WO2011063958A1

WO2011063958A1 - A directional precision implant

Info

Publication number: WO2011063958A1
Application number: PCT/EP2010/007152
Authority: WO
Inventors: Andrew Dawood
Original assignee: Andrew Dawood
Priority date: 2009-11-25
Filing date: 2010-11-25
Publication date: 2011-06-03
Also published as: GB2475679A; GB0920579D0

Abstract

A fixture for use in guided surgery, comprising a guide portion with a surface substantially concentric with the central longitudinal axis of the fixture, a threaded body located coronally of the guide portion, and a connection interface for connection to a fixture mount for inserting the fixture into an osteotomy site. The guide portion is unthreaded over a length sufficient to guide insertion of the fixture along an osteotomy site.

Description

A Directional Precision Implant

Field of the Invention

This invention pertains in general to the field of an implant system. More particularly, the invention relates to a fixture having a threaded body and an unthreaded guide portion at the apical end of the fixture. In combinations, the fixture may be used for guided surgery together with a drill template, and, when need be, a bone tap having similar features as the fixture.

Background of the Invention

Dental implants are typically screw shape structures which when screwed in into the jawbone provide anchorage for dental prostheses. These endosseous implants later osseointegrate as bone cells grow onto their surface. Typical materials used for their fabrication include titanium, zirconium, titanium-aluminium-vanadium and titanium-zirconium, alloys but other possibilities will exist. The portion of the implant that is osseointegrated is also referred to as the fixture. When preparing a site in the jawbone with rotary drills the operator would anticipate that the implant would precisely follow the prepared site. However this is not always the case for several reasons: one important reason is that the tip of many implant varieties is provided with sharp threads or cutting flutes or other sharp or 'acute' geometrical apical attributes, which may be provided with the intention of assisting in the process of cutting through the bony site, or providing retention in the bone.

Other fixtures have rounded tapered, threaded or unthreaded ends which are blunt but do not impose a specific directionality on the fixture. The direction in which the fixture travels will be much affected by the inclination of the fixture at the point of entry, as the fixture may be inserted at a slightly different angle to the intended site preparation, and then forced off-course as it is threaded into place.

The ability to precisely follow the site prepared by a drill or sequence of drills is particularly important in narrow bone stock and in guided surgery situations.

In guided implant surgery, a drill guide or surgical guide is provided with constraining guiding sleeves, which restrict and constrain drill position so as to prepare the bony osteotomy exactly along a prescribed path. Typically this sort of surgery is planned using CAD software, in a virtual environment. The intention is that by carefully following an incremental drilling protocol, implants may be precisely inserted along the planned trajectory with such precision that prefabricated dental prostheses may be fitted Immediately upon completion of the surgery.

CONFfRMATiON COPY Because this is the most exacting circumstance for a high precision insertion for a dental implant, the fixture according to embodiments of the invention is described with this exacting role in mind, although this sort of fixture might be used in any conventional or non-conventional implant situation, where precise fixture positioning or guiding is required even without a drill gudie.

In the course of implant site preparation, an initial osteotomy is generally performed with a narrow drill, which might be described as preparing the way for further incremental preparation with further, wider drills.

If a straight-sided cylindrical type fixture is planned, site enlargement will typically take place from a narrow 'starting' drill diameter e.g. 2mm, up to a larger drill diameter drill, e.g. 3.2mm for a standard 4mm diameter fixture, to create a generally cylindrical osteotomy. Because the constraining drill guides are parallel walled the drill is guided and constrained along its entire length.

If a widely tapered implant is selected then the site will be opened up with tapered drills or reamers, which will enlarge the site with a typically narrower but similar geometry to the shape of the planned fixture. Because the tapered drill is tapered, it is able to drop further into the site, which may improve guidance offered by the guiding sleeve, by virtue of the fact that the guiding surface at the hilt of the tapered drill will be quicker to contact the guiding sleeve. Accurate preparation of the site is also enhanced by the fact that the drills are 'side-cutting' reamers, so with the drill firmly seated in the constraining sleeve, the walls of the osteotomy may be definitively shaped.

