FIELD OF THE INVENTION

The present invention relates in general to the field of artificial teeth.

Specifically, the present invention relates to the problem of fixating a replacement device for all teeth or for a portion of the teeth, such replacement piece will hereinafter be indicated as "dentures" or "dental prosthesis".

BACKGROUND OF THE INVENTION

The traditional dental prosthesis is resting on the gums of the upper or lower jaw. One problem is that, with time, the jaw bone and/or the gums shrink, so that the prosthesis loses retention.

In order to solve this problem, it is already known to attach one or more anchoring devices to the jaw bone, and to attach the prosthesis to such anchoring device(s). This, however, involves complicated and time-consuming processing steps which need to be performed very accurately to ultimately obtain an accurate fit. It is necessary to work the jaw bone in order to install dental implants; it is necessary to manufacture a bar, and to attach the bar to the implants; and it is necessary to work the prosthesis in order to provide it with an attachment member, that will eventually engage the bar. If either one of the implants, the bar and the attachment member are not arranged in the correct position and/or correct orientation, the end result is that the prosthesis does not fit properly.

In the current state of the art, two holes are drilled in the jaw bone, implants are installed in these holes, and a bar is fixed to these implants. The drilling is performed by hand, and the exact location and direction of the bore holes will differ from case to case. Consequently, it is necessary that an individual anchoring bar is made to measure per case, adapted to the actual bore holes of the case. This is complicated, time-consuming and expensive.

SUMMARY OF THE INVENTION

An object of the present invention is to make it possible to use standard pre-fabricated bars. More particularly, the present invention aims to provide a method and tools with which it is possible to work accurately and in a reproducible manner.

For this purpose, the present invention provides a drilling accessory that can be fixated with respect to the jaw bone, the accessory having two (or more) guide holes for guiding a drill bit used for drilling holes in the jaw bone. Because the accessory has two guide holes of which the mutual distance is standard, it becomes possible to use standard bars. Because the accessory is fixated (temporarily) to the jaw bone, it is possible to arrange the drilled holes with a high level of accuracy, as far as position is concerned as well as direction. Preferably, the drills used are provided with an axial stop capable of cooperating with the accessory, so that also the depth of the bore hole is accurate and reproducible.

For fixating the accessory to the jaw bone, the present invention proposes to first attach two temporary fixation pins in the jaw bone. To this end, a second drilling accessory is provided that is designed to fit snugly on the jaw concerned. This second drilling accessory may be the actual prosthesis or a replica derived from the actual prosthesis, and is provided with drill guiding holes for drilling auxiliary holes for the two temporary fixation pins.

On the other hand, a clamping device indicated as "clipper" is fixed to the prosthesis, the clipper being capable of engaging the anchoring bar in a strong yet detachable manner. It is important that this clipper is positioned very accurately, matching the position of the bar on the jaw. In other words, the positioning of the bar and the positioning of the clipper must be adapted to each other accurately.

For obtaining an accurate positional conformation, the present invention proposes to use a computer-controlled drilling machine, having a memory that contains information defining the precise spatial shape of the patient's jaw structure, as well as a scanner for obtaining this information, using a reference platform that, during drilling, offers a position reference for placing the prosthesis. The memory further contains information defining the shape of the drilling accessory that is to be fixated to the jaw bone. It is noted that these are standard accessories, to be used multiple times, not individual accessories to be used only once.

It is noted that it may happen in practice that the position of the temporary fixation pins is not fully accurate. However, the final holes that will be drilled for the anchoring bar, which will be drilled with accurate reference to the temporary pins, will in any case be located correctly with respect to each other, so that it is nevertheless possible to use a standard bar.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the present invention will be further explained by the following description of one or more preferred embodiments with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

figure 1 schematically shows a perspective view of a reference platform;

figure 2 is a block diagram schematically showing an imaging system; figures 3A-3C illustrate steps of processing a replica;

figures 4A-4D illustrate steps of drilling holes in a jawbone;

figures 5A-5E illustrate steps of placing temporary reference pins in the jawbone; figures 6A-6H illustrate a drilling guide;

figures 7A-7C illustrate a fixation tool;

figure 8 schematically illustrates a jawbone with the drilled holes;

figure 9 schematically illustrates a bar.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 schematically shows a perspective view of a possible embodiment of a reference platform 100. The reference platform 100 comprises a thin, plate-shaped carrier 101 of a rigid material, such as for instance carbon composite, which is transparent for rontgen rays. On opposite sides, the carrier 101 is provided with a layer 110, 120 of an imprint material, capable of making an imprint of a set of teeth. The imprint material preferably is a deformable and hardenable plastic, most preferably a thermoplast having a melting point or melting range of about 70 °C. The layers 110, 120 will also be indicated as imprint layers.

