Dental zirconia treatment technology

1. Nine groups of color masking liquids were prepared by the above method, wherein the formula of these group of color masking liquids comprises 96.83% of a mother liquor, 1.52% of ethanol, 1.1% of potassium nitrate, 0.2% of yttrium chloride and 0.35% of citric acid. The formula of the mother liquor is shown in Table 1, wherein the numerals in the table indicate the mass percentages of the corresponding components in the color masking liquid, and the balance is deionized water, with the sum of all the components being 100%.

The zirconia powder used in this example was purchased from Shanghai Linghao Metal Material Co., Ltd., with an article number of ZR-2. The zirconia powder was isostatically pressed at 150 MPa for 10 min (e.g., to form a pressed or “green” zirconia pre-ceramic). Then, it was pre-sintered at 1050° C. for 2 h. Thereafter, the pre-sintered zirconia ceramics were taken out, equal amounts of color masking liquids from each group were painted on or over the surface of the zirconia ceramics respectively, which was repeated twice. Then, the zirconia ceramics were put into an oven for drying at 90° C., and half an hour later, taken out, put into a crucible with zirconium beads, put into a sintering furnace, and heated at 1530° C. for 2 hours to complete secondary sintering. At the same time, a control group was provided, where the pre-sintered zirconia ceramics were directly heated at 1530° C. for 2 h without prior painting with the color masking liquid.

2. Light transmittance test, three-point bending strength test, thickness test and color masking test were carried out for each group of zirconia bases. Among them, the thickness test is carried out as follows: the thickness of the zirconia bases in each group is measured at three points (the positions of the three points selected are the same for all the bases) respectively, and compared with that in the blank control group to obtain three groups of difference ratios which are then averaged. Thickness difference ratio lower than 1/10,000 is regarded as no difference. The color masking test comprises the following steps: the zirconia bases prepared in each group are fit onto the same metal abutments, and observed for whether the zirconia bases are transparent to color or not with naked eyes under a typical daily illumination condition, and observed for translucency and aesthetic quality. The results of these tests are shown in Table 2.

3. A mother liquor was prepared with the formula of the mother liquor in group 2 in step 1, and then 14 groups of color masking liquids (group 10-group 23) were prepared with the mother liquor, wherein the formulas of these groups of color masking liquids are shown in Table 3, and the numerals in the following Table indicate the mass percentages of the corresponding components in the color masking liquid. The color masking liquid was used in the same way as above.

4. Light transmittance test, three-point bending strength test, thickness test and color masking test were carried out on each group of zirconia bases. Among them, the thickness test is carried out as follows: the thickness of the zirconia bases in each group is measured at three points (the positions of the three points selected are the same for all the bases) respectively, and compared with that in the blank control group to obtain three groups of difference ratios which are then averaged. The color masking test comprises the following steps: the zirconia bases prepared in each group are fit onto the same metal abutments, and observed for whether the zirconia bases are transparent to color or not with naked eyes under a typical daily illumination condition. The results of these tests are shown in Table 4.

1. Eight groups of color masking liquids were prepared using the formula of group 16 in Example 1, and then applied by different methods. Specifically, the treatment methods for these groups are shown in Table 5.

2. A group of zirconia bases were prepared separately without painting with the masking liquid, and other preparation and sintering conditions were completely the same, which served as the blank control group. The results of these groups are shown in Table 6. Among them, “not dried” means the bases are directly sintered without drying.

Zirconia bases were obtained with the formula of group 16 in Example 1 using the method of group 1 in Example 2. Then, the zirconia base was colored. Of course, the zirconia base can be colored directly without being treated with the color masking liquid. In the latter case, the translucency and color masking property of the zirconia base may be inferior.

The present disclosure provides the following two coloring methods. Method 1 involves preparing a first coloring liquid, roughening the surface of the zirconia base, soaking the zirconia base in the first coloring liquid for more than 15 s, then taking out the zirconia base, and subjecting the zirconia base to surface protection treatment using the adhesive solution. The advantage of Method 1 is that the coloring speed is fast, and the coloring depth does not change after a certain time (15 s), which is convenient for dentists to operate.

