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.
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elongation at rupture | Bruchdehnung |
Wax build-up technique Wax build-up technique The various anatomical structures (such as cusp tips and slopes as well as marginal ridges) are usually built up one after another by adding small portions of wax (often using differently coloured waxes for didactic purposes). The firm, special waxes first have to be melted at room temperature. This can be carried out by warming small portions on differently shaped working tips of hand instruments in an open flame (such as a gas burner) or using electrically heated instruments which provide for more accurate temperature control and avoid contamination (e.g. electric wax-knife, induction heaters, wax dipping units). The wax is applied drop-by-drop to ensure that the warmer molten wax added last fuses seamlessly with the firm, cooler material. After hardening, the wax pattern can be reduced by sculpting, milling guidance surfaces or drilling to add retainers. Modern procedures include flexible, occlusal preforms for adding contours to soft wax. In addition, wax preforms, such as for occlusal surfaces or bridge pontics, are available in various shapes and sizes. Recently, irreversible, light-curing materials have been introduced for use instead of reversible thermoplastic waxes. Wax preforms To ensure that the wax pattern can be released without being damaged, model surfaces, opposing dentition and preparations must be hardened/sealed with special lacquer (applied by spraying, brushing or dipping). These waxes are mostly relatively rigid/elastic after cooling. Attaching wax sprues to a removable framework supported on double crowns using a hand instrument When employing the lost wax technique, prefabricated wax sprues, bars and reservoirs are attached to the patterns. Once the pattern has been released and its sprues waxed onto the crucible former, it is invested in a casting ring with refractory investment material. The wax can then be burnt out residue-free and casting completed. Unlike standard wax build-up techniques, a diagnostic wax-up is not intended for fabricating an indirect restoration, but rather for simulating the appearance and/or external contouring for producing orientation templates. |