Abstract:
One-part implant for attachment of artificial teeth comprising an anchoring part and a mounting part, wherein the anchoring part and the mounting part are configured in one piece. The anchoring part of the one-part implant has a bone contact surface B and a soft tissue contact surface S. The soft tissue contact surface S is at least partially hydroxylated or silanated, which results in an improved soft tissue integration.

Description:
FIELD OF THE INVENTION  
       [0001]    he present invention relates to a one-part implant comprising an anchoring part and a mounting part, wherein the anchoring part and the mounting part are configured in one piece, and the anchoring part has a bone contact surface and a soft tissue contact surface; the invention further relates to a method for preparing such an implant. 
       BACKGROUND  
       [0002]    Implants which are used for insertion into bone, for example for attachment of artificial teeth, are known per se. Different types of implants are known, for example one-part implants. A one-part implant comprises an anchoring part for anchoring within the bone and a mounting part. Onto the mounting part prosthesis elements, such as bridges or crowns, are screwed or cemented usually using intermediate so-called abutments. 
         [0003]    A central property of said implants is their osteointegration time, that is to say the time that passes before the bone substance has become connected with sufficient strength and permanently to the bone contact surface, that is to say it has become integrated with it. 
         [0004]    Therefore, much effort has been made in order to improve the osteointegration of said implants, such as described in WO 03/045268. It was shown that the osteointegration time was significantly shorter if the bone contact surface of the implant is roughened and hydroxylated or silanated. 
         [0005]    U.S. Pat. No. 5,397,362 discloses an implant prosthesis comprising a substrate of ceramic material, a glass layer coated over the adhering interface of the substrate and a thermally sprayed layer of calcium phosphate based material formed over the glass layer. 
         [0006]    US 2004/0049287 discloses an endosseous implant having a surface with a smooth or rough texture, whereby said surface has been treated with at least one pharmaceutically acceptable organic compound carrying at least one phosphonic acid group or a derivative thereof. It has been found that the modified surfaces of said implants enhance the bone bonding strength. 
         [0007]    However, there is considerable evidence supporting the view that the supracrestal connective tissue plays a fundamental role in establishing an effective seal between the oral environment and the endosseous part of a dental implant. Indeed, the presence of bacteria on the implant surface may lead to an inflammation of the peri-implant mucosa, and, if left untreated, the inflammation spreads apically and results in bone resorption. As a consequence of the fact that rough surfaces accumulate and retain more plaque than smooth surfaces, nowadays, the soft tissue contact surface of implants is highly polished (see Oral Implantology, Thieme Verlag, 1996, page 438). 
         [0008]    Various experiments have been carried out to investigate the difference of early inflammatory response to mucosa-penetrating implants prepared with varying surface roughness. Despite the fact that a rough surface may accumulate greater amounts of plaque than a smooth surface, no relation was found between inflammatory response and implant surface roughness (Wennerberg et al, J. Clin. Periodontol 2003: 30: 88-94; Quirynen et al, The International Journal of Oral and Maxillofacial Implants, 11, No. 2, 1996). U.S. Pat. No. 5,496,374 discloses an orthopedic, dental or soft tissue implant which accelerates implant-tissue bond formation. Said implant is made of ceramic and has been exposed to ion beams. 
         [0009]    It is the problem of the present invention to provide an implant with improved soft tissue integration. 
       SUMMARY OF THE INVENTION  
       [0010]    A one-part implant according to the invention comprises an anchoring part and a mounting part, wherein the anchoring part and the mounting part are configured in one piece. The anchoring part has a bone contact surface and a soft contact surface. The soft contact surface has the potential to promote formation of soft tissue attachment, if the soft tissue contact surface is at least partially hydroxylated or silanated. In contrast to conventional implants having a roughened, in some cases also hydroxylated bone contact surface and a smooth unhydroxylated soft tissue contact surface, the implant according to the present invention leads to the formation of new connective tissue adjacent to the soft tissue contact surface of the implant and the new connective tissue tends to be in close contact with said surface. The loose connective tissue seems to become organized and replaced by newly formed collagen fibers, originating from its outer zone. These fibers tend to be organized in a perpendicular way towards the implant surface, similarly to the naturally occurring fibers most responsible for compensating forces on the tooth. 
