An ultrasonic nondestructive technique for evaluating layer thickness in human teeth

An ultrasonic nondestructive evaluation technique of the layer thickness in human teeth using a leaky Lamb wave device with two arch-shaped interdigital transducers (IDTs) is proposed. Each of the two IDTs on a piezoelectric ceramic plate operates as an input or an output transducer at a plate/water interface, in the configuration of an acoustic delay line of reflected ultrasound beams from the tooth section at the spot under investigation. The use of a higher-order mode, second symmetric (S2) mode, leaky Lamb wave with a phase velocity higher than the longitudinal wave velocity in the human tooth is essential to enable the oblique incidence of the focused ultrasound beam. The echoes from dentin-pulp and enamel-dentin junctions are similar in the oscilloscope traces. The layer thickness of dentin or enamel for a number of teeth, estimated from the measured time interval between two reflected echoes, from the tooth surface and from the interface in the tooth, is in good agreement with the optically measured data.