STOP ELEMENT FOR A SURGICAL TOOL

FIELD OF THE INVENTION This invention relates to a novel stop element, for use in conjunction with a surgical tool such as, for example, a drill, screw tap, or counter bore, wherein the stop element is capable of prohibiting insertion of the tool beyond a predetermined depth into bone tissue, for example

BACKGROUND

Dentists and dental surgeons use tools, such as drills, screw taps and counter bores to create bores in bone tissue. Drills are generally provided in various types, sizes, lengths and styles. Importantly, the diameter of the drill used will dictate the diameter of the bore produced in the bone tissue. The length of the bore is generally not dependent upon the size or length of the drill, but is determined by the dentist or dental surgeon.

However, the length of the bore can be critical, for example, if the length of the bore is too long, it can puncture the mandibular canal which contains nerves if it is placed in the mandible, or the sinus cavity if it is placed in the maxilla. Furthermore, the roots of adjacent teeth also can be affected by the size of the bore.

To ensure that a drill bit is inserted into the bone to a known length, the drill bit often contains several markings on it which signify specific depths. For example, a drill bit may have a visual marking on it that, when located at the surface of the bone, indicates the bore depth is 1 mm. The use of a visual marker is of limited value and depends upon the dentist or dental surgeon's ability to see the marker as the drill is

being inserted into the patient's mouth. Visual markers may, in use, be difficult to see and therefore they do not lend themselves to speed of use and/or accuracy.

There have been various attempts to overcome or mitigate this problem. For example, international patent application no. WO 00/25695 (Implant Innovations, Inc) describes penetration limiting stop elements for a drill bit used for bone tissue. The stop element limits the penetration of the drill bit beyond a predetermined axial distance on the drill bit. The stop element consists of a connecting portion and an extending portion, both having an inner wall defining a bore extending entirely through the connecting portion and extending portions. The connecting portion has a surface that contacts the drill bit, in use, to limit the rearward axial movement of the stop element relative to the drill bit. The extending portion terminates in a lower or forwardmost end for engaging the bone surrounding the bore to limit the penetration of the drill bit. Rotation of the stop element about the longitudinal axis of the drill bit is not limited and may result in undesirable wobbling during use which may be uncomfortable for the patient and adversely affect the accuracy of the drilling. Furthermore, the stop element of WO '695 is intended for use only with specially designed drills which have an appropriate exterior surface thereon for abutment against the relevant surface on the connecting portion of the stop element. Therefore, the drill stops of WO '695 require a drill to be specially made, which generally makes their use expensive. Furthermore, because the drill stops of WO '695 locate on the exterior surface of the tool, they are relatively bulky in design. They may therefore make visibility worse for the surgeon and hinder access to the region where treatment is required, as well as preventing proper cooling, perhaps to the extent that more expensive drills with internal irrigation are required. Drills with internal irrigation provide increased risk of issues such as fatal air embolism. Consequently, WO '695 does not satisfactorily solve the problem set out above.

We have now found a novel form of a stop element which overcomes or mitigates the problems of prior art stop elements.

STATEMENT OF INVENTION Therefore, according to a first aspect of the invention we provide a stop element for use with a fluted surgical tool, wherein the stop element comprises a collar consisting of a generally tubular main body for surrounding the surgical tool, the body being provided with an internal body face and an external body face; and a first end face and a second end face; wherein the internal body face is provided with one or more lugs adapted to engage with a flute on the surgical tool.

By the term "fluted surgical tool" we mean, without limitation, any tool used in surgery, e.g. orthopaedic or orthodontic surgery, that is provided with at least one flute, recess, indentation or groove along a portion of its length. Examples of fluted surgical tools include fluted drills such as a spade drill or a twist drill. Furthermore, the flute may comprise a helical or a straight groove or combinations thereof.

By the term "lug" we mean, without limitation, any shape of lug, projection, protrusion or the like which projects inwardly from the internal body face of the main body of the stop element and is capable of engaging with at least part of a fluted surgical tool.