The size of the carrier 101 with the imprint layers 110, 120 is such that it easily fits in a patient's mouth, between his upper teeth and lower teeth. It may be necessary to have different platforms for children and grown ups. The figure shows that at one end the platform 100 may have a recess 102 for accomodating the tongue. The figure further shows that the platform 100 is provided with at least three reference markers 131 , 132, 133. Each marker is made from a material that is recognizable in a rontgen scanner; a preferred material is titanium. The markers are not located on one line but in a triangular configuration with a sufficiently large baseline.

The platform 100 is heated sufficiently for the imprint layers 110, 120 to become soft. The patient is asked to wear the dentures, to place the platform 100 in his mouth, between his teeth, and to bite firmly into the platform, so that an

impression of his teeth is made in the imprint layers 110, 120.

Instead of a reference platform having two imprint layers at opposite sides of the carrier, to be used for imprinting the upper teeth and the lower teeth, it is also possible that the reference platform has only one imprint layer, to be used either for the lower teeth or for the upper teeth. For instance, when only making a prosthesis for replacing the lower set of teeth, it suffices to make an imprint of such prosthesis at one side of the carrier. It is noted that, even if it is intended that both the lower set of teeth and the upper set of teeth are eventually replaced by a respective prosthesis, it is not necessary that such replacement is done simultaneously. When working on one set of teeth, for instance with a prosthesis for the lower set of teeth, whether the reference platform has two imprint layers or only one, it is possible that the impression of the dentures into one imprint layer is done manually outside the patient's mouth, after which the patient is asked to put the combination of dentures and platform into his mouth.

Figure 2 is a block diagram schematically showing an imaging system 200, comprising a rontgen scanner 210 and a data memory 201 . The scanner may particularly be a cone beam scanner. The figure further schematically shows a patient's head 1 . With the platform 100 still in situ, a three-dimensional rontgen image is made of the patient's head 1 , or at least of the relevant parts of the head, such as particularly the upper jaw bone and/or the lower jaw bone. Specifically, the scanner 210 takes a plurality of pictures from the head 1 , in a large number of mutually different directions, and combines the collected image data to construct (calculate) a three-dimensional image. The image is shown (projected) on a display 220. Through a user interface (not shown for sake of simplicity), an operator is capable to manipulate the image display such as to view the three-dimensional image from a certain angle, and such as to selectively show or hide specific image portions such as soft tissue, bone, metal. The rontgen data will also contain the three reference markers 131 , 132, 133 of the platform 100, as should be clear to a person skilled in the art. It is noted that imaging software for calculating such images on the basis of data obtained by the rontgen scanner 210 is known per se, and such software will not be explained in further detail here.

Since there is a well-defined relationship between the positions of the reference markers 131 , 132, 133 and the carrier 101 with the imprint layers 1 10, 120, the three-dimensional rontgen image will contain a positional relationship between the patient's jaw structure, the dentures and the reference platform 100. This relationship will hereinafter also be indicated as "platform - jaw relation".

In a second step, the locations for drilling holes into the patient's jaw are determined. The exact locations of these holes, and the directions thereof, and even the depths thereof, will depend on the actual situation of the actual jaw of this specific patient. These exact locations and directions will be determined from the three- dimensional rontgen image, i.e. the data in data memory 201 . This determination can be done automatically by a computer, using specially designed software, or by skilled personnel via the user interface of the imaging system 200.

When determining the locations, directions, and depths of these holes, these may originally be determined in coordinates associated with the head. Using the above-mentioned platform - jaw relation, it is possible to translate the coordinates of the holes to a coordinate system associated with the reference platform 100. Alternatively, considering the fact that it is difficult to define an accurate and reproducible coordinate system for the head, whereas the three reference markers 131 , 132, 133 of the reference platform 100 define a linear orthogonal coordinate system, it is possible that the locations, directions, and depths of these holes are immediately defined in coordinates with respect to the reference platform 00.

After determining the locations, directions, and depths of said holes, the conceived holes may be shown, i.e. projected, in the three-dimensional image and shown on the display 220. This allows the operator to visually verify the correctness of the calculated holes, and to possibly correct.

Particularly in cases where drilling (see below) would involve drilling through a tooth, in a third step, a replica can be made of the dentures. It is noted that this third step may be performed later than the second step, or before the second step, or simultaneously. The replica may be made in the traditional manner of first making a negative contact print and then using the negative contact print as a mould for a positive form piece.

In a fourth step, the replica is processed. This processing is illustrated in figures 3A-3C. A computer-controlled drilling apparatus 300 in accordance with the invention comprises a drill 380 and a control computer 390, having an operational memory 391 . Data obtained from the scanner 210 is tranferred into the computer's operational memory 391 , either by the computer 390 being linked to the scanner 210 by means of a wired link or a wireless link, such as for instance a wifi network, or by the data being transferred using a suitable data carrier such as for instance a DVD or a USB stick, as should be clear to a person skilled in the art. Particularly, it is possible that the computer 390 is part of the imaging system 200.

