JPH0335253B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a calcium phosphate sintered body made of hydroxyapatite, tertiary calcium phosphate, or a mixture thereof. Calcium phosphate sintered bodies have high biocompatibility, so they are used as bioimplant materials for artificial tooth roots, artificial bones, and the like. (Prior art) As a method for producing a dense calcium phosphate sintered body, an overcake is removed from the synthesized apatite precipitate by a normal dehydration method (vacuum, pressurization, etc.), and this overcake is not pulverized. A method of directly drying and sintering is known, and one example of this is described in JP-A-51-40400. (Problems to be Solved by the Invention) When producing an artificial tooth root by the method described above, in which the overcake is taken out and the overcake is dried and sintered as it is without powdering, the obtained sintered body Although it has sufficient compressive strength as an artificial tooth root, its toughness is still insufficient. Therefore, an object of the present invention is to obtain a calcium phosphate sintered body with high toughness by improving the method of removing the above-mentioned overcake, drying and sintering the overcake as it is without pulverizing it. (Means for Solving the Problems) As a result of intensive studies to solve the problems, the present inventors have arrived at the present invention described below.
The present invention produces calcium phosphate by pressing a lumpy dried body obtained by drying a precipitate of calcium phosphate using a rubber press method, and calcining the dried calcium phosphate thus obtained at a temperature of 900°C or higher and lower than 1000°C. This is a method for producing a calcium phosphate sintered body, which is characterized in that it is made into a sintered body. In the gelatinous calcium phosphate precipitate used in the present invention, calcium ions and phosphate ions are adjusted so that the molar ratio of calcium to phosphorus is 1.4 or more and 1.7 or less, and the calcium ions and phosphate ions are adjusted to have a pH of 8 or less. It can be obtained by reacting in the above aqueous medium. Next, the obtained gelatinous calcium phosphate precipitate is washed by decantation or centrifugal dehydration, and then separated from the solution by vacuum filtration, centrifugation, etc., and dried and then rubber pressed. A dried calcium phosphate body to be used in the apparatus is obtained. Preferably, the dried calcium phosphate is a slurry that is prepared by washing the gelatinous calcium phosphate precipitate, adding water to form a slurry, and drying and sintering the slurry to obtain a molded product having a desired shape. This is desirable because the product obtained by placing it in a settling tube, centrifuging to remove water, and drying can be obtained in a desired shape without substantially post-processing. When drying a gelatinous precipitate in a centrifuge tube, the gelatinous precipitate is dispersed in an aqueous medium to form a slurry with a solid content concentration of 5 to 25% by weight, and this slurry is poured into a centrifuge tube and heated at 1100 G or more. It is possible to separate the supernatant liquid layer and the precipitate layer by centrifugation, and remove the supernatant liquid layer to obtain a precipitate layer with a water content of 73% by weight or less.The result is that during the subsequent drying process, the precipitate layer shrinks and deforms less and is free from cracks. This is desirable in that it is possible to obtain a molded article of a desired shape that conforms to the mold without any blemishes. In this case, in order to prevent cracking during drying, it is preferable to use a centrifuge tube whose inner wall surface is made of hydrophobic polymer or metal and has a smooth surface. Examples of such materials include hydrophobic polymers with a water absorption rate of 10% or less, such as polyolefin, polystyrene, Teflon, polycarbonate, polymethyl acrylate, and polymethyl methacrylate;
Metals such as stainless steel, titanium alloys, aluminum alloys, and aluminum alloys are used, but the former include polyethylene, polypropylene, Teflon, etc.
As the latter, stainless steel, titanium alloy, etc. are preferable. When drying the calcium phosphate precipitate, rapid heating is not preferred because it increases shrinkage of the precipitate and makes it more likely to crack.
Usually the temperature is between room temperature and 130°C. The dried calcium phosphate precursor obtained by drying to a moisture content of 5% or less in a centrifuge tube by the above method is pressed by a rubber press method, and the pressing pressure is usually 300 Kg/cm ² to 5000 Kg/cm ^{2 Preferably 500 Kg/cm 2}
Kg/ ^cm2 to 3000Kg/ ^cm2 . Press pressure is 300Kg/
cm ² or less, a dense sintered body cannot be obtained when a dried calcium phosphate body is fired. Furthermore, if the press pressure is 5000 kg/cm ² or more, cracks will occur in the calcium phosphate during firing. The rubber-pressed calcium phosphate molded product is heated to a temperature of 900°C or higher and lower than 1000°C (preferably 980°C).
(below). At temperatures below 900°C, a dense calcium phosphate sintered body cannot be obtained and both compressive strength and toughness are low. Moreover, at temperatures above 1000°C, although the compressive strength is high, sufficient toughness cannot be obtained for the artificial tooth root. In the present invention, when the slurry is dried in a centrifuge tube whose shape is adjusted as described above, the desired shape of the calcium phosphate sintered body can be obtained without further processing, but in some cases, sintering The formed body may be further partially cut into the desired shape, or the dried body may be cut into the desired shape after sintering without being shaped into the desired shape. In addition, in the present invention, other inorganic oxides such as silica, alumina, etc. are added to the calcium phosphate slurry.
It is also possible to manufacture by adding titania, zirconia, etc. in small amounts of 10% by weight or less. As for the form of such other inorganic oxides, sol-like inorganic oxides are preferred. For example, silica sol, alumina sol, etc. are suitable. In addition, in the present invention, collagen is added to the calcium phosphate slurry in order to prevent cracking during drying of the calcium phosphate precipitate.
Organic substances such as powdered cellulose and polyvinyl alcohol can also be added. The amount of organic matter added is 5
