Patent Application
20220387050
The present disclosure relates to a surgical milling cutter with a shaft for rotationally driven coupling with a drive unit about a rotational axis extending in the longitudinal direction of the shaft and a cutter head arranged distally on the shaft, which has at least two teeth with cutting edges for rotationally removing tissue, said teeth each being designed for the removal of tissue both in the distal direction and in the lateral direction and extending radially outward starting at the distal part of the rotational axis of the milling cutter toward the proximal direction, wherein a chip space is formed as clearance between adjacent teeth in the circumferential direction. It also relates to a method for obtaining bone material and/or cartilage material, wherein a bone and/or cartilage is machined with a tool and the removed bone/cartilage material obtained is collected and, if required, stored and used for growing bone material.
Surgical milling cutters are generally known from the prior art and are used for the removal of hard tissue such as bone or cartilage by driving them rotationally about a rotational axis running in their longitudinal direction. Rose-head burs or rose drills are milling tools with an approximately spherical cutter head, which is provided with many teeth carrying cutting edges, six to 14 teeth depending on the diameter. The teeth and their cutting edges converge at the distal end of the cutter head on the rotational axis of the milling cutter. As a result of the large number of teeth, their height decreases in the direction of the distal end area and is zero directly at the rotational axis. This means that there is no interdental space between the individual teeth directly at and near the distal end of the milling cutter. It may be possible to create a somewhat larger tooth height and thus somewhat larger chip spaces in the region of the distal end of the cutter head by appropriate geometric optimization. However, since the cutting edges meet in the center, i.e. at the axis of rotation of the milling head, even in the case of such optimization there are the disadvantages of difficult chip removal, relatively high heating as a result, and a severely restricted or non-existent view of the situs.
The teeth/cutting edges of such rose drills are usually produced by grinding. So-called pointed disks are used for this purpose. These usually have a grinding angle of 60° to 90° and form the interdental space through their material removal in the cutter head. The penetration depth of the pointed disk in the cutter head is set in such a way that a tooth with a corresponding cutting edge is formed from the tooth front of a previous interdental space together with the tooth back of a subsequent interdental space. The teeth are usually inserted into the cutter head with a twist, i.e. helically, so that the pointed disk does not run into the cutter shaft when grinding the proximal region of the cutter head. In this way, the teeth or the cutting edges in the proximal region of the cutter head can be formed somewhat closer to the rotational axis. The pointed disks are adjusted in such a way that the rake angle of the cutting edges is negative and is usually between −10° and −40°. The relief angle at the cutting edges is correspondingly very large and is between 40° and 70°.
A disadvantage of such rose drills in terms of production is the long running time of the grinding machine during production due to the high number of teeth/cutting edges, which leads to high production costs.
A disadvantage of this type of milling tool with regard to practical use is that due to the production-related, relatively pointed teeth and their large number, so-called ‘rattling’ may often occur when machining bones, which manifests itself by uncontrolled jumping away from the area to be machined, so that precise work is not possible or is extremely difficult.
A further disadvantage is caused by the relatively small interdental space between the teeth in the distal end region, which acts as a chip space. Bone material removed during machining accumulates in the chip space and has to be transported away from there to make room for newly removed material. If the material transport through the interdental spaces is insufficient, the chip space will become blocked and the cutting edges will be shielded by material accumulated in the chip space. As a result, further material removal is no longer possible. This is one of the reasons why it is problematic to achieve satisfactory cutting performance and cutting power in the axial direction with such milling cutter heads. This disadvantage is particularly serious since surgical procedures very often have to be performed in depth (i.e. axially) in order to remove bone in the axial direction. An obstructed cutting edge or interdental space in the center of the cutter head is difficult or impossible to detect for the surgeon, since the view is blocked by the cutter head itself. It is very difficult to clean the blocked interdental space during surgery. Once the interdental space is blocked and the surgeon then continues to work on the bone, this may lead to increased pressure forces and increased friction, which in turn leads to an increase in temperature. This is particularly critical, as temperatures above just 45° C. can already lead to coagulation of the patient's protein with known adverse consequences.
