Abstract:
A method of producing an endodontic file that involves grinding in a plane substantially parallel to the longitudinal axis of a rotating dental instrument blank. By grinding the dental instrument blank in this manner, the torsional strength of the resulting endodontic file is not eroded during its production, thereby providing a file that is less susceptible to breakage during its use.

Description:
REFERENCE TO PENDING APPLICATIONS 
     This application is not based upon any pending domestic or international patent applications. 
     REFERENCE TO MICROFICHE APPENDIX 
     This application is not referenced in any microfiche appendix. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of dentistry and more particularly to endodontic instruments used for cleaning and enlarging a root canal of a tooth. 
     2. Description of the Related Art 
     Instruments that enable an endodontist to clear and clean the canal of a tooth are well-known in the art. These instruments, typically referred to as endodontic files, experience significant flexing and twisting while in use, making them susceptible to breakage. Because of the breakage problem and the danger that it poses to a patient, nickel-titanium alloy (NiTi or Nitinol™) generally is viewed as a better material for use in manufacturing these instruments than is stainless steel. Relative to stainless steel, NiTi is able to withstand a far greater amount of twisting or bending without experiencing permanent deformation or breaking. 
     The manufacturing methods typically used for producing stainless steel instruments have proven themselves unsatisfactory when applied to NiTi. These methods include (1) twisting a prismatic rod having a square or triangular cross section to create a file with a fluted cutting edge and (2) grinding helical flutes along the length of a circular or tapered rod to create a file with one or more helical cutting surfaces. Twisting cannot be used because of the superelastic property of NiTi and traditional grinding methods leave areas of stress having radial planar components that reduce the torsional resistance of a file. 
     Methods of manufacturing specifically designed for NiTi provide a clean cutting edge but involve grinding or hacking methods that reduce the torsional strength of the file by creating stress areas lying perpendicular to the longitudinal axis of the file. The same is true of the traditional grinding and hacking methods used to form a file made of stainless steel. Breakage of the file due to torsion usually occurs in one or more of these cross-sectional areas. Additionally, currently available methods of grinding NiTi for use as an endodontic file are relatively expensive and slow. Therefore, a need exists for a method of manufacturing an endodontic file made of stainless steel or NiTi—or other materials that exhibit the desired superelastic properties of NiTi—that does not erode the torsional strength of the file. None of the prior art alone or in combination meets this need or renders the present invention obvious. 
     For background information relating to instruments of the type that is the subject of this patent application, reference may be had to the following issued United States patents and publications: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 U.S. Pat. No. 
                 Inventor 
                 Title 
               
               
                   
               
             
             
               
                 4,871,312 
                 Heath 
                 Dental Compactor Instrument 
               
               
                 4,934,934 
                 Arpaio, Jr. et al. 
                 Dental File/Reamer Instrument 
               
               
                 5,035,617 
                 McSpadden 
                 Endodontic Instrument 
               
               
                 5,065,549 
                 Speiser et al. 
                 Method and Apparatus For Manufacturing K-Files and Reamers 
               
               
                 5,184,926 
                 Hemmings 
                 Root-Strength Drill Bit and Method of Making 
               
               
                 5,628,674 
                 Heath et al. 
                 Endodontic Instrument 
               
               
                 5,653,590 
                 Heath et al. 
                 Kit of Endodontic Instruments and Method of Utilizing Same 
               
               
                 5,735,689 
                 McSpadden 
                 Endodontic Dental Instrument 
               
               
                 5,735,690 
                 Malentacca 
                 Set of Drills For The Boring Of The Coronary Part of Dental 
               
               
                   
                   
                 Radicular Canals 
               
               
                 6,149,501 
                 Farzin-Nia et al. 
                 Superelastic Endodontic Instrument, Method of Manufacture, and 
               
               
                   
                   
                 Apparatus Therefor 
               
               
                 6,299,445 
                 Garman 
                 Endodontic Instrument, Instrument Blank and Method of 
               
               
                   
                   
                 Manufacture 
               
               
                 7,018,143 
                 Moore 
                 Reduced Energy Consuming, Lateral Cutting Twist Drill 
               
               
                 7,018,205 
                 Abel 
                 Barbed Endodontic Instrument 
               
               
                 2004/0,219,484 
                 Scianamblo 
                 Endodontic Instrument Having Reversed Helix 
               
               
                 2006/0,014,480 
                 Aloise et al. 
                 Method of Manufacturing A Dental Instrument 
               
               
                 2006/0,265,858 
                 McSpadden 
                 Endodontic Instrument Having Notched Cutting Surfaces 
               
               
                   
               
             
          
         
       
     
