WI TH CASE HARDENED CUTTING EDGES AND ME THOD OF MAKING SAME

Summary Of The Invention

[0001] This invention relates generally to a tip of an ultrasonic surgical tool. More particularly, this invention relates to a tip with hardened teeth that resist wear and a method of making the tip.

Background Of The Invention

[0002] The availability of powered surgical tools has both improved the ability to perform surgical procedures and has made it possible to perform some procedures that, previously, were difficult, if not impossible, to perform.

[0003] One such powered surgical tool is the ultrasonic handpiece. This type of tool includes three basic components.

There is the handpiece itself. Internal to the handpiece are one or more drivers. The drivers, upon the application of AC drive signal, cyclically expand and contract at a relatively high frequency, typically at least 10 kHz or more. A console, the second component, provides the AC drive signal. The tip is the third component of the tool. The tip is mechanically coupled to and extends forward from the drivers. At the distal end, the tip has a head. The head is formed with teeth. The vibrations of the drivers cause like vibrations of the head and, by extension, the teeth. When the vibrating teeth are applied to hard tissue such as bone, the back and forth movement of the teeth shear away, remove, the tissue.

When an ultrasonic tool is actuated the teeth typically engage in a relatively narrow range of motion, often 5 mm or less.

This makes the ultrasonic surgical tool a very useful tool for precisely removing small masses of hard tissue. Thus ultrasonic tools have proven to be very practical tools for, at any given instant, removing a small section of bone in procedures such as laminectomies.

[0004] Owing to the delicate nature of the surgical

procedures that ultrasonic tools are used to perform, it should be appreciated that the tips of these tools are

relatively small in size. It is not uncommon for the head of the tip to have a length of 20 mm or less and a diameter of 5 mm or less. A head may be have three or more teeth. Each tooth may have a base to peak height of 3 mm or less and a cross width of 5 mm or less.

[0005] Generally, ultrasonic tools work reasonably well for the purposes for which these tools are designed. Sometimes though, the application of the teeth to hard tissue can result in appreciable wear of the teeth. This wear naturally reduces the ability of the teeth to shear away, remove, the tissue the teeth are employed to remove. In some procedures, such as laminectomies, the tip is required to, over the course of the procedure, remove significant amount of tissue. Over time, the wear of the teeth results in appreciable loss in the ability of the tip to perform the intended tissue removal.

This may require the surgeon to interrupt the procedure to substitute the tip with the worn teeth with a new tip the teeth of which are not worn. Having to so interrupt a

procedure to replace a tip increases the time it takes to perform the procedure. Increasing the length of time it takes to perform a surgical procedure runs contrary to one of the accepted best techniques of modern surgical practice. A procedure should be performed as quickly as possible to minimize the time the patient is exposed to anesthesia. A second reason to perform a procedure as quickly as possibility is to minimize the time to which the patient's normally concealed internal tissue is exposed to the ambient environment and the infection-causing agents inherently in this environment.

[0006] In theory, it should be possible to coat the head and teeth of an ultrasonic tip with a layer of material such as diamond like carbon. This would increase the hardness of the teeth. By extension, this would reduce the rate at which the teeth wear in comparison to uncoated teeth. One

disadvantage of providing a tip with type of coating is the presence of the coating would cause the resonant frequency of the tip to move away from the resonant frequency of the drivers internal to the handpiece to which the tip is

attached. The resonant frequency is the frequency at which, when the drive signal is at given voltage or current, the application of the drive signal at that frequency induces vibrations in the tip that are at a relatively large amplitude in comparison to the application of the same voltage or current at a frequency that is off resonance. Ideally, a tip should have a resonant frequency that, as closely as possible, matches the resonant frequency of the drivers. As the

resonant frequency of the tip moves away from the resonant frequency of the drivers, the ability of the tip transfer the mechanical energy of the drivers to the teeth is reduced.

This reduces the efficiency of the removal of the tissue by the tip.

[0007] There is another reason why adding a coating to the head of an ultrasonic tip may not be the optimal means of increasing the hardness of the tip's teeth. The vibrating of the tip may result in the tip and coating vibrating at

different frequencies. This can result the material forming the coating delaminating off of the tip. These delaminated bits of tip, owing to gravity, can fall into the open surgical site at which the procedure is being performed. Clearly, an undesired result of any surgical process is the introduction of unwanted material into the body of the patient.

