Many physical or chemical phenomena give rise to a specific electrical response on application of an electrical stimulus. Consequently, such measurements are widely used in a variety of laboratory and industrial environments.
The application of these measurements may use AC or DC based methods such as potential steps, voltammetry and electrochemical impedance spectroscopy (EIS), also known by the present inventors as the AC impedance spectroscopy technique (ACIST™). EIS has become particularly useful in the investigations of charge transfer, ion transport and adsorption processes, among others. In addition, impedance measurements have little or no effect on the sample under investigation making it applicable where changes in the measured system due to the effect of electrical polarisation are undesirable, and thus particularly suitable for non-destructive testing and material characterisation in general.
Measurements of impedance spectra can be made using one of two methods, that is, the frequency domain or the time domain. In the frequency domain impedance measurements made using, for example, the EIS technique can be performed using a single sine method. With the single sine technique, a small amplitude fixed frequency sinusoidal signal is applied to the system under study, and the response signal is measured. In this frequency domain the in-phase (real) and out-of-phase (imaginary) components of the total impedance are determined. From this information, the phase shift between source and response waveforms is calculated which defines the magnitude of the impedance. To construct an impedance spectrum, the single sine technique requires a number of measurements to be performed at discrete frequencies in a sequential manner.
In some studies in which the measurements are performed in the frequency domain, the impedance spectra are achieved by analysis of the response of a test system to an applied signal of single frequency and then repeating the process at different frequencies to achieve the desired frequency range. This technique has become colloquially known as the “swept sine technique” whereby a single frequency signal is applied to the test system and the response analysed and recorded, the process then being repeated for signals of different frequency and by this means an impedance spectrum is built up.
The equipment which is used to perform measurements in the frequency domain, as described above, is typically a computer controlled Frequency Response Analyser (FRA) attached to an electrochemical interface to measure current or voltage response. An example of such a swept sine arrangement is shown in FIG. 1. This equipment which is used to measure AC impedance in the frequency domain, comprises a frequency response analyser (FRA), in this case a Solartron 1255, an electrochemical interface (ECI), in this case a Solartron 1286, a PC with general-purpose interface bus (GPIB) and controller software which links all of these devices. In such an arrangement of equipment, the FRA generates and measures AC signals and the ECI operates as a potentiostat/galvanostat; however it may simply be used as a current measuring resistor and amplifier. Both applied signals and response signals would be returned to input channels of the FRA and subsequently acquired by the PC via the interface board for further data manipulation.
Similar equipment exists for measurements in the time domain such as Stanford Research Systems SR780. However, for these measurements the equipment typically comprises a spectrum/network analyser, a PC with GPIB and controller software linking each of these devices.
As can be seen, such equipment is usually heavy and expensive. These types of equipment arrangements also require mains power therefore making them unsuitable for use with human subjects without the provision of isolation apparatus. Additionally, complex software is required to be installed in each equipment arrangement to link the component devices and perform the required processing functions. Further, due to its cumbersome nature the usefulness of known conventional apparatus is limited in some circumstances. In particular, known apparatus is unable to be easily used in small or awkward spaces, nor is known apparatus convenient for performing measurements in environments outside of the laboratory as this would require the disassembly and moving of the components of the testing apparatus and the reassembly in the testing environment.
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 or radiographic examination. A patient may also seek an examination by a dental surgeon when in pain. This symptom itself is often not a reliable indicator of the presence of caries and the surgeon must identify the offending tooth by visual examination and/or by the use of a mechanical probe.
Caries is often at an advanced stage by the time diagnosis is made using conventional examinations or when it gives rise to symptoms. This may reduce options available 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.
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.
Electrical 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. Known ECD's suffer from a number of problems, eg as mentioned hereinbefore.
WO 98/12983 (ORMCO CORPORATION) discloses an apical detection apparatus, comprising: a first electrode, the first electrode including a conductive probe shaped for penetrating a root canal of a tooth; a second electrode configured to electrically contact a patient's body; a phase detector coupled to the first and second electrodes, the phase detector being operative to detect a phase of a complex impedance having a real component and a reactive component; and a user interface coupled to the phase detector to provide an indication to a user of a parameter that is a function of the detected phase.
WO 97/42909 (UNIVERSITY OF DUNDEE) discloses 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 sequentially varied over a predetermined frequency range and the electrical impedance is measured for a plurality of frequency values within said range.
An object of at least one embodiment of at least one aspect of the present invention is to obviate or mitigate at least one of the aforementioned problems/disadvantages.
It is also an object of the at least one embodiment of at least one aspect of the present invention to provide a dedicated test equipment or portable test device providing signal generation means, signal receiving means and signal processing means beneficially within a unitary body or within a single casing or enclosure or alternatively in a modular form which is advantageously readily assembled and disassembled.
It is further an object of at least one embodiment of at least one aspect of the present invention to provide a test equipment or device which generates a signal and receives a response signal in the time domain and analyses said signals in the frequency domain, ie measures in the time domain and analyses in the frequency domain.
It is a yet further object of at least one embodiment of at least one aspect of the present invention to provide a test equipment or portable test device capable of testing a whole tooth in vivo, and in a time frame acceptable to clinician and/or patient, eg in less than 10 to 15 seconds, and preferably in less than 1 to 3 seconds.