Abstract:
An apparatus for controlling asymmetrical coasting of an endodontic reciprocating motor includes a controller operatively connected to the endodontic motor. The controller may include a processing unit that is configured to direct the rotation of the endodontic motor in the forward direction for a coast time and configured to direct the rotation of the endodontic motor in the reverse direction for a coast time. The forward coast time is separately calculated from the reverse coast time. A method for asymmetrically coasting a reciprocating endodontic motor includes rotating an endodontic motor in a forward direction and calculating a forward coast time for the forward direction and coasting the endodontic motor in the forward direction for the calculated forward coast time. After coasting the endodontic motor in the forward direction, the endodontic motor is rotated in a reverse direction. The reverse coast time is different than the forward coast time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/608,946, filed on Mar. 9, 2012, the disclosure of which is expressly incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to an apparatus and a method for enhancing the performance of an endodontic motor for use during endodontic treatment. 
     BACKGROUND 
     Root canal therapy may include clinical instrumentation that is driven by an endodontic motor. Endodontic motors have traditionally been designed to maintain constant rotation of between 300 RPM and 1000 RPM. Typically, a clinician sets the rotation speed. Despite the application of variable torque and friction to the motor during use, constant motor rotation is often maintained by a feedback control loop that dynamically monitors and then acts to maintain the speed of the motor. In this manner, the power output to the endodontic motor varies in accordance with the variable torque and friction observed by the motor to maintain the preset motor speed. 
     More recently, developments within the endodontic field suggest a performance benefit from a reciprocating endodontic motor. Reciprocating endodontic motors drive the rotor and attached endodontic drill or file through a clockwise rotation and then a counterclockwise rotation. This clockwise-counterclockwise rotation cycle may be repeated very rapidly during treatment. By way of example, the reciprocating endodontic motor may rotate a file clockwise 160 degrees followed by a counterclockwise rotation of 40 degrees. This reciprocating motion may be repeated with any combination of clockwise and counterclockwise rotations of differing degrees to create novel and complex filing cycles. Moreover, by introducing two directions of movement, the attached drill or file has two potentially useful directions, each rotation direction of which is capable of specialization. For instance, a file may be designed for dual use such that it may cut while rotating clockwise, but grind or buff while rotating counterclockwise. 
     A further modification to the reciprocating endodontic motor is a coast feature. In this regard, at the end of a clockwise or counterclockwise rotation, the motor and attached file will coast under only the influence of its own momentum. For example, an endodontic motor programmed with the coast feature may be programmed to drive a file through a 120 degree clockwise rotation followed by an 80 degree counterclockwise rotation. Following the 120 degree clockwise rotation, the endodontic motor and attached file will continue to rotate, but such rotation will be the result of coasting beyond the specified clockwise rotation. Thus, coasting occurs prior to beginning a counterclockwise rotation of 80 degrees. Regardless of the prescribed angular values, the coast feature permits additional, though unpowered, rotation of the endodontic motor. The amount of such additional rotational coast is dynamically determined and may depend on the time permitted to coast, the angular momentum of the system, and/or the amount of friction encountered by the system. It will be appreciated that generally angular momentum of the motor increases coast time while increased friction reduces coast time. 
     As applied to reciprocating endodontic motors, the coast feature is a desirable feature because it allows the motor and file to dynamically and automatically respond to various and complex environmental factors, including the specific anatomy encountered during root canal therapy. Rather than the traditional preset and forced control drive which forces a highly prescribed motion, the coast feature allows for greater flexibility of rotational movement. For instance, where the file is spinning freely within the root canal, coast will allow the file to continue spinning while also cutting efficiently to reduce the time to complete the procedure. On the other hand, where the file encounters increased friction due to resistance, coast will decrease the rotation of the endodontic motor to reduce torsional and bending loads applied to the file. In either case, the coast feature provides significant procedural benefits. 
     Presently, a clinician must choose an amount of coast that is symmetrically applied to the tool. That is, coasting following a clockwise rotation is the same as the coasting following a counterclockwise rotation. Unfortunately, different tools create different frictional forces, which, in turn, affect the amount of optimal coast for a counterclockwise rotation and a clockwise rotation. For instance, a file cutting in the clockwise direction will encounter greater friction and resistance than the same file which produces a buffing action in the counterclockwise direction. Such divergent uses may force a clinician to choose a coast for either cutting or buffing, but not both simultaneously. Thus, a clinician desiring a particular coast in the clockwise direction must also accept this coast in the counterclockwise direction due to the nature of such symmetrical coast control. Identical coast settings are not necessarily advantageous, because significant rotation in the counterclockwise direction may lead to undesirable procedural phenomena such as extrusion of canal debris out of the canal apex, creating post operative pain for the patient. 