In general, the operator will prepare soft bone less than dense bone so as to allow the implant to firmly engage the bony site as it is inserted, such that insertion torque is sufficient to stabilise the fixture adequately, but does not exceed the level prescribed for the particular implant system selected - typically 30-70 Ncm.

Fixtures with sharp cutting tips will progress more easily through a narrow osteotomy site, whereas fixtures with blunter tips require more preparation of the site, or may not be able to force their way along the site. In guided implant insertion, implant insertion may be constrained by a close fitting guiding sleeve which contacts the fixture mount, which is typically parallel sided, such that the walls of the fixture mount constrain insertion as they are guided through the guiding sleeve. However the height of this guiding sleeve may be such that only a fixture which has a shorter length than the extent of the guiding sleeve above the prepared site, may be fully guided by the sleeve. Alternatively, a cylindrical fixture might itself be directly guided by a sleeve, and the affixed mount might similarly guide the fixture, if it has the same width as the fixture. However, unless the sleeve tightly constrains the fixture there may be a tendency for the fixture to proceed off- course. In a typical situation where the guiding sleeve guides the fixture mount but not the implant, the sleeve will only start to guide insertion when the walls of the fixture mount come into contact with the sleeve. Thus for example, if the outer edge of the guiding surface of the sleeve is at a distance of 9mm away from the bony site, as is the case in one particular current system, then the tip of a fixture which is longer than 9mm will engage the prepared bony site before the walls of the fixture mount. The longer the implant is than this distance, the more will be the tendency for the thread of the implant to start contacting the bone before the sleeve in the drill guide guides the fixture mount. Without extreme care by the surgeon, the implant may deviate, since it will initially not be guided, from the planned trajectory and end position. As a consequence, a pre-made prosthesis may not fit the installed implant and a new prosthesis has to be made.

All this means that in contemporary implant systems, fixtures that are longer than the distance between the bone and the coronal end of the guiding sleeve are not guided along the first few millimetres of their passage through the osteotomy as they are inserted through the guided sleeve. These parameters will change with the length of the guiding sleeve, the distance off the tissues and the length of the fixture.

Furthermore, once a fixture proceeds off-course there will be a tendency for the fixture to develop friction against the guiding sleeve, causing stress and strain on the drill guide, which may lose its intended relationship with the bony substrate, causing deviation of all the other planned fixtures from their pre-planned positions according to the computer plan.

Hence, an improved fixture, that may used alone or together with a drill guide, would be advantageous and in particular allowing for improved precision, increased flexibility, cost- effectiveness, and/or patient safety would be advantageous.

Summary of the Invention

Accordingly, embodiments of the present invention preferably seek to mitigate, alleviate or eliminate one or more deficiencies, disadvantages or issues in the art, such as the above- identified, singly or in any combination by providing a fixture according to the appended patent claims.

According to an aspect, a fixture, for example a dental fixture, for use in guided surgery, comprises a guide portion with a surface substantially concentric with the longitudinal axis of the implant and located at the apical end of t he fixture, a threaded body located coronally of the guide portion, and a connection interface for connection to a fixture mount for inserting the fixture into an osteotomy site. The guide portion is unthreaded over a length sufficient to guide insertion of the fixture along an osteotomy site. Hence, the fixture may be used for guided surgery by its own since it is guided by the osteotomy site or for guided surgery in combination with a drill guide.

The fixture may forma combination with a drill guide comprising a guiding surface. The guiding surface may be provided by a recess in the drill guide, which may or may not have a guiding sleeve or similar guiding feature positioned therein. The guiding surface of the drill guide may have a length between a coronal end and apical end, the length of the fixture from a coronal end thereof to an apical end thereof may be longer than the length of the guiding surface, wherein when the coronal end of the fixture is aligned with the coronal end of the guiding surface, an apical portion of the fixture that extends outside the guiding surface comprises the guide portion.

