Composition and method for generating a shade gradient in zirconia dental restoration

Abstract

Disclosed are compositions and methods for bleaching and optionally coloring a shaded zirconia, particularly mono-chromatic pre-shaded dental zirconia. The compositions and methods are useful in generating a shade gradient in milled dental restorations. The compositions comprise metal salts or complex dissolved in a solvent.

Claims

1. A method of generating a color gradient by bleaching a pre-shaded zirconia, the method comprising: applying, to the pre-shaded zirconia, a liquid comprising a metal compound or metal compounds comprising one or more metal selected from zinc, gallium, and aluminum in an amount sufficient to cause bleaching by the formation of oxides in the pre-shaded zirconia after sintering at a temperature greater than or equal to 1450? C., and optionally solvent, wherein the liquid reduces the intensity of color in the pre-shaded zirconia, and wherein the liquid substantially maintains the flexural strength of the pre-shaded zirconia.

2. The method of claim 1, wherein the metal compound is a metal salt or complex comprising a metal and a counterpart selected from halides (Cl, F, Br, and I), nitrate, acetate, sulfate, lactate, propionate, formate, and alkoxides.

3. The method of claim 1, wherein the metal compound is a solid salt or complex of zinc, aluminum, or gallium and is present at about 0.1 wt % to about 80 wt % by weight of the bleaching liquid.

4. The method of claim 1, wherein the metal compound is a liquid metal compound of zinc, aluminum, or gallium and is present at about 0.1 wt % to about 100 wt % of the bleaching liquid.

5. The method of claim 1, wherein the metal is selected from zinc, gallium, and aluminum.

6. The method of claim 2, wherein the metal salt or complex is selected from: TABLE-US-00003 Conc. salt/complex (wt %) ZnCl.sub.2 1-80 Zn(NO.sub.3).sub.26H.sub.2O 1-80 Ga(NO.sub.3).sub.3xH.sub.2O 1-80 Al(NO.sub.3).sub.39H.sub.2O 1-80

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graphic depicting how warpage is measured.

(2) FIG. 2 is a table showing the composition of the various examples and comparative examples and results.

(3) FIG. 3 is a photo comparing various examples.

(4) FIG. 4 is a photo comparing various examples.

DETAILED DESCRIPTION

(5) Compositions and methods for bleaching and optionally coloring unsintered, shaded zirconia, such as but not limited to pre-shaded zirconia or colored but previously unshaded zirconia, are disclosed herein. Simple bleaching of shaded zirconia makes the use of shaded zirconia, regardless of source, more universal because shade can be customized by applying the bleaching solution where color gradient is required.

(6) The following characteristics are desirable for a bleaching liquid: 1. has no or small effect on strength to maintain the class of the material; 2. does not act as a colorant in zirconia. Though it is not desirable for the bleaching component in the liquid to have a color, the bleaching effect optionally can be combined with other coloring liquid to enhance features of teeth, for example enamel effect by adding additional colorants to make incisal area look more translucent.

(7) Bleaching liquids were made by solving solid or liquid metal compounds in solvents.

(8) The metal is believed to drive the compounds bleaching ability. Some metal compounds exist as liquid. Liquid metal compounds can be used with or without dilution with the solvents.

(9) In some embodiments, the metal is selected from zinc, gallium, and aluminum. In some embodiments, the metal is present as a dissolved solid salt or complex. Particularly, salts or complexes of halogens, particularly chlorides, nitrates (NO.sub.3), and NO.sub.3 hydrates are useful in the compositions described herein. The salts or complexes are present at about 0.1 wt % to about 80 wt % by weight of the bleaching liquid. In some embodiments, the metal compound is present at 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value or range of values between any two of these. When liquid metals are used, the liquid metal compound is present at about 0.1 wt % to about 100 wt % of the bleaching liquid. In some embodiments, the metal compound is present at 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or any value or range of values between any two of these.

