Patent Description:
Field of the Invention. The invention relates generally to tools for preparing a hole to receive a screw-in fixture, and more particularly to rotary tools and methods implemented thereby for expanding a hole in bone to receive an implant or other fixation device.

Description of Related Art. An implant is a medical device manufactured to replace a missing biological structure, to support a damaged biological structure, or to enhance an existing biological structure. Bone implants are implants of the type placed into the bone of a patient. Bone implants may be found throughout the human skeletal system, including dental implants in a jaw bone to replace a lost or damaged tooth, joint implants to replace a damaged joint such as in hips and knees, and reinforcement implants installed to repair fractures and remediate other deficiencies like pedicle screws used in spinal stabilization, to name but a few. The proper placement of an implant often requires expert preparation using precision drills with highly regulated speed to prevent burning and pressure necrosis of the bone.

There are several known ways to expertly form a receiving hole, which hole is also sometimes referred to as an osteotomy. More recently, a novel biomechanical bone preparation technique called "osseodensification" has been pioneered by the Applicant of this invention. The osseodensification technique is based on the preservation of host bone and has gained rapid acceptance in the worldwide dental community. In many medical communities, osseodensification is considered a preferred standard of care. Examples of osseodensification can be seen in <CIT>, and in <CIT>, and <CIT>. <CIT> is an example of a tool for extracting bone screws known in the art.

Generally stated, osseodensification is a procedure for enlarging an osteotomy using a specially designed, multi-fluted, rotary tool or bur. An example of a suitable rotary tool is described in the above-mentioned <CIT>. Rotary tools configured to achieve osseodensification for dental applications are marketed as Densah® Burs under license through Versah, LLC of Jackson, Michigan USA.

Unlike traditional drilling techniques, osseodensification excavates little if any bone tissue while forming a hole suitable to receive a screw-in fixture. Rather, the majority of bone tissue is simultaneously compacted in outwardly expanding directions from the osteotomy and auto-grafted (i.e., directly re-patriated). When rotated at high speed in a reversed, non-cutting direction with steady external irrigation, osseodensification burs form a strong and dense layer of bone tissue along the walls and base of the osteotomy. Dense compacted bone tissue produces stronger purchase for the implant and may facilitate faster healing.

There are many different and specialized techniques in the medical field. Despite the impressive benefits of osseodensification, not all techniques are conducive to the osseodensification. The well-known socket shield technique is an example of a dental procedure that has yet to be adapted for osseodensification. To avoid tissue alterations of the ridge after tooth extraction, the socket shield technique was first introduced in <NUM> by Hurzeler. Hurzeler suggested that instead of extracting the whole tooth, the buccal aspect of the root could be left intact to preserve the buccal plate of bone and prevent post extraction resorption, at the same time an immediate implant is placed; this would lead to an optimal stable esthetic result after the final delivery of the restoration. To extract the tooth while keeping the buccal aspect intact, Hurzeler advocated use of a fissure bur to cut the tooth mesiodistally, after which the lingual aspect of the tooth is extracted leaving a socket where the implant is to be placed. In some cases, a bone trephine may be used to take out the remaining root leaving a space to receive an implant. The socket shield technique is not currently considered a widely accepted practice due in part to its reputation as being of limited applicability. Those of skill in the art will welcome advances and improvements that expand the applicability of the socket shield technique.

Osseodensification is a relatively new field. As with any emerging technology, new and improved tools and techniques are required as the technology begins to mature and be perfected. Furthermore, there is a continuing need to improve the efficiency of surgical operations so that they can be performed with greater speed and greater ease. Therefore, any improvements in osseodensification tools and/or techniques that result in wider applicability, greater speed and/or greater ease will be welcomed by the medical and industrial communities.

The invention pertains to a rotary tool that is configured to be turned at high speed in both condensing and cutting rotary directions (e.g., clockwise and counter-clockwise) to accomplish different effects while forming a hole in a host material. The host material can be bone or not bone. The rotary tool comprises a shank that will establish a longitudinal axis of rotation. The shank is an elongated shaft having upper end and lower ends. A body extends axially from the lower end of the shank. The body has an apical end which is remote from the shank. A plurality of flutes are disposed about the body. Each flute has a cutting face on one side thereof defining a cutting rake angle and a densifying face on the other side thereof defining a densifying rake angle. Each flute has an axial length and a radial depth. A land is formed between each adjacent pair of flutes. Each land has a substantially margin-less working edge along the cutting face of one the flute. A cavity is disposed in the body. The cavity extends axially within the body and opens through the apical end. A plurality of spurs are disposed on the apical end of the body. The spurs are located around the opening of the cavity.

The present invention represents an improvement of the rotary tool designed to densify when used in a non-cutting direction (typically the counter-clockwise direction when viewed from the surgeon's perspective), as described in <CIT>. The tool can be used in densifying mode with easier application and less vertical force compared with the design of <CIT>. Therefore, this tool can be used in a wider variety of applications, including but not limited to bone preparation applications.

