Use of Zirconia (ZrO2) in medicine dates to 1969, when this material was adopted for the manufacture of hip prosthetics. As an alternative to titanium, steel or alumina, the new material guaranteed better resistance to breakage and corrosion, as well as a high degree of biocompatibility, confirmed by the fact that no negative response has been recorded, in around forty years of application, in 300 thousand patients with Zirconia prosthetics.
Use of ceramic materials to manufacture dental prosthetics dates to the 18th century. However, although these materials generally had excellent aesthetic properties, they were not widely used in dentistry due to low toughness which did not guarantee resistance to fractures. Porcelain was therefore used in a metal composite. Doubts over use of metal in the mouth, which has a low level of biocompatibility, shifted attention to other metal-free materials.
Over recent years, Zirconia has proved to be an excellent material for use in high-quality dental restorations, since its high mechanical/shock-resistant characteristics, fracture toughness and elastic module (Young) are associated with a high level of biological compatibility with gum and bone tissues.
The technology which allowed stabilisation of the tetragonal phase, thereby preventing the typical transformation of Zirconia at room temperature (monoclinic crystalline structure) and keeping the tetragonal structure even after cooling at room temperature, was fundamental.
Partial stabilisation of Zirconia is obtained with the addition of ceramic oxides like Yttrium Oxide, Magnesium Oxide, Calcium Oxide or Cerium Oxide.
Yttria-stabilized Zirconia (ZrO2Y2O3) is the one mainly used for dental applications.
Partially Stabilized Zirconia
The minimum characteristics for clinical uses of Zirconia are indicated by standard EN-ISO 13356:
|Chemical composition||Standard ISO 13356:2008|
|ZrO2 + HfO2 + Y2O3 Y2O3||>99%|
|Y203||from 4.5 % to 5.4 %|
|Hf203||< 5 %|
|Other oxides||< 0,5 %|
Many qualities make Yttria-stabilized Zirconia (ZrO2Y2O3) particularly suitable for modern dentistry:
- excellent biocompatibility
- low specific weight
- high aesthetic quality, particularly in terms of translucidity
- elasticity similar to steel
- flexural strength (higher than 1,000 MPa) more than two times higher than steel
- compression resistance four times higher than steel
- breakage resistance which allows thicknesses lower than 1 mm to be used (maximum limit in use of precious alloys such as gold-platinum alloys), allowing extended, light and robust bridges to be manufactured
- high resistance to acids and therefore greater resistance to contact with food
- transparency to X-rays and non-magnetic (extremely useful in the case of X-rays, CAT scans, etc.).