Summary Of The Invention

[0008] This invention is related to the structure of a surgical ultrasonic cutting accessory with at least one cutting edge. More particularly the cutting accessory of this invention is formed so that the surfaces of the accessory that meet to form the at least one cutting edge are case hardened. This case hardening reduces the wear of the surfaces forming the at least one cutting edge of the cutting accessory without adversely affecting the ultrasonic and acoustical properties of the accessory. One such cutting accessory of this

invention is a surgical ultrasonic tip with teeth that are case hardened. This case hardened layer reduces the wear of the teeth. This invention is also directed to a method of manufacturing this type of ultrasonic cutting accessory.

[0009] A tip of this invention includes an elongated stem and a head that is located at the distal end of the stem.

Teeth project outwardly from the stem. The teeth are shaped to scrape away, remove, the tissue to which the teeth, when vibrated are applied. A further feature of this invention is that material that hardens the tip is diffused into the outer layer of the teeth. In some versions of the invention the material is diffused into a distal portion of the neck of the tip and the tip head. Since the teeth are part of the tip head it is understood that the hardening material is diffused into the teeth. In more preferred versions of the invention, the hardening material is diffused into only the head. In the most preferred versions of the invention, the hardening material is only diffused into the teeth. The resultant hardened layer is sometimes referred to as a case hardened layer . [00010] In some preferred versions of this invention, the tip is manufactured from a titanium alloy. Also, in some preferred versions of the invention the material that is diffused into the outer layer of the teeth is nitrogen.

[00011] In one method of assembling a tip of this invention, the tip is machined to form the head, including the teeth. The machined tip is placed in chamber in which a significant percentage of the ambient gas is a gaseous form of the

hardening agent. Only the portion of the tip that is to be hardened is subjected to a targeted heating process. This heating is performed to cause the sections of the tip into which the hardening agent is to be diffused to rise to a temperature at which the gaseous state hardening agent will diffuse into the outer layer of the section of the tip to be hardened. In some of these versions of the invention, a laser is directed to the teeth. The photonic energy, (the light) of the laser beam heats the teeth to a temperature at which the hardening agent will diffuse into the outer layer of the teeth .

[00012] In an alternative version of the invention, after the tip is machined, a mask is disposed over the sections of the tip that are not to be hardened. Once the tip is so masked, the tip is placed in a chamber in which a significant percentage of the ambient gas is a gaseous form of the

hardening agent. The chamber is then heated so the tip rises to a temperature at which the hardening agent will diffuse into the outer layer of the tip. More particularly, as a result of this heating of the tip, the hardening agent

diffuses into the unmasked portions of the tip. These

unmasked sections of the tip are the sections of the tip into which it is intended the hardening agent be present.

[00013] In a third method of manufacture of this invention, the tip is formed by a laser cutting process. In this type of processes a focused beam of light, a laser beam, is applied to the workpiece from which the tip is to be formed. At a minimum, the laser beam is used to shape the teeth.

Simultaneously with the application of the laser beam an assist gas is directed towards the workpiece. The assist gas is applied to the workpiece along a vector that is close to if not overlaps the vector along which the laser beam is applied. The assist gas blows the metal that is turned into the molten state by the laser beam away from the workpiece. A

substantial fraction of the assist gas is a gaseous state form of the hardening agent.

[00014] Thus, in this method of manufacture of this

invention, the application of the assist gas to the workpiece performs two functions. The gas removes the cut molten state metal away from the workpiece to facilitate the shaping of the workpiece into the tip. During this process, the assist gas flows over the heated skin of the workpiece as the workpiece is shaped into the tip. Given that this section of the tip is heated, the fraction of the hardening agent in the assist gas stream will diffuse into the tip. Thus, the assist gas serves as the media that applies the hardening agent to the tip so as to foster the diffusion of the hardening agent into the tip.

BRIEF DESCRIPTION OF THE DRAWINGS

[00015] The invention is pointed out with particularity in the claims. The above and further features and benefits of this invention are understood from the following Detailed Description taken in conjunction with the following drawings in which:

[00016] Figure 1 depicts the basic components of an

ultrasonic surgical tool system that includes the tip of this invention; [00017] Figure 2 is a diagrammatic depiction of the components of the handpiece, including the tip, of the system of Figure 1 ;

[00018] Figure 3 is a perspective view of a tip of this invention;

[00019] Figure 4 is a top plan view of the tip;

[00020] Figure 5 is an enlarged top plan view of the head of the tip;

[00021] Figure 6 is a cross sectional view taken along line 6-6 in Figure 5 of the head of the tip and the adjacent distal portion of the stem of the tip;

[00022] Figure 7 depicts a first method of fabricating a tip of this invention;

[00023] Figure 8 depicts a second method of fabricating a tip of this invention; and

[00024] Figure 9 depicts a third method of fabricating a tip of this invention.