These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:.

The present invention represents an improvement of the rotary tool designed to densify when used in a non-cutting direction, as described in <CIT>.

A tool according to one embodiment of this present invention is generally shown at <NUM> throughout the Figures. The rotary tool <NUM>, which may be referred to as a bur or osteotome when configured for use in surgical applications, is designed to be turned at high speed in alternative condensing and cutting rotary directions to accomplish different effects in the host material. To be clear, in surgical applications the host material is bone. In other applications, the host material could be wood, plastic, solid metal, foam metal, solid plastic, cellular plastic, and the like. The tool <NUM> has a shank <NUM> and a body <NUM>. For convenience and purposes of illustration, references to the surgical application dominate the following descriptions. And in this context, the host material may occasionally be referred to as bone and any hole therein an osteotomy. Despite these application-specific references, it is to be understood that the tool <NUM> may be used in suitable non-surgical applications.

The shank <NUM> establishes a longitudinal axis of rotation A for the tool <NUM>. The shank <NUM> is an elongated shaft, typically (but not necessarily) cylindrical in shape, having an upper end and a lower end. A drill motor engaging interface <NUM> is formed at the upper end of the shank <NUM> for connection to a drill motor (not shown). The particular configuration of the interface <NUM> may vary depending on the type of drill motor used, and in some cases may even be merely a smooth portion of the shank <NUM> against which the jaws of a collet grip. The body <NUM> joins to the lower end of the shank <NUM>, which joint may be formed with a tapered or domed transition <NUM>. The transition <NUM> acts like flow diffuser as the surgeon irrigates with water during a procedure. The gentle transition <NUM> facilitates the flow of irrigating fluid onto the osteotomy site while the tool <NUM> is spinning. <FIG> and <FIG> evidence the inclusion of an optional annular locking notch <NUM> disposed in the shank <NUM> between its upper and lower ends. The notch <NUM> may be used for various purposes, including to couple a depth-stop device like that shown, for example, in <CIT>.

The body <NUM> extends axially from the lower end of the shank <NUM>. The body <NUM> has a leading or apical end located remote from the shank <NUM>. In the example of <FIG>, the body <NUM> is configured with a conically tapered exterior profile. The outside shape of the body <NUM> can be seen as decreasing from a maximum diameter adjacent the shank <NUM> to a minimum diameter adjacent its apical end. However, in some contemplated embodiments the body <NUM> may be non-tapered (i.e., straight or cylindrical). For example, <FIG> shows an example where the body <NUM> has a generally straight exterior profile that maintain a generally constant diameter along its entire length.

The working length or effective length of the body <NUM> is proportionally related to its taper angle and to the size and number of tools <NUM> in a kit. <FIG> shows three tools <NUM>, each members of the same kit. Preferably, all tools <NUM> in a kit will have the same taper angle, or approximately the same taper angle. Taper angles between about <NUM>° and <NUM>° (or more) are possible depending upon the application. More preferably taper angles between about <NUM>°-<NUM>° will provide satisfactory results. And still more preferably, a taper angle of about <NUM>°<NUM>'. is known to provide outstanding results for dental applications when the body <NUM> length is between about <NUM> and <NUM>.

In kit arrangements like that exemplified in <FIG>, the diameter at the upper end of the body <NUM> for one tool <NUM> is approximately equal to the diameter adjacent the apical end of the body <NUM> for the next larger size tool <NUM>. That is to say, the diameter at the upper end of the body <NUM> for the lowermost/smallest tool <NUM> is approximately equal to the diameter adjacent the apical end of the body <NUM> for the middle tool <NUM>. And then the diameter at the upper end of the body <NUM> for the middle tool <NUM> is approximately equal to the diameter adjacent the apical end of the body <NUM> for the uppermost/largest tool <NUM>. However, these dimensions are only suggested as examples.

A plurality of grooves or flutes <NUM> are disposed about the body <NUM>. The flutes <NUM> may or may not have common axial length and common radial depths. That is to say, it is possible that the flutes <NUM> could, in some configurations, not all be identical. The flutes <NUM> are preferably, but not necessarily, equally circumferentially arranged about the body <NUM>. The diameter of the body <NUM> may influence the number of flutes <NUM>. In the illustrated embodiment, the flutes <NUM> are formed with a helical twist. If the cutting direction is in the right-hand (clockwise) direction, then preferably the helical spiral is also in the right-hand direction.

