Patent ID: 8594782

Claim:
An apparatus for determining the location of the apex of a root canal of a tooth, wherein the apparatus comprises the following components: (a) a first electrode shaped to be insertable into the root canal of a tooth of a patient and a second electrode which is shaped to be placed in contact with another body part of said patient, preferably with the oral mucosa or with a hand of said patient; (b) a frequency sweep generator capable of generating a succession of at least four voltage signals with different frequencies between the first and the second electrode; (c) a measuring device capable of measuring the impedances between the first and the second electrode corresponding to the voltage signals generated by said frequency sweep generator; (d) a computing unit, capable of: controlling the voltage signals generated by the frequency sweep generator; reading the respective impedance values from the measuring device; and computing the distance between said first electrode and said tooth apex from said impedance values; wherein the computing unit comprises hardware capable of carrying out a method which comprises the following steps: (i) carrying out a first frequency-sweep at a frequency rate γ and recording for each generated voltage signal the respective impedance value and time point of the impedance measurement; and (ii) determining the distance between said first electrode and said tooth apex from the impedance values recorded in (i), and wherein step (ii) comprises fitting a first curve to the impedance values obtained from the first frequency sweep and determining said distance using a curve characteristic of said first curve, or wherein step (ii) comprises the following steps: (iii) fitting a first curve through the impedance values obtained from the first frequency sweep, wherein said first curve defines which time points during the first frequency sweep correlate with which respective impedance value of the first sweep; (iv) carrying out a second frequency-sweep at a frequency rate β, which is different to the frequency rate γ, analogous to (i) or by extrapolating the impedance and time point values from the first curve obtained in (iii); (v) fitting a second curve through the impedance values obtained from the second frequency sweep, wherein said second curve defines which time points during the second frequency sweep correlate with which respective impedance value of the second frequency sweep; (vi) obtaining a third curve which is the difference between the first and the second curve; (vii) finding the maximum of the third curve which is the maximal impedance difference ΔR max recorded at the time point t max ; and optionally determining the area F under the third curve between t=0 and t=t max and (viii) determining the distance x between the apex of said dental root canal and said first electrode using the determined t max and ΔR max values and optionally the F value, and (e) optionally an output device capable of outputting said computed distance.