The length of the unthreaded guide portion of he fixture may be in the range of 2-5mm. This may provide for suitable guiding of the fixture, such as in an osteotomy site having a shape that is complementary to the shape of the guiding portion. The length of the threaded body of the fixture may be in the range of 8 to 55mm, such as any of 8 to 24mm, 10 to 18mm, and 30 to 55mm. Such fixtures are prune to the issues discussed above and particularly suitable to have the guiding portion. Fixtures in the range of 8 to 24 mm are normally anchored only in the jaw bone. For such fixtures, the embodiments of the invention may be particular useful for lengths in the range of 10 to 18mm. Embodiments of the invention may also be useful for fixtures anchored in the zygomatic bone, which may have lengths in the 30 to 55mm range.

The fixture may form a combination with a drill, preferably a cylindrical drill, or a set of drills, preferably a set of cylindrical drills. The diameter over the length of the guide portion of the fixture may substantially correspond to the drill diameter of the drill or the largest drill diameter of a drill of the set of drills. Hence, the diameter of the guide portion may be slightly less than the drill diameter such that it is guided by the osteotomy site formed by the drill, which will have a shape that is complementary to the shape of the guide portion. The fixture may for a combination with a drill guide having a guiding surface, such as a guiding sleeve or similar guiding feature, and a fixture mount. The fixture mount may have a guiding surface at the apical end thereof. Also the fixture mount comprises a connection interface for connection to the connection interface of the fixture. The diameter of the guiding surface of the drill guide and the diameter of the guiding surface of the fixture mount may be configured to provide a guiding fit therebetween, and the diameter of the guide portion of the fixture may be configured to pass through the guiding surface of the drill guide with a clearance fit. Hence, guiding surface of the fixture mount but not the guiding portion of the fixture is guided by the guiding surface of the drill guide.

The fixture may form a combination with a bone tap having a non-thread cutting guide portion, such as having a shape substantially corresponding to the shape of the guide portion of the fixture. The bone tap may have an extended non-thread cutting guide portion, such as substantially corresponding to the guide portion of the fixture, but longer to permit precise thread cutting at the coronal aspect of the osteotomy. Hence, the surface of the guide portion of the bone tap may extend substantially concentric with the central longitudinal axis of the bone tap. Also, the bone tap may have a guiding surface at its coronal end configured to provide a guiding fit with the guiding sleeve.

According to another aspect, a method for planning guided surgical procedure, comprises obtaining first scan data of the oral anatomy of the patient; generating a virtual model of the oral anatomy of the patient based on the first scan data; obtaining second scan data of a reference guide; generating a virtual model of the reference guide based on the second scan data; visualising the virtual model of the reference guide in a predetermined relationship relative to the model of the oral anatomy; determining, based on the virtual model of the oral anatomy, a point of entry of a planned osteotomy site for a dental fixture; determining, based on virtual model of the reference guide, a coronal end of a guide surface for a drill guide, said drill guide to be based on the second scan data; determining a length from an apical end of a threaded portion of a fixture to a coronal end of the fixture for the osteotomy site measured in the longitudinal direction of the fixture; wherein when the length from the apical end of the threaded portion of the fixture to the coronal end of the fixture is longer than the distance between the point of entry of the planned osteotomy site and the coronal end of the guide surface for the drill guide measured in the longitudinal direction of the guide surface, selecting a fixture for the guided surgical procedure having a guide portion with a surface substantially concentric with the central longitudinal axis of the fixture, a threaded body located coronally of the guide portion, wherein the selected fixture has a length such that guide portion is located within the planned osteotomy site when the coronal end of the fixture is aligned with the coronal end of the guide surface.

Against this background, a fixture having a superior ability to follow a prepared osteotomy site will be described in the following specific embodiments. Brief description of the Drawings

Figure 1 a is a representation of an embodiment of a fixture having a generally cylindrical form; Figure 1 b depicts a similar, but slightly tapered version of the fixture of Figure 1a.

Figure 1c illustrates an embodiment of a fixture having a threaded body TB without any self- cutting features.

Figure 2 is a representation of a blunt ended fixture, without self-tapping threads.