Each flute <NUM> has a cutting face <NUM> on one side thereof defining a cutting rake angle, and a densifying face <NUM> on the other side thereof defining a densifying rake angle. That is, each flute <NUM> has a densifying face <NUM> and an opposing cutting face <NUM>. A rib or land <NUM> is formed between adjacent flutes <NUM>, in alternating fashion (i.e., flute-land-flute-land-flute, etc.). Each land <NUM> bridges the densifying face <NUM> of the flute <NUM> on one side to the cutting face <NUM> of the flute <NUM> on its other side. The sharp interface between each land <NUM> and its associated cutting face <NUM> is referred to as a working edge <NUM>. Depending on the rotational direction of the tool <NUM>, the working edge <NUM> either functions to cut bone or compact (densify) bone. That is, when the tool <NUM> is rotated in the cutting direction, the working edges <NUM> slice and excavate bone (or other host material). When the tool <NUM> is rotated in the densifying (non-cutting) direction, the working edges <NUM> compress, compact, and radially displace bone (or other host material) with little-to-no cutting whatsoever. This compaction and radial displacement is exhibited as gentle pushing of the osseous structure laterally outwardly in a condensation, i.e., compaction, mechanism.

The working edges <NUM> are shown throughout the illustrations as being substantially margin-less. The term margin-less is defined as the entire portion of each land <NUM> is cut away behind the working edge <NUM> to provide complete clearance. In standard prior art burs and drills, margins are incorporated behind the cutting edge to help guide the drill in the hole and maintain the drill diameter. In the illustrated examples, the working edge <NUM> can be seen helically twisting about the body <NUM>. Furthermore, the working edges <NUM> wind about the body <NUM> in a direction that turns away from a non-cutting direction. This is perhaps best perceived from the full side views of <FIG>. As the conically tapered profile decreases in diameter, i.e., moving toward the apical end, the working edges <NUM> twist about the body <NUM> in the same direction as the cutting direction.

As mentioned, the cutting face <NUM> establishes the cutting rake angle for each respective working edge <NUM>. The cutting rake angle can be any one of several forms. In some embodiments the cutting rake angle remains continuously negative angle along its entire length. In some cases, the pitch of the continuously negative cutting rake angle fluctuates along the length of each flute <NUM> with a total variance of less than <NUM>°. In other cases, the pitch of the continuously negative cutting rake angle may fluctuate with greater than <NUM>° total variance. In those examples where the cutting rake angle fluctuates (and yet remains continuously negative angle along its entire length), changes in pitch along the length of the flute <NUM> can be progressive or, regressive. A progressive pitch becomes sharper (closer to <NUM>°), whereas a regressive pitch becomes flatter.

Preferably, the densifying rake angle for each working edge <NUM> will remain continuously negative angle along its entire length. This is to maximus the condensing attributes of the tool <NUM> when operated in the densifying direction. When the tool <NUM> is counter-rotated in the densifying mode (i.e., condensing direction per <FIG>), the densifying rake angle established between the working edge <NUM> and the land <NUM> may lie at a large negative angle in the order of about <NUM>°-<NUM>°. The large negative densifying rake angle of the working edge <NUM> (when rotated in a densifying direction) applies outward pressure at the point of contact between the wall of the osteotomy and the working edge <NUM> to create a compression wave ahead of the point of contact, loosely akin to spreading butter on toast. Osseodensification may also be loosely compared to the well-known process of burnishing metal to improve metal surface quality. The densifying rake angle can any one of several forms. In one embodiment, the densifying rake angle is generally constant along the length of each flute <NUM>. In another embodiment, the densifying rake angle fluctuates along the length of the flutes <NUM> with a total variance of less than <NUM>°.

These variations in cutting and densifying rake angles can be matched with variations in the length and depth of each flute <NUM>. Each flute <NUM> has an axial length and a radial depth. The smooth, non-fluted portion of the body adjacent the domed transition <NUM> is referred to as a stopper section <NUM>. The stopper <NUM> is that section of the body <NUM> disposed between the flutes <NUM> and the shank <NUM>. In cutting mode, once the stopper section <NUM> enters an osteotomy all excavated bone debris becomes trapped in the flutes <NUM>, which enables some advantageous compaction activity.

The axial lengths of the flutes <NUM> are shown in the drawings to be generally equal, however other options are available. For example, the axial length of one or some flutes <NUM> (e.g., every other flute <NUM>) could be shortened to provide certain effects. The radial depth of the flutes <NUM> are also subject to modest manipulation. In one example. The radial depth of each flute <NUM> remains generally constant along its length. In another example, the radial depth of each flute <NUM> has a regressive characteristic, in that the depth measure adjacent the apical end is largest moving progressively shallower toward the stopper section <NUM>.

In the condensing/densifying mode, downward pressure applied by the surgeon is needed to keep the working edges <NUM> in contact with the bone surface of the osteotomy as it is being expanded. That is, pressure is needed to generate and propagate a compression wave in the host material that begins when the contact stresses exceed the yield strength of the host material. This is aided by the taper effect of the osteotomy and tool <NUM> to create lateral pressure (i.e., in the intended direction of expansion). The harder the surgeon pushes the tool <NUM> into the osteotomy, the more pressure is exerted laterally. This gives the surgeon complete control of the expansion rate irrespective to a large degree on the rotation speed of the tool <NUM>, which is a factor underlying the short learning curve required to master the osseodensification technique. Thus, the intensity of the compaction effect depends chiefly on the amount of force exerted on the tool <NUM>, which is controlled by the surgeon. The more force exerted; the quicker expansion will occur.

