Patent Publication Number: US-2007099149-A1

Title: Endodontic device and method of utilizing and manufacturing same

Description:
FIELD OF THE INVENTION  
      The present invention is in the field of endodontistry and more particularly, the present invention concerns an endodontic device and a method for endodontic treatment. More specifically, the present invention relates to an endodontic device for cleaning, filing and reaming root canals and to a method for using and manufacturing same.  
     BACKGROUND OF THE INVENTION  
      Modern endodontic treatment involves removal of the damaged pulp, followed by cleaning and shaping of the root canal space, irrigating, and filling with biocompatible material such as gutta-percha and a root canal sealer.  
      Shaping of the canal is performed either manually, using hand-held stainless steel endodontic, substantially rapid files, or mechanically, using rotary nickel-titanium files adapted to fit a standard or dedicated dental handpiece.  
      The manual process relies on the experience of the dentist, is physically difficult to perform and is time consuming. The use of files requires repeated changing between numerous different files, conical in shape, progressively increasing from the smallest to the largest. Hand-held steel files are limited in angle of rotation to about thirty degrees back and forth and may not reach the apical portion of the root canal if the canal is curved or meandered. The reason for such limitations relates to the moderate elasticity of the steel files and the risk of fracture when excessive force is applied. The round cross-section of the file eliminates adequate cleaning when the canal cross-section is oval or narrow in shape. In such cases enlargement of the canal cross-section to accept the round cross-section of the file, may weaken or perforate the wall or the apical portion of the canal.  
      Although the field of elastic rotary nickel-titanium endodontic files has developed greatly over the last few years, fracture of nickel-titanium rotary files is still often reported, and hence the use of such is restricted. In order to overcome the fracture problem, a large range of dedicated handpiece systems, powered by slow speed electric motors equipped with torque limitation circuits, were developed. As a result the cost of files and the related equipment per endodontic treatment became significantly higher.  
      In order to overcome the problem of breakage of files in the root canal during endodontic treatment and the potential risk of having to leave a broken file tip in the root canal, it was suggested in U.S. Pat. No. 6,443,730 to use a break-resistant, multi-filament composite for producing an endodontic reamer, comprising a plurality of twisted fibers “that are molded with a polymer matrix to form a pre-twisted core  12 ” (col. 3, lines 65-66). In the polymer matrix there can be embedded abrasive particle material.  
      Another drawback of the prior art nickel-titanium and composite files is related to the flexibility of these files, which are more likely to follow root canal curvature and to remain in the center of the root canal, as stated in the U.S. Pat. No. 6,746,245. By remaining in the center, the file instrument works contemporaneously and indiscriminately on all walls within reach of the file. Since root canal walls do not have equal thicknesses in all directions and at all different points along a root canal, some walls can be overthinned or perforated. Additionally, nickel-titanium thin file instruments can be too flexible to adequately clean the root canal as the file may bend and be deformed when it encounters a hard substance. Since the nickel-titanium files are flexible, they tend to follow the path of least resistance and cannot be used to aggressively clean the portions that need to be cleaned and are difficult to reach. Accordingly, when a nickel-titanium file is used to clean a non-cylindrically shaped root canal, the file moves only at the center of the canal and/or the area of least resistance and fails to remove all of the necrotic tissue.  
      During cleaning and shaping, the canal is commonly irrigated with a solution of sodium hypochloride (bleach). It is able to lubricate, wash out debris, dissolve organic tissue and destroy microorganisms present in the root canal. The bleach should be irrigated from the canal with a final saline irrigation. Most irrigation techniques involve the use of a flexible syringe, so that during the repeated wash cycle, the handpiece holding the file is put to rest in its seat. Some other solutions, such as those suggested in U.S. Pat. No. 6,464,498, include the use of a specific handpiece equipped with pressure inlet and suction outlet coupled to a surgical needle. All such procedures, however, require a long cessation in the canal shaping operation while switching between different tools.  
      Consequently, there exists a need for an efficient root canal treatment with minimal tool changing and removal of healthy dentine layer while shaping the root canal.  
     SUMMARY OF THE INVENTION  
      It is therefore a broad object of the present invention to provide an endodontic device and method utilizing a flexible, break resistant endodontic device for cleaning, filing and reaming of a tooth root canal, for performing an endodontic treatment.  
