Coated dental powders

[0018]The object of the invention consists in applying a coating, preferably a nanocoating, to a dental powder, whereby, when using a liquid, preferably water, a slip of the type results which is readily processable and an optimal jointing and adhesion to the substrate is achieved without a joint gap occurring. Furthermore, it is the aim to achieve optimal shrinkage reactions of dental powders (ceramics, glass ceramics, glasses) without substrates.

[0020]It was surprisingly found that an inorganic powder coated with organic components made possible a high adhesion of the inorganic powder to the substrate and inorganic components, such as, for example, ZnCl2, make possible an optimal processing and stability of the aqueous slips. The additionally surprising effect consisted in the fact that both mechanisms acting oppositely per se could be realized by the coating on a pulverulent dental material.

[0045]It is known that the shrinkage process of the dental powder during the heat treatment to about 900° C. is influenced by various parameters. Surprisingly, it was found that by means of the specific packing density, that by the larger particles, which are adhered to small ones, has a particular advantage on the shrinkage. The shrinkage process in conjunction with the release of volatile constituents (liquid of the slip, liberation of the enclosed air etc.) is markedly lower with the dental powder according to the invention than with uncoated dental powder. The result of the experiments shows that the physicochemical reactions of shrinkage, the release of volatile gaseous constituents and the activation of the particles in the “low-temperature range” (not only below the sintering temperature, but even also below the transformation range of the glass matrix of the leucite-apatite glass ceramic used) are of particular importance and as a result of the dental powder according to the invention no distortion of the desired geometry or lifting of the substrate occurs up to the sintering temperature.

[0046]During the sintering process, the small particles of the fine-grain spectrum of the dental powder are of particular importance. These small particles have, in comparison to the larger ones, a high sintering activity and initiate the sintering process. At the same time, owing to their more rapidly occurring liquidity, these make possible the production of a compact and low-pore dental restoration (cf. FIGURE).

After this coating process of the substrate with slip and initial removal of the liquid, the subsequent heat treatment is carried out from room temperature up to the termination of the sintering process, which is typically between 700° C. and 1000° C. Despite the use of mixing fluids, at various times situations occur where the dental powder does not adhere optimally to the substrate during the heat treatment, such that an optimal jointing process between dental powder and the substrate is not achieved in the finished product.

On the other hand, it is known of pulverulent dental ceramics, dental glass ceramics or dental glasses that during the shrinkage operation in the process of tightly sintering, uncontrolled reactions can occur, which alter the desired geometry (“distortion of a molded part”).

The fillers are not suitable for veneers of dental structures.

These coated particles are not employable as a glassy or glass ceramic veneer for dental restoration.