Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
1999-08-05
2001-05-08
Hoang, Tu Ba (Department: 3742)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
C600S590000, C128S126100
Reexamination Certificate
active
06230050
ABSTRACT:
BRIEF SUMMARY OF THE INVENTION
This invention relates to methods and apparatus for use in detecting dental carious (i.e. dental decay, or “caries” or “carious lesions”) by electrical and/or electronic means.
BACKGROUND OF THE INVENTION
Caries is defined as the progressive decay of tooth or bone, and dental caries is the most common ailment known world wide. Dental caries can be treated by either removing the decayed material in the tooth and filling the resultant space with a dental amalgam, or in severe cases, by removal of the entire tooth.
The early diagnosis of dental caries is of utmost importance to any subsequent treatment since by the time pain is felt due to decay of the tooth, the treatment required to restore the tooth may be extensive and in some cases, the tooth may be lost.
Historically, the diagnosis of dental caries has been primarily visual, frequently accompanied by tactile examination using a mechanical probe. The patient may only seek an examination by a dental surgeon when in pain due to the caries and the surgeon must then identify the offending tooth by visual examination and/or by use of a mechanical probe which causes discomfort or pain in the decayed tooth. This experience is painful and distressing for the patient and acts as a disincentive to regular visits to the surgeon for routine examinations. In addition, the diagnosis of caries at this late stage of decay reduces the available options for treatment.
The diagnosis of caries by conventional techniques has become increasingly difficult. This is a result of several factors, including apparent changes in the morphology and in the rate of progress and distribution of carious lesions, as well as the inaccessibility of approximal (mutually contacting) dental surfaces and the complicated anatomy of pit and fissure sites on the occlusal (biting) surfaces.
An additional problem with conventional techniques is that decay on the approximal surface of the tooth resulting from plaque on the inter dental spaces may not be detected by simply prodding the tooth, since the approximal surfaces may not be reached by the probe. The limitations of conventional visual, tactile and radiographic diagnosis are well recognised. Decay may progress to an advanced stage on both occlusal and approximal sites without being detected until substantial tooth destruction has occurred.
In response to these generally unsatisfactory and unreliable methods of diagnosis attempts have been made to develop electrical/electronic means for the diagnosis of caries.
Electronic Caries Detectors (ECD's) generally comprise a probe having a first, probe electrode which is placed in contact with the tooth to be tested, and a second, counter electrode separate from the probe which is placed in contact with another part of the body of the patient in order to complete an electrical circuit connecting the two electrodes. The second electrode may be held by the patient or may be placed in contact against the gingiva (gum) or oral mucosa (inside cheek). An alternating electric current of fixed frequency is passed through the tooth and the resistance to this is measured. This electrical resistance has been found to correlate approximately inversely with the extent of caries in the tooth. The technique may involve measurement at a single point on the surface of the tooth, or the use of an electrically conductive paste, providing a measurement for the surface as a whole.
The configuration of conventional designs of ECD probes are such that they cannot contact approximal tooth surfaces, and therefore cannot detect approximal caries which does not extend to the occlusal or free smooth surfaces of the tooth. No satisfactory means to detect such approximal caries is currently known, although the problem of approximal caries has been prevalent for many years. Hitherto, the most accurate method of diagnosing approximal caries has been bitewing radiography, but this method is only about 30% accurate and requires the use of ionising radiation.
Even where good electrical contact can be established between the probe electrode and the relevant site, conventional ECD apparatus is of limited usefulness in the detection of caries.
DETAILED DESCRIPTION OF THE INVENTION
Among the objects of the various aspects of the present invention are the provision of: improved apparatus and methods for the electrical/electronic diagnosis of dental caries of all types; electrical/electronic probes for the detection of approximal caries; and improved electrical/electronic probes for the assessment of the occlusal and free smooth surfaces of the tooth.
In accordance with a first aspect of the invention there is provided a method for use in the detection of dental caries, comprising the steps of placing at least one probe electrode in electrical contact with a surface of a patient's tooth, placing a second electrode in electrical contact with another part of the body of the patient, passing an alternating electrical current between said probe and second electrodes, and measuring the electrical impedance between the electrodes to said electrical current; wherein the frequency of said alternating current is varied over a predetermined frequency range and the electrical impedance is measured for a plurality of frequency values within said range.
In the preferred embodiment of the invention, the impedance measurement and corresponding frequencies are analyzed by means of an alternating current impedance spectroscopy technique (ACIST) and a diagnosis of the tooth is based on the form of the impedance spectrum obtained thereby. The measurement frequencies are preferably in the range up to 500 kHz. Most preferably, the lower and upper frequencies in the range and the number of frequencies at which impedance measurements are made are selected on the basis of the type, size and configuration of the probe electrode(s), the specific tooth surface(s) and/or site(s) being contacted and whether or not the tooth has previously been restored (filled).
The probe electrode may comprise an array of miniature electrodes, enabling simultaneous or sequential impedance measurements to be made at multiple sites on one or more surfaces of the tooth.
Preferred forms of apparatus for use in the method, including preferred types of probe electrodes for approval and other tooth surfaces, are as defined below in relation to further aspects of the invention and as described more fully in the following description of embodiments of the various aspects of the invention.
In accordance with a second aspect of the invention, there is provided apparatus for use in the detection of dental caries, said apparatus comprising: at least one probe electrode adapted to be placed in electrical contact with a surface of a patient's tooth, a second electrode adapted to be placed in electrical contact with another part of the body of the patient, an alternating current source adapted for passing an alternating electrical current between said probe and second electrodes, and impedance measurement means for measuring the electrical impedance between the electrodes to said electrical current; wherein said alternating current source is a variable frequency alternating current source whereby the frequency of the alternating current applied to the tooth may be varied over a predetermined frequency range and the impedance measurement means is adapted to measure impedances corresponding to a plurality of frequency values within said range.
In accordance with a third aspect of the invention, there is provided a probe electrode device for use in the electrical/electronic detection of dental caries, comprising a substrate of electrically insulating material, and at least one electrode of electrically conductive material disposed on at least one surface of said substrate.
Preferably, said substrata comprises a generally planar, flexible, hydrophobic material, preferably PTFE, and most preferably Goretex. Where the device is intended for examination of approximal tooth surfaces, said substrate is sufficiently thin to fit between t
Berry Pitts Nigel
Longbottom Christopher
Los Przemyslaw
Hoang Tu Ba
Ratner & Prestia
The University Court of The University of Dundee
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