JPH031972B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a novel method for manufacturing a dental implant comprising a metal core and a bioactive glass layer covering the core. (Background of the Invention) Research into dental implants has been carried out in order to form an artificial tooth root (implant) and an artificial crown on top of it when the root of a natural tooth is damaged or lost due to progression of tooth decay. It is actively practiced.
This implant must be made of a strong material since it is subjected to considerable stress when chewing food. Early research suggested biocompatible metals such as cobalt-chromium alloys, stainless steel, titanium, and tantalum; however, although metal materials have excellent mechanical strength, especially impact strength, they do not interact well with living tissue. are not connected in any way, and there is a clear boundary between them. Therefore, the metal implant itself must be formed into a screw type and fixed in the jawbone by screwing. In addition, implants using ceramics such as single-crystal alumina have recently been proposed, since metal materials may elute harmful metal ions. In this case as well, there is a clear boundary between the living tissue and the ceramic material, so the implant is fixed to the jawbone by screwing. However, implants that rely on mechanical bonding force, such as screw-in implants, have a clear interface with the jawbone, making them susceptible to bacterial infection from this interface, and the screw type also causes unevenness in the jawbone. There is a problem in that bone resorption is likely to occur due to stress. In response, Hench et al. proposed a bioactive glass that chemically bonds with the bone tissue of the living body. This bioactive glass is chemically bonded to the jawbone and does not form a clear interface with the jawbone, so it is less susceptible to bacterial infection. In addition, since it is chemically bonded, there is no need for the shape to be screw-shaped, so it can be a ``conical shape with a rounded tip like a cannonball'' that does not cause stress concentration on the jawbone. However, since it is made of glass, its mechanical strength is poor, so an implant in which a metal core is coated with bioactive glass has been proposed. (Refer to Japanese Patent Application Laid-open No. 145394/1983). The proposed implant employs a melt-dipping method to coat the bioactive glass. However, the melt dipping method has the disadvantage that it is difficult to freely control the thickness of the glass coating layer, and it is also difficult to make the thickness of the coating layer uniform when coating relatively thickly. In addition, in the melt immersion method, the glass near the surface of the glass melt in the crucible is likely to be coated, but the glass near the surface is likely to be coated with volatile components.
In many cases, Na and F evaporate and the glass composition differs from the desired glass composition.Furthermore, during the process of lifting the core from the glass melt, volatile components evaporate from the coating layer and the composition changes, resulting in a change in the desired glass composition. There is a drawback that a glass coating of the same composition cannot be obtained. Unfortunately, these Na and F have a large influence on biological activity. In addition, in the case of industrial mass production, if the metal core is immersed in the glass melt many times, the glass melt will be contaminated by trace amounts of metal ions eluted from the metal core, and as a result, the desired biological activity will be lost. It is not possible to obtain an implant with (Object of the Invention) Therefore, the object of the present invention is to provide a dental implant that does not use the melt-immersion method and has the above-mentioned drawbacks, that is, a dental implant consisting of a metal core and a bioactive glass layer covering the core. Our objective is to provide a new manufacturing method for "implants." (Summary of the Invention) Therefore, the present invention provides a method for manufacturing a dental implant comprising a metal core and a bioactive glass layer covering the core, including: (1) a mold having an opening at the top; (2) inserting the core into the molten glass in the cavity; (3) injecting the core into the molten glass; (4) slowly cool the obtained glass gob and core back to room temperature; (5) grind the glass gob to obtain a bioactive glass layer with a predetermined thickness; Provided is a method for manufacturing a dental implant characterized by: The mold used in the present invention has a cavity larger than the shape of the intended implant, and has an opening at the top for injecting glass melt. The mold may be a split mold split along a vertical plane through the center to facilitate demolding.