         [0011]    “Hydroxylated” in terms of the present invention means hydroxyl groups which are present in the outermost atomic layer of the implant surface. If the implant comprises titanium, zirconium, tantalum, niobium, hafnium or alloys thereof as well as chemically similarly reacting alloys, it is assumed that the surface of said metal oxidizes spontaneously in air and water and that a reaction then takes place with water on the surface to form hydroxyl groups. This surface containing hydroxyl groups is referred to in the literature as a “hydroxylated” surface; cf. H. P. Boehm, Acidic and Basic Properties of Hydroxylated Metal Oxide Surfaces, Discussions Faraday Society, vol. 52, 1971, pp. 264-275. The same applies to ceramic surfaces (either on a ceramic implant or a metallic implant with a ceramic coating). A metal surface whose hydroxyl groups are covalently blocked, e.g. because of chemical modification, is not a “hydroxylated” surface in terms of the present invention. 
         [0012]    Silanated in terms of the present invention means that the implant surface is covered by a silanole or by an organo silane compound which has at least one free hydroxyl group. Examples of such organo silane compounds are X n SiR 4-n , wherein X is selected from the group consisting of Cl, Br, I, F or OR, and R is selected from the group consisting of lower alkyl groups, such as methyl, ethyl, propyl etc. Implants made of metals are preferably covered by silanole, whereas implants made of ceramic are preferably covered by an organo silane compound. Implants made of metal can also be covered by an organo silane compound and implants made of ceramic can also be covered by silanole. 
         [0013]    In a preferred embodiment of the present invention the soft tissue contact surface is completely hydroxylated. Such an implant showed good results in vivo and said implants are economically interesting and can be produced in a controlled process. In addition it has been shown that with the implants according to the present invention the healing process is improved, that is a good osteointegration as well as an excellent soft tissue integration is achieved. Therefore, the implants comprise a reduced risk of periimplantitis and as a consequence fewer implants will have to be replaced. Due to their purity, meaning that the soft tissue contact surface is free of organic compounds, the surface charge is better available. Therefore, the surface is hydrophilic, which results in an improved soft tissue integration. Therefore they do not bear the risk of autoimmune reaction and other unwanted side effects. 
         [0014]    In a further embodiment of the present invention the soft tissue contact surface is roughened and hydroxylated. A roughened surface in terms of the present invention means a macroscopic texture of the surface which is obtained for example by sandblasting the soft tissue contact surface. It has been found that if the soft tissue contact surface is roughened and hydroxylated the blood coagulum is stabilized which accelerates the healing procedure. 
         [0015]    In a further embodiment of the present invention the soft tissue contact surface is smooth but hydroxylated. A smooth surface in terms of the present invention means a macroscopic texture of the surface which is obtained for example by machining or additional polishing, preferably by electropolishing the soft tissue contact surface. With a smooth surface the accumulation of plaque can be prevented or at least minimized, and such a soft tissue contact surface has outstanding wettability properties which is highly preferred. 
         [0016]    In a further embodiment of the present invention the surface roughness of the soft tissue contact surface increases towards the bone contact surface continuously or stepwise. This means that at the upper end of the anchoring part of the implant the soft tissue contact surface is smooth or only slightly roughened. Said surface roughness increases towards the bone contact surface continuously or stepwise until the surface roughness of the bone contact surface is reached. 
