Abstract:
An endodontic instrument eliminates the need for conventional flutes by employing a tapered tip having an axially extending relief surface such as a flat permitting the passage of liquid and the ejection of debris from the tooth. In one embodiment, an abrasive surface of the tapered tip is produced by electrical discharge machining which provides randomly arrayed microscopic pits directly in the metallic surface of the instrument.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application 61/231,155 filed Aug. 4, 2009 hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to the field of endodontics and, in particular, to improved endodontic instruments for operating within the tooth root, dental pulp and surrounding area. 
         [0003]    The dental pulp is made up of vascular and neural tissue found within a tooth. It is surrounded by the hard mineralized tissue of dentin, cementum, and enamel. The root canal is the pulp-filled channel within the hard tissue in the tooth&#39;s root structure. In the event that the pulp tissue becomes inflamed or infected, the treatment is to remove the pulp using fine instruments, known as endodontic files, capable of getting into narrow canals. These files are typically made of surgical metals, such as stainless steel, and more recently nickel titanium, and can be used by hand in a reciprocal motion or in an electric rotary handpiece device. 
         [0004]    The current metal rotary endodontic files on the market are manufactured in various tip sizes and tapers that allow the instrument to remove pulp and enlarge the canal walls. The canals narrow and curve as they extend down through the tooth&#39;s root. As such, to reach the end of a root canal system where it is the narrowest, very small shank diameter files are used to manipulate through the curved path of the canal while removing pulp and enlarging the canal walls. 
         [0005]    The current endodontic file cuts by the flutes engaging into the soft tissue of the pulp and the hard tissue of the canal wall. Advancements in the construction of endodontic files have given rise to many different designs of these flutes. The material composition of rotary endodontic files has improved as well, such as the use of nickel titanium, which allows the file to flex through the canal bends and thereby improve the ability to remove pulp tissue while enlarging the canal in the smaller regions with a tooth&#39;s root. 
         [0006]    One of the major drawbacks with the current nickel titanium rotary endodontic instruments is the nickel titanium has a propensity to break in the root canal while in use. It has been documented in the endodontic literature that the reason for this breakage is there are two main forces that are placed on a file during usage: cyclic fatigue and torsional stress. Cyclic fatigue is the breakage of the file due to continuous use while it is freely rotating in the canal. Torsional stress occurs when a file binds within the canal due to the engaging of the flutes in the soft or hard tissue of the canal while the instrument continues to rotate. 
         [0007]    Nickel-titanium rotary endodontic files are manufactured by machining the flute design into the metal cylindrical blank. These nickel titanium blanks inherently have imperfections in the metal that are further weakened by the machining of the flutes. When these files are then placed under clinical usage it is not uncommon for a file to break when performing endodontic treatment on a patient. 
         [0008]    Replacement of the file delays the procedure and can be costly. Moreover, when this happens it is possible for the broken end of the file to become lodged within the canal. This can affect the long-term prognosis of the endodontic treatment because the lodged file can block the remaining portion of the canal and prevent the inflamed or infected pulp tissue from being removed. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides an endodontic instrument that may replace conventional nickel titanium devices to provide reduced risk of breaking through the use of a robust tapered shaft without helical machined flutes. A relief surface, for example a flat running down at least a portion of the taper, provides a passageway for the exchange of fluid in the removal of debris from the tooth channel during cutting. In one embodiment, the cutting surface on the taper is formed from microscopic pits produced, for example, with an electric discharge machining (EDM). 
         [0010]    Specifically, in one embodiment, the invention provides an endodontic instrument for use with a powered hand-piece. The instrument includes a shaft extending along an axis and having a first end adapted to engage a receiving chuck of a hand piece. A second end of the shaft tapers inward toward the axis in a direction from the first end to the second end and a portion of the taper near the second end provides a first periphery substantially following a circumference about the axis and presenting an outwardly exposed cutting surface, and a second periphery provides a recessed clearance surface beneath the circumference extending in a line along the axis. 
         [0011]    It is thus a feature of at least one embodiment of the invention to provide for a robust endodontic instrument that may replace the helically fluted nickel titanium design which may be prone to breakage. 
         [0012]    The tip of the second end may be substantially smooth and, in addition or alternatively, may have a rounded end. 
         [0013]    It is thus a feature of at least one embodiment of the invention to reduce the cutting action at the tip of the instrument so as to promote a following of the tool along the existing tooth canal structure. 
         [0014]    The cutting surface may be provided by a diamond abrasive coating. 
         [0015]    It is thus a feature of at least one embodiment of the invention to providing a cutting surface that does not require the formation of possibly weakening flutes and that may work with a variety of different shaft materials. 
         [0016]    Alternatively the cutting surface may be provided by a series of randomly placed microscopic pits. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide an improved cutting surface for endodontic instruments. 
         [0018]    The first end of the shaft may be over-molded thermoplastic on a metallic core forming a remainder of the shaft. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide an improved handpiece interface eliminating the need for complex machining operations on small shafts. 