In order to reduce the latter problem, such milling cutters are flushed or cooled with liquid during operation. The liquid supports chip removal and reduces heating at the point to be machined. However, if the cutting performance is not adequate and liquid is added, increased heating can occur at specific points, which can lead to coagulation of the machined bone. In addition, excessive heating of the material located in the interdental space may occur, which may coagulate there as a result of the heating and is very difficult to remove.
A further disadvantage may be that, due to the geometry of the milling cutter, a surgeon cannot see the situs, i.e. the surgical area in the region of the tool tip. This applies to both milling cutters that are in operation and those that are at a standstill. In order to inspect the situs, it is therefore necessary to remove the milling cutter at least partially, if not completely, from the operating area.
Finally, the many deep interdental spaces of such rose drills or rose-head burs are difficult to clean in everyday clinical practice as part of their processing.
In addition to the milling cutters described above, milling tools with two cutting edges, for example so-called olive cutters or neuro cutters as well as so-called twin cutter milling tools are known in medical technology. However, these have a significantly smaller chip space.
A relatively large chip space is provided by a surgical milling cutter with only one cutting edge, a so-called single-cutter. An example of such an instrument is disclosed in U.S. Pat. No. 2,017,015 0974 A1. However, due to the provision of only one cutting edge and a design of the cutter head that is asymmetrical/eccentric to the rotational axis, its mass is distributed eccentrically so that an imbalance occurs during operation. This leads to rough, unsteady running of the milling tool, which places a high load on the handpiece and especially its bearings, and results in increased running noise.
Against this background, the object of the present disclosure is to reduce the above-mentioned disadvantages of the prior art, in particular to provide a milling cutter with improved cutting performance in the axial direction, low heat production and improved chip removal from the distal end region, in particular for high-speed applications in medicine for machining bone. A further object is to provide a milling cutter that is particularly easy to clean, in particular suitable for obtaining tissue material such as bone or cartilage for further artificial material acquisition. Finally, the disclosure is intended to provide an improved method for obtaining bone material and/or cartilage material.
This object is solved according to the present disclosure by a surgical milling cutter having a shaft for rotationally driven coupling with a drive unit about a rotational axis extending in a longitudinal direction of the shaft, in particular with a surgical handpiece, and a cutter head arranged distally on the shaft, wherein the cutter head has at least two teeth with respective cutting edges for rotationally removing tissue, wherein the cutting edges are each designed for the removal of tissue both in the axial and/or distal direction and in the radial and/or lateral direction, wherein a chip space, also referred to as interdental space, is formed as clearance in each case between teeth adjacent in the circumferential direction, wherein each chip space extends on the side of the rotational axis facing the respective cutting edge from the cutting edge into a region on the side of the rotational axis facing away from the corresponding cutting edge, at least in a distal section of the milling cutter. It can also be said that according to the disclosure, each chip space is formed on the cutting edge side of the rotational axis of the milling cutter and extends at least in a distal region on the side of the rotational axis facing away from the respective cutting edge. The surgical milling cutter according to the disclosure is preferably designed rotationally symmetrical to its rotational axis and/or with a mass distribution symmetrical to the rotational axis, so that it can be operated without imbalance.
It is a particular advantage of the disclosure that the design of the teeth or cutting edges is such that the interdental space/chip space in the distal end region of the cutter head near or at the rotational axis (at the tip) is as large as possible. This ensures good evacuation of the material removed by the milling cutter (in particular bone dust or bone chips). A liquid-based support for material evacuation can basically be reduced in most cases in an advantageous manner. Coagulation of the processed bone and also of the removed material in the interdental space as a result of excessive heating can be reliably avoided. Therefore, and due to the good accessibility of the teeth, of the interdental spaces and of the cutting edges, the milling cutter is particularly easy and good to clean. A further particular advantage of the disclosure is that the shape of the milling cutter and its chip spaces according to the disclosure enables the surgeon to have a particularly good view of the situs without having to remove all or part of the milling cutter from the operating area. Finally, the heat generation is markedly low, so that disproportionate heating, in particular to temperatures of 45° C. and more, of bone material during processing with the milling cutter according to the disclosure can be reliably avoided. An advantageous consequence of this may be that removed bone material is not damaged/does not get damaged and can therefore be used for further use, for example growing of bone material.
Advantageous embodiments of the disclosure are explained in more detail below.
