All Zirconia

As briefly mentioned yesterday's blog post (sep. 7), zirconia based restorations can be made with or without a porcelain overlay. The advantages to the porcelain overlay are aesthetics - similar to the PFM - porcelain will create the tooth like appearance and can be built up with multiple shades or stains. However, adding porcelain has its drawbacks - namely the strength of the restoration is only as strong as the porcelain, and porcelain exhibits a significantly lower flexural strength than zirconia.

In addition, it has been reported that incidence of porcelain fracture or chipping off of zirconia is more common than off of metal substructures. There is little empirical evidence to support these claims, but as zirconia is a relatively new material compared to the PFM, porcelain fusing to zirconia is still a new art and science.

As a result of these issues, there has been a recent increased interest in all ceramic restorations that are less likely to fracture. One such product - the All Zirconia restoration - has become increasingly popular for molars. The reason for this is that the All Zirconia is entirely milled by a machine (including occlusal anatomy) and as such is one homogeneous material. Chipping or fracture lines that porcelain exhibits are almost non-existent. However, aesthetics - especially shading - continues to be a challenge. As zirconia blocks come in monolithic shades, it is difficult for labs to offer true shade match especially at the incisal edge. For this reason, most all zirconia restorations are prescribed for teeth not inside the smile zone.

However, with more research and development spurred by the high costs of precious alloys, it may be only a few years before we see All Zirconia restorations with multilevel shade options and more translucency. This is a product in its infancy and we look forward to seeing a great deal of new materials come into the market that will help doctor, patient and lab.