It is preferably less than % by weight. (Effects) As described above, the sintered body of calcium phosphate obtained by the present invention is dense and has high compressive strength and
It has great toughness. Therefore, this material is useful as a biological implant material, especially as a material for artificial tooth roots. (Example) Example 1 Commercially available calcium nitrate [Ca(NO ₃ ) ₂・4H ₂ O] 250
g was dissolved in 0.7 g of distilled water, 0.08 g of 28% ammonia water was gradually added to this solution, and this solution was further diluted with 0.3 g of distilled water. On the other hand, 84 g of commercially available ammonium hydrogen phosphate [(NH ₄ ) ₂ HPO ₄ ] was dissolved in distilled water from Step 1, and 0.48 g of 28% ammonia water was added to this solution.
and 1 part of distilled water were quickly added. The latter aqueous ammonium hydrogen phosphate solution was added dropwise to the former aqueous calcium nitrate solution while stirring. After the dropwise addition was completed, the mixture was heated while stirring, kept under reflux for 20 minutes, and after cooling, was left standing for another day and night.
Subsequently, the solution was filtered through a glass filter under reduced pressure, and the filter cake was further washed with distilled water, and then dried together with the glass filter in a dryer at 80° C. overnight. The dried filter cake of calcium phosphate obtained in this way was turned into a lathe and a dental turbine engine (diamond disk, double-edged, thickness 0.15
mm) to obtain 20 cylindrical molded dried bodies with a diameter of 4.0 mm and a length of 10.0 mm. Each of the dried calcium phosphate molded bodies was placed in a polyethylene film bag, vacuum packed, and pressed using a rubber press at a pressure of 1200 kg/cm ² . Calcium phosphate molded body 20 after pressing obtained in this way
Heat the pieces in an electric furnace from room temperature to 950℃ for 3 hours.
It was baked at 950°C for 5 hours. The calcined calcium phosphate sintered body (diameter 3.2 mm, length 81 mm) was measured by X-ray diffraction, and the diffraction lines matched those of hydroxyapatite. Furthermore, the relative density, compressive strength, and fracture toughness of these calcium phosphate sintered bodies were measured, and the following average values were obtained. Relative density 97.1% Compressive strength 7200Kg/cm ² Fracture toughness 1.01MPa・m ^1/2 In these measurements, the relative density was measured using the Archimedes method, the compressive strength was measured using Instron, and the fracture toughness value was measured using the Bitkers hardness. Each was calculated using a meter using the following formula. K _IC = 0.203 H _V・a ^1/2・(b/a) ^-3/2 (Nihara et al.'s formula) H _V : Bitkers hardness [MPa] 2a: Indentation diagonal length [m] b: From the center of the indentation Average crack length [m] K _IC : Fracture toughness value [vMPa・m ^1/2 ] E: Young's modulus of calcium phosphate sintered body [Kgf/
mm ² ] (measured by ultrasonic echo method) Furthermore, before measurement, each sample of the calcium phosphate sintered body was polished with #1500 abrasive paper and 0.3μ Al ₂ O ₃ powder. Comparative Example 1 The cylindrical shaped dried product obtained by processing the dried filter cake of calcium phosphate in Example 1 was heated from room temperature to 900°C in an electric furnace without rubber pressing.
The temperature was raised in 2 hours to 900℃, held at 900℃ for 30 minutes, and then
Temperature rises from 900℃ to 1150℃ in 1 hour, then 1150℃
Calcination was carried out by holding at ℃ for 3 hours. The obtained calcium phosphate sintered body was similar to Example 1,
It was hydroxyapatite, and the dimensions were the same as in Example 1, with a diameter of 3.2 mm and a length of 81 mm. The relative density, compressive strength, and fracture toughness of the calcium phosphate sintered body thus obtained were measured in the same manner as in Example 1, and the following average values were obtained. Relative density 98.1% Compressive strength 6900Kg/cm ² Fracture toughness 0.62MPa・m ^1/2 Example 2 and Comparative Example 2 Commercially available calcium nitrate [Ca(NO ₃ ) ₂・4H ₂ O] 300
Dissolve 1.5 g of distilled water and add 28 g to this dissolution.
0.64% aqueous ammonia was added with sufficient stirring. On the other hand, 100 g of commercially available ammonium hydrogen phosphate [(NH ₄ ) ₂ HPO ₄ ] was dissolved in distilled water from step 1, and 0.60 g of 28% aqueous ammonia was added to this solution. The latter ammonium hydrogen phosphate was added dropwise to the former calcium nitrate aqueous solution while stirring. After the dropwise addition was completed, the mixture was heated while stirring, kept under reflux for 10 minutes, and after cooling, was allowed to stand for an additional 3 days. Next, the solution was dehydrated using a centrifugal dehydrator equipped with a polypropylene filter cloth (1000 mesh), and further washed with distilled water until the alkalinity disappeared.The filtered calcium phosphate precipitate was collected, and distilled water was added to it. It was made into a 19% slurry. Next, add a polypropylene centrifuge tube (outer diameter x length:
16.5 x 105mm, shape: cylindrical round bottom, capacity: 10ml) 110
Pour 8 ml into each tube and spin these centrifuge tubes at 5000 rpm using a swing centrifuge.
(5300G) and a rotation time of 15 minutes. After centrifugation, the supernatant liquid in the centrifuge tubes was discarded, and the 110 centrifuge tubes containing the calcium phosphate precipitate layer (water content 65% by weight) were dried at 80° C. for 3 days in an electric dryer. After drying, the calcium phosphate layer was peeled off from the wall surface of the centrifuge tube without cracking in all the centrifuge tubes, and in this way, 110 cylindrical dried calcium phosphate molded bodies were obtained. These were processed into cylindrical shapes with a diameter of 5.0 mm and a length of 10 mm as Example 1, and 110 of the obtained cylindrical molded dried bodies were pressed in the same manner as in Example 2 to yield 2000 kg/cm ² using a rubber press.
Pressed with a press at a pressure of Twenty cylindrical dried calcium phosphate molded bodies after pressing were placed in an electric furnace and fired at various temperatures for 3 hours each. The average values of relative density, compressive strength, and fracture toughness of the calcium phosphate sintered bodies (hydroxyapatite as in Example 1) obtained at each temperature were as shown in Table 1.

