A device for the detection of smooth surface lesions of dental caries on a tooth crown surface, having an ultrasonic transducer for transmitting ultrasonic waves and receiving ultrasonic wave reflections produced by lesions present on the surface, and an interface operatively connected to the transducer. The interface has a contact surface forming an angle .alpha. with a longitudinal axis of the ultrasonic transducer, where .alpha. is substantially different from 90.degree.. When the contact surface is in at least partial contact with a tooth crown surface at the longitudinal axis, ultrasonic waves generated by the ultrasonic transducer are imparted by the interface onto the tooth crown surface as surface ultrasonic waves which migrate along the tooth crown surface. Any lesions present on the tooth crown surface are then identifiable as surface ultrasonic wave reflections produced thereat.