An example of a split mold consisting of two parts is shown in FIG. 1 (perspective view). In principle, the size of the cavity should be larger than the size of the intended implant, but considering work efficiency, economy, and the heat capacity of the glass,
It is preferable that the diameter is about 2 to 5 times larger than the size of the implant. The materials used for the mold include iron, stainless steel, and graphite carbon, which are the same materials used for glass casting. On the other hand, the metal materials constituting the metal core are:
Biocompatible cobalt-chromium alloys, nickel-chromium alloys, iron-based austenitic alloys such as stainless steel are preferably used. Although the shape of the metal core differs depending on the site where it is implanted, a conical shape with a rounded tip like a cannonball is preferable because it transmits uniform stress to the jawbone. The dimensions of the core body are, for example, an upper diameter of about 3 to 6 mm and a length of about 8 to 12 mm. As shown in FIG. 2, the center of the core body 1 is provided with, for example, a recess 1a for attaching an upper structure (crown), or a protrusion as the case may be. It is preferable that an oxide layer of, for example, 0.2 to 1.5 μm in thickness is previously formed on the surface of the metal core in order to enhance the adhesive strength with the glass coating layer. For example, the formation of such an oxidized layer occurs when the metal core is exposed to about 700 ~
This can be done by heating to 900°C for about 3 to 10 minutes. In addition, if there is only a bioactive glass layer, a reactive layer (a rather brittle layer with a different composition and properties from the original glass) formed by chemically bonding the glass layer to the jawbone will form on the core body. Over a long period of time, such as 5 years, the reaction layer may eventually reach the core or its oxidized layer. When this condition is reached, the strength of the bond between the core or oxidized layer and the reaction layer is reduced due to the large compositional gap, and there is therefore a risk that the implant will fall out of the jawbone. Therefore, it is preferable that the core is previously coated with glass that has substantially no or very low bioactivity. The thickness of the glass coating layer, which can be called an inner layer, is, for example, 100 μm, and it is sufficient if it is less than 200 μm at most. The glass used for this inner layer has a coefficient of thermal expansion that is substantially the same as that of the metal core (substantially the same here means exactly the same as the core or 0.1×10 ^-5 It has a coefficient of thermal expansion that is substantially the same as that of bioactive glass (which can be called the outer layer) (here, "substantially the same" refers to the thermal expansion of the inner layer ^and the outer layer). A glass having a higher melting temperature ^{than bioactive} glass is preferred. The specific composition of such inner layer glass will be described later. Bioactive glasses as such, also referred to as outer layers, are already known, for example with the following composition: SiO ₂ 35-60 mol % B ₂ O ₃ 0-15 Na ₂ O 10-30 CaO 5-40 TiO ₂ 0 From the composition range consisting of ~2 P ₂ O ₅ 0-15 K ₂ O 0-20 Li ₂ O 0-10 MgO 0-5 La ₂ O ₃ + Ta 2 O ₅ + Y _{2 O 3} 0-8 F ₂ 0-15 To be elected. The bioactive glass has a coefficient of thermal expansion that is substantially the same as that of the metal core (here, "substantially the same" refers to the difference in the coefficient of thermal expansion between the bioactive glass and the metal core).
0.1 × 10 ^-5 °C ^-1 ), but with a coefficient of thermal expansion substantially the same as the biocompatible metals previously exemplified from the glass composition ranges exemplified above. It is possible and expedient to choose a glass with Furthermore, the specific composition of the glass that has substantially no or very low bioactivity, also referred to as the inner layer, is a bioactive glass selected from the composition range exemplified above with the addition _of TiO ₂ . content of 4~
Preferably, the content is increased to 10 mol%. The reason for this is
By adding TiO ₂ (a) its bioactivity decreases rapidly and the activity is virtually lost or becomes very low, leading to the progression of the bioactive glass to the core of the reaction layer formed by bonding with the bone. (b) The thermal expansion coefficient does not substantially change, and (c) The melting temperature is 30 to 50℃.
This is because it does not deform when the bioactive glass is coated on the outside, and (d) has a high adhesive strength with the bioactive glass layer because it has a composition very similar to that of the bioactive glass. In addition, bioactive glass prevents damage to the metal core,
It is desirable to have a low melting temperature from the viewpoint of workability and energy consumption. In this regard, the bioactive glass compositions exemplified above are preferable because they have relatively low melting temperatures (below 1250°C), but glasses with the following compositions have even lower melting temperatures (1000°C or less).