In the condensing/densifying mode, as each working edge <NUM> wipes across the bone, the applied forces can be decomposed into two components: one normal to the bone surface, pressing it outwardly, and the other tangential, dragging or smearing it along the inner surface of the osteotomy. As the tangential component is increased, the working edge <NUM> will start to slide along the bone. At the same time, the normal force will deform the softer bone material. If the normal force is low, the working edges <NUM> will rub against the bone but not permanently alter its surface. The rubbing action will create friction and heat, but this can be controlled by the surgeon by altering, on-the-fly, the rotation speed and/or pressure and/or irrigation flow. Because the body <NUM> of the tool <NUM> is tapered, the surgeon may at any instant during the surgical procedure lift the working edges <NUM> away from contact with the surface of the bone to allow cooling. This can be done in a controlled "bouncing" fashion where pressure is applied in short bursts with the surgeon continuously monitoring progress and making fine corrections and adjustments.

A distinguishing characteristic of the tool <NUM> as compared to that described in <CIT> is a cavity <NUM> disposed in the body <NUM> and passing through its apical end. That is, the cavity <NUM> extends axially within the body <NUM> and opens at the apical end, creating the appearance of a hollow point. The presence of the cavity <NUM> removes a substantial portion of the formations at the apical end, leaving only the radially outermost features. The cavity <NUM> extends into the body <NUM> of the tool <NUM> about as deep as the flutes <NUM> extend along the exterior surface. That is to say, the cavity <NUM> and the exterior flutes <NUM> are generally/approximately co-extensive, with both terminating near the conical transition region of the body <NUM> below the tool shank <NUM>. However, this is subject to variation, it being contemplated that in some cases the cavity <NUM> may have a short axial length than the axial length of the flutes <NUM>, or alternatively may have a longer axial length than the axial length of the flutes <NUM> along the exterior surface of the body <NUM>.

As perhaps best seen in <FIG>, the cavity <NUM> may have a frusto-conical profile. Its conical shape being widest adjacent the apical end and narrowest adjacent the shank <NUM>. In this sense, the frusto-conical profile can be considered the negative or opposite of the tapered exterior profile of the body <NUM>. In some embodiments, it has been found advantageous to form the frusto-conical taper angle of the cavity <NUM> generally equal, albeit negative, to the conically tapered exterior profile of the body <NUM>. That is, the cavity <NUM> may be formed with a frusto-conical taper that matches, or generally approximates, the exterior taper angle of the working end of the tool <NUM>. However, this is only a general preference. In other embodiments, the frusto-conical taper angle of the cavity <NUM> is not matched to the conically tapered exterior profile of the body <NUM>. Indeed, straight side wall exteriors as well as cavities are entirely possible and, in some cases, may even be preferred. See for example the embodiment of <FIG>.

<FIG> and <FIG> offer enlarged views of the apical end, which is also distinguished in configuration from the aforementioned <CIT> by a plurality of spurs <NUM> disposed on the apical end of the body <NUM>. The spurs <NUM> are arranged around the opening of the cavity <NUM>. While four spurs <NUM> are shown in these examples, it is contemplated that a tool <NUM> could have fewer or more spurs <NUM>. In particular, smaller diameter burs <NUM> might have just two or three spurs <NUM>, whereas larger burs might have six or eight or any suitable number of spurs <NUM>.

Each spur <NUM> has a grinding edge <NUM> in the shape of a ridgeline. On one side of each grinding edge <NUM> is a leading flank <NUM>, and on the other side is a trailing flank <NUM>. The terms "leading" and "trailing" are in refence to the non-cutting condensing direction which is indicated in <FIG>. (Naturally, when the tool <NUM> is rotated in the cutting direction, these "leading" and "trailing" designations will be antithetical. ) Thus, each spur <NUM> has a grinding edge <NUM> that forms the ridgeline between leading <NUM> and trailing <NUM> flanks.

The included angle between the leading <NUM> and trailing <NUM> flanks (B + C in <FIG>) may be between about <NUM>-<NUM> degrees. In the illustrated examples, the included angle (B + C) at the grinding edge <NUM> is between about <NUM>-<NUM> degrees and is generally equally set so that each flank <NUM>, <NUM> angles away from a normal (perpendicular) plane about (but not necessarily exactly) the same degree. That is to say, in the illustrated embodiments, B ≈ C. In an example where the included angle at the grinding edge <NUM> is exactly <NUM> degrees, each of its flanks <NUM>, <NUM> will be canted at about <NUM> degrees relative to the horizontal surface. (B = C = <NUM>°. ) In this configuration, i.e., where each flank <NUM>, <NUM> angles away from a normal plane about the same degree, the grinding edge <NUM> will form the same negative rake angle regardless of whether the tool <NUM> is rotated in a cutting or non-cutting condensing direction. However, this is not necessarily the case; in some contemplated examples B ≠ C. It may, for example, be desirable to establish a larger rake angle in condensing mode than in cutting mode (B > C), or vise versa (B < C).