Figure 3 is a representation of an embodiment of the guide portion of the fixture. Figures 4 and 5 are representations of embodiments of taps for cutting a thread in bone. Detailed Description of Embodiments

Specific embodiments of the invention will now be described with reference to the

accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements.

Figure 1 a is a representation of a fixture having a generally cylindrical form, said fixture having a threaded body TB.

The head HD of the fixture is designed for the connection of a prosthesis, as is generally known in the art. Hence, it comprises a connection interface, such as an internal connection interface with an at least partially non-round recess, or an external connection interface with e.g. a non- round protrusion.

Aspect of embodiments of this invention relates to the guide portion of the fixture a and the initial threaded part b following the guide portion when viewed from the apical towards the coronal end of the fixture.

The guide portion a of the fixture of the embodiment of Fig. 1 macroscopically may take the form of a cylinder, such as a blunt cylinder, having a diameter that corresponds to, or is close to that of the drill diameter of the last drill size for the intended implant system. The guide portion may have a non-cutting surface, i.e. does not have any features for cutting a thread in the bone as the fixture is inserted. This blunt non-cutting guide portion has little option but to follow a prepared site as the fixture is rotated into place. Although there may be surface characteristics present to enhance osseointegration, it is not macroscopically threaded in a way that will determine a path through the bone.

The surface of the guide portion may be substantially concentric with the central longitudinal axis of the fixture. The length of the surface of the guide portion in measured parallel to the central longitudinal axis of the fixture may be in the range of about 2-5mm long. Hence, the guide portion may guide the fixture as it is inserted in an osteotomy site. The guidance may be provided when the overall shape of the guide portion is complementary to the overall shape of the osteotomy site. Hence, even if the guide portion has microscopic features to promote osseointegration, its macroscopic shape is complementary to the shape of the osteotomy site. Figures 1a and 1b illustrates an embodiment of a fixture with a threaded body TB having a base portion b. The base portion may be located coronally of the guide portion a. The base portion b may comprise self-cutting threads i. The length of the base portion b may be in the range of about 3mm to about 5mm. Where bone is of intermediate quality a fixture may be selected which incorporates the self- tapping cutting threads i into the base portion of the threaded portion b, as is illustrated in Figures 1a and 1b. These self-cutting threads will prepare the walls of the osteotomy site as the fixture is advanced, but as there are no threads in the guide portion, this further preparation will not result in a deviation of the fixture.

Figure 1c illustrates an embodiment of a fixture having a threaded body TB without any self- cutting features. This may be beneficial in situations where the bone is relatively soft. For such situations, a cylindrical or slightly tapered, or distinctly tapered version of the fixture may be available without cutting threads, e.g., as is shown in figure 1c. At least one of the guide portion of the thread and the base of the thread may be tapered relative to the central longitudinal axis of the fixture.

In the following, reference will be made to a drill guide and a guiding sleeve for guiding a drill and/or a fixture mount. A guide sleeve has an inner guiding surface. In other embodiments, a recess made directly in the drill guide provides the guiding surface. In such embodiments a guiding sleeve is not necessary. Also other features having a guiding surface may be provided. The guiding surface may be substantially cylindrical in all embodiments. For ease of description, a guiding sleeve will be discussed. However, in all embodiments described below with a guiding sleeve, a guiding surface provided by other features, such as described above, may be used.