     There is a need for an apparatus and method for use in endodontic procedures, such as root canal therapy, that addresses present challenges and characteristics such as those discussed above. 
     SUMMARY 
     The present invention overcomes the foregoing and other shortcomings and drawbacks of endodontic motor control systems heretofore known. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention. 
     In accordance with the principles of the present invention, an apparatus for controlling asymmetrical coasting of an endodontic reciprocating motor comprises an endodontic motor capable of rotating a tool in a clockwise direction and in a counterclockwise direction. The apparatus further comprises a controller operatively coupled to the endodontic motor. The controller is capable of transmitting electronic signals to the endodontic motor to change the direction of rotation of the tool from the clockwise direction to the counterclockwise direction. The controller is capable of controlling a forward coast time during which the endodontic motor coasts in the clockwise direction and controlling a reverse coast time during which the endodontic motor coasts in the reverse direction. The forward coast time is different from the reverse coast time. 
     In one embodiment, the controller includes a processing unit operatively connected to the endodontic motor. The processing unit is configured to direct the rotation of the endodontic motor in the forward direction for a forward coast time and configured to direct the rotation of the endodontic motor in the reverse direction for a reverse coast time. The processing unit is configured to calculate the forward coast time separately from the reverse coast time. 
     In accordance with the principles of the present invention, a method for asymmetrically coasting a reciprocating endodontic motor, comprises rotating an endodontic motor in a forward direction and determining a forward coast time for the forward direction. The method further includes coasting the endodontic motor in the forward direction for the determined forward coast time, and, after coasting the endodontic motor in the forward direction, rotating the endodontic motor in a reverse direction. The method further includes determining a reverse coast time for the reverse direction separately from the determined forward coast time. The reverse coast time is different than the forward coast time. The method further includes coasting the endodontic motor in the reverse direction for the determined reverse coast time. 
     In one embodiment, determining the forward coast time includes calculating the forward coast time based on a forward coast setting. 
     In one embodiment, determining the reverse coast time includes calculating the reverse coast time based on a reverse coast setting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
         FIG. 1  is a perspective view of one embodiment of an apparatus for controlling asymmetric coasting of an endodontic motor; 
         FIG. 1A  is a block diagram of the apparatus of  FIG. 1 ; and 
         FIG. 2  is a flow chart of one embodiment of a method for asymmetrically coasting a reciprocating endodontic motor according to another aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , in one embodiment of the present invention, an apparatus for controlling asymmetric coasting of an endodontic reciprocating motor  10  includes a console  14  and an on/off control switch  16 . The console  14  may be operatively coupled to a motor handpiece  12  that is configured to couple to and rotate a tool for use in endodontic treatment. In particular, as is described below, the apparatus  10  is configured to rotate the tool in both the clockwise and counterclockwise directions during a single endodontic operation. The clockwise and counterclockwise rotations may be iteratively repeated over very short periods of time, for example, on the order of seconds or less. The apparatus  10  is also configured to allow the tool to coast in each of the clockwise and counterclockwise directions for a predetermined period of time. This may be referred to as the “coast time” herein. Further, as used herein, the term “coast” means that the rotation of the tool is unpowered. In other words, rotation of the tool is not being forced or acted upon by the apparatus  10 . Allowing the tool to coast for a long period of time may result in the tool coming to rest or a complete stop without internal braking of the rotation thereof. By contrast, coasting does not include intentionally reducing the rotation rate of the tool by braking the motor or by other means internal to the apparatus. However, friction inherent in the construction of the handpiece  12  and between the tool and its environment, such as a tooth surface, is contemplated. 
     In the representative embodiment shown, the motor handpiece  12  is operatively coupled to the console  14  via a cable  18 . As is known, the cable  18  may transmit electrical or mechanical power and provide a pathway for electrical feedback from the motor handpiece  12  to the electronics (not shown) housed within the console  14 . It will be appreciated that the motor handpiece  12  may not require a cable connection to the console  14 , as cordless-type motor handpieces are known in the art. Similarly, the on/off control switch  16 , as represented by the foot pedal shown, may be operatively coupled to the console  14  and associated electronics via a power cable  20 . A clinician may utilize the control switch  16  to turn the electrical power to the motor handpiece  12  on and off during endodontic treatment. 
