DENTAL IMPLANT

Abstract

A dental implant made of a ceramic material including an implant surface having at least partially a contact angle of less than 20, the implant surface being at least partially covered by a protective layer. The protective layer includes a dextran having a molecular weight of more than 15,000 Da.

Claims

1. A dental implant made of a ceramic material comprising an implant surface having at least partially a contact angle of less than 20, said implant surface being at least partially covered by a protective layer, wherein the protective layer comprises a water-soluble dextran having a molecular weight of more than 15,000 Da.

2. The dental implant according to claim 1, wherein the nonionic water-soluble dextran has a molecular weight of 35,000 to 50,000 Da.

3. The dental implant according to claim 1, wherein the protective layer additionally comprises at least one salt.

4. The dental implant according to claim 3, wherein said at least one salt is selected from the group consisting of NaCl, KCl, MgCl.sub.2, CaCl.sub.2, SrCl.sub.2, KH.sub.2PO.sub.4 and Na.sub.2SO.sub.4 or a mixture thereof.

5. The dental implant according to claim 1, wherein the protective layer has a thickness of 0.2 to 5 m.

6. The dental implant according to claim 3, wherein in the protective layer, the molar ratio of dextran to salt is between 1:1 and 1:10.

7. The dental implant according to claim 1, wherein the ceramic material comprises zirconia.

8. The dental implant according to claim 1, comprising at its apical end a body portion, wherein the surface of said body portion has a contact angle of less than 20, which is essentially entirely covered by the protective layer.

9. The dental implant according to claim 1, wherein the dental implant has a storage stability of more than 4 months.

10. A method for preparing a dental implant made of a ceramic material according to claim 1 by a) treating at least partially the surface of a dental implant to obtain a contact angle of less than 20, b) covering at least partially the surface of the implant having a contact angle of less than 20 with an aqueous solution comprising at least a water-soluble dextran having a molecular weight of more than 15,000 Da, c) drying said surface by removing at least partially the water from said surface to obtain a protective layer.

11. The method according to claim 10, wherein in step b) the surface is covered by dipping the implant into an aqueous solution.

12. The method according to claim 10, wherein in step c) the water is removed by microwave treatment, by airstream or by drying in a convection or a vacuum oven.

13. The method according to claim 10, wherein the aqueous solution comprises at least a water-soluble dextran having a molecular weight of more than 15,000 Da in a concentration of 1 to 10% (w/v).

14. The method according to claim 10, wherein the implant comprising the protective layer is sterilized by ethylene oxide.

15. The dental implant according to claim 2, wherein the nonionic water-soluble dextran has a molecular weight of about 40,000 Da.

16. The dental implant according to claim 3, wherein the at least one sale is a divalent salt.

17. The dental implant according to claim 4, wherein said at least one salt is selected from the group consisting of SrCl.sub.2 and MgCl.sub.2.

18. The dental implant according to claim 17, wherein said at least one salt is SrCl.sub.2.

19. The dental implant according to claim 6, wherein in the protective layer, the molar ratio of dextran to salt is between 1:1 and 1:5.

20. The dental implant according to claim 19, wherein in the protective layer, the molar ratio of dextran to salt is between 1:1 and 1:2.

21. The dental implant according to claim 7, wherein the zirconia is an yttria stabilized zirconia.

22. The dental implant according to claim 9, wherein the dental implant has a storage stability of 6 months.

23. The dental implant according to claim 9, wherein the dental implant has a storage stability of 24 months.

24. The method according to claim 13, wherein the water-soluble dextran has a molecular weight of more than 15,000 Da in a concentration of 2.5 to 5% (w/v).

25. A method according to claim 24, wherein the water-soluble dextran has a molecular weight of more than 15,000 Da in a concentration of 3 to 4% (w/v).