         [0017]    In a further preferred embodiment of the present invention the soft tissue contact surface is hydrophilic. In terms of the present invention, the soft tissue contact surface is referred to as “hydrophilic” if it is freely accessible to the body fluid and not covered with foreign substances, for example substances with a hydrophobic action. Various volatile hydrocarbons are conventionally present in non-purified air. These are rapidly adsorbed in a thin layer by hydroxylated and hydrophilic surfaces, whereafter such surfaces are no longer hydrophilic. Likewise, such a hydroxylated and hydrophilic surface can become hydrophobic if the hydroxyl groups present on the surface associate or react chemically e.g. with carbon dioxide present in the air or with organic solvents, such as methanol or acetone, introduced via the cleaning process. The hydrophilic properties of the soft tissue contact surface may result in a higher wettability when compared to an untreated soft tissue contact surface. A higher wettability may promote formation of the soft tissue. Further, the charge on the surface is better available which may accelerate the formation of soft tissue attachment as well. 
         [0018]    In one embodiment of the present invention the implants comprise mainly a metal selected from the group consisting of titanium, zirconium, niobium, hafnium or tantalum, preferably titanium or zirconium. Alternatively the implants comprise an alloy of metals selected from the group consisting of titanium, zirconium, niobium, hafnium or tantalum, preferably a binary titanium/zirconium alloy. Such implants, their nature and the metal materials used to produce them are known per se and are described for example in J. Black, G. Hastings, Handbook of Biomaterials Properties, pages 135-200, published by Chapman &amp; Hall, London, 1998. From an aesthetic point of view, in particular in the front visible region, the soft tissue contact surface is preferably covered with a ceramic coating or comprises a ceramic ring element. Such a ceramic coating comprises typically zirconia, aluminia, silica or mixtures thereof with possible further constituents, preferably they are made of zirconia. Such implants and the method to produce them are known and are described for example in U.S. Pat. No. 4,746,532 or in EP 1 566 152. The cubic structure of zirconium oxide (zirconia) may be stabilized by metallic oxides at room temperature. Preferred metallic oxides are magnesium oxide, calcium oxide, oxides of the lanthanide group, preferably yttrium oxide. Depending on the content of said metallic oxides the cubic high temperature phase of zirconia can be stabilized fully or partly at room temperature (cubic stabilized zirconium oxide). Preferably zirconia is stabilized by yttrium oxide. Alternatively the whole one-part implant according to the present invention may be made of ceramic. One-part implants which are made of ceramic are described for example in EP 1 450 722 which is hereby incorporated by reference. 
         [0019]    In a most preferred embodiment the implant according to the present invention is made of ceramic comprising a zirconium oxide based material. 
         [0020]    The present invention also relates to the process for preparing the above disclosed implant. 
         [0021]    To obtain the hydroxylated surface, the soft tissue contact surface of the one-part implant is preferably etched with an inorganic acid, an inorganic base, a mixture of inorganic bases or a mixture of inorganic acids. Particularly preferred are inorganic acids such as hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid or a mixture of such acids. Preferably the one-part implant is etched with a mixture of hydrochloric acid (conc.), sulforic acid (conc.) and water in a weight ratio of about 2:1:1. Alternatively the surface is activated with hydrochloric acid (conc.), hydrogen peroxide (conc.) and water in a weight ratio of about 1:1:5. The soft tissue contact surface is then washed with pure water in an inert atmosphere. 
         [0022]    A roughened soft tissue contact surface can be obtained by sandblasting said surface and keeping the surface in the resulting state if it is already hydroxylated and hydrophilic or converting the sandblasted surface to a hydroxylated and hydrophilic state in a separate process step. 
         [0023]    In particular, the roughened soft tissue contact surface can be produced by shot peening or sandblasting said surface and/or roughening it by using plasma technology, and then treating the mechanically roughened surface by an electrolytic or chemical process until a hydroxylated and hydrophilic surface is formed. 
