DE19816865B4 - Use of a silicate glass coating - Google Patents

Abstract

Use of a silicate glass coating (5) for coating an implant which has at least in one section the coating (5) made of a bioactive silicate glass, which has been obtained by melting together highly pure synthetic metal oxides, as a growth surface for cells of the gingiva, the coating (5 ) based on the weight basis consists of SiO2 40–50% Al2O3 8–12% K2O 7–15% Na2O 8–15% B2O3 4–10% Li2O 0.8-1% and possibly TiO2 3–5% and / or ZrO2 7 –11% and / or SnO2 0.1–3%, characterized in that the proportion of crystalline areas of the coating based on the silicate glass is less than 60%.

Description

The invention relates to the use of a silicate glass coating for coating an implant.

A natural tooth consists of the crown, which extends beyond the gum and is coated by the enamel, as well as from the root, which is in the alveole of the jaw. The root is covered by cement, a braided bone. About the periodontal membrane (desmodontium), the tooth is suspended elastically in the bony alveolus of the jaw. For this purpose, fibers run in different directions between the alveolar wall and the cement, so that a tensile resistance is created against any mechanical action. The part of the tooth where enamel and cement are contiguous is called the tooth neck.

The gums consist of multi-layered non-squamous squamous epithelium and its lamina propria, which is firmly attached to the periosteum of the jaw. As an outer junctional epithelium it covers the alveolar process outside; it is high and toothed by papillary processes with the lamina propria. In places, cornification may occur. As an internal junctional epithelium, it pulls over the upper edge of the alveolus to the neck of the tooth and covers the desmodontium from above.

The dental implants currently used usually consist of an anchoring part made of metal, which is designed in the form of a plate, a cylindrical needle or a screw and is anchored by mechanical gearing in the bone. In order to enable bone bone to be engrafted and thus to allow a better fixation of the anchoring in the bone tissue, it has been proposed to coat the metallic body with a polymer matrix in which spherical particles of resorbable, bioactive calcium phosphates are incorporated ( DE 27 33 394 A1 ). With the absorption of the phosphates, bone material can sprout into the cavities, so that an intensive connection between the anchoring part and the bone is formed. On the anchoring part, a crown can be placed after ingrowth into the bone. For this purpose, an intermediate piece is provided between the artificial root and the crown attached above the gum, which corresponds to the tooth neck of the natural tooth. This adapter is made of gold or a gold-plated material. A metal ceramic can also be used for this section. At this intermediate piece, the gum is on. This is done so that the opening in the gum, which was created when inserting the anchoring part in the jaw, is sutured while the gum is placed as closely as possible around the lateral edge of the intermediate piece. However, since the cells of the gum can not grow on the metal surface of the spacer, a gap is formed through which bacteria can penetrate along the implant in the direction of the alveolar bone. This can lead to inflammation, bone loss and, in unfavorable cases, loss of anchoring of the implant in the bone. Problems continue to exist in that the transition between anchoring part and gum is difficult to clean, so at this neuralgic site increased bacterial deposits must be taken into account. Finally, there are also aesthetic concerns, especially when an implant is to replace a frontal tooth, as the golden intermediate piece protrudes beyond the gum and thus is visible.

In the DE 24 55 828 A1 It is proposed to provide a constriction in the anchoring part at the point of passage through the gingiva. This is to extend the path the bacteria have to travel on the way to the alveolar bone, thus reducing the risk of infection. The surface of the anchoring part is covered with a thin layer of porcelain, which is additionally covered by a glazed top strip at the constriction. Due to the constriction, the opening in the gum, which is required for the passage of the anchoring part into the oral cavity, smaller, whereby the expansion of the gap between anchoring part and gum can be reduced. In order to achieve a reduction in the risk of infection, so on the one hand, the expansion of the gap along the circumference of the anchoring part is reduced and on the other hand, the way that bacteria have to travel in the direction of the alveolar bone, extended. Even with this structure, however, a risk of infection remains. Likewise, the problem of cleaning the transition between the implant and the gums is not solved and the mentioned aesthetic disadvantages persist.