<FIG> illustrate contemplated configurations where the flanks <NUM>, <NUM> are each angled so that the resulting grinding edges <NUM> are also angled thereby forming an apex <NUM> at the radially inward most end of each grinding edge <NUM>, adjacent the cavity <NUM>. Furthermore, the manufacturing is carried out in such a way that each apex <NUM> is disposed in a common plane that perpendicularly bisects the longitudinal axis. That is to say, if the tool <NUM> were placed apical end down on a flat surface, all of the apexes <NUM> would make point-contact with the horizontal surface at the same time. In another contemplated embodiment, which is not illustrated, the flanks <NUM>, <NUM> are formed so that placement of the tool <NUM> apical end down on a flat surface will result in only one or some of the apexes <NUM> making point-contact with the horizontal surface while the remaining apexes <NUM> hover above the flat surface.

In yet another contemplated embodiment, which is not illustrated, the resulting grinding edges <NUM> are angled so as to form apexes <NUM> at the radially outward most end of each grinding edge <NUM>, spaced away from the cavity <NUM>. In this configuration, each apex <NUM> could either lay in a common plane that perpendicularly bisects the longitudinal axis, or alternatively only one or some of the apexes <NUM> lay in a common perpendicular plane.

In a still further contemplated embodiment, which is not illustrated, the flanks <NUM>, <NUM> may be ground so that the resulting grinding edges <NUM> all lay in a common plane that perpendicularly bisects the longitudinal axis. In this variation, there would be no point-like apex. When the tool <NUM> is stood point-down on a flat surface, its grinding edges <NUM> will either be in line contact with the horizontal surface or hover parallel above the surface.

All of these variations are considered viable alternatives having beneficial application in different scenarios.

Referring still to <FIG> and <FIG>, it can be seen that each trailing flank <NUM> is abruptly truncated by a steep face <NUM>. The steep faces <NUM> each lay in a plane that is parallel to, or nearly parallel to, the longitudinal rotary axis A of the tool <NUM>. Each steep face <NUM> can be observed intersecting the leading flank <NUM> of the next adjacent the spur <NUM>, to form a gullet <NUM> therebetween. Said another way, the steep face <NUM> of one spur <NUM> merges with the long sloping leading flank <NUM> of the next adjacent spur <NUM> at a gullet <NUM>. Thus, a gullet <NUM> exists between each spur <NUM>. And by corollary, the number of gullets <NUM> equals the number of spurs <NUM>. A tool <NUM> with four spurs <NUM> will have four gullets <NUM>; a tool <NUM> with six spurs <NUM> will have six gullets <NUM>; and so forth. When the tool <NUM> is used in the cutting direction, the gullets <NUM> will collect bone debris.

And preferably, at least some of the flutes <NUM> will be positioned so as to open directly into a respective gullet <NUM>. In an eight fluted tool <NUM> having four spurs <NUM> and four gullets <NUM>, one, two, three or four flutes <NUM> will open directly into a respective gullet <NUM>. It is acceptable for the tool <NUM> to have more gullets <NUM> than flutes <NUM> (as in the example of <FIG>), so long as at least one flute <NUM> opens directly into one gullet <NUM>. Also, it is preferable that at least one flute <NUM> opens directly onto a leading flank <NUM>. A flute <NUM> opening onto a leading flank <NUM> can be either just behind the associated grinding edge <NUM> (as visible in <FIG>) or partially overlapping the grinding edge <NUM> (as visible in <FIG>). In the examples of <FIG>, the tool <NUM> is fashioned with eight flutes <NUM> and four spurs <NUM>/gullets <NUM>. Every other flute <NUM> opens into a respective gullet <NUM>, whereas the intervening flutes <NUM> each intersecting a respective leading flank <NUM> just behind a grinding edge <NUM>. In this manner, bone debris is directly and efficiently channeled up the flutes <NUM> regardless of whether the tool <NUM> is used in the cutting direction or in the non-cutting condensing direction.

When the tool <NUM> is used in the non-cutting condensing direction, bone debris is ground by the grinding edges <NUM> and pushed along the long leading flanks <NUM> directly into the waiting flutes <NUM> that open into the respective leading flanks <NUM> near a grinding edge <NUM>. And when the tool <NUM> is used in the cutting direction, bone debris is ground in larger quantities by the grinding edges <NUM> and pushed along the short trailing flanks <NUM> into the gullets <NUM>, which in turn feed into the flutes <NUM> associated therewith. There is therefore benefit in coordinating the number of spurs <NUM> as a whole-number multiple of the number of flutes <NUM>. A four-flute <NUM> tool <NUM> may be optimized with either four or two spurs <NUM>. An eight-flute <NUM> tool <NUM> may be optimized with two, four or eight spurs <NUM>. A six-flute <NUM> tool <NUM> may be optimized with three or six spurs <NUM>. A twelve-flute <NUM> tool <NUM> may be optimized with two, three, four, six or twelve spurs <NUM>. And so forth.

