Dental drill guiding system

Abstract

A dental drill guiding system includes a drill guide including a hollow tube having an exterior surface and a guide sleeve including an internal surface defining a through bore configured to receive the hollow tube of the drill guide. The exterior surface of the hollow tube and guide sleeve's internal surface have complementary anti-rotation sections. The drill guide's hollow tube further includes at least one radially extending protrusion limited in the axial extent and formed by an increase in radius of the hollow tube in the apical direction and dimensioned for accommodation in at least one undercut of the guide sleeve, such that when at least one protrusion of the hollow tube is housed in at least one undercut of the guide sleeve the hollow tube is axially retained within the guide sleeve such that removal of the drill guide from the guide sleeve in the coronal direction is prevented.

Claims

1. A dental drill guiding system for use in dental implant surgery, the system comprising a drill guide and a guide sleeve, the guide sleeve of the dental drill guiding system comprising: an internal surface defining a through bore extending along a central longitudinal axis of the guide sleeve from a coronal end of the guide sleeve to an apical end of the guide sleeve, the internal surface of the guide sleeve comprising: an anti-rotation section having a non-circular cross-section in a plane perpendicular to the central longitudinal axis of the guide sleeve, and at least one radially extending undercut formed by an increase in a radius of the through bore in an apical direction towards the apical end, and the drill guide of the dental drill guiding system comprising: a handle for gripping by a surgeon, and a hollow tube sized for insertion into the coronal end of the through bore of the guide sleeve in the apical direction and having an exterior surface and an interior surface, the interior surface defining a through hole extending along a central longitudinal axis of the hollow tube from a coronal end of the hollow tube to an apical end of the hollow tube, the through hole being configured to receive and guide a dental drill, the coronal end of the hollow tube being connected to the handle, the exterior surface of the hollow tube comprising: an anti-rotation section having a non-circular cross-section in a plane perpendicular to the central longitudinal axis of the hollow tube, the anti-rotation section of the hollow tube being complementary to the anti-rotation section of the guide sleeve, such that when the anti-rotation section of the hollow tube is inserted into the anti-rotation section of the guide sleeve, the hollow tube is rotationally fixed relative to the guide sleeve, and at least one radially extending first protrusion limited in an axial extent and formed by an increase in a radius of the exterior surface of the hollow tube in the apical direction, the at least one radially extending first protrusion being dimensioned for accommodation in the at least one radially extending undercut of the guide sleeve, such that when the at least one radially extending first protrusion of the hollow tube is housed in the at least one radially extending undercut of the guide sleeve, the hollow tube is axially retained within the guide sleeve against movement in a coronal direction towards the coronal end of the guide sleeve, wherein the drill guide is monolithic.

2. The dental drill guiding system of claim 1, wherein the anti-rotation section of one of the hollow tube and the guide sleeve comprises a plurality of radially extending second protrusions limited in a circumferential extent and spaced about the central longitudinal axis, and the anti-rotation section of the other of the hollow tube and the guide sleeve comprises a plurality of radially extending grooves limited in a circumferential extent and spaced about the central longitudinal axis, the plurality of radially extending second protrusions being dimensioned to fit within the plurality of radially extending grooves in a rotationally fixed manner.

3. The dental drill guiding system of claim 2, wherein the plurality of radially extending second protrusions are evenly spaced about the central longitudinal axis and/or the plurality of radially extending grooves are evenly spaced about the central longitudinal axis, and the plurality of radially extending second protrusions are identical and the plurality of radially extending grooves are identical.

4. The dental drill guiding system of claim 2, wherein a cross-section of the plurality of radially extending grooves and the plurality of radially extending second protrusions, in a plane perpendicular to the central longitudinal axis, are fully curved.

5. The dental drill guiding system of claim 1, wherein the at least one radially extending first protrusion of the hollow tube comprises a single radially extending annular protrusion which is limited in the axial extent and extends about a full circumference of the hollow tube in a plane perpendicular to the central longitudinal axis.

6. The dental drill guiding system of claim 1, wherein the at least one radially extending first protrusion is located apical of the anti-rotation section of the hollow tube.

7. The dental drill guiding system as claimed in claim 6, wherein a radius of the at least one radially extending first protrusion is less than a maximum radius of the anti-rotation section of the hollow tube.

8. The dental drill guiding system of claim 1, wherein the anti-rotation section of the guide sleeve extends from the coronal end to the apical end of the guide sleeve, the at least one radially extending undercut of the guide sleeve being formed in the anti-rotation section at a location apical of a coronal end of the anti-rotation section, the at least one radially extending undercut having a radius greater than a minimum radius but less than a maximum radius of the anti-rotation section of the guide sleeve.