Method 2 involves preparing a second coloring liquid, preparing an adhesive solution, mixing the second coloring liquid and the adhesive solution, painting the mixed solution on or over the surface of the zirconia base, or soaking the zirconia base in the mixed solution, then crystallizing at a high temperature, and finally painting a layer of silane coupling agent on or over the surface of the zirconia base for protection. The advantage of Method 2 is that the coloring process is simple, and a protective film will be formed on or over the surface of the zirconia base after coloring, thus prolonging the service life of the base.

Method 1 and Method 2 are described in detail below.

Method 1:

1. The first coloring liquid comprises a first coloring agent, a first dispersant and a first solvent which are, in mass percentages, 0.01-26%, 0.2-35% and 60-97% of the first coloring liquid respectively.

The first coloring agent is at least one of erbium chloride, ferric chloride and manganese nitrate. Preferably, the coloring agent includes each of erbium chloride, ferric chloride and manganese nitrate in mass percentages of 0.5-13% of erbium chloride, 0.5-6% of ferric chloride, and 0.01-6% of manganese nitrate by weight of the coloring liquid. The first dispersant is polyethylene glycol; and the first solvent is deionized water.

The method for preparing the first coloring liquid comprises the following steps: weighing raw materials according to the above-mentioned mass percentages, adding erbium chloride, ferric chloride, manganese nitrate and polyethylene glycol into the deionized water, stirring them uniformly, and sub-packaging the mixture for later use.

2. The method for coloring the zirconia base specifically comprises the following steps.

(1) Surface roughening treatment is carried out on the zirconia base. Specifically, surface sandblasting treatment and hot acid treatment are carried out on the zirconia denture to control the surface roughness of the zirconia denture.

The sandblasting treatment involves sandblasting the zirconia denture with 30-60 μm zirconia powder under a pressure of 0.2-0.3 MPa for 5-10 s. The hot acid treatment involves mixing hydrochloric acid and nitric acid thoroughly, heating them to 70-80° C. to obtain a mixed acid solution, and soaking the zirconia denture with sandblasted surface in 15-30 ml of the mixed acid solution (e.g., at 70-80° C.) for 10-15 min. The concentration of hydrochloric acid is 1-2 mol/L, the concentration of nitric acid is 1-2 mol/L, and the volume ratio of hydrochloric acid to nitric acid is 1:2-3.

(2) The roughened zirconia base is washed 3-5 times with deionized water, and then the zirconia base is soaked with the first coloring liquid for more than 15 s. After 15 s, the color of the colored zirconia base will not deepen with prolonged soaking times (i.e., soaking times longer than 15 seconds). (3) The colored zirconia base is put into a denture sintering furnace, where the base is heated to 1530° C. at a rate of 5° C./min, kept at this temperature for crystallization for 120 min, and then allowed to cool down along with the furnace. (4) Preferably, after step (2) is finished, the zirconia base is soaked in a silane coupling agent for 1-2 min, and then soaked in a resin binder for 3-10 min. After soaking, the zirconia base is put in an oven at 90-150° C. for drying for 30 min, and then put in a denture sintering furnace where the base is heated to 1530° C. at a rate of 5° C./min, kept at this temperature for crystallization for 120 min, and then allowed to cool down along with the furnace.

Method 1 will be further explained with specific examples below.

According to the above method, zirconia dentures were subjected to surface roughening treatment. A total of 18 groups were set, with their specific parameters as shown in Table 7 below. Specifically, the zirconia dentures after surface sandblasting were soaked in 20 mL of the mixed acid solution at a temperature of 80° C. Those receiving no treatment were used as the control.

The treated zirconia dentures in the individual groups were soaked in water for 2-5 min, and then air-dried for later use.

Coloring liquids were prepared, with the formula of raw materials including erbium chloride, ferric chloride, manganese nitrate, polyethylene glycol and deionized water in ratios as shown in Table 8 below. The results showed that there was no obvious change in the color of the three coloring liquids prepared in each group. The color of groups a-c gradually deepened from orange, the color of groups d-f gradually deepened from yellow, the color of groups g-i gradually deepened from gray red, and the color of groups j-l gradually deepened from yellow red.

