Abstract:
A handpiece for measuring root canal length comprises an outer sleeve that is substantially non-insulating, a connecting device, an instrument carrier, at least one transmission element within the outer sleeve, a length measuring circuit portion, a contact portion and an insulating portion. The instrument carrier is configured to receive a dental instrument. The transmission element transmits force to move the instrument carrier so that a dental instrument received in the instrument carrier executes a rotating, reciprocating and/or vibrating working movement. The length measuring circuit portion is disposed inside the handpiece and operable to transmit measuring signals for measuring length. The contact portion is operable to establish a conductive path between the dental instrument serving as an electrode and the length measuring circuit portion. The insulating portion insulates the length measurement circuit portion and the contact device, through which a voltage is applied during measurement, from the outer sleeve.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 11/239,956, filed Sep. 29, 2005, and claims priority from pending European Patent Application No. 04023260.5, filed Sep. 30, 2004, which are hereby incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present application concerns a dental handpiece for the treatment of root canals and the measurement of the root canal length. 
         [0004]    2. Description of Prior Art 
         [0005]    Such a handpiece is part of a device for the determination of the length (depth) of a root canal and of the position of the treatment instrument attached to the handpiece, respectively. The device comprises, together with the handpiece, two electrodes and a control and evaluation unit. The first electrode, usually in the form of a clip-on electrode, is attached to the oral mucosa of the patient. The instrument attached to the handpiece, for example a file moving back and forth (executing reciprocating movements), a reamer or a rotating dental drill, serves as the second electrode. Both electrodes are connected to the control and evaluation unit. The control and evaluation unit is connected to a current source, which generates a measuring signal, and furthermore includes a measuring device, preferably a measuring circuit, which determines the length of the root canal and the position of the dental instrument, respectively, on the basis of the change in the electrical resistance or the change in the impedance of the measuring signal between the two electrodes. 
         [0006]    From EP 1 444 966 A1, a handpiece is known with which the signal line is implemented by a conducting wire outside of the handpiece, the wire being connected to the dental instrument, serving as the second electrode, with a clip-on connection and a clip holder. The disadvantage with this arrangement is the conducting wire is attached to the sleeve of the handpiece handle, which restricts the manageability of the handpiece. 
         [0007]    In order to avoid this disadvantage, handpieces are manufactured with which conductors or components of the handpiece implement the signal line within the handpiece. DE 197 02 370 A1 (DE &#39;370 A1) discloses an arrangement of conducting wires within the handpiece or in the sleeve of the handpiece which make contact with the instrument serving as an electrode by way of a contact device. In the DE 195 20 765 A1 (DE &#39;765 A1) components serving for the transmission of the drive power, especially shafts and gears, parts of the outer sleeve and components in contact with these components are used for signal transmission. 
         [0008]    With both designs, it is necessary that at least parts of the outer sleeves are insulated in order to prevent the impairment of the measuring circuit due to contact between the handpiece and the oral cavity of the patient or the hand of the user. Insulation may be achieved by manufacturing part of the handle from plastic, as seen in the DE &#39;370 A1. Alternatively, an insulating film can be attached to the outer surface of the outer sleeve, as explained in connection with the DE &#39;765 A1. 
         [0009]    These known handpieces have the disadvantage on the one hand of the greater manufacturing costs due to the coating and on the other hand that plastics used for coating or as a material for the handle sleeve sections are not stable relative to the prevailing ambient conditions for sterilization, particularly steam-sterilization. Since however the handpieces must be sterilized following each use, the life of such coatings or handle sleeve sections is very limited. 
         [0010]    The present application is therefore in response to the need for a dental handpiece for the treatment of root canals and the measurement of the root canal length while at the same time avoiding the disadvantages discussed above. In particular, the handpiece must be insensitive to the prevailing ambient conditions for sterilization. 
       SUMMARY 
       [0011]    In the present application, the outer sleeve of the handpiece described below is comprised of non-insulating, preferably metallic, material and also has substantially no insulating coating. In relation to the prevailing ambient conditions for sterilization, it is therefore insensitive. Furthermore, to ensure faultless measurement of the root canal length and signal line integrity, all components of the handpiece which are part of the device for the transmission of the measuring signals or the contact device, and therefore “live,” are insulated from the outer sleeve by insulating material. The components which establish a conductive path between the device for the transmission of the measuring signals and the instrument serving as electrode are part of the contact portion. 
