Patent Description:
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 a hip or knee, and reinforcement implants installed to repair fractures and remediate other deficiencies, to name but a few.

In some applications, the placement location for the implant is very difficult to access. These so-called "deep reach" situations include (but are not limited to) zygomatic implants like those illustrated in <FIG>. A long drill bit or bur in usually needed to prepare the osteotomy to receive the implant as depicted in <FIG>. (Please note, the drilling tool shown in <FIG> is in accordance with one embodiment of the present invention, and is not admitted prior art.

Recently, the industry has embraced the osseodensification protocols for preparing an osteotomy. This popular new protocol was pioneered by Dr. Salah Huwais, inventor of this present invention, and has been marketed as a rotary osteotome by Versah, LLC of Jackson, Michigan under the brand name Densah® bur. <CIT>) and <CIT>) describe various examples of the Densah® bur osteotomes and their functionality.

In particular <CIT> discloses a rotary osteotome comprising: a shank establishing a longitudinal axis of rotation, said shank extending between a drive end and a transition interface, a body extending from said transition interface to an apical end, a plurality of flutes disposed about said body and extending from adjacent said apical end to respective terminus, each said flute having a cutting face on one side thereof defining a rake angle and a densifying face on the other side thereof defining a heel-side angle, a land formed between each adjacent pair of flutes, each said land having a working edge along said cutting face of the one adjacent said flute, a stopper section of said body disposed between said terminus of said flutes and said transition interface of said shank.

A key element of the usage protocol for the Densah® bur osteotome is copious irrigation applied at the external end of the bur, such as by an irrigation-enabled hand piece. Please see <FIG>. The irrigation fluid is preferably sterile saline solution or water. When a continuous flow of irrigating fluid is provided, the reverse twist of the flutes (in relation to the rotational direction of the osteotome) will have the effect of propelling and pumping the irrigation fluid down toward the bottom of the osteotomy. That is, the flutes transport the irrigating fluid something akin to the vanes of a turbine. As a result, irrigating fluid is forcefully driven toward the bottom of the osteotomy throughout the surgical procedure. This pumping or propelling action is depicted by the downwardly twisting arrows in <FIG>. A hydraulic pressure is created that pushes outwardly within the osteotomy, as depicted in <FIG> as a pressure gradient with small, outwardly pointing arrows. When operated in the densifying mode, the pressure gradient pushes against the bone side walls, preparing and preconditioning the interior surface of the hole. Excess irrigation fluid is exhausted (overflows) out of the osteotomy through the small circular gap that appears around the rotary osteotome when lifted slightly. The pressure gradient will thus increase and decrease in direct response to the amount of force applied by the surgeon as he or she repeatedly advances and relaxes the rotating rotary osteotome into the osteotomy.

By modulating the position of the rotary osteotome in combination with a continuous supply of irrigation fluid, the surgeon can apply an evenly distributed, expansive pressure with piston-like effect to the inner side walls of the osteotomy. This throbbing hydraulic effect has many documented preconditioning advantages, which include: <NUM>) gentle pre-stressing of the bone structure of the osteotomy in preparation for subsequent compacting contact, <NUM>) haptic feedback transmitted through the rotary osteotome that allows the surgeon to tactically discern the instantaneously applied pressure prior to actual contact between the rotary osteotome and side walls, <NUM>) enhanced hydration of the bone structure which increases bone toughness and increases bone plasticity, <NUM>) hydraulically assisted infusion of bone fragments into the lattice structure of the surrounding bone, <NUM>) reduced heat transfer, <NUM>) hydrodynamic lubricity, <NUM>) dampening or cushioning of the trauma sensed by the patient, and so forth.

However, the aforementioned "deep reach" situations complicate the external irrigation protocol of the Densah® bur osteotome. For example, it can be practically impossible to apply sufficient quantities of irrigating fluid to the flutes of a deeply embedded bur while preparing an osteotomy for a zygomatic implant like those illustrated in <FIG> and <FIG>.

There is therefore a need for improved tools and techniques that prepare bone and other types of host materials to receive an anchor or implant in "deep reach" applications.

The invention is defined in any independent claims. Optional embodiments are set out in the dependent claims. A rotary osteotome is configured for deep reach applications. The osteotome comprises a shank that establishes a longitudinal axis of rotation. The shank extends between a drive end and a transition interface. A body extends from the transition interface to an apical end. A plurality of flutes are disposed about the body. Each flute extends from adjacent the apical end to respective terminus. Each flute has a cutting face on one side thereof that defines a rake angle. Each flute also has a densifying face on the other side thereof that defines a heel-side angle. A land is formed between each adjacent pair of flutes. Each land has a working edge along the cutting face of the one adjacent flute. A stopper section of the body is disposed between the terminus of the flutes and the transition interface of the shank. An irrigation conduit passes from the inlet in the shank to the outlet orifice. The outlet orifice is disposed in the stopper section.