The spurs <NUM> may be identical to one another or of two or more different styles. The illustrated examples depict spurs <NUM> of two different styles set in alternating pattern: close-offset spurs 46A and far-offset spurs 46B. In these examples, at least one spur is a close-offset spur 46A and/or at least one spur is a far-offset spur 46B. The suffix "A" here denotes features of the close-offset spurs 46A, whereas suffix "B" denotes features of the far-offset spurs 46B.

As perhaps best shown in <FIG>, the grinding edges 48A of the close-offset spurs 46A are indicated by extension lines 60A. From these extension lines 60A, it can be seen that each grinding edge 48A is offset a short distance 62A from the longitudinal axis of rotation A of the tool <NUM>. Consequently, none of the grinding edges 48A lay along radials from the longitudinal axis of rotation A. Also, it is noteworthy that the offset 62A is in the cutting direction, which will result in a more aggressive grinding action when the tool <NUM> used in the cutting direction, and a less-aggressive grinding action when the tool <NUM> is used in the condensing action. Still considering <FIG>, the grinding edges 48B of the far-offset spurs 46B are indicated by extension lines 60B. From these extension lines 60B, it can be seen that each grinding edge 48B is offset a relatively large distance 62B from the longitudinal axis of rotation A of the tool <NUM>. Consequently, none of the grinding edges 48B lay along radials from the longitudinal axis of rotation A. As in the case of the close-offset spurs 46A, the offset 62B is also in the cutting direction. This difference in offsets 62A:62B is optional and considered generally helpful to enhance the aggressiveness of cutting action. For instance, with none of the grinding edges 48A/B laying along radials from the longitudinal axis of rotation A, and offset in the cutting direction, particles of host material ground and/or displaced by the grinding edges 48A/B will be directed into the surrounding host material with a wiping action. That is to say, the offset grinding edges 48A/B will further contribute to, and even enhance, the autografting function of the tool <NUM>. However, the invention also contemplates and fully embraces an apical end in which the grinding edges <NUM> all share a common offset distance <NUM> as well as grinding edges <NUM> radially arranged from the longitudinal axis of rotation A.

In the dentistry example, an osteotomy is required to receive a bone implant. As previously made clear this invention is not limited to dental applications but may be applied across a wide spectrum of applications. Human (orthopedic) applications are typical, but animal applications are equally plausible and fully within the scope of this invention. Furthermore, the invention is not limited to bone applications, but may be used to prepare holes in non-organic materials for industrial and commercial applications, including but not limited to wood, metal foam plastics and other materials both solid and cellular alike.

A series of steps are required to accomplish the fully formed osteotomy. In some procedures, the series of steps include first boring a pilot hole (<FIG>) into the recipient bone to form the initial osteotomy, and then incrementally expanding the osteotomy using progressively wider bur devices or tools <NUM>, as shown in <FIG>, until a final intended diameter is achieved. Once the osteotomy has been prepared, the implant or fixture (not shown) is screwed into place. The procedure of forming an osteotomy is described, generally, below.

In other procedures, such as the previously-described socket shield technique, the series of steps include first extracting a portion of a tooth to form the initial osteotomy, then incrementally expanding the osteotomy using progressively wider bur devices or tools <NUM> until a final intended diameter is achieved. Once the osteotomy has been prepared, the implant or fixture is screwed into place.

However, the invention is not limited to socket shield procedures. In some applications, it will be desirable to use the improved tool <NUM>, such as in certain hard bone and socket shield conditions. Referring again to <FIG>, it can be observed that while the tool <NUM> continues to provide much the same osseodensification attributes known from <CIT>, the hollow point configuration allows a small quantity of bone debris to collect inside the cavity <NUM>. This can be beneficial for many reasons, including a desire to limit or subdue expansion, or to facilitate penetration when the host material is especially hard.

The Figures do not show the concurrent application of irrigating fluid which is typical in procedures using the tool <NUM>. In normal circumstances, the irrigating fluid will wash into the cavity <NUM> and help flush out the bone debris to be immediately re-patriated/auto-grafted into the side walls of the osteotomy according to the known principles of osseodensification. <FIG> show alternative embodiments in which irrigation ducts may be integrated into the rotary tool <NUM>.

Osseodensification is a method to preserve bone and its collagen content. Osseodensification is effective because it enhances the plasticity of the host material. Osseodensification allows for enlarging an osteotomy by compacting (and/or by cutting when rotation is reversed) with a bur tool <NUM> in preparation for a subsequently placed implant or fixture. The basic steps of the method begin with the provision of a host material, which in the illustrated embodiment is bone however in other contemplated applications could a non-bone material. A precursor hole is also created in the host material as depicted in <FIG>. This precursor hole may be a pilot hole drilled with a relatively small diameter standard twist drill <NUM> or a hole formed by other methods. In any case, the precursor hole has an interior surface (i.e., sidewall) that extends between a generally circular entrance in an exposed surface of the host material and a bottom that is closed, most commonly by the host material itself. The bottom of the precursor hole may have a generally conical shape as created by the tip of the pilot drill <NUM>.

