Abstract:
The invention provides an assembly for measuring the penetration depth of a dental instrument into a root canal of a tooth. The assembly has a base element configured to be clampingly braced onto a tooth to be treated; an electrically conductive guiding member affixable to the base element and disposed, when assembled, above the tooth, thereby, in use, a portion of the dental instrument makes electrical contact with it. The guiding member further includes an electrical terminal connectable to an apex location measuring device. Methods for continuously measuring penetration depths of a dental instrument into a root canal of a tooth are also provided.

Description:
FIELD OF THE INVENTION 
   The present invention relates to dental instruments and more particularly to assemblies and methods for measuring and indicating penetration depth of a dental instrument into a root canal of a tooth. 
   BACKGROUND OF THE INVENTION 
   There are known in the art devices for measuring and indicating the penetration of a dental instrument into a tooth, e.g., for root canal treatments. Such devices, called apex locators, identifying the location of the biological apex, are based on relative measurement between a flexible disc-shaped depth stopper, slidingly affixed on the shaft of a dental instrument, leaning against the upper surface of the tooth to be treated, and a predetermined bore length which is believed the tooth can accommodate. It can be easily realized that the use of, and dependency on, the reference marker such as a flexible disc-shaped stopper, leaning against or touching the uneven wavy upper surface of a tooth, is less than desirable when it is necessary to attain accuracies of less than e.g., 0.5 mm. To be on the safe side, dentists take a precautionary distance of say between 0.5 mm and 1 mm from the predetermined apex, thereby leaving the edge of the root canal untreated, eventually constituting a source for development of future infection. 
   SUMMARY OF THE INVENTION 
   It is therefore a broad object of the present invention is to ameliorate the above shortcoming of the known technique of measuring the depth of a tooth root canal and to provide assemblies and methods for more accurately determining the apex location. 
   It is a further object of the present invention to provide assemblies and methods for accurately determining the root canal apex, while maintaining the dental instrument drilling or filing in the root canal substantially free for manual manipulation by the dentist. 
   In accordance with the invention, there is therefore provided an assembly for measuring the penetration depth of a dental instrument into a root canal of a tooth, comprising a base element configured to be clampingly braced onto a tooth to be treated; an electrically conductive guiding member affixable to said base element and disposed, when assembled, above said tooth, thereby, in use, a portion of said dental instrument makes electrical contact with it, and said guiding member further including an electrical terminal connectable to an apex location measuring device. 
   The invention further provides a method for continuously measuring penetration depth of a dental instrument into a root canal of a tooth, comprising clamping an electrically conductive guiding member above a tooth; connecting an apex location measuring device to said guiding member, and making contact between a dental instrument having a pin-shaped electrically conductive portion and the electrical conductive guiding member. 
   The invention still further provides a method for continuously measuring penetration depths of a dental instrument into a root canal of a tooth, comprising clamping a base element on a tooth to be treated; providing a conductive guiding member; at least indirectly affixing said conductive guiding member on the base element, above and in alignment with, said tooth; connecting a device for measuring penetration depth of a dental instrument into a tooth; providing a dental instrument having a pin-shaped electrical conductive portion, and making contact between said pin and guiding member, whereby upon a point along said conductive portion of the pin making contact with the guiding member, the device measures the penetrating depth and provides an indication thereof. 

   
     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  illustrates the assembly for measuring the penetration depth of a dental instrument into a root canal of a tooth, according to the present invention; 
       FIG. 2  is an enlarged exploded view of the assembly of  FIG. 1 , according to the present invention; 
       FIG. 3  is a side view of the assembly as mounted on a tooth; 
       FIG. 4  illustrates stages of mounting the assembly on a tooth; 
       FIG. 5  is a perspective view of another embodiment of the present invention; 
       FIG. 6  is a perspective of still a further embodiment of the present invention; 
       FIGS. 7 and 8  are side views illustrating the steps in assembling the assembly shown in  FIG. 6 ; 
       FIG. 9  is an exploded view of a modification of the present invention; 
       FIG. 10  is a perspective view of the assembly of  FIG. 9 ; 
       FIG. 11  is an exploded view of a further modification of the present invention, and 
       FIG. 12  is a perspective view of the embodiment of  FIG. 11 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The assembly  2  for measuring the penetration depth of a dental instrument into a tooth according to the present invention is illustrated in  FIG. 1 . Also illustrated is an electronic apex locator device  4  for continuously processing, displaying or otherwise indicating the depth of penetration of the dental instrument into the tooth during treatment. As seen, the device  4  is electrically connectable to the assembly, preferably by means of a plug  6  and socket  8  connection, however, the device  4  may just as well be directly plugged into a socket arranged at  10  (not shown), presently the connection point of the plug  6 . Since the device  4  is per-se known, and does not constitute a part of the assembly  2  according to the present invention, no further detailed description is necessary. 