A rotary osteotome is configured for deep reach applications. The osteotome comprises a shank that establishes a longitudinal axis of rotation. The shank extends between a drive end and a transition interface. A body extends from the transition interface to an apical end. At least a portion of the body has a conically tapered profile that decreases from a maximum diameter to a minimum diameter adjacent the apical end. A plurality of flutes are disposed about the body. The flutes each extend from adjacent the apical end to a respective terminus. Each flute helically spirals about the conically tapered profile of the body. The plurality of flutes are arranged about the body in equal circumferential increments. Each flute has a cutting face on one side thereof that defines a rake angle and a densifying face on the other side thereof that defines a heel-side angle. A land is formed between each adjacent pair of flutes. Each land has a working edge along the cutting face of the one adjacent the flute. A stopper section of the body is disposed between the terminus of the flutes and the transition interface of the shank. The stopper section is generally cylindrical. An irrigation conduit passes from an inlet in the shank to a plurality of outlet orifices in the stopper section. The inlet is disposed in the drive end of the shank and is aligned along the longitudinal axis. The plurality of outlet orifices are spaced apart from one another in equal circumferential increments about the body.

By locating the outlet orifice(s) on the stopper section of the body, an energetic feed of irrigating fluid is enabled to flow into the flutes and toward the apical end, thus better mimicking external irrigation practices of the prior art. By flowing irrigation fluid into the flutes and toward the apical end, hydraulic effects can be generated with known preconditioning advantages, which include: <NUM>) gentle pre-stressing of the bone structure of the osteotomy in preparation for subsequent compacting contact, <NUM>) haptic feedback transmitted through the rotary osteotome that allows the surgeon to tactically discern the instantaneously applied pressure prior to actual contact between the rotary osteotome and side walls, <NUM>) enhanced hydration of the bone structure which increases bone toughness and increases bone plasticity, <NUM>) hydraulically assisted infusion of bone fragments into the lattice structure of the surrounding bone, <NUM>) reduced heat transfer especially in areas of plastic deformation, <NUM>) hydrodynamic lubricity, and <NUM>) dampening or cushioning of the trauma sensed by the patient, to name a few.

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:.

Referring to the figures, wherein like numerals indicate like or corresponding parts throughout the several views, <FIG> and <FIG> show examples of dental implants, in which preparation of osteotomies are required to receive a bone implant <NUM>, <NUM> or <NUM>. It will be understood that this invention is not limited to dental applications, but may be applied across a wide spectrum of orthopedic applications. Human applications are typical, but animal applications are equally plausible and not outside the scope of this invention.

For illustrative purposes only, the externally irrigated prior art style rotary osteotome of <FIG> can be useful to explain the manner in which an expanded and near final fully formed osteotomy <NUM> can be prepared to receive an implant or other fixture. Once the osteotomy <NUM> has been prepared, the implant or fixture screw is screwed into place (e.g., implant <NUM>, <NUM>, <NUM> in <FIG>). A series of steps are required to accomplish the fully formed osteotomy <NUM>, which include first boring a pilot hole into the recipient bone to form the initial osteotomy, then incrementally expanding the osteotomy <NUM> using progressively wider rotary expander devices or osteotomes until final intended diameter and depth are achieved. This sequential expansion method is well-suited for the externally irrigated prior art style rotary osteotome (<FIG>) as well as for the novel, internally irrigated rotary osteotome of this present invention.

Turning now to <FIG>, a rotary osteotome <NUM> according to an embodiment of this invention is shown including a shank <NUM> and a body <NUM>. The shank <NUM> has an elongated cylindrical shaft that establishes a longitudinal axis of rotation A for the rotary osteotome <NUM>. A drill motor engaging coupling <NUM> is formed at the distal upper end of the shaft for connection to the drill motor (not shown). The particular configuration of the coupling <NUM> may vary depending on the type of drill motor used, and in some cases may even be merely a smooth portion of the shaft 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>. In some cases, the shank <NUM> may include an annular groove <NUM> disposed a predetermined distance from the transition interface <NUM>. The groove <NUM> can be used to locate a depth stop (not shown) used to limited the depth of penetration for the osteotome <NUM>.

A lower portion of the body <NUM> preferably has conically tapered profile decreasing from a maximum diameter to a minimum diameter adjacent an apical end <NUM>. However, in some contemplated embodiments the lower end of the body <NUM> may be non-tapered (i.e., cylindrical). The apical end <NUM> is thus remote from the shank <NUM>. Preferably, all osteotomes <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.