The coloring liquid with an orange color and a polyethylene glycol content of 6% in group a in Table 8 was selected to color the treated zirconia dentures in Table 1, with the coloring time and color change of zirconia dentures shown in Table 9 below. In particular, coloring time refers to the time when the color of zirconia denture no longer changes. The results showed that after the zirconia denture was treated according to the parameters in group 7, the time for the zirconia denture to reach the specified color and balance became shorter.

After the zirconia denture was treated according to the parameters in group 7, the effect of polyethylene glycol content on coloring time was investigated, as shown in Table 10 below. The results showed that when the content of polyethylene glycol was 10%, the color of the denture remained unchanged with the extension of soaking time after 15 s.

The dentures colored in group 3 in Example 6 were soaked in the silane coupling agent for 1-2 min, and then soaked in the resin binder for 3-10 min, so that the resin binder infiltrated into micro-pores on the surface of zirconia dentures to seal the coloring liquid soaked into the pores and form a transparent film on or over the surface of zirconia dentures, which effectively avoided the fading of dentures and the penetration of bacteria, acids, enzymes and products thereof in human oral cavities into the pores on the surface of zirconia dentures. After soaking, the zirconia dentures were dried in an oven at 90-150° C. for 30 min, then put into a denture sintering furnace, heated to 1530° C. at a rate of 5° C./min, kept at this temperature to crystallize for 120 min, and then cooled down along with the furnace.

Specifically, the resin binder contains 10-methacryloxydecyl phosphate (MDP) monomer, and the resin binder and silane coupling agent are common dental reagents.

Method 2:

1. The second coloring liquid comprises a second coloring agent, a second dispersant, a complexing agent and a second solvent in mass percentages of 0.01-48%, 0.1-5%, 0.05-2%, and 45-99% of the coloring liquid, respectively.

Specifically, the second coloring agent is one or a mixture of two or more of erbium chloride, ferric chloride, neodymium nitrate, manganese nitrate, ammonium metavanadate, cerium nitrate, praseodymium nitrate, cobalt nitrate and nickel nitrate. The second dispersant is polyethylene glycol, polyacrylic acid or polyurethane. The complexing agent is citric acid, glucose, ethylenediaminetetraacetic acid, sodium citrate or 2,3-dimercaptosuccinic acid. The second solvent is deionized water. Different coloring agents can be mixed to obtain coloring liquids with different colors which can be any one of blue, gray, tetracycline yellow, tetracycline gray, tetracycline brown, brown, pink, red, purple, green or black.

The coloring liquid is prepared by adding all the components into the solvent and mixing them well.

2. The adhesive solution consists of 40-100 parts of a matrix, 2-6 parts of a diluent, 3-5 parts of an adhesive monomer, 6-15 parts of a polymerization inhibitor, 30-55 parts of carbon nanotubes, 20-60 parts of a filler, 1-8 parts of tartaric acid and 30-70 parts of water.

The matrix consists of bisphenol A-glycidyl methacrylate (Bis-GMA), an epoxy resin and 10-methacryloxydecyl phosphate (MDP); or bisphenol-s-bis(3-methacryloyloxy-2-hydroxypropyl)ether, epoxy resin and 10-methacryloyloxydecyl phosphate. Preferably, the matrix is a mixture of bisphenol A-glycidyl methacrylate, the epoxy resin and 10-methacryloxydecyl phosphate in a mass ratio of 1:1:1-3.

The diluent is a methacrylate, the adhesive monomer is 4-methacryloyloxyethyl trimellitic anhydride (4-META), and the polymerization inhibitor is one or a mixture of two or more of tert-butyl hydroquinone (TBHQ), hydroquinone (HQ) and p-tert-butyl catechol (TBC). Preferably, the polymerization inhibitor is a mixture of tert-butyl hydroquinone, hydroquinone and p-tert-butyl catechol in a mass ratio of 1:1:1.

