Dental Compositions

Abstract

A dental composition is provided as a coating comprising glass flakes providing improved wear-5 resistance and aesthetic properties. The compositions may be used in the treatment of dentine hypersensitivity, dental caries, or in the protection of a tooth from the external environment of the mouth.

Claims

1. A dental composition comprising glass flakes and a resin wherein the glass flakes and resin have a refractive index difference of less than 0.04, wherein the glass flakes have a thickness in the range of between 0.5 and 10 microns and an aspect ratio in the range of between 20:1 and 90:1, wherein the glass flakes are coated with a silane, wherein, upon application of the composition to a tooth surface, the glass flakes align substantially parallel to the surface; and wherein the resin is a vinyl resin comprising a monomer selected from urethane dimethacrylate (UDMA), methyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, polyethyleneglycol dimethacrylate (PEGDMA), 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), tetrahydrofurfuryl methacrylate, and mixtures thereof; and optionally further comprising a carboxylic acid or phosphate functional monomer; the weight fraction of glass flakes in the composition is from 10% to 40% and the weight fraction of resin in the composition is from 50% to 90%; and wherein the dental composition is a sealant coating which seals a tooth from exposure to the external environment in the mouth.

2. (canceled)

3. A dental composition according to claim 1 wherein the aspect ratio is in the range of between 20:1 and 40:1.

4. (canceled)

5. A dental composition according to claim 1 wherein the weight fraction of the glass flakes is between 20% and 40%.

6. (canceled)

7. A dental composition according to claim 1 wherein the resin is a methacrylate resin.

8. A dental composition according to claim 7 wherein the resin is a dimethacrylate resin.

9. A dental composition according to claim 7 wherein the resin comprises a hydrophilic monomer.

10. A dental composition according to claim 1 further comprising a photoinitiator system.

11. A dental composition according to claim 10 wherein the photoinitiator system can be cured by the application of light within one minute.

12. A dental composition according to claim 1 further comprising a carboxylic acid or phosphate functional monomer.

13. A dental composition according to claim 1 further comprising a fluoride releasing agent.

14-17. (canceled)

18. A method of treating or preventing caries or dentine hypersensitivity comprising administration of a dental composition according to claim 1 to a tooth of a subject in need thereof.

19. (canceled)

20. A method of sealing a tooth from exposure to the external environment in the mouth comprising administration of a dental composition according to claim 1 to a tooth of a subject in need thereof.

21. A method of sealing a dental restoration, comprising administration of a dental composition according to claim 1 to a dental restoration and surrounding tooth of a subject in need thereof.

22. The dental composition accordingly to claim 12, wherein the carboxylic acid or phosphate functional monomer is selected from 4-methacryloxyethyl trimellitic acid or its anhydride, bis[2-(methacryloyloxy)ethyl]phosphate, and 2-hydroxyethyl methacrylate phosphate.

Description

FIGURES

[0047] FIG. 1 shows the microstructure of a composite made with a flake particles with a low aspect ratio of 14:1 (1A) and high aspect ratio (20:1).

[0048] FIG. 2 shows a schematic aligned flake glass composite.

[0049] FIG. 3 shows flake orientation relative to aspect ratio.

[0050] FIG. 4 shows calcium release from Enamelin-coated and non-coated teeth.

EXAMPLES

Example 1: Formulation of Composition

[0051] Formulation of Resin: Resin formulation is given in table 1 below. All ingredients were mixed together by stirring continuously at room temperature in a dark room to prevent curing of the resin. Urethane dimethacrylates and 2-Hydroxyethyl methacrylate, can be replaced with any other methacrylate such as bisphenol A glycidyl methacrylate, poly(propylene glycol) dimethacrylate, Triethylene glycol dimethacrylate, Siloranes). 4-META can be replaced by other carboxylate functional monomers and also by HEMA Phosphate and other phosphate functional monomers such as 2-dimethylaminoethyl methacrylate

TABLE-US-00002 TABLE 2 Percentage Monomer (wt) Urethane-di-methacrylate (UDMA) 64.55% Hydroxyethyl Methacrylate (HEMA) 34.39% 4- META 0.83% Camphorquinone (CQ) 0.11% Dimethyl p toluidine 0.12%

[0052] Glass flakes: Glass Flakes (GF) were obtained from Glassflake Ltd, Leeds UK as milled glass flakes product GF100M.