Figure 2 illustrates an embodiment of the fixture in combination with an embodiment of a drill guide DG. The drill guide DG may alternatively be used in combination with any of the other embodiments of the fixture disclosed herein. As is illustrated in this embodiment, the guiding sleeve has a length between its coronal end and its apical end. The length of the fixture from a coronal end thereof to an apical end thereof is longer than the length of the guiding sleeve. When the coronal end of the fixture is aligned with the coronal end of the guiding sleeve, as is illustrated, an apical portion of the fixture that extends outside the guiding sleeve comprises the guide portion. In this case, the entire guide portion extends outside the guiding sleeve. In other embodiments, a portion of the guide portion extends outside the guiding sleeve. Hence, in embodiments, at least a portion of the guide portion may extends outside the guiding sleeve The fixture in Figure 2 is blunt ended i.e. has a non-threaded guide portion as described above, but in this embodiment lacks self-tapping threads. As is shown, the fixture is being placed with the aid of the drill guide DG, which is seated in position over the Jaw Bone JB. In this embodiment, the drill guide DG is supported by a soft tissue surface, but may equally or in addition be supported directly by at least one of a bone tissue surface, and one or several teeth or previously placed fixtures. The surface of the drill guide facing the soft tissue/bone tissue generally has a complementary shape to the shape of the surface by which it is supported. Hence, the inner surface of the drill guide has a shape that substantially corresponds to the shape of the oral anatomy of the patient. When placing a cylindrical or slightly tapered fixture, the osteotomy site is often prepared with a sequence of drills to its full depth. This leaves a cylindrical osteotomy c of a diameter, which is generally smaller than that of the threaded body of the fixture, such that the threads of the fixture are able to engage the freshly prepared bony walls of the site, which is illustrated in the embodiment of Fig. 2. A core or thread base d of the threaded body TB of the fixture may be cylindrical or tapered. The fixture is being inserted through the guiding sleeve e of the drill guide by a surgical handpiece, and is connected to the handpiece by means of a fixture mount f. The fixture mount f comprises a guiding surface g, which contacts the walls of the guiding sleeve e. Thus, the fixture mount f is guided by the inner surface of the guiding sleeve e during insertion of the fixture. However, the diameter of the guiding sleeve e is larger than the major diameter of the fixture, such that the fixture can be inserted there through without contacting the inner surface of the guiding sleeve e. Hence, a clearance fit is provided there between. The fixture and fixture mount f combination for use together with the drill guide DG thus has guiding surfaces, one at the base on the mount and one at the guide portion a of the fixture. Hence, the fixture may be guided through the osteotomy by its guide portion and the fixture mount f by the guiding sleeve e. If it is a relatively short fixture - i.e. shorter than the distance from guiding surface to the start of the osteotomy, both guiding surfaces will act together, i.e. the guiding surface g of the fixture mount f will contact the inner surface of the guiding sleeve e while the guide portion a contacts bone but before any part of the threaded body TB of the fixture contacts the bone. If it is a longer fixture, the guide portion a may guide the fixture on its own until the mount f contacts the sleeve. Hence, the fixture according to embodiments of the invention is suitable for combination with the fixture mount f and drill guide DG according to embodiments shown herein.

Figure 3 shows an embodiment of the guide portion a of the fixture. In order to enhance and expedite healing of bone onto the fixture surface (osseointegration), the surface of the fixture is prepared with a microscopic structure h, such as micro grooves, and/or other forms of surface treatment, as typically found on the surface of dental fixtures but generally not at an unthreaded guide portion of the fixture.

The threaded body TB of the fixture may be cylindrical or parallel walled overall, but may have a tapering 'core' or base of the thread, or alternatively may have a slightly tapered or cylindrical central core and a tapered threaded form, such as the tip of the thread, overall. If intended for soft bone, no self-tapping element is necessary.

Figures 4 and 5 illustrate embodiments of a bone tap. In dense bone situations, opening the osteotomy site to the width of the guide portion may be inadequate to allow the threads to cut through the bony walls without further preparation. This situation may be dealt with by the use of a dedicated bone tap, having a guide portion j similar to the guide portion a of the fixture, and a core of diameter equivalent to that of the last drill used so that it too follows the course of the prepared osteotomy. A tapping portion has tapping threads k which remove material from the walls of the osteotomy site, thus reducing friction between the fixture and the walls of the site, and perhaps providing a threaded preparation for the threads of the fixture to follow. The guide portion j may be concentric with the central longitudinal axis of the bone tap.