The computer-controlled drilling apparatus 300 comprises a platform holder 330, having a main surface 330 with recesses 331 , 332, 333 having mutual distances corresponding to the mutual distances of the reference markers 31 , 132, 133.

Actually, for multiple patients multiple reference platforms may be used, all having the same configuration of reference markers such that all reference platforms fit on the one platform holder 330.

The reference platform 100 is placed on the platform holder 330, with the reference markers 131 , 132, 133 arranged in the respective recesses 331 , 332, 333. The replica 360 is placed on the reference platform 100, with the teeth 361 of the replica 360 fitting in the impressions 161 of the imprint layer 1 10 or 120. This situation is shown in figure 3A. A clamp (not shown) firmly presses down on the replica 360 to hold the replica 360 and the reference platform 100 in place on the platform holder 330. Since the impressions 161 define a 1 -to-1 position relationship between the dentures and hence the replica on the one hand and the reference platform 100 on the other hand, and since the reference markers 131 , 132, 33 and recesses 331 , 332, 333 define a 1 -to-1 position relationship between the platform holder 330 on the one hand and the reference platform 100 on the other hand, there thus is a 1-to-1 position relationship between the replica 360 on the one hand and the platform holder 330 on the other hand. Further, since the platform holder 330 is part of the computer-controlled drilling apparatus 300 and the computer "knows" the exact position of the platform holder 330, the computer also knows the exact position of the dental replica 360.

In the second step mentioned above, the locations, directions, and depths of holes to be drilled in the jaw bone were defined in spatial coordinates with respect to the reference platform 100. In figure 3A, an imaginary jaw bone is schematically indicated at JB, and an imaginary hole to be drilled in the bone is schematically indicated at H. Based on the data in its memory 391 , the computer 390 "knows" the spatial coordinates of the holes H with respect to the reference platform 100 and the platform holder 330, and consequently "knows" the spatial coordinates with respect to the reference platform 100 and the platform holder 330 of a central axis A of such hole H. The computer 390 is programmed to control the drill 380 such that, as illustrated in figure 3B, the drill 380 drills a hole into the replica 360 in alignment with this central axis A. It is noted that, in the example shown in figure 3B, this hole is drilled into the replica 360 from the side directed away from the platform 100, which will be the side directed to the jaw if the patient would put this replica in his mouth.

Figure 3C schematically shows the replica 360 with the drilled hole 368. It is noted that the hole 368 is a through hole extending through the entire height of the replica. Thus, the hole 368 has an exit opening at the daylight side of the replica. This is the reason why the use of a replica is preferred. In principle, it is possible to use the actual dentures in stead of the replica, but then a finishing step will be necessary for closing said exit opening and processing the closure such as to become invisible to the eye.

It is further noted that, for each of the holes to be drilled in the jaw bone, a corresponding hole 368 is drilled in the replica 360, and that, since the holes to be drilled in the jaw bone are mutually parallel, the holes 368 are mutually parallel.

The angle between the orientation of the hole H, i.e. the direction of the axis A, on the one hand and the normal of (i.e. a line perpendicular to the surface of) plate-shaped carrier 101 on the other hand will in practice normally be equal to zero, but in some cases a non-zero angle may be needed, with the exact direction depending among other things on the actual jawbone situation. The processed replica can now be removed from the platform holder 330 and placed in the patient's mouth to be used as a drilling guide. Figure 4A illustrates schematically the situation of the processed replica 360 when placed on the patient's jaw. With reference to figure 3A, it should be clear that the hole 368 in the replica 360 is precisely aligned with the hole H to be drilled (shown in broken lines) in the jaw bone JB.

In a fifth step, with the replica 360 placed in the patient's mouth and used as a drilling guide, the dentist manually drills the hole H into the jaw bone JB, using a manual drill tool 400 with a drill bit 401 , as shown in figure 4A.

It is possible to use the replica 360 as drilling guide directly. Typically, however, the replica material may be not sufficiently hard to act as a robust drilling guide actually keeping the drill bit 401 aligned against transverse deviations.

Therefore it is preferred to first place a drill guiding bush 410 into the replica's hole 368. The drill guiding bush 410 is made from a material harder than the replica's plastic, and may typically be made from a metal such as for instance stainless steel.

Figure 4B illustrates an intermediate step where the replica and the platform 100 are arrange upside-down in the drilling apparatus 300. In this orientation, the drill 380 drills into the hole 368 from the opposite direction, i.e. from the side directed away from the jaw if the patient would put this replica in his mouth. The drill 380 uses a drill of a wider diameter, and drills up to a predetermined depth, so that eventually the hole 368 has a first portion 368a having a relative small diameter, a second portion 368b having a wider diameter, with a shoulder 368c at the transition in between. The drill guide bush 410 (see figure 4D) is placed in the second hole portion 368b and abuts the shoulders 368c.