By the terms "proximal end" or "rearward end", we mean the end furthest from the patient and the working end of a tool, in use.

By the terms "distal end" or "forward end", we mean the end nearest the patient and the working end of a tool, in use.

It will be appreciated by a person skilled in the art that conventional drills may include a pair of linear or helical grooves or flutes. The stop element of the invention will function with a single lug, but preferably the number of lugs corresponds to the number of flutes present in the surgical tool and therefore, preferably, the stop element of the invention is provided with a pair of lugs if there are a pair of flutes on the tool. The surgical tool may comprise a screw tap or a counter bore, however, in a preferred embodiment, the surgical tool is a surgical drill.

Various possible shapes for the lug are envisaged. Preferably the lug is provided with a wall which abuts or is joined onto the inner face of the collar and the opposing wall, i.e. the wall facing the working end e.g. the drill bit, may be substantially straight or arcuate, i.e. convex so as to correspond, for example, to the usually concave surface of the drill flute. A conventional surgical tool such as a drill comprises a helical groove or flute provided with a shoulder at the end of the flute distal to the drill tip. Thus, preferably, the lug is provided with a corresponding shoulder which is adapted to abut the drill flute shoulder when the drill stop is pushed up the drill shaft. When more than one lug is present, each lug may be the same or different shape to one another.

In one embodiment of the invention the stop element may be provided with one or more break grooves. The stop element is preferably constructed from a frangible material, at least in the frangible region of the break grooves.

The presence of one or more break grooves enables the length of the stop element to be selectively varied. The break grooves may extend entirely around the circumferential exterior of the stop element or around only a part of the circumference. Although the shape of the one or more break grooves may vary, preferably they will generally have a V-shaped cross-section. Preferably, a set of

break grooves is provided at a plurality of axial locations so that a range of desired stop element lengths are available to the user, -i.e. the dentist or dental surgeon, from a single stop element.

The stop element of the invention may comprise a variety of rigid materials such as metal, plastic or a composite material. A stop element including break grooves will need a frangible region, at least in the region of the break grooves. A composite material may be used such that only the frangible region comprises a frangible material, the rest optionally being non-frangible.

The stop element of the invention is advantageous since, inter alia, it can be quickly and easily fitted onto a surgical tool, such as a drill. Furthermore, in use, rotation of the stop element relative to the surgical tool is reduced or prevented by the interaction between the lugs and flutes. This can significantly improve the stability of the tool, in use, reducing undesirable wobble.

In addition, the longitudinal stop element of the invention is advantageous since, inter alia, it reduces the number of stop elements required per surgical tool since one stop element may be altered using the break grooves to accommodate each length associated with each depth marking of a specific surgical tool, e.g. drill.

In addition, the stop elements of the present invention can be used with a conventional, i.e. existing, surgical tool, such as a drill. It is not necessary to use the stop element in conjunction with a specially-designed tool having the required abutment surfaces for the stop element (as in WO '695 described above). Furthermore, since the lugs of the stop element located within the flutes of the tool, the overall diameter of the stop element can be significantly reduced in comparison

with the prior art. Thus, for example, a slim drill may be used without the need for a wide shoulder region which might hinder vision of the area to be operated upon.

A further advantage of the present invention is that the stop element can have a press fit or friction fit onto the tool. The ability to press or friction fit may be achieved in one or more ways.

Thus, for example, the diameter of the internal bore of the stop element may be greater at one end than the other, such that the internal wall(s) of the stop element essentially form a frusto-conical surface.

Alternatively, the internal cross section of the stop element may be non circular, for example it may be elliptical or preferably, may be substantially circular but having one or more, preferably opposing friction fit regions which are preferably substantially straight or flat. The friction fit regions have the function of improving a friction fit between the stop element and the tool, in use and may comprise regions where the diameter of the internal bore of the stop element is reduced. The one or more friction fit regions may be provided along the full axial length of the stop element or along part of the length, for example only at one end. When they are provided at one end, the friction fit regions are preferably at proximal end i.e. that which, in use, is furthest from the working end of the tool e.g. the cutting tip of the drill.