(10) In some embodiments, the metal is selected from zinc, gallium, and aluminum. In some embodiments, solid salts or complexes of zinc, aluminum, and gallium are present at about 0.1 wt % to about 80 wt % by weight of the bleaching liquid. In some embodiments, the metal compound is present at 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or any value or range of values between any two of these. When liquid metal compounds of zinc, aluminum, and gallium are used, the liquid metal compound is present at about 0.1 wt % to about 100 wt % of the bleaching liquid. In some embodiments, the metal compound is present at 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or any value or range of values between any two of these.

(11) In some embodiments, the metal compound is a metal salt or complex comprising a metal and a counterpart selected from halides (Cl, F, Br, and I), nitrate, acetate, sulfate, lactate, propionate, formate, and alkoxides.

(12) Solvents can be water and/or any organic solvent such as methanol, ethanol, propanol, isopropanol, ethyl acetate, hexane, toluene, etc., and mixture of these solvents as long as the salt and/or complex are soluble in the solvents. The solvents are not limited to the solvents listed above.

(13) Bleaching power of the bleaching liquids depends on metal in the bleaching liquid, type of the zirconia and how shading was performed. In 3Y and 4Y zirconia, bleaching liquids shows strong effect, but 5Y zirconia requires higher concentration of metal compounds for strong enough bleaching. Pre-shaded zirconia readily absorbs bleaching liquid, so the bleaching is more effective. In contrast, unshaded zirconia shaded by coloring liquid does not absorb bleaching liquid as much as pre-shaded zirconia unless the unshaded zirconia is thoroughly dried after shading. The preferred concentration range of metal compounds in the bleaching liquid for each case is:

(14) TABLE-US-00002 Preferred concentration range Type of zirconia Shading* of metal compound 3Y/4Y Unshaded/user-shaded 3-30 wt % pre-shaded 3-30 wt % 5Y Unshaded/user-shaded 15-80 wt % pre-shaded 10-40 wt %

(15) When more than one metal compound is present in the bleaching liquid, the concentration indicates the total concentration of the metal compounds. In some zirconia, yttrium concentration falls between 4Y and 5Y. The preferred concentration can be changed accordingly.

(16) The solution may contain viscosity modifier to control penetration depth of the solutions. The viscosity modifiers are glycerol, polyethylene glycol (PEG), polyacylic acid (PAA) and its salts, polyvinylalcohol (PVA), polymethacrylic acid (PMAA) and its salts, polyvinylpyrrolidone (PVP), etc., and mixture of these chemicals. The viscosity modifiers are not limited to the substances listed above.

(17) Acid may be dissolved in the solution to enhance solubility of the metal compounds or stability of the solutions. Dye may be added to the solution as a marker to distinguish applied area from unapplied area.

(18) Bar shaped samples were milled for a flexural strength test from pre-shaded zirconia blanks. Metal compound solutions were applied to one side of the bars by brushing. In some examples, solutions contain copper or a manganese compound which is added as a coloring agent for enamel effect. Sintering was done at 1530? C. for 2 hours for 3Y zirconia and at 1450? C. for 2 hours for 5Y zirconia. The final dimensions of sintered bars were about 30 mm in length, 4 mm in width, and 3 mm in thickness. Flexural strength test was performed using a three-point bending setup. Unless any description is provided, 16 samples of each group were tested for strength measurement. The treated side was placed downward to make the treated side under tensile stress. Warping was quantified by percent increase of thickness from original thickness, t.sub.1, to warped thickness, t.sub.2, as depicted in FIG. 1.

EXAMPLES

(19) As a control, bars were prepared from a pre-shaded 3Y zirconia blank without any treatment.

(20) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of Nacera Blue X solution which contains 50-70 wt % yttrium nitrate hexahydrate.

(21) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 50 wt % magnesium chloride hexahydrate solution.

(22) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 10 wt % zinc chloride solution.

(23) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 10 wt % zinc nitrate hexahydrate solution.