The apical end <NUM> is defined by at least one, but preferably a pair of lips <NUM> best seen in <FIG>. The lips <NUM> are edges disposed on opposite sides of the apical end <NUM>, and in the illustrated embodiment do not lie within a common plane. In other words, as shown the lips <NUM> may be slightly offset (in terms of a direct diametrical alignment) by the short length of a chisel point <NUM> extending centrally through the longitudinal axis A. The chisel point <NUM> is a common feature found in drilling tools, but alternative apical end <NUM> formations to the chisel point <NUM> are of course possible, including rounded and simple pointed shapes, etc. As mentioned, the lips <NUM> are edges that angle upwardly and outwardly (radially) from the apical end <NUM>. The angle of the lips <NUM> may be varied to optimize performance for the application. Lip <NUM> angles relative to the longitudinal axis A may range between about <NUM>° (very pointed) and <NUM>° (very blunt). In the illustrated examples, the lip angle is approximately <NUM>° measured relative to longitudinal axis A, or <NUM>° measured between the two opposing lips <NUM>.

Each lip <NUM> has a generally planar first trailing flank <NUM>. The first trailing flanks <NUM> are canted from their respective lips <NUM> at a first angle. The first angle may be varied between about <NUM>° and <NUM>° to optimize performance for the application. In practice, the first angle may be approximately <NUM>° measured relative to longitudinal axis A. It will be appreciated therefore that the two opposing first trailing flanks <NUM> are set in opposite directions so that when the rotary osteotome <NUM> is rotated in use, the first trailing flanks <NUM> either lead or follow their respective lips <NUM>. When first trailing flanks <NUM> lead their respective lips <NUM>, the osteotome <NUM> is said to be turning in a non-cutting direction for the densifying mode; and conversely when the first trailing flanks <NUM> follow their respective lips <NUM>, the osteotome <NUM> is said to be turning in a cutting direction where the lips <NUM> cut or slice bone on descent. In the densifying direction, the first trailing flanks <NUM> form, in effect, a large negative rake angle for the lips <NUM> to minimize chip formation and shear deformation in the bone (or other host material) at the point of contact with the lips <NUM>.

A generally planar second trailing flank <NUM> is formed adjacent to, and falls away from, each first trailing flank <NUM> at a second angle. The second angle is smaller than the first angle, preferably less than about <NUM>°. In an example where the first trailing flanks <NUM> are formed at <NUM>° (relative to the axis A), the second trailing flanks <NUM> may be <NUM>° or less. A generally planar relief pocket <NUM> is formed adjacent to, and falls away from, each second trailing flank <NUM> at a third angle. The third angle is smaller than the second angle. In an example where the second trailing flanks <NUM> are formed at <NUM>° (relative to the axis A), the relief pockets <NUM> (i.e., the third angle) may be <NUM>° or less. Each relief pocket <NUM> is disposed in a sector of the apical end <NUM> between a second trailing flank <NUM> and a lip <NUM>. When the rotary osteotome <NUM> is rotated in the cutting direction, a significant amount of bone chips collect in the relief pocket <NUM> regions. When the rotary osteotome <NUM> is rotated in the densifying direction, little to no bone chips collect in the relief pocket <NUM> regions.

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 radial depths. , 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 tapered lower end of the body <NUM>. The diameter of the body <NUM> may influence the number of flutes <NUM>. As an example, bodies <NUM> in the range of about <NUM>-<NUM> may be formed with three or four flutes; bodies <NUM> in the range of about <NUM>-<NUM> may be formed with five or six flutes; bodies <NUM> in the range of about <NUM>-<NUM> may be formed with seven or eight flutes. Of course, the number of flutes <NUM> may be varied more or less than the examples given in order to optimize performance and/or to better suit the particular application.

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. This RHS-RHC configuration is shown throughout the Figures, although it should be appreciated that a reversal of cutting direction and helical spiral direction (i.e., to LHS-LHC) could be made if desired with substantially equal results.