DETAILED DESCRIPTION

[00025] Figures 1 and 2 depict a powered surgical tool system 30 that includes an ultrasonic tip 70 of this

invention. System 30 includes a handpiece 50, sometimes called an ultrasonic surgical tool or an ultrasonic aspirator. Handpiece 50 includes a body or shell 52 that forms the proximal end of the handpiece. ("Proximal" is understood to mean towards the practitioner holding the handpiece, away from the site to which the handpiece is applied. "Distal" is understood to mean away from the practitioner, towards the site to which the handpiece is applied.) The body 52 is the portion of the handpiece 50 that is actually held by the medical practitioner. Tip 70 extends distally forward of the handpiece 50. [00026] One or more vibrating piezoelectric drivers 54 (four shown) are disposed inside shell 52. In Figure 2 the handpiece shell 52 is not seen so the internal components of the

handpiece 50 are exposed. Each driver 54 is formed from material that, when an AC voltage is applied to the driver, undergoes a momentary expansion or contraction. These

expansions/contractions are on the longitudinal axis of a driver 54, the axis that extends between the proximally and distally directed faces of the driver. A pair of leads 58, only two leads seen in Figure 2, extend away from each

driver 54. The leads 58 are attached to the opposed

proximally and distally directed faces of the drivers 54.

Many, but not all handpieces 50, include piezoelectric

drivers 54 that are disc shaped. These drivers 54 are

arranged end to end in a stack. Leads 58 are the components of system 40 which the voltage, in the form of a drive signal, is applied to the drivers 54. In Figure 2, drivers 54 are shown spaced apart from each other. This is for ease of illustrating the components. In practice, drivers 54 tightly abut .

[00027] The drivers 54 are understood to convert the

electrical energy applied to the drivers to mechanical power. Accordingly, drivers 54 collectively function as the

(mechanical) power generator of the system 30.

[00028] A post 60 extends longitudinally through drivers 54. The post 60 extends through the drivers 54 along the collinear longitudinal axes of the drivers. Not seen are through bores internal to the drivers 54 through which post 60 extends.

Post 60 projects outwardly of both the most proximally located driver 54 and the most distally located driver 54.

[00029] A proximal end mass 51 is located adjacent the proximally directed face of the most proximally located driver 54. The exposed proximal end section of the post 60 is fixedly attached to mass 51. If post 60 is threaded, then mass 51 may be a nut.

[00030] A horn 62 extends forward from the distally directed face of the most distally located driver 54. While not shown, an insulating disc may be between the distal driver 54 and horn 62. Horn 62 has a proximal end base with a diameter approximately equal to the diameter of the drivers 54.

Extending distally forward from the drivers 54, the diameter of the horn 62 decreases. The exposed distal end section of post 60 is affixed to the horn 62. If the post 60 is

threaded, the horn base may be formed with a threaded bore

(not identified) for receiving the post. Handpiece 50 is constructed so that the stack of drivers 54 is compressed between proximal end mass 51 and horn 62.

[00031] A sleeve 66 is typically disposed over the proximal portions of the tip 70. Sleeve 66 typically extends from a location near where the tip 70 is attached to the handpiece 50 to a location approximately 0.5 cm proximal to the most distal head 86 of the tip 70. Collectively, the handpiece 50, sleeve 66 and tip 70 are constructed so that the sleeve defines a fluid flow conduit that extends between the outer surface of the tip and the surrounding inner surface of the sleeve. The sleeve 66 has a fitting 68 adjacent the proximal end of the sleeve that extends to this conduit. The conduit is open at the distal end of the sleeve 66. When the

handpiece 50 is in use, irrigating solution is flowed from the sleeve fitting 68, down the sleeve and discharged adjacent the tip head 86. In some versions of the system, the fluid serves as a medium through which the mechanical vibrations of the tip head are transferred to the tissue. This irrigating solution also functions as a heat sink for the thermal energy developed by the tip head 86 as a consequence of the vibration of the head . [00032] Handpiece post 60, horn 62 and tip 70 are often formed with conduits. Not seen are the conduits internal to the post 60 and horn 62. These conduits collectively define a fluid flow path from the tip head 86 to the proximal end of the handpiece 50. When handpiece 50 is in operation, suction is drawn through these conduits. The suction draws the irrigating fluid discharged through the sleeve 66 away from the site to which the tip is applied. Entrained in this irrigating fluid are debris generated as a result of the actuation of the tip 70. The suction also draws the tissue towards the tip head 86. The shortening of the distance between the tip head and the tissue improves the transmission of the mechanical vibrations from the tip head to the tissue that is to be subjected to removal.

