Zirconium dioxide block
Zirconium dioxide (ZrO2), also referred to as zirconium(IV) oxide or zircon oxide, is a high performance oxide-ceramic. In dentistry it is now mainly used as Y-TZP, a partially or fully stabilised zirconium dioxide achieved by the addition of a few percent of yttrium oxide (Y2O3).
Uniaxial (along a single spatial direction/axis) or isostatic (uniformly along different spatial directions/axes) compression of highly pure zirconium dioxide powder and binding agents without heat treatment produces a press blank, known as a green compact or green body.
The binding agents are eliminated by subsequent presintering at approx. 1000°C. During presintering the volume undergoes further reduction by approx. 5%. This creates a still porous partially sintered blank.
All-ceramic, single-winged, free-end bridge
Prefabricated blanks, so-called "blocks" with or without holders are manufactured from this partially sintered material, which can be processed using many conventional dental CAD-CAM milling systems. Different companies provide extensive ranges of prefabricated milling blocks made from translucent or opaque material in various sizes, shapes and shades.
They can be mechanically milled or ground either wet or dry. They are manufactured respectively enlarged in order to factor into the calculation subsequent shrinkage of approx. 20% to 25% during (post) sinter firing (dense sintering). Some blocks are pre-shaded industrially in advance. Alternatively, the blocks can be shaded manually using appropriate acidic or water-based staining solutions. The final sinter firing is completed at 1350°C to 1550°C. The material attains a high final flexural strength of approx. 900 MPa.
In addition to the prefabricated milling blocks, mainly made from zirconium dioxide, zirconium-dioxide reinforced aluminium oxide blocks are also available.