Description

FIGURES

[0092] The present invention is further illustrated by the following figures and examples:

[0093] FIG. 1 refers to a first embodiment of the present invention;

[0094] FIG. 2 refers to a second embodiment of the present invention;

[0095] FIG. 3 refers to a third embodiment of the present invention;

[0096] FIG. 4 refers to a forth embodiment of the present invention;

[0097] FIG. 5 refers to a fifth embodiment of the present invention;

[0098] FIG. 6 refers to a sample coated with NaCl 1M (left), KCl 1M (right);

[0099] FIG. 7 refers to static contact angle measurements of ZLA discs stored for 30, 60 and 166 days and washed with ultrapure water before measurement;

[0100] FIG. 8 refers to dynamic contact angle (measurements of coated ZLA implants stored for 30 and 60 days and washed with ultrapure water before measurement;

[0101] FIG. 9 refers to SEM pictures of ZLA implants coated with dextran (left) and NaCl (right).

[0102] FIG. 1 shows an anchoring part 1 of a two-part implant system. Such an anchoring part 1 is made of a ceramic material, preferably of a yttria stabilized zirconia. Said anchoring part 1 is in a cylindrical shape, having an apical end 25 with a body portion 20 and a coronal end 35 with a neck portion 30 intended to receive an abutment, and a transition portion 40 being arranged in axial direction A between the body portion 20 and the neck portion 30. The neck portion 30 includes an unthreaded part 31 which is in coronal direction outwardly tapering and ends in a shoulder portion 32 with an inwardly-tapering surface. The body portion 20 is intended to be directed against the bone tissue in the implanted state, whereas the neck portion 30 is intended to be directed against the soft tissue in the implanted state. The transition portion 40 may be directed towards the soft tissue and the bone tissue depending on the depth to which the implant is screwed or on the tissue reaction. The surface of the body portion 20 has a contact angle of less than 20, which is preferably entirely covered with the protective layer 10.

[0103] FIG. 2 shows another embodiment of the present invention. In contrast to the embodiment of FIG. 1, not only the body portion 20 but also the transition portion of the anchoring part is at least partly, preferably entirely coated with said protective layer 10. Preferably, in apical direction, at least 25%, most preferably at least 50% of the circumferential surface area of the transition portion is covered with the protective layer 10. Preferably, also at least a part preferably the entire surface of the transition portion has a contact angle of less than 20, before covering it with the protective coating 10. However, it is also possible, that only the surface of the body portion of the dental implant has a contact angle of less than 20, but the protective layer covers both, body portion and transition portion. This allows to ensure that also the hydrophilic surface of the edges is fully protected by the protective layer.

[0104] FIG. 3 shows another embodiment of the present invention. In contrast to the embodiment of FIG. 1, not only the body portion 20 but also the transition portion 40 and the neck portion 30 except for the shoulder portion are completely coated with the protective layer 10. Also at least a part, preferably the entire surface of the transition portion and at least a part of the neck portion has a contact angle of less than 20, before covering it with the protective layer 10. It could be shown, that a hydrophilic surface not only ensures a good osseointegration but also positively influences the adherence to the soft tissue. However, it is also possible, that only the surface of the body portion of the dental implant and optionally part of the transition portion has a contact angle of less than 20, but the protective layer covers both, body portion and transition portion.

[0105] FIG. 4 shows an anchoring part 101 of a so-called bone level implant. Such a bone level implant is usually embedded completely in the bone, that is to say to the height of the alveolar crest. Said anchoring part 101 is made of a ceramic material, preferably of a yttria stabilized zirconia. The anchoring part 101 is in a cylindrical shape, having an apical end 125 with a body portion 120 and a coronal end 135 intended to receive an abutment. In contrast to the dental implant shown in FIG. 1, the anchoring part of a bone level implant has no neck portion. The body portion 120 is intended to be entirely directed against the bone tissue in the implanted state. The surface of the body portion 120 has a contact angle of less than 20, which is entirely covered with the protective layer 110.