[00033] A handpiece 50 of system 30 able to draw suction is sometimes referred to as an aspirator or an ultrasonic

aspirator .

[00034] From Figure 1 it can be seen that system 30 includes a console 40. Internal to the console 40 are components that output an AC drive signal that is applied to the handpiece drivers 54. In some versions of the invention this drive signal is between 10 kHz and 100 kHz. Often this drive signal is between 20 kHz and 50 kHz. The structure of the console 40 is not relevant to this particular invention. Footswitch 42 represents the component actuated by the surgeon to both actuate the console and set the characteristics of the drive signal. Further understanding of the structure of the console can be obtained from WO 2015/021216 Al/US Pat. Pub. No. US Pat. Pub. No. 2017/0071621 Al, PCT App . No. PCT/US2016/ 031651 the contents of which are contained in WO 2016/183084 Al/US

Pat. Pub. No. and US Prov. Pat. App.

No. 62/343,433, the contents of which are contained in PCT Pub. No. /US Pat. Pub. No. , each of which is explicitly incorporated herein by reference.

[00035] Control console 40 sources drive signals over a cable 48 to which handpiece 50 is connected. It is common, but not required, to assemble cable 48 and handpiece 50 as a single unit.

[00036] Tip 70 of this invention, as seen in Figures 3 and 4, is a single piece unit. The tip 70 is formed out of titanium or an alloy of titanium. One titanium alloy from which the tip 70 can be formed in Ti-6A1-4V.

Titanium Ti-6A1-4V is an alloy of titanium that by weight is approximately 6% aluminum, approximately 4% vanadium, the remainder substantially titanium. The tip 70 is formed to have a number of different sections. At the most proximal end tip 70 has a base 74. Base 74 is cylindrical in shape. In many versions of the invention, the proximal end of the base 74, which is the proximal end of the tip 70, is formed with features that facilitate the releasable coupling of the tip 70 to the horn 62. In Figure 4 a closed end bore 72 is shown extending distally from the proximal end of the base partially through the base. Bore 72 represents that the base 74 is typically formed with features to tightly

releasably mechanically couple the tip 70 to the horn 62. For example, the horn 62 may have a threaded boss. The inner surface of the tip that defines bore 72 may be formed with threading that engages the threading of the boss. The actual tip components that facilitate the releasable coupling of the tip 70 to the horn 62 are not part of the present invention.

[00037] Extending forward from the base 74 tip 70 has a torso 76. The torso 76 is cylindrical in shape and has a diameter less than that of the base 74. Not identified is the tapered transition section between the base 74 and the

torso 76. The illustrated torso 76 is formed with helical slots 78. Owing to the presence of slots 78, when the horn 62 vibrates the tip 70 longitudinally, that is proximally to distally along the longitudinal axis of the tip, the sections of the tip distal to the slots also engage in vibrations that are torsional. Torsional vibrations are understood to be vibrations around the longitudinal axis that extends between the opposed proximal and distal ends of the tip 70.

[00038] Forward of the torso 76, tip 70 has two transition sections 80 and 82. Transition section 80 is the section immediately distal to the torso 76. Transition section 82 extends forward from transition section 80. Both transition sections are tapered. The diameter of each section 80 and 82 decreases as the section extends distally forward. The taper of section 82 is steeper than the taper of section 80. Tip 70 has a stem 84 that extends forward from transition section 82. Stem 84 has a shallow taper. The taper of stem 84 is less than the taper of transition section 82. Tip 70 is formed so the stem subtends a length that is approximately 25% to 50% of the total length of the tip.

[00039] The head 86, located at the distal end of stem 84, is the most distal section of the tip 70. In the depicted version of the invention, one side of the head projects laterally outwardly from the adjacent distal section of the stem 84. This section of the head 86 is formed with teeth 88. Teeth 88 project laterally outwardly from the head 86. The teeth 88 thus project outwardly from the longitudinal axis of the tip 70. While not identified, in the illustrated version of the invention, each tooth is generally in the form of a four-sided pyramid. The edges where two sides of tooth meet form a cutting edge of the tooth. The point from which the sides of a tooth extend outwardly is the cutting point of a tooth . [00040] In Figure 6 a bore 92 can be seen extending proximally from the distally directed face of head 86.