Said bone tap may also have a guiding surface I at its base or coronal end. The guiding surface I of the coronal end may be cylindrical. Hence, the tap may be guided through the osteotomy by its guide portion j and its guiding surface at the base if it is a short tap, and by its guide portion first, if it is a long tap, until the base comes into play and is guided by the guiding sleeve e in the same manner as the fixture mount. Hence, the tap may be provided in combination with the fixture, drill guide DG, and fixture mount, described in embodiments above.

In practice there may be more than one tap produced for the system, such that the width of the cutting threads of the tap are available in different sizes or with different pitches, so that the bulk of bone that is removed by the tap may be varied in accordance with the operators perception of the bone quality.

Thus when a fixture is placed it is guided into position by its guide portion initially, and as the fixture mount comes into contact with the guiding surface it is also guided by the fixture mount.

However, in some situations, the fixture may be placed using conventional rather than 'guided' instrumentation, without the guided mount as guidance from the guide portion is considered to be adequate.

In a 'guided' surgical environment in which Cone beam CT or CT scan data are used as the basis of the planning, the software may suggest an appropriate bone tap based on the Hounsfield value or the grey levels as measured by the software. The fixture described above can be used for planning guided surgical procedure, such as planning drill guide described above and selecting a suitable type and length of the fixture. The method may comprise obtaining first scan data of the oral anatomy of the patient. A virtual model of the oral anatomy of the patient may be generated based on the first scan data. The virtual model may e.g. be 2D CT data, or a 3D surface model. Second scan data of a reference guide may also be obtained. The reference guide may e.g. be a radiographic guide having dentures to guide the positioning of the fixture. The first and second scan data may be obtained together or separately. Hence the reference guide may comprise fiduciary markers such that the datasets may be aligned if generated separately. If generated together, the reference guide may contain a radio-opaque material such that it can be distinguished from patient data in a CT scan. A virtual model of the reference guide is generated based on the second scan data. The virtual model of the reference guide is visualised in a predetermined relationship relative to the model of the oral anatomy, i.e. in the same relationship the reference guide had relative to the patient during scanning, such as based on the fiducial markers, or already aligned if the first and second scan data are generated together. Based on the virtual model of the oral anatomy, a point of entry of a planned osteotomy site for a dental fixture is determined. Also, based on the virtual model of the reference guide, a coronal end of the guide surface for a drill guide is determined. The drill guide will in a later stage be produced based on the second scan data. A length from an apical end of a threaded portion of a fixture to a coronal end of the fixture for the osteotomy site measured in the longitudinal direction of the fixture is determined. When the length from the apical end of the threaded portion of the fixture to the coronal end of the fixture is longer than the distance between the point of entry of the planned osteotomy site and the coronal end of the guide surface for the drill guide measured in the longitudinal direction of the guide surface, a fixture is selected for the guided surgical procedure that has a guide portion with a surface substantially concentric with the central longitudinal axis of the fixture, and a threaded body located coronally of the guide portion. The selected fixture has a length such that guide portion is located, at least partially to provide guidance, within the planned osteotomy site when the coronal end of the fixture is aligned with the coronal end of the guide surface. The length of the fixture is such that the threaded body is located outside the planned osteotomy site until the coronal end of the fixture is aligned with the coronal end of the guide surface of the drill guide. This is illustrated in Fig. 2.

Embodiments

Below follow various embodiments of the fixture and implant system described above. The embodiments described above may be combined, also with the embodiments described above, as is appreciated by the man skilled in the art.

An implant system for guided surgery or other situations where there is a demand for increased accuracy, which uses matched bone taps and fixtures having apical elements that are specifically intended to follow the osteotomy site as prepared by cylindrical drills.

An implant system for guided surgery or other situations where there is a demand for increased accuracy, which uses matched bone taps and fixtures have apical elements that are specifically intended to follow the osteotomy site as prepared by tapered drills.

An implant system for guided surgery or other situations where there is a demand for increased accuracy which uses matched bone taps and fixtures have apical elements that are specifically intended to follow the osteotomy site as prepared by slightly tapered drills.