One embodiment is characterized in that the cutting edges are each arcuate from distal-radial-inward to proximal-radial-outward. They can also be almost semicircular and/or extend from the widest point of the cutter head in the radial direction back to the cutter shaft in an arc. Preferably, the cutting edges of the cutter head extend radially outward starting at the distal part at the rotational axis of the milling cutter toward the proximal direction. In particular, the cutting edges of each cutter head may be formed on the edge side and may be shaped in such a way that, when the milling cutter rotates about its rotational axis (longitudinal axis), they run along an envelope curve that is preferably essentially spherical in shape. Such a milling cutter may also be referred to as a spherical cutter and is particularly well suited for uses in which material is to be removed in a lateral/radial and/or axial/distal direction. In the context of the disclosure, the cutter head may also be designed in such a way that the envelope geometry described by the cutting edges during a rotation of the milling cutter has other shapes, for example that of a flame cutter, conical cutter, cylindrical cutter or oval cutter.
According to a further embodiment, the teeth or cutting edges may each be non-helical and/or twist-free. This improves the accessibility of the interdental spaces and thus the cleaning suitability. In addition, such tooth/cutting edge shapes can be produced relatively easily, quickly, and inexpensively.
According to a further embodiment, the milling cutter may have exactly two teeth or cutting edges arranged on diametrically opposite sides of the rotational axis of the milling cutter. The cutting edges are formed on the sides of the two teeth facing away from each other, so that both cutting edges cause material removal when the milling cutter rotates about its rotational axis. The cutting side surface of the tooth is also referred to as the tooth front, while the side of the tooth facing away from the cutting edge is referred to as the tooth rear. The respective clearance on the cutting side (i.e. on the side of the tooth front) represents the chip space in the sense of the disclosure for material removed with the corresponding cutting edge. Due to the described arrangement and design of the cutting edges/teeth, the two interdental spaces are particularly large, so that particularly good transport of removed material is ensured and fast healing of non-coagulated bone can be achieved.
Such a two-toothed or two-edged design can be achieved particularly effectively and simply by machining the cutter head on both sides of the rotational axis (laterally) at least at the distal end of the milling cutter down to the rotational axis. This machining then forms a surface which is preferably flat in large parts and which forms the tooth front of the respective tooth.
Alternatively or additionally, a step or shoulder may extend starting at the distal part at the rotational axis in the proximal direction, so that the surface forming the tooth front transitions with a step or shoulder into the tooth rear of the opposite tooth. This step or shoulder forms a boundary between the tooth front of one tooth and the rear surface of the adjacent tooth in the cutting direction, i.e. the tooth rear of the other tooth. In a particularly advantageous embodiment with regard to manufacturing, the step or shoulder extends from the tip of the cutter head, as from the point of intersection of the distal end of the cutter head with the rotational axis, at an oblique angle to the rotational axis, so that the rear (proximal) region of the cutter head does not have any contact with the shaft of the milling cutter. This angle is preferably in the plane of the respective front surface, is also referred to as setting angle and is preferably in a range of 2° to 10°. In other words, the tooth front together with the circumferential relief angle forms the cutter or cutting edge. Alternatively or additionally, the tooth rear may be designed with a constant width.
The tooth front is designed and/or arranged in such a way that the rake angle at the cutting edge is 0°.
According to a further embodiment of the disclosure, the teeth may be arranged and formed transversely to the rotational axis (37) diametrically opposite each other without offset in one plane. In particular, this plane also contains the rotational axis. In particular, the teeth may be formed in such a way that a front surface of one tooth and a rear surface of the other tooth together form a flat surface. The rear surface of one tooth and the front surface of the other tooth together form a further flat surface opposite the aforementioned surface. The two surfaces may be parallel to each other. Preferably, they are parallel to each other in a direction transverse to the rotational axis and inclined to each other by a tooth thickness angle in the direction of the rotational axis.