         [0020]    The relief surface may be a flat extending along a chord of the circumference. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a simple relief surface that can be quickly formed by a grinding operation or the like. 
         [0022]    The relief surface may be an outwardly concave trough. 
         [0023]    It is thus a feature of at least one embodiment of the invention to provide increased passage for fluid and tooth debris. 
         [0024]    The shaft may be a stainless steel material. 
         [0025]    It is thus a feature of at least one embodiment of the invention to permit the use of a robust shaft material. 
         [0026]    These particular features may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a perspective view of the endodontic instrument of the present invention linked to cross-sections at various positions along its length and showing a handpiece, in phantom, to which it may connect; 
           [0028]      FIG. 2  is a fragmentary detailed view of the tip of the endodontic instrument of  FIG. 1  showing its freedom from cutting surfaces; 
           [0029]      FIG. 3  is a cross-sectional view through the shaft of the endodontic instrument of  FIG. 1  as may be treated by an electrical discharge machining to create a series of surface pits providing a cutting action; 
           [0030]      FIG. 4  is a side elevational view of fixturing for the EDM machine of  FIG. 3  showing extension of the tip of the instrument beyond the EDM tool for limiting the formation of cutting surface in the tip area; 
           [0031]      FIG. 5  is a cross-sectional view through the shaft of the instrument of  FIG. 1  showing alternative relief designs; 
           [0032]      FIG. 6  is a side elevational view of an alternative embodiment of the endodontic instrument having a flexible abrasive whip; and 
           [0033]      FIG. 7  is a cross-sectional view through a tooth during use of the endodontic instrument of  FIG. 6  showing a spiraling action of the whip which provides flutelike ejection of cut material. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Referring now to  FIG. 1 , an endodontic instrument  10  of the present invention may provide a shaft  12  extending along an axis  14  between a first end  16  and a second end  18 . 
         [0035]    A first length  20  of the shaft  12  provides a taper of decreasing diameter as one moves along the shaft  12  toward the second end  18  terminating at a tip  22  having a rounded non-cutting end. The length  20  of the shaft  12  is desirably constructed of a metallic material such as stainless steel, aluminum titanium, or nickel titanium. 
         [0036]    A relief channel  24  extends along a portion of the length  20  near the second end  18  stopping before the tip  22 . The relief channel  24  provides a relief surface permitting the expulsion of cut tooth material from a channel to be formed in a tooth (not shown) by rotation or reciprocation of the instrument  10  about axis  14 . The relief channel  24  may extend generally along but not necessarily parallel to axis  14  and in a preferred embodiment follows the taper of the shaft  12 . 
         [0037]    A periphery of the shaft  12  adjacent to the length of the relief channel  24  but outside of the relief channel  24  may provide a cutting surface  26 , for example, by means of a diamond or other abrasive materials including for example abrasive material coated on that surface or by microscopic pits formed in that surface as will be described. 
         [0038]    A cross-section  28   a  at the tip  22  will generally be circular whereas a cross-section  28   b  at the portion of the length  20  holding the relief channel  24  will be noncircular as a result of the relief channel  24 . A portion of the length  20  beyond the relief channel  24  toward the first end  16  will again have a circular cross-section  28   c  larger than cross-section  28   a  as a result of the taper. 
         [0039]    As one moves along the shaft  12  from the portion of the length  20  toward the first end  16 , the shaft  12  increases in diameter abruptly to provide a handle section  30  that maybe integrally formed with the metal of the shaft  12  at length  20 , for example, by machining the appropriate taper in a cylindrical rod on a lathe or the like. 
         [0040]    An over-molded plastic portion  32  may be positioned at the first end  16  (over a smaller diameter boss machined extending out of the end of the handle section  30 ) to provide key surfaces  34  (for example flats and notches) allowing the first end  16  to be received and retained by a handpiece  36  that provides powered reciprocation rotation or the like. The molded plastic portion  32  may be formed of a thermoplastic including glass fibers or the like to provide torsional resilience to this portion. 
         [0041]    Referring now generally to  FIGS. 2 and 5 , the cross-section  28   a  of the tip  22  may be sized to have a radius curving beneath the relief channel  24  so that it may maintain its circular cross-section and maybe devoid from cutting materials or the effect of a cutting edge of the relief channel  24  so as to help pilot in the instrument  10  along the natural canal of the tooth. The relief channel  24  is preferably along a chord of a circumference  38  taken in cross-section at points along the length  20 . Alternatively the relief channel  24  may be slightly outwardly convex ( 24 ″) or an outwardly concave trough ( 24 ′) in either case to provide a passageway in the generally circular bore that will be formed by the instrument  10  allowing movement of liquid and removed tooth debris during the cutting process. 
         [0042]    In one embodiment, the total length of the endodontic instrument  10  may be approximately 1 inch with the length  20  of the shaft being approximately 0.75 inches and of the length of the tip being approximately 0.040 inches. The handle section  30 , for example, may have a diameter of 0.09 inches. The rounded end of the tip  22  may be, for example, a 45° chamfer or a series of successive chamfers defining a non cutting tip. It is anticipated that the endodontic instrument  10  will be provided in a variety of sizes meeting the ISO standards of 20-04, 20-06, 30-08, 40-10, 50-12 as well as others. 