     BRIEF SUMMARY OF THE INVENTION 
     The invention herein relates to a method of producing a dental instrument, commonly referred to as an endodontic file. The endodontic file produced has one or more flutes continuously spiraled over its working length, and the file can be cylindrical-shaped or tapered and cylindrical-shaped. The method involves feeding a rotating dental instrument blank past a rotating grinding wheel so that all grinding is done in a plane substantially parallel to that of the longitudinal axis of the dental instrument blank. By grinding the blank in a plane parallel to its longitudinal axis, the torsional strength of the blank is not eroded during the method of producing the endodontic file. The blank also can be advanced past the grinding wheel at a feed rate that corresponds to a distance that the blank rotates in a single revolution. The rotational axis of the grinding wheel can be positioned relative to a tapered dental instrument blank so as to maintain a selected depth-of-grind over the working length of the blank as a helical-shaped flute is ground. 
     This invention also includes an apparatus for producing an endodontic file according to the above method. The apparatus includes a gripping fixture to which the dental instrument blank is secured during grinding. The gripping fixture helps to move the dental instrument blank in a linear path past the grinding wheel as the fixture rotates the blank about its longitudinal axis. The rotation of the blank is indexed to the displacement of the gripping fixture so that all grinding takes place in a plane substantially parallel to the longitudinal axis of the blank. 
     A better understanding of the invention will be obtained from the following detailed description of the preferred embodiments and claims, taken in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a dental instrument blank in the form of a tapered, cylindrical-shaped rod as it is rotated about and advanced along its length in contact with a grinding wheel. The grinding wheel is oriented perpendicular to a rotational axis of the wheel. As the rod is moved past the wheel, the wheel cuts a first flute along a surface of the rod. All grinding takes place in a plane substantially parallel to a longitudinal axis of the rod. 
         FIG. 2  is a view of the rod after the grinding wheel has completed cutting the first flute. 
         FIG. 3  is a cross-sectional view of the rod taken along section line  3 - 3  of  FIG. 2  and showing a profile of the first flute and the grinding wheel. 
         FIG. 4  is a cross-sectional view of the rod taken along section line  4 - 4  of  FIG. 3 . 
         FIG. 5  is a view of the rod after the grinding wheel has completed cutting a third flute. 
         FIG. 6  is a cross-sectional view of the rod taken along section line  6 - 6  of  FIG. 5  and showing a profile of the rod and the grinding wheel after the grinding wheel has completed cutting the third flute. 
         FIG. 7  is a cross-sectional view of the rod taken along section line  7 - 7  of  FIG. 6 . 
         FIG. 8  is a view of a finished endodontic file. 
         FIG. 9  is a view of a dental instrument blank in the form of a cylindrical-shaped, non-tapered dental instrument rod prior to grinding a taper and a flute along a surface of the rod. 
         FIG. 10  is a view of the rod as the grinding wheel cuts a first flute in the rod. The rod is rotated about a longitudinal axis of the rod and advanced along its length in contact with a grinding wheel. The grinding wheel is oriented perpendicular to a rotational axis of the grinding wheel. The relative path of the wheel follows a slight angle relative to the longitudinal axis of the rod and all grinding takes place in a plane substantially parallel to the longitudinal axis of the rod. The shape of the wheel and the slight angle produces the flute and a taper as a surface of the rod comes into contact with and moves past the wheel. 
         FIG. 11  is a view of the finished endodontic file. 
         FIG. 12  is a view of the cylindrical-shaped rod as grinding begins. The rod is rotated about its cylindrical axis and the relative path of the wheel is at a slight angle to the longitudinal axis of the rod. 
         FIG. 13  is a cross-sectional view of the rod taken along section line  13 - 13  of  FIG. 12 . 
         FIG. 14  is a view of the rod after a first pass past the grinding wheel to form a first helical-shaped groove along a surface of the rod. 
         FIG. 15  is a cross-sectional view of the rod taken along section line  15 - 15  of  FIG. 14  and showing the taper of the rod toward a distal end of the rod. 
         FIG. 16  is a cross-sectional view of the rod taken along section line  16 - 16  of  FIG. 14 . 
         FIG. 17  is a cross-sectional view of the rod after its first pass past the grinding wheel. 
         FIG. 18  is a cross-sectional view of the rod taken along section line  18 - 18  of  FIG. 17 . 
         FIG. 19  is a cross-sectional view of the rod after a first pass past the grinding wheel to form a second-helical shaped groove along a surface of the rod. 
         FIG. 20  is a cross-sectional view of the rod taken along section line  20 - 20  of  FIG. 19 . 
         FIG. 21  is a cross-sectional view of the rod after a first pass past the grinding wheel to form a third-helical shaped groove along a surface of the rod. 
         FIG. 22  is a cross-sectional view of the rod taken along section line  22 - 22  of  FIG. 21 . 
         FIG. 23  is cross-sectional view of the rod after a second pass past the grinding wheel to complete a first helical-shaped groove along a surface of the rod. 
         FIG. 24  is a cross-sectional view of the rod taken along section line  24 - 24  of  FIG. 23 . 
         FIG. 25  is cross-sectional view of the rod after a second pass past the grinding wheel to complete a second helical-shaped groove along a surface of the rod. 
         FIG. 26  is a cross-sectional view of the rod taken along section line  26 - 26  of  FIG. 25 . 
         FIG. 27  is cross-sectional view of the rod after a second pass past the grinding wheel to complete a third helical-shaped groove along a surface of the rod. 
         FIG. 28  is a cross-sectional view of the rod taken along section line  28 - 28  of  FIG. 27 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is to be understood that the invention that is now to be described is not limited in its application to the details of the construction and arrangement of the parts illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. The phraseology and terminology employed herein are for purposes of description and not limitation. 
     Elements illustrated in the drawings are identified by the following numbers: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                   
                 10 
                 Endodontic file 
               