(24) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 40 wt % ytterbium nitrate pentahydrate solution.

(25) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 40 wt % gadolinium nitrate hexahydrate solution.

(26) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 40 wt % lanthanum nitrate hexahydrate solution.

(27) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 10 wt % gallium nitrate hydrate solution.

(28) Bars prepared from a pre-shaded 3Y zirconia blank were treated with one coat of 10 wt % aluminum nitrate nonahydrate solution.

(29) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of 10 wt % aluminum nitrate nonahydrate solution.

(30) Bars prepared from a pre-shaded 3Y zirconia blank were treated with three coats of 10 wt % aluminum nitrate nonahydrate solution.

(31) As a control, bars were prepared from an unshaded 5Y zirconia blank without any treatment.

(32) Bars prepared from an unshaded 5Y zirconia blank were treated with two coats 10 wt % aluminum nitrate nonahydrate solution. These unshaded bars were used for flexural strength test. Bars prepared from a pre-shaded 5Y zirconia blank were treated with two coats 10 wt % aluminum nitrate nonahydrate solution for bleaching test.

(33) Bars prepared from an unshaded 5Y zirconia blank were treated with three coats of 10 wt % aluminum nitrate nonahydrate solution. These unshaded bars were used for flexural strength test. Bars prepared from a pre-shaded 5Y zirconia blank were treated with three coats of 10 wt % aluminum nitrate nonahydrate solution for bleaching test.

(34) Bars prepared from an unshaded 5Y zirconia blank were treated with two coats of 20 wt % zinc nitrate hexahydrate solution.

(35) Bars prepared from an unshaded 5Y zirconia blank were treated with two coats of 20 wt % gallium nitrate hydrate solution.

(36) As a control, bars prepared from an unshaded 5Y zirconia blank were dipped in A4 coloring liquid and dried.

(37) Bars prepared from an unshaded 5Y zirconia blank were dipped in A4 coloring liquid and dried at 70? C. for 30 minutes. The bars were treated with two coats of a solution containing 40 wt % aluminum nitrate nonahydrate, 20 wt % zinc nitrate hexahydrate, and 0.05 wt % cupric chloride dihydrate.

(38) As a control, bars were prepared from a pre-shaded 3Y zirconia blank without any treatment.

(39) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of a solution containing 10 wt % aluminum nitrate nonahydrate and 0.05 wt % cupric chloride dihydrate.

(40) Bars prepared from a pre-shaded 3Y zirconia blank were treated with two coats of a solution containing 10 wt % aluminum nitrate nonahydrate and 0.03 wt % manganese chloride tetrahydrate.

(41) FIG. 2 is a table listing the experimental conditions and results. It can be seen from the results that use of the metals salts or metal complexes disclosed herein reduces warpage, without negatively affecting flexural strength, and thus without reducing the class of the material.

(42) Though any metal compounds that have bleaching effect on the Table in FIG. 2 can be used for bleaching liquids, there are some limitations. According to ISO 6872, class 5 materials have flexural strength of at least 800 MPa. (Notably, ytterbium, gadolinium, and lanthanum did not exhibit meaningful bleaching effect.) 3Y zirconia is a class 5 material. However, the samples treated with yttrium nitrate hexahydrate (Blue X solution, example 2) and magnesium chloride hexahydrate (example 3) showed flexural strength lower than 800 MPa. The class of the material changed to a lower level. The decrease of flexural strength due to co-doping of stabilizers to yttria-stabilized zirconia limits usage of the materials down to 3 unit bridges. Other bleaching liquids containing zinc, gallium, or aluminum salts have no considerable decrease of flexural strength; in some instances, an increase in flexural strength was seen. This means no class change of 3Y zirconia materials. Considering bleaching effect, warping, and flexural strength, compounds of aluminum, zinc, and gallium are proper to be used as bleaching liquid of shaded zirconia, even in multi-unit bridges.