Abstract:
An endodontic file is provided for shaping and/or preparing a root canal. The file may include multiple cutting segments separated by non-cutting segments. The cutting segments are tapered and may have a cutting edge formed by plural helical flutes. Alternatively, the cutting segments may be formed of a substantially non-circular geometric shape with substantially straight cutting edges. The file is flexible and has increased resistance to cyclic fatigue breakage. The file further controls or limits which areas of the root canal are shaped and/or prepared during file use. The file may form part of a series of files to shape and/or prepare a root canal. Each file in the series may have cutting segments and non-cutting segments strategically placed in different regions along the working portion of the file to shape and/or prepare different portions of the root canal.

Description:
[0001]    This invention claims the benefit of co-pending U.S. Provisional Application No. 60/439,479, entitled “ENDODONTIC INSTRUMENT”, filed Jan. 13, 2003, the entire disclosure of which is hereby incorporated by reference as if set forth in its entirety for all purposes. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to endodontic instruments known as endodontic files, used by dentists when performing root canal procedures. A root canal procedure is a common dental procedure for treating or preventing a dental abscess. During a root canal procedure, the infected nerve and pulpal tissue are removed from the root canal of the involved tooth. The root canal is then cleaned by shaping or reaming the root canal with endodontic files to produce a clean environment to receive a root canal filling material. The standard filling material, which has been used for over fifty years, is an inert material called gutta-percha.  
           [0003]    Endodontic files are used to remove the contents of the root canal and to prepare or shape the root canal prior to filling it. Endodontic files may be designed to be manually manipulated by the fingers of a dentist or to be engine driven by a rotating hand piece, which rotates the file during use. Endodontic files typically consist of a tapered distal working portion containing a plurality of helical spiraled flutes, a shaft portion located proximal to the working portion, and a handle located on the proximal end of the instrument. The flutes form planing or cutting surfaces, which dislodge and remove the infected tissue within the root canal being treated. For all currently available tapered endodontic files the helical or spiral flutes turn continuously along the entire working portion of the file.  
           [0004]    [0004]FIGS. 1 and 2 show a prior art endodontic file  10  that is representative of the type currently in use. File  10  includes a handle  12  at a proximal end  14 , a shaft portion  16 , and a working portion  18  that tapers toward a distal end  20 . Working portion  18  is formed of a plurality of helical or spiral flutes  22  that form cutting surfaces  24  as seen most clearly in FIG. 2. Flutes  22  extend continuously along working portion  18 . File  10  may be manipulated by hand or be engine driven to rotate so that cutting surfaces  24  remove infected tissue from the root canal.  
           [0005]    Because root canals are seldom straight, but usually curved or twisted in multiple planes, it is important that endodontic files be flexible so that the file can follow the curved canal to its terminus during the cleaning process. Another advantage to having endodontic files with enhanced flexibility is that file breakage during the cleaning process of the root canal is greatly reduced. The recognized need for flexible endodontic files has led to the use of nickel-titanium alloys as the preferred material of choice for constructing endodontic files.  
           [0006]    Understanding that file breakage during a root canal procedure is an undesired event and its prevention is critical to a successful root canal procedure, providing an endodontic file with a resistance to breakage would be of great benefit to the field of endodontics. File breakage generally occurs from two causes. The first cause is cyclic fatiguing of the instrument material caused by repeated bending of the file. The incidence of cyclic fatigue file breakage is inversely related to file flexibility, therefore as instrument flexibility increases, cyclic fatigue file breakage decreases. The second cause of file breakage is the application of excessive torque to the endodontic file leading to torque failure. Such excessive torque is caused, at least in part, by the fact that substantially the entire length of the file working portion is in contact with the canal wall.  
           [0007]    Some current cleansing and shaping techniques used to prepare the root canal employ numerous endodontic files having a continuously tapered helical fluted working portion. The numerous files used during a root canal procedure may have different tip diameter sizes and/or tapers to allow the different files to clean different regions of the root canal. However, such current endodontic files encounter the problems discussed above.  
