Dispersions of nanoscale dental glass particles and methods for preparing the same

Abstract

Provided are a dispersion of a nanoparticulate mixed oxide of SiO.sub.2 with at least one further metal oxide in a matrix monomer, methods for preparing such a dispersion, a dental composite producible by curing such a dispersion, and uses of the dispersion as a precursor for dental composites.

Claims

1. A dispersion suitable for use as a precursor for a dental composite, comprising: a filler material and a matrix monomer having at least one polymerizable group, the filler material comprising nanoscale mixed oxide particles that are sterically stabilized by a sol stabilizer, the nanoscale mixed oxide particles including silicon, at least one metal M having an atomic number Z >36 in oxidic form, and at least one covalently bound polymerizable group that is copolymerizable with the at least one polymerizable group of the matrix monomer, wherein the nanoscale mixed oxide particles including the silicon and the metal M have a formula: SiO.sub.2-MO.sub.x and/or SiO.sub.2-MO.sub.x-M′O.sub.y, where M′ is a metal having an atomic number Z >36 in oxidic form, wherein the nanoscale mixed oxide particles further comprising at least one further organic group covalently bound thereto.

2. The dispersion as in claim 1, wherein the nanoscale mixed oxide particles have a spherical shape.

3. The dispersion as in claim 1, wherein the matrix monomer is at least one acrylate selected from a group comprising methyl, ethyl, butyl, benzyl, furfuryl, and phenyl (meth)acrylate, bisphenol A di(meth)acrylate, bis-GMA, ethoxylated bisphenol A di(meth)acrylate, UDMA, di-, tri-, and tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, butanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, and mixtures thereof.

4. The dispersion as in claim 1, wherein the metal M is an element selected from the group consisting of Ba, Sr, La, Cs, Sn, Zr, Yb, Y, Ta, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Bi, and combinations thereof.

5. The dispersion as in claim 1, wherein the filler material has an average particle size ranging from 5 to 100 nm.

6. The dispersion as in claim 1, wherein the at least one covalently bound polymerizable group of the filler material is selected from the group consisting of an acrylate group, a methacrylate group, and a 3-methacryloxypropyl (MPTM) group.

7. The dispersion as in claim 1, wherein the filler material is present in a content from 10 to 70 wt %.

8. The dispersion as in claim 1, wherein the filler material is present in a content from 30 to 50 wt %.

9. The dispersion as in claim 1, wherein the at least one further organic group is selected from the group consisting of an organic side chain and an alkyl group.

10. The dispersion as in claim 1, wherein the filler material has a refractive index that differs from a refractive index of the matrix monomer by less than 0.1.

11. A dental composite obtained by curing the dispersion according to claim 1.

12. The dental composite as in claim 11, wherein, at a content of filler material of at least 10 wt %, translucency for light of a wavelength from 400 to 750 nm is at least 30% and/or transparency for light of a wavelength from 400 to 750 nm is at least 75%.

13. The dental composite as in claim 11, wherein the nanoscale mixed oxide particles have an X-ray opacity from 50 to 15,000%Al.

14. A method for preparing a dental composite using a dispersion as a precursor, the precursor comprising a nanoscale mixed oxide having at least one polymerizable group, as a filler material, and a matrix monomer, and is obtained by preparing a sol, and subsequently curing the precursor, comprising the steps of: a) preparing nanoscale mixed oxide particles of SiO.sub.2 and an X-ray opaque metal oxide of a metal M starting from at least one silicon precursor and a metal salt M.sub.aX.sub.b or a metal hydroxide M.sub.a(OH).sub.b, the metal hydroxide being at least partially neutralized by adding an organic acid HA; b) functionalizing the mixed oxides prepared in step a); c) removing a counter ion X or conjugate base of the organic acid used in step a) from the reaction solution; d) dispersing the filler particles functionalized in step b) in the matrix monomer; e) processing the dispersion; wherein first, in step a), a solution A and a solution B are provided, wherein solution A includes a solvent, an organic silicon precursor, and an X-ray opaque metal M in form of a salt or as a hydroxide, and solution B includes a solvent and an aqueous base, and wherein solution A or solution B further includes a sol stabilizer, and wherein solution B and solution A are mixed under stirring, and the reaction solution is stirred to complete formation of particles; wherein subsequently, in step b), a silane having a polymerizable group is added for functionalizing; and wherein in step e) solvents, water and base are removed.