[0106] FIG. 5 shows a monotype dental implant 200. Said monotype dental implant 200 is made of a ceramic material, preferably of a yttria stabilized zirconia. It comprises an anchoring part 205 having a threaded section 210. The anchoring part 205 at its upper end 215 transitions via a slightly enlarged conical neck portion 220 to the outside into a mounting part 225 being integral therewith and extending within an extension of the longitudinal axis 230 of the threaded section. Said anchoring part 205 is in a cylindrical shape, having an apical end 235 with a body portion 240 and a coronal end 245 with a neck portion 220, and a transition portion 250 being arranged in axial direction A between the body portion 240 and the neck portion 220.

[0107] The mounting part 220 has a frusto-conical or a conical shape and may be provided with at least one a flattening 230 at one side thereof.

[0108] At the side opposite the at least one flattening 260 there may be a groove 265 within the outer surface that extends from the coronal front surface of the mounting part 225 toward the apical side and ends in a conical section which forms the transition to the conical section of the anchoring part 205. The flattening 260 in combination with the groove 265 located on the opposite side functions to provide a positive a screwing tool which has a plug-in seat matched thereto. Alternatively, the mounting part may be provided with other means for receiving a screwing tool.

[0109] The body portion 240 is intended to be directed against the bone tissue in the implanted state and the neck portion 220 is intended to direct against the soft tissue, whereas the transition portion 250 may direct against the bone tissue or the soft tissue depending on the patient. The surface of the body portion 240 has a contact angle of less than 20, which is at least partly, preferably entirely covered with the protective layer 270. Optionally, not only the body portion 240 but also the transition portion 250 of the anchoring part is hydrophilic. Preferably, the transition portion 250 has a contact angle of less than 45, preferably of less than 20, which is covered by the protective layer 270. Preferably, at least 25%, most preferably at least 50% of the apical circumferential surface area of the transition portion is covered with said protective layer 250. This allows more flexibility when implanting the implant and ensures that the whole surface, which is intended to be in contact with the bone tissue, is hydrophilic.

EXAMPLES

[0110] 1. Methods

[0111] 1.1. Cleaning and Coating: Experimental Procedures

[0112] Samples used for coating experiments were cleaned and stored as follows:

[0113] i. O.sub.2 plasma cleaning of clean discs: Pressure vacuum chamber 1*10.sup.1 mbar; power: 35 W; countdown timer: 2 min; oxygen gas flow: 5 sccm, cleaning steps: 2.

[0114] ii. Coating: The sample was dipped in the solution for 30 seconds, placed on a Teflon mesh and dried. The drying was carried out by [0115] a. let drying for at least 20 h in air, [0116] b. in a convection oven (for example Heraeus; serial no. 95104542, type) or [0117] c. in a vacuum oven (for example Salvis Typ. KVTS 11).

[0118] iii. Storage: The samples were stored in a 24-well plate and placed in a closed laminar flow box without ventilation. The contact angle measurements were performed after 1 week of storage.

[0119] 1.2. Static Contact Angle Measurements, Sessile Drop Method

[0120] Contact angle measurements were performed in order to determine the degree of hydrophilicity or hydrophobicity. Usually, the contact angles of plates and discs were determined by static contact angle measurements. The static contact angles were determined using a sessile drop test with ultrapure water (EasyDrop DSA20E, Krss GmbH). The water droplets with a size of 0.3 l were dosed using an automated unit. Values for contact angles were calculated by fitting a circular segment function to the contour of the droplet placed on the surface. Contact angles were determined after rinsing (washing) the samples with ultrapure water for about 15 seconds followed by blow drying in a stream of Ar in order to remove the coating. Contact angles were measured after different storage periods in air. Samples were stored for up to 166 days.

[0121] 1.3. Dynamic Contact Angle Measurement

[0122] Usually, the contact angles implants were determined by static contact angle measurements. Dynamic contact angles (DCA) of implants were determined by the Wilhelmy method by means of a tensiometer (Lauda TE 3, Lauda Dr. R. Wobser GmbH & Co. KG). The advancing contact angle is presented in all cases, and was determined by immersion of the implant into ultrapure water.