         [0024]    The preferred procedure is to 
         [0025]    shot-peen the soft tissue contact surface of the one-part implant and then etch it with diluted hydrofluoric acid at room temperature; or 
         [0026]    sandblast the soft tissue contact surface of the one-part implant, e.g. with aluminium oxide particles having a mean size of 0.1-0.25 mm or 0.25-0.5 mm, and then treat it at elevated temperature with a hydrochloric acid/sulfuric acid mixture and wash it with pure distilled and carbon-free (CO 2  and other carbons) water; or 
         [0027]    sandblast the soft tissue contact surface of the one-part implant with coarse particles, e.g. with a mixture of particles as defined above, and then treat it with a hydrochloric acid/nitric acid mixture and wash it with pure distilled and carbon-free (CO 2  and other carbons) water; or 
         [0028]    treat the soft tissue contact surface of the one-part implant with a mixture of hydrochloric acid (conc.), hydrogen peroxide (conc.) and water in a weight ratio of about 1:1:5 and wash it with pure distilled and carbon-free (CO 2  and other carbons) water; or 
         [0029]    roughen the soft tissue contact surface by using plasma technology and then hydroxylate it in a mixture of hydrochloric acid (conc.), hydrogen peroxide (conc.) and water in a weight ratio of about 1:1:5 and wash it with pure distilled and carbon-free (CO 2  and other carbons) water; or 
         [0030]    treat the soft tissue contact surface by an electrolytic process, optionally after mechanical roughening of the surface, and then wash it with pure distilled and carbon-free (CO 2  and other carbons) water; or 
         [0031]    treat the soft tissue contact surface of the implant by plasma cleaning or UV-treatment. 
         [0032]    These methods are known to those skilled in the art and are described for example in U.S. Pat. No. 5,071,351. The hydroxylated soft tissue contact surface of the implant is after such a treatment free of organic debris and has increased wettability. As a result, the implant becomes more intimately involved with the surrounding bone and tissue structure. 
         [0033]    Whatever the case may be, according to the invention the one-part implant is not subjected to further aftertreatment, i.e. it is not treated with alcohol, acetone or any other organic solvent. In particular, said pure water contains neither carbon dioxide nor hydrocarbon vapours and especially no acetone and no alcohols like methanol or ethanol. However, it can contain special additives as described below. The “pure” water used for washing has preferably been distilled several times or prepared by reverse osmosis; the water has preferably been prepared in an inert atmosphere, i.e. under reduced pressure in a nitrogen or noble gas atmosphere, for example. 
         [0034]    Following these procedures, the one-part implant obtained is left in pure water and stored in a closed vessel or a covering. In addition to water, the interior of the covering can contain inert gases, for example nitrogen, oxygen or a noble gas such as argon. The one-part implant obtained is preferably stored in pure water optionally containing selective additives, and in a covering which is practically impermeable to gases and liquids, especially to carbon oxides, the interior of the covering being devoid of any compounds capable of impairing the activity of the implant surface. 
         [0035]    Alternatively, the implant could be placed in an inert gas atmosphere. 
         [0036]    The one-part implant according to the invention, or at least its hydroxylated and hydrophilic surface, is preferably sealed in a gas-tight and liquid-tight covering, the interior of the covering being devoid of any compounds capable of impairing the biological activity of the implant surface. In this way it is avoided that the surface loses its activation fully or partially by means of air constituents, before the dental implant is applied. 
         [0037]    In a preferred embodiment there is a reducing atmosphere in the interior of the covering. This gas-tight and liquid-tight covering is preferably a heat-sealed ampoule made of glass, metal, a synthetic polymer or some other gas-tight and liquid-tight material, or a combination of these materials. The metal preferably takes the form of a thin sheet, it being possible for polymeric materials and metal sheets, as well as glass, to be combined together to form a suitable packaging in a manner known per se. 