15. The method as in claim 14, wherein steps a) through e) are performed as a one-pot synthesis.

16. The method as in claim 14, wherein in step a) particles form in self-organizing manner.

17. The method as in claim 14, wherein a silane of the formula SiX.sub.4 is used as the silicon precursor in solution A, the silane including 4 hydrolyzable groups X selected from a group of X═OR, halogen, NR.sub.2 (R=alkyl, aryl), H, a tetraalkoxysilane selected from a group comprising tetramethylorthosilicate (TMOS) having a formula Si(OCH.sub.3).sub.4, tetraethylorthosilicate (TEOS) having a formula Si(OC.sub.2H.sub.5).sub.4, tetrapropoxysilane having a formula Si(OC.sub.3H.sub.7).sub.4; and/or a silane of the formula RSiX.sub.3, including 3 hydrolyzable groups X selected from a group of X═OR, halogen, NR.sub.2 (R=alkyl, aryl), H, and a non-hydrolyzable organic side group R, wherein R is an alkyl or aryl.

18. The method as in claim 14, wherein a further metal salt M.sup.T.sub.cX.sub.b or a hydroxide of an X-ray opaque metal M.sup.T is added to solution A.

19. The method as in claim 14, wherein the metal M and/or the metal M.sup.T comprise barium or strontium.

20. The method as in claim 14, wherein barium and/or strontium perchlorate is employed as the metal salt.

21. The method as in claim 14, wherein barium and/or strontium hydroxide is employed as the metal hydroxide.

22. The method as in claim 14, wherein a low boiling alcohol is employed as a solvent in solutions A and B, the low boiling alcohol being selected from a group consisting of ethanol, methanol, and isopropanol.

23. The method as in claim 14, wherein a sterically demanding silane and/or a protective colloid is employed as a sol stabilizer in solution A or B.

24. The method as in claim 14, wherein step b) additionally uses a silane having an organic non-copolymerizable residue, the silane having a formula RSiX.sub.3 or RR.sup.TSiX.sub.2, including hydrolyzable groups X selected from a group of X═OR, halogen, NR.sup.T′.sub.2, with R.sup.T′=alkyl, aryl, and non-hydrolyzable organic residues R and/or R.sup.T.

25. The method as in claim 14, wherein in step c) the counter ion X of the metal salt or the conjugate base of the organic acid used in step a) is replaced by hydroxide ions using an ion exchanger.

26. The method as in claim 14, wherein a methacrylate is employed as the matrix monomer, the methacrylate being selected from a group consisting of methyl, ethyl, butyl, benzyl, furfuryl, and phenyl (meth)acrylate, bisphenol A di(meth)acrylate, bis-GMA, ethoxylated bisphenol A di(meth)acrylate, UDMA, di-, tri-, and tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, butanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, and mixtures thereof.

27. The method as in claim 14, wherein the dispersion is transformed into the dental composite by irradiating light of an appropriate wavelength.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 schematically illustrates a first embodiment of the preparation method;

(2) FIG. 2 schematically illustrates a second embodiment of the preparation method, in which the mixed oxide particles have a further surface modification, in addition to the copolymerizable group;

(3) FIG. 3 schematically illustrates the transformation of the dispersion according to the invention into a dental composite;

(4) FIG. 4 schematically illustrates the transformation of the dispersion as prepared according to FIG. 2 into a dental composite; and

(5) FIG. 5 schematically illustrates the transformation of a dispersion including additional functionalized mixed oxide particles into a dental composite.

DETAILED DESCRIPTION

(6) FIG. 1 schematically illustrates an embodiment of the inventive method for preparing a corresponding dispersion 10 of nanoscale mixed oxide particles 6 in a monomer matrix 9. In step a), first a sol 3 is formed. For this purpose, solutions 1 and 2 are mixed. Solutions 1 and 2 are the solutions A and B as described above, with solution 1 (solution A) including a silicon precursor and a salt of an X-ray opaque metal M, a sol stabilizer (not shown) and a solvent 4, and solution 2 (solution B) including an aqueous base (not shown) and also the solvent 4. The reaction mixture is stirred until particle formation is completed. The resulting sol 3 comprises nanoscale mixed oxide particles 5 in solvent 4, and further comprises undesired reaction products from step a) (not shown). In subsequent step b), surface modification of mixed oxide particles 5 is effected using a silane 25. In this embodiment, silane 25 has a formula X.sub.3SiA, wherein functionality A is a group that is copolymerizable with the matrix monomer. Group X is a hydrolyzable group and is preferably selected from X═OR, halogen, NR″.sub.2, with R″=alkyl, aryl.