The filler is obtained by pretreating various metal oxides. The metal oxides are a mixture of two or more of silicon dioxide, aluminum oxide, calcium fluoride and titanium dioxide, and preferably, a mixture of silicon dioxide, aluminum oxide and calcium fluoride in a mass ratio of 1:1:1. The specific pretreatment process comprises melting the metal oxides, uniformly mixing them, and then subjecting them to quenching and grinding. In one example, the metal oxides may be melted in sequence, according to their melting points, from high to low. The particle size of the filler after grinding is smaller than the diameter of the carbon nanotube.

The adhesive solution is prepared as follows:

(1) Bisphenol A-glycidyl methacrylate, epoxy resin and 10-methacryloyloxydecyl phosphate in the specified ratio are added into water, mixed uniformly, then the methacrylate and 4-methacryloyloxy ethyl trimellitic anhydride are added, and the mixture is stirred uniformly for later use. (2) Silicon dioxide, aluminum oxide and calcium fluoride are melted in sequence according to their respective melting points, from high to low. Specifically, aluminum oxide is melted firstly, then silicon dioxide and finally calcium fluoride. The melted compounds are kept at the melting point of calcium fluoride for 15-30 min to achieve phase balance. Thereafter, the melted compounds are put into water for quenching, so that the melted compounds are solidified into a solid mixture, and when the temperature of the solid mixture is 200-300° C., the solid mixture is put into an oil and cooled to room temperature. The solid mixture is taken out and dried, and then crushed until the particle size is smaller than the diameter of the carbon nanotubes. In some cases, the particle size of the filler changes with the diameter of the carbon nanotubes used, and the particle size of the filler is always kept smaller than the diameter of the carbon nanotubes, preferably smaller than ¼-½ of the diameter of the carbon nanotubes, thereby obtaining a filler powder. (3) The filler powder obtained in step (2) is added into the mixed liquid obtained in step (1), and then ultrasonic dispersion is carried out, wherein the vibration frequency is 12-16 kHz, and the dispersion time is 10-20 min. Then, a mixture of tert-butyl hydroquinone, hydroquinone and p-tert-butyl catechol is added thereto, and stirred uniformly to obtain a mixed solution. Finally, carbon nanotubes with a diameter of 10-20 nm and a length of 0.5-2 μm are added into the mixed solution, and ultrasonic dispersion is continued for 15-30 min with a vibration frequency of 19-25 kHz. (4) Tartaric acid (TA) is added to the solution obtained in step (3), so as to adjust the solidification time of the whole reaction system and improve its operability, and an adhesive solution is obtained after stirring uniformly. Meanwhile, according to the situation, an appropriate amount of water can be added to the adhesive solution to adjust the consistency and/or viscosity of the adhesive solution.

3. The coloring treatment method of the zirconia base is specifically as follows.

(1) The zirconia base is roughened according to the surface roughening treatment method in Method 1, and then washed. If necessary, a neutralization reaction is carried out before washing. (2) The second coloring liquid is added into the adhesive solution. The amount of the adhesive solution is conventionally selected according to the actual condition of the zirconia denture to be colored, and the color depth of the coloring liquid is adjusted by controlling the concentration of metal ions in the coloring liquid, so as to control the color finally displayed after the coloring liquid is mixed with the adhesive solution. Finally, the zirconia denture is colored to be consistent with the color of the patient's teeth. Specifically, the volume ratio of adhesive solution to the second coloring liquid is 1-3:1. According to this ratio, the color of the mixed solution is adjusted to make the color of the mixed solution consistent with the color of the patient's teeth, so that the color of the colored zirconia denture is consistent with the color of the patient's teeth.

Specifically, the coloring process is carried out as follows. According to the color of the patient's teeth, a small amount of the coloring liquid with the adhesive solution is taken by dipping with a 2 mm coloring pen to paint the surface of the denture surface, with the painting amount controlled according to the color depth of the patient's teeth. After painting, the denture is put into an oven at 90-150° C. for drying for 30 min, then taken out and put into a denture sintering furnace to heat up to 1530° C. at a rate of 5° C./min, kept at this temperature for crystallization for 120 min, and then cooled down along with the furnace. Alternatively, the zirconia denture can be put into the coloring liquid with the adhesive solution, and after the color of the zirconia denture is observed to be consistent with that of the patient's teeth, the zirconia denture can be taken out, and then the subsequent sintering operation can be carried out.