9. The dental drill guiding system of claim 8, wherein the at least one radially extending undercut is a plurality of undercuts that are circumferentially spaced, each undercut of the plurality of undercuts having a radius less than the maximum radius and greater than the minimum radius of the anti-rotation section of the guide sleeve, the plurality of undercuts being dimensioned such that, at the location of the plurality of undercuts, all areas of the anti-rotation section having a radius less than the radius of the plurality of undercuts are removed, the plurality of undercuts being interposed by areas of anti-rotation section having a greater radius than the plurality of undercuts.

10. The dental drill guiding system of claim 1, wherein the at least one radially extending undercut of the guide sleeve is open ended in the apical direction.

11. A drill guide comprising: a handle for gripping by a surgeon, and a hollow tube having an exterior surface and an interior surface, the interior surface defining a through hole extending along a central longitudinal axis from a coronal end of the hollow tube to an apical end of the hollow tube, the through hole of the drill guide being configured to receive and guide a dental drill, the coronal end of the hollow tube being connected to the handle, the exterior surface of the hollow tube comprising: at least one radially extending first protrusion limited in an axial extent and formed by an increase in a radius of the exterior surface of the hollow tube in an apical direction towards the apical end, and an anti-rotation section comprising a plurality of radially extending second protrusions limited in a circumferential extent and spaced about the central longitudinal axis, wherein: said at least one radially extending first protrusion is located apical of said anti-rotation section, and wherein the drill guide is monolithic.

12. The drill guide as claimed in claim 11, wherein the plurality of radially extending second protrusions are evenly spaced about the central longitudinal axis, and the plurality of radially extending second protrusions are identical.

13. The drill guide as claimed in claim 11, wherein the at least one radially extending first protrusion of the hollow tube comprises a single radially extending annular protrusion which is limited in the axial extent and extends about a full circumference of the hollow tube in a plane perpendicular to the central longitudinal axis.

14. The drill guide as claimed in claim 11, wherein the at least one radially extending first protrusion is separated from the anti-rotation section of the hollow tube by a portion of the exterior surface of the hollow tube, said portion having a radius less than a maximum radius of the anti-rotation section of the hollow tube.

15. The drill guide as claimed in claim 11, wherein a radius of the at least one radially extending first protrusion is less than a maximum radius of the anti-rotation section of the hollow tube.

16. A combination of the drill guide as claimed in claim 11 and a guide sleeve, the guide sleeve being one of a first guide sleeve and a second guide sleeve, the first guide sleeve comprising: an internal surface defining a through bore extending along a central longitudinal axis from a coronal end of the first guide sleeve to an apical end of the first guide sleeve, the internal surface of the first guide sleeve comprising an anti-rotation section comprising a plurality of radially extending grooves limited in a circumferential extent and spaced about the central longitudinal axis of the first guide sleeve, and at least one undercut formed by an increase in a radius of the through bore in an apical direction towards the apical end, the at least one undercut being located apical of a coronal end of the anti-rotation section, a radius of said at least one undercut being greater than a minimum radius of the anti-rotation section, the second guide sleeve comprising an internal surface defining a through bore extending along a central longitudinal axis of the second guide sleeve from a coronal end of the second guide sleeve to an apical end of the second guide sleeve, the apical end of the second guide sleeve comprising a radially extending, apically facing end surface, the internal surface of the second guide sleeve comprising an anti-rotation section having a non-circular cross-section in a plane perpendicular to the central longitudinal axis of the second guide sleeve, the anti-rotation section of the hollow tube being complementary to the anti-rotation section of the guide sleeve, such that when the anti-rotation section of the hollow tube is inserted into the anti-rotation section of the guide sleeve, the hollow tube is rotationally fixed relative to the guide sleeve, and the at least one radially extending first protrusion of the hollow tube being dimensioned for engagement with one of the radially extending, apically facing end surface of the second guide sleeve and the at least one undercut of the first guide sleeve, such that when the at least one radially extending first protrusion of the hollow tube is located apical of said radially extending, apically facing end surface or housed in said at least one undercut, the hollow tube is axially retained within the guide sleeve against movement in a coronal direction towards the coronal end of the guide sleeve.

17. A guide sleeve comprising: an internal surface defining a through bore extending along a central longitudinal axis from a coronal end of the guide sleeve to an apical end of the guide sleeve, the internal surface of the guide sleeve comprising: an anti-rotation section comprising a plurality of radially extending grooves limited in a circumferential extent and spaced about the central longitudinal axis of the guide sleeve, and at least one undercut formed by an increase in a radius of the through bore in an apical direction towards the apical end, the at least one undercut being at a location apical of a coronal end of the anti-rotation section, a radius of said at least one undercut being greater than a minimum radius of the anti-rotation section, and less than a radius of an outer surface of the guide sleeve at a location of the at least one undercut.