Each flute <NUM> has a densifying face <NUM> and an opposing cutting face <NUM>. A rib or land is formed between adjacent flutes <NUM>, in alternating fashion. Thus, a four-flute <NUM> rotary osteotome <NUM> will have four lands, a six-flute <NUM> rotary osteotome <NUM> will have six interleaved lands, and so forth. Each land has an outer land face <NUM> that extends (circumferentially) between the densifying face <NUM> of the flute <NUM> on one side and the cutting face <NUM> of the flute <NUM> on its other side. The sharp interface between each land face <NUM> and its associated cutting face <NUM> is referred to as a working edge <NUM>. Depending on the rotational direction of the rotary osteotome <NUM>, the working edge <NUM> either functions to cut bone or compact bone. That is, when the osteotome <NUM> is rotated in the cutting direction, the working edges <NUM> slice and excavate bone (or other host material). When the osteotome <NUM> is rotated in the densifying (non-cutting) direction, the working edges <NUM> compress 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 mechanism.

The working edges <NUM> are shown throughout the illustrations as being substantially margin-less, in that the entire portion of each land face <NUM> is cut away behind the working edge <NUM> to provide complete clearance as can be appreciated from the in-use depiction of <FIG>. As mentioned above in connection with the angle of the helical twist, the substantially margin-less working edges <NUM> are shown turning away from the densifying direction as the conically tapered profile portion of the body <NUM> decreases in diameter. In other words, when the densifying direction is counter-clockwise (see directional arrow in <FIG>), the helical twist of the working edges <NUM> winds in the counter-clockwise direction when viewed from the top of the body <NUM> looking toward its apical end <NUM>. Or conversely, as shown in <FIG> when viewed from the apical end <NUM> looking toward top of the body <NUM>, the twist will appear to be in the clockwise direction. Thus, when the densifying direction is counter-clockwise, the working edges <NUM> will turn away from the densifying direction when all of the land faces <NUM> and flutes <NUM> orbit counter-clockwise about the longitudinal axis A as one traces each land face <NUM> and flute <NUM> downwardly toward the apical end <NUM>.

The cutting face <NUM> establishes a rake angle for each respective working edge <NUM>. A rake is an angle of slope measured from the leading face of the working edge <NUM> to an imaginary line extending perpendicular to the surface of the worked object (e.g., inner bone surface of the osteotomy). Rake angles can be: positive, negative or zero. According to <FIG>, the rake angle for working edge <NUM> when rotated in a cutting direction is preferably zero or negative provided a crisp cutting edge <NUM> is established that will be well-suited to cut/slice bone when the rotary osteotome <NUM> is rotated in the cutting direction. In practice, it has been discovered that the cutting functionality of the rotary osteotome <NUM> can be optimized when the rake angle of the cutting face <NUM> is between about <NUM>° and about -<NUM>° (negative rake), which may vary as a function of distance from the apical end <NUM>. The same or generally the same negative rake angle may be maintained along the entire length of the flute <NUM>. Intentional changes in the rake angle can be regressive or progressive. A progressive change would indicate that the rake angle is at its smallest (closest to zero) adjacent the apical end <NUM> and grows smoothly to a maximum adjacent the stopper section <NUM>. A regressive change, on the other hand, would mean the negative rake angle is larger at the apical end <NUM> and grows smaller (and thus more aggressive in cutting mode) near the stopper section <NUM>.

When the rotary osteotome <NUM> is counter-rotated, in the densifying mode, the effective rake angle is established between the working edge <NUM> and the land face <NUM>, which may lie at a large negative rake angle in the order of about <NUM>°-<NUM>°. The large negative 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 <NUM> and the working edge <NUM> to create a compression wave ahead of the point of contact. Osseodensification may also be loosely compared to the well-known process of burnishing metal to improve metal surface quality.

Downward pressure applied by the surgeon is needed to keep the working edge <NUM> in contact with the bone surface of the osteotomy <NUM> being expanded. That is, pressure is needed to generate and propagate a compression wave in the bone that begins when the contact stresses exceed the yield strength of the host bone material. This is aided by the taper effect of the osteotomy <NUM> and tool <NUM> to create lateral pressure (i.e., in the intended direction of expansion). The harder the surgeon pushes the rotary osteotome <NUM> into the osteotomy <NUM>, 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 rotary osteotome <NUM>, which is a factor underlying the short learning curve required to master the osseodensification technique. Thus, the compaction intensity depends chiefly on the amount of force exerted on the rotary osteotome <NUM>, which is controlled by the surgeon. The more force exerted; the quicker expansion will occur.

As each working edge <NUM> drags across the bone, the applied forces can be decomposed into two components: one normal to the bone's surface, pressing it outwardly, and the other tangential, dragging it along the inner surface of the osteotomy <NUM>. 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 lower portion of the body <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. As the surgeon-applied downward force increases, eventually the stresses in the bone surface exceed its yield strength. When this happens, the working edges <NUM> will plow through the surface and create a trough behind. The plowing action of the working edges <NUM> thus progressively enlarges the osteotomy until the rotary osteotome <NUM> reaches full/maximum depth, at which time a different larger rotary osteotome <NUM> must be used to achieve further expansion if desired.