In a further alternative the stop element may be provided with for example, one or more slots, preferably a plurality of slots, positioned around an end face of the stop element. When such slots are present they may be positioned on one or both ends of the stop element. When they are positioned at one end they may be positioned at the distal end i.e. that closest to the working end of the surgical tool, e.g. the drill cutting tip. However, when the stop element of the invention includes break grooves

as hereinbefore described, then such one or more slots are preferably at the proximal end which, in use, is furthest from the working end of the tool-, the cutting tip of the drill. In a still further alternative the one or more lugs may be made larger than would otherwise be required (i.e. the internal diameter defined by the lugs is less than the minimum external diameter of the tool, inside a flute) and may be deformable, such that, in use, the one or more lugs may form a friction fit against the surgical tool. It will be appreciated by the person skilled in the art that more than one of the press fit functions as hereinbefore described may be included in the stop element of the invention at any one time.

Optionally the stop elements may be coded, e.g. colour coded, so as to distinguish their parts by diameter or length. Alternatively or in addition, the stop elements may be inscribed so as to indicate different lengths/depths. In a further aspect of the invention the stop elements may be provided with a holder. When the stop element includes break grooves, such a holder may optionally incorporate, optionally integrally, a cutter.

According to a further aspect of the invention there is provided a kit comprising one or more surgical tools, e.g. drills, and at least one stop element as hereinbefore described. The kit may comprise a mixture of stop elements with and without break grooves.

According to a further aspect of the invention there is provided a surgical tool, e.g. a drill, including a stop element as hereinbefore described.

In another aspect of the invention there is provided a method of insertion of a surgical tool into bone tissue up to a predetermined depth which comprises the use of a surgical tool and stop element as hereinbefore described. We especially provide a

method of preventing the over insertion of a surgical tool into bone tissue which comprises the use of a surgical tool and stop element as hereinbefore described.

Preferred aspects of the present invention will now be more particularly described, by way of example only, with reference to the following Figures in which:

Figures 1 a to c are perspective views of a stop element according to one aspect of the invention;

Figure 2 is a partially-transparent perspective view of the stop element of Figure 1 positioned on a drill;

Figure 3 is a perspective view of a non-circular stop element;

Figure 4 is a perspective view of a frangible stop element;

Figure 5 is a cross-section of a frangible stop element;

Figure 6 is a cross-section of a frangible stop element provided with a slot; Figures 7A-7E show perspective, side, end and two cross-sectional views of a stop element;

Figures 8A-8E show perspective, side, end and two cross-sectional views of a frangible stop element having slots at its distal end;

Figures 9A-9E show perspective, side, end and two cross-sectional views of a frangible stop element having slots at its proximal end;

Figures 7F, 8F and 9F are perspective views of the stop elements of Figures 7-9 mounted on a drill;

Figure 10 is a side view, shown partially transparent, of a stop element mounted on a drill; and Figure 11 shows the stop element and drill of Figure 10, in cross-section.

Referring to figures 1a to c, a stop element 1 for use with a drill (not shown) comprises a collar 2. The collar 2 comprises a generally tubular main body 4 for

surrounding a drill, being provided with a first end face 5 and a second end face 6; an external face 7 and an internal face 8. The internal face 8 is provided with lugs 9 and 10, such that the lugs 9 and 10 correspond to the fluted surface of a drill (not shown). The collar 2 includes a plurality of slots 16 positioned around the second end face 6. The plurality of slots 16 provides flexibility to the collar 2.

Referring to figure 2, a drill stop element is positioned over a drill 11. To put the stop element in place, the collar 2 is slid over the end of the drill tip, the lugs 23, 24 engaging in the flutes of the drill 11. The stop element can be slid up the fluted shaft of the drill 11 , rotating as it goes with the path of the lugs being guided by the flutes, until the stop element stops around the point where the flute 12 of the drill 11 ceases, this providing an axial endstop for the stop element.

Once in place, in use during drilling, the end face 5 acts as an axial depth stop when the drill is used to produce a bore in a bone.