~1100°C), which is particularly preferred. SiO ₂ 35-55 mol% B ₂ O ₃ 0-15 Na ₂ O 15-30 CaO 8-30 TiO ₂ 0-2 P ₂ O ₅ 0-8 F ₂ 5-15 The melt of bioactive glass is It can be obtained by methods known in the art, and according to the prescribed composition, oxides, carbonates,
Using nitrates, fluorides, etc., mix them in a predetermined ratio, crush them and use them as raw materials for preparation, and process this into 1000~1300
It is obtained by putting it into a platinum crucible in an electric furnace heated to ℃, melting and clarifying it, and then stirring and homogenizing it. The melt thus obtained is poured into the cavity of a mold according to the invention (first step). The mold may be preheated. Next, the core is inserted into the glass melt before the molten glass solidifies (second step). This state is the third
As shown in the figure (cross-sectional view). In Fig. 3, 1 is a core, 2 is a support rod for supporting the core, 3 is molten glass,
4 is a mold. The core may be preheated before insertion, but since the core is small and the melt is large, there is little need to preheat the core. The speed of inserting the core into the glass melt is 25cm/25cm if the metal core is pre-coated with an inner layer of glass.
A speed of min or more is preferred. This is because if it is too slow, the inner glass may soften and deform during insertion. After inserting the core into the glass melt, leave it to cool and wait for the glass to solidify (third step). This time is usually 10-15 seconds. Once the glass melt has solidified, the core containing the still hot glass gob is removed from the mold and transferred to the next slow cooling step (fourth step). The glass gob may be transferred to the slow cooling process without being removed from the mold, but if the glass gob is returned to room temperature while still in the mold, the glass may adhere to the mold and become difficult to remove. In the slow cooling step (fourth step), the core containing the still hot glass gob is placed in a constant temperature oven set at the glass transition point (Tg) of the glass used or a temperature at most 40°C lower than Tg for 30 minutes or more. The temperature is maintained for about 24 hours to make the temperature of the core body and the glass layer the same and to release the stress that has been generated in the glass. Next, the temperature is returned to room temperature at a rate of 0.8° C./min or less in order to prevent a temperature difference between the core body and the glass layer, and also to prevent a temperature difference from occurring in each part of the glass layer itself. The bioactive glass coating layer of the core body having the cooled glass lump is ground to a predetermined thickness (preferably 0.2 to 1 mm) using a conventional glass grinding technique (fifth step). The roughness of the grindstone required for this grinding is approximately 20~
Approximately 40 μm is appropriate. After this, further buffing may be performed. The bioactive glass in the present invention may be converted into glass ceramic (crystalline) by heat treatment, for example, before grinding. Next, the present invention will be specifically explained with reference to Examples. Example 1 The metal core 1 is made of a cobalt-chromium alloy with a coefficient of thermal expansion of 1.43×10 ^-5 °C ^-1 , and has a shape as shown in Figure 2 (perspective view) and dimensions of 5 mm in top diameter and 11 mm in length. and a cylindrical recess 1 with a diameter of 3.0 mm and a depth of 8.5 mm on the top surface.
It has a. This metal core has been heat-treated in advance to form an oxide layer on its surface. The mold 4 is made of iron and has an opening with a diameter of 16 mm at the top and a cavity with a depth of 20 mm. This mold can be divided into two parts as shown in FIG. First, a molten liquid (1010°C) of bioactive glass having the composition and properties listed in Table 1 is prepared and poured into the cavity of the mold 4. Thereafter, the support rod 2 is immediately attached to the metal core 1, and the core 1 is inserted into the molten glass 3 at a speed of 30 cm per minute (see FIG. 3). Leave it as it is and wait for the glass to solidify. Once the molten glass has solidified, separate the mold into two parts, remove the support rod holding the still hot glass lump, and then place it in a constant temperature oven at 525℃ and hold for 1 hour. to match the temperature of the core and the glass layer, and then
Cool slowly to room temperature at a rate of 0.5°C/min. Thereafter, the glass layer was ground with a grindstone having a roughness of 34 to 37 μm to a thickness of 0.5 mm. After this, the support rod is removed and the desired dental implant is obtained.