18. The guide sleeve as claimed in claim 17, wherein the plurality of radially extending grooves are evenly spaced about the central longitudinal axis, and the plurality of radially extending grooves are identical.

19. The guide sleeve as claimed in claim 17, wherein the anti-rotation section of the guide sleeve extends from the coronal end to the apical end of the guide sleeve, the at least one undercut of the guide sleeve being formed in the anti-rotation section at a location apical of the coronal end of the anti-rotation section, the radius of the at least one undercut being greater than the minimum radius but less than a maximum radius of the anti-rotation section of the guide sleeve.

20. The guide sleeve as claimed in claim 19, wherein the at least one undercut is a plurality of undercuts that are circumferentially spaced, each undercut of the plurality of undercuts having a radius less than the maximum radius and greater than the minimum radius of the anti-rotation section of the guide sleeve, the plurality of undercuts being dimensioned such that, at the location of the plurality of undercuts, all areas of the anti-rotation section having a radius less than the radius of the plurality of undercuts are removed, the plurality of undercuts being interposed by areas of anti-rotation section having a greater radius than the plurality of undercuts.

21. The guide sleeve according to claim 17, wherein the at least one undercut is formed in a wall of the guide sleeve on a radially inner side, and the at least one undercut does not penetrate entirely through the wall of the guide sleeve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain preferred embodiments of the present invention shall now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows an example of a standard dental surgical template;

(3) FIG. 2A shows a guide sleeve according to an embodiment of the present invention and its insertion into the template of FIG. 1;

(4) FIG. 2B shows an alternative dental surgical template in which a preferred embodiment of the guide sleeve of the present invention is integrally formed;

(5) FIG. 3A illustrates the use of a dental drill guide according to a preferred embodiment of the present invention with the guide sleeve and template shown in FIG. 2A;

(6) FIG. 3B illustrates the use of a dental drill guide according to a preferred embodiment of the present invention with the template shown in FIG. 2B;

(7) FIG. 4 illustrates a dental drill guide of a particularly preferred embodiment of the invention;

(8) FIG. 5A shows a front view of one of the hollow tubes of the dental drill guide of FIG. 4;

(9) FIG. 5B shows detail Y of FIG. 5A;

(10) FIG. 5C shows detail X of FIG. 5A;

(11) FIG. 5D shows cross-section A-A of FIG. 5A;

(12) FIG. 5E shows sectional view B-B of FIG. 5A;

(13) FIG. 6A shows a perspective view of a guide sleeve of a preferred embodiment of the present invention;

(14) FIG. 6B shows a cross-sectional view C-C of FIG. 6A;

(15) FIG. 6C shows detail Y of FIG. 6B;

(16) FIG. 6D shows a sectional view D-D of FIG. 6A;

(17) FIG. 7A shows a cross-section, in a plane perpendicular to the longitudinal axis, through an assembly of the hollow tube of the drill guide of FIGS. 5A-E and the guide sleeve of FIGS. 6A-D when positioned in a dental template;

(18) FIG. 7B shows a longitudinal cross-section through the assembly of FIG. 7A;

(19) FIG. 8A shows a cross-sectional view, in a plane perpendicular to the central longitudinal axis, of the anti-rotation section of a hollow tube according to an alternative embodiment of the present invention;

(20) FIG. 8B shows a schematic representation of the anti-rotation section of a guide sleeve according to a further embodiment of the present invention:

(21) FIG. 9 shows a cross-sectional view, in a plane containing the central longitudinal axis, of a modified guide sleeve according to an alternative aspect of the present invention;

(22) FIG. 10 shows a longitudinal cross-section through an assembly of the hollow tube of FIG. 5A-E of the dental drill guide of FIG. 4 and the guide sleeve of FIG. 9 when positioned in a dental template;

(23) FIG. 11A shows a longitudinal cross-section through a template comprising a guide sleeve in accordance with another preferred embodiment of the present invention; and

(24) FIG. 11B shows the template of FIG. 11A in combination with the hollow tube of FIGS. 5A-E.