   Referring now also to  FIGS. 2 and 3  showing the preferred embodiment of assembly  2  in detail, it should be pointed out that while the Figures illustrate three major components of which the assembly  2  is composed, in fact the invention can be realized with two components only, namely, with a base element  12  and an electrically conductive guiding member  14 . The third optional bracket  16  conveniently serves two purposes: clamping the guiding member  14  to the base  12 , and insulating the metallic guiding member  14  from the base  12  which, due to considerations of strength, is usually made of metal. 
   The base  12  is configured in the form of an Ω, the two legs  18 ,  20  of which are adapted to be fastened on two opposite sides of a tooth  22 , while the plane of the arched portion  24  is laterally displaced from the legs  18 ,  20 , so as not to obscure the upper surface of the tooth  22 . 
   The guiding member  14  has two interconnected portions, a first portion  26  made with an aperture  28  facilitating its connection, at least indirectly, to the base element  12 , by means of a screw  30 . The plane of the second portion  32  is vertically offset from the plane of the first portion  26 , so as to extend in close proximity to the upper surface of the tooth  22 , when assembled. The portion  32  has an opening  34  e.g., in the form of a hole or a slot, the diameter or the width of which is such as to allow the shaft  36  of a standard dental instrument  38 , e.g., a drilling or filing instrument, to pass therethrough with clearance. 
   The bracket  16 , made of an insulating material, is advantageously, similarly Ω-shaped, the two opposite sides of which are configured to straddle the flanks of the arched portion  24  of the base element  12  while a flat roof portion  40  abuts against the top section of the arch. If the bracket  16  is used, the guiding member  14  is screwed or otherwise coupled to the bracket by means of the threaded hole  42 . The flanges  44 ,  46  of the bracket  16  are furnished with pegs  48 ,  50 , configured to be pressure-fit into holes  52 ,  54  of legs  18 ,  20 , so as to fixedly tighten the bracket  16  onto the base element  12 . 
   It can now be understood that instead of the bracket  16 , the guiding member  14  may be insulated at the portion where it makes contact with the metallic base element  12 , and thus, the guiding member  14  may be directly coupled onto the base element  12 , without short-circuiting. Obviously, guiding member  14  may, similarly, be made with insulated side sections providing better support thereof on the base element  12 . 
   A preferred method of utilizing the assembly  2  will now be described with reference to  FIG. 4 . First, the base element  12  is clamped around the tooth  22  with the aid of a suitable tool, the edges of which are advantageously inserted in holes  52 ,  54  made in the legs  18 ,  20  for this purpose. After the base element  12  is clamped around the tooth  22 , the guiding member  14  is screwed onto the bracket  16  and the combined unit is pressure fitted over the base element  12 . The aperture  28  allows fine adjustment of the guiding member  14  above the tooth  22  in the direction of arrow A, as well as allows its swivelling, as indicated by arrow B, so as to align the slot above the required drilling and filing point in the tooth. The plug  6  is inserted in socket  8  and the assembly  2  in position, is now ready to accommodate the shaft  36  of the dental instrument  38 . 
   Upon drilling or filing, the shaft  36  continuously or intermittently contacts the side walls of the opening  34 , thereby closing an electrical circuit in the apex locator device  4  and activating same. It operates on the principle of impedance measurements between two electrodes, the first electrode constituted by the point on the shaft  36  of the instrument  38 , making contact with the opening  34  of the guiding member  14 , and the second electrode constituted by the electrode  56  ( FIG. 1 ), which measurements differ depending on the frequencies. The device  4  monitors the changes in impedances, as the shaft  36  of the instrument  38  approaches the apex. The measurements performed and indicated by the apex locator device  4  are actually per-se known, e.g., from International Patent Application No. PCT/IL02/00556. 
     FIG. 5  illustrates another embodiment according to the present invention showing a base element  12  made of electrical insulating material, e.g., plastic, or alternatively, is plastic coated, and a guiding member  14  directly attachable thereon by means of the screw  30 . Also seen is a plug  58  for electrically connecting to a suitable socket  8  of an apex locator device  4  (not shown). 