[0123] 1.4. Surface Analysis Using SEM and EDS

[0124] Scanning electron microscopy (SEM) and electron dispersive x-ray spectroscopy (EDS) were used for the analysis of the coated samples. The surface topography of the samples was scanned in detail with the SEM and the chemical composition of the surface of the samples was analysed with the EDS. All analyses were done with the table top SEM TM-3030Plus from Hitachi (SEM voltage: 5-15 kV, Detector: EDS-, back scattered and secondary electron detector, EDS-Analysis Bruker Quantax 70 EDS, Acquisition time 180 s, 15 kV).

[0125] 1.5. Stress Test of Protective Layer

[0126] The stability of the coatings was assessed by exposing the sample to harsh conditions like high humidity, low temperature or low pressure. This stress test was carried out as follows: [0127] i) Relative humidity>95%, 15 minutes [0128] ii) Freezing at 19 C., 15 minutes [0129] iii) Drying at 40 C. in vacuum<0.1 mbar

[0130] The cycle was applied 3 times continuously.

[0131] Material

[0132] The term ZLA within the context of the present invention stands for yttria stabilized zirconia, i.e. 3Y-TZP according to DIN ISO 12677, having a sand blasted (corundum 0.1-0.4 mm, 6 bar) and acid etched surface (for example HF).

Example 1: Coating of Machined Ceramic Discs

[0133] The samples were cleaned as disclosed under Chapter 1.1. The experiments were performed on yttria stabilized zirconia discs (3Y-TZP, 5 mm1 mm) featuring a machined surface.

[0134] The samples were given into the respective coating solution and coated in the ultrasonic bath for 3 minutes.

[0135] The sample were in air for at least 20 h.

[0136] All samples were stored in a 24-well plate after coating and the static contact angle was measured after different storage times.

[0137] The contact angle was measured after rinsing the samples with ultrapure water and dried with argon gas.

TABLE-US-00001 TABLE 1 Contact angle results of coated, machined ZrO.sub.2 discs after a storage period of 7 days in air (contact angles CA 1 and CA2 measured after one week). *CA 1 *CA 2 *mean No. Sample.sup..diamond-solid. [] [] [] Ref Reference after O.sub.2 plasma treatment <10 <10 <10 Ref Reference 80.4 84.2 82.3 1 NaCl 1M 73.6 70.0 71.8 2 KCl 1M 41.8 48.6 45.2 3 MgCl.sub.2 0.5M <10 13.2 13.2 4 CaCl.sub.2 1M 12.4 8.8 10.6 5 SrCl.sub.2 1M 32.7 21.2 27.0 6 Dextran 3.1% <10 5.5 5.5 7 Dextran/SrCl.sub.2 (3.1%, 1M) 95:5 4.8 4.8 4.8 8 Dextran/MgCl.sub.2 (3.1%, 0.5M) 5:95 4.5 4.6 4.6 9 Dextran/SrCl.sub.2/MgCl.sub.2 6.2 4.6 5.4 (3.1%, 0.5M, 0.5M) 90:5:5

[0138] The contact angle results show that coatings with a monovalent salt, like NaCl, led to high contact angles after one week storage time. These salts did not coat the whole sample surface as it can be seen in FIG. 6: Sample coated with NaCl 1 M (left), KCl 1 M (right).

[0139] Other salts like MgCl.sub.2 or CaCl.sub.2) led to contact angles around 10. In case of these salts a liquid layer remained on the surface and these samples were thus hygroscopic.

[0140] Dextran formed closed coating layers and the dextran coatings with or without mixtures with salts led to low contact angles.

Example 2: Long-Term Study

[0141] The long-term study was performed with ZLA discs (Ceramtec) and ZLA implants (Straumann, Villeret) where samples were stored in air for 30 and 60 days. Some of the ZLA discs were even stored for 166 days.