         [0012]    Parts of the contact device may also be disposed outside of the handpiece. In particular, this is necessary when a dental instrument having a non-conductive shaft is used. Such an instrument, for example a file, is comprised of a metallic—and thus conductive—working area and a shaft attached to this, which is at least partly surrounded (especially in the area in which the spindle is connected to the instrument carrier of the handpiece) by a plastic sleeve. In order to establish a connection between the conductive section of the dental instrument and the device for the transmission of the measuring signals, a contact device is required which makes physical contact with the dental instrument outside of the handpiece. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  shows a sectional view of a first embodiment for the handpiece. 
           [0014]      FIG. 2  shows the head of the handpiece in  FIG. 1  on an enlarged scale. 
           [0015]      FIG. 3  shows a sectional view of a second embodiment for the handpiece. 
       
    
    
       [0016]    The same components are numbered identically in all figures. 
       DETAILED DESCRIPTION 
       [0017]    The contra-angle handpiece  1  illustrated in  FIG. 1  is comprised of an outer sleeve  2  with a head section  3  and a handle section  4 . The entire outer sleeve  2  (including pushbutton  29 ) is not insulating, i.e. it is made substantially of a non-insulating, preferably metallic, material and also has substantially no insulating coating. At the proximal end of the outer sleeve  2  is a connecting device  5  for coupling the handpiece to a control and evaluation unit, a measuring circuit with a current source for the measurement of the root canal length and drive unit. The connecting device  5  is preferably designed in the form of the twist-on connection familiar to dental specialists, so that no further description is necessary here. 
         [0018]    As used herein, the terms “non-conductive,” “insulating” and “insulated” mean that the component or material so described reduces or prevents the transmission of electricity. Conversely, the terms “conductive,” “conducting” and “non-insulating” mean that the component or material so described has the quality of conducting electricity. As would be understood by those of ordinary skill in the art, these terms are used to describe relative rather than absolute qualities. 
         [0019]    The inside of the handle section  4  is interspersed with several elements for the transmission of the drive movement, including a first spindle designated the central drive spindle  6 , a second spindle designated the drive spindle  7 , and a hollow spindle  8 . The drive spindle  7  is received by the distal end of the hollow spindle  8  and fixed by a straight grooved pin  9 . A spring  10  preloads the hollow spindle  8  against the drive spindle  7  and allows an axial play of hollow spindle  8  relative to drive spindle  7 . At the proximal end, the hollow spindle  8  is detachably connected by a carrier  11  to the rotating spindle of the drive unit, preferably an electrical motor. 
         [0020]    The first spindle  6  and second spindle  7  are connected through a gear unit  12 , consisting of two gearwheels  13 ,  14  pressed onto the two spindles  6 ,  7  and supported by several rolling bearings  15 ,  16 ,  17 ,  18  in the coupling and bearing sleeves  19 ,  20 ,  21 . The rolling bearings  15 ,  16 ,  17 ,  18  are pre-stressed by spring washers, as illustrated by way of example for the bearing  18  in  FIG. 2 . Here, the spring washer  56  is mounted in an annular groove of the spacer disk  55 . Another gear wheel  22  is pressed onto the distal end of the first spindle  6 , which meshes with a gear wheel  23 , connected to a hollow spindle, designated the head spindle  24 . The head spindle  24  is simultaneously part of the instrument carrier  25 , which detachably receives a dental instrument in the known manner. The rotary motion of the drive device is thus transmitted via the elements for the transmission of the drive movement  6 ,  7 ,  8  to the head spindle  24 , the instrument carrier  25  and the dental instrument, preferably a rotating dental drill. Instead of the gear wheels  22 ,  23  of course an eccentric gear can be placed between the first spindle  6  and the head spindle  24 , so that the dental instrument, preferably a file, executes stroke (reciprocating) movements. 
         [0021]    A pushbutton  29 , the cover  30  of which is pre-stressed by a spring  31  and the inside of which is provided with wedges  36  ( FIG. 2 ), is provided for releasing the dental instrument from the instrument carrier  25 . Pressing the pushbutton cover  30  in the direction of the opening  31 A of the instrument carrier  25  up to the collar  32  of the supporting ring  33  moves the cylindrical slider  34 , pre-stressed by another spring  35 , radially through the wedges  36  (to the right in  FIG. 2 ) until it is positioned coaxially with the instrument carrier  25  and the user can remove the dental instrument from the instrument carrier  25 . 
