Background of the Invention Measurement devices and systems for detecting apical foramen position during root canal treatment have been on the market for a long time. The physical size of all devices is similar and most of them are large table models requiring lengthy wires to connect with the patient so as to measure apical foramen position in the patient's mouth. The technology of all of these devices and systems is not significantly different, and in practice, they more or less accurately measure the length of waves generated in an electronic sensor system, one element of which may be a tooth wherein root canal treatment is to be performed. The existing devices on the market can be categorized as resistance, impedance, frequency-dependent positioning, and ratio method types.

Resistance Type Devices Resistance type devices are exemplified by products such as Sono-Explorer, Foramation IV, Dentometer, and Neo-Sono. These devices suffer from the disadvantages of requiring calibration before each use, and of imparting to the patient a medium-to-light pain from the electric current when in use. These devices are also characterized as cumbersome desk-top units which trail wires to the patient under treatment and generally require their operator to divert his attention from the area of treatment close to the patient's mouth in order to read critical information from a display unit, which is usually located on a nearby table-top or desk, but away from the working area. A further drawback of these devices is electromagnetic interference (EMI), which may preclude their use with heart patients.

Impedence Type Impedence type devices were developed to solve the problem of measuring length of frequency in the presence of a conductor. An example of this type of device is Endocater, which operates at 400KHz and can be placed on the patient's chair so as to contact one of his hands to complete the inductance circuit. However, such a device cannot be used with a digital display and it is doubtful if it is effective for use for patients under the age of 17. There is a need to calibrate this instrument after each use. Although they are more convenient than most desk-top units, these devices require powerful batteries to function properly, adding to their cost.

Frequency-dependent Positioning Type Frequency-dependent positioning type devices currently on the market include the Endex (lKHz) and the Apit (5 KHz). These devices use a conducting medium introduced into the root canal of a tooth being treated, and do not require a special probe. They can be operated at two frequencies and at two different voltages. The unit operates at 2 pA ; the lower voltage provides the patient with more comfort.

Rechargeable batteries are used, making the devices relatively independent of long, connecting wires. The reset calibration is done automatically. The major disadvantage of this type of device is that it is not completely accurate in measuring the distance to the apical foramen.

Ratio Method Type Ratio method type devices are often referred to as"third generation"tools. The concept driving this type of device was first suggested by Kubayashi (1991). An example of a ratio method type device is the Root Zx, which does not need calibration, is easy to operate, and has a user-friendly display screen. However, it has mixed reviews regarding its accuracy in locating the area of the major foramen and it is recommended-to use the device in conjunction with X-rays of the tooth prior to treatment.

Newer devices on the market, such as Kobayashi's wireless tool, Tri-Auto Zx (1997) incorporate the Root Zx device inside a portable, battery-operated unit. The Solfy Zx is another portable device based on the Root Zx. There is a serious question about the accuracy of some of these devices ; they stop short of actual penetration down to the last 2 mm of a root canal. The operator must then use manual methods for completing the treatment.

The display units used in the existing systems described above are analog as well as digital, and may generally be characterized as similar-in type to those described, although they may display information regarding the linear advance of a probe in the root canal of a tooth in different ways.

The disadvantages of the prior art include the fact that most devices for measurement require precise frequency calibration, which increases the cost of the final device to the operator-user. Also, there are measurement errors resulting from problems with harmonic phases in the existing devices. Most of the newer, wireless devices which are now appearing on the market require expensive batteries (e. g., <BR> <BR> NiTi) and work only for limited lengths of time (e. g. , 15-20 hours) before recharging or replacement of batteries is required.

The present invention is intended to overcome the problems of the prior art, and provides a portable display unit, which is the smallest size over that of existing devices. The display unit of the invention is ergonomic in design and is provided with a means for attachment in a direct, inherent and universal way to the immediate surroundings, as close as possible to the work area where it is most needed during root canal treatment, that is, close to the mouth of the patient and within the field of view of the operator. This proximity also considerably shortens the length of the wires required to connect parts of the system, thus making the system easy to use, more comfortable to the patient, and less sensitive to electromagnetic radiation. The display unit comprises three indicators, which provide differentiation by indicating the minimal areas related to root canal treatment: the work area, a danger area, and a neutral area.

An additional advantage of the present invention over prior art systems is that its components are significantly less expensive than the devices used in other systems on the market, which may cost 4 to 8 times as much.

Summary of the Invention Accordingly, it is a broad object of the present invention to overcome the disadvantages and limitations of the prior art and to provide a portable, ergonomic system for detecting apical foramen position in performing dental treatment.

It is another object of the present invention to provide a portable display unit for indicating the areas of treatment along a tooth in relation to the reference position of a probe inserted into the root canal of the tooth during root canal treatment.

The invention therefore provides a system for detecting and indicating apical foramen position of a tooth during root canal treatment, the system comprising a probe insertable into the root canal of the tooth during treatment; an electrically conductive contact-making member; an electronic sensor including the probe and the tooth, and a portable control and display unit electrically connected to the probe and sensor, the unit having a display including indicators indicating the areas of treatment along the tooth; the unit being removably affixale in close proximity to the mouth of a patient undergoing the treatment, with the display facing an operator effecting the treatment and within the field of view of the operator during the treatment.

There is also provided a portable display unit electrically connected to a probe and a sensor, including indicators indicating the minimal areas related to the root canal treatment.