           [0008]    Examples of prior art endodontic instruments are seen in U.S. Pat. Nos. 4,934,934; 5,628,674; 5,653,590; and 6,074,209, all of which are hereby incorporated by reference in their entireties for all purposes.  
           [0009]    It would be an improvement in the art of endodontics to provide an endodontic file that has enhanced flexibility to reduce the likelihood of breakage. It would be a further improvement to provide an endodontic file having limited or dedicated cutting regions along the working portion of the file to limit the root canal surface area that is engaged by the endodontic file and to control which portion of the root canal is shaped and/or prepared. Decreasing the surface area of the endodontic file in contact with the root canal wall would effectively reduce the frictional torque applied to the instrument and would decrease the incidence of torque failure breakage  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides an endodontic file for shaping and/or preparing a root canal during a root canal procedure. The file has a proximal shaft portion connected to a handle portion and a distal working portion. The file may be manipulated by the fingers of an operator or inserted into a rotary engine driven hand piece. The unique working portion of the file may include multiple tapered cutting segments separated by non-cutting segments. The cutting segments have a cutting edge formed by a plurality of helical flutes. Each non-cutting segment preferably has a diameter that is significantly smaller than the diameter of the adjacent cutting segments. This arrangement provides overall flexibility of the file and increases the resistance to cyclic fatigue breakage. This arrangement further controls or limits which areas of the root canal are shaped and/or prepared during file use. The non-cutting segments limit the surface area of the root canal that is engaged by the cutting segments of the file. The cutting segments are located and arranged along the working portion to control which portion of the file actively shapes and/or prepares the root canal. The cutting segments may have a substantially continuous taper. Alternatively, the taper of each cutting segment may vary.  
           [0011]    In another embodiment, the cutting segments may have a non-circular geometric configuration and may be formed as straight and oriented substantially parallel to the long axis of the file rather than formed as helical or spiraling cutting segments. This embodiment prevents the file from self-feeding into the root canal.  
           [0012]    In another embodiment, the endodontic file forms part of a series of endodontic files to shape and/or prepare a root canal. Each file in the series may have cutting segments and non-cutting segments strategically placed in different regions along the working portion of the file to allow each file in the system to shape and/or prepare different portions of the root canal.  
           [0013]    The present invention provides an endodontic file for use in root canal treatment in which the cutting segments are located along the working portion in a manner to correspond with a portion of a root canal that is to be actively cut. The cutting segments and non-cutting segments may be of any length and may by of any number.  
           [0014]    The non-cutting segments have a diameter that is substantially less than the diameter of the cutting segments in order to provide flexibility and to control which region of the root canal is shaped or prepared by the file.  
           [0015]    These and other embodiments are described in more detail in the following detailed descriptions and the figures.  
           [0016]    The foregoing is not intended to be an exhaustive list of embodiments and features of the present invention. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a view of a prior art endodontic file.  
         [0018]    [0018]FIG. 2 is a cross-sectional view of the endodontic file of FIG. 1 taken along line A-A.  
         [0019]    [0019]FIG. 3 is a view of one embodiment of an endodontic file of the present invention having multiple tapered cutting sections.  
         [0020]    [0020]FIG. 4 is a view of another embodiment of an endodontic file of the present invention having a non-cutting section at the distal end of the file.  
         [0021]    [0021]FIG. 5 is a view of another embodiment of an endodontic file having straight cutting sections.  
         [0022]    [0022]FIG. 6 is a cross-sectional view of the endodontic file of FIG. 5 taken along line B-B.  
         [0023]    [0023]FIG. 7 is a view of an endodontic file system comprised of plural endodontic files each having cutting sections located at different locations along the working portion of the file.  
         [0024]    [0024]FIG. 8 is a view of another embodiment of an endodontic file system showing an alternative arrangement of cutting sections along the working portion of the file.  