Thus, the result is a stepped hole 368. In the above example, this hole is provided in a two-step process. Figure 4C schematically illustrates a one-step drilling process, wherein the combination of replica 360, reference platform 100 and platform holder 330 is placed upside-down in the drilling apparatus (compare with figure 3B), and wherein a stepped drill 381 is used to drill into the replica from the side of the platform holder 330, which for that purpose is provided with a void 340 for allowing the drill to pass.

In any case, the drill guide bush 410 is placed in the wider portion 368b of the stepped hole 368 to act as a drill guide. Since the replica can be discarded

afterwards, the drill guide bush 410 may be clamped or even fixed with a suitable adhesive. In order to assure that the hole H is drilled to exactly the correct depth, it is preferred to use a stepped drill bit 40 , shown separately in figure 4D on a larger scale, so that the drill guide bush 410 also acts as a drill stop. The stepped drill bit 401 has a distal end 402 designed for drilling, and a proximal end 404 designed for holding the drill bit in a drill head. Between the distal end 402 and the proximal end 404, the stepped drill bit 401 has a shoulder 403 having a diameter larger than the distal end 402. In use, this shoulder 403 will act as a stop when the shoulder 403 contacts the drill guiding bush 410 to indicate that the hole H has been drilled to the correct depth.

It is noted that, before the hole H is drilled into the jaw bone JB, the gums (not shown in the schematic drawings) are cut and folded open to expose the jaw bone JB, and a flat face is ground to the jaw bone JB, substantially normal to the hole direction A, to obtain a suitable reference face. It is further noted that, in this stage, the depth of the hole H with respect to this reference face is a reference for the depth of the future holes to be drilled.

Figure 5A schematically shows the jaw bone JB with the finished hole H.

While only one hole H is shown, it should be clear that actually two such holes H have been made, mutually parallel.

In principle, these holes H may be the holes in which the actual implants are installed. However, for placing a standard bar it is required that two holes are drilled in precisely the correct location and direction, specifically parallel to each other, and it is quite difficult for the dentist to achieve this precision using only the replica 360 as drilling guide, considering that the replica 360 will always allow some movement with respect to the jaw. Further, it is preferred that the holes for the implants are not drilled in one drilling operation, but in several drilling operations with successively increasing diameter, which further complicates the above problem. Therefore, in the preferred embodiment of the invention, these holes H are auxiliary holes for placing therein temporary reference pins. In a sixth step, as illustrated in figure 5B, a temporary reference pin 500 is placed in the hole H. Figure 5C illustrates an embodiment of such temporary reference pin 500 in more detail. The temporary reference pin 500 comprises an insertion portion 501 for inserting into the hole H, and an engagement portion 502 projecting from the jaw bone JB when the temporary reference pin 500 has been inserted into the hole H. In figure 5C, these two portions 501 , 502 are shown with different diameters, in which case a shoulder 503 between the insertion portion 501 and the engagement portion 502 acts as a stop that contacts the jaw bone JB when the temporary reference pin 500 is inserted into position. It is however preferred that the pins 500 have a constant diameter over their entire length (see figure 5D), and that the temporary reference pin 500 is pushed into the jaw bone until the pin's tip contacts the bottom of the hole H. If desired, the insertion portion 501 may be provided with a thread for screwing, in which case an end face 505 of the engagement portion 502 may have a profiling, not shown for sake of simplicity, for engaging with a suitable insertion tool, as will be clear to a person skilled in the art. The engagement portion 502 may be provided with one or more markings 504, of which the function will be explained later.

Figure 5E schematically illustrates an embodiment of a temporary reference pin 500 that, at a well-defined position between the insertion portion 501 and the engagement portion 502, is provided with a portion 510 having a diameter wider than the engagement portion 502 and thus providing a stop face 511 towards the engagement portion 502. Portion 510 may be a ring-shaped portion, as shown. The function will be explained later. In a next phase of the process, the actual holes for the anchoring pins are drilled, using a drilling guide that is attached to the temporary reference pins 500 for stability. While it is possible to drill these holes in one go, it is preferred to drill in at least two, preferably three, and perhaps even four or more steps with always increasing drill diameter. For each of these drill steps, corresponding drilling guides are used, so it is desirable to be able to attach and detach the drilling guides quickly. For that purpose, the present invention proposes a design of a drilling guide and corresponding fixation tool as will be explained in the following.

Figure 6A schematically shows a drilling assistance assembly 1000 according to the present invention. The drilling assistance assembly 1000 comprises the two temporary reference pins 500, a plurality of drilling guides 600, an implant guide 690, a fixation tool 700, and possibly a tongue rest 800. In principle, it is possible to implement the present invention with a drilling assistance assembly 1000 that includes only one drilling guide 600, but preferably the drilling assistance assembly 1000 includes at least two, preferably three, and perhaps even four or more drilling guides 600, always corresponding to the number of drilling steps mentioned above. In principle, it is possible to have one common fixation tool 700, but preferably the drilling assistance assembly 1000 comprises a plurality of fixation tools 700, with always one dedicated fixation tool 700 for each drilling guide 600. Likewise, it is possible to have one common tongue rest 800, but preferably the drilling assistance assembly 000 comprises multiple tongue rests, with always one tongue rest associated with a particular drilling guide.

