Detection of Restoration Faults under Fillings in Human Teeth using Ultrasound

An ultrasound contact imaging technique for detecting the restoration faults under the fillings in human tooth is proposed. A linear frequency modulated chirp signal is used to improve the signal-to-noise ratio and increase the penetration depth to allow the detection of the echoes from restoration-tooth boundary at 200 kPa acoustic pressure. Although the detection threshold is improved, it is observed that the duration of the excitation signal is longer than the duration of time of flight in the restoration, which causes signal overlapping between consecutive internal reflections. Due to these reverberations, the applied chirp signals interfere arbitrarily with the successive reflections, where the received echoes are not identifiable in the time domain. Separation in the frequency domain is not possible, since all reflections have the same bandwidth and the center frequency. In this work, the fractional Fourier transform (FrFT) is employed to separate chirp signals overlapping in both time and frequency domains. By analyzing the received echoes with FrFT, this work presents the ultrasonic non-destructive evaluation of dental restorations in human teeth.