         [0025]    [0025]FIG. 9 is a view of another embodiment of an endodontic file in which each cutting segment has a different taper. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    Representative embodiments of the present invention are shown in FIGS.  3 - 9 , wherein similar features share common reference numerals.  
         [0027]    [0027]FIG. 3 shows one embodiment of an endodontic file  30  of the present invention. File  30  may include a handle  32  located at a proximal end  34 , a shaft  36 , and a working portion  38  extending to a distal end  40 . Working portion  38  may be formed of a plurality cutting segments  41  formed of helical or spiral flutes  42  that form cutting edges  44  and separated by non-cutting segments  46 . Cutting segments  41  may be of any desired shape but are shown in this embodiment as being tapered in a direction from proximal end  34  toward distal end  40 . Non-cutting segments  46  are shown in this embodiment to have a smooth circular cross-section having a diameter that is less than the diameter of the adjacent cutting segments  41 . The relationship between cutting segments  41  and non-cutting segments  46  provide flexibility to file  30  to eliminate or reduce the chance of breakage as working portion  38  follows any curved and/or twisted portions of the root canal.  
         [0028]    In addition to providing flexibility, file  30  provides control over which portion or portions of the root canal are shaped and/or prepared. This is accomplished by the location of cutting segments  41  along working portion  38 . Cutting segments  41  may be located along working portion  38  at selected locations depending on which areas of the root canal are to be shaped and/or prepared. For example, in the embodiment of FIG. 3, only the portions of the root canal adjacent cutting segments  41  are shaped and/or prepared. The embodiment of file  30  shown in FIG. 3 shows cutting segments  41  located along working portion  38  in a spaced arrangement in which a cutting segment  41  is located at distal end  40 . FIG. 4 shows another embodiment of an endodontic file similar to file  30  of FIG. 3 in which like parts will be given like reference numbers indicated with a prime (′). Thus, file  30 ′ includes cutting segments  41 ′ located and arranged along working portion  38 ′ so that a non-cutting segment  46 ′ is located at distal end  40 ′. It should be further noted that other aspects of working portion  38 ,  38 ′ may vary. For example, although only three cutting segments  41 ,  41 ′ are shown in FIGS.  3  and  4 , the number of cutting segments  41 ,  41 ′ may vary. Additionally, the length  48 ,  48 ′ of cutting segments  41 ,  41 ′ and/or the length  50 ,  50 ′ of non-cutting segments  46 ,  46 ′ may vary.  
         [0029]    [0029]FIGS. 5 and 6 show another embodiment of a file  52  that includes a handle  54  located at a proximal end  56 , a shaft portion  58 , and a working portion  60  extending to a distal end  62 . Working portion  60  may be formed of a plurality cutting segments  64  each having a geometrical shape that forms a cutting edge  66  and separated by non-cutting segments  68 . In this embodiment, cutting segments  64  may have a non-circular shape and are shown as being triangular (FIG. 6). However, it should be understood by those skilled in the art that the invention is not limited to cutting segments having a triangular shape and that other geometric shapes may be contemplated. Preferably, the geometric shape of cutting segments  64  form cutting edges  66  that are substantially parallel to the long axis  70  of file  52 . Non-cutting segments  68  are shown in this embodiment to have a smooth circular cross-section having a diameter that is less than the cross-sectional shape of the adjacent cutting segments  64 . Cutting segments  64  have a length  72  and non-cutting segments  68  have a length  74  both of which may vary. The relationship between cutting segments  64  and non-cutting segments  68  provide flexibility to file  30  to eliminate or reduce the chance of breakage as working portion  60  follows any curved and/or twisted portions of the root canal.  