A particularly advantageous embodiment of the disclosure with regard to material evacuation is characterized in that at least one of the cutting edges has at least one interruption or flute, in particular as a chip-breaking flute. This may be incorporated into the tooth in particular in the centripetal direction. The interruption of the cutting edges reduces their width so that penetration of the cutting edges into the bone is facilitated, which in turn leads to better cutting performance. The chip-breaking flutes of adjacent teeth/cutting edges may be designed and/or arranged offset to each other, in particular in such a way that the flutes of one tooth are located at the points corresponding to the cutting edges of the other tooth and vice versa, so that the cutting edges of the teeth are alternately involved in the removal. In this way, the size and shape of the removed chips can be determined so that the transport of removed material can be optimized. In addition, this ensures that only one cutting edge is engaged in relation to the region swept by the respective cutting edge section during its rotation about the axis of rotation, even though the milling cutter nominally has more cutting edges.
The rear side of the tooth in the cutting direction, i.e. the tooth rear, may in particular be formed and/or arranged inclined relative to the rotational axis so that the tooth widens conically from distal to proximal towards the shaft. The tooth rear may in particular be designed in the form of a flat surface, which favors accessibility, cleaning suitability, and ease of manufacture.
In particular, the tooth thickness may increase at an angle of 1° to 10° relative to the rotational axis from distal to proximal. This angle is referred to as the tooth thickness angle. This results in particularly high stability and also good cleanability. The distal thickness of the tooth or cutting edge may in particular be between 1/20 and 1/10 of the diameter of the cutter head in the radial direction. In this way, a particularly large clearance can be provided as chip space with simultaneously high stability of the tooth/cutting edge. In addition, the cutting performance and the rattling tendency can be influenced by an appropriate design of the tooth thickness. Finally, the strength of the cutter head may be defined by the tooth thickness at the required height.
A further embodiment of the disclosure is characterized in that the cutting edge has a constant relief angle in a range between 2° and 30°. Alternatively, the cutting edge may have a relief angle that varies along a course from distal to proximal, in particular in a range between 2° and 30°. The cutting edge may also have a rake angle of 0°. The circumferential relief angle forms the shape of the cutter head that defines the material removal. The cutting performance and the rattling tendency can be influenced by a corresponding design of the relief angle. By varying the relief angle over its course as described above, the cutting performance and the rattling tendency can be further positively influenced.
A particularly user-friendly embodiment is characterized in that the cutter head has a tip with an angle of 110° to 150° at its distal end, which ensures particularly good and simple centering and thus handling during use, in particular when working axially with the milling cutter tool. This angle is referred to as the tip angle. Proximally adjacent to the tip, the cutting edge/tooth may be arc-shaped, in particular circular, in the further course.
According to the disclosure, the milling cutter may be designed either as a clockwise milling cutter (right-hand cutter) or as a counterclockwise milling cutter (left-hand cutter).
With regard to a method, the solution according to the disclosure consists in a method for obtaining bone material and/or cartilage material, wherein a bone and/or cartilage is machined with a tool and the bone/cartilage material obtained is collected and, if required, stored and used for growing bone material, wherein the machining of the bone and/or cartilage is carried out with a cutting tool, in particular with a surgical milling cutter according to the disclosure, in particular according to the present description.
In summary, it can be said that the disclosure provides a surgical milling cutter, which in particular may have only two cutting edges. The interdental space is preferably designed in such a way that the removed tissue can be transported away with as little obstruction as possible. In particular, the tooth form may be designed in such a way that all material not required for the strength of the tooth is removed. In addition, surfaces of the milling cutter, in particular of the cutter head, may be designed to be smooth and flat with particular ease, which favors chip evacuation. As a result of the low temperature development and the particularly good chip evacuation, particularly gentle material removal can be achieved with the milling cutter according to the disclosure, wherein changes and/or damage to the material removed are largely, or even completely, avoided. Material removed via a milling cutter according to the disclosure is therefore particularly well suited for artificial re-growth of such material as part of the method according to the disclosure.
In particular, the disclosure brings about the following advantages:
Further features and advantages of the present disclosure result from the following exemplary and non-limiting description of the figures. These are merely schematic in nature and serve only to aid understanding of the disclosure. The following is shown:
The cutter head 18 has exactly two teeth 21, 22, namely a first tooth 21 and a second tooth 22. The tooth 21 has a cutting edge 23 for rotationally removing tissue. The tooth 22 has a cutting edge 24 for rotationally removing tissue. The two teeth 21, 22 and thus also the cutting edges 23, 24 are arranged on diametrically opposite sides of the rotational axis 19 of the milling cutter 16, offset from each other transverse to the rotational axis 19. The cutting edges 23, 24 are each arranged on the side of the corresponding tooth 21 or 22 facing away from the rotational axis 19 and are each arc-shaped. They begin at the distal end 20 on the rotational axis 19 and extend first from distal-radial-inward to proximal-radial-outward to then run from the widest point 25 of the cutter head 18 further in an arc towards proximal-radial-inward to the cutter shaft 17. The cutting edges 23, 24 are each non-helical and twist-free. Due to this design, the milling cutter 16 has an envelope curve of essentially spherical shape when rotating about its rotational axis 19.