Brief Description of the Drawings The invention will now be described in connection with certain 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 only by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention, 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 view of the components of the system for detecting foramen position during root canal treatment, in accordance with an embodiment of the present invention; Fig. 2 is a view of the system showing the disposition of the various components of the system in close proximity to the patient's mouth; Fig. 3 illustrates the system during use; Fig. 4A is a schematic view of root canal probe components of the system in a circuit incorporating a tooth; Fig. 4B illustrates an electronic circuit equivalent to that of Fig. 4A; Fig. 5 is a circuit diagram of the system according to the present invention; Fig. 6 is a front view of a display unit in accordance with an embodiment of the invention, and Fig. 7 is a rear view of the display unit of Fig. 6.

Detailed Description Referring now to Fig. 1, there are shown the components of the system for detecting and indicating apical foramen position in accordance with an embodiment of the invention. The system includes a probe 2, which is a per se known dental tool for performing root canal treatment in a tooth, electrically connected in parallel with a hook-shaped, lip-and/or gum-contacting, electrically conductive member 4, which is drapable over the patient's lip for making contact with the gums or interior members of the patient's mouth, thus electrically closing a sensor circuit. Probe 2 and member 4 are linked by insulated electrical cord 6 to a portable control and display unit 8 having indicators 10 for indicating the depth of penetration of probe 2 along the root canal of a tooth in relation to the apical foramen position. A universal type clip 12 conveniently attaches to the patient's garment 14, for holding the unit 8 with indicators 10 within the operator's field of view and close to the work area, adjacent to the patient's mouth.

Fig. 2 illustrates the disposition of the various components of the system in relation to the patient, attached by clip 12 to the patient's garment 14.

In Fig. 3, there is shown the system during use. Conveniently, the system's components are removably affixed to a rim of a mouth-mask like device having a semi-rigid or rigid, substantially circular ring 16 to which there may be attached an apertured fabric 18 covering sections of the mouth not being treated. As shown, the display unit 8 is clamped or otherwise affixed to rim 16 at any angularly convenient location around the mouth, so as to be disposed within the field of view of the operator when working on a specific tooth.

Fig. 4A illustrates a root canal probe 2 in a circuit incorporating a tooth 24.

The conductive lip-or gum-contacting member 4 makes contact with the gums 26 surrounding tooth 24 to close the circuit with a signal generator through resistor R1.

The electronic equivalent circuit is shown in Fig. 4B. Tooth 24 and probe 2 are the electrical equivalents of a resistor R2, in parallel with a capacitor C1, both connected in parallel with signal generator 28. Signal generator 28 generates signals at high and low frequencies for comparison purposes, resulting in reliable measurements. The measurements are performed with two square waves, which are easy to generate, and then the value of the capacitance is determined by calculating the time of charge of the capacitor C 1 at high frequency and calculating the value of the resistor R2 at low frequency.

Referring now to Fig. 5, there is illustrated an embodiment of a circuit diagram of the system in which the circuit is advantageously powered from a D. C. power source 30 feeding a CPU 32. The probe 2 and a contact member 4 are connectable to the CPU 32 via signal generator 28, consisting of operational amplifiers 34,36 and resistors R3 to R7. The output from CPU 32 is constituted by an indicator 38, composed of light sources 40,42, 44, advantageously colored yellow, green and red, respectively, similar to the familiar traffic signals, however more than three light sources can also be used. Each of the light sources is electrically connected to the <BR> <BR> CPU 32, respectively via resistors R8, R9 and RIO. An ON-OFF switch e. g. , a touch button 48, is also provided.

Advantageously, the unit 8 is configured in a tooth shape, providing the operator with an additional, clear perception, at a glance, of the instant depth drilled in the tooth. Figs. 6 and 7 show front and rear views, respectively, of unit 8 configured in such a tooth shape. An ON-OFF touch button 48 is advantageously located on the front display panel of unit 8. Upon switching on the unit, the front display area depicts the image of a tooth 50 for ease of orientation by the operator.

Below the image of tooth 50, there are provided sites, generally arranged as a traffic light having a set of three distinct light indicators 52,54, 56, each having one of the light sources 40,42, 44 positioned below it. In the embodiment shown, the front display area is formed by a sticker 58 bearing the desired graphics. The indicating lights are colored, to differentiate the minimal areas of treatment in relation to the apical foramen position in the tooth. For example, a blinking yellow light 52 indicates a distance of more than 2 mm to the apex. A constant, non-blinking light indicates a distance of 2 mm from the apex. A green light 54 indicates a distance from 1.0 mm down to 0.7 mm from the apex. A constant red light 56 indicates to the operator that the danger area of 0.5 mm from the apex has been reached. A blinking red light provides the operator with a warning, indicating that a closer penetration, say, smaller than 0.4 mm, has been reached.

Fig. 7 shows the rear surface of the display unit 8, a portion of which is a textured cover 60, concealing a compartment where the batteries of unit 8 are mounted. The display unit 8 may actually be constructed of two separate parts, a control unit and a display unit. What is more important, is that the display portion of the unit should be clamped or affixed within the field of view of the operator, to enable simultaneous viewing of the treated tooth and the display.

In addition to the visual signals, the unit may also provide an audible signal, alerting the operator when the danger area is reached.

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.