               
                   
                 12 
                 Rod 
               
               
                   
                 14 
                 Shank end 
               
               
                   
                 16 
                 Shank end diameter 
               
               
                   
                 18 
                 Distal end 
               
               
                   
                 20 
                 Distal end diameter 
               
               
                   
                 22 
                 Linear travel path of the blank 
               
               
                   
                 24 
                 Helical-shaped travel path 
               
               
                   
                 26 
                 Working length 
               
               
                   
                 28 
                 Rod rotation 
               
               
                   
                 30A 
                 First flute 
               
               
                   
                 30B 
                 Second flute 
               
               
                   
                 30C 
                 Third flute 
               
               
                   
                 36 
                 Helical land 
               
               
                   
                 38 
                 Grinding wheel 
               
               
                   
                 40 
                 Spindle 
               
               
                   
                 42 
                 Spindle rotation 
               
               
                   
                 44 
                 Handle 
               
               
                   
                 46 
                 Shank portion 
               
               
                   
                 48 
                 Calibrated depth markings 
               
               
                   
                 50 
                 File portion 
               
               
                   
                 52 
                 Longitudinal axis of the rod 
               
               
                   
                 54 
                 Longitudinal axis of the spindle 
               
               
                   
                 58 
                 Relative travel path of the wheel 
               
               
                   
               
             
          
         
       
     