[0053] Silylation of Flake: The silylation was conducted by immersing glass flakes (GF) into silane coupling agent [3-Tri methoxysilyl Methacrylate Propylene (MPS)] of Sigma-Aldrich, UK under control environment. The ratio of GF and silane agent was maintained at 0.3 and 0.7 respectively. The GF were mixed with resin on magnetic stirrer at room temperature (23° C.) or 2 h in order to able GF particles to be more incorporate with resin. The samples were then placed into vacuum oven (Touson Mercer-Altrincham, England) under dynamic conditions at 400 C for 2 h to allow the acetone to completely remove. Later the samples were washed with methanol (Sigma Aldrich, UK) to remove the unreacted resin and vacuum dried for 2 h.

[0054] Incorporation of flakes in Resin: The resultant 10 g of resin was mixed with 4.2 g of silylated GF for 1 h to achieve the uniform distribution of GF into resin. The obtained material was denoted as “Enamelin”.

Example 2: Flake Glass Alignment

[0055] Uo et al. Journal of the Ceramic Society of Japan 118 425-7 (2010) have investigated the use of flake glass particles in dental composites however the aspect ratio of the flakes is low and the microstructure of the composite is isotropic. Compositions of the invention are anisotropic and align parallel to the surface. FIG. 1a shows a scanning electron micrograph of a flake glass composite with an aspect ratio of 14:1 whilst FIG. 1b with an aspect ratio >20:1. The composite with a low aspect ratio is largely isotropic whilst the high aspect ratio composite is highly anisotropic. FIG. 3 indicates that an aspect ratio greater than 14:1 is critical for the parallel alignment of the flakes. Flake glass coatings of the invention offer a potential replacement for enamel because the flake glass particles can be aligned parallel to the surface of the tooth. Alignment of the flakes can provide improved resistance to abrasive wear in the mouth.

Example 3: Adhesion with Human Tooth

[0056] This example tests the tooth adhesion of a flake glass filled methacrylate tooth coat Enamelin, and a commercially available nano silica filled methacrylate dental varnish Equia Coat (GC Corp). 12 non-carious first molars were selected from the Tissue Bank at Barts and the London School of Medicine and Dentistry. The teeth were sectioned mid-coronally using a diamond saw. The sectioned teeth were embedded in embedding resin (ClaroCit, Strauers) so that the cut dentine surface was exposed. After the acrylic resin had set hard, the exposed surfaces were acid-etched using 35% phosphoric acid solution for 20 seconds and then washed with copious amounts of water. The material, either Enamelin or Equia coat, was packed in cylindrical moulds, which were then placed on top of the tooth surface and light cured for 40 seconds. 6 specimens were produced in this manner for both the materials. The specimens were stored in deionised water at 37° C. for 24 hours. After 24 hours the samples were taken out from water and the Shear Bond Strength Test was performed by securing the specimens in a mounting jig and a sharp straight-edge chisel attached to the Instron cross-head was used to apply a shearing force at a rate of 0.05 mm/min. Mean Values for tooth adhesion for Enamelin were 5.680±2.27 MPa whereas for Equia Coat these were 4.63±0.705 MPa. The results indicate that Enamelin has superior chemical adhesion with the organic and inorganic phases in the tooth.

Example 4: Adhesion with Conventional Glass Ionomer Cement

[0057] This example compares adhesion of a flake glass filled methacrylate dental coat Enamelin, and a commercially available nano silica filled methacrylate dental varnish to a conventional glass ionomer cement Fuji IX (GC Corp). GC Fuji IX capsules were mixed according to manufacturer's instructions and then packed into Teflon mould measuring 10 mm in diameter and 1 mm thickness. The cements were covered with an acetate sheet and allowed to set for 1 hour at 37° C. and 100% relative humidity. The discs were then embedded in resin (ClaroCit, Strauers) with the flat surface exposed. Enamelin and Equia coat were then bonded on to the discs using the method described in Example 1. 6 samples were produced for the both the materials. Thereafter the samples were stored in deionised water at 37° C. for 24 hours. After 24 hours the samples were taken out from water and the Shear Bond Strength Test was performed as described in example 1. The mean bond strength for adhesion with glass ionomer cement were 6.57±2.96 MPa for Enamelin and 1.94±1.11 MPa for Equia coat. Results indicate Enamelin has a superior bonding with conventional glass ionomer cements.