   A slight modification of the embodiment of  FIG. 5  is shown in  FIGS. 6 to 8 . Accordingly, the base element  12  is formed with flexible ledges  60 ,  62  and the bridge-like conductive guiding member  14  is formed with inwardly curved lips  64 ,  66 , configured to substantially match the curvature of the ledges  60 ,  62 . The inter-connection between the base element  12  and guiding member  14  is thus effected in two stages, as illustrated in  FIGS. 7 and 8 . First, the lip on one side of the guiding member  14  is hooked into one ledge, say lip  66  into ledge  62 , and thereafter, the other lip  64  is pressed into place in ledge  60 . The conductive element  14  can be moved in the direction of Arrow C during use. While guiding member  14  of  FIGS. 1 to 5  is oriented across the base element  12 , the guiding member  14  of  FIGS. 6 to 8  extends parallel thereto. In both cases, however, the opening  34  in guiding member  14  is located above the tooth  22  and is not obscured by the base element  12 . 
   A further modification is illustrated in  FIGS. 9 and 10 . This assembly of this embodiment, similar to the embodiment of  FIG. 2 , is composed of three parts: the standard base element  12 , an electrically non-conductive bracket  68  and an resilient electrically conductive guiding member  70 , advantageously made of a bent electrical wire. The bracket  68  is composed of an arched portion  72  and two side shoulders  74 ,  76  and is configured to be press-fitted onto the base element  12 , so as to straddle at least the arched portion  24  thereof and be fixedly retained by it. The shoulders  74 ,  76  of the bracket  68  are provided, on their lateral outside surfaces, with recesses  78 ,  80 , for retaining outside loops  82 ,  84  of the resilient conductive guiding member  70 . The loops  82 ,  84  are made with lugs  86 ,  88 , serving as sockets into which a hook-shaped electrical conductor  90 , leading to an electronic apex locator device  4  ( FIG. 1 ), can be inserted. As seen in the drawings, the intermediate portion  92  of the guiding member  70 , made of a meandering piece of wire, defines an opening  94  through which the shaft  36  of a dental instrument  38  can pass and contact the wire defining the opening  94 . The intermediate portion  92 , disposed at a higher level than the level of loops  82 ,  84  and the loops  82 ,  84  are interconnected by pieces of wire  96 ,  98 . 
   Still a further modification of the present invention is illustrated in  FIGS. 11 and 12 . This modification is similar to that of  FIGS. 9 and 10  in that it utilizes an electrically conductive guiding member  100 , constituted by a bent metal wire. The assembly is composed of three parts: a base element  12 , an electrically non-conductive bracket  102  and the resilient conductive guiding member  100 . The bracket  102  is U-shaped, having two parallelly extending legs  104 ,  106  and a web portion  108 . The legs  104 ,  106  define between themselves a slot  110  sized to accommodate the arched portion  24  of the base element  12 . The upper leg  104  has a through-going hole commencing at its front edge  112  and terminating at its top surface at  114 . The size of the hole is calculated to be substantially the same as the diameter of the conductive guiding member  100 . As seen in  FIG. 11 , the conductive guiding member  100  has three major portions: a first portion  116 , in assembly, protruding from the upper leg  104  through the hole at  114 , the portion advantageously being provided with a bent edge  118  for connection with a socket  120 , leading to an electronic apex locator device  4  (see  FIG. 1 ); a second portion  122  being configured to extend inside the leg  104  and exit the front edge  112 , and a third portion  124  extending above a tooth  22  clamped between legs  18 ,  20  of the base element  12 . Portion  124  may also be vertically offset from portion  122 , in the direction of tooth  22 , by a connecting part  126  and may also be provided with a bent extension  128 . 
   As can be understood and seen in the Figures, the non-conductive bracket  102  is preferably produced e.g., by molding together with the guiding member  100 . The bracket  102 , together with the guiding member  100  is slid under pressure onto the arched portion  24  of the base element  12 . In order to assure that the bracket  102 , will stay in place during use, the arched portion  24  may be provided with a cutout  130 , having a width substantially the same as the width of the web portion  108  of the bracket  102  for abutting against opposite sides  132  of the web portion  108 , as can be seen in  FIG. 12 . The portion  116  of the member  100  is resilient, and thus, it can be angularly swung, as indicated by the arrows D in all directions and any convenient angle, and retained in this position, as conveniently disposed by the user. During use, the shaft  36  of the dental instrument  38  makes electrical contact with the portion  124  of the member  100 , conducting the electrical signals from and to the electronic device  4 , e.g., an apex location measuring device. 
   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.