JPH0429617B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a calcium phosphate cast body used as a ceramic material for living bodies such as dental materials and artificial bone materials. In recent years, the range of applications for ceramics has expanded rapidly, reaching the medical field.
Attempts are also being made to apply ceramics to medical materials for which plastics have been primarily used, such as artificial bones and artificial tooth roots. The reasons behind this are as follows. In other words, metals, plastics, etc. all lack compatibility with living organisms, which is one of the most important properties for medical materials, and depending on the conditions of use, metal ions or plastic monomers may elute into living organisms and cause harmful effects. This is not a desirable material. On the other hand, these problems can be completely eliminated by making them into ceramics. However, at the current stage, the application of ceramics in the medical field cannot be said to be sufficient.
The main reason for this is that ceramics have poor moldability and cannot be flexibly adapted to medical materials that often require a variety of shapes. In other words, unlike metals, plastics, etc., which can be easily formed into any shape by methods such as casting or injection molding, ceramics are usually formed by mechanically forming powder and then sintering it, or by forming it into a single crystal block. It is necessary to use a complicated method of growing the material and then machining it to form the desired material, which makes it extremely difficult to precisely mold it into an arbitrary shape. For this reason, it is virtually impossible to handle applications that require precise reproduction of complex and diverse shapes, such as artificial joints, artificial tooth crowns, inlays, and bridges, or even if it is possible, it is extremely complicated. Moreover, as a result of requiring an inefficient work process, it is inevitable that the cost will be extremely high. For these reasons, ceramics have not necessarily become popular as medical materials, even though they have fundamentally excellent properties. The inventors of the present invention have conducted extensive research into methods for manufacturing high-strength ceramics by freely and precisely molding ceramics into arbitrary shapes, and have found that by selecting calcium phosphate glass as the material,
We have discovered that this is possible and have arrived at the present invention. Ceramic materials generally have a three-dimensional structure and therefore have an extremely high melting point, and even in the molten state, the viscosity of the melt is higher than that of metals used in dental materials, so the lost wax method used in dental technology is used. Not applicable to casting. The use of vitreous ceramics has been considered in order to lower the melting point and viscosity of the melt, but the high shrinkage rate during cooling results in poor shape reproducibility and the resulting cast body lacks mechanical strength. On the other hand, calcium phosphate glass has a relatively low melting temperature because it has a one-dimensional short chain structure, and even if it slightly exceeds the melting temperature, the viscosity of the melt decreases significantly, so it cannot be formed by casting. It was found that it is suitable for That is, the calcium phosphate glass of the present invention can be heated to a temperature of 900 to 1600°C to obtain a low-viscosity melt, and like metal materials, it can be cast into any shape by the lost wax method or the like by applying an external force. be. A suitable mold is a so-called lost wax mold, which is obtained by making a wax prototype in advance, burying it in a refractory investment material, and then heating it to incinerate the wax. It is also possible to create The solidification shrinkage of calcium phosphate glass is small, about 1%, and can be completely compensated for by using an inflatable fireproof investment material in the mold, or by oversizing the mold by the amount of shrinkage in advance if the mold is used as a mold. I can do it. Therefore, the obtained cast body can perfectly reproduce the original model with extremely high dimensional accuracy and shape reproducibility. The preheating temperature of the mold is highly correlated with castability, dimensional accuracy, and surface condition of the casting surface. For example, if the preheating temperature is increased, the flow of the melt into the finer parts of the mold will be improved, but on the other hand, the casting surface will be more likely to become rough. On the other hand, since the preheating temperature is directly correlated with the expansion of the mold, it is important to select an appropriate preheating temperature depending on the type of mold material in order to improve dimensional accuracy. In the present invention, it is necessary to set this preheating temperature to 900°C or less. The obtained glass casting can be used as it is for its original purpose, but depending on the application, it can also be used as a crystallized glass casting as shown below. In other words, one of the major characteristics of calcium phosphate glass is that it transforms into crystallized glass by reheating, and the transition allows it to be made into a crystallized glass casting with superior fracture toughness. . The thus obtained crystallized glass casting has a mechanical strength 1.5 to 2 times that of a glass casting, and is suitable for applications requiring resistance to breakage or abrasion, for example. Artificial bones, artificial tooth roots, artificial tooth crowns,
It can be said to be a suitable material for inlays, bridges, etc. The method for producing a calcium phosphate cast body of the present invention will be described in detail below. The starting material of the present invention is calcium oxide, calcium hydroxide, calcium carbonate, etc.
calcium-containing compounds and phosphoric acid, producing CaO;
It is a phosphorus-containing compound, such as polyphosphoric acid, which also produces phosphorus oxide upon firing. Further, calcium salts of phosphoric acids such as calcium phosphate and apatite can be used alone or in combination with other calcium-containing compounds or phosphorus-containing compounds. Selecting one or more starting materials for calcium-containing compounds and phosphorus-containing compounds,