      It is a further object of the present invention to provide a method of manufacturing a flexible break-resistant endodontic device for cleaning, filing and reaming of a tooth root canal.  
      Yet another object of the present invention is to provide a complement irrigation system to be used in conjunction with the endodontic device according to the present invention, during endodontic treatment.  
      In accordance with the present invention there is provided an endodontic device for cleaning, filing or reaming root canals, comprising at least one metallic, flexible strand having an edge, an effective section and a connecting section and a coupling head connected thereto, said strand being coated along its effective section with a thin layer of a binder having abrasive particles embedded therein.  
      The invention further provides a method for cleaning, filing or reaming root canals, comprising providing an endodontic device, as claimed in claim  1 , inserting said effective section into the root canal, rotating said device at a selected speed, advantageously using the radial centrifugal forces acting on the thin flexible effective section of the device, to follow the natural curvature and complex cross-section of the root canal.  
      The invention still further provides a method for manufacturing an endodontic device, comprising providing at least one metallic, flexible strand, covering intermittent portions of said strand with a binder blocking layer, coating exposed sections of said strand with a layer of a binder having abrasive particles embedded therein to form an effective section, dissolving the blocking layer, molding a coupling head and coupling member onto said dissolved portions while leaving non-coated portions between said effective section and said coupling head, and cutting said strand between the effective sections and said coupling head.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures, so that it may be more fully understood.  
      With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
      In the drawings:  
       FIG. 1  is a cross-sectional, exploded view of the endodontic device, according to the present invention;  
       FIG. 2  is a cross-sectional assembled view of the endodontic device of  FIG. 1 ;  
       FIG. 3  is a perspective view of the assembled endodontic device of  FIG. 2 ;  
       FIG. 4  is a cross-sectional view of another embodiment of the device according to the present invention;  
       FIG. 5  is a side view of an endodontic device according to the present invention, fitted with a spring absorber;  
       FIG. 6  is a side view of a further embodiment of the device according to the present invention;  
       FIG. 7  is a side view of a modification of the device of  FIG. 6 ;  
       FIG. 8  is a side view of still a further embodiment of the device of the present invention;  
       FIG. 9A  is a side view of a variant of  FIG. 8 ;  
       FIG. 9B  is an enlarged view of an encircled detail of  FIG. 9A ;  
       FIG. 10  is a cross-sectional view of the endodontic device according to the present invention, inserted in a root canal;  
       FIG. 11  is a cross-sectional view of the endodontic device, during use;  
       FIG. 12  is a cross-sectional view across line A-A of  FIG. 10 ;  
       FIG. 13  is a cross-sectional view similar to  FIG. 11 , illustrating the rotation of the device in an opposite sense;  
       FIG. 14  is a perspective view of the device according to the present invention coupled to a hand piece equipped with an irrigation system;  
       FIG. 15  is a perspective view of a further embodiment of the system of  FIG. 14 , and  
       FIG. 16  is a modification of the system of  FIG. 15 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The structure of the endodontic device  2  for cleaning, filing and reaming of a tooth root canal according to the present invention, will now be described in detail with reference to FIGS.  1  to  3 . The device  2  advantageously includes three connectable portions, the work performing or effective portion  4 , coupling member  6  and head  8 . The portion  4  is made of a section of one or more strands  10 , preferably of metal, e.g., stainless steel, nickel-titanium or beryllium-bronze, with or without springy properties. If more than one strand is used, at least the edges  12  may be twisted, welded, brazed or otherwise connected, to form a connected pointed edge, while the remaining portion of the individual strands may be unconnected, loosely or tightly, twisted or braided. For effective endodontic work in a root canal, i.e., cleaning, filing or polishing, a section A of the strands  10  is coated with an abrasive layer  14 . The uncoated connecting section  16  is used for fixing the strands  10  to the head  8 . Such an abrasive layer  14  is normally composed of grains of abrasive particles embedded, during an electro-plating process in a thin layer of typically, nickel, serving as a binder. Suitable abrasives can be aluminum oxide, silicon carbide, zirconia or diamond powder, or any other abrasive powder. Grain size larger than the average thickness of the nickel layer is selected, such that the sharp edges of the abrasive grains are exposed from the layer to perform an abrading action. If a multi-strand cable is used, the coating process may be performed on individual strands  10  before twisting to a cable, or on the already twisted cable, coating only the outer surface of section A of the strands. Optionally, as seen in  FIG. 2 , a sub portion A′ of the section A, away from the edge  12 , may be coated with coarse grains to form a thicker layer  14  to better fit the root canal shape.  