The method further includes the step of providing a tool <NUM> configured to be turned at high speed in either a cutting or densifying direction. Whether the tool <NUM> is enlarging by compacting or by cutting, it rotates at high speed as opposed to low-speed oscillating/rocking motions as taught by some prior art systems. To achieve high speed rotation, the tool <NUM> is operatively connected to a surgical motor, with its rotation speed set somewhere between about <NUM>-<NUM> RPM. For dental applications, the torque setting may be about <NUM>-<NUM> Ncm. (Possibly higher for general orthopedic and non-medical/industrial applications. ) During the procedure, copious irrigation is provided in the form of a continuous stream of a substantially incompressible liquid (e.g., saline) onto the rotating body <NUM> adjacent the entrance to the precursor hole as suggested in <FIG>.

Returning to <FIG>, the body <NUM> of the tool <NUM> is continuously rotated in a densifying direction while its apical tip is forcibly advanced into the entrance of the precursor hole. Continued advance results in an enlargement of the precursor hole as shown in <FIG>. The rotating body <NUM> has been by forcibly pushed so that its working edges <NUM> sweep against the interior surface of the precursor hole to gently expand the bone by incremental plastic deformations that cause a progressive enlargement of the precursor hole beginning adjacent the entrance and developing in a frustoconical pattern downwardly toward the bottom of the hole. This enlarging step preferably includes axially stroking or pumping the rotating body <NUM> within the precursor hole so that the working edges <NUM> alternately lap against the bone interior surface with downward motion and then separate from the interior surface with upward motion in ever deepening movements that cause a progressive plastic deformation of the interior surface of the precursor hole. When the working edges <NUM> are in physical contact with the bone or dentin (tooth), the surgeon can manually apply variable axial pressure depending on the haptic sensed responsiveness of the bone. The enlarging step also includes lapping the working edges <NUM> against the interior surface of the precursor hole without the working edges <NUM> cutting into the surrounding bone, and in a manner where the rate of advance toward the bottom of the precursor hole is independent of the rate of rotation of the body <NUM>. This latter characteristic contrasts with some prior art systems that couple tool rotation with the rate of advance.

<FIG> show of the osteotomy using a slightly larger tool <NUM>. Whether this further enlargement is required will be dictated by the specific protocol on a case-by-case basis. If even greater enlargement is needed, a still larger tool <NUM> can be used to expand the osteotomy, as illustrated in <FIG>. Indeed, the number of expansion steps required to achieve the correct size osteotomy is dictated by the implant to be placed and the conditions of the host material.

As shown in <FIG>, if desired, the surgeon may choose a traditional osseodensification tool like that shown in <CIT> to perform the final expansion/densification step. This will assure that all remaining bone debris in the osteotomy is re-patriated/auto-grafted directly into the side walls of the osteotomy in preparation to receive an implant or anchor.

In one contemplated alternative embodiment shown in <FIG>, the tool <NUM> is configured with an internal duct <NUM> to conduct a flow of irrigating fluid longitudinally through the shank <NUM> to a downstream outlet <NUM> and/or <NUM>' located at a suitable position on or within the body <NUM>. <FIG> shows the outlet <NUM> as in internal feature discharging directly into the narrow breach end of the cavity <NUM>. In this manner, the irrigation duct <NUM> is in direct and exclusive fluid communication with the cavity <NUM>. The flow of irrigating fluid will naturally urge debris out of the cavity <NUM>, thus encouraging maximum autografting. In another contemplated embodiment depicted in <FIG>, the irrigation duct <NUM> is routed externally to two or more circumferentially distributed outlets <NUM>' in the stopper section <NUM> similar to that shown, for example, in <CIT>. In this latter case, the irrigation duct <NUM> is not in direct fluid communication with the cavity <NUM>. In a still further contemplated embodiment combining both of the preceding designs, which is illustrated in <FIG>, the irrigation duct <NUM> discharges directly into the breach of the cavity <NUM> through outlet <NUM>, but also includes two or more circumferentially distributed spur outlets <NUM>' like those shown in <FIG>. In this third case, fluid pumped through the irrigation duct <NUM> will concurrently flush the cavity <NUM> and also wash the external body <NUM>. During post-operative cleaning, the external outlets <NUM>' can be temporarily covered with fingertips or other measures to force all irrigation flow through the internal outlet <NUM> thereby flushing debris from the cavity <NUM>.

