DENTAL IMPLANT THREAD

Abstract

A dental implant includes a threaded portion extending along a central longitudinal axis from an apical end to a coronal end. The threaded portion includes a core from which threading extends radially outwards, the threading including an apical flank, a coronal flank and a lateral surface connecting the apical and coronal flanks, the lateral surface defining the radially outermost surface of the threading. The threading extends along the length of the threaded portion in a helical manner and the thread width narrowing in the radially outwards direction such that the threading is widest where it contacts the core and narrows towards the lateral surface. The core diameter of the threaded portion is defined by the outer diameter of the core and the outer diameter of the threaded portion is defined by the lateral surface of the threading.

Claims

1. A dental implant comprising a threaded portion extending along a central longitudinal axis from an apical end to a coronal end, the threaded portion comprising a core from which threading extends radially outwards, the threading comprising an apical flank, a coronal flank and a lateral surface connecting the apical and coronal flanks, the lateral surface defining the radially outermost surface of the threading, the threading extending along the length of the threaded portion in a helical manner and the thread width narrowing in the radially outwards direction such that the threading is widest where it contacts the core and narrows towards the lateral surface, the core diameter of the threaded portion being defined by the outer diameter of the core and the outer diameter of the threaded portion being defined by the lateral surface of the threading, wherein, over at least a section of the axial extent of the threaded portion, the thread profile of the threading is formed of exactly three sub-segments arranged sequentially in the radial direction, wherein in each sub-segment the apical and coronal flank taper towards one another at a constant angle, the middle sub-segment having a taper angle that is greater than the taper angles of the radially innermost and radially outermost sub-segments, the taper angle formed between the apical and coronal flanks in the radially outermost sub-segment being less than 30°.

2. A dental implant as claimed in claim 1, wherein the base thread profile of the threading and the thread width at the core diameter remain constant along the full axial extent of the threaded portion, the base thread profile being formed of said three sub-segments.

3. A dental implant as claimed in claim 1, wherein the core diameter of the threaded portion tapers radially inwards in the apical direction over the full axial length of the threaded portion.

4. A dental implant as claimed in claim 1, wherein the outer diameter of the threaded portion tapers radially inwards in the apical direction along at least the apical half of the threaded portion.

5. A dental implant as claimed in claim 4, wherein the threaded portion comprises an apical section and a main body section, wherein within apical section the taper angle of the outer diameter, relative to the central longitudinal axis, is always greater than 20°, the taper angle of the core diameter relative to the central longitudinal axis being less than the taper angle of the outer diameter at all axial locations of the apical section, such that the thread depth in the apical section continuously decreases in an apical direction, the apical section having an axial length of less than 2 mm, and wherein within the main body section the taper angle of the outer diameter, relative to the central longitudinal axis, is always less than 5°.

6. A dental implant as claimed in claim 5, wherein within the main body section, the width of the lateral surface of the threading is never less than 0.08 mm and never greater than 0.45 mm.

7. A dental implant comprising, a threaded portion extending along a central longitudinal axis from an apical end to a coronal end, the threaded portion comprising a core from which threading extends radially outwards, the threading comprising an apical flank, a coronal flank and a lateral surface connecting the apical and coronal flanks, the lateral surface defining the radially outermost surface of the threading, the threading extending along the length of the threaded portion in a helical manner and the thread width narrowing in the radially outwards direction such that the threading is widest where it contacts the core and narrows towards the lateral surface, the base thread profile of the threading and the thread width at the core remaining constant along the axial extent of the threaded portion, the core diameter of the threaded portion being defined by the outer diameter of the core and the outer diameter of the threaded portion being defined by the lateral surface of the threading, wherein the core diameter of the threaded portion tapers radially inwards in the apical direction along the full axial length of the threaded portion and the outer diameter of the threaded portion tapers radially inwards in the apical direction along at least the apical half of the threaded portion, the threaded portion comprising an apical section and a main body section, wherein, within the apical section, the taper angle of the outer diameter, relative to the central longitudinal axis, is always greater than 20°, the taper angle of the core diameter relative to the central longitudinal axis being less than the taper angle of the outer diameter at all axial locations of the apical section, such that the thread depth in the apical section decreases in an apical direction, the apical section having an axial length of less than 2 mm, and wherein, in the main body section, the taper angle of the outer diameter relative to the central longitudinal axis is always less than 5°, the taper angles of the core diameter and outer diameter within the main body section being such that, over the axial length of the main body section, the depth of the threading varies such that the depth of the threading at the apical end of the main body section is greater than the depth of the threading at the coronal end of the main body section, and the width of the lateral surface of the threading at the apical end of the main body section is less than the width of the lateral surface of the threading at the coronal end of the main body section, wherein the width of the lateral surface of the threading within the main body section is never less than 0.08 mm and never greater than 0.45 mm.

8. A dental implant as claimed in claim 7, wherein the base thread profile of the threading is formed of exactly three sub-segments arranged sequentially in the radial direction, wherein in each sub-segment the apical and coronal flank taper towards one another at a constant angle, the middle sub-segment having a taper angle that is greater than the taper angles of the radially innermost and radially outermost sub-segments, the taper angle formed between the apical and coronal flanks in the radially outermost sub-segment being less than 30°.