      The term “strand” or “strands” will be used herein to designate a single strand or a multiplicity of strands, whether loosely or tightly twisted or wound into a cable.  
      Coupling member  6  configured as an arrowhead, preferably made of soft material such as rubber or thermoplastic elastomer, has two portions: a first tapered portion  6 ′, fixedly attached to the strands connection section  16 , and a second portion  6 ″, configured to fit into a bore  8 ′ made in the head  8 . As seen in  FIG. 2 , the connection section  16  of the strands  10  may extend through and beyond the member  6  and be anchored in the head  8 . Obviously, this kind of connection can be achieved by molding of the head  8  and the member  6  onto the strands  10  during manufacture, using plastics and thermoplastic elastomers respectively. The head  8  is configured with a standard coupling end  18  for releasable attachment to an endodontic hand piece. Optionally a metal head  8  may be crimped over the strands  10  or otherwise soldered, brazed or bonded.  
      In addition to the relatively soft coupling member  6 , having a flexible tapered part  6 ′ that can follow the movement of the strands  10  during operation, it was found that even better results can be achieved when a portion  20  ( FIG. 2 ) adjacent to the connection between the strands  10  and the member  6 , is optionally left uncoated. This preserves the portion of the strands most liable to break under rigorously rotational and bending actions, with maximal flexibility. In addition, the uncoated bare portion  20  can also serve as an electrical connection location between the metallic strands  10  and an apex locator, as per-se known.  
      A modification of the structure of the device  2  is illustrated in  FIG. 4 . Here the coupling member  6  is formed with a bore  22  having an annular projection  24  and the head  8 , which advantageously may be made of two parts, as shown, and has an annular groove  26  configured to match the projection  24 , when assembled. As can be understood, this kind of a device is most suitable for use with an endodontic hand piece, as well as manually.  
      Referring to  FIG. 5 , there is illustrated a different embodiment for flexibly attaching the strands  10  to the head  8 . A groove  28  is cut on the outer circumference of the head for accepting a conical spiral spring  30 . The small end of the spring  30  grips the connecting section of the strands  10  and has the same effect as the flexible member  6 , which is, to absorb vibration and eliminate stress concentration in the root of the strands  10  during operation.  
      Still further embodiments of the device  2  are shown in FIGS.  6  to  10 B. Seen in  FIG. 6  is the device  2 , to the strands  10  of which is attached a loosely wound helical spring  32 , which prevents the wrapped portion of the strands  10  from buckling. The spring  32  may itself be coated with an abrasive layer  14 , while the portion of the strands  10 , wrapped by the spring  32  remains uncoated, preserving greater flexibility. A variant of the embodiment of  FIG. 6  is illustrated in  FIG. 7  showing a tightly wound spring  34  providing less flexibility. In both embodiments, a portion  20  between the springs  32 ,  34  and the handle  6  may be left exposed.  
      Referring to  FIG. 8 , here the strands  10  themselves are formed with a spring portion  36 , namely, the spring portion  36  is an integral part of the strands  10 . The spring portion may be loosely or tightly wound and may be coated with an abrasive layer  14 .  
      While the strands  10  illustrated hereinbefore have been shown as having a circular cross-section, this need not necessarily be the case. For example, in  FIGS. 9A and 9B  there are shown non-circular strands  10  having an integral spring portion  38  of a non-circular, multi-sided cross-section. This type of configuration provides the strands  10  with sharp edges having improved cutting capabilities along the periphery. Also, the non-circular cross-section renders the strands  10  with greater surface areas to which the abrasive coated layer is applied, thus increasing abrasion without substantially increasing the diameter of the strands.  