         [0038]    Examples of suitable additives which can be incorporated in the pure water are cations and anions which already occur in the body fluid. In order to stabilize the positive charge the implant according to the present invention is preferably stored at a pH ranging from pH 3 to 7, preferably 4 to 6. Alternatively it is also possible to store the implant at a pH ranging from pH 7 to 10 in order to stabilize the negative charge. Preferred cations are Na + , K + , Mg 2+  and Ca 2+ . The preferred anion is Cl − . The total amount of said cations or anions ranges preferably from about 50 mM to 250 mM, particularly preferably from about 100 mM to 200 mM, and is preferably about 150 mM. If the covering contains divalent cations, especially Mg 2+ , Ca 2+ , Sr 2+  and/or Mn 2+ , on their own or in combination with the above-mentioned monovalent cations, the total amount of divalent cations present preferably ranges from 1 mM to 20 mM. 
         [0039]    The invention is explained below on the basis of figures and illustrative embodiments, without in any way limiting the invention to the embodiments shown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0040]      FIG. 1  a side view of a first embodiment of an implant according to the invention. 
           [0041]      FIG. 2  a side view of an embodiment of an implant according to the invention slightly modified with respect to the embodiment of  FIG. 1 . 
           [0042]      FIG. 3  a side view of a further embodiment of an implant according to the invention wherein the mounting part is slightly offset with respect to the anchoring part. 
       
    
    
     DETAILED DESCRIPTION  
       [0043]      FIG. 1  shows the different areas of an implant  1  according to one embodiment. It comprises an anchoring part  5  having a threaded section  10  and a rounded lower end  15 . The anchoring part  5  at its upper end transitions via a slightly enlarged conical section  12  to the outside into a mounting part  20  being integral therewith and extending within an extension of the longitudinal axis  22  of the threaded section. The mounting part  20  has a frustoconical or a conical shape and is provided with a flattening  25  at one side thereof. At the side opposite the flattening  25  a groove  30  is provided within the outer surface that extends from the upper front surface of the mounting part  20  towards the lower side and ends in a conical section  27  which forms the transition to the conical section  12  of the anchoring part  5 . The anchoring part  5  is subdivided into a bone contact surface B and a soft tissue contact surface S. In the boundary area of these surfaces, there is a transition area B/S from bone contact surface B to soft tissue contact surface S, which transition area is assigned to both aforementioned areas. The question of whether this area, in the implanted state, is located in the bone or in the soft tissue depends on a large number of factors, for example the depth to which the implant is screwed, the tissue reaction, etc. The transition area has to be treated in the same way as the bone contact surface, in order to make sure, that in any case an optimal osteointegration is ensured. The bone contact surface of such implants is preferably roughened, and even more preferred hydroxylated and hydrophilic as well. In a preferred embodiment the soft contact surface is also roughened and hydrophilic. The soft tissue contact surface of an implant according to the present invention may be made of titanium, zirconium, tantalum, niobium, hafnium or alloys thereof as well as chemically similarly reacting alloys, but it is also possible that the implant has a ceramic coating which is hydroxylated or that the implant may be made completely of ceramic. Further it is possible that parts of the implant are made of metal and parts of the implant are made of ceramic, for example if the inner part is made of titanium and the outer part of the implant is made of ceramic. 
         [0044]      FIG. 2  shows a slightly modified embodiment of a dental implant  1 ′ which again comprises an anchoring part  5 ′ having a threaded section  10 ′ being followed by a conical mounting part  20 ′ on which the groove  30 ′ can be seen; here the dental implant  1 ′ is depicted rotated by 90° C. with respect to the dental implant  1 ′ of  FIG. 1 . 
         [0045]    By contrast to the embodiment shown in  FIG. 1  the dental implant  1 ′ does not have a conical section within the transitional region between the anchoring part  5 ′ and the mounting part  20 ′. Instead, the mounting part  20 ′ is configured as a conical section directly adjoining the anchoring part  5 ′ which is shaped cylindrically. Again on the side opposite to the groove  30 ′ a respective flattening (not shown) may be provided, such as can be seen in  FIG. 1 . Also here the anchoring part  5 ′ is subdivided into a bone contact surface B and a soft tissue contact surface S, and a transition area B/S. The soft tissue surface is hydroxylated and roughened. In a further embodiment the soft tissue surface is hydroxylated and smooth. 