Bore 92 extends distally through head 86 and stem 84. While not seen it should be understood that bore 92 opens up into the closed end of bore 72. Bore 92 is the conduit through which suction is drawn through the tip 70.

[00041] While tip 70 is formed from a single piece of metal, a hardening agent is embedded in at least the outer portion of the teeth 88. In Figure 6, core 96 represents the portion of the head 86, including the teeth 88, in which the hardening agent is not present. Layer 94 the outer layer of teeth in which the hardening agent is present. Layer 94 is sometimes called the case hardened layer. One such hardening agent that can be embedded in the teeth is nitrogen. In some versions of the invention case hardened layer 94 extends at least 1 micron into the tip from the outer surface of the teeth. Often the case hardened layer 94 extends at least 3 microns into the tip from the outer surface of the teeth. In most versions of the invention case hardened layer should not extend more than 50 microns into the tip from the outer surface of the teeth.

[00042] The ultrasonic handpiece 50 of this invention is used by positioning head 86 integral with the tip 70 in close proximity to the tissue to removed. The handpiece 50 is actuated by sourcing a drive signal from the console 40 to the drivers 54. The resultant cyclic expansions/contractions of the driver 54 results in the vibration of the tip and more particularly, the tip head 86 and teeth 88. The tip head is positioned so the teeth 88 bear against the tissue to be cut.

The back and forth movement of the teeth 88 against the tissue results in the shearing away of, the removal of, the tissue.

[00043] The presence of hardened layer 94 of the teeth 88 means that the teeth, when they shear against the tissue to be removed are less prone to wear than the teeth of an identical tip that does not include the hardened layer. Consequently, in comparison to a conventional tip, a tip without the

hardened layer being present, there is less likelihood that, during a procedure, tip 70 will wear to the level at which there will be an appreciable decrease in the ability of the tip 70 to remove tissue. This results in a like reduction in the likelihood that, during a procedure, teeth 88 of tip 70 will become so worn that, to timely perform the procedure, it will be necessary to interrupt the cutting process to provide a new tip with sharp teeth.

[ 00044 ] A further feature of tip 70 of this invention, is that the case hardened layer does not extend over the whole of the tip. To understand the limit of the extent to which a tip is provided with a hardened layer it should be understood that a tip has a fundamental vibrational mode. Many tips are designed to vibrate longitudinally. This means the tip is vibrated the head oscillates along a proximal to distal path that extends along a line coincident with the proximal to distal longitudinal axis through the tip. Other tips are designed to engage in torsional vibrations. When a tip vibrates torisionally, the head of the tip rotates around an axis close to if not centered on the longitudinal axis through the tip. Still other tips are designed to undergo flexural vibration. When a tip engages in flexural vibrations, the stem 84 bends relative to the linear extension of the

longitudinal axis through the base 74 of the tip 70. This means that when the tip head 86 moves back and forth, to the left and the right, of the linear extension of the

longitudinal axis through the base 74 of the tip 70. Some tips are designed to, when excited into vibrational movement, engage in vibrations that are combination of two or more or all three of the different types of vibrations: longitudinal; torsional and flexural. [00045] Regardless of the type of vibrations the tip 70 is designed to undergo, there is a fundamental vibration mode associated with the tip. This mode is characterized by a resonant frequency. Each tip also has a characteristic wavelength. The length of this wavelength is the quotient calculated by dividing the speed of sound by the

characteristic resonant frequency of the fundamental vibration mode. This characteristic resonant frequency is sometime referred to as the natural frequency of the vibration mode of interest .

[00046] For the purposes of this invention, the

"characteristic resonant frequency" is understood to be the resonant frequency of the tip, when vibrated, at the ambient environment and the tip is not subjected to mechanical

loading. This characteristic resonant frequency is typically a function of the following characteristics of the tip:

material; shape; and dimensions. Based on these variables, mathematical processes such as finite element analysis can be used to determine this frequency. Post manufacture, it is possible to determine the characteristic resonant frequency of a tip by vibrating the tip at a number of frequencies centered on what is to believe the characteristic resonant frequency of the tip. The frequency at which the vibrations are of

greatest magnitude may be considered the characteristic resonant frequency of the tip. The finite element analysis and the empirical of vibrating the teeth may be combined to determine the characteristic resonant frequency of the tip 70.