      A proposed automatic process for manufacturing the endodontic device  2  will now be described. A long strand or twisted cable, preferably supplied coiled on a reel, is pulled and intermittent portions thereof are dipped or otherwise covered with coat blocking layer. The strand or cable is then continuously passed in an electro plating bath for the process of coating abrasive layer embedded in a thin nickel binder to form effective portions  4 . The strand or cable is then dipped in a solvent bath to remove the blocking layer and directed continuously into a plastic injection mold machine for the molding of the coupling head  8  directly on the strand or cable. The coupling member  6  composed of thermoplastic elastomer is preferably over molded as a second step in a multi component molding machine, while optionally leaving non-coated portions  20  between said effective section and said coupling head  8 , and member  6 . The last step includes cutting the strand or cable between the effective section  4  and the coupling head  8 .  
      In operation and with reference first to FIGS.  10  to  14 , when a multi-strand twisted portion is used, it will act differently when rotated in a sense further tightening the twist, or in the opposite sense releasing the twist and spreading out the individual strands.  
      Seen in  FIG. 10  is a portion  40  of a strand inserted into a root canal  42  of a tooth  44  showing the internal dentine layer  46 . During a first step, the strand section of the endodontic device is inserted into the root canal  42  to the apex, preferably measured by an electronic apex locator. During a second step ( FIG. 11 ), the strands are mechanically rotated by a handpiece (shown in  FIG. 14 ) to moderate or high speed. The thin, flexible portion  40  of the device is not able to hold the radial centrifugal forces developed; therefore it contacts the canal wall following the natural curvature and complex cross-section of the root canal in exact manner. As also seen in  FIG. 12 , which is the cross-section A-A of  FIG. 10 , the thin portion  40  of the device  2  mainly follows an oval canal cross-section. The locations of the thin portion of the device  2  are shown as if a series of high speed camera shots are captured on the same film. During an optionally third step ( FIG. 13 ), the portion  40  is rotated in an opposite sense to that of the second step, while slight pressure can be applied in the direction of arrow P. During this special mode of operation, each of the free strands will better follow even a small local widening or indent of the root canal such as the area referenced  48 .  
      Similarly, using a device according to the embodiment of  FIGS. 8 and 9 A, when the device  2  is rotated in the same sense of the winding of the spring portions  36 ,  38 , the diameter of the spring tends to decrease and adapt itself to the diameter of the root canal  42 . When, however, the device  2  is rotated in a sense opposite to the winding of the spring, the diameter of the latter tends to increase and during operation, tends to cling to the wall of the root canal  42  and perform a more prominent abrasive action.  
      During endodontic treatment it is usually required to intermittingly or constantly irrigate the root canal. The irrigation becomes even more important when using high-speed operation. The present invention also proposes a complement irrigation system to be used in conjunction with the endodontic device disclosed above.  
      The irrigation system illustrated in FIGS.  14  to  16  is composed of a flexible pipe  50 , stiffened at its end portion with a metal stiffener  52 , and equipped with a nozzle  54 . The pipe  50  is attached to a standard hand piece  56 , e.g., with suitable an elastic or plastic strip  58 . A valve  60  is fitted over the flexible pipe  50  normally blocking the pipe by clamping jaws. When required, the dentist can admit a small amount of irrigant during the endodontic treatment. The nozzle  54  is adjusted to spray the irrigation fluid on the active portion of the device  2 , on demand.  
      The invention further proposes three options of delivering the irrigation fluid to the pipe  50  and nozzle  54 . Referring to  FIG. 14 , a small U-shaped reservoir  62  attached to the hand piece  56 , suitable to withstand certain pressure, is partially filled with irrigant and pressurized with air through a one-way needle valve  64 . The reservoir outlet is connected to the flexible pipe  50 .  
      With reference to  FIG. 15 , a second option is shown, with a bigger pressurized reservoir  66  hung or fixed to a stand-alone base. A foot-operated valve  68  is used to release irrigant from the pressurized reservoir  66  through a long flexible pipe connected to the handpiece.  
      Referring to  FIG. 16 , a third option is suggested where the outlet of an optionally distant, vented, reservoir  70  is connected to an electric pump  72 , operated by a manual or foot switch (not shown). The pump outlet is connected to the hand piece  56  with a long flexible pipe  50 .  
      It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.