While the elastic properties of bone are well-known, if the load imposed by the surgeon does not exceed the bone's ability to deform elastically, the bone will promptly return to its initial (un-deformed) condition once the stress is removed. On the other hand, if the load imposed by the surgeon exceeds the bone's ability to deform elastically, the bone will deform and change shape permanently by plastic deformation. In bone, the permanent change in shape may be associated with micro-cracks that allow energy release, a compromise that is a natural defense against complete fracture. If these micro-cracks are small, the bone remains in one piece while the osteotomy expands. The region of plastic deformation extends from the yield point of the material, all the way to the point of fracture. The peak of the curve between yield point and fracture indicates the material's ultimate tensile strength. When a material (e.g., bone) is subjected to stress in the region between its yield point and its ultimate tensile strength, the material experiences strain hardening. Strain hardening, also known as work hardening or cold working, is the strengthening of a ductile material by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material - which for bone materials corresponds with the dislocation of the cross-links between collagen fibers in the bone tissue. The material tends to experience necking when subjected to stress in the region between its ultimate tensile strength and the point of fracture.

The direction of helical twist can be designed to play a role in contributing to the surgeon's control so that an optimum level of stress (in the strain hardening zone) can be applied to the bone (or other host material) throughout the expansion procedure. In particular, the RHS-RHC configuration described above, which represents a right-hand spiral for a right-hand cutting direction (or alternatively an LHS-LHC configuration, not shown) applies a stress that provokes a beneficial opposing axial reaction force (Ry) in the host bone when the rotary osteotome <NUM> is continuously rotated at high speed in a densifying direction and concurrently forcibly advanced (manually by the surgeon) into an osteotomy <NUM>. This opposing axial reaction force (Ry) is illustrated graphically in <FIG> as being directionally opposite to the forcibly advanced direction into the osteotomy <NUM>. In other words, if the surgeon operating the rotary osteotome <NUM> is pushing the rotary osteotome <NUM> downwardly into an osteotomy <NUM>, then the opposing axial reaction force (Ry) works in the opposite direction to push the osteotome upwardly. The opposing axial reaction force (Ry) is the vertical (or perhaps more accurately the "axial" vis-à-vis the longitudinal axis A) component of the reaction force that is the Newtonian "equal and opposite reaction force" applied by the bone against the full length of the working edges <NUM> of the rotary osteotome <NUM>. An opposing axial reaction force (Ry) is also created by the effectively large negative rake angle at the lips <NUM> when the rotary osteotome <NUM> is rotated in a densifying direction. Those of skill in the art will appreciate alternative embodiments in which the opposing axial reaction force (Ry) is created by either the configuration of the lips <NUM> alone or of the working edges <NUM> alone rather than by both (<NUM>, <NUM>) acting in concert.

For a surgeon to advance the apical end <NUM> toward the bottom of the osteotomy <NUM> when the rotary osteotome <NUM> is spinning in the densifying direction, he or she must push against and overcome the opposing axial reaction forces (Ry) in addition to supplying the force needed to plastically displace/expand the bone as described above. The rotary osteotome <NUM> is designed so that the surgeon must continually work, as it were, against the opposing axial reaction forces (Ry) to expand the osteotomy <NUM> by compaction, i.e., when in the densifying mode. Rather than being a detriment, the opposing axial reaction forces (Ry) are a benefit to the surgeon by giving them greater control over the expansion process. Because of the opposing axial reaction forces (Ry), the rotary osteotome <NUM> will not be pulled deeper into the osteotomy <NUM> as might occur with a standard "up cutting" twist drill or burr that is designed to generate a tractive force that tends to advance the osteotome toward the interior of the osseous site. Up-cutting burrs have the potential to grab and pull the burr more deeply into the osteotomy, which could lead to inadvertent over-penetration.

In the densifying mode, the intensity of the opposing axial reaction forces (Ry) is always proportional to the intensity of force applied by the surgeon in advancing the body <NUM> into the osteotomy <NUM>. This opposing force thus creates real-time haptic feedback that is intuitive and natural to inform the surgeon whether more or less applied force is needed at any given instant. This concurrent tactile feedback takes full advantage of the surgeon's delicate sense of touch by applying reaction forces (R, and in particular the axial component Ry) directly through the rotary osteotome <NUM>. In this densifying mode, the mechanical stimulation of the opposing axial reaction forces (Ry) assists the surgeon to better control the expansion procedure on the basis of how the bone (or other host material) is reacting to the expansion procedure in real time.