Figure 6B schematically shows a more detailed perspective view of a possible embodiment of a drilling guide 600 according to the present invention. The drilling guide 600 has two mutually parallel main surfaces 601 , 602. In use, one of these surfaces will be directed to the jaw bone JB; this surface will be indicated as jaw face 601 , whereas the opposite surface will be indicated as instrument face 602. In figure 6B, the drilling guide 600 is seen from the side of the jaw face 601. Figure 6D shows a projection view of the drilling guide 600 from the instrument face 602, and figure 6E shows a projection view of the drilling guide 600 from the jaw face 601 .

The drilling guide 600 has two mesas 61 1 , 612 projecting from the jaw face

601 . Each mesa 61 1 , 612 has a top face 613, 614, respectively,

The drilling guide 600 has two through reference holes 621 , 622, each reference hole being substantially centered with a corresponding mesa 61 1 , 612 and extending from the corresponding top face 613, 614 to the opposite instrument face

602. The mutual distance of the reference holes 621 , 622 corresponds to the mutual distance of the two holes H drilled in the jawbone JB, and hence the mutual distance of the two temporary reference pins 500 when inserted in these holes. The diameter of the reference holes 621 , 622 is substantially equal to, or perhaps slightly larger than, the diameter of the engagement portion 502 of the temporary reference pins 500.

In use, the drilling guide 600 will be placed on the patient's jaw bone JB, with the engagement portion 502 of the temporary reference pins 500 extending through the respective reference holes 621 , 622, and will be pushed along the temporary reference pins 500 until the top faces 613, 614 of the mesas 61 1 , 612 contact the flattened portions of the jaw bone JB, or, in the embodiment of figure 5E, until the top faces 613, 614 of the mesas 61 1 , 612 contact the respective stop faces 51 1 of the respective temporary reference pins 500. Therefore, the end of the holes 621 , 622 at the level of the mesa top faces 613, 614 will be indicated as the entrance end. Figure 6C shows a cross section of the drilling guide 600 to show that the reference holes 621 , 622 may be tapered at their entrance ends to facilitate entrance of the temporary reference pins 500.

The length of the engagement portion 502 of the temporary reference pin 500 is larger than the distance from the top faces 613, 614 of the mesas 61 1 , 612 to the opposite instrument face 602 of the drilling guide 600, so that, when the drilling guide 600 is placed on the temporary reference pins 500 as described above, the free end of the engagement portion 502 of the temporary reference pin 500 projects from the instrument face 602 and the markings 504 are visible. As will become clear from the following description, the drilling guide 600 will be the reference determining location and depth of the final implantation holes to be drilled, so it is important that the drilling guide 600 is positioned correctly. The markings 504 allow the dentist to visually check whether the drilling guide 600 is positioned correctly.

When placed on the temporary reference pins 500, the drilling guide 600 has one side directed to the tongue of the patient, which side will be indicated as rear side 641 . The opposite side of the drilling guide 600 will be directed to the outside of the mouth, and will be indicated as front side 642. For further explanation of the structure of the drilling guide 600, it is useful to define a first imaginary plane which contains the axes of the two through reference holes 621 , 622, and to define an imaginary plane of symmetry extending between the two through reference holes 621 , 622, parallel to the axes of these holes and perpendicular to said first imaginary plane. In the following, positions closer to or further away from the plane of symmetry will be indicated as "inside" and "outside", respectively, or similar words. Further, positions closer to or further away from the front side will be indicated as "at the front of and "at the rear of, respectively, or similar words.

The drilling guide 600 has two through drilling guide holes 631 , 632 extending from the instrument face 602 to the opposite jaw face 601 , and located "outside" and "at the rear of the reference holes 621 , 622. The drilling guide holes 631 , 632 are designed to tightly fit around a dentist's drill bit of a predetermined standard diameter, to accurately guide such drill bit. To be able to do so, the drilling guide 600 is made from a suitably hard or hardened material, for instance stainless steel. Alternatively, the drilling guide 600 may have insert bushes defining the drilling guide holes. With the drilling guide 600 clamped to the temporary reference pins 500, the dentist drills anchoring holes into the jawbone. In view of the stable fixation of the drilling guide 600 to the jawbone, the anchoring holes are drilled with great accuracy as regards position and direction. The drill bits to be used will be stepped dril bits, similar to 401 in figure 4D, and the instrument face 602 of the drilling guide 600 acts as a stop for such bit. Thus, with the drilling guide 600 fixated at the correct height with respect to the jawbone, the final implantation holes will be accurately drilled to the correct depth with respect to the jawbone.