         [0022]    The inside of the handpiece  1  also has a device  26  for the transmission of the measuring signal for the length measurement. For the handpiece  1  illustrated in  FIG. 1 , the device  26  is formed by a conducting wire  27 , to which a voltage is applied while performing the length measurement and which is surrounded by a casing  28  of insulating material, in particular plastic. The proximal end of the conducting wire  27  in the region of the connecting device  5  is in the form of the sliding contact  57 , which is joined through the connecting device  5  to a slip ring of the connecting element, for example the drive unit or a coupling. If the connecting device  5  is a non-rotating plug-in connector, the proximal end of the conducting wire  27  is in the form of a contact pin to be seated in a socket connector of the connecting element coupled to the handpiece  1 . 
         [0023]    The distal end of the connecting wire  27  is split into two ends,  27 A and  27 B. At each of the two ends  27 A,  27 B is a contact device  37 A,  37 B, respectively, which establishes a conductive path between the dental instrument serving as electrode and the connecting wire  27 . The contact device  37  B is intended for dental instruments having a non-conductive section and is in the familiar U-shaped form, comprising an elastic wire  38  with two legs  39  (in the sectional view only one leg can be seen). In the frontal end region both legs  39  are curved inward. This curvature region is essentially under the opening  31  of the instrument carrier  25 , so that a dental instrument placed in the instrument carrier  25  runs between the two legs and makes physical contact on two sides of the legs  39 . 
         [0024]    The base  40  of the U-shaped wire  38  is connected to a sleeve  41 , preferably using a terminal connection. At one end, the sleeve  41  has a flange  42  attached, preferably by a cement bond, to the inside of the outer sleeve  2 . A stem  43  of the sleeve  41  projects outwards through a bore  44  in the outer sleeve  2 , with the diameter of the bore  44  smaller than that of the flange  42 . The sleeve  41  on the end opposite the flange  42  has a groove  45  with two ledges  46  and  47 , with the diameter of the groove  45  smaller than the diameter of the base  40  of the U-shaped wire  38 . Since the side walls of the groove  45  have a slight spring mounting, when the user applies pressure while connecting the base  40  to the ledges  46 ,  47  they are pushed aside, so that the base  40  reaches the connective region  45 A of the groove  45  and is fixed by the ledges  46 ,  47  returning as a result of the spring mounting to their original positions. To disconnect the base  40 , the user pulls on the U-shaped wire  38 , causing the ledges  46 ,  47  to again move aside and release the base  40 . 
         [0025]    The end  27 B of the connecting wire  27  is received inside the sleeve  41  and makes contact with the base  40  of the U-shaped wire  38  clamped in the section  45 A of the groove  45 , so that a conductive path is established between the dental instrument serving as electrode, the legs  39  and the base  40  of the wire  38 , the end  27 B and the connecting wire  27  to the sliding contact  57 . 
         [0026]    In order to prevent disturbances in the measuring and signal wire, the sleeve  41  should be in the form of an insulating element, i.e. made of non-conductive material, preferably plastic, or coated with plastic. It is of course possible to use a separate component made of conductive material, for example a spring or a flexing element making contact with the connecting wire  27 , in place of the end  27 B of the conducting wire. 
         [0027]    When using a dental instrument consisting entirely of a conductive material, the user may disconnect the wire  38  from the sleeve  41 . In this case, the contact device  37 A with the end  27 A of the connecting wire  27  serves to connect the dental instrument to the sliding contact  57 . The end  27 A makes contact with the outer ring  48 A of the spring washer  48  via a bore  54  in the socket  49 . The spring washer  48  in turn makes a sliding contact with the head spindle  24 , as part of the instrument carrier  25 , and the dental instrument attached. A voltage is applied to the spring washer  48  with outer ring  48 A and head spindle  24  while executing the measurement of the root canal length. The spring washer  48  is bearing-mounted in the socket  49  and serves for the pre-stressing of the rolling bearing  50 , which is pressed onto the head spindle  24  and supports the head spindle  24  rotatably. A second rolling bearing  51  is analogously arranged on the pushbutton side of the head spindle  24  and fixed by an O-ring  52 , which is bearing-mounted in a ring groove  53  of the supporting ring  33 . As the sliding contact between the head spindle  24  and the connecting wire  27  other elements, such as a brush or a contact pin, can also be used. 
         [0028]    In order to ensure fault-free measurement of the root canal length and signal transmission through the contact device  37 A, at least the following components must serve as insulating means, i.e. must be made of non-conductive material: the socket  49 , the supporting ring  33  and the gearwheel  22  and/or  23 . To obtain better insulation of the outer sleeve  2 , in a preferred embodiment, in addition one or more of the rolling bearings  18 ,  50 ,  51  and/or the spacer disk  55  and/or the first spindle  6  should be made of insulating, i.e. non-conductive, material. In another embodiment, the first spindle  6  is comprised of several spindle sections, at least one of which is in the form of a non-conductive, insulating element. 