9. A dental implant as claimed in claim 7, wherein over at least a section of the axial extent of the main body section the thread profile is formed of exactly three sub-segments arranged sequentially in the radial direction, wherein in each sub-segment the apical and coronal flank taper towards one another at a constant angle, the middle sub-segment having a taper angle that is greater than the taper angles of the radially innermost and radially outermost sub-segments, the taper angle formed between the apical and coronal flanks in the radially outermost sub-segment being less than 30°.

10. A dental implant as claimed in claim 1, wherein the angle between the apical and coronal flank in the radially outermost sub-segment is between 20° and 29° and most preferably between 24° and 26°.

11. A dental implant as claimed in claim 1, wherein the taper angle of the middle sub-segment is at least twice the taper angle of the radially outermost sub-segment.

12. A dental implant as claimed in claim 1, wherein the taper angles of the radially inner and outermost sub-segments are substantially the same.

13. A dental implant as claimed in claim 1, wherein the thread profile of the threading is formed by said three sub-segments over at least one quarter of the axial extent of the threaded portion, most preferably over at least half the axial extent of the threaded portion.

14. A dental implant as claimed in claim 1, wherein the thread profile of the threading is formed by said three sub-segments at an axial location within the apical most half of the threaded portion, more preferably within the apical most quarter of the threaded portion.

15. A dental implant as claimed in claim 5, wherein the thread profile of the threading is formed by said three sub-segments over at least one quarter of the axial extent of the main body section, most preferably over at least half the axial extent of the main body section.

16. A dental implant as claimed in claim 5, wherein the thread profile of the threading is formed by said three sub-segments at an axial location within the apical most half of the main body section, more preferably within the apical most quarter of the main body section.

17. A dental implant as claimed in claim 4, wherein the taper angle of the outer diameter in the main body section is always less than 2.5°

18. A dental implant as claimed in claim 1, wherein the threading comprises a double start thread.

19. A dental implant as claimed in claim 4, wherein in the outer diameter tapers radially inwards over at least the apical half of the main body section.

20. A dental implant as claimed in claim 4, wherein in the outer diameter of the main body section comprises an apical segment, in which the outer diameter tapers radially inward in the apical direction, and a coronal segment, in which the outer diameter has a taper angle of 0° and thus defines a cylindrical surface.

21. A dental implant as claimed in claim 4, wherein within the main body section the core comprises at least two adjacent segments, the core diameter of each segment tapering at a different angle relative to the central longitudinal axis of the threaded portion.

22. A dental implant as claimed in claim 4, wherein in the main body section at every axial location the taper angle of the core diameter is greater than the taper angle of the outer diameter, such that the thread depth in the main body section continuously increases in the apical direction and the width of the lateral surface continuously increases in the coronal direction.

23. A dental implant as claimed in claim 1, wherein the threaded portion comprises, at its coronal end, a thread run out section in which the outer diameter tapers radially inwards in the coronal direction such that, at the coronal end of the run out section, the outer diameter is equal to the core diameter.

24. A dental implant as claimed in claim 1, wherein the threaded portion comprises at least two flutes which extend in a helical manner along the full length of the threaded portion.

25. A dental implant as claimed in claim 24, wherein the cross-section of the flutes within the threading, in a plane perpendicular to the central longitudinal axis, comprises a circular arc and two opposing straight sections located adjacent to the radially outer ends of the circular arc, said straight sections tapering towards one another in the radially outwards direction.

26. A dental implant as claimed in claim 25, wherein said straight sections are present in the threading over 15-100% of the axial length of the main body section, more preferably over at least 50% of the axial length of the main body section.

27. A dental implant as claimed in claim 25, wherein the cross-section of the flutes within at least a portion of the threading comprises a circular arc and, adjacent each end of the circular arc, opposing straight sections which taper towards one another in the radially outwards direction, and, adjacent each straight section, transition surfaces which connect the radially outer ends of the straight sections to the lateral surface of the threading, the lateral surface of the threading having a greater radius than the outer end of the straight sections such that the leading cutting edge of the flute is located radially inward of the lateral surface.

28. A dental implant comprising a threaded portion extending along a central longitudinal axis from an apical end to a coronal end, the threaded portion comprising a core from which threading extends radially outwards, the threading comprising an apical flank, a coronal flank and a lateral surface connecting the apical and coronal flanks, the lateral surface defining the radially outermost surface of the threading, the threading extending along the length of the threaded portion in a helical manner and the thread width narrowing in the radially outwards direction such that the threading is widest where it contacts the core and narrows towards the lateral surface, the core diameter of the threaded portion being defined by the outer diameter of the core and the outer diameter of the threaded portion being defined by the lateral surface of the threading, wherein the threaded portion comprises at least one flute which extends in a helical manner along the full length of the threaded portion, the cross-section of the flute within at least a portion of the threading comprising a circular arc and, adjacent each end of the circular arc, opposing straight sections which taper towards one another in the radially outwards direction, and, adjacent each straight section, transition surfaces which connect the radially outer ends of the straight section to the lateral surface of the threading, the lateral surface of the threading having a greater radius than the outer end of the straight sections such that the leading cutting edge of the flute is located radially inward of the lateral surface.