[0142] One batch was treated with the cyclic stress test (see Chapter 1.5.) after an initial storage period of 60 days and were stored for finally 166 days prior to analysis. Contact angle values below 5 could not be quantified because of experimental limitations (limitations in the determination of the proper contour of the droplet) and in the following, values below 5 will be stated as 5 and visualized with a red frame in the graphs.

[0143] The rinsing (washing) step with ultrapure water was performed in order to measure the bare surface.

[0144] Results can be seen in FIG. 7: Static contact angle measurements of ZLA discs stored for 30, 60 and 166 days and washed with ultrapure water before measurement.

[0145] Coatings with CaCl.sub.2), MgCl.sub.2, MgCl.sub.2/NaCl, dextran or dextran/SrCl.sub.2 prevented the surfaces from turning hydrophobic also after storage periods of 60 days as it could be shown with contact angles around 10 or lower. Contact angles of 14.2 and 18.7 were measured for ZLA discs coated with 1 M NaCl after storage in air for 30 and 60 days, respectively. The lowest contact angle could be measured for dextran and MgCl.sub.2/NaCl coatings with values below 5 after 60 days.

[0146] For all samples, except for coatings containing dextran or the MgCl.sub.2/NaCl coating, slightly higher contact angles were measured for washed samples after 166 days. For MgCl.sub.2/NaCl and the dextran coatings, contact angles below 5 were measured. The biggest increase from 18.7 to 32.9 was measured for the NaCl coating. Only minor differences in contact angle were present for samples that underwent the stress cycle. No effect could be measured for dextran coated samples. In case of glucose coatings, the stress cycle lead to a rearrangement of the coating resulting in a new orientation of glucose crystals on the surface.

Example 3: Coating of ZLA-Implants

[0147] The implants were cleaned as disclosed under Chapter 1.1.

[0148] The implants were fixed on an own designed implant holder. The implants were then dipped into the coating solution until the whole ZLA area was immersed. The implants were coated in the ultrasonic bath for 3 minutes.

[0149] The holder with implants was placed in the convection oven (thread oriented to ground) at 70 C. for 30 minutes. The ventilation was reduced to the minimum.

[0150] All implants were stored in a 24-well plate after coating and the dynamic contact angle (advancing contact angle) was measured after different storage periods.

[0151] ZLA implants with a diameter of 3.3 mm were coated with selected substances. Implants with the following coatings were prepared: NaCl, MgCl.sub.2, mixture of MgCl.sub.2 and NaCl, glucose, dextran, mixture of dextran and SrCl.sub.2.

[0152] The error bars in FIG. 6 show the highest and lowest values measured. The mean value is calculated based on three implants, those of substances marked with an asterisk (*) are calculated based on two implants only.

[0153] The results can be seen in FIG. 8: Dynamic contact angle (advancing contact angle) measurements of coated ZLA implants stored for 30 and 60 days and washed with ultrapure water before measurement. The reference resulted in a value of 73 after 30 days and 96 after 60 days compared to all coated implants with values lower than 40. NaCl coatings contained the highest value with 34.2 (30 days). These layers were not hygroscopic like MgCl.sub.2 (DCA 18.9 after 30 days) or the mixture MgCl.sub.2/NaCl with a DCA of 18.2 after 30 days. The saccharide coatings led to low DCA of 15.3 for glucose, 12.7 for dextran and 11.9 for the dextran/SrCl.sub.2 coated implants after 60 days. SEM analyses (FIG. 9) of coated implants have shown that saccharide coatings formed smooth and thin layers with a closed surface over a wide area. All coating solutions were coloured with methylene blue. The layer thickness of dextran decreases towards the edge of the thread. The NaCl coating formed more crystals on the flank and edge of the thread with big non-coated areas in the valley of the thread. In comparison, the dextran coating led to much more complete layers.

[0154] Hygroscopic salts like MgCl.sub.2 and CaCl.sub.2) formed thin liquid layers over the ZLA implant surface. The 3.1% dextran coating was thicker than the 1 M NaCl coating (estimated by REM). The dextran coating covered the whole implant surface with a thickness that the structure of the implant was still visible by SEM.