         [0046]    In  FIG. 3  a further embodiment of a dental implant  1 ″ according to the present invention is shown. The dental implant  1 ″ comprises an anchoring part  5 ″ corresponding to the embodiment according to  FIG. 1  and having a threaded section  10 ″ which transitions via an outer conical section  12 ″ into a mounting part  20 ″. The anchoring part  5 ″ is subdivided into a bone contact surface B and a soft tissue contact surface S, and a transition area B/S. The soft tissue contact surface is hydroxylated. 
         [0047]    Again the mounting part  20 ″ has a conical basic shape, however, here it is offset with respect to the longitudinal axis  22  of the anchoring part  5 ″, e.g. by an angle of about 15°, this being particularly suitable for applications within the incisor region in many cases. 
         [0048]    The anchoring part  5  may, e.g. have an axial length of 10 mm, wherein the other dimensions result in a corresponding manner. However, it should be understood that the dimensions may be modified in a suitable way depending on the indication. 
         [0049]    The examples which follow illustrate the invention. 
       EXAMPLE 1 
     Implant with a Roughened Hydroxylated Soft Tissue Contact Surface 
       [0050]    A common shape of a one-part implant was produced using the known CNC standard procedure. 
         [0051]    The bone contact surface as well as the soft tissue surface of the anchoring part were sandblasted with particles having a mean size of 0.25-0.5 mm. The roughened surface was then treated for about five minutes at a temperature above 80° C. with an aqueous hydrochloric acid (conc.)/sulfuric acid (conc.) mixture having an HCl:H 2 SO 4 :H 2 O ratio of 2:1:1. The implant formed in this way was washed with pure water and then heat-sealed directly in a glass ampoule filled with pure water containing 150 mM Na +  ions, and the corresponding amount of Cl −  anions. 
         [0052]    To test the soft tissue integration, the above implants were placed to four female fox hounds. Each animal received 6 implants bilaterally in the upper jaw and 10 implants bilaterally in the lower jaw. The implants with a roughened hydroxylated soft tissue contact surface showed unexpectedly a much better soft tissue integration than comparable implants with an unhydroxylated surface. Soft tissue adhesion was seen already after a few days, the soft tissue integration was apparent within two weeks. 
       EXAMPLE 2 
     Implant with a Smooth Hydroxylated Soft Tissue Contact Surface 
       [0053]    A common shape of a one-part implant was produced using the known CNC standard procedure. 
         [0054]    The bone contact surface of the anchoring part was then provided with a macro-roughness by being sandblasted with particles having a mean size of 0.25-0.5 mm, whereas the soft tissue contact surface of the anchoring part has been electropolished or machined. The sandblasted bone contact surface as well as the electropolished soft tissue contact surface were then treated for about five minutes at a temperature above 80° C. with an aqueous hydrochloric acid (conc.)/sulfuric acid (conc.) mixture having an HCl:H 2 SO 4 :H 2 O ratio of 2:1:1. The implant formed in this way was washed with pure water and then heat-sealed directly in a glass ampoule filled with pure water containing 150 mM Na +  ions, 10 mM Mg ions and the corresponding amount of Cl −  anions. 
         [0055]    To test the soft tissue integration, the above implants were placed to four female fox hounds. Each animal received 6 implants bilaterally in the upper jaw and 10 implants bilaterally in the lower jaw. The implants with a smooth hydroxylated soft tissue contact surface showed unexpectedly a much better soft tissue integration than comparable implants with an unhydroxylated surface. Soft tissue adhesion was seen already after a few days, the soft tissue integration was apparent within two weeks.