An implant in which the apical portion of the fixture macroscopically appears generally as a smooth cylinder having no bone engaging threads or projecting features of a type which would generally be used to stabilise the body at the time of insertion, e.g. macroscopic screw threads. An implant, in which the apical portion of the fixture macroscopically appears as a smooth cylinder having no bone engaging threads or projecting features of a type which would generally be used to cut threads, or engage the bony walls of the osteotomy, e.g. macroscopic screw threads or self-tapping threads; instead, microscopic non-spiral or spiral screw threads or 'grooves' are provided, intended to encourage osseointegration, and biological stabilisation during the subsequent post insertion healing process.

A tap in which the apical portion is a smooth cylinder having no bone engaging or cutting threads.

An implant, such as a fixture, in which the apical portion of the fixture takes the form of a macroscopically smooth cylinder having no bone engaging threads or retentive features of a type which would generally be used to stabilise the fixture at the time of insertion, e.g. macroscopic screw threads. Having surface treatments, grooves, or other retentive features designed to encourage osseointegration.

An implant, such as a fixture, and matched tap in which the apical portion of the tap is a macroscopically smooth cylinder having no bone engaging threads or retentive features of a type which would generally be used to stabilise the fixture at the time of insertion, e.g. macroscopic screw threads. The implant having surface treatments, grooves, or other retentive features designed to encourage osseointegration, said microscopic or retentive features may be of a type that is currently found at the coronal aspect of contemporary implant systems, such as micro grooves, and other surface treatments intended to encourage osseointegration.

A fixture having a blunt cylindrical tip, such as a guide portion, as described in any of the above embodiments, said blunt cylinder may have a slight taper so as to develop a 'press-fit' into the prepared site. A fixture and matched screw tap as described in any of the above embodiments, in which there is provided in addition to the blunt apical element a threaded body, said threaded body having a central core diameter equivalent to the diameter of the apical part, and a screw thread extending outwards from the central core to engage the bony walls of the osteotomy site. A fixture and matching screw tap as described in any of the above embodiments, in which there is provided in addition to the blunt apical element, a threaded body, said threaded body having a central core diameter equivalent to the diameter of the apical part, and a screw thread that extends outwards from the central core to engage the bony walls of the osteotomy site, said screw thread having a cylindrical outer configuration.

A fixture and matching screw tap as described in any of the above embodiments, wherein in addition to the apical element, there is provided a threaded body, said threaded body having a central core diameter equivalent to the diameter of the apical part, and a screw thread that extends outwards from the central core to engage the bony walls of the osteotomy site, said screw thread having a tapering configuration, that is, wider at the neck of the fixture than apically. A fixture and matched screw tap as described in any of the above embodiments, in which in addition to the apical element there is provided a threaded body, said threaded body having a central core diameter which tapers slightly to more firmly engage the bony walls of the osteotomy site. The associated screw thread also having a tapering or cylindrical configuration. A bone tap as described in any of the above embodiments, in which the tapping elements intended to tap threads into the walls of the osteotomy, are selected according to the perceived density of the bone in the site, such that larger amounts of bone are removed from the bony site in dense bone environments and lesser amounts of bone are removed in soft bone environments, thus allowing a fixture to be inserted in bone of differing density without needing to widen the osteotomy with drills of a differing diameter.

A threaded fixture having threads for its insertion that begins above a blunt tip, such as a guide portion, that is intended to follow the pre-prepared osteotomy. A fixture as described in the previous claim where some of the threads have self tapping properties.

A bone tap for the ongoing preparation of an osteotomy for a dental implant, such as a dental fixture, having cutting / tapping threads for its insertion that begin above a blunt tip, such as a guide portion, that is intended to follow the pre-prepared osteotomy

An implant system described in any of the above embodiments in which a variety of taps are available having different arrangement of thread form, such that a different tap is selected for use with bone of different perceived density.

An implant system as described in previous claims in which software associated with implant planning software, or Cone beam computed tomography systems make an assessment of osteotomy site density and suggest an appropriate tap from the system so as to optimise preparation of the osteotomy site.