Thus, the controlled "bouncing" or "pumping" action described above is made more effective and substantially more controllable by the opposing axial reaction forces (Ry) so that the surgeon can instinctively monitor progress and make fine corrections and applied pressure adjustments on-the-fly without losing control over the rate of expansion. The tactile feedback from the opposing axial reaction forces (Ry) allows a surgeon to intuitively exert stress on the bone material so that its strain response preferably resides in the strain hardening zone, that is, between its yield point to its ultimate tensile strength. In any event, the surgeon will endeavor to maintain the stress (as generated by the force he or she applies through the rotating rotary osteotome <NUM>) above the elastic limit and below the point of fracture. Of course, until the applied stress passes the elastic limit, the bone will not permanently deform at all; and to apply stress beyond the point of fracture will cause the bone (or other host material) to break - possibly catastrophically.

<FIG> and <FIG> illustrate the ability of the rotary osteotome <NUM> to simultaneously auto-graft and compact bone. The compaction aspect may be defined as the gentle push of osseous structure laterally outwardly to compact the cells throughout the region surrounding the osteotomy <NUM>. The rotary osteotome <NUM> is configured to simultaneously auto-graft and compact the small quantities of ground/milled bone resulting from each larger size osteotome <NUM> as it is rotated and forcibly advanced into the osteotomy <NUM>. The auto-grafting phenomena supplements the basic bone compaction and condensation effects described above to further densify the inner walls <NUM> of the osteotomy. Furthermore, auto-grafting - which is the process of repatriating the patient's own bone material - enhances natural healing properties in the human body to accelerate recovery and improve osseointegration.

<FIG> shows an enlarged view of the interface between the apical end <NUM> and the host bone material at the point where the outermost edge of each rotating and forcibly advancing lip <NUM> contacts the bone. Attrition causes the bone to be ground away. The bone debris collects mainly on the second trailing flanks <NUM>, i.e., immediately behind the respective first trailing flanks <NUM>. Some of the accumulated bone debris migrates radially inwardly along the lips <NUM> and is carried all the way to the very bottom of the osteotomy <NUM>. The remainder of the accumulated bone debris is distributed along the plurality of flutes <NUM> that directly intersect the second trailing flanks <NUM> by the pressure exerted through the surgeon's manual pushing efforts. This is illustrated in <FIG>. Observe that a plurality of flutes <NUM> open into the second trailing flanks <NUM> for receiving an upflow of boney slurry in densifying mode. These flutes <NUM> readily carry bone debris away from the grinding interface, thereby reducing the possibility of heat- and/or pressure-induced necrosis in the bone particles.

Mixed with blood and collagen and irrigating fluid, the bone chips have the consistency of a semi-viscous slurry. Bone debris that is distributed up the flutes <NUM> works its way toward the associated land faces <NUM> where it is wiped and pressed into the cellular walls of the osteotomy <NUM> and immediately grafted back into the patient's bone very near to the sight were it was harvested. Bone debris that is carried to the bottom of the osteotomy <NUM> is wiped and pressed into the bottom of the osteotomy <NUM>. As a result, an auto-grafting zone is developed around and under the compaction region. And at the osteotomy bottom, where this is little-to-no compaction at all, there is a significant zone of auto-grafting which serves to densify and positively stimulate an area of the osteotomy <NUM> which could otherwise not be densified. The osseodensification method thus preserves bone and its collagen content to enhance plasticity. The osseodensification method allows for enlarging an osteotomy <NUM> by compacting (and/or by cutting when rotation is reversed) with a rotary osteotome <NUM> in preparation for a subsequently placed implant or fixture.

The rotary osteotome <NUM> of this present invention is particularly configured for zygomatic and other deep reach applications. As such, the body <NUM> of the rotary osteotome <NUM> includes an elongated stopper section <NUM> that extends between the terminus <NUM> of the flutes <NUM> and the transition <NUM>. The stopper section <NUM> produces a vital plugging action to prevent the continued migration of bone particles along the flutes <NUM> in cutting mode, and thereby self-arrest the cutting performance of the osteotome <NUM> when operated in the cutting direction. In practice, the axial length of the stopper section <NUM> can vary depending on the intended application. <FIG> and <FIG> show rotary osteotomes <NUM> having relatively short stopper sections <NUM> intended for pacing medium <NUM> and short <NUM> implants. By contrast, <FIG> and <FIG> show rotary osteotomes <NUM> having relatively long stopper sections <NUM> intended for pacing long implants <NUM>.

