ZrO2 Bruxzir 16 Shaded
Zirconium oxide with its excellent properties can fully replace metals in dental frame production. Over 30 years of the successful development in human medicine this material has proved very well in hip and knee joint production – thanks to its biological compatibility.
Other undisputable benefits are its high functional strength and resistance to corrosion as well as its excellent aesthetic or mechanical properties.
Zirconium oxide does not cause any irrigation of the tissue and a human is not allergic to it. Moreover, this material does not enter any galvanic processes and can be penetrable even by X-rays.
Its thermal insulation properties and low thermal conductivity cause that unlike metal materials you need not take into account any thermal sensitivity. Zirconium oxide resists to multiple times the forces occurring in the mouth cavity.In the ceramic industry the following moulding procedures are used for production of zirconium oxide semi-products for dental use:
- Non-axial pressing
In this production procedure the compacting pressure is developed in a single direction. It cannot be excluded that friction of powder against the die will give rise to a semi-product showing an evident density gradient in the Z direction. The microstructure is not isotropic, which gives rise to a direction-dependent material and binding properties as well as non-homogeneous bond. Too high pressure can cause a problem as well. Local tensile tensions can be generated during release of a semi-product (raw piece), which may cause cracks in the moulded piece when the action of force is released.
The biggest advantage of this procedure is the lower material loss in the production process and the result is a cheaper semi-product of inferior quality.
- Isostatic pressing
During isostatic pressing powder is filled in an elastic mould placed in a metal cage.
Pressing of such tightly closed mould occurs in water/oil emulsion in the isostatic press.
In this production process the compacting pressure is equally high in all directions. The result if a semi-product with a high degree of isotropy (material properties dependent on the direction) and uniform compaction.
Homogeneous compaction is the basic condition of a faultless sintering process and excludes torsion forces, while guaranteeing high-quality semi-products.
- Sintering process in puck production
During the sintering process material previously moulded and compacted in a press is heated over the melting point and then maintained at its final temperature for certain time.
It is virtually a temperature/time cycle, during which the porosity and volume of fresh moulding piece are .... (chýba sloveso). Compaction occurs by regrouping of particles and by the change of their shape or size. The properties decisive for the quality of zirconium oxide semi-products are homogeneous grain size and distribution of pores. In the sintering process these are significantly affected by the heat-up rate, “holding” times and final temperature.
At very high temperatures or too long sintering cycles huge grains grow in the material, which can achieve (to the detriment of the others) up to 100–1000 times the value of their initial volume (0.3-0.4 µm).
This phenomenon leads to extremely non-homogeneous distribution of grains and to a threat that the metastable tetragonal phase will spontaneously change to the monoclinic phase.
The uniform distribution of pores in a micro-bond is largely influenced by the heat-up rate. When it is not exactly adapted to the material, it may give rise to areas with strongly concentrated and loosely placed ZrO 2 grains. These “loose” areas burst during the sintering process and often remain in the bond as errors and thus as potential defective zones in the semi-product. The failure of ceramic work pieces is mostly based on inhomogeneities in the bond (principle of failure of the weakest link). These inhomogeneities manifest themselves among others by different strength values in a single semi-product. The largest informative value for dispersion in strength of ceramic materials is offered by Weibull modulus. The higher is its value, the more homogenous is the material, i.e. defects are distributed very evenly over its whole volume. High-quality zirconium oxide semi-product is characterized by the value of Weibull modulus equal to 20 and determined by the bending stress at four points.
- Ageing process
In the clinical practice dental renovations are exposed to factors such as humidity and dynamic permanent load.
These factors finally lead to the decrease of strength and thus to the hydrothermal ageing of material.
This hydrothermal ageing can be very well simulated in an autoclave at temperature of 130-150°C and at steam pressure of 10 bar. By adding 0.5-1% of aluminium oxide resistance of zirconium oxide to the hydrothermal ageing is achieved.
Some producers of zirconium oxide semi-products do not add the aluminium oxide at all, because it negatively influences material transparency.
The significant increase of zirconium oxide transparency can also be achieved by exceeding of the recommended sintering temperature and “holding” time at the final temperature. The “burn-out” of zirconium oxide leads to a growing hydrothermal ageing and so-called “growth of grain”, due to the decrease of strength of up to 40%. The bending strength of 800 MPa (as required by the standards DIN for dental ceramics) is not fulfilled anymore and premature failure of dental renovation can be expected.
The CAD/CAM area is characterised by a highly competition environment, irrespective of whether the milling centre or the dental industry is concerned.
Some workers use non-economic milling systems in production and thus are forced to purchase the “cheapest” material to be able to offer their products for competitive prices.
We do not and will not share this philosophy. We rely on effective and most modern production systems and on high-quality and original semi-products from renowned and proved producers.
We use isostatically-pressed zirconium oxide semi-products with addition of 0.5-1% of aluminium oxide. We do not make compromises even in the sintering process. We programme the sintering process individually for the respective material.
Electronic documentation of each sintering process guarantees maximum safety and “traceability” of the material burning. In this way we can achieve our objective to offer a high-quality product from provably best material for each indication.
We found all these properties in the US brand BruxZir, which made zirconium oxide a high-aesthetic material in the last years. With its long-term development it brought a high-quality semi-product on the market.
- bridges with up to 16 elements
- individual abutments
- implant-supported crowns
- implant-supported bridges
- secondary and tertiary frameworks
(Only indicative values – specific composition is a secret)
|ZrO2/ HfO2/ Y2O3 / Al2O3 (%)||>99,0||>99,0|
|5,15 %||< 3%||< 0,5%||< 0,02%||< 0,01%||< 0,04%|
|Distal teeth||≥ 1.5 mm²||≥ 0.5 mm²|
|Frontal teeth||≥ 0.7 mm²||≥ 0.5 mm²|
|with 1 pontic||with 2 pontics|
|Framework in the distal section||9 mm²||12 mm²|
|Framework in the frontal section||7 mm²||9 mm²|