A drilling guide 600 is designed for one drill size only. For successively drilling the same hole with increasing diameter, different drilling guides 600 are provided, which are mutually exactly the same except for the diameter of the drilling guide holes 631 , 632. For instance, a first drilling guide 600 may have drilling guide holes 631 , 632 with a diameter of 2 mm, a second drilling guide 600 may have drilling guide holes 631 , 632 with a diameter of 3,2 mm, a third drilling guide 600 may have drilling guide holes 631 , 632 with a diameter of 4 mm. In the following, the diameter of the drilling guide holes may also be indicated as the size of the drilling guide.

The following description will apply to each drilling guide, whatever the size. In order to be able to accurately drill holes into the jaw bone, it is not sufficient if the drilling guide holes 631 , 632 guide the drill bit with little or no play. It is also important that the drilling guide 600 is firmly attached to the temporary reference pins 500 and thus positionally fixated with respect to the jaw bone JB. It is further important that all drilling guides 600 are accurately positioned with respect to the jaw bone JB in the same way so that, with respect to the hole to be drilled, the respective drilling guide holes are always perfectly aligned. On the other hand, the required accuracy is at odds with the inevitable play between the reference holes 621 , 622 and the respective pins 500. Thus, the present invention provides a fixation tool for eliminating said play and fixating the drilling guide 600 with respect to the respective pins 500 in a simple yet strong and reproducible manner.

Figure 7A schematically shows a perspective view of an embodiment of a fixation tool 700 according to the present invention, and figure 7B is a projection view showing some details at a larger scale. This tool, which may be manufactured by punching it or cutting it from a metal plate, has a generally elongate U-shape with two substantially parallel leg sections 701 , 702 joined by a curved midsection 703, which is elastically deformable such as to allow for the leg sections 701 , 702 to be moved slightly towards each other or away from each other. As will be explained in more detail, the fixation tool 700 has two operative conditions. In a first operative condition, which typically is a relaxed, stress-free condition, the leg sections 701 , 702 have moved towards each other so that their mutual distance is relatively small. In a second operative condition, the leg sections 701 , 702 have moved away from each other so that their mutual distance is relatively large. For converting the fixation tool 700 from its first operative condition to its second operative condition and vice versa, and to reliably and firmly hold the fixation tool 700 in either of these conditions, this embodiment of the fixation tool 700 comprises a fixation slider 790. Figure 7C is a schematic cross section of the fixation tool 700, also showing the fixation slider 790.

The fixation slider 790 has a general T-shaped cross section, with a central body 791 extending between the leg sections 701 , 702, two feet portions 792 protruding from the central body 791 and extending under the leg sections 701 , 702, and two arm sections 793 extending sideways from the central body 791 over and beyond the leg sections 701 , 702, the arm sections 793 having extremities 794 directed towards the feet portions 792. To allow the fixation slider 790 to be put in place, the curved midsection 703 of the fixation tool 700 surrounds a space 704 of sufficient width to allow the two feet portions 792 to pass.

The leg sections 70 , 702 have inner edges 705, 706 which, in the first operative condition, are not quite parallel: at the end away from the curved

midsection 703, the mutual distance between the inner edges 705, 706 is smaller than the width of the central body 791 of the fixation slider 790, while at the opposite end close to the curved midsection 703, the mutual distance between the inner edges 705, 706 is larger, typically equal to or even larger than the width of the central body 791 of the fixation slider 790. With the fixation slider 790 in a position close to the curved midsection 703, the fixation tool 700 is in its first operative condition.

When the fixation slider 790 is shifted away from the curved midsection 703, towards the free ends of the leg sections 701 , 702, the central body 791 of the fixation slider 790 engages the inner edges 705, 706 of the leg sections 701 , 702 and progressively pushes the leg sections 701 , 702 apart.

At their free ends, the leg sections 701 , 702 are shaped to cooperate with the drilling guide 600, for fixating the drilling guide 600 with respect to the temporary reference pins 500.

As can be seen in the view of figure 6D, the drilling guide 600 has a free inner space 650 that opens to the instrument face 602. Figure 6G is a cross section along said first imaginary plane, showing that this inner space 650 extends from the instrument face 602 up to a ceiling 651 , and is as wide to include the reference holes 621 , 622.

It can be seen in figure 6B that the drilling guide 600 has a front face 603, that may be substantially perpendicular to the jaw face 601 and instrument face 602. Approximately midway between the jaw face 601 and the instrument face 602, the drilling guide 600 has two openings 652, 653 in its front face 603, on opposite sides of the said plane of symmetry, with a separation 654 in between. The openings 652, 653 extend from the front face 603 to the inner space 650, and have a height substantially corresponding to the thickness of the fixation tool 700. Figure 6F is a cross section along a plane perpendicular to said first imaginary plane and to said plane of symmetry, through said openings 652, 653. This figure further shows that the drilling guide 600 has a central opening 655 in its rear face 604, aligned with said two openings 652, 653.

