A device and method for the detection of smooth surface lesions such as caries and tooth crown surface cracks on a tooth crown surface, the device having an ultrasonic surface wave transmitter/receiver comprising a focused ultrasonic surface waves along a tooth crown surface. Surface lesions encountered by the ultrasonic surface waves produce ultrasonic surface wave reflections which are receivable at the generator/receiver, thus enabling the presence of the lesion, and particularly small lesions, to be detected. The ultrasonic surface wave generator/receiver may comprise a focused transducer, having a focusing element integral therewith or separate therefrom, operatively connected to a wedge-like coupler. Longitudinal ultrasonic waves generated by the transducers are at least partially focused by the focusing element and then imparted onto the tooth surface by the coupler which has a contact surface in contact with the tooth surface being tested. The coupler also enables ultrasonic surface wave reflections to be received by the transducer.