More recently, efforts have been made to adapt the materials for implants and prostheses as closely as possible to the conditions in the cell environment. The materials should not only be accepted by the body, so be biocompatible, but bioactive. By this is meant that tissue grows on the implant, so the implant is integrated into physiological processes. Suitable for this purpose are bioactive glasses and bioactive glass ceramics. Wangpeng Cao and Larry L. Hench give an article in "Bioctive Materials" (Ceramics International 22 (1996) 493-507) an overview of the current state of knowledge about such materials.

The DE 696 15 337 T2 describes that bioactive glass-ceramic materials are composites comprising crystals embedded in an amorphous glass fiber and containing different crystalline phases in controlled amounts in the material. It is also mentioned that bioactive glasses, to which potassium and optionally also magnesium are added, achieve their own viscosity-temperature dependence and that glass does not degglaze.

In the WO 97/045377 A1 describes the use of a silicate glass composition as a high strength primer, preferably for joints between metal and plastic workpieces.

It is therefore an object of the invention to increase the stability and bioactivity of an implant, preferably a dental implant.

The object is achieved by the use of a silicate glass coating defined in claim 1 for coating an implant. Surprisingly, it has been found that cells, especially epithelial cells of the gingiva, can grow on the surface of the bioactive silicate glass coating. This is attributed on the one hand to the high purity of the synthetic metal oxides, on the other hand to the reproducibility of the silicate glass composition and its properties.

To date, glazes and ceramic coatings have been produced from naturally occurring minerals, in particular feldspar. Although these minerals can be purified to a very high degree, contaminants always remain. These impurities diffuse out of the finished ceramic. These ceramics therefore exhibit biocompatibility, i. H. no rejection reactions are observed in the body, but the impurities prevent bioactivity of the ceramic, i. H. Growth of tissue has not hitherto been observed with such materials. Due to the purity of the starting materials, the physical conditions of the ceramic can be controlled very accurately. For example, the formation of the leucite crystals can be controlled very accurately. The crystal content in turn has an effect on the biological activity of the surface of the glass or of the glass ceramic. Likewise, the hardness of the coating and its adhesion to the substrate can be influenced very accurately.

Favorable has proven to be a composition in which the coating based on the weight basis as defined in claim 1.

Glasses of this composition can be fired, for example, on a metallic skeleton of titanium or other common in the dental restoration metals or alloys. Due to the oxide layer formed on the metallic skeleton during the firing process, an intensive connection between the skeleton and the coating is achieved, as required, for example, in dental or femoral implants because of the extreme mechanical loads present there.

In this composition, the coating exhibits a low melting point of 700 ° C-950 ° C, a softening point of <600 ° C and a transformation point of <550 ° C. The glaze can therefore be easily processed in dental laboratories and applied to metallic supports.

The properties of the coating can be further changed if the coating contains, based on the weight basis: K ₂ O 7-10% and Na ₂ O 8-10% and B ₂ O ₃ 4-6%.

In particular, for dental implants in which a lifelike appearance is required, it can be provided that the coating further contains based on the weight basis: TiO ₂ 3-5% and / or ZrO ₂ 7-11% and / or SnO ₂ 0.1-3%.

As a result, the coloration, brightness and opalescence of the implant can be adjusted.

The bioactivity of the coating can be further increased if, based on the total mass, the coating has a proportion of 10-40% hydroxylapatite. Hydroxylapatite can be absorbed by the body and has a positive effect on cell growth. In the resulting cavities can then sprout tissue. There are thus two further parameters available with which the properties of the coating can be varied. While the biocompatibility of the implant is increased by calcium phosphates, the aluminum oxide increases the mechanical strength of the coating. Due to the ratio of aluminum oxide to calcium phosphate or aluminum hydroxide, the stability or the biocompatibility of the coating can be optimally adapted to the respective requirements.

The growth of the epithelial layer improves when the proportion of crystalline portions of the silicate glass relative to the silicate glass is less than 60%. It was found that the smaller the proportion of crystalline areas in the silicate glass, the easier it is for growth to take place. Regions of leucite crystals are each surrounded by a layer of amorphous glass. The content of crystalline areas has, above all, effects on the degree of bioactivity of the surface of the ceramic. Presumably, the amorphous areas that are thermodynamically at a higher level, easier to dissolve from the body's own media, so that by the cells, a change in the surface of the implant coating can be achieved. Alkali ions, in particular, can easily be dissolved out of the glass and thus allow a change in the surface of the implant. This dynamics corresponds to the natural processes in which, depending on the load, constantly changing processes to adapt to. the body's structures are carried out.