[00047] It is believed that the case hardened layer 94 should be formed over the all the teeth 88 and extend

proximally a distance from the proximal most tooth 88 that is a maximum of one-eighth of the length of the characteristic wavelength. Thus, in most versions of the invention, the case hardened layer 94, at the most, extends over the whole of the head 86 and an adjacent distal section of the tip stem 84. In still other versions of the invention, the case hardened layer 94 only extends over the head 86 of the tip. In still more preferred versions of the invention, only the teeth 88 include the case hardened layer 94.

[00048] It should be understood that the distal end head 86 of a tip 70 is, in terms the vibratory movement of the tip, the anti-node. (For the purposes of defining a point location for the antinode, the proximal most tooth 88 is considered the point on the head 86 where this anti-node exists.) This means that while the head 86 itself engages in vibratory movement relative to a reference point in space, the atomic material forming the head and teeth 88 does not itself engage in inter atomic vibratory movement (vibratory movement between adjacent atoms) . The movement of the of the tip head 86 and teeth 88 is due to the inter atomic vibratory movement that occurs proximal to the head. This movement is at a maximum at the vibratory node and decreases distally from this node. This node is located a distance of one-quarter of the

characteristic wavelength proximal to the anti-node. Thus it should be appreciated that the wave of the characteristic wavelength is a wave of the extent to which individual

sections of the tip extending distally to proximally along the tip, engage in different magnitudes of inter-atomic vibratory motion .

[00049] The hardened layer 94 and the underlying layer of the tip naturally have different degrees of stiffness. If both layers simultaneously expand/contract, twist and/or bend, owing to these layer having different stiffness, the inherent tendency would be for the outer hardened layer to, over time, separate from the underlying layer.

[00050] If this separation occurs over an opening into the patient, there is possibility that the cracked off portions of the hardened layer could fall against the internal tissue of the patient. To avoid infection and irritation of the tissue, this is a result of the tip that practitioners naturally want to avoid.

[00051] However as described above, the node of maximum inter atomic vibration is located a distance proximal to the teeth that is a distance of one-quarter the characteristic wavelength of the tip 70 from a location proximal to the head 86. The hardened layer 94 typically only extends a distance of one-eighth the characteristic wavelength proximal to the head 86. This means that the hardened layer 94 is spaced a distance of at least one-eighth the length of the characteristic wavelength from where the maximum inter atomic vibrations are occurring.

[00052] Hardened layer 94 is thus spaced distally away from where molecules forming tip 70 are subjected to their greatest inter molecular, vibration-induced stress. The

expansion/contraction, twisting or bending of adjacent

molecules that occurs at and near the vibratory node only nominally, if at all, occurs where the hardened layer 94 is embedded into the tip. Consequently, the vibratory movement necessary to induce the desired vibrations of the tip head 86 does not result in stress between the atomic material forming the hardening agent and the atomic material into which the hardening agent is embedded. Tip 70 of this invention is therefore designed so that the likelihood that the material forming the case hardened layer 94 will be subjected to vibratory stress is substantially eliminated. The substantial elimination of this stress results in a like substantial elimination that this stress can cause the material forming the case hardened layer 94 to separate from the rest of the tip 70. [00053] One means to manufacture a tip 70 of this invention is now described by reference to Figure 7. In this method of manufacture, the tip 70 is initially completely shaped. This means, by grinding, machining or coining or three-dimensional printing the whole of the tip 70, including base 74,

intermediate sections 76 and 80, slots 78, stem 84, head 86 and teeth 88, are formed. For the purposes of this operating, base 74, intermediate sections 76 and 80 and stem 84 are collectively considered the shaft 71 of the tip. Once the tip 70 is fully shaped, the tip is placed in a chamber 110. The environment in the chamber is set so the gas in the chamber includes an appreciable fraction of the gaseous state hardening agent. In the depicted invention, dots 112

represent the gaseous state hardening agent. If Nitrogen is employed as the hardening agent the chamber 110 is

substantially filled with N2 gas and the purity of the gas is typically at least 97% if not 99% or greater. The pressure within the chamber is typically a minimum of 1 Atmosphere and may be as high as 4 Atmospheres.

[00054] Once the environment in chamber 110 is established, a beam of light 118 from a laser 114, is directed to the portions of the tip 70 into which the hardening agent is to embed. The photonic energy of the light beam 118 heats the portions of the tip against which the light beam is applied.