In figure 7A, a center line of the fixation tool 700 is indicated at 709. The fixation tool 700 may be mirror-symmetric with respect to this center line, although precise symmetry is not essential. In the following, directions towards this center line will be indicated as "inwards", while directions away from this center line will be indicated as "outwards".

At the free ends of the respective leg sections 701 , 702, said leg sections widen inwards, so that the inner edges 705, 706 have end sections 735, 736, respectively, at a relative short distance from each other. Each end section 735, 736 has a recess 737, 738, respectively. The free end of each leg section 701 , 702 is shaped as a wedge 741 , 742, respectively, with, at some distance from the

respective end edges, hook portions 751 , 752 that are directed outwards. Below each hook portion 751 , 752, i.e. at the side directed away from the end edges, the respective leg sections 701 , 702 have accomodation pockets 713, 714 for

accommodating the temporary reference pins 500. Each accomodation pocket 713, 714 extends partly below the corresponding hook portion 751 , 752 and partly extends further outside than the corresponding hook portion 751 , 752. Towards the outside, each accomodation pocket 713, 714 is bordered by a respective projection 71 1 , 712.

In the longitudinal direction, i.e. the direction parallel to said center line 709, the distance between the recessed bottom of the accomodation pockets 713, 714 and the corresponding hook portion 751 , 752, indicated at "d1 ", corresponds to the diameter of the engagement portion 502 of the temporary reference pin 500, or is slightly larger. In the transverse direction, i.e. the direction perpendicular to said center line 709, the distance between the projection 71 1 , 712 and the corresponding hook portion 751 , 752, indicated at "d2" and defining an entrance opening to the accomodation pockets 713, 714, corresponds to the diameter of the engagement portion 502 of the temporary reference pin 500, or is slightly larger.

At its rear side, the fixation tool 700 has two arms 771 , 772 located on opposite sides of said place of symmetry, projecting from the rear face 604 and curved inwards to point to each other. The spaces 773, 774 thus defined between the rear face 604 and the arms 771 , 772 are accommodation spaces for accommodating mounting bars 801 of a tongue support 800. The precise design of such tongue support is not essential; suffice it to say that such support allows the patient to rest his tongue and to prevent the patient's tongue to come close to the drilling area.

The use of the fixation tool 700 is as follows.

First, a tongue support 800 is attached to the drilling guide 600 by placing its mounting bars 801 in the accommodation spaces 773, 774.

Second, the two legs 701 , 702 of the fixation tool 700 are moved apart manually to such distance, that their wedge-shaped ends 741 , 742 can be inserted into the two openings 652, 653 in the front face 603, cross the free inner space 650, and exit the opening 655 in the rear face 604, up to a point where the hook portions 751 , 752 abut a rear wall 656 of the free inner space 650. At that point, the recesses 737, 738 are aligned with the separation 654. Now, the two legs 701 , 702 are released so that they spring back towards each other, so that the separation 654 enters the two recesses 737, 738; the fixation tool 700 is now locked with respect to the drilling guide 600. As can be seen in figure 6H, the wedge-shaped ends 741 , 742 of the fixation tool 700 also serve to lock the mounting bars 801 of the tongue support 800.

In this way, all drilling guides 600 are prepared, i.e. provided with a dedicated tongue support 800 and fixation tool 700.

When the drilling operation is performed, the drilling guides 600 with their tongue support 800 and fixation tool 700 attached are lying ready for the dentist. The dentist first takes the drilling guide 600 having the smallest size. More particularly, the dentist takes hold of the corresponding fixation tool 700 as a grip, and places the drilling guide 600 on the temporary reference pins 500, pushing the drilling guide 600 down as far as possible. At this point, the reference marks 504 of the reference pins 500 should be visible, and a predetermined reference mark should be aligned with the instrument face 602. This is an indication that the drilling guide 600 is in the correct axial distance from the jawbone to drill the anchoring hole to the correct depth.

Now, the two legs 701 , 702 of the fixation tool 700 are moved apart. It is noted that this action is performed by the dentist moving the slider 790 forward with his thumb, which he can simply do with the same hand as holding the fixation tool 700. It can be seen in figures 7B and 6H that the front faces 753, 754 of the hook portions 751 , 752, i.e. the faces directed to the rear of the drilling guide 600, are slightly slanted, corresponding to a slanting of the rear wall 656 of the inner space 650.

Pushing the legs 701 , 702 apart will thus result in the hook portions 751 , 752 being pushed to the front side of the drilling guide 600. The hook portions 751 , 752 will abut the reference pins 500 and will thus push the reference pins 500 to the front side of the drilling guide 600 (or push the drilling guide 600 to the rear side).