29. A dental implant as claimed in claim 1, wherein the implant further comprises a neck portion coronal of the threaded portion, the neck portion being circular cylindrical with an external diameter which is less than the maximum outer diameter of the threaded portion.

30. A dental implant as claimed in claim 1, wherein the implant further comprises, coronal of the threaded portion, a head portion arranged to extend, in use, into the soft tissue of a patient.

31. A dental implant as claimed in claim 30, wherein the head portion comprises a flared out section which extends radially outward in the coronal direction, wherein the diameter of the coronal end of the flared out section is greater than the maximum outer diameter of the threaded section.

32. A plurality of dental implants as claimed in claim 1, at least two of the plurality of implants having different maximum outer diameters of threaded portion, within the range from 3 mm-8 mm, and at least two of the plurality of implants having different axial lengths, within the range from 5 mm to 25 mm.

33. A plurality of implants as claimed in claim 32, wherein the pitch of the threading of the threaded section of each implant varies depending on the maximum outer diameter and axial length of the implant, wherein for a given maximum outer diameter of threaded portion, the pitch of the threading in the threaded portion increases with the axial length of the threaded portion and for a given length of threaded portion, the pitch of the threading in the threaded portion increases with the maximum outer diameter of the threaded portion.

Description

[0151] Preferred aspect of the present invention will now be described, by way of example only, in which:

[0152] FIG. 1A shows a dental implant according to a preferred embodiment of the present invention;

[0153] FIG. 1B shows a cross-section through a blank of the dental implant shown in FIG. 1A;

[0154] FIG. 2A shows a dental implant according to a second preferred embodiment of the present invention;

[0155] FIG. 2B shows a cross-section through a blank of the dental implant shown in FIG. 2A;

[0156] FIG. 3A shows a dental implant according to a third preferred embodiment of the present invention;

[0157] FIG. 3B shows a cross-section through a blank of the dental implant shown in FIG. 3A;

[0158] FIG. 4A shows a dental implant according to a fourth preferred embodiment of the present invention;

[0159] FIG. 4B shows a cross-section through a blank of the dental implant shown in FIG. 4A;

[0160] FIG. 5A shows a dental implant according to a fifth preferred embodiment of the present invention;

[0161] FIG. 5B shows a cross-section through a blank of the dental implant shown in FIG. 5A;

[0162] FIG. 6A-B shows thread profiles according to the first aspect of the present invention, which can be applied to each of the implants shown in FIGS. 1A-5A;

[0163] FIG. 7 shows a cross-section of the flute according to the third aspect of the present invention, which can be applied to each of the implants shown in FIGS. 1A-5A.

[0164] Throughout the following description, like features will be referenced with like reference numerals.

[0165] FIGS. 1A, 2A, 3A, 4A and 5A each show a dental implant 100, 200, 300, 400, 500 according to alternative preferred embodiments of the present invention. FIGS. 1B, 2B, 3B, 4B and 5B show cross-sections through the respective blanks 101, 201, 301, 401, 501 of implants 100, 200, 300, 400, 500. These blanks 101, 201, 301, 401, 501 show the shape of the implant prior to machining of the threading of each implant, and thus provide a clear indication of the outer diameter formed by the lateral surface of the threading.

[0166] Each of implants 100, 200, 300, 400, 500 comprises a threaded portion 110, 210, 310, 410, 510 which extends along a central longitudinal axis L from an apical end 102, 202, 302, 402, 502 to a coronal end 103, 203, 303, 403, 503. The threaded portions 110, 210, 310, 410, 510 each comprise a core 104, 204, 304, 404, 504, from which threading 105, 205, 305, 405, 505 extends radially outwards. The threading 105, 205, 305, 405, 505 comprises an apical flank 106, 206, 306, 406, 506, a coronal flank 107, 207, 307, 407, 507 and a lateral surface 108, 208, 308, 408, 508 connecting the apical and coronal flanks, the lateral surface 108, 208, 308, 408, 508 defining the radially outermost surface of the threading 105, 205, 305, 405, 505. The threading 105, 205, 305, 405, 505 extends along the full length of the threaded portion 110, 210, 310, 410, 510 in a helical manner and, as can be seen in each of FIGS. 1A-5A, the thread width narrows in the radially outwards direction such that the threading is widest where it contacts the core and narrows towards the lateral surface 108, 208, 308, 408, 508. In each of the implants 100, 200, 300, 400, 500 the threading 105, 205, 305, 405, 505 is a double start thread.