     Referring to the drawings and first to  FIGS. 1 and 2 , a dental instrument blank in the form of rod  12  with a shank end  14  and a distal end  18  is secured at the shank end  14  to a gripping fixture (not shown). The gripping fixture is of a type well-known in the art and is capable of moving rod  12  in a linear travel path  22  past and in contact with a fine-grit grinding wheel  38  while simultaneously rotating rod  12  about a longitudinal axis  52  of the rod  12 . The combination of linear travel path  22  and rotation  28  produces a helical-shaped travel path  24  along the working length  18  of rod  12  as rod  12  moves past grinding wheel  38 . 
     The rod  12  is of a type, size, and geometry well-known in the art for producing an endodontic file  10 , and is typically cylindrical-shaped or tapered and cylindrical. The shank end diameter  16  and distal end diameter  20  of the rod  12  closely conform to a desired shank end diameter  16  and a desired distal end diameter  20  of the endodontic file  10  to be produced. The diameter of rod  12  might also closely conform to the shank end diameter  16  of the endodontic file  10  and then be ground along the working length  26  of rod  12  to produce a desired taper and distal end diameter  20 . 
     The rotation  28  of rod  12  is indexed to the linear displacement of the gripping fixture (not shown) relative to grinding wheel  38  in order to create the spiral-shaped travel path  24  necessary to produce a desired continuous helical configuration in the form of a flute  30 A along a surface of rod  12  and throughout the working length  26  of rod  12 . In cases in which the endodontic instrument  10  to be produced is to be tapered along its working length  26 , the gripping fixture that holds rod  12  is angled relative to the geometry of the grinding wheel  38  so as to control and vary depth-of-grind along the working length  26  of rod  12 . Grinding wheel  38  may also be angled relative to the geometry of rod  12 . 
     The grinding wheel  38  is mounted on a spindle  40  of a standard grinding machine M. Grinding wheel  38  is oriented on the spindle  40  so that the grinding wheel  38  rotates about a longitudinal axis  54  of spindle  40  that is substantially perpendicular to the longitudinal axis  52  of the linearly advancing and rotating rod  12 . This arrangement produces rotation of the grinding wheel  38  that is in a plane substantially parallel to the longitudinal axis  52  of rod  12 . As illustrated by  FIG. 3 , all grinding on the surface of rod  12  takes place in a plane substantially parallel to the longitudinal axis  52  of the rod  12 . Because grinding of flute  30 A is being done in a plane substantially parallel to—and not perpendicular to—the longitudinal axis  52  of rod  12 , the torsional strength of endodontic file  10  is not eroded. As illustrated by  FIG. 4 , the curved-shaped geometry of the cutting surface of grinding wheel  38 —in combination with the appropriate rate and depth of helical-shaped travel  24 —produces the desired geometry of the flute  30 A. 
     The feed rate of rod  12  past grinding wheel  38 , speed of grinding wheel  38 , and depth-of-grind of grinding wheel  38  may be sufficient to remove in a single pass the amount of material required to produce the desired geometry of flute  30 A, or multiple passes may be employed with grinding wheel  38  set at a successively lower depth-of grind. In cases in which a single pass is used, working length  26  of rod  12  is moved past grinding wheel  38  a number of times equal to the number of flutes required for the endodontic file  10 . Between each successive pass of rod  12  past grinding wheel  38 , rod  12  is indexed by the gripping fixture so as to present a non-ground surface of rod  12  for grinding the next flute  30 . For an endodontic instrument having three flutes,  30 A,  30 B,  30 C, rod  12  would be indexed 120° between successive passes past grinding wheel  38 . 
     As illustrated by  FIGS. 5 to 7 , a first, second, and third pass of rod  12  past grinding wheel  38  produces the first flute  30 A, a second flute  30 B, and third flute  30 C, respectively. Each flute  30 A,  30 B, and  30 C has a substantially similar geometry and continuous helical configuration along the working length  26  of rod  12 . The grinding of rod  12  that produces flutes  30 A,  30 B, and  30 C also forms a helical land  36  on the outer periphery of rod  12 . Helical land  36  is continuous along the working length of the rod  12  and is located between adjacent flutes. 
       FIG. 8  illustrates an endodontic file  10  produced by the method described above. The file  10  comprises a handle  44 , a shank portion  46  having calibrated depth markings  48 , and a file portion  50 . 
     In a preferred embodiment, a file blank  12  is used, having a circular cross-section and composed of NiTi, a working length  26 , a shank end diameter  16 , a distal end diameter  20  of, and a degree of taper along its working length  26 , all in accord with the specification of the file  10  being manufactured. The gripping fixture is angled relative to vertical so as to control and vary the depth-of-grind in the peripheral surface of rod  12  along its working length  26 . Rod  12  is rotated  28  about its longitudinal axis  52  and moved in a linear travel path  22  past a rotating grinding wheel  38 . Grinding wheel  38  is substantially convex-shaped and oriented so that all grinding takes place in a plane substantially parallel to the longitudinal axis  52  of rod  12 . The combination of rotation  28  and linear advancement of the rod  12  past the grinding wheel  38  produces a continuous helical configuration  28  in rod  12 . Because all grinding is in a plane substantially parallel to the longitudinal axis  52  of rod  12 , creation of stress areas having radial planer components in rod  12  are eliminated or at least substantially reduced. That is, grinding is accomplished in a manner to reduce the creation of torsional stress weakness in finished file  10 . A total of three passes are used to create a final endodontic instrument  10  having three continuous flutes  30 A,  30 B, and  30 C and associated helical lands  36 . 
     Referring now to  FIGS. 9 to 11 , in another preferred embodiment a substantially concave-shaped grinding wheel  38  is used to simultaneously form a taper and the helical-shaped flutes  30 A,  30 B, and  30 C. A dental instrument blank in the form of a cylindrical-shaped rod  12  is rotated about its longitudinal axis  52  and moved in a linear direction  22  past grinding wheel  38  in order to create a helical-shaped travel path  24  along a surface of rod  12 . As rod  12  rotates and linearly advances helical-shaped flutes  30 A,  30 B,  30 C are formed. 
     As illustrated by  FIGS. 12 to 17 , the travel  58  of grinding wheel  38  relative to the geometry of rod  12  follows a slight angle so that a desired degree of taper is achieved. Alternatively, the gripping fixture (not shown) may be angled relative to grinding wheel  38 . In a first pass, a groove to form helical-shaped flute  30 A is ground along a surface of rod  12 . Depth-of-grind of flute  30 A increases toward the distal end  18  of rod  12 . As illustrated by  FIGS. 19 to 22 , rod  12  is then moved past grinding wheel  38  a second and third time to grind helical-shaped grooves forming flutes  30 B and  30 C, respectively. Similar to flute  30 A, depth-of-grind of flute  30 B,  30 C increases toward the distal end  18  of rod  12 . As illustrated by  FIGS. 23 to 28 , a fourth, fifth, and sixth pass completes flutes  30 A,  30 B, and  30 C, respectively, to completely form flutes  30 ,  32 , and  34 . The finished endodontic file  10  has the desired taper and flute configuration. 
     While the invention has been described with a certain degree of particularity, many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.