The two teeth 21, 22 are identical, so that the description of the tooth 21 applies in the same way to the tooth 22. As can be seen particularly well in
The rear surface 27a/27b is inclined relative to the front surface 26a/26b in the axial direction by a longitudinal tooth angle g′ of between 4° and 12.5°, so that the cutter head 18 has an overall tooth thickness angle g of between 8° and 25° (see
Between the front surface 26a of the tooth 21 and the rear surface 27b of the tooth 22, a step 28a or shoulder 28a with a shoulder surface 29a is formed, which extends in the proximal direction starting at the distal end 20 at the rotational axis 19. Between the front surface 26b of the tooth 22 and the rear surface 27a of the tooth 21, a step 28b or shoulder 28b with a shoulder surface 29b is formed, which extends in the proximal direction starting at the distal end 20 at the rotational axis 19. The transition from the front surface 26a, 26b to the shoulder surface 29a, 29b is rounded and is arranged at a setting angle fin the range of 2° to 10° (see
The cutter head 36 has a first tooth 39 and a second tooth 40. The tooth 39 has a cutting edge 41 for rotationally removing tissue. The tooth 40 has a cutting edge 42 for rotationally removing tissue. The two teeth 39, 40 and thus also the cutting edges 41, 42 are arranged in a common plane, in the center of which lies the rotational axis 37, on diametrically opposite sides of the rotational axis 37 of the milling cutter 34. The cutting edges 41, 42 are each arranged on the side of the corresponding tooth 39 or 40 facing away from the rotational axis. The cutting edges 41, 42 are each arc-shaped. They begin at the distal end 38 on the rotational axis 37 and extend first from distal-radial-inward to proximal-radial-outward, then from the widest point 43 of the cutter head 34 they continue in an arc towards proximal-radial-inward to the cutter shaft 35. The cutting edges 41, 42 are each non-helical and twist-free. This shaping of the cutting edges 41, 42 gives the milling cutter 34 an envelope curve of essentially spherical shape when rotating about its rotational axis 37.
The two teeth 39, 40 are formed identically in that, as can be seen particularly well in
The surface 44 is inclined relative to the surface 45 in the axial direction by a tooth thickness angle h between 0° and 20° (see
The milling cutter 46 is thus designed for both clockwise rotation and counterclockwise rotation, i.e. it cuts in both clockwise and counterclockwise rotation. Due to its shape, the mass of the cutter head 48 is minimized by the omission of the pointed surface 66 asymmetrical to the rotational axis 49 and results in very smooth running. In addition, the cutter head 48 may be designed with surprisingly small dimensions, in particular with a diameter smaller than, for example, 3 mm, 4 mm, or 5 mm.
The cutter head 58 has a cutter-head thickness S at its tip 63. Starting from the tip 63, the front surface 61 and the rear surface 62 are inclined relative to each other by a tooth thickness angle h. In addition, the front surface 61 is inclined relative to the rotational axis 59 by an upper tooth thickness angle n and the rear surface 62 is inclined relative to the rotational axis 59 by a lower tooth thickness angle o, so that the relationship h=n+o applies.
Due to its shape, the milling cutter 56 has a somewhat less favorable mass distribution with respect to eccentricity than the milling cutter 46 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 130 568.3 | Nov 2019 | DE | national |
This application is the United States national stage entry of International Application No. PCT/EP2020/081822, filed Nov. 12, 2020, and claims priority to German Application No. 10 2019 130 568.3, filed Nov. 13, 2019. The contents of International Application No. PCT/EP2020/081822 and German Application No. 10 2019 130 568.3 are incorporated by reference herein in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/081822 | 11/12/2020 | WO |