[Table] After this implant is placed in the alveolar bone and complete union is confirmed, a superstructure such as an artificial tooth crown is attached. Example 2 The metal core is a nickel-chromium alloy with a coefficient of thermal expansion of 1.36 x 10 ^-5 °C ^-1 , and has the shape shown in Figure 2 (perspective view) and dimensions of 4.5 mm in top diameter and 10 mm in length. death,
It has a cylindrical recess with a diameter of 2.5 mm and a depth of 7.5 mm on the top surface. This metal core was heat-treated in advance to form an oxide layer on its surface, and then coated with a base glass layer having almost no bioactivity and having the composition and components listed in Table 2 to a thickness of approximately 100 μm using a melt-dipping method. There is. The method of melting and immersion is to immerse the metal core in the glass melt (1070℃) listed in Table 2, pull it out, let it cool, and then put it in a constant temperature oven at 530℃ and hold it for 1 hour to separate the core and the covered glass. After matching the temperature with that of the layer, it is slowly cooled to room temperature at a rate of 0.5°C/min. The mold is made of stainless steel and has a diameter of 18mm at the top.
It has a cavity with a depth of 24 mm. After fitting a stainless steel support rod into the recess in the center of the metal core, the core is preheated to 530°C. Next, a molten liquid (1000°C) of bioactive glass having the composition and properties described in the second notation is prepared, and after pouring this into a mold, a metal core is inserted into the molten glass at a speed of 25 cm/min. Once the glass has solidified, the support rod with the still hot glass gob is released from the mold, placed in a constant temperature oven at 520°C for 1 hour to equalize the overall temperature, and then heated at a rate of 0.5°C/min. It was returned to room temperature. The bioactive glass layer was then ground to a thickness of 0.5 mm using a grindstone with a roughness of 25 to 30 μm. In this way, the dental implant of the present invention is obtained.

[Table] Example 3 The same metal core as in Example 2 was used, but
The underlying glass layer is not coated. Other than that, the dental implant of the present invention was manufactured in the same manner as in Example 2, by coating with a bioactive glass layer having the structure and properties listed in Table 3 and grinding.

[Table] Example 4 The core is an iron-based austenitic alloy with a thermal expansion coefficient ^{of 1.61} It has a cylindrical recess with a diameter of 2.5 mm and a depth of 7.5 mm on the top surface.
This metal core was heat-treated in advance to form an oxide layer on its surface, and then a base glass layer (about 120 μm thick) with almost no bioactivity and having the composition and properties listed in Table 4 was formed. The mold is the same as that in Example 2, and as in Example 2, pour the molten liquid (840°C) of the bioactive glass listed in Table 4 into the mold, insert the core, and once the glass has solidified, remove the still hot The core body containing the glass lump was removed from the mold and placed in a constant temperature oven at 410℃ for 3
The mixture was held for a period of time and then slowly cooled to room temperature at a rate of 0.5°C/min. Finally, the glass was ground using a grindstone with a roughness of 34 to 37 μm to give a thickness of the bioactive glass layer of 0.6 mm.
In this way, the dental implant of the present invention was obtained.

[Table] (Effects of the Invention) As described above, according to the manufacturing method of the present invention, an implant in which a core body is coated with bioactive glass having a uniform thickness and a desired composition can be obtained,
In addition, even when mass-produced industrially, unlike the melt dipping method, there is no need to replace the entire bioactive glass melt due to contamination with harmful metal ions before coating, making it economical. can be manufactured according to In addition, this method is advantageous in that it is easy to mechanize in terms of operation when automatic production is performed by a machine.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing an example of a split mold consisting of two parts. FIG. 2 is a perspective view showing an example of a metal core. FIG. 3 is a sectional view showing the metal core inserted into the glass melt. [Explanation of symbols of main parts], 1...Metal core,
2...Support rod, 3...Glass melt, 4...Mold.

Claims (1)

[Claims] 1. A method for manufacturing a dental implant comprising a metal core and a bioactive glass layer covering the core, comprising: (1) a mold having an opening in its upper part; (2) inserting the core into the glass melt in the cavity; and (3) allowing the core to solidify until the glass solidifies. (4) slowly cooling the obtained glass gob and core back to room temperature; (5) grinding the glass gob to obtain a bioactive glass layer of a predetermined thickness. Method of manufacturing dental implants. 2. The manufacturing method according to claim 1, wherein the predetermined thickness is 0.2 to 1 mm.