[0058] Example 5: Adhesion with Light Cured Resin Modified Glass Ionomer Cement

[0059] This example compares adhesion of a flake glass filled methacrylate dental coat Enamelin, and a commercially available nano silica filled methacrylate dental varnish with a resin modified glass ionomer cement Fuji II LC (GC Corp). GC Fuji II LC capsules were mixed according to manufacturer's instructions and then packed into mould measuring 10 mm in diameter and 1 mm thickness. The discs (n=12) were light cured for 20 s using dental curing light. The discs were then embedded in resin (ClaroCit, Strauers) with the flat surface exposed. Enamelin and Equia coat were then bonded on to the discs using the method described in Example 1. Six samples were produced for both the materials. Thereafter the samples were stored deionised water at 37° C. for 24 hours. After 24 hours the samples were removed from the water and the Shear Bond Strength Test was performed as described in example 1. The mean bond strength for adhesion with resin modified glass ionomer cement were 12.50±4.55 MPa for Enamelin and 11.76±3.15 MPa for Equia coat. Results indicate Enamelin has a superior bonding with conventional glass ionomer cements.

Example 6: Vickers Hardness Test

[0060] Equia coat and Enamelin were packed into cylindrical moulds measuring 5 mm (L)×2 mm (D) and were then light cured for 20 s from both ends using a dental curing light. Six samples for each material were prepared. The samples were embedded in mounting resin with the flat surface exposed. The prepared samples were ground with the silicon carbide grid papers (Buehler-Met) ranges from 400, 600, 1,000, 2,400, 4,000 and finally polished with the 1p aluminium oxide (MetPrep Ltd) paste for final smooth surface. The Vickers micro hardness test is used to assess the depth of penetration of a diamond into the material surface in order to determine its hardness. This test was carried out using a Shimadzu Micro hardness Tester, type-M by applying a load of 300 g for 10 seconds. Hardness is calculated by dividing the force with the cross sectional area of the indent. Enamelin gave an average hardness of 76.68±2.96 where Equia Coat had a lower hardness of 29.35±5.68. The results show that Enamelin provides a harder coating than Equia Coat and is thus likely to be more durable in the mouth.

Example 7: Tooth Bush Wear Resistance Test

[0061] Caries free human teeth (1st & 2nd premolars)—were sectioned longitudinally into two equal halves using a diamond saw. The sectioned teeth (n=6) were stored in sodium hypochlorite solution at 37° C. until use. The sectioned teeth were embedded in acrylic resin so that the cut enamel and dentine surfaces were exposed. The exposed surfaces were then polished with 3 μm, 0.25μ and 0.1 μm diamond polishing pastes. (Kemet International Ltd, Maidstone, UK).

[0062] Enamelin (n=3) and Equia Coat (n=3) was applied using dental brushes to the prepared polished tooth samples and then light cured for 30 s using a dental curing light for 30 sec. Prior to subjecting the samples to wear profilometric analysis was conducted using computerized Incise dental scanner (Renishaw, UK), with scanning interval of 0.05 mm along with the speed of 500 mm/min.

[0063] Colgate Whitening Tooth paste with an RDA value of 145 (highly abrasive) was selected for the wear study. 2 ml of the toothpaste was applied to the sample surfaces which were then individually placed in troughs. Tooth brush heads with flat bristles were lowered onto the samples under a constant load of 200 g and 20, 000 cycles of brushing were performed using the automated equipment. After every 5,000 cycles the 2 ml of distilled water along with the 2 mm length toothpaste was re-applied. Wear was quantified using the profilometer again using the same parameters as described previously. Enamelin showed a wear of 0.074±0.003 mm whereas Equia coat had a much higher wear of 0.129±0.002 mm. This suggests Enamelin is more resistant to wear as compared to the tested commercial product. This complements the finding of the previous example as harder coating would be expected to provide a better wear resistance.

Example 8: Protective Coating Against Acid Dissolution

[0064] Non-carious first molars were selected from the Tissue Bank at Barts and the London School of Medicine and Dentistry. The teeth were sectioned using a diamond saw to remove the tooth roots. The obtained crowns were fully coated with Enamelin using a dental brush and then light cured for 20 seconds using a LED dental light. The coated teeth were then placed in 0.1 M acetic acid solution (pH 4.5). Release of calcium ions was measured over a period of 24 hours using Calcium Ion Selective Electrode (Nico 2000 Ltd, UK). Non coated crowns were used as control. These were also immersed in acetic acid of the same concentration and pH.

[0065] The results for the calcium release from coated and non-coated samples are given in FIG. 4. Results indicate that tooth crowns coated with Enamelin showed negligible Calcium release when compared to non-coated samples. This indicated that Enamelin forms an effective barrier against acid dissolution of teeth.