In some contemplated embodiments, the entire length of the body <NUM>, from apical end <NUM> to transition <NUM>, has a continuous taper or conical profile. In these cases, the stopper section <NUM> will share this tapered configuration. However, in the illustrated examples the stopper section <NUM> has a straight cylindrical profile. Thus, only the lower end of the body <NUM> is tapered; a cylindrical shape occupies the stopper section <NUM>, which is ideally suited to accommodate the shape of may zygomatic and other deep reach style implants <NUM>, <NUM>, <NUM>.

In reference to <FIG> and <FIG>, observe that once the entire lengths of the flutes <NUM> have entered the osteotomy <NUM>, there is no convenient egress for the bone particle slurry from the flutes <NUM>. The stopper section <NUM> seals or traps the bone particles between the flutes <NUM> and the sidewalls of the osteotomy <NUM> like a cork or piston. If the surgeon continues to advance the rotating osteotome <NUM> deeper into the osteotomy <NUM>, substantial resistance will be encountered. The trapped bone chip slurry will become pressurized inside the flutes <NUM> in response to the force of the surgeon's push. Hydraulic pressure can be pulsated through the bone particle slurry, if the surgeon wishes, by the aforementioned pumping action which forces the slurry into the surrounding wall surfaces of the osteotomy <NUM>, thereby forming a densification crust.

As perhaps best shown in <FIG>, the rotary osteotome <NUM> includes an irrigation conduit passing from at least one inlet <NUM> in the shank <NUM> to at least one outlet orifice <NUM> in the body <NUM>. The inlet <NUM> is disposed in the drive end of the shank <NUM>, being aligned along the longitudinal axis A within the feature of the drive coupling <NUM>. The irrigation conduit is defined by a generally cylindrical, i.e., tubular, main trunk <NUM> that extends through the shank <NUM>, coincidentally along the longitudinal axis A, and also through a portion of the body <NUM>. More specifically, the main trunk <NUM> passes through a significant portion of the stopper section <NUM>, coincidentally along the longitudinal axis A. Due to the sometimes-high rotational velocities of the osteotome <NUM> in normal use (~<NUM> RPM), the central disposition of the main trunk <NUM> has at least two important benefits: <NUM>) rotational balance of the osteotome <NUM> is preserved; and <NUM>) minimal transfer of motion via boundary layer friction to irrigation fluid transiting the main trunk <NUM>.

As stated previously, it is contemplated that the irrigation conduit is provided with at least one outlet orifice <NUM>. And the outlet orifice <NUM> is preferably disposed in the stopper section <NUM>. However, to maintain rotational balance, a plurality of outlet orifices <NUM> are preferred. The plural outlet orifices <NUM> are spaced apart from one another in equal circumferential increments about the body <NUM>. In the illustrated examples, the osteotome <NUM> is provided with two outlet orifices <NUM> diametrically opposed to one another. However, more than two outlet orifices <NUM> are certainly possible, provided the circumferential spacing maintains rotational balance. Naturally, one could envision an equivalent configuration of outlet orifices <NUM> arranged in clusters, where the clusters are equally circumferentially spaced apart even though individual orifices <NUM> may be unequally spaced. The main objective is thus to maintain rotational stability and balance at speeds approaching <NUM> RPM.

A flow splitter <NUM> is disposed between the main trunk <NUM> and the plurality of outlet orifices <NUM>. The flow splitter <NUM> is configured to divide the flow of irrigating fluid traveling through the main trunk <NUM> into substantially equal branches <NUM> to be emitted through the respective the orifices <NUM>. Each branch <NUM> is angled at an acute trajectory B relative to the longitudinal axis in the direction of the apical end, as best seen in <FIG>. The acute trajectory B of each branch <NUM> is between about <NUM>° and <NUM>°. Preferably, the acute trajectory B is the same for all branches <NUM> to preserve rotational balance. However, those of skill in the art can envision ways to maintain rotational balance while making the acute trajectories B unequal among the branches <NUM>. In the illustrated examples, the acute trajectory B of each branch is about <NUM>°, which has been shown to provide satisfactory results.

Each outlet orifice <NUM> has a generally elliptical shape defined by a longer major axis and a shorter minor axis according to the normal rules of geometry. The major axis is oriented axially, whereas the minor axis is oriented circumferentially in the illustrated examples. The elliptical shape creates a specialized nozzle effect that is particularly adapted for zygomatic and deep reach applications. In particular, the elliptical shape of each orifice <NUM> has the effect of naturally bending the emitted streams of water into the waiting flutes <NUM>. Surface tension along the boundary layer of the transiting liquid causes the irrigating fluid to cling to the inside surface of the branch <NUM>. That means water exiting each orifice <NUM> will be urged by this natural effect to remain in contact with the body <NUM> and roll into the flutes <NUM>.

