SEM Image Microstructure HiPer®-DENT-Z Zirconia
Zirconia: a Ceramic Material
Zirconia is a refractory oxide ceramic material exhibiting three polymorphs. At room temperature a monoclinic phase is present. Above 900 °C the monoclinic phase transforms into a tetragonal phase which itself is stable up to approximately 1400 °C. Above this temperature transformation into a cubic phase occurs.
Zirconia materials with excellent mechanical properties are obtained by alloying zirconia with suitable stabilisation elements (Ca-, Mg-, Ce- or Y-ions). Stabilisation leads to preservation of high temperature polymorphs (tetragonal or cubic, depending on the amount stabiliser) down to room temperature.
The amount of stabiliser can be adjusted in a fashion that a more or less large portion of zirconia crystallites are present in a metastable state. These metastable crystallites transform spontaneously into the monoclinic polymorph when subjected to mechanical stress.
Due to a significantly higher density of the tetragonal phase compared to the monoclinc phase, this transformation inhibits propagation of occurring cracks – e. g. when mechanically strained – by volume expansion. This phenomenon is called transformation toughening and determines the high fracture toughness of densely fired zirconia containing proper amounts of stabiliser.
3-Unit Framework made from HiPer®-DENT-Z Zirconia
Yttria Partially Stabilized Zirconia
Dental frameworks are usually made from yttria partially stabilized zirconia because it exhibits the highest available transformation toughening of all stabilisation types. Many yttria partially stabilized zirconia materials - also HiPer®-DENT-Z Zirconia - contain small amounts of alumina due to the improvement of hydrothermal aging resistance. Chemically very stable alumina is mainly deposited on the grain boundaries in the densely fired zirconia microstructure acting as a barrier for yttria to leach from the zirconia lattice. Corrosion processes induced by the pharyngeal environment always ongoing to a minor degree are slowed down significantly.
Besides yttria and alumina pure yttria partially stabilized zirconia only contains hafnia as a natural companion. Colored HiPer®-DENT-Z Zirconia is doped with small amounts of coloring ions. Yttria stabilized zirconia is fully biocompatible. Undesirable effects in medical applications – e. g. total hip arthroplasty – are despite of more than three decades of medical application history not puplished to date. The natural occurring radioactivity of zirconia minerals is removed during its processing almost completely. HiPer®-DENT-Z Zirconia typically shows radioactivity levels of much less than 0,2 Bq/g and complies even with the allowed radiation limits for implants given in ISO 13356:2008.
Microscopic Image hMSC's on HiPer®-DENT-Z Zirconia
HiPer®-DENT-Z Zirconia
HiPer®-DENT-Z framework material is based on almost twenty years of experience with the advanced ceramic zirconia – www.hiper-ceramics.de -. HiPer®-DENT-Z Zirconia is formulated from selected raw materials and completely manufactured in HiPer Medical premises in Oberkrämer.
Compared to other yttria partially stabilised zirconia materials HiPer®-DENT-Z is characterised by a more robust sintering behaviour therefore able to withstand several veneering firings without significant loss of fracture toughness.
Biocompatibility-checked
HiPer®-DENT-Z Zirconia was teted at mdt medical device testing GmbH and at the sister company Zellwerk GmbH – www.zellwerk.biz – in numerous cell culture models (L929 murine fibroblasts, human umbilical cord stem cells, human bone marrow-derived mesenchymal stem cells, human HepG9 liver cell line) with respect to biocompatibility.
In none of these cell models indications for cytotoxicity, loss of viability or other cell damaging properties of HiPer®-DENT-Z Zirconia were found.