The aesthetic appearance of the dental implant can be advantageously improved if the implant is formed in two parts, with an anchoring part 4 and a crown 2 , wherein the anchoring part 4 has a height chosen to be in the implanted state of the gingiva 3 is surmounted, preferably concludes with the alveolar bone, and the junction between anchoring part 4 and crown 2 completely from the gingiva 3 is covered. The implant gets thereby the appearance of a natural tooth, because the transition between anchoring part 4 and crown 2 is not visible. As is the crown 2 in the area of the gingiva 3 has a coating of bioactive silicate ceramic, fused both anchoring part 4 as well as crown 2 with the surrounding epithelial cells. The existing hygiene problems can thus be eliminated. The implant fits into the body's own purification processes, which are eg. B. done by movements of the tongue, a. Furthermore, the implant can be cleaned like a natural tooth with the aid of a toothbrush. In the space between the crown 2 and gingiva 3 No food particles or bacteria can accumulate as this gap is eliminated by the shape of the implant, which is closely approximated by the natural shape of a tooth. It is also possible, the mechanical stress of the tooth, the z. B. arises during chewing, better dissipate in the jawbone.

The connection of anchoring part 4 and crown 2 done by a bond. This is at the anchorage part 4 and at the crown 2 an adhesive surface 6 and between the adhesive surfaces a cement 7 intended. Because the splice of the gingiva 3 enclosed, the cement may 7 no substances, eg. As monomers or plasticizers bleed, as this would lead to a retreat of the tissue.

The high tissue compatibility of a silicate glass coating, as defined in claim 1, which is made by fusing together the high purity metal oxides, justifies their use as growth surface for cells, particularly gingival epithelial cells, in implants, preferably dental implants.

The suitability of the silicate glass composition as a growth surface for cells can be further improved if the coating further contains, based on the weight basis: K ₂ O 7-10% and Na ₂ O 8-10% and B ₂ O ₃ 4-6%.

In particular, for use as growth surface epithelial cells in dental implants, it is favorable if the silicate glass composition further contains: TiO ₂ 3-5% and / or ZrO ₂ 7-11% and / or SnO ₂ 0.1-3%.

A further increase in suitability as a growth surface is achieved when the coating has a proportion of 10-40% hydroxyapatite.

The coating can be easily fired in a dental laboratory on a base body of the dental implant. For this purpose, the metal oxides are finely powdered and mixed in the selected ratio, transferred with a mixing liquid, preferably ethanol, in a creamy consistency, applied to a base body of the implant, which is preferably shaped according to the anatomical conditions of an implant carrier, applied in a thin layer and after Drying at a temperature <850 ° C burned. Because the procedure is very simple to carry out by conventional means, individually adapted implants can be produced. This was not possible with the previous implants. The osseointegrated part of the implant has been standardized in the factory, with a coating of hydroxyapatite or other ceramic by pressing or Aufsprayen, z. B. by plasma spray method was applied. By the process in which the ceramic is fired, now a much better connection to the skeleton can be made. The bioactive ceramic is burned in particular in the section of the implant, which is later enclosed by the gingiva.

Processing can be further simplified if the metal oxides are first fused into a glass, the melt is quenched, and the quenched melt is ground to a powder.

The invention will be described in a preferred embodiment with reference to a drawing, wherein further advantageous details are shown in the figures of the drawing. Functionally identical parts are provided with the same reference numerals.

The figure shows in detail:

1 : A schematic section through an implanted in the alveolar bone according to the invention dental implant.