Referring to figure 3 a further embodiment of the stop element comprises a collar 17. The collar 17 comprises a generally tubular main body 18 for surrounding a drill, being provided with a first end face 19 and a second end face (not shown); an external face 21 and an internal face 22. The internal face 22 is provided with lugs 23 and 24, furthermore, although the internal face 22 is substantially circular, the face 22 is provided with a pair of substantially straight or flat opposing regions 25 and 26 ("friction fit regions") which, in use, facilitate a friction fit to the drill (not shown).

Referring to figures 4, 5 and 6, a further embodiment of the stop element 14 is constructed from a frangible material, such as a polymeric material like polyethylene or polyoxymethylene (i.e. Delrin™). The stop element 14 is provided with plurality of break grooves 15 which enables the length of the stop element 14 to be selected.

The grooves 15 may extend entirely around the exterior of the stop element 14 or around a part of it. The grooves 15 may generally comprise a V-shaped cross- section. The break grooves 15 are preferably arranged at locations which correspond with depth markings of a particular drill bit (or bits). Thus, in use, the length of the stop element may be chosen to correspond with the length of the bore desired by the dentist or dental surgeon.

The material of part or all of the stop element can be selected to permit flexibility of the lugs and/or the main body of the stop element so as to enable the stop element to snap fit or press fit onto the surgical tool.

Figures 7-9 show three embodiments of the stop element in more detail. Figures 7A- 7F show a stop element 17 of the type shown in Figure 3. The stop element is generally cylindrical with numbering or other depth markings on the exterior thereof. The internal bore of the stop element is also generally cylindrical, except for two opposing friction fit regions 25, 26 which are generally flat or straight. These flat regions 25, 26 are preferably positioned close to but axially-rearward of the internal lugs 23, 24 (which are described above). The flat regions 25, 26 facilitate a friction fit with the tool. The internal bore of the stop element is generally cylindrical along most of its axial length and its internal diameter is such that it does not impinge greatly on the tool during the sliding of the stop element into position. However, once the stop element has been slid axially rearwardly enough to approach an axial endstop (provided for example by the abutment of the lugs 23, 24 against flute shoulders), the flat regions 25, 26 (which have a reduced internal diameter in comparison with the rest of the internal bore of the stop element) engage with the external surface of the tool to achieve a friction fit between the tool and stop element. Figures 8A-8F show a frangible stop element of the type shown in Figure 4 but with the addition of radially-spaced slots 16 at its distal end. The stop element is

generally cylindrical with axially-spaced break grooves 15. The internal bore of the stop element is also generally cylindrical, except for two opposing regions 25, 26 which are generally flat or straight. These flat regions 25, 26 facilitate a friction fit with the tool as described above. The stop element is also provided with two internal lugs 23, 24 as described above.

Figures 9A-9F show a stop element 14' of the type shown in Figure 6. The stop element is generally cylindrical with axially-spaced break grooves 15. Radially- spaced slots 16 are provided at the proximal end of the stop element. The internal bore of the stop element is also generally cylindrical. The stop element is also provided with two internal lugs 23, 24 as described above.

Referring to Figures 2, 10 and 11 , it can be seen how the stop element 1 , 17 fits onto the tool 11. The lugs 23, 24 locate within the flutes 12 of the drill and are rearwardly axially limited by the abutment of the lugs 23, 24 against flute shoulders 30. The fit is further improved by the abutment of the flat regions 25, 26 of the stop element against sections 31 , 32 of the external surface of the drill 11.

The bulk of the stop element, i.e. its external diameter, can be considerably reduced in comparison to the prior art as a result of the lugs locating within the flutes of the surgical tool. In contrast to the prior art stop elements, the stop element of the present invention does not need to "sit" on the maximum external diameter of the surgical tool because the lugs locate at least partially within the- reduced diameter of the flutes.

It will be apparent to those skilled in the art that as well as being used with drills, the stop element of the invention can just as well be used with other surgical tools where at least one flute is present, for example screw taps and counter bores.