More specifically, these portions of the tip are heated to a temperature at which the gaseous state hardening agent will diffuse across the outer surface of the heated section of the tip and into the layer of the tip below this surface. When the tip is formed from Ti-Al-4V, the surface of the tip is often heated to a temperature of between 700 and 1700°C. More specifically, the hardening agent diffuses into the lattice of the metal forming the tip. This heating is often between 30 seconds and 3 minutes for each portion of the tip into which the hardening agent is to be embedded. When the heating is of this short duration the heating does not result in the

liquefaction of the metal forming the tip to the extent to which the shape of the tip will be deformed. This heating does, however, cause the vibrational range of the atoms forming the teeth to increase. This increase in range of vibrational movement of the atoms causes the atoms to move a sufficient distance so the hardening agent diffuses through the surface of the tip. The diffusion of the hardening agent into the teeth result in the formation of the case hardened layer 94.

[00055] It should be understood that by varying the length of time the section of the tip is heated, the depth to which the nitrogen embeds in the tip to form the case hardened layer 94 can be controlled. The longer the section of the tip is heated, the deeper the hardening agent will embed into the tip .

[00056] A second method of manufacture of this invention is understood by reference to Figure 8. In this method of manufacture, as in the first method of manufacture, the tip, including the sections of the tip to which the hardened layer is to be added, is fully shaped. A mask 122 is disposed over the sections of the tip to which a hardened layer is not be formed. In Figure 8, the mask 122, depicted as stippling, is disposed over the sections of the tip into which the hardening agent is not be diffused. If nitrogen is employed as the hardening agent, the mask may be masking paint.

[00057] Once mask 122 is disposed over the tip 70, the tip is placed in a chamber 124. The environment of chamber 124 is set so as to be rich in a gaseous state form of the hardening agent. In Figure 8 dots 112 represent the gaseous form of the hardening agent. The chamber 124 is then heated to a

temperature at which the hardening agent will diffuse into the unmasked portions of the tip. Coil 126 internal to the chamber 124 represents the components that heat the inside of the chamber.

[00058] As a result of the heating of the tip 70, the atoms forming the tip expand apart a sufficient distance apart from each other so that the hardening agent is able to diffuse across the outer surface of the tip. More particularly, the hardening agent diffuses across the unmasked sections of the tip. The hardening agent that diffuses into the tip hardening agent thus forms the case hardened layer 94 of the tip on the sections of the tip at which such layer is wanted.

[00059] Figure 9, discloses a third method of manufacturing a tip 70 of this invention. In this version of the invention the tip is initially first only partially shaped. More particularly, the section of the tip into which the hardened layer is not to be embedded are shaped.

[00060] Once the tip is partially shaped, a laser 132 is used to shape the portions of the tip into which the hardened layer is to be formed. In this process, a beam of light

(photonic energy), represented by solid line 134, is directed to the sections of the tip to be shaped. The energy of the energy of the beam is absorbed by and heats the partially assembled tip. The heating of the tip results in the surface of the tip reaching a molten state.

[00061] Simultaneously with the light being applied to the tip 70 a jet of assist gas is applied to the tip. The assist gas is applied from a nozzle 138so as to flow over the section of the tip being heated to a molten state. In Figure 9 two nozzles 138 are shown. Dashed lines 140 represent the flow of assist gas from the nozzles 138. In this invention, the assist gas is composed at least in part of a gaseous form of the hardening agent . [00062] The jet of assist gas, upon striking the tip 70, performs two functions. First the jet of assist gas blows the molten state material away from the rest of the tip. The removal of this material within microseconds of being formed facilitates the shaping of the tip. The second function the assist gas performs is due to the fact that the assist gas is at least partially composed of the gaseous state form of the hardening agent. Accordingly, given that the remaining portion of the tip is in a heated state, a fraction of the hardening agent forming the jet of assist gas will diffuse across the surface of the tip.

[00063] Thus the application of the jet of assist gas results during the application of a laser beam to shape the tip results in the simultaneous shaping of the tip and the diffusion of the hardening agent into the tip.

[00064] The above is specific versions of this invention. Alternative versions of this invention may be possible. For example, the materials from which both the tip and hardening agent are formed may be different from what has been

described. In alternative versions of the invention, the tip may be formed material other than Titanium based materials. Generally the tip is formed metal. Metals from which the tip may be formed include iron-based alloys and aluminum based alloys. In alternative versions of the invention, carbon or boron may be employed as the hardening agent.

