Abstract:
Differences in the diameters of successive cutting instruments, either hand- or engine-powered, within sets of instruments described herein progress sequentially by constant percentages of increase, rather than by constant linear increase as is currently the practice in the dental manufacturing industry.

Description:
SUBJECT MATTER OF INVENTION 
     The present invention relates to an improved set of endodontic instruments, and in particular to an improved set of reamers, files and shapers. 
     BACKGROUND OF INVENTION 
     The standardization of endodontic instruments is considered important by endodontists since it assures them of optimal selection, uniform availability, convenience and comparability of such endodontic instruments. Over the years, the industry has developed several standards for root canal instruments and in particular for reamers and files. The industry use ISO standard 3630 to define all standard instruments for root canal preparation. Among other things, shapes, profiles, lengths, sizes, acceptable manufacturing tolerances and minimum requirements of mechanical stress are carefully defined, as are other factors such as color codes. The ISO standard 3630 was established by the Technical Committee 106, of the International Standardizations Organization. Pursuant to these standards, an international order numbering system has been developed by which defined sizes for reamers and files are identified. Because such accepted standards have been so ingrained in the practice of endodontics, efforts have been limited in the reexamination of some of the principles upon which these standards have been based. Specifically, the use of reamers and files in endodontics conventionally begins with an instrument having a small diameter. As the endodontist works on a root canal to properly shape and enlarge it, larger instruments are substituted as the endodontist&#39;s work progresses. The gradation of increased sizes has become part of the standardization established under the ISO standards. Specifically, the diameters of the cones of successively larger reamers or files are increased under ISO standard sizes, from 0.10 mm to 0.60 mm in uniformly incremental steps of 0.05 mm and in sizes from 0.60 mm to 1.40 mm in uniformly incremental steps of 0.10 mm. These incremental steps are made with acceptable deviations of plus or minus 0.02 mm. Conventionally available standard sets of reamers, files and shapers are all incrementally larger from one to the next larger one by exactly the same absolute dimension. The incremental increases are the same as each larger instrument is used. Thus, the ratio of material removed to the diameter of the canal is much greater at the beginning of the treatment when the canal is small than it is when the larger tools are used towards the end of the reaming or filing process. Accordingly, the necessary delicate feel of the endodontist is impaired by the relatively large incremental steps at the beginning and is less than satisfactory with existing sets of files and reamers. This lack of appropriate feel is particularly apparent in smaller diameter instruments in which, for instance, there is a 50% increase from the 0.10 mm to the 0.15 mm reamer under the ISO standards. This difference is not altogether satisfactory because this change in size does not permit an endodontist a proper control in the deep narrow portions of root canals. 
     Reference to the use of sets of reamers or files do not consider problems inherent in the absolute diameter differentials between adjacent instruments. For example, U.S. Pat. No. 4,536,159 simply makes reference to the use of sets with uniform 0.05 mm diameter differentials as typically used in preparing the root canal. Other references such as U.S. Pat. Nos. 4,538,989, 4,340,364, 4,332,561 and 4,674,979 either have similarly limited references or do not even discuss the use of endodontic tools such as reamers or files in sets. 
     BRIEF SUMMARY OF INVENTION 
     The present invention recognizes the importance of utilizing a set of endodontic instruments, such as files or reamers, as a set in a manner which permits the endodontist to prepare a root canal effectively and with maximum sensitivity and flexibility. In the present invention there is provided a set of instruments in which the size from the smallest to the largest increases in uniformly constant incremental percentages. Thus for example, the increase in a reamer or file size is at a uniform percentage, rather than at a uniform 0.05 mm increase in diameter. In a typical set of six files with the smallest 0.10 mm diameter each of the six increases over the next smallest by exactly the same diameter percentage. Similar uniform incremental changes occur in sets having greater than six instruments. Thus, in the present invention there is provided a plurality of individual elongated endodontic cutting instruments as a set in which each differs in size at corresponding diameters of a cutting section at a constant percentage ratio of one instrument to the next larger instrument. 
     Root canals are rarely parallel and rarely straight. They tend to taper toward the root apex, being generally narrower in the apical third of the root, and greatly wider in the coronal third of the root. They tend to have curvatures which, while occurring potentially anywhere along the lengths of the canal, tend to be more common and more pronounced in the deeper, more apical portion of the canal. These naturally occurring realities of root canal shape, taper and tortuosity, sometimes severe, make manipulations in the apical portion of root canals more difficult and complex than manipulations in the coronal portions of root canals, which tend to be wider and straighter. 
     Manipulation in the apical portion of root canals is aided by the use of more flexible, more finely graded instruments, which allow for more delicate feel by the dentist. 
     Root canal enlarging instruments manufactured in accordance with the present invention provide fine percentage gradations where they are most needed (and do not currently exist) in smaller sizes of any given set, and few gradations where they are least needed (and do presently exist) in larger sizes. 
     Thus, use of these instruments provide faster, more controlled, and more effective cleaning and shaping of root canals with the use of fewer instruments. 
    