DETAILED DESCRIPTION

(25) The present invention relates to a dental drill guiding system comprising a drill guide and a guide sleeve, for use with a dental surgical template. Such a template 1 is shown in FIG. 1. The template 1 is individually formed to fit over a patient's bone and existing dentition. Template drill holes 2 are created in the template 1 having the position and orientation necessary for drilling boreholes for the optimal placement of dental implants within the patient's jaw. In addition, the template 1 comprises fixation holes 3, through which screws can be temporarily fastened to the jaw bone in order to fix the template in place. The exact location and orientation of the drill holes 2 is usually determined using preoperative planning software and the template 1 is designed using CADCAM methods. Templates are typically formed using milling and increasingly 3D-printing technology. As these technologies cannot always be relied upon to create an accurately dimensioned template drill hole 2, separate guide sleeves are traditionally placed in the template drill holes 2 in order to ensure that the drills, often in combination with a drill guide, are accurately guided.

(26) FIG. 2A shows a separate guide sleeve 10 in accordance with a preferred embodiment of the present invention. This separate guide sleeve 10 is inserted into the drill hole 2 of a template 1. Following insertion into the template drill hole 2 the guide sleeve 10 remains permanently within the template 1.

(27) As template manufacturing methods, in particular 3D printing, become more accurate, the need for separate guide sleeves is reduced. Instead the internal geometry of the guide sleeves 10 can be accurately printed directly into the template drill holes 2. Such a possibility is shown in FIG. 2B. Here template 1 comprises a drill hole 2 in which the internal features of the guide sleeve 10 are integrally formed.

(28) The dental drill guiding system of the present invention comprises a guide sleeve, which can either be provided as a separate component 10 or as an integral part of the template 2, and a drill guide 30 having a hollow tube 40 for insertion into the guide sleeve 10, 2. FIGS. 3A and 3B show how the drill guide 30 of the present invention can be inserted into the guide sleeve, regardless of whether the guide sleeve is a separate component 10 fixed in the template 1 (FIG. 2A) or forms an integral part of the template 1 (FIG. 2B). As will be discussed further below, the exterior surface of the hollow tube 40 mates with the internal surface of the guide sleeve 10, 2 in order to rotationally fix and axially retain the hollow tube 40 within the guide sleeve 10, 2, while the internal surface defines a through hole 41 for receiving and guiding a drill in a standard manner.

(29) FIGS. 4 and 5A-E show a preferred embodiment of a drill guide 30 according to the present invention. FIG. 4 shows a drill guide 30 comprising a handle 31 for gripping by the surgeon. At each end of the handle 31 the drill guide 30 comprises hollow tubes 40a, 40b. Each hollow tube 40a, 40b is connected to the handle at its coronal end by a first section 32 of the handle 31 which extends at approximately right angles to the central longitudinal axis L.sub.T of the hollow tube 40a, 40b. A second section 33 of the handle 31 extends at an angle of approximately 45 to the first section 32 in the coronal direction. These second sections 33 join to opposing ends of a central section 34 which has a similar angular orientation to the first sections 31. The first 32, second 33 and central 34 sections therefore form two S-shaped portions at either end of the handle 31. This shape is beneficial for placing the hollow tubes 40a, 40b within the mouth with maximum ease for the surgeon and comfort for the patient.

(30) Hollow tube 40a is shown in more detail in FIGS. 5A-E. Hollow tube 40a has an exterior surface 42 and an interior surface, the interior surface defining a through hole 41 extending along a central longitudinal axis L.sub.T from a coronal end 43 to an apical end 44, the hollow tube 40a being sized for insertion into a guide sleeve, as shown in FIGS. 2A and B.

(31) Through hole 41 is circular cylindrical along its entire longitudinal length L. The majority of through hole 41 has minimum diameter D.sub.1. This minimum diameter D.sub.1 corresponds to the diameter of the dental drill which will be guided by hollow tube 40a. The coronal end of through hole 41 has a slightly greater diameter D.sub.2 than the minimum diameter D.sub.1 in order to assist with insertion of the drill into the through hole 41.

(32) The exterior surface 42 of the hollow tube 40a comprises an anti-rotation section 45 and a radially extending annular protrusion 46 limited in the axial extent and positioned apical of and axially distinct from the anti-rotation section 45.