     With continued reference to  FIG. 1 , in one embodiment, the motor handpiece  12  includes a motor  22  and a gearbox  24  operatively coupled to the motor  22 . Motor handpieces that may be coupled to the apparatus  10  are known in the art and include brushless DC motors. As is known, these motors may contain sensors by which the rotor rotation is monitored, for example. The gearbox  24 , which may be referred to as a contra angle, may further include a head  26  that is configured to hold an endodontic tool  28 , such as, an endodontic file. Energizing the motor  22  causes rotation of a rotor which, in turn, rotates the linkage in the gearbox  22  and ultimately rotates the tool  28  for use in treatment. By way of example, the gearbox  24  may have a gear ratio of 4:1, 8:1, 18:1, or 20:1. Alternatively, the gearbox  24  may have a ratio of 1:10. It will be appreciated that other endodontic tools may be utilized with the apparatus for controlling asymmetrical coasting of an endodontic reciprocating motor  10 . Thus, in one embodiment of the invention, the tool  28  is rotated in one direction for a predetermined number of rotations or time, electric power to the motor  22  is shut off or removed, which allows the tool  38  to coast for a predetermined coast time, and, once the predetermined coast time is reached, the tool  28  may be forcibly brought to a stop by braking. Once the brakes are applied, the coast ends. The direction of the tool  28  is then reversed though, according to embodiments of the present invention, the predetermined coast time for the reverse direction is different. According to embodiments of the present invention, the coast time following a clockwise rotation of the tool  28  is separately controlled from the coast time for a counterclockwise rotation of the tool  28 . 
     As introduced above, in one embodiment, the apparatus  10  is configured to rotate the tool  28  in a clockwise direction and is also configured to rotate the tool  28  in a counterclockwise direction. While the clockwise direction may be referred to herein as the forward direction and the counterclockwise direction may be referred to as the reverse direction, such reference is merely for the convenience of description and embodiments of the present invention are not limited to any specific association between forward or reverse and clockwise or counterclockwise. 
     In the representative embodiment shown, the apparatus  10  includes a control panel  30  by which a clinician may select an operating mode of the apparatus  10 . In this regard, the control panel  30  may include numerous pushbuttons  32  by which the clinician can set parameters that ultimately control the rotation of the tool  28 . Once selected, an individual parameter may be displayed on screen  34 . Of the available parameters, it will be appreciated that the apparatus  10  may be operated in a clockwise rotation mode, a counterclockwise rotation mode, or a reciprocating mode. In one embodiment, in the reciprocating mode, control of the coast time in the forward direction is separate from the control of the coast time in the reverse direction. Thus, in one embodiment the forward coast time is different from the reversed coast time, as is described more fully below. 
     In particular, and in one embodiment of the present invention, the clinician may select a reciprocating mode for operation of the motor  22  during endodontic treatment. The reciprocating mode includes coasting of the tool in the forward and reverse directions. The coast time in each direction may be asymmetric or different. In this regard, the term “asymmetric” refers to the capability of the apparatus  10  to allow the tool  28  to coast for a preset period of time when rotated in the clockwise direction and/or to allow the tool  28  to coast for a preset period of time when rotated in the counterclockwise direction. The apparatus  10  may thus include independently selectable parameters for each of the clockwise coast and the counterclockwise coast. 
     In one embodiment and with reference to  FIG. 2 , once the reciprocating mode is selected, the clinician may select, via the pushbuttons  32  ( FIG. 1 ), a desired coast setting for coast in the forward direction, i.e., “Forward Coast,” at  40 . The clinician may, in addition or alternatively, select (via pushbuttons  32 ) a desired coast setting for the coast in the reverse direction, i.e., “Reverse Coast,” at  42 . The clinician may also independently select a forward motor speed for the endodontic motor  22  and/or a reverse motor speed for the endodontic motor  22  at  44  and  46 , respectively. 