    
     DESCRIPTION OF DRAWINGS 
     The present invention will be more clearly understood when considered in connection with the accompanying drawings in which: 
     FIG. 1 is a plan view of a file which may comprise a component of the invention; 
     FIG. 1A is an enlarged detail of a part of FIG. 1; and 
     FIG. 2 is a somewhat schematic view of a set of six endodontic files illustrating the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described in connection with the accompanying drawings which illustrate a typical file adapted and used in a set of six in relative dimensions which embody the present invention. However, the principles of the present invention may also be applied to any elongated cutting, shaping, or abrading endodontic instruments, both hand and engine powered. As illustrated in the present invention each instrument is conventionally made using conventional technology. Thus, the cutting edge of the instrument may be made by grinding an elongated blank or by twisting a blank having a polyhedric cross-section in accordance with well-known techniques. As illustrated, in the case of a file it includes a handle 10, with a working part 11, a working length 12, a tip 13, a cone diameter d 1  (as measured in hundredths of a millimeter, one millimeter from the cone tip), and a diameter d 2  at the end of the working part 11. D 1  identifies an instrument&#39;s size, i.e. 0.1=ten one-hundreths or #10; 0.15=fifteen one-hundreths or #15. D2 is, under ISO standards 0.3 mm wider than d 1  16 mm from the tip. This determines the slope of the instrument. Every instrument has a constant taper between d 1  and d 2 . For example, #45, which is 0.45 mm at d 1 , is 0.75 at d 2 . In the ordinary standard the length of the working part 11 is 16 mm minimum. In these instruments, too, the working parts are a minimum of 16 mm long. The working length l 3  of the tip 13 is always equal or less than the cone diameter d 1  of the tip as illustrated in FIG. 1A. For reamers and files, the measurement set forth above are always uniformly applied. For other types of instruments such as rasps, barbs, broaches, etc. these dimensions may vary, depending upon functional differences and constructional features of the devices. 
     Under ISO standards, instruments having d 1  diameters between 0.10 mm and 0.60 mm increase linearly at 0.05. Thus eleven instruments span these sizes. In the embodiment of the invention illustrated in FIG. 2 which may be used in place of the ISO standard #10 to #60 instruments, there is illustrated a set of six endodontic instruments 1 to 6 inclusive with instrument 1 having the smallest diameter and increasing to the largest diameter instrument 6. The overall length of each instrument within the set is the same. In a typical set the working length 12 may be 25 mm. Within any set, however, the instruments may typically vary from 17 mm to 32 mm in their working length. The smallest diameter file in the embodiment illustrated has a d1 diameter of 0.10 mm±0.02 mm. Each larger diameter file in the set of six has a d1 diameter which is larger by 43.09691 percent than the next smaller one. Thus, instrument 2 has a d1 diameter of 0.143 mm±0.02 mm, instrument 3 has a d1 diameter of 0.205 mm±0.02 mm, instrument 4 has a d1 diameter of 0.293 mm±0.02 mm, instrument 5 has a d1 diameter of 0.419 mm± 0.02 mm, and instrument 6 has a d1 diameter of 0.600 mm ±0.02 mm. 
     Similarly incremental changes in the uniform percentage basis may occur in sets of seven and sets of eight or more instruments. In a set of seven instruments between ISO sizes #10 and #60, the incremental increase is 34.8% while the incremental increase in the set of eight reamers is 29.17% in order to provide the smallest working tool with a d1 diameter of 0.10 mm and the largest with a d1 diameter of 0.60 mm. These incremental differences are reflected in the charts set forth below. 
     
         ______________________________________                d1 diameter  d1 diameterInstrument   % d1 Increase                increase (mm)                             (mm)______________________________________SET OF SIX INSTRUMENTS1       --           --           .100 mm2       43.09691%     .043 mm     .143 mm3       43.09691%    .0617 mm     .205 mm4       43.09691%    .0883 mm     .293 mm5       43.09691%    .1263 mm     .419 mm6       43.09691%    .1807 mm     .600 mmSET OF SEVEN INSTRUMENTS1       --           --           .100 mm2        34.8%       .035         .135 mm3        34.8%       .047         .182 mm4       34.8         .063         .245 mm5       34.8         .085         .330 mm6       34.8         .115         .445 mm7       34.8         .155          .6 mmSET OF EIGHT INSTRUMENTS1       --           --           .100 mm2       29.17        .029         .129 mm3       29.17        .038         .167 mm4       29.17        .049         .216 mm5       29.17        .063         .297 mm6       29.17        .087         .366 mm7       29.17        .107         .473 mm8       29.17        .138         .601 mm______________________________________ 
    
     Although instruments between d1 diameter sizes 0.10 and 0.60 are conventionally the most frequently used, occasionally smaller or larger instruments are desirable. Thus, there may be occasions when an ISO size as low as 0.06 mm or as great as 1.40 mm d1 diameter is desired. Under those requirements, sets may be designed using the principle outlined, by making each larger diameter instrument larger by a constant d1 diameter percentage. Under such circumstances, a set of eight may be expanded to a set of 13 instruments by adding instruments having both smaller and larger d1 diameters. Such a set is reflected in the following chart. 
     
         ______________________________________SET OF THIRTEEN INSTRUMENTS                d1 diameter  d1 diameterInstrument   % d1 Increase                increase (mm)                             (mm)______________________________________1       --           --           .060 mm2       29.17        .017         .077 mm3       29.17        .023         .100 mm4       29.17        .029         .129 mm5       29.17        .038         .167 mm6       29.17        .049         .216 mm7       29.17        .063         .297 mm8       29.17        .087         .366 mm9       29.17        .107         .473 mm10      29.17        .128         .601 mm11      29.17        .174         .775 mm12      29.17        .225         1.000 mm13      29.17        .293         1.293 mm______________________________________ 
    
     It is apparent than the principle may be applied to any reasonable number of instruments in a set with starting and ending d 1  diameters as may be desired. 
     It has been found that the use of these sets significantly increase the flexibility, control and ease of use of the instrument in enlarging the root canal. They are particularly useful in the apical 1/3 of the canal.