(33) The anti-rotation section 45 of the hollow tube 40a comprises a plurality of identical radially extending protrusions 47 limited in the circumferential extent and evenly spaced about the central longitudinal axis L.sub.T of the hollow tube 40a. As each protrusion 47 is circumferentially limited, it does not extend about the full circumference of the hollow tube 40a and consequently each protrusion 47 has lateral surfaces 47a, 47b when viewed in a plane perpendicular to the central longitudinal axis L.sub.T (see FIG. 5E). In the present embodiment the anti-rotation section 45 is formed by a circular cylindrical outer surface 48 in which a plurality of evenly circumferentially spaced identical grooves 49 are created, said grooves 49 having a cross-section in a plane perpendicular to the central longitudinal axis L.sub.T of a circular arc. The protrusions 47 are thus formed between these grooves 49 and have a cross-section in a plane perpendicular to the central longitudinal axis L.sub.T formed of three circular sections: a central section 47c, formed by the circular cylindrical outer surface 48, and opposing lateral surfaces 47a, 47b which are each formed by the circular arc of the adjacent grooves 49. Forming the protrusions 47 using circular cross-sections provides a good width to depth ratio, maintaining the thickness and hence strength of the hollow tube 40a.

(34) The protrusions 47 of the anti-rotation section 45 have a longitudinal length greater than their circumferential extent and therefore form a plurality of radially protruding, longitudinally extending ribs, the cross-sections of these ribs remaining constant along the length of the ribs.

(35) The annular axially limited protrusion 46 is located at the apical end 44 of the hollow tube 40a. As the protrusion 46 is limited in the axial extent it does not extend along the full length of the hollow tube 40a. Instead it is formed by an increase in the radius of the exterior surface 42 in the apical direction, thus creating a radially extending coronally facing exterior surface 50.

(36) In the present embodiment the axially limited protrusion 46 is separated from the anti-rotation section 45 by a portion 51 of the exterior surface 42 which has a radius R.sub.2 less than the maximum radius of the anti-rotation section R.sub.ARM (see FIG. 5C). This enables the increase in radius which forms the protrusion 46 to start from a radius less than the maximum radius of the anti-rotation section R.sub.ARM. In this way the radius R.sub.1 of the protrusion 46 is less than the maximum radius of the anti-rotation section R.sub.ARM. This has benefits when inserting the hollow tube 40a into the guide sleeve, as will be discussed further below.

(37) The axially limited protrusion 46 has a longitudinal cross-section formed by a circular arc. This creates a tapered apically facing surface 52, the apical end of which forms the apical end 44 of the hollow tube 40a. The tapered nature of surface 52 assists with insertion of the hollow tube 40a into the guide sleeve, and also reduces the area of the protrusion 46 which will be brought into contact with the anti-rotation section of the guide sleeve.

(38) The hollow tube 40a of the drill guide 30 further comprises a circular cylindrical guide portion 53 coronal of the anti-rotation section 45 and, coronal of guide portion 53, a radially extending collar 54. This collar forms an apically facing bearing surface 55 which extends about through hole 41 in a plane perpendicular to the central longitudinal axis L.sub.T. In use bearing surface 55 rests against the upper surface of the template 1, 1. Additionally the collar 54 has a coronally facing bearing surface 56, which forms the coronal end 43 of the hollow tube 40a. This bearing surface 56 can be used in combination with a drill stop attached to a drill shaft, of the type well known in the art, in order to limit the penetration depth of the drill. Collar 54 has a height h.sub.a.

(39) Hollow tube 40b is almost identical to hollow tube 40a and therefore will not be described in detail. In particular hollow tube 40b has an identical anti-rotation section 45, axially limited protrusion 46 and circular cylindrical guide portion 53 to hollow tube 40a. In this way, both hollow tubes 40a, 40b can rotationally and axially lock to the same guide sleeve. Hollow tube 40b differs from hollow tube 40a in that the height h.sub.b of the collar 54b is greater, thus altering the depth to which the same drill can be inserted into the bone. In addition, the diameter of through hole 41b may differ to that of through hole 41, such that hollow tube 40b can be used to guide a different diameter of drill to hollow tube 40a.

(40) The length, L, of the hollow tubes 40a, 40b may be within the range of from 3 to 9 mm such as about 6-8 mm.

(41) The drill guide 30 of FIGS. 4 and 5A-E is intended for use with guide sleeve 10, shown in FIGS. 6A-D. While this guide sleeve 10 is shown as a separate component, all the internal features of this guide sleeve could alternatively be integrally formed in a template drill hole 2.

(42) As best seen in FIG. 6A, guide sleeve 10 comprises an external surface 11 extending from the coronal end 12 to the apical end 13 of the guide sleeve along longitudinal axis L.sub.G. The external surface 11 comprises a plurality of longitudinally extending ribs 14. These ribs 14 enable the external surface 11 to contract in order to assist in the insertion and fixation of the guide sleeve 10 within a template drill hole 2. In addition, the external surface 11 has two diametrically opposing longitudinally extending planar surfaces 15, to reduce the width of the sleeve 10. At its coronal end 12 the external surface 11 further comprises a radially extending flange 16 which extends about the full circumference of the guide sleeve 10 and which acts as a depth stop when placing the sleeve 10 in the template 1.