     Once the clinician selects the desired parameters, as described above, the apparatus  10  calculates the forward coast time for the forward coast and/or the reversed coast time for the reverse coast at  60 . The resulting forward coast time and/or reverse coast time as indicated at  48  are utilized to control coasting of the tool  28  during endodontic treatment. Other factors that may be used by the apparatus  10  to control the coasting of the tool  28  may include the angular momentum of the endodontic motor  22  at  52  and/or torsional and frictional forces applied to the endodontic motor  22  at  50 . As is noted in  FIG. 2 , in one embodiment, the apparatus  10  may ultimately calculate the amount of dynamic angular rotation in one or both of the forward and reverse coasts, as is indicated at  54 . 
     As noted above, the clinician may select a coast setting for each of the forward coast and the reverse coast. In general, the coast setting may affect the time that the tool  28  coasts in a given direction. In one embodiment, the desired coast setting for the forward direction is directly related to or is numerically scaled to the amount of coast time observed by the tool  28  in the forward direction. In other words, if the clinician desires more coast time in a particular rotation direction, the clinician may simply set a relatively greater coast setting, for example, by activating a pushbutton  32 , for that direction. Similarly, the desired coast setting for the reverse direction may be directly related to or be numerically scaled to the amount of coast time observed by the tool  28  when rotating in the reverse direction. In this sense, the clinician may independently select a coast setting for each of the forward and reverse directions that is optimal for a particular tool. It will be appreciated that the selection may be based upon the clinician&#39;s experience with a particular tool, the treatment desired, the patient&#39;s anatomy, among other factors. Ultimately, the selected parameters affect the amount of dynamic angular rotation during one or both of the forward and/or reverse coasts as is indicated at  54 . 
     In one embodiment, the coast setting is numerically scaled to increase or decrease the amount of time the endodontic motor allows for one or both of the forward and reverse coasts of the tool  28 . Thus, by increasing the coast setting, the permitted dynamic angular travel is increased or, by decreasing the coast setting, the permitted dynamic angular travel is decreased. By way of example only and without limitation, the numerical scale may include predetermined from values of −7 to +7. In this case, −7 may provide for the least amount of coast time, and +7 may provide for the most coast time. By way of further example, a setting of −7 may equate to a coast time range from 0 milliseconds to 24 milliseconds and a setting of +7 may equate to a coast time range from 60 milliseconds to 90 milliseconds. Coast settings of from −7 to +7 may fall approximately between the range of 0 milliseconds to 90 milliseconds in accordance with one embodiment of the electronic control algorithm. 
     In one embodiment, while the apparatus  10  may provide the controls to vary the coast time for both forward and reverse directions per a coast setting, as described above, the available parameters are not limited to the coast setting. Rather, with reference to  FIG. 2 , the apparatus  10  may include additional parameters by which the endodontic motor  22  may be operatively controlled to account for applied torque and friction at  50  and/or angular momentum of the handpiece/tool at  52 . Such additional metrics may be beneficial to promote greater procedural efficiency as well as to improve the effective life of the endodontic motor  22  and/or the tool  28 . 
     In one embodiment, and with reference to  FIG. 1A , the apparatus for controlling asymmetrical coasting of an endodontic reciprocating motor  10  includes a controller, which in the representative embodiment is a CPU or a processing unit  70 , a memory  72 , a motor interface  74 , and input/output (“I/O”) interface  78 . The I/O interface  78  may be configured to receive data or signals from the control panel  30 , and in particular the pushbuttons  32 , and from the on-off control switch  16  that are then communicated to the processing unit  70 . The I/O interface  78  may be configured to output data from the processing unit  70  to the control panel  30 , and in particular, to the display  34 . Though not shown, other devices external to the housing may include additional user input devices such as a keyboard, a keypad, a mouse, a microphone, etc. Embodiments of the present invention are not limited to the external devices shown. The memory  72  is configured to store a software module or an application  80 , such as, an electronic control algorithm, as described below, and an operating system  82 . The application  80  and operating system  82  each generally comprise one or more instructions stored as program code that may be read from the memory  72  by the processing unit  70 . The instructions, when executed by the processing unit  70 , may cause the processing unit  70  to perform one or more operations or calculations to thereby perform the steps necessary to execute steps, elements, and/or blocks according to various embodiments of the invention. The memory  72  may represent random-access memory (RAM) comprising the main storage of a computer, as well as any supplemental levels of memory, e.g., cache memories, non-volatile backup memories (e.g., programmable or flash memories), mass storage memory, read-only memories (ROM), etc. 
