Sol gel composition for producing glassy coatings

Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form

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106 35, 514835, 424 49, 424 50, 424 52, 4332171, 433226, 433229, A61K 6093, C09D 400, C09D18302

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054339561

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a sol gel composition for use in producing glassy coatings, to a process for producing a glassy coating using the composition, to a method for cosmetic colouring of teeth using the process and to a method for prophylactic protection of teeth using the process.


BACKGROUND OF THE INVENTION

Fissure sealants have been demonstrated as effective in reducing incidence of tooth decay and inhibiting decay even after it has started, but have not gained universal acceptance in general practice. These fissure sealants are understood to have relatively low durability, adhering to the tooth with a rather short half-life (5 years).
Sol-gels would not be considered for dental use, since the curing of sol gels is typically undertaken in a slow furnace, which would pose clinical difficulties. Japanese Patent Publication 1083671 (published 29 Mar. 1989), in the name of Kobe Steel, proposes a calcium phosphate sol gel, but for coating artifical teeth to be subsequently embedded in the human body.


DESCRIPTION OF THE INVENTION

According to the invention, a sol gel, xerogel or heat-consolidated gel composition comprises a hydrolysable silicic ester (such as silicon tetrahalide or tetraalkoxysilicon), 1 (preferably 11/2)-4 moles water (which may be added later) per mole of silicon, a solvent (alcoholic or non-alcoholic) and a filler, such as laponite, zeolite, kaolinite or vermiculite, or preferably a filler in the form of flat plates such as talc or mica, or a mixture, optionally coated (preferably by chemical vapour deposition) with for example titanium dioxide, chromium oxide or ferric oxide or a mixture, the filler preferably amounting to up to 30% by weight based on the gel. Part of the silicic ester can be substituted by appropriate compounds of other non-metallic glass formers. Other coating methods may also be used, alternatively or in addition, such as deposition of silane. This can promote adhesion and enhance mechanical properties. As silanising agents, compounds containing a glycidoxy group and a polyalkoxy (e.g. trimethoxy) silyl group may be used, for example Dow Corning Z6040 (trade mark), ##STR1## Also according to the invention, a coated composition comprises a hydrolysed and cured silicic ester containing a filler as set forth above. Such filler materials are harmless if swallowed in the small quantities in which they might spall off. The mean filler particle size is preferably up to 3 .mu.m (e.g. 0.1 to 2 .mu.m) in one dimension and 5-100 .mu.m in the other two dimensions. Where the latter dimensions are 5-20 .mu.m, the filler preferably comprises from 20 to 30% by weight of the composition, and where those dimensions are 10-60 .mu.m, the filler preferably comprises 10-20% by weight of the composition. Cross-laid fibres may be used. In the case of xerogel, which is 90 volume % air, a platey filler will improve its mechanical properties such that it could be used as an insulating material, or the cavities can be used as drug reservoirs, which will slowly release, on a tooth or otherwise.
The filler reduces the incidence of crazing in the cured sol-gel (not only in dental applications) by physically reducing the bulk of sol gel needed, thus making what there is of it more elastic. It also absorbs incident laser energy and re-emits it to the sol gel, accelerating the latter's curing. The filler also improves the abrasion resistance of the cured sol gel glassy coating. Given that the yield of glass from sol-gels is preferably about 5-10% by weight, and can be 0.1 to 1% or even less the filler will thus be a major component of the product. In the case of mica, which tends to fall out of sol-gel suspension quite rapidly, it may be incorporated into the sol-gel when or immediately after the latter is made up; as the sol-gel `polymerises`, the polymers grow on the mica, improving its suspension and bonding, but as a precaution it may be advisable to shake it before use, or else the mica may be added to the sol gel at any later stage, e.g. immediately before use. On the other hand, a too-

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