         [0029]    The materials used for the components serving as the insulating portion are in particular plastic, preferably PEEK (polyetheretherketone) or silicone, or ceramic materials. Coatings with these materials applied to the components serving as the insulating means also ensure sufficient insulation. Preferably, the raceways and/or the rolling elements of the rolling bearings  18 ,  50 ,  51  are made of ceramic materials, such as silicon nitride, zirconium nitride or silicon carbide. The gearwheel  22 , the supporting ring  33 , the socket  49  and at least part of the first spindle  6  and spacer disk  55  are preferably made of plastic. 
         [0030]    A handpiece can of course be equipped with only a contact device  37 A or  37 B as well, however it is advantageous to implement both contact devices  37 A and  37 B in the handpiece, since this handpiece  1  may then be used with dental instruments having an insulated instrument shaft as well as those not having an insulating instrument shaft. 
         [0031]    The handpiece  100  shown in  FIG. 3  in principle has the same design as handpiece  1 , so that it is not necessary to repeat the detailed description. The entire outer sleeve  2  with handle section  4  and head section  3  (including pushbutton  29 ) is once again made of completely non-insulating, preferably metallic, material and has no insulating coating. 
         [0032]    With the handpiece  100 , the device for the transmission of the measuring signal  26  for the determination of the root canal length consists of the elements for the transmission of the drive movement (first spindle  6 , second spindle  7 , hollow spindle  8 ). A voltage is applied to these elements while executing the measurement of the root canal length, which must therefore be made of conductive material. For dental instruments with a conductive section, the head spindle  24  with gearwheel  23  and gearwheel  22  serve as the contact device  60 A with applied voltage. For dental instruments with a non-conductive section of the instrument shaft, the contact device  60 B must be used in order to establish a conductive path of the dental instrument with the elements  6 ,  7 ,  8  for the transmission of the drive movement via the head spindle  24  and the gearwheels  22 ,  23 . The contact device  60 B consists of a U-shaped elastic wire  38 , connected through its base  40  to the sleeve  41 , preferably using a terminal connection, and a conducting wire  61  with a first end  61 A and a second end  61 B. The first end  61 A is taken up in the sleeve-shaped stem  43  of the sleeve  41 , which makes contact with the base  40  of the U-shaped wire  38 , clamped in section  45 A of the groove  45 . The second end  61 B of the conducting wire  61  is connected through the bore  54  of the socket  49  to the outer ring  48 A of the spring washer  48  ( FIG. 2 ). Via the sliding contact between the spring washer  48  and the head spindle  24 , as part of the instrument carrier  25 , a connection is established through the gearwheels  22 ,  23  to the elements for the transmission of the drive movement  6 ,  7 ,  8 . 
         [0033]    The retransmission of the measuring signals takes place from the hollow spindle  8 , via the driver  11  to the connecting piece coupled to the handpiece  100  through the connecting device  5 , for example the rotor shaft of the drive unit or the shaft of a coupling. 
         [0034]    In order to ensure fault-free measurement of the root canal length and signal transmission through the contact device  60 A, at least the following components should be insulating, i.e., must be made of non-conductive material: the supporting ring  33  and the socket  49 . When using the contact device  60 B, in addition the sleeve  41  should be in the form of an insulating material. Preferably, the conducting wire  61  is also surrounded by an insulating sheath  62 . To obtain better insulation of the head section  3  of the outer sleeve  2 , in another preferred embodiment, in addition one or more of the rolling bearings  50 ,  51  should be made of insulating, i.e. non-conductive, material. 
         [0035]    To insulate the handle section  4  of the outer sleeve  2 , at least the rolling bearings  15 ,  16 ,  17 ,  18  should be in the form of insulating means. Preferably, one or more of the coupling and bearing sleeves  19 ,  20 ,  21  are also made of non-conductive material. The materials for the components comprising the insulating portion are the same as described for handpiece  1 . 
         [0036]    The invention is not limited to the embodiments discussed above, but encompasses all embodiments which do not change the fundamental functional principle of the invention. In particular, the handpiece according to the invention for the measurement of the root canal length does not depend on the type of drive unit and includes pneumatic, piezoelectric or magnetostrictive vibration drives as well. Depending on the type of drive unit, the elements for the transmission of the drive movement to the instrument carrier are different in form and can, for example, also include or vibrating rods or flexible spindles.