(43) The guide sleeve 10 further comprises an internal surface 20 which defines a through bore 21 extending along the central longitudinal axis L.sub.G of the guide sleeve 10 from the coronal end 12 to the apical end 13. The internal surface comprises an anti-rotation section 25 extending from the coronal end 12 to the apical end 13 of the guide sleeve 10. The anti-rotation section 25 comprises a plurality of identical, radially extending grooves 27 limited in the circumferential extent and evenly spaced about the central longitudinal axis L.sub.G of the guide sleeve 10. The cross-section of each groove 27, in a plane perpendicular to the central longitudinal axis L.sub.G, forms a circular arc. The grooves 27 are formed in a circular cylindrical inner surface 28 and small sections of this surface 28, in this case approximately 8% of the total circumference of surface 28 remains interposed between the grooves 27. The radius R.sub.min of the inner surface 28 forms the minimum radius of the anti-rotation section 25. When viewed in a plane perpendicular to the central longitudinal axis L.sub.G each groove 27 can be seen to have lateral surfaces 27a, 27b.

(44) Apical of the coronal end of the anti-rotation section 25, in an apical portion 22 of the through bore 21, a plurality of undercuts 26 are formed. These undercuts 26 are formed by an increase in radius of the through bore 21 in the apical direction, such that at the coronal end of each undercut 26 a radially extending, apically facing internal surface 29 is formed. The radius R.sub.a of the undercuts 26 is greater than the minimum radius R.sub.min of the anti-rotation section 25 but less than the maximum radius R.sub.max of the anti-rotation section 25. The undercuts 26 are dimensioned such that, at the axial location of the undercuts 26, all areas of the anti-rotation section 25 having a radius less than the radius R.sub.a of the undercuts 26 are removed. Consequently, the plurality of undercuts 26 are interposed by the areas of grooves 27 having a greater radius than the radius R.sub.a of the undercuts 26. The plurality of undercuts 26 extend the full length of apical portion 22, such that these undercuts 26 are open ended in the apical direction. This increases the ease of manufacture of the undercuts 26.

(45) In use the hollow tubes 40a, 40b are inserted into the through bore 21 of guide sleeve 10 and the exterior surface 42 of the hollow tubes 40a, 40b and internal surface 20 of the guide sleeve 10 mate to provide rotational fixation and axial retention as will be described below with reference to FIGS. 7A and 7B.

(46) The plurality of protrusions 47 of the hollow tube 40a are dimensioned to fit within the plurality of grooves 27 disposed on the internal surface 20 of the guide sleeve 10. When a protrusion 47 is housed in a groove 27, any relative rotation of the hollow tube 40a relative to the guide sleeve 10 results in the abutment of a lateral surface 47a, 47b of the protrusion 47 against a lateral surface 27a, 27b of the groove 27, if indeed these surfaces were not already in contact. Relative rotation about the longitudinal axis L.sub.T, L.sub.G is thereby restricted when the hollow tube 40a of the drill guide 30 is disposed within the guide sleeve 10, thus rotationally fixing the drill guide 30 relative to the guide sleeve 10.

(47) The number of grooves 27 corresponds to the number of protrusions 47 in order to provide a secure rotational lock and to provide an even and optimal force distribution. However, in other embodiments there may be a lesser number of protrusions than grooves.

(48) Moreover, upon insertion of the hollow tube 40a into the guide sleeve 10, the annular protrusion 46 of the hollow tube 40a is housed in the plurality of undercuts 26 of the guide sleeve 10. Once the annular protrusion 46 is housed in the plurality of undercuts 26, any movement of the hollow tube 40a in the coronal direction will cause the coronally facing exterior surface 50 of the protrusion 46 to abut against the apically facing surfaces 29 of the undercuts 26, thereby preventing inadvertent axial disengagement when the hollow tube 40 of the drill guide 30 is disposed within the guide sleeve 10. The hollow tube 40 is thus axially retained in the guide sleeve 10.

(49) In this particular embodiment, the radius, R.sub.1, of the annular protrusion 46 of the hollow tube 40 is slightly greater than the minimum radius R.sub.min of the anti-rotation section 25 of the guide sleeve 10 as measured after insertion of the guide sleeve 10 into the template 1, during which the guide sleeve 10 may be slightly radially compressed, e.g. by approximately 1%. As disclosed hereinbefore, this difference in radius is preferably less than 0.05 mm. This small difference in radius assists in the passage of the protrusion 46 through the anti-rotation section 25 while still providing a secure axial retention. During insertion of the hollow tube 40a through the guide sleeve 10, the surface 28 will be slightly radially compressed in the radially outwards direction by the annular protrusion 46. However, once the annular protrusion 46 reaches apical portion 22, surface 28 will decompress and the annular protrusion 46 of the hollow tube 40a of the drill guide 30 will be retained in the undercuts 26 of the guide sleeve 10 until enough axial force is applied to disengage the annular protrusion 46 from the undercuts 26.