[Table] Comparative Example 3 The molded dried body processed into a cylindrical shape in Example 1 was placed in an electric furnace without rubber pressing, and fired at various temperatures for 3 hours each. The average values of relative density, compressive strength, and fracture toughness of the calcium phosphate sintered bodies obtained at each temperature were as shown in Table 2.

[Table] Example 3 and Comparative Example 4 A sintered body of calcium phosphate was produced in the same manner as in Example 1 except that the pressure of the rubber press was changed. As a result of measuring their relative density, compressive strength, and fracture toughness in the same manner as in Example 1, the average values shown in Table 3 were obtained.

[Table] Almost all cracks were caused.
Example 4 74 g of commercially available calcium hydroxide was dispersed in 2 parts of distilled water. This was stirred vigorously, and 1.96% of a 3.0% by weight phosphoric acid aqueous solution was added dropwise into this solution. After the addition is complete, add the above mixture while continuing to stir.
The temperature was raised to 60°C, after which stirring was stopped and the temperature was maintained at 60°C for 1 hour. After cooling, the above liquid was further left to stand for 3 days. A calcium phosphate sintered body was produced from the calcium phosphate precipitate thus obtained in the same manner as in Example 2. The relative density, compressive strength, and fracture toughness were measured in the same manner as in Example 1, and the following average values were obtained. Relative density 97.5% Compressive strength 6900Kg/ ^cm2 Fracture toughness 1.15MPa・m ^1/2The obtained calcium phosphate sintered body is
As a result of measurement by line diffraction, as in Example 1, the diffraction line coincided with that of hydroxyapatite. Example 5 88 g of commercially available calcium hydroxide was dissolved in 2 parts of distilled water. This was vigorously stirred at room temperature, and 2.0% of a 3.9% aqueous phosphoric acid solution was added dropwise into this solution. of solution
The pH was maintained at 8-9 with 5% aqueous ammonia. After the addition was completed, stirring was continued for an additional 3 hours. A calcium phosphate sintered body was produced in the same manner as in Example 1, except that the precipitate thus obtained was fired at 970°C. The relative density, compressive strength, and fracture toughness were measured in the same manner as in Example 1, and the following average values were obtained. Relative density: 97.2% Compressive strength: 7200 Kg/cm ² Fracture toughness: 1.25 MPa·m ^1/2 The obtained calcium phosphate sintered body was measured by X-ray diffraction, and the diffraction lines matched those of β-calcium phosphate.

Claims (1)

[Claims] 1. Calcium ions and phosphate ions at pH 8
The molar ratio of calcium to phosphorus in an aqueous medium of
The gelatinous precipitate of calcium phosphate obtained is dried as a lump, and the dried lump is then pressed by a rubber press method, and then heated at a temperature of 900°C or more and less than 1000°C. A method for producing a calcium phosphate sintered body characterized by sintering at a high temperature. 2 The press pressure by the rubber press method is 300
The manufacturing method according to claim 1, wherein the production method is at least Kg/cm ² and at most 5000 Kg/cm ² . 3. The manufacturing method according to claim 1, wherein the sintering temperature is 980°C or lower.