Further preferably, in order to make the bonding between the coloring liquid containing the adhesive solution and the zirconia denture firmer, a layer of silane coupling agent can be painted on or over the surface of zirconia denture, so as to improve the bonding strength between the coloring liquid containing the adhesive solution and the zirconia denture.

Method 2 will be further explained with specific examples below.

1. Blue second coloring liquids were prepared using raw materials including neodymium nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 11 below.

2. Second coloring liquids with gray color were prepared using raw materials including manganese nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 12 below.

3. Coloring liquids with tetracycline yellow color were prepared using raw materials including erbium chloride, manganese nitrate, ammonium metavanadate, cerium nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 13 below.

4. Coloring liquids with tetracycline gray color were prepared using raw materials including erbium chloride, ferric chloride, manganese nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 14 below.

5. Coloring liquids with tetracycline brown color were prepared using raw materials including erbium chloride, ferric chloride, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 15 below.

6. Brown coloring liquids were prepared using raw materials including erbium chloride, ferric chloride, praseodymium nitrate, cobalt nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 16 below.

7. Coloring liquids with pink color were prepared using raw materials including erbium chloride, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 17 below.

8. Coloring liquids with red color were prepared using raw materials including erbium chloride, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 18 below.

9. Coloring liquids with purple color were prepared using raw materials including neodymium nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 19 below.

10. Coloring liquids with green color were prepared using raw materials including nickel nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 20 below.

11. Coloring liquids with black color were prepared using raw materials including erbium chloride, ferric chloride neodymium nitrate, polyethylene glycol, citric acid and deionized water. The specific raw material composition and displayed color of the coloring liquids are shown in Table 21 below.

It can be seen from the coloring liquids prepared in the above tables that with the increase of metal ion concentration, the color of the coloring liquid deepened correspondingly.

The adhesive solution was prepared according to the above method, with the specific composition shown in Table 22 below.

According to the above method, the zirconia ceramic was subjected to surface roughening treatment, totally 18 groups were set, with the specific parameters of each group as shown in Table 23 below, wherein the zirconia denture after surface sandblasting was soaked in 20 mL of the mixed acid solution, and the heating temperature of the mixed acid was 80° C.

The treated zirconia dentures in the above groups were soaked in water for 2-5 min, and then air dried for later use.

A coloring liquid with any one of the colors from Table 11 to Table 21 was selected, mixed with the six groups of adhesive solutions in Table 22, and the color of the mixed solution was adjusted to be consistent with the color of the patient's teeth. Specifically, the color of the coloring liquid can be adjusted by increasing or decreasing the concentration of metal ions, so as to adjust the color of the mixed solution until it is consistent with the color of the patient's teeth. The volume ratio of the adhesive solution to the second coloring liquid was 1:1.

The treated zirconia dentures in Table 23 were colored with the six groups of mixed coloring liquids containing the adhesive solution, that is, the treated zirconia dentures in each group in Table 23 were colored with the six groups of coloring liquids respectively. The coloring results are shown in detail in Table 24 below, wherein the bonding strength refers to the bonding strength between the coloring liquid containing the adhesive solution and the treated zirconia denture. The results showed that the treated zirconia denture in group 7 had the best bonding effect with the zirconia denture after being mixed with the adhesive solution and coloring liquid prepared in group d.

In another embodiment of Method 2, the second coloring liquid is not mixed with the adhesive solution. First, the zirconia base after surface roughening treatment is colored with the second coloring liquid. When the color of the zirconia base is observed to be consistent with that of the patient's teeth, coloring is stopped, the zirconia base is oven-dried and then soaked in the adhesive solution for 1-20 min, so that the adhesive solution seals the coloring liquid in the pores of the zirconia and fills the pores on the surface of the zirconia to form a protective film on or over the surface of the zirconia ceramic, which prevents bacteria, enzymes and other substances in the oral cavity from entering the pores and causing infection and other hazards. Finally, the zirconia base is taken out, put into a denture sintering furnace, heated up to 1530° C. at a rate of 5° C./min, kept at this temperature for crystallization for 120 min, and then cooled down along with the furnace.