In the case of a solid, it is pulverized and weighed so that the calcium-containing compound and the phosphorus-containing compound have an atomic ratio of calcium to phosphorus, Ca/P, of 0.35 to 1.7. When this atomic ratio exceeds 1.7, the melting temperature becomes high and vitrification does not occur. On the other hand, if the atomic ratio is less than 0.35, the melting temperature decreases and vitrification becomes easier, but on the other hand, the crystallization process becomes difficult, and excessive phosphoric acid is liberated, resulting in chemical instability, which is undesirable. This raw material mixture is mixed well, placed in a suitable container, and heated and melted at 900-1600°C. The melting temperature varies depending on the atomic ratio of calcium and phosphorus, Ca/P.
Within the above temperature range, the viscosity of the melt can be kept sufficiently low, and excellent castings can be obtained relatively easily. Higher melting temperature, especially 1700℃
If the temperature exceeds this level, the phosphorus component will begin to evaporate, and the composition will tend to be too calcium-rich, causing the melting point to gradually rise, so care must be taken. This melt is cooled to form a glass. The cooling method is not particularly limited. Alternatively, a large amount of raw material may be melted and cooled while being divided into portions required for the following casting. Next, the glassy material is cast and molded using the lost wax method, and the melting temperature at this time is also 900 to 1600℃.
It is. In the lost wax method, the mold may be made of refractory material or metal. Casting is preferably a casting method that applies external force, such as centrifugal casting, compression casting, or vacuum compression casting. Preheating for casting is below 900℃,
The temperature is preferably selected in the range of 300 to 900°C depending on the casting material and glass composition. In addition, the above-mentioned operation of melting and cooling the raw materials once and vitrifying them is omitted,
The raw material mixture may be heated and melted directly in a lost wax-based casting apparatus. The castings cast according to the present invention based on the lost wax method are vitreous. Even in its glassy state, it has relatively high mechanical strength and wear resistance, and can be put to practical use as dental materials, artificial bone materials, etc. However, by applying appropriate heat treatment to this glassy material to make it crystallized glass, the properties can be further improved. The method for crystallizing the calcium phosphate-based crystallized glass according to the present invention is as follows. The material cast by the lost wax method is removed from the mold,
It is heated in a suitable heating device such as an electric furnace. Heating rate: 50-600℃/hr, heating temperature: 550-900℃,
Retention time is 0.5-100hr. This crystallization operation produces a large number of fine calcium phosphate crystals of 1 to 5 microns in the material. The higher the degree of crystallinity, the better from the viewpoint of strength and wear resistance, and the degree of crystallinity should be at least 10% or more, preferably 50% or more. The method for producing a calcium phosphate-based cast body according to the present invention basically consists of phosphoric acid and calcium, which are the same main components that make up natural teeth and bones.
Needless to say, it has essentially excellent compatibility with living organisms, and has no harmful effects on living organisms, which is a concern with metals and plastics. A feature of the present invention is that calcium phosphate glass is melted and then cast using an external force in a mold to produce calcium materials for living bodies such as dental materials and artificial bone materials, which will be described below with reference to examples. Example 1 The atomic ratio of calcium to phosphorus Ca/P is 0.5
Orthophosphoric acid was added to calcium carbonate powder weighed so that After completely melting, the temperature was raised to 1300°C and held for 1 hour to clarify, and the mixture was poured onto a graphite plate and rapidly cooled to vitrify. Next, the glass was remelted at 1050° C. and cast using a centrifugal casting method into a mold in the shape of an artificial tooth crown, which was made based on the lost wax method using a cristobalite-based refractory investment material. The preheating temperature of the mold was 400°C. The obtained calcium phosphate artificial tooth crown was glassy, had extremely excellent shape reproducibility, and had no casting defects such as shrinkage cavities. Example 2 The cast product of Example 1 was heat-treated at 645° C. for 12 hours in an electric furnace to obtain crystallized glass. The crystallinity was 90%, shrinkage and deformation due to crystallization were negligible, and excellent shape reproducibility was maintained. Comparative Example 1 Feldspar-based porcelain (SiO ₂ 26.1%, Al ₂ O ₃ 63.0%,
We attempted to cast 0.3% CaO, 4.0% K ₂ O + Na ₂ O, and 5.3% B ₂ O ₃ at a melting temperature of 1200°C based on the Stowax method, but the structure could not be formed because the melt did not wrap around the details. Therefore, the material was cast into a block body and the physical properties of the sample were measured. The measured values of the physical properties of Examples 1 and 2 and Comparative Example 1 were
Shown in the table. The porcelain of the comparative example cannot be cast into complex shapes such as tooth crowns, and must be processed.

【table】

[Table] The method of the present invention can be manufactured with good shape reproducibility by simply casting the molten material, and its physical properties are superior to porcelain even if it is glassy. When it is crystallized, its strength improves dramatically. did.

Claims (1)

[Claims] 1. The atomic ratio of calcium to phosphorus, Ca/P, is
Calcium compounds and phosphorus compounds are selected to have a ratio of 0.35 to 1.7, melted at a temperature of 900 to 1600℃,
A method for manufacturing a cast body, which comprises casting into a mold preheated to a temperature of 900°C or less to produce a calcium phosphate glass. 2 The atomic ratio of calcium to phosphorus, Ca/P, is
Calcium compounds and phosphorus compounds are selected to have a ratio of 0.35 to 1.7, melted at a temperature of 900 to 1600℃,
Cast into a mold preheated to a temperature of 900°C or less, and heat the cast body to a temperature of 550 to 900°C to reduce the crystallinity.
A method for producing a cast body, characterized by transforming the cast body into a 10% or more calcium phosphate crystallized glass.