The zirconium crowns, were imposed in dentistry due to the medical advantages, on which the zirconium offers them, as well as due to existence of the necessary technology of its extraction, purification and processing.
The zirconium is known from antiquity but was discovered as chemical element in the year 1789 by Martin Henrich Klaproth. The zirconium (Zr40) makes part of the metals group and is used in dental prosthetics and oral implantology under the zirconium dioxide form (ZrO2), a ceramics of white color.
The physicochemical properties of the zirconium ceramics gives it medical advantages compared with others metal alloys that are used in the present to perform dental crowns. The performing of zirconium dental crowns, is made by using a high technology, thing that determine increasing of their price.
The physicochemical characteristics of the zirconium dioxide are the following:
- High hardness (9,4), which is approaching to the hardness of the diamond (10);
- Small particle size (0,5 μm- 1 μm);
- High resistance to fracturing;
- high resistance to flexion (1000MPa);
- Low thermal conductivity meaning 20% of the aluminium's conductivity;
- Density (6,511g/cm3);
- White color;
- Paramagnetism(the property of the material to magnetize itself - low and temporary - when is included into a magnetic field);
- Resistance to the corrosion given by oxygen and by liquid electrolyte from oral environment;
- The crystalline chemical structure of compact tetragonal shape.
having in view all these, the ceramics crowns on zirconium offer to the patient the following advantages:
- Biocompatibility characterized by the absence of allergic reactions, cytotoxic and inflammatory. It was found that zirconium exists in the human body in the concentration of 5x10-6%;
- Natural color appearance/aspect of the dental crowns due to the color and the opacity of the zirconium dioxide. The appearance/aspect is very important in case of prosthetics of the incisors and the canines..
- Easy accommodating of the patient with their presence due to the low weight, compared with the crowns made from other materials;
- High resistance in time to shocks and wear;
- Protection of the pulp of the teeth and gums against the thermal variations caused by the hot and cold foods;
- Posibility that the patient to do electro-nuclear magnetic resonance (NMR) when is is needed, due to the paramagnetism property of the zirconium crowns;
- Absence of bimetallism appearance characterized by metallic taste, in case of existing even of others dental bridges made of metal alloy in cazul existentei si altor punti dentare din aliaje metalice.
In dentistry the crowns and dental bridges can be made either only by zirconium ceramics, or by zirconium ceramics covered vitreous ceramics.