The holes 621 , 622 are shaped to take up any tolerance of the placing of the temporary reference pins 500 in a reproduceable manner. A first one of said holes 622 is, at its front side, shaped in a V-shape, as clearly visible in figure 6F.

Consequently, the pin 500 in this hole is pushed into this V-shape, until it abuts both walls of the V-shape. This clearly defines the position of this pin in two dimensions; with respect to this pin, the drilling guide 600 only has the freedom to slightly rotate around this pin. A second one of said holes 621 has, at its front side, a wider flat wall portion 623 perpendicular to the plane of symmetry, as clearly visible in figure 6F. Consequently, the pin 500 in this hole is pushed to abut this wall portion 623, thus defining the rotary position with respect to the other pin and eliminating all play, while the exact location of abutment will depend on the precise distance between the two pins 500.

The fixation tool 700 and the drilling guide 600 are now fixated with respect to the temporary reference pins 500. The dentist drills the final implantation holes, and then removes the drilling guide 600.

The above steps are then repeated with successive drilling guides. According to an important aspect of the present invention, thanks to the special shapes of the holes 621 , 622, it is assured that the drill guide holes 631 , 632 are always located to the same position with respect to the pins 500 and hence with respect to the jaw bone. Figure 8 is a schematic cross section through a jawbone JB, with the reference pins 500 in the reference holes H (only one pin 500 in one hole H being visible), with a drilling guide 600 and fixation tool 700 clamped to the pins 500, and a tongue support 800 fixed to the drilling guide 600. Reference markings 504 are visible to indicate that the drilling guide 600 is placed at the correct height. A final implantation hole, drilled with the aid of the drilling guide 600, is shown at Hfi.

After completion of the final implantation holes, the pins 500 are removed and an anchoring bar is attached to the jaw bone. Thanks to the present invention, a standard prefabricated bar 900 can be used. Such standard prefabricated bar 900 comprises a cross rod 903 (also indicated as "steg") provided at its ends with two mutually parallel fixation bushes 901 , 902 to be fixated by screwing screws 904, 905 in the final implantation holes Hfi, and extending substantially perpendicular to the cross bar 903, as illustrated schematically in figure 9.

The screws 904, 905 will not engage the final implantation holes Hfi directly.

First, implants 910, 920 will be installed into the final implantation holes Hfi, such implants having a threaded bore 912, 922 matching with the screws 904, 905. It is noted that the implants are standard components. Typically, the implants 910, 920 have a cylindrical shape, and are provided with a threaded outer surface 91 1 , 921 for being screwed into the final implantation holes Hfi. Screwing the implants 910, 920 into the final implantation holes Hfi is performed by the dentist. In a further preferred elaboration of the present invention, the dentist is also assisted in this screwing operation by using an implant guide 690. The implant guide 690 is, in all features, identical to the drilling guide 600 described above, except that its guide holes 631 , 632 are not used for guiding a drill bit but are used for guiding the implants 910, 920. Thus, the guide holes 631 , 632 of the implant guide 690 have a diameter

corresponding to the outer diameter of the implants 910, 920. Depending on the precise design of the implants 910, 920, the outer diameter may be the outer diameter of the threading or, if the implants 910, 920 are provided with an abutment flange, said outer diameter will be the outer diameter of the abutment flange.

The implant guide 690 is provided with a fixation tool 700, as described above, and is fixated to the reference pins 500, in the same way as described for the drilling guides 600. The dentist places an implant into one of the guide holes 631 , 632 and pushes/screws it down into the corresponding implantation hole. As already explained earlier, the guide holes 631 , 632 will be perfectly aligned with the

respective implantation holes, and thus the implants will be screwed into the respective implantation holes in a perfectly aligned manner.

With the implants in place, the guides 600 and 690 are no longer needed, and hence the reference pins 500 can now be removed. The bar 900 is put in position, with the fixation bushes 901 , 902 aligned with the implants 910, 920, and the screws 904, 905 are now screwed to the implants 910, 920. Thanks to the invention, with the mutual distance between the drill guide holes 631 , 632 being equal to the standard mutual distance between the two fixation bushes 901 , 902, and the implantation holes being drilled to the correct depth, the bar 900 will fit perfectly.

For engaging the rod 903, a clamping device will be mounted in a recess in the dentures. Milling the recess will be done by the device 300, using a miller instead of a drill. The mutual positional interrelationship between the recess and hence the clamping device on the one hand and the rod 903 on the other hand will be very accurate.

It should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims. For instance, instead of using a rontgen scanner as described in the above, it is technically possible to use any type of scanner capable of obtaining three-dimensional image data of a patient's head while recognizing markers on a carrier with an imprint layer, with the obvious provision that regulations allow such scanner type to be used.

Further, two or more functions may be performed by one single entity, unit or processor. Even if certain features are recited in different dependent claims, the present invention also relates to an embodiment comprising these features in common. Any reference signs in a claim should not be construed as limiting the scope of that claim.

In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, digital signal processor, etc.