[0167] The core diameter D.sub.C of the threaded portions 110, 210, 310, 410, 510 is defined by the outer diameter of the core 104, 204, 304, 404, 504 and the outer diameter D.sub.O of the threaded portions 110, 210, 310, 410, 510 is defined by the lateral surface 108, 208, 308, 408, 508 of the threading 105, 205, 305, 405, 505. The outer diameter D.sub.O of the threaded portion 110, 210, 310, 410, 510 can be visualised by drawing two axially extending lines on either side of the implant, each line contacting and extending along the lateral surface 108, 208, 308, 408, 508 of the threading 105, 205, 305, 405, 505, the diameter at any given axial location of the threaded portion being given by the distance between these lines.

[0168] Alternatively the outer diameter can be clearly seen in FIGS. 1B-5B. In the blanks 101, 201, 301, 401, 501 the threading 105, 205, 305, 405, 505 has not yet been machined and therefore the lateral surface 108, 208, 308, 408, 508 extends over the full length of the threaded portion 110, 210, 310, 410, 510. After milling of the threading 105, 205, 305, 405, 505 only sections of this lateral surface 108, 208, 308, 408, 508 will remain, but this surface still defines the outer diameter D.sub.O.

[0169] For simplicity the core diameter D.sub.C and outer diameter D.sub.O have only been indicated in FIG. 4A, and in respect of the outer diameter D.sub.O also in FIG. 4B. However the core and outer diameters D.sub.C, D.sub.O of implants 100, 200, 300, 500 are obtained in an identical manner.

[0170] It should be noted that the core diameter D.sub.C is not shown in the blanks 101, 201, 301, 401, 501, as the left hand half of these cross-sections shows the depth of the flute, and not the core, as will be discussed further below.

[0171] As will be appreciated, particularly by viewing the blanks 101, 201, 301, 401, 501, in each of the preferred embodiments shown the thread depth D.sub.T varies over the axial length of the threaded portion 110, 210, 310, 410, 510. At any given axial location within the threaded portion 110, 210, 310, 410, 510, the thread depth D.sub.T is given by the difference in radial length between the outer surface of core 104, 204, 304, 404, 504 and the lateral surface 108, 208, 308, 408, 508. Once again this dimension is indicated only in FIG. 4B for simplicity.

[0172] As the thread width of threading 105, 205, 305, 405, 505 narrows in the radially outwards direction, this change in the thread depth D.sub.T within the threaded portion 110, 210, 310, 410, 510 will affect the width of the lateral surface 108, 208, 308, 408, 508 along the length of the threaded portion 110, 210, 310, 410, 510, as is clearly seen in each of FIGS. 1A-5A.

[0173] The change in core diameter D.sub.C in each of implants 100, 200, 300, 400, 500 is shown in FIGS. 1B-5B respectively by lines 109, 209, 309, 409, 509, while the change in outer diameter D.sub.O is indicated by lines 111, 211, 311, 411, 511.

[0174] In each of the described preferred embodiments, the threaded portion 110, 210, 310, 410, 510 comprises an apical section 115, 215, 315, 415, 515 and a main body section 120, 220, 320, 420, 520.

[0175] Within the apical section 115, 215, 315, 415, 515 the taper angle of the outer diameter, relative to the central longitudinal axis L, is always greater than 20°, the taper angle of the core diameter relative to the central longitudinal axis being less than the taper angle of the outer diameter at all axial locations of the apical section, such that the thread depth D.sub.T in the apical section 115, 215, 315, 415, 515 decreases in an apical direction. In the preferred embodiments the apical section 115, 215, 315, 415, 515 have an axial length of less than 1.6 mm.

[0176] The apical sections 115, 215, 315, 415, 515 each comprise two adjoining segments 216, 217 each segment 216, 217 having an outer diameter that tapers at a constant angle relative to the longitudinal axis L of the threaded portion 110, 210, 310, 410, 510. The outer diameter of the apical most segment 216 having a greater taper angle, as measured from the central longitudinal axis L, than the outer diameter of the coronal most segment 217. For simplicity these segments 216, 217 of the apical section 115, 215, 315, 415, 515 are indicated only in FIG. 2B, however these segments are also present in each of implants 100, 300, 400, 500. Having a greater taper angle in the apical most segment 216 causes the thread depth to very quickly increase in the coronal direction before increasing at a gentler amount, thus creating a more rounded apical section 115, 215, 315, 415, 515.

[0177] In each of the described preferred embodiments, the taper angle of the outer diameter of the apical most segment 216 is approximately 60°, while the taper angle of outer diameter of the coronal most segment 217 is between 28° and 48°. As can be seen from a comparison of FIGS. 1B and 2B for example, the taper angle of the coronal most segment 217 varies depending on the outer diameter D.sub.O of the of the threaded portion 110, 210, 310, 410, 510 at the coronal end of the apical section 115, 215, 315, 415, 515. The larger the outer diameter D.sub.O, the greater the taper angle within the coronal most segment 217.

[0178] In the main body section 120, 220, 320, 420, 520 the taper angle of the outer diameter relative to the central longitudinal axis is always less than 5°.

[0179] By limiting the taper angle in this way, the outer diameter D.sub.O of the main body section 120, 220, 320, 420, 520 increases only very gradually in the coronal direction, thus controlling the torque required during insertion of the implant 100, 200, 300, 400, 500 into hard bone. In addition, having a low taper angle in the main body section 120, 220, 320, 420, 520 increases primary stability as, for a given diameter of bore hole, a larger number of thread peaks can cut into the bore wall.

