Compositions: coating or plastic – Coating or plastic compositions – Dental
Patent
1995-07-25
1996-09-24
Group, Karl
Compositions: coating or plastic
Coating or plastic compositions
Dental
4332171, 433226, 501 12, 2523156, 2523157, C09K 300, A61K 6093
Patent
active
055587011
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.
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. Thus, U.S. Pat. No. 5,068,208 discloses a method of making optical elements of gradient-index glass by a sol-gel route including adding together a partially hydrolysed silicon alkoxide, an alkoxide of Ti or Zr, and an alkoxide of B, Al or Ge, adding water while agitating, moulding the mixture for sufficient time to form a gel, washing the moulded gel, acid-leaching the washed gel to remove some metal oxide, fixing the gel in aqueous alcohol, drying the gel and sintering.
Silicon-based sol gels often rely on the presence of sodium alkoxide, and it has been suggested that sodium does not enhance the chemical resistance or mechanical durability of glass. However, an alternative is taught by EP-A-482659, in which a thin glass film is produced on a substrate by a sol-gel method, comprising applying to the substrate a hydrolysable solution containing a metal alkoxide, water, alcohol and an acid, exposing to ammonia and heating to form a thin glas film in situ. The metal alkoxide is selected from Si, Ti, Ge, Al and B, of which Si, and Si+Ti, are exemplified.
According to the present invention, a sol gel, xerogel or heat-consolidated gel composition comprises: a hydrolysable boron ester (such as boron triethoxide or tripropoxide) or boron salt convertible to the oxide by thermal or oxidative decomposition (such as boron nitrate or citrate); a solvent (alcoholic or non-alcoholic); alkoxide(s) of any one, two or more of aluminium and of Gp VB and/or GpIVB metals (preferably zirconium together with titanium); and a filler having a mean particle size of up to 3 .mu.m in one dimension and 5-100 .mu.m in the other two dimensions. Part of the boron ester can be substituted by appropriate compounds of other non-metallic glass formers. Some of these compositions have been found to be usefully stable. Where not deleterious, a GpIA or IIA metal alkoxide (such as sodium or calcium) may be present. Some or all of such metal may advantageously be present as the fluoride. Preferably the number of metals present (not counting B or Si) is at least two, e.g. three or four, of which one is preferably Ti. The composition may further comprise water, which may however be supplied otherwise, e.g. by exposure to air. The metal alkoxide, if there is just one, may be Ti or Zr or Al. Preferred combinations of metal alkoxides are: (i) Zr, Ti; (ii) Al, Ti, Na; (iii) Ti, Na, Zr; (iv) Al, Ti, Zr; and (v) Al, Ti, Zr, Na. The metals (not counting Na) are preferably present in amounts up to one-sixth (by number of atoms) of the boron. Solid oxides e.g. fine neodymium oxide powder may be dispersed into the sol gel.
Preferably, the sol gel composition synthesis was characterised by an ageing step, during which moisture was admitted to the composition at a rate under 1% of the rate in free air. This controls the rate of hydrolysis and consequently of `polymerisation` of the molecules of the composition without destabilisation, which rate can in principle be monitored via an increase in viscosity of the composition, or e.g. by infra-red spectroscopy, by differential scanning calorimetry, by thermogravimetric analysis, by nuclear magnetic resonance or by electron spin resonance.
The filler may be for example laponite, zeolite, kaolinite or vermiculite, or preferably the filler is in
REFERENCES:
patent: 3847583 (1974-11-01), Dislich et al.
patent: 4431451 (1984-02-01), Mabie et al.
patent: 5068208 (1991-11-01), Haun et al.
patent: 5433941 (1995-07-01), Patel
patent: 5433956 (1995-07-01), Patel
British Technology Group Limited
Group Karl
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