1 shows a section through a dental implant in the alveolar bone 1 was implanted. The implant consists of a crown 2 which about the gingiva 3 protrudes into the oral cavity, and an anchoring part 4 , The anchoring part 4 consists of a section 4a which is submerged in the alveolar bone. It may be in the form of known implants, for example as a plate, pin or, as shown, in the form of a screw. There are no restrictions on the design and the material. Likewise, the section 4a be provided with a coating of hydroxyapatite to facilitate the ingrowth of the anchoring part into the bone. For the coating of the section 4a For example, any known coatings, including a silicate glass coating, may be used. The anchoring part 4 protrudes in the embodiment with the collar 4b over the alveolar bone 1 out into the gingiva 3 into it. However, it is also possible to sink the anchoring part in the bone so far that it is flush with the top of the bone. The collar is cylindrical in the embodiment and has the same shape in cross section as the adjoining crown. Other forms are also possible. On the side surfaces of the collar 4b is a coating 5 made of silicate glass. The firing process and composition are described below. On the upper side of the anchoring part 4 is an adhesive surface 6 intended. On the adhesive surface 6 is by means of a cement 7 the crown 2 glued. The crown 2 is made of ceramic according to the known methods. It can be made entirely of ceramic, but also, for example, have a metal core. The crown has a section 2a on that within the gingiva 3 runs, as well as a section 2 B who cares about the gingiva 3 protrudes. At least in the area within the gingiva 3 is the outer surface of the section 2a the crown 2 with a coating 5 made of bioactive silicate glass. Mostly, however, the entire outer surface of the crown 2 coated with the bioactive silicate glass layer. In the area where the anchoring part 4 and the crown 2 within the gingiva, ie in the sections 4b and 2a , the gingiva is fused with the dental implant. It creates a tight seal to the oral cavity, preventing bacteria from moving towards the alveolar bone 1 can penetrate along the outer surface of the dental implant. The junction between anchoring part 4 and crown 2 is completely covered by the gingiva, the transition is therefore not visible, resulting in a better aesthetics of the implant. Because the gingiva with the implant is fused, the transition between crown 2 and gingiva 3 Also clean easily and thoroughly, which leads to a further reduction of the risk of infection.

The composition of the silicate glass coating selected according to claim 1.

The finely powdered metal oxides used in the highest commercial purity grade are intimately mixed. The powder thus obtained is mixed with ethanol to a creamy consistency and applied in a thin layer to the desired areas of the anchoring part or the crown, the surface of which was previously roughened. The subsequent burning process is carried out with the following parameters: Starting temperature: 400-500 ° C Dry season: 2 minutes Burning time: 2 minutes Vacuum: 0 Heating rate: 55-65 ° C / min Firing temperature: 600-780 ° C Hold time: 2 minutes Cooling down: 2 minutes.

In order to be able to process the ceramic powder better, alternatively, a glass can first be melted from the intimately mixed metal oxides. The melt is quenched and ground to a fine powder. The order of the ceramic and the firing process then carried out as described.

The biocompatibility of the silicate glass coating was tested according to standard procedures.

1. MEM elution cytotoxicity test

Reference method: BTP 2-4-005-83 MEM elution cell culture cytotoxicity test.

A sample of the silicate glass composition used in the invention, which was added a proportion of 40 wt .-% hydroxyapatite, was fired. The specimens were in the form of platelets measuring 5 × 5 × 2 mm. The sample was extracted for 24 hours at 37 ° C in Minimal Essential Medium, adding 5 ml of medium per gram of sample. After extraction, the medium was filtered through a 0.2 μm filter and 2 ml of the extract was added to a cell culture consisting of a monolayer of healthy L929 cells. The culture was incubated for 24 hours and then examined and classified under the microscope. Cell number: 1929; 22/1/13 Positive Control: BTL code pos. 0179 Negative control: BTL Code Neg. 1080

The classification was made according to the following specifications: 0 no cytotoxicity 1 1% -25% of cells damaged 2 26% -50% of cells damaged 3 51% -75% of cells damaged 4 76% -100% of cells damaged.

The confluence of the monolayer, crenation, vacuolization and cytolysis of the cells was assessed. The specimen is considered non-cytotoxic if it receives the value 0 in all categories. confluence Crenation vacuolization cytolysis Sample negative 0 0 0 0 control 0 0 0 0 positive control 0 0 0 0

According to the measurement results, the sample body has no cytotoxicity.