[0180] It is possible for the outer diameter D.sub.O to taper along the full axial length of the main body section 120, 220, 320, 420, 520, at either a constant taper angle or varying taper angles. However, in each of the preferred embodiments shown, the outer diameter of the main body section 120, 220, 320, 420, 520 comprises an apical segment 121 in which the outer diameter tapers radially inward in the apical direction with a taper angle of less than 2.5°, and a coronal segment 122, in which the outer diameter D.sub.O has a taper angle of 0°, thus defining a cylindrical surface in the coronal most part of the main body section 120, 220, 320, 420, 520. For simplicity these segments 121, 122 of the main body section 120, 220, 320, 420, 520 are indicated only in FIG. 1B, however these segments are also present in each of implants 200, 300, 400, 500.

[0181] In each of the shown embodiments, the axial length of coronal segment 122 is approximately 2 mm. The taper angle of the apical segment 121 is less than 1° in implants 100, 300, 400, 500 and less than 1.5° in implant 200.

[0182] While this taper angle is small, in order to control insertion torque and increase primary stability, the slight increase in outer diameter D.sub.O over the apical segment 121 helps to compress soft bone in the radial direction when the implant 100, 200, 300, 400, 500 is inserted into soft bone.

[0183] In each of the shown preferred embodiments, the core diameter D.sub.C of the threaded portion 110, 210, 310, 410, 510 tapers radially inwards in the apical direction over the full axial length of the threaded portion, as shown by lines 109, 209, 309, 409, 509. The fully tapered nature of the core diameter D.sub.C enables the implant 100, 200, 300, 400, 500 to compress soft bone along the full axial extent of the threaded portion 110, 210, 310, 410, 510 when placed in an underprepared bore hole, that is, a bore hole having a diameter less than the core diameter D.sub.C of the threaded portion 110, 210, 310, 410, 510. As the implant is inserted into the bone, the gradually increasing diameter of the core 109, 209, 309, 409, 509 compresses the soft bone in the radial direction around the threaded portion 110, 210, 310, 410, 510 of the implant 100, 200, 300, 400, 500.

[0184] As discussed above, while compression of soft bone is desirable in order to increase primary stability, when the implant is inserted into hard bone compression of the bone is not desirable and/or not possible. Therefore, when inserting the implant 100, 200, 300, 400, 500 into hard bone, the surgeon creates a bore hole having a diameter greater than the maximum diameter of the core diameter D.sub.C, such that the core will not compress the hard bone during insertion. As discussed above, the taper angle of the main body section 120, 220, 320, 420, 520 is less than 2.5° in each of the shown embodiments in order to control the insertion torque when inserting the implant 100, 200, 300, 400, 500 into hard bone. In addition, in each of the preferred embodiments the thread profile of the threading 105, 205, 305, 405, 505 is shaped to assist insertion of the implant into hard bone, as will be discussed further below, in relation to FIGS. 6A and 6B.

[0185] While the core diameter D.sub.C of the threaded portion 110, 210, 310, 410, 510 of each implant 100, 200, 300, 400, 500 tapers continuously over the full axial extent of the threaded portion 110, 210, 310, 410, 510, the taper angle is not constant.

[0186] In particular, within the main body section 120, 220, 320, 420, 520 the core 104, 204, 304, 404, 504 comprises at least two adjacent segments, 223, 224, 225 the core diameter D.sub.C of each segment tapering at a different angle, α.sub.1, α.sub.2, α.sub.3, relative to the central longitudinal axis L of the threaded portion. In some embodiments, such as implant 200, the main body section 220 comprises exactly three core segments 223, 224, 225. In such embodiments the taper angles α.sub.1, α.sub.2, α.sub.3 preferably increase sequentially in the coronal direction. In other embodiments, such as implant 300, the main body section 320 comprises exactly four core segments 323, 324, 325, 326. In such embodiments, the taper angles α.sub.1, α.sub.2, α.sub.3, α.sub.4, preferably do not increase sequentially.

[0187] Instead one segment 325 is bordered in both the apical and coronal directions by a core segment 326, 324 having a smaller taper angle. In such embodiments therefore the rate of increase of the core diameter D.sub.C increases and then decreases in the coronal direction. In other embodiments, such as implant 500, the main body section 520 comprises exactly two core segments 523, 524.

[0188] For simplicity the core segments of implants 100 and 400 are not shown, however, the main body section 120, 420 each comprise four core segments 123, 124, 125, 126, 423, 424, 425, 426 having different taper angles α relative to the central longitudinal axis L

[0189] The core segments 123-126, 223-225, 323-326, 423-426, 523, 524 are used in conjunction with the outer diameter D.sub.O of the threaded portion 120, 220, 320, 420, 520 in order to control the width of the lateral surface 108, 208, 308, 408, 508 of the threading 105, 205, 305, 405, 505 within the main body section 120, 220, 320, 420, 520. In each of the shown embodiments, the width of the lateral surface W.sub.L, shown for simplicity only in FIG. 3A, of the threading 105, 205, 305, 405, 505 within the main body section 120, 220, 320, 420, 520 is never less than 0.08 mm and never greater than 0.45 mm.

