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 . referring to the drawings and first to fig1 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 fig3 , 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 fig4 , 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 fig5 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 . fig8 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 fig9 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 fig1 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 fig1 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 fig2 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 .
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 .