(50) In this embodiment, circular cylindrical guide portion 53 of the hollow tube 40 has a radius equal to the minimum radius R.sub.min of the anti-rotation section 25 of the guide sleeve 10. This enables this portion 53 of the hollow tube 40a to provide further support and stability to the drill guide 30.

(51) As can be seen in FIG. 7B, bearing surface 55 rests on the upper surface of the flange 16 of guide sleeve 10. This flange 16 provides a flat, level surface on which the bearing surface 55 can be supported. In other embodiments however the bearing surface 55 may rest directly on the template 1, 1.

(52) As discussed above, according to the alternative aspect of the present invention the guide sleeve does not comprise at least one undercut in its internal surface. Guide sleeve 10 of FIGS. 6A-D could be adapted to form a guide sleeve according to this alternative aspect by removing the part of the guide sleeve apical of dotted line X. This adapted guide sleeve therefore does not comprise any undercuts 26 and instead a radially extending, apical facing external surface is created at the apical end of the guide sleeve.

(53) In this alternative aspect, upon insertion of the hollow tube 40a into the adapted guide sleeve, the annular protrusion 46 of the hollow tube 40a is located apical of the apical end of the guide sleeve, i.e. apical of dotted line X. Once the annular protrusion 46 is in this location, any movement of the hollow tube 40a in the coronal direction will cause the coronally facing exterior surface 50 of the protrusion 46 to abut against the radially extending, apically facing external apical end surface of the adapted guide sleeve, thereby preventing inadvertent axial disengagement when the hollow tube 40 of the drill guide 30 is disposed within this adapted guide sleeve 10. The hollow tube 40 is thus axially retained in the adapted guide sleeve 10.

(54) This alternative aspect is shown in FIGS. 9 and 10. FIG. 9 shows a longitudinal cross-section, i.e. a cross-section in a plane containing the central longitudinal axis L.sub.G, through alternative guide sleeve 10. The internal surface 20 of guide sleeve 10 defines a through bore 21 and comprises an identical anti-rotation section 25, with grooves 27 and circular cylindrical inner surface 28, to that of guide sleeve 10. However, in contrast to guide sleeve 10, alternative guide sleeve 10 does not comprise any undercuts and instead the cross-section of the anti-rotation section 25 perpendicular to the longitudinal axis L.sub.G remains constant to the apical end 13 of the guide sleeve 10. The apical end 13 of the guide sleeve 10 forms a radially extending, apically facing external end surface 23.

(55) In this alternative aspect, upon insertion of the hollow tube 40a into the alternative guide sleeve 10, the annular protrusion 46 of the hollow tube 40a is located apical of the apical end 13 of the guide sleeve. Once the annular protrusion 46 is in this location, any movement of the hollow tube 40a in the coronal direction will cause the coronally facing exterior surface 50 of the protrusion 46 to abut against the radially extending, apically facing external end surface 23 of the alternative guide sleeve 10, thereby preventing inadvertent axial disengagement when the hollow tube 40a of the drill guide 30 is disposed within this alternative guide sleeve 10.

(56) The hollow tube 40a is thus axially retained in the alternative guide sleeve 10, as shown in FIG. 10.

(57) As mentioned above, in other embodiments of the present invention it is not necessary for the anti-rotation sections of the guide sleeve and hollow tube to comprise equal numbers of grooves and protrusions. FIG. 8A shows an alternative hollow tube 400 for use with the guide sleeve 10 of FIGS. 6A-D. FIG. 8A is equivalent to FIG. 5E and like features are identified with like reference numerals. FIG. 8A shows a cross-section through the anti-rotation section of hollow tube 400 in a plane perpendicular to the central longitudinal axis L.sub.T. In contrast to hollow tube 40a, the anti-rotation section of hollow tube 400 comprises only three protrusions 447 unevenly spaced about the axis L.sub.T. These protrusions 447 are interposed by grooves 449 and have the same shape as the protrusions 47 of hollow tube 40a. As a result, protrusions 447 have an identical central section 447c and lateral surface 447a, 447b to the protrusions 47 of hollow tube 40a. The hollow tube 400 is therefore able to be inserted into and rotationally lock with guide sleeve 10. Protrusions 447 will be housed in the plurality of grooves 27 disposed on the internal surface 20 of the guide sleeve 10. When a protrusion 447 is housed in a groove 27 any relative rotation of the hollow tube 400 relative to the guide sleeve 10 results in the abutment of a lateral surface 447a, 447b of the protrusion 447 against a lateral surface 27a, 27b of the groove 27. Relative rotation about the longitudinal axis L.sub.T, L.sub.G is thereby restricted.