[0190] These upper and lower limits on the width of the lateral surface W.sub.L prevent this surface from becoming too narrow (which could result in fracture or distortion of the apical parts of the thread) or too broad (which could lose the cutting function of the thread and increase the insertion torque within hard bone to unacceptable levels). These upper and lower limits on the width of the lateral surface W.sub.L therefore improve the ability of the implants 100, 200, 300, 400, 500 to self tap into hard bone while maintaining insertion torque within acceptable levels.

[0191] As mentioned above, the width of the threading 105, 205, 305, 405, 505 of each implant 100, 200, 300, 400, 500 tapers in the radially outwards direction, such that the threading 105, 205, 305, 405, 505 is widest where it contacts the core 104, 204, 304, 404, 504 and narrows towards the lateral surface 108, 208, 308, 408, 508.

[0192] In each of the shown preferred embodiments, the base thread profile of the threading and the thread width at the core remain constant along the axial extent of the threaded portion 110, 210, 310, 410, 510. This means that the the shape of the apical 106, 206, 306, 406, 506 and coronal 107, 207, 307, 407, 507 flanks remain constant along the axial extent of the threaded portion 120, 220, 320, 420, 520, such that changes in the width W.sub.L of the lateral surface 108, 208, 308, 408, 508 are the results of changes in the thread depth D.sub.T along the threaded portion 110, 210, 310, 410, 510.

[0193] FIGS. 6A and 6B show the examples of thread profiles according to the first aspect of the present invention, both of which can be used as the base thread profile for the threading 105, 205, 305, 405, 505 of implants 100, 200, 300, 400, 500.

[0194] FIGS. 6A and 6B each show a thread profile 600, 610 formed of exactly three sub-segments 601-603, 611-613 arranged sequentially in the radial direction, wherein in each sub-segment the apical 606, 616 and coronal 607, 617 flank taper towards one another at a constant angle β, the middle sub-segment 602, 612 having a taper angle β.sub.2 that is greater than the taper angles β.sub.1, β.sub.3 of the radially innermost 601, 611 and radially outermost 603, 613 sub-segments, the taper angle formed between the apical 606, 616 and coronal 607, 617 flanks in the radially outermost sub-segment 603, 613 being less than 30°.

[0195] The angles β.sub.1, β.sub.2, β.sub.3 are shown in FIG. 6B as half angles.

[0196] In these preferred embodiments, the taper angles β.sub.1, β.sub.3 of the radially innermost 601, 611 and radially outermost 603, 613 sub-segments are substantially the same and approximately 25°. The taper angle β.sub.2 of the middle sub-segment 602, 612 is over twice that of the radially outmost 603, 613 sub-segment at approximately 60°.

[0197] The thread profiles of FIGS. 6A and 6B are formed exclusively by the three sub-segments 601-603, 611-613 described, to the extent possible by manufacturing techniques. Therefore in both profiles a small curved transition R is necessitated between the core 604, 614 and the radially innermost sub-segment 601, 611. Therefore, the radially innermost sub-segment 601, 611 effectively begins at the core diameter and the radially outermost sub-segment 603, 613 ends at the lateral surface of the threading, with no intervening additional sub-segments positioned between the three sub-segments.

[0198] The thread profile of FIGS. 6A and 6B has benefits during insertion into both hard and soft bone. The narrow angle β.sub.3 of the radially outermost sub-segment 603, 613 provides a good cutting ability, which is particularly important when the implant is inserted into hard bone. The provision of the middle sub-segment 602, 612 widens the thread at location radially inwards of the sharp cutting angle of the radially outmost sub-segment 603, 613, thus strengthening the thread as well as providing a greater axial compression of soft bone when the implant is inserted into an underprepared bore hole. The radially innermost sub-segment 601, 611 of the thread profile has a taper angle β.sub.1 less than that of the middle sub-segment 602, 612, resulting in a better cutting function.

[0199] The thread profile shown in FIGS. 6A and 6B differ from one another in the relative radial lengths of the sub-segments 601-603, 611-613 and in the width of the thread at the core 604, 614. It can be seen for example that the middle sub-segment 612 has a greater radial length than middle sub-segment 602, resulting in a greater increase in thread width. The thread width, relative radial lengths and taper angles of the sub-segments can be adjusted depending on the implant with which the thread profile is intended to be used.

[0200] The base thread profile of the threading 105, 205, 305, 405, 505 of implants 100, 200, 300, 400, 500 can be formed by the three sub-segments 601-603, 611-613 described in relation to FIG. 6A or 6B.

[0201] Because the thread depth D.sub.T of the threading 105, 205, 305, 405, 505 varies along the axial extent of the threaded portion 110, 210, 310, 410, 510, the radially outermost sub-segment 603, 613, and even the middle sub-segment 602, 612, may not be present along the full axial length of the main body section 120, 220, 320, 420, 520.