(7) The mixed oxide particles 6 so obtained have a covalently bound functionality A which is copolymerizable with the matrix monomer 9 added in step d). The degree of modification of the functionalized mixed oxide particles 6 may be adjusted through the amount of the silane 25 added in step b). In step c), undesired sol components are separated through a ion exchanger. The so conditioned sol 8 is redispersed in matrix monomer 9, in step d). Subsequently, solvent 4, water, and base (not shown) are removed to obtain the dispersion 10.

(8) FIG. 2 schematically illustrates another embodiment of the preparation method. Here, in addition to the silane 25, a silane 26 having another, non-polymerizable functionality B is used in step b). Therefore, the mixed oxide particles 12 have functionalities B, in addition to copolymerizable groups A. Here, again, modification degrees may be adjusted through the amount of employed silanes 25 and 26.

(9) FIG. 3 schematically illustrates the transformation of dispersion 10 according to the invention into a corresponding dental composite 16. By irradiating light of a suitable wavelength, polymerization of the matrix monomers 9 occurs, so that a resin matrix 18 is obtained. Here, copolymerization of matrix monomer 9 and functional groups A of mixed oxide particles 6 is accomplished, so that in dental composite 16 the mixed oxide particles 17 are covalently bound to the resin matrix 18. Depending on the degree of modification of the mixed oxide particles 6a, the latter may also act as a crosslinker 17a.

(10) FIG. 4 schematically illustrates the transformation of another embodiment of a nanoscale dispersion 14 into a corresponding dental composite 21. Mixed oxide particles 12 of the dispersion have, besides copolymerizable groups A, another functionality B which is not reactive under the polymerization conditions and therefore is also present in the cured dental composite 21. Thus, the physical and mechanical properties of dental composite 21 may be influenced by the group B of mixed oxide particles 12. For example, a modification of the mixed oxide particles with flexible side chains as a functionality B counteracts embrittlement of dental composite 21.

(11) FIG. 5 schematically illustrates another possibility to improve flexibility of the dental composite. In this embodiment, further mixed oxide particles 22 are added to the sol 8 which includes mixed oxide particles 6 having a copolymerizable functionality A. The functional group B of the second mixed oxide particles 22 is not reactive under the reaction conditions of polymerization. Therefore, once the dispersion is cured, dental composite 26 comprises mixed oxide particles 17 covalently bound to the resin matrix, and functionalized mixed oxide particles 22 which are not covalently bound into the resin matrix 18.

(12) Exemplary Embodiments

EXAMPLE 1

(13) Dispersion of SiO.sub.2—BaO Nanoparticles in a Bis-GMA/TEG-DMA Matrix Using Barium Perchlorate as a Precursor and Hydroxypropylcellulose as a Sol Stabilizer

(14) Step a): Particle Synthesis

(15) Solution A: 8 g of anhydrous barium perchlorate is dissolved in 238 ml of ethanol. To stabilize the solution, 1.2 ml of acetylacetone is added. Subsequently, 26.8 ml of TEOS is added to the solution.

(16) Solution B: 278 ml of ethanol is mixed with 29 ml of a 25% NH.sub.4OH solution, and 3 g of hydroxypropylcellulose (HPC) is added as a sol stabilizer. The solution is stirred until the sol stabilizer dissolved.

(17) To start the reaction, solution A is rapidly added to solution B with vigorous stirring. Subsequently, the reaction mixture is stirred for 24 h. As a result of particle formation, the solution gradually becomes turbid.

(18) Step b): Surface Modification

(19) For silanization of the particles synthesized in step a), 2.8 ml of 3-methacryloxypropyltrimethoxysilane (MPTMS) is added to the reaction solution. The reaction solution is stirred again for 24 hours.

(20) Step c): Separation of the Counter Ion

(21) To remove the perchlorate ions present in the reaction mixture, the solution is filtered through a column filled with 50 g of ion exchanger Lewatit M500 OH. The ion exchanger is loaded with hydroxide ions, so that during the filtration perchlorate ions are removed from the solution and are replaced by hydroxide ions.

(22) Step d): Dispersing of the Particles in the Matrix Monomer

(23) 90 g of a mixture of bis-GMA and TEG-DMA with a mixing ratio of 1:1 are added to the reaction solution ion-exchanged in step c).

(24) Step e): Processing of the Reaction Solution

(25) Components ammonia, ethanol, and water present in the solution are removed from the mixture by vacuum distillation on a rotary evaporator. What remains is a 10% dispersion of silanized SiO.sub.2—BaO nanoparticles with Bis-GMA/TEG-DMA as the matrix monomer.

