.Max Press (400 MPa), zirconia is quite a bit stronger. This allows for the use of zirconia in the both posterior and anterior regions of the mouth, and allows for large bridges spanning even 3 pontics. One important note to understand about zirconia is that it is a material - not a brand. As such, each lab may purchase the material from a different supplier which results in different strengths and shades of the coping.
Preparation style requires a chamfer or shoulder finish. Knife edge or chamfer bevels are not recommended.
However, like the PFM, zirconia actual strength is dependent on the porcelain overlay. So even a quoted strength of 1000 MPa, may refer only to the understructure. Once porcelain is added, the strength may reduce to 600 MPa or less - which is why porcelain can fracture off of zirconia. The use of All Zirconia (popularized by Glidewell Dental Labs as the Bruxzir crown) allows zirconia to exhibit its actual flexural strength. However, aesthetics are compromised as there is no porcelain added. We will discuss the the All Zirconia restorations in an upcoming blog post.