[0202] However, as can be seen in FIGS. 1A-5A, the radially outermost sub-segment 603, 613 is present at least at the apical most part of the main body section 120, 220, 320, 420, 520 and is present along varying axial extents of the main body section 120, 220, 320, 420, 520. This is beneficial as it enables the radially outermost sub-segment 603, 613, with its enhanced cutting function, to be present in an apically located part of the threaded portion 110, 210, 310, 410, 510.

[0203] As the implants 100, 200, 300, 400, 500 of the shown preferred embodiments are driven into dense bone, the threading 105, 205, 305, 405, 505 initially cuts a groove into the bone corresponding to the thread shape at the apical end of the threaded portion 110, 210, 310, 410, 510. As described above, the thread depth D.sub.T in the apical section 115, 215, 315, 415, 515 of the threaded portion 120, 220, 320, 420, 520 increases rapidly in order to enable the threading 105, 205, 305, 405, 505 to cut into the bone. As the radially outermost sub-segment 603, 613 is located in the apical part of the main body section 120, 220, 320, 420, 520, this provides an enhanced cutting action, which is particularly beneficial in hard bone. As described above, the middle sub-segment 602, 612 strengthens the threading 105, 205, 305, 405, 505 and increases the compression provided to soft bone in under-prepared bore holes. As the implant 100, 200, 300, 400, 500 is driven further into the bone, the initial groove formed by the threading 105, 205, 305, 405, 505 is gradually widened in both the axial direction, as the lateral surface 108, 208, 308, 408, 508 widens, and radial direction, as the outer diameter D.sub.O increases. In this way, the groove within the bone is formed incrementally, ensuring that the insertion torque is not too great while at the same time providing a firm fixation within the bone. Furthermore, as the lateral surface width W.sub.L of the threading 105, 205, 305, 405, 505 within the main body section 120, 220, 320, 420, 520 is maintained with the range of 0.08-0.45 mm, this prevents the lateral surface 108, 208, 308, 408, 508 from becoming too narrow (which could result in fracture or distortion of the apical parts of the thread) or too broad (which could lose the cutting function of the thread and increase the insertion torque within hard bone to unacceptable levels).

[0204] The implants 100, 200, 300, 400, 500 of the shown preferred embodiments further comprise at least 2 flutes 700. Implant 200 comprises four flutes 700. The flutes 700 extend in a helical manner along the full length of the threaded portion 110, 210, 310, 410, 510. In this way cutting edges are provided along the full length of the threaded portion 110, 210, 310, 410, 510. The helical nature of the flutes 700 enables bone chips to be transported and distributed along the length of the threaded portion 110, 210, 310, 410, 510.

[0205] The flutes 700 extend into the core 104, 204, 304, 404, 504 of the threaded portion 110, 210, 310, 410, 510. This is shown by line 190, 290, 390, 490, 590 respectively in FIGS. 1B-5B. This line 190, 290, 390, 490, 590 shows the depth of the flute 700 along the axial extent of the threaded portion 120, 220, 320, 420, 520. By comparing this line 190, 290, 390, 490, 590 to the line 109, 209, 309, 409, 509 indicting the core diameter D.sub.C, it can be seen that the flute 700 always extends into the core 104, 204, 304, 404, 504. In this way each flute forms a continuous channel over the length of the threaded section 120, 220, 320, 420, 520 for bone chip transport.

[0206] In each of the implants 100, 200, 300, 400, 500, the cross-section of the flute 700, at least in a portion of the threading 105, 205, 305, 405, 505, is shown in FIG. 7.

[0207] As shown in this figure, the cross-section of the flute 700 within at least a portion of the threading 705 comprises a circular arc 701 and, adjacent each end of the circular arc 701, opposing straight sections 702 which taper towards one another in the radially outwards direction, and, adjacent each straight section 702, transition surfaces 703 which connect the radially outer ends of the straight sections 702 to the lateral surface 708 of the threading 705, the lateral surface 708 of the threading having a greater radius than the outer end 702a of the straight sections 702 such that the leading cutting edge of the flute is located radially inward of the lateral surface 708.

[0208] As discussed in more detail above, the straight sections 702 form undercuts in the thread, which creates a more aggressive cutting edge. The fact that the flute 700 comprises straight sections on both sides means that the flute 700 provides the same cutting ability regardless of the direction of rotation of the implant. This is beneficial for exact placement of the implant.

[0209] The transition surfaces 703, when brought into contact with soft bone, guide and compress the bone radially outwards. Therefore, rather than this bone being cut away by the sharp cutting edge of the flute 700, it instead forms part of the bone mass which is compressed around the implant, improving primary stability. When inserted into hard bone however, this bone will not compress and hence is contacted and cut by the leading edge 702a within the flute 700.

[0210] In each of the shown embodiments, the thread depth D.sub.T generally decreases in the coronal direction along the main body section 120, 220, 320, 420, 520 of the threaded portion 110, 210, 310, 410, 510. Therefore, depending on the length of the straight sections 702, the undercut may not be present along the full length of the threading 105, 205, 305, 405, 505.