EXAMPLE 2

(26) Dispersion of SiO.sub.2—BaO Nanoparticles with a Mixture of Bis-GMA/TEG-DMA as a Matrix Monomer Using 3-Methacryloxypropyltrimethoxysilane (MPTMS) as a Sol Stabilizer

(27) Steps a) and b): Particle Synthesis and Silanization

(28) Solution A: 8 g of anhydrous barium perchlorate is dissolved in 214 ml of ethanol. To stabilize the solution, 1.2 ml of acetylacetone is added. Then, 12.3 ml of TEOS is added to the solution. Subsequently, 13.1 ml of 3-methacryloxypropyltrimethoxysilane (MPTMS) is added to the solution.

(29) Solution B: 252 ml of ethanol is mixed with 26 ml of a 25% NH.sub.4OH solution.

(30) To start the reaction, solution B is rapidly added to solution A with vigorous stirring. Subsequently, the reaction mixture is stirred for 24 h. As a result of particle formation, the solution gradually becomes turbid.

(31) Step c): Separation of the Counter Ion

(32) To remove the perchlorate ions present in the reaction mixture, the solution is filtered through a column filled with 50 g of ion exchanger Lewatit M500 OH. The ion exchanger is loaded with hydroxide ions, so that during the filtration perchlorate ions are removed from the solution and are replaced by hydroxide ions.

(33) Step d): Dispersing of the Particles in the Matrix Monomer

(34) 90 g of a mixture of bis-GMA and TEG-DMA with a mixing ratio of 1:1 are added to the reaction solution ion-exchanged in step c).

(35) Step e): Processing of the Reaction Solution

(36) Volatile components ammonia, ethanol, and water present in the solution are removed from the mixture by vacuum distillation on a rotary evaporator. What remains is a 10% dispersion of silanized SiO.sub.2—BaO nanoparticles with Bis-GMA/TEG-DMA as the matrix monomer.

EXAMPLE 3

(37) Use of Ba(OH).sub.2 as a BaO Precursor

(38) Steps a) and b): Particle Synthesis and Silanization

(39) Solution A: 220 ml of ethanol are provided in a reaction vessel, and first 12.3 ml of tetraethyl orthosilicate and 13.1 ml of 3-methacryloxypropyltrimethoxysilane (MPTMS) are added with stirring, and then 1.4 ml of methacrylic acid is added to stabilize the solution. Finally, 71.5 ml of saturated barium hydroxide solution (i.e. 4.6% aqueous Ba(OH).sub.2 solution) is added to the mixture, likewise under stirring.

(40) Solution B: 256 ml of ethanol are mixed with 85 ml of a 2 molar NH.sub.3 solution in ethanol.

(41) To start the reaction, solution B is rapidly added to solution A with vigorous stirring. Subsequently, the reaction mixture is stirred for 24 h. As a result of particle formation, the solution gradually becomes turbid.

(42) Step c): Separation of the Counter Ion

(43) To remove the methacrylate ions present in the reaction mixture, the solution is filtered through a column filled with 50 g of ion exchanger Lewatit M500 OH. The ion exchanger is loaded with hydroxide ions, so that during the filtration methacrylate ions are removed from the solution and are replaced by hydroxide ions.

(44) Step d): Dispersing of the Particles in the Matrix Monomer

(45) 40 g of a mixture of bis-GMA and TEG-DMA with a mixing ratio of 1:1 are added to the reaction solution ion-exchanged in step c).

(46) Step e): Processing of the Reaction Solution

(47) Volatile components ammonia, ethanol, and water present in the solution are removed from the mixture by vacuum distillation on a rotary evaporator. What remains is a 20% dispersion of silanized SiO.sub.2—BaO nanoparticles with Bis-GMA/TEG-DMA as the matrix monomer.

EXAMPLE 4

(48) Synthesis of a Commercialized System Including SiO.sub.2 Particles, as a Comparative Example

(49) A commercially available sol of 50 wt % of SiO.sub.2 in TEG-DMA is mixed with bis-GMA in a 2:1 ratio. The resulting dispersion has a solids content of 33%.

EXAMPLE 5

(50) Polymerization of the Nano-Composites

(51) The dispersions obtained in Examples 1 to 4 are mixed with a mixture of camphorquinone and ethyl dimethylaminobenzoate, and then are cured under UV light. Subsequently, the optical properties of the cured, i.e. polymerized, composites are determined on a Hunterlab Colorquest colorimeter. The results are shown in Table 1.

(52) TABLE-US-00001 TABLE 1 Summary of optical properties Solids X-ray opacity content Transparency Translucency of filler material Example [wt %] [%] [%] [% Al] 1 10 78.4 61.8 73.5 2 10 91.4 83.0 114.2 3 20 88.5 86.6 107.5 4 33 88.2 73.8 35.5