         [0030]    [0030]FIG. 7 shows a file system  76  that includes a series of individual files  78 ,  80 , and  82  being of substantially equal length, each file having cutting segments and non-cutting segments strategically located along the file to allow each file to shape and/or prepare a different region of the root canal and to divide the workload of shaping and/or preparing the root canal among the files in the file system  76 . For example, in the embodiment shown in FIG. 7, file  78  may include multiple cutting segments  84  separated by non-cutting segments  86  located along working portion  88 . File  80  may include cutting segments  90  and non-cutting segments  92  located along working portion  94 . Working portion  94  extends over a greater portion of file  80  than working portion  88  of file  78 . Additionally, the lengths of cutting segments  90  and non-cutting segments  92  may vary so that they may overlap with cutting segments  84  and non-cutting segments  86  of file  78 . File  82  may have cutting segments  96  and non-cutting segments  98  located along working portion  100 , which extends over a greater portion of file  82  than working portion  94  of file  80  or working portion  88  of file  78 . In a manner similar to files  78  and  80 , the length of cutting segments  96  and non-cutting segments  98  may vary so that they may overlap with cutting segments  90  and non-cutting segments  92  of file  80  and cutting segments  84  and non-cutting segments  86  of file  78 . The cutting segments  84 ,  90 ,  96  of individual files  78 ,  80 ,  82  are arranged so that, when taken together, they effectively form one continuous cutting segment covering the entire working portion  100 .  
         [0031]    [0031]FIG. 8 shows an alternative file system  102  that includes a series of individual files  104 ,  106 , and  108  being of substantially equal length. Similar to files  78 ,  80 ,  82  in FIG. 7, each file  104 ,  106 ,  108  have cutting segments and non-cutting segments strategically located along the file to allow each file to shape and/or prepare a different region of the root canal and to divide the workload of shaping and/or preparing the root canal among the files in the file system  102 . However, the cutting segments and non-cutting segments of files  104 ,  106 ,  108  are arranged in an alternative manner. For example, file  104  may include multiple cutting segments  110  separated by non-cutting segments  112  located along working portion  114 . File  106  may include cutting segments  116  and non-cutting segments  118  located along working portion  120  so that a non-cutting segment  118  is located at distal end  121 . Working portion  120  extends over a greater portion of file  106  than working portion  114  of file  104 . Additionally, the lengths of cutting segments  116  and non-cutting segments  118  may vary so that they may overlap with cutting segments  110  and non-cutting segments  112  of file  104 . File  108  may have cutting segments  122  and non-cutting segments  124  located along working portion  126 , which extends over a greater portion of file  108  than working portion  120  of file  106  or working portion  114  of file  104 . A non-cutting segment  124  is located at a distal end  128 . In a manner similar to files  104  and  106 , the length of cutting segments  122  and non-cutting segments  124  may vary so that they may overlap with cutting segments  116  and non-cutting segments  118  of file  106  and cutting segments  110  and non-cutting segments  112  of file  104 . The cutting segments  110 ,  116 ,  122  of individual files  104 ,  106 ,  108  are arranged so that, when taken together, they effectively form one continuous cutting segment covering the entire working portion  126 . The staggered cutting segments and non-cutting segments of the files of each system  76 ,  102  have been described as overlapping. However, it is within the scope of this invention that the staggered cutting segments of the related files in each system  76 ,  102  do not overlap. Regardless of whether or not the cutting segments overlap the files in both systems  76 ,  102 , when taken together, form a cutting segment along the entire working portion.  
         [0032]    [0032]FIG. 9 shows an alternative embodiment for a file  130  having variable tapered cutting segments for added flexibility. In this embodiment, the percentage taper of one cutting segment may be different from the percentage taper of the other cutting segments. For example, first cutting segment  132  may have an 8% taper, second cutting segment  134  may have a 6% taper, and third cutting segment  136  may have a 4% cutting taper.  
         [0033]    It should be understood by those skilled in the art that either file system  76 ,  102  may be comprised of files having tapered cutting segments, variable tapered cutting segments, or geometrically shaped cutting segments.  
         [0034]    Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of this invention and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein.  
         [0035]    While the inventor understands that claims are not a necessary component of a provisional patent application, and therefore has not included detailed claims, the inventor reserves the right to claim, without limitation, at least the following subject matter.