[0211] However, the above described straight sections 702 of the flute 700 are present in the apical part of the main body section 120, 220, 320, 420, 520. It is the apical part of the threaded section 110, 210, 310, 410, 510 which will need to have the greatest cutting ability and therefore it is this area of the implant which benefits most from the inclusion of the flute undercut.

[0212] The straight sections 702 and transition surface 703 of the flute 700 enhances the ability of the threading 105, 205, 305, 405, 505 to cut into hard bone while assisting in the compression of soft bone.

[0213] The threaded portion 120, 220, 320, 420, 520 of each implant further comprises, at its coronal end 103, 203, 303, 403, 503, a thread run out section 130, 230, 330, 430, 530, in which the outer diameter D.sub.O tapers radially inwards in the coronal direction such that, at the coronal end of the run out section, the outer diameter D.sub.O is equal to the core diameter D.sub.C. This run out section 130, 230, 330, 430, 530 is as short as possible and in each embodiment has an axial length of less than 1 mm.

[0214] The threaded portions 120, 220, 320, 420, 520 described above can be used in one-part and two part implants.

[0215] In each of the embodiments of FIG. 1A-5A the implant 100, 200, 300, 400, 500 is the anchoring part of a two part implant, wherein the implant as a whole extends along the central longitudinal axis L of the threaded portion 120, 220, 320, 420, 520.

[0216] Implants 100 and 200 are bone level implants, whereas implants 300, 400 and 500 are tissue level implants.

[0217] Each implant 100, 200, 300, 400, 500 comprises a neck portion 140, 240, 340, 440, 540 coronal of the threaded portion 120, 220, 320, 420, 520. For simplicity the neck portion 140, 240, 340, 440, 540 will only be described in detail in relation to FIG. 1A, however all elements of the neck portion 140 described below are also present in neck portions 240, 340, 440, 540.

[0218] The neck portion 140 is circular cylindrical with an external diameter D.sub.E (see FIG. 1B) which is less than the maximum outer diameter D.sub.O of the threaded portion 120, 220, 320, 420, 520. the neck portion 140, 240, 340, 440, 540 comprises two axially arranged, adjacent sections 141, 142. The apical neck section 141, which lies directly adjacent to the coronal end of the threaded portion 120 comprises a helical micro-thread 143 include a flute 144.

[0219] The coronal neck section 142, in contrast to the apical neck section 141, does not comprise any grooves or threading. This section is therefore smoother than the apical neck section 141.

[0220] In addition to the neck portion 340, 440, 540, implants 300, 400, 500 further comprise a head portion 350, 450, 550 arranged to extend, in use, into the soft tissue of a patient.

[0221] In each case the diameter of the apical end of the head portion 350, 450, 550 is equal to the diameter of the coronal end of the neck portion 340, 440, 540 such that the neck portion smoothly transitions into the head portion.

[0222] In FIGS. 3A and 3B the head portion 350 is circular cylindrical, while in FIGS. 4A, 4B, 5A, 5B the head portion 450, 550 comprises a flared out section which extends radially outward in the coronal direction, wherein the diameter of the coronal end of the flared out section is greater than the maximum outer diameter D.sub.O of the threaded section 120, 220, 320, 420, 520.

[0223] In the embodiment of FIGS. 4A-B the flared out section tapers radially outwards in the coronal direction over a radius R.sub.I, thus creating a curved longitudinal cross-section.

[0224] In the embodiment of FIG. 5A-b the flared out section comprises both a curved and a straight, tapered cross-section, the apical end of the flared out section tapering radially outwards over a radius R.sub.2 before continuing to flare outwards in a conical manner; namely, with a straight, tapered cross-section 551.

[0225] In each of the described embodiments the implant 100, 200, 300, 400, 500 comprises at its coronal end a beveled part 160, 260, 360, 460, 560 which tapers radially inwards in the coronal direction to form a truncated cone and a flat shoulder 170, 270, 370, 470, 570 which defines the coronal end of the dental implant 100, 200, 300, 400, 500.

[0226] As implants 100, 200, 300, 400, 500 are two-part implants these comprise standard abutment connection geometry which will be described briefly in relation to FIG. 3B, this description being valid for all of implants 100, 200, 300, 400, 500. The implant 300 comprises a blind bore 380 extending from the coronal end 370 of the implant along the central longitudinal axis L of the threaded portion, the blind bore 380 comprising an anti-rotation means 381 having a non-circular-symmetric cross-section in a plane perpendicular to the central longitudinal axis L and, apical of said anti-rotation means, a threaded section 382. The blind bore 380 further comprises, coronal of the anti-rotation means 381, a conical portion 383 tapering radially outwards in the coronal direction. Such a tapered portion 383 can form a secure seal with a complementary shaped abutment, thus preventing bacteria from entering the implant 100, 200, 300, 400, 500.

[0227] The above described embodiments are for illustrative purposes only and the skilled person will realize that alternative arrangements are possible which fall within the scope of the claims. For example, the threaded portion can be used with one-part implants or two part implants comprising alternative implant connection geometries, neck portions and head portions.