<FIG> is a perspective view of a rotary tool <NUM> according to another embodiment of this invention in which the body <NUM> is straight-sided (i.e., not tapered). <FIG> is a cross-section taken generally along lines <NUM>-<NUM> in <FIG>. The flutes <NUM> are shaped with cutting <NUM> and densifying <NUM> faces, lands <NUM> and working edges <NUM> to provide osseodensification when operated in the densifying mode. The number of flutes <NUM> is not necessarily correlated to the number of gullets <NUM> in this embodiment, resulting in only some of the flutes <NUM> opening directly into a gullet <NUM>. And likewise, only some of the flutes <NUM> open directly onto a leading flank <NUM> in this variation of the tool <NUM>.

This rotary tool <NUM> includes other unique attributes mentioned previously as optional or alternative features. For one, the grinding edges <NUM> are offset in the densifying direction of rotation. This creates a significantly more aggressive cutting characteristic than the design of <FIG>. Also, the apex <NUM> of each grinding edge <NUM> appears at the radially outmost position. Again, this design cuts more aggressively in the cutting mode than the design of <FIG>. Another distinguishing feature of the embodiment of <FIG> can be seen in the cavity <NUM>, which has straight cylindrical sidewalls to match the outside shape of the body <NUM>. Furthermore, irrigation ducts <NUM> are integrated into the body <NUM> of the rotary tool <NUM> rather than axially through the shank <NUM> as in <FIG>, <FIG>. In <FIG>, the irrigation ducts <NUM> are formed in the valleys of each flute <NUM>. Those of skill in the art will appreciate other placements, including straight axial designs, circular or oval holes, and the like. In whatever form, the irrigation ducts <NUM> facilitate externally applied irrigation fluid to enter the cavity <NUM> in the lateral direction through the body <NUM>. The flow of irrigating fluid through the ducts <NUM> will naturally urge debris out of the cavity <NUM>, thus encouraging autografting.

The present invention, when operated with a continuous supply of irrigating fluid, may be used to form holes in many different types of materials in addition to bone. For examples, malleable metals, wood and plastics may be used at the host material. The irrigating fluid in these circumstances may be an oil or cutting-fluid substance rather than water or saline. When the non-bone host material is cellular, like in the case of foam metals, wood and some polymers, the host material may behave somewhat like bone. However, when the host material in not cellular but rather solid, displaced stock will have a tendency to mound above and below the hole rather than being auto-grafted into the sidewalls of the hole. This mounding represents malleable material that is plastically displaced by the compression wave of the working edge <NUM>. As a result, the effective stock thickness around a hole formed in non-cellular material will be substantially greater than the original stock thickness, which is considered beneficial to provide greater purchase for an anchor screw.

Advantages of the hollow-point tool <NUM> of this invention include but are not limited to the following. The torque for use can be as high as 80ncm for dental applications. Possibly higher for non-dental orthopedic applications. This tool <NUM> can be used in reverse and act as an osseodensifying bur with easier application and less vertical force as compared with the design of <CIT>. Therefore, the hollow-point shape can be used in all bone preparation applications, including but not limited to socket shield procedures. The tool <NUM> may have multiple spurs <NUM> to grind the bone prior to compaction by the working edges <NUM> in non-cutting rotation. And the cavity <NUM> contributes positively to reduce the vertical force needed to advance the tool <NUM> into an osteotomy.

Claim 1:
A rotary tool (<NUM>, <NUM>) configured to be turned at high speed in both condensing and cutting rotary directions to accomplish different effects while forming a hole in a host material, said rotary tool (<NUM>, <NUM>) comprising:
a shank (<NUM>, <NUM>) establishing a longitudinal axis of rotation (A), said shank (<NUM>, <NUM>) being an elongated shaft having an upper end and a lower end;
a body (<NUM>, <NUM>) extending axially from said lower end of said shank (<NUM>, <NUM>), said body (<NUM>, <NUM>) having an apical end remote from said shank (<NUM>, <NUM>), a plurality of flutes (<NUM>, <NUM>) disposed about said body (<NUM>, <NUM>), each said flute (<NUM>, <NUM>) having a cutting face (<NUM>, <NUM>) on one side thereof defining a cutting rake angle and a densifying face (<NUM>, <NUM>) on the other side thereof defining a densifying rake angle, each said flute (<NUM>, <NUM>) having an axial length and a radial depth, each said flute (<NUM>, <NUM>) being formed with a continuously negative densifying rake angle along the length thereof, a land (<NUM>, <NUM>) formed between each adjacent pair of flutes (<NUM>, <NUM>), each said land (<NUM>, <NUM>) having a working edge (<NUM>, <NUM>) along said cutting face (<NUM>, <NUM>) of one said flute (<NUM>, <NUM>), each said working edge (<NUM>, <NUM>) being substantially margin-less;
characterised by:
a cavity (<NUM>, <NUM>) disposed in said body (<NUM>, <NUM>), said cavity (<NUM>, <NUM>) extending axially within said body (<NUM>, <NUM>) and opening through said apical end; and
a plurality of spurs (46A, 46B) disposed on said apical end of said body (<NUM>, <NUM>), said spurs (46A, 46B) disposed around said opening of said cavity (<NUM>, <NUM>).