[00065] Methods other than described methods may be employed to form the case hardened layer of the tip. For example, an induction coil may be used to heat the tip during the process of embedding the hardening agent in the tip. In Figure 9, the paths along which the laser beam 134 and streams 140 of assist gas are applied to the tip are shown as being angled relative to each other. In some versions of the invention these paths may be coaxial. In some embodiments of this version of the invention the laser beam and assist gas are applied in the same direction to the tip. In other versions of the invention the laser beam and the assist gas may be applied from oppose locations relative to the tip.

[00066] Further this invention may be used to form hardened layers of surgical cutting accessories other than the teeth of ultrasonic tips. Other surgical cutting accessories that can be provided with hardened layers according to this invention include saw blades, burs, drills and rasps. The invention may be used to form case hardened layer on the features of other ultrasonic cutting accessories that have cutting edges. For example, this invention may be employed to form case hardened layers on the adjacent surfaces of an ultrasonic scalpel that meet to form the cutting edge of the scalpel.

[00067] It should thus be appreciated that other ultrasonic cutting accessories of this invention may have different shapes. For example, not all ultrasonic tips may have shafts that have linear longitudinal axes. A tip of this invention may have a shaft with proximal and distal sections that are angled relative to each other. The proximal section extends outwardly from the handpiece 50 along a first longitudinal axis. The distal end of the shaft, the end from which teeth extend is centered on a second longitudinal axis. This second longitudinal axis is angled relative to the first longitudinal axis. Between the proximal and distal sections, the shaft has an intermediate section. The intermediate section connects the proximal and distal sections and is curved or bent. Thus, the intermediate section has a curved or bent longitudinal axis .

[00068] Not all ultrasonic tips of this invention may have features that convert a fraction of the longitudinal

vibrations into torsional vibrations. Some ultrasonic tips of this invention may have features that facilitate the flexural vibration of the tip head. This flexural vibration is

understood to be a bending of the shaft so that the tip head moves in arc towards and away from a line that would be an extension of the longitudinal axis of the base of the tip.

[00069] Similarly, it should be appreciated that not all cutting accessories fabricated according to this invention may be single piece units. For example, an ultrasonic tip that is relatively long in length, 15 cm or more in length, may be a two piece assembly. The base 74 and first intermediate section 76 may form a first piece. The second intermediate section 80, stem 84 and form a second piece. These two pieces are after being individually manufactured are threaded

together. This version of the invention only the distal end piece, the piece with the surfaces forming the cutting edges that are to be case hardened are subjected to the case

hardening process.

[00070] Likewise, while not typical, some tips of this invention may be formed with a single tooth.

[00071] Likewise, it should be understood that when

manufacturing tips of this invention, it will typically not be necessary to, for each tip, determine the characteristic resonant frequency in order to then determine the

characteristic wavelength. Typically, once a tip is designed, mathematical processes and/or the empirical analysis (the frequency sweep process) are used to determine the

characteristic resonant frequency for the tip. This

characteristic resonant frequency is assigned to as the characteristic resonant frequency for tips having the same shape and dimensions and formed from the same material as this tip. In practice, between any two supposedly identical tips, owing to manufacturing tolerances, there may be minor

variations in the characteristic resonant frequencies of the tips and, by extension, their characteristic wavelengths. These variations do not typically adversely affect the

processes used to determine the extent to which the hardening agent should be embedded along the length of the tip.

[00072] Variations in the process of manufacturing a

surgical instrument according this invention are also

possible. For example, while it is preferably that the tip be completely shaped before the hardening agent is diffused into the distal end of the tip, this is not always required. There may be manufacturing reasons to first only form the head 86, at least one tooth 88 and a small adjacent portion of the shaft. Then, the hardening agent is diffused into the portion of the tip in which the hardening layer is be formed. After these steps are completed, the rest of the stem 84 of the tip is formed.

[00073] Also, while targeting heating of the tip or the workpiece from which the tip is formed is typically performed with a laser, it may not be needed to use a laser in method of targeted heating performed to fabricate a tip according to this invention. For example, in some versions of the invention an induction coil may be used to perform the targeted heating of a portion of the tip according to this invention. Thus, induction heating may be used for a short period of time to simultaneously heat plural surfaces of one or more teeth to facilitate the diffusion of the hardening agent into these plural surfaces.

[00074] It should be likewise understood that this invention may be employed to case hardened layers of articles other than the cutting accessories of power surgical tools. Thus, this invention may be used to harden the teeth of a saw blade used to cut objects such as wood, plastic metal or concrete.

[00075] Accordingly, it is an object of the appended claims to cover all such variations and modifications that come within the true spirit and scope of this invention.