2. Agar diffusion cytotoxicity test

Reference method: BTP 2-4-001-83 Agar diffusion cytotoxicity test.

A layer of the above-mentioned silicate glass composition to which 40% by weight of hydroxyapatite was added was fired on a platinum foil (specimen). The specimen was irradiated with UV light for 30 minutes. Subsequently, the sample was placed directly on a monolayer of healthy L929 cells on an agarose agar and incubated for 24 hours. After incubation, the specimen was removed and the cell layer examined and classified under the microscope. Cell number: 1929; 22/1/21 Positive Control: BTL code pos. 0179 Negative control: BTL Code Neg. 1080

The classification index consists of a surface index and a lysis index. In the area index, the area of the specimen is set in relation to the area of the cell layer on which influences on the cells can be observed. The lysis index assesses the proportion of damaged cells on the affected area.
Classification index = area index / lysis index.

The classification was made according to the following conditions.

area Index

• 0

  no changes under or around the specimen

  1

  Changes in the area under the specimen

  2

  Changes extend up to 0.5 cm beyond the surface of the specimen

  3

  Changes extend 0.5-1.0 cm beyond the surface of the specimen

  4

  Changes extend beyond 1.0 cm beyond the surface of the specimen

  5

  Changes affect the entire surface of the nutrient shell.

Lysis Index

• 6

  no cytotoxicity

  7

  <20% damage

  8th

  20% -39% damage

  9

  40% -59% damage

  10

  60% -80% damage

  11

  > 80% damage.

negative control positive control specimen overall index  0/0 0/0 0/0

Cytotoxicity of the specimen could not be observed.

3. in vivo implantation

A cylindrical specimen having a diameter of 2 mm and a length of 5 mm was made of the above-mentioned silicate glass composition added with a content of 40% of hydroxyapatite. The specimen was inserted into a teflon tube open on both sides and implanted in a hamster in the subcutaneous tissue. After one week, the environment of the implant was assessed visually.

An increase in the connective tissue was observed on the exposed surfaces of the ceramic specimen. The tissue had a basal lamina and hemidesmosomes formed. Inflammatory signs in the vicinity of the implant were not detectable.

LIST OF REFERENCE NUMBERS

1

alveolar bone

2

Crown

2a, b

sections

3

gingiva

4

anchoring part

4a

section

4b

collar

5

coating

6

adhesive surface

7

cement

Claims (6)

Use of a silicate glass coating ( 5 ), for coating an implant, which at least in one section, the coating ( 5 of a bioactive silicate glass obtained by fusing together high purity synthetic metal oxides as growth surface for cells of the gingiva, the coating ( 5 ) based on the weight basis consists of SiO ₂ 40-50% Al ₂ O ₃ 8-12% K ₂ O 7-15% Na ₂ O 8-15% B ₂ O ₃ 4-10% Li ₂ O 0.8-1% and optionally TiO ₂ 3-5% and / or ZrO ₂ 7-11% and / or SnO ₂ 0.1-3% characterized in that the proportion of crystalline areas of the coating relative to the silicate glass is less than 60%. Use according to claim 1, characterized in that the coating ( 5 ) based on the weight basis contains: K ₂ O 7-10% and Na ₂ O 8-10% and B ₂ O ₃ 4-6%. SnO ₂ 0.1-3% Use according to claim 1 or 2, characterized in that based on the total mass, the coating has a proportion of 10-40% calcium phosphate, preferably hydroxyapatite, and / or aluminum hydroxide. Use according to claim 1, 2 or 3, characterized in that the implant is formed in two parts, with an anchoring part ( 4 ) and a crown ( 2 ), the anchoring part ( 4 ) has a height chosen to be in the implanted state of the gingiva ( 3 ), preferably terminates with the alveolar bone, and the joint between anchoring part ( 4 ) and crown ( 2 ) completely from the gingiva ( 3 ) is covered. Use according to claim 4, characterized in that on the anchoring part ( 4 ) and on the crown ( 2 ) an adhesive surface ( 6 ) and between the adhesive surfaces a cement ( 7 ) is provided. Use according to claim 1, characterized in that the silicate glass coating serves as a growth surface for epithelial cells of the gingiva.

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