As will be apparent, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Conditional language used herein, such as, among others, "can," "could," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. The present invention has been described above with reference to specific embodiments. However, other embodiments than the above described are equally possible within the scope of the invention. Different method steps than those described above may be provided within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.

Claims

1. A fixture for use in guided surgery, comprising:

a guide portion with a surface substantially concentric with the central longitudinal axis of the fixture located at the apical end of the fixture,

a threaded body located coronally of the guide portion, and

a connection interface for connection to a fixture mount for inserting the fixture into an osteotomy site, wherein

the guide portion is unthreaded over a length sufficient to guide insertion of the fixture along an osteotomy site.

2. The fixture according to claim 1, in combination with a drill guide comprising a substantially cylindrical guiding surface for guiding a drill or fixture mount, wherein the guiding surface has a length between a coronal end and apical end, the length of the fixture from a coronal end thereof to an apical end thereof is longer than the length of the guiding surface in the longitudinal direction of the guiding surface, wherein when the coronal end of the fixture is aligned with the coronal end of the guiding surface of the drill guide, an apical portion of the fixture that extends outside the guiding surface comprises the guide portion.

3. The fixture according to claim 1 , wherein the length of the unthreaded guide portion is in the range of 2-5mm.

4. The fixture of claim 1 , wherein the length of the threaded body is in the range of 8 to 55mm, such as any of 8 to 24mm, 10 to 18mm, and 30 to 55mm.

5. The fixture according to any of the previous claims, in combination with a drill, preferably a cylindrical drill, or a set of drills, preferably a set of cylindrical drills, wherein the diameter over the length of the guide portion of the fixture substantially corresponds to the drill diameter of the drill or the largest drill diameter of a drill of the set of drills.

6. The fixture according to any of the previous claims, in combination with a drill guide having a cylindrical guiding surface, and a fixture mount, wherein the fixture mount has a guiding surface at the apical end thereof for guiding by the guiding surface of the drill guide.

7. The fixture according to claim 6, wherein the diameter of the guiding surface of the drill guide and the diameter of the guiding surface of the fixture mount are configured to provide a guiding fit therebetween, and the diameter of the guide portion of the fixture is configured to pass through the recess provided by the cylindrical guiding surface of the drill guide with a clearance fit.

8. The fixture according to any of the previous claims, in combination with a bone tap having a non-thread cutting guide portion, such as substantially corresponding to the guide portion of the fixture.

9. The fixture according to any of the previous claims, in combination with a bone tap having an extended non-thread cutting guide portion, such as substantially corresponding to the guide portion of the fixture, but longer to permit precise thread cutting at the coronal aspect of the osteotomy.

10. A method for planning guided surgical procedure, comprising

obtaining first scan data of the oral anatomy of the patient;

generating a virtual model of the oral anatomy of the patient based on the first scan data;

obtaining second scan data of a reference guide;

generating a virtual model of the reference guide based on the second scan data; visualising the virtual model of the reference guide in a predetermined relationship relative to the model of the oral anatomy;

determining, based on the virtual model of the oral anatomy, a point of entry of a planned osteotomy site for a dental fixture;

determining, based on virtual model of the reference guide, a coronal end of a guide surface for a drill guide, said drill guide to be based on the second scan data;

determining a length from an apical end of a threaded portion of a fixture to a coronal end of the fixture for the osteotomy site measured in the longitudinal direction of the fixture; wherein

when the length from the apical end of the threaded portion of the fixture to the coronal end of the fixture is longer than the distance between the point of entry of the planned osteotomy site and the coronal end of the guide surface for the drill guide measured in the longitudinal direction of the guide surface, selecting a fixture for the guided surgical procedure having a guide portion with a surface substantially concentric with the central longitudinal axis of the fixture, a threaded body located coronally of the guide portion, wherein the selected fixture has a length such that guide portion is located within the planned osteotomy site when the coronal end of the fixture is aligned with the coronal end of the guide surface.

11. An implant substantially as described in the accompanying description and figures.

12. A bone tap substantially as described in the accompanying description and figures.

13. An implant system substantially as described in the accompanying description and figures.