Patent Application
20090229129
This application is not based upon any pending domestic or international patent applications.
This application is not referenced in any microfiche appendix.
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:
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.
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:
Referring to the drawings and first to
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 30A 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
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 30A, 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, 30A, 30B, 30C, rod 12 would be indexed 120° between successive passes past grinding wheel 38.
As illustrated by
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 30A, 30B, and 30C and associated helical lands 36.
Referring now to
As illustrated by
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.