     The coast setting is operatively implemented via the processing unit  70  of apparatus  10 . In this regard, the apparatus  10  may include various pre-programmed operating modes that include predetermined asymmetric coast times. The modes may be stored in the memory  72  that is accessible by the processing unit  70 . Advantageously, the pre-programmed operating modes may include specific parameters for the coast time and the rotation rate for each of the forward and reverse rotation directions. These specific predetermined parameters may be based on prior experience with a particular tool, a particular motor, and/or a particular treatment. In one embodiment, the pre-programmed operating modes preclude any changes to either the forward or reverse coast setting by the clinician. Thus, at least the forward coast setting and the reverse coast setting for a particular pre-programmed operating mode are factory settings. 
     Furthermore, it will be appreciated that while the apparatus  10  includes a process unit  70  and other components for controlling the coast of the tool, one of ordinary skill will observe that the controller, which may not be the processing unit  70 , determines the coast of the tool according to embodiments of the present invention. The controller may include fixed hardware and electrical timing circuits capable of controlling the forward coast time and the reverse coast time. In this embodiment, the forward and the reverse coast time may not be adjustable or selectable. Rather, these times are factory settings, similar to that set out above. Embodiments of the present invention are therefore not limited to the use of a processing unit, though use of fixed hardware would generally preclude software control and would thus make adjustments to the coast setting substantially more complex. 
     In view of the apparatus  10  described above, a clinician, who has selected a particular tool for a particular endodontic procedure may simply select, via the pushbuttons  32 , the desired operating mode that includes all of the optimum parameters for that tool and procedure, for example. Therefore, once the preprogrammed operating mode is selected, the processing unit  70  automatically loads the pre-determined values for the coast setting with respect to a desired coast time for one or both of the forward and reverse directions. The processing unit  70  may then provide one or more signals to the motor interface  74  that then controls the rotation of the motor  22  by regulating the power to the motor  22  according to the one or more signals from the processing unit  70 . The apparatus  10  may further include a feedback loop  76  by which rotation of the rotor of the motor  22  may be monitored by the motor controller  74  and/or the processing unit  70 , according to known methods in the art. Feedback electrical signals from the motor  22  may be processed by the processing unit  70  and/or the motor interface  74  according to the loop  76  so that the processing unit  70  and/or the motor interface  74  may change the control signal or power to the motor  22  to make adjustments to the rotation of the tool  28 . 
     In one embodiment, the apparatus  10  includes an electronic control algorithm  80 . In particular, the electronic control algorithm  80  may be stored in the memory  72  and when the clinician desires control of the forward coast time and/or the reverse coast time by the processing unit  70 , the control algorithm  80  may accessed and utilized by the processing unit  70 . In one embodiment, and with reference to  FIG. 2 , the processing unit  70  calculates the forward coast time and/or the reverse coast time via the electronic algorithm at  60 . As shown, this calculation may include various parameters, including the coast setting at  40  and  42  and the angular speed for one or both of the forward and reverse directions at  44  and  46 . The output from this calculation is the forward coast time for the forward coast and the reverse coast time for the reverse coast, as is indicated at  48 . 
     With continued reference to  FIG. 2 , a representative electronic control algorithm for controlling a reciprocating endodontic motor is shown at  60 . The electronic control algorithm may provide the necessary output to cause the endodontic motor to rotate for a predetermined amount of coast time in one or both of the forward and reverse directions. As shown, the electronic control algorithm calculates the forward coast time and reverse coast time via the preset algorithm:
 
Forward Coast Time [sec]=(−0.00005)(Forward Angular Speed)+(0.08)+(0.0044)(Forward Coast Setting)
 
and
 
Reverse Coast Time [sec]=(−0.00005)(Reverse Angular Speed)+(0.08)+(0.0044)(reverse Coast Setting).
 
By so doing, the dynamic advantages of coasting are more effectively implemented within a reciprocating endodontic motor.
 
     The program code embodied in any of the applications described herein is capable of being distributed as a computer program product of various different forms. In particular, the program code may be distributed using computer readable storage media. Computer readable storage media are inherently non-transitory, and may include volatile and non-volatile, and removable and non-removable tangible media implemented in any manner. Computer readable storage media may further include random access memory, read-only memory, erasable programmable read-only memory, electrically erasable programmable read-only memory, flash memory or other solid state memory technology, portable compact disc read-only memory, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be read by a computer. The program code may also be distributed using communication media, which may embody computer readable instructions, data structures, or other program modules. Communication media may include wired and wireless media. 
     While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.