To fully exploit this law of fluid mechanics, each outlet orifice <NUM> can be axially aligned with the terminus <NUM> of a respective flute <NUM>, as shown throughout the illustrations. This alignment of orifices <NUM> and flutes <NUM> only improves the transfer of irrigating fluid into the flutes <NUM> where it can be pumped toward the apical end <NUM>. Proximity of the orifice <NUM> to its associated flute terminus <NUM> naturally plays a role. In practice, it has been found that the distance from an orifice <NUM> to an adjacent flute terminus <NUM> should be no more than three lengths, regardless of alignment condition. That is to say, there should be no more than three times (3x) the major diameter of the elliptical shape in space between orifice and terminus <NUM> even if they are not axially aligned. Closer is generally considered better in this instance, such that a spacing less than a length (i.e., major diameter of orifice <NUM>) coupled with axial alignment is considered optimal in many applications.

In practice, many zygomatic and other deep reach applications call for particularly narrow (slim) implants <NUM>, <NUM>, <NUM>. That means the diameters of the rotary osteotomes <NUM> are likewise narrow/slim. The aforementioned hydraulic pumping effect that is enhanced by the flutes <NUM> is somewhat muted or frustrated when the diameter of the rotary osteotome <NUM> is narrow. (Larger diameters naturally generate larger angular velocities. ) Therefore, even minor improvements in efficiency are welcomed.

<FIG> shows that when the outlet orifices <NUM> pass deep into the osteotomy <NUM>, an energetic feed of irrigating fluid through the branches <NUM> is needed to maintain the desired hydraulic effect with its many preconditioning advantages, which include: <NUM>) gentle pre-stressing of the bone structure of the osteotomy <NUM> in preparation for subsequent compacting contact, <NUM>) haptic feedback transmitted through the rotary osteotome that allows the surgeon to tactically discern the instantaneously applied pressure prior to actual contact between the rotary osteotome and side walls, <NUM>) enhanced hydration of the bone structure which increases bone toughness and increases bone plasticity, <NUM>) hydraulically assisted infusion of bone fragments into the lattice structure of the surrounding bone, <NUM>) reduced heat transfer especially at the point of plastic deformation, <NUM>) hydrodynamic lubricity, and <NUM>) dampening or cushioning of the trauma sensed by the patient, to name a few.

<FIG> provides side-by-side comparisons for two sets of rotary osteotomes <NUM>. Each set is composed of a pilot drill <NUM> and four rotary osteotomes <NUM> of the same length but progressively larger diameters. The set on the left are formed with extended lengths to enable placement of long implants <NUM>. Although presumably these extended length osteotomes <NUM> could be used to place the other implants <NUM>, <NUM> as well. The set on the right are formed with shorter lengths to enable placement of medium <NUM> and short <NUM> implants only.

The pilot drill <NUM> can be of any suitable type. The version shown in <FIG> is a lance style having a triangular cross-section. This style has been found to provide satisfactory results. As can be appreciated from the inclusion of outlet orifices <NUM>, the pilot drill <NUM> may also be configured for internal irrigation using a similar irrigation conduit scheme to that described above in connection with the rotary osteotomes <NUM>.

Methods of use have been well-documented, at least in the context of externally irrigated osteotomes. Detailed descriptions for methods of use may be had, for example, in <CIT>.

Claim 1:
A rotary osteotome (<NUM>) configured for deep reach applications, said osteotome (<NUM>) comprising:
a shank (<NUM>) establishing a longitudinal axis of rotation (A), said shank (<NUM>) extending between a drive end and a transition interface (<NUM>),
a body (<NUM>) extending from said transition interface (<NUM>) to an apical end (<NUM>), a plurality of flutes (<NUM>) disposed about said body (<NUM>) and extending from adjacent said apical end (<NUM>) to respective terminus (<NUM>), each said flute (<NUM>) having a cutting face (<NUM>) on one side thereof defining a rake angle and a densifying face (<NUM>) on the other side thereof defining a heel-side angle, a land (<NUM>) formed between each adjacent pair of flutes (<NUM>), each said land (<NUM>) having a working edge (<NUM>) along said cutting face (<NUM>) of the one adjacent said flute (<NUM>), a stopper section (<NUM>) of said body (<NUM>) disposed between said terminus (<NUM>) of said flutes (<NUM>) and said transition interface (<NUM>) of said shank (<NUM>), and
an irrigation conduit passing from at least one inlet (<NUM>) in said shank (<NUM>) to at least one outlet orifice (<NUM>), said at least one outlet orifice (<NUM>) disposed in said stopper section (<NUM>).