         [0043]    When the cutting surface is formed by a diamond abrasive  44  or by microscopic pits  42 , the cutting surface is preferably but not necessarily applied only to the circumference  28  outside of the relief channel  24 . Diamond abrasive may, for example, be attached by a nickel-plating process known in the art. Other abrasive materials may also be used including carbon boron nitride, carbide, zirconium, and various ceramics. 
         [0044]    Referring now to  FIG. 3 , when the cutting surface is formed from microscopic pits  42 , these pits may be generated through the use of an electronic discharge machine  50  having one electrode connected to a tool  52  and the other electrode connected to the shaft  12  of the instrument  10 . The tool  52  may have a channel  54  cut therein conforming generally to the taper of the shaft  12  in the vicinity of the relief channel  24 . The EDM machine  50  may be adjusted for high current flows to produce sparks  54  generating the microscopic pits  42  in the outer surface of the shaft  12 . The current may be adjusted to produce pits of the desired size in a particular material, for example stainless steel. As is understood in the art, the tool  52  and shaft  12  may be immersed in a fluid  56 . The tool  52  may be constructed, for example, of graphite or copper material or the like. 
         [0045]    Referring to  FIG. 4 , in one embodiment, the tool  52  may cover approximately half of the circumference of the shaft  12  and may extend only along the length  20  of the shaft  12  for the extent of the relief channel  24  to stop short of the tip  22  and the shaft  12  above the relief channel  24  thereby limiting the formation of the cutting surface to the area of the relief channel  24  (but not within the relief channel  24 ). The shaft  12  may be rotated slightly to provide for the necessary coverage of the periphery of the shaft  12  as supported in a retaining chuck  56 . 
         [0046]    During use, the instrument  10  may be inserted into a tooth for cleaning of the coronal and mid-root portion of the tooth&#39;s root. The combination of the taper which provides a generally conical shaft and a straight relief channel  24  provides sufficient debris removal to prevent locking in the tooth canal during rotation. 
         [0047]    The microscopic pits produced by the EDM machine  50  are generally too small to be resolved by the naked eye but produce a surface that is generally rough looking. Other possible techniques for producing these pits include photo etching processes in which the length  20  is coated with a photo resist selectively removed after photo exposure of areas in which pits should be formed. Dipping in a mild acid then provides for pit formation. Patterned pits, for example, in herringbone patterns or lines or the like may also be possible with this process. In addition it may be possible that to use a bead blasting or sandblasting or other mechanical process to create the necessary microscopic pits or scores providing a required cutting action. 
         [0048]    Referring now to  FIG. 6 , in an alternative embodiment, the instrument  10  may provide a shaft  12  having a metal core  70  over-molded with a polymer  72  to provide similar elements to over-molded plastic portion  32  and key surfaces  34  described above. The polymer  72  may include torsion resistant glass fibers  71  and the metal core  70  may, for example, be stainless steel. The metal core  70  may be exposed at the second end  18  and attached, for example by welding, to an end of a flexible abrasive whip  73 . The flexible abrasive whip  73  may be, for example, a metallic wire (such as stainless steel) coated with an abrasive such as diamond  40 , and is attached to extend back toward first end  16  so that it may lie generally along the shaft  12 . 
         [0049]    Referring now to  FIG. 7 , when this instrument  10  of this embodiment is rotated, for example clockwise, by the handpiece  36  (shown in  FIG. 1 ) in a canal  74  of a tooth  80 , rotation of the shaft  12 , as indicated by arrow  75 , causes the abrasive whip  73  to wrap around the shaft  12  in a helix to create a virtual flute that is able to clean and shape the canal system at the end of a tooth&#39;s root (apical portion) removing debris in the manner of an Archimedean screw pump. 
         [0050]    These instruments contrast with current endodontic files on the market which have flutes that have been machined into the metal blank create the file cut much the way a wood planer is able to remove slivers of wood. The problem remains that these file flutes engage in the hard and soft tissue in the tooth&#39;s root canal and bind, causing file breakage due to torsional stress. The present invention employing a more evenly distributed cutting surface removes tooth material more like using sandpaper to smooth a wood surface. Thus, the instruments do not bind in the soft or hard tissue of the root canal. This lack of binding eliminates breakage from torsional stress. 
         [0051]    The present invention may provide for multiple relief channels  24  for example on opposite sides of the shaft  12 , if additional relief is desired. In addition, in some applications, the tip  22  may be made cutting (as opposed to non-cutting) by extending the cutting surface to the tip  22  or by providing flutes or axial edges or the like at the tip  22 . It will be appreciated that by simple modification of the over-molded plastic portion  32 , present invention may be used as a hand tool without the hand piece  36 . 
         [0052]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0053]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0054]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.