(58) FIG. 8B shows a schematic representation of the cross-section, in a plane perpendicular to the central longitudinal axis L.sub.G, of an anti-rotation section 225 of an alternative embodiment of a guide sleeve 100. Here, the anti-rotation section 225 is formed by a plurality of grooves 227 arranged in an unevenly spaced manner about the central longitudinal axis L.sub.G. The grooves 227 are interposed by sections of circular cylindrical surface 228. Such an anti-rotation section 225 can be used, for example, with a complementary hollow tube having a plurality of complementary protrusions for accommodation within the grooves 227.

(59) The number of complementary protrusions could be equal to the number of grooves 227, in which case the protrusions will be spaced in an identical manner to grooves 227. However, it is also possible for the cooperating hollow tube to have a lesser number of protrusions. In such cases the complementary protrusions could be either unevenly or evenly spaced about the central longitudinal axis of the hollow tube, e.g. four protrusions arranged at 90 to one another.

(60) FIGS. 8A and 8B therefore provide examples in which the protrusions and grooves of the anti-rotation sections do not need to be evenly spaced about the central longitudinal axis.

(61) Finally, FIGS. 11A and B provide an example of a guide sleeve in which the anti-rotation section does not extend to the apical end of the sleeve. In this embodiment, guide sleeve 100 is an integral part of template 1. Internal surface 200 defines a through bore 210 extending along the central longitudinal axis L.sub.G of the guide sleeve 100 from the coronal end 112 to the apical end 113. The internal surface 200 comprises an anti-rotation section 225 having a plurality of identical, radially extending grooves 227 limited in the circumferential extent and evenly spaced about the central longitudinal axis L.sub.G of the guide sleeve 100. The cross-section of each groove 227, in a plane perpendicular to the central longitudinal axis L.sub.G, forms a circular arc. The grooves 227 are formed in a circular cylindrical inner surface 228 and small sections of this surface 228, remain interposed between the grooves 227. In this regard the anti-rotation section 225 is identical to the anti-rotation section 25 of guide sleeve 10, described in relation to FIGS. 6A-D.

(62) However, in contrast to anti-rotation section 25, anti-rotation section 225 does not extend to the apical end 113 of the through bore 210. Instead guide sleeve 100 comprises an undercut 226 apical of the anti-rotation section 225. The radius R.sub.3 of the undercut 226 is greater than the maximum radius of the anti-rotation section 225 and the undercut 226 extends about the full circumference of through bore 210. The radius of the through bore 210 is not subsequently decreased, such that the undercut 226 is open ended in the apical direction. At the coronal end of the undercut 226 a radially extending, apically facing internal surface 229 is formed.

(63) Hollow tube 40a of the drill guide 30 described in relation to FIGS. 4, 5A-E can be used in combination with guide sleeve 100 of template 1, as shown in FIG. 11B. Upon insertion of hollow tube 40a into guide sleeve 100 the anti-rotation sections 45, 225 interact to prevent relative rotational movement as described above in relation to FIGS. 7A and 7B. The annular protrusion 46 of the hollow tube 40a is housed in the undercut 226 of the guide sleeve 100. Once the annular protrusion 46 is housed in the undercut 226, any movement of the hollow tube 40a in the coronal direction will cause the coronally facing exterior surface 50 of the protrusion 46 to abut against the apically facing surface 229 of the undercut 226, thereby preventing inadvertent axial disengagement when the hollow tube 40a of the drill guide 30 is disposed within the guide sleeve 100. The hollow tube 40a is thus axially retained in the guide sleeve 100.

(64) 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, numerous alternative shapes are possible for the anti-rotation sections of the hollow tube and guide sleeve. Additionally, the axially limited protrusion may be formed directly apically of the anti-rotation section of the hollow tube and may be a plurality of axially limited protrusions, for example directly apically adjacent to the grooves 49. Alternatively the at least one axially limited protrusion could be positioned coronally of the anti-rotation section of the hollow tube. The internal surface of the guide sleeve may be configured such that the anti-rotation section does not extend the length of the sleeve and the undercut may be positioned axially remote from the anti-rotation section in either the apical or coronal direction.