A comparative study of ultrasonic direct contact, immersion, and layer resonance methods for assessment of enamel thickness in teeth

Wear of dental enamel is a growing problem, but is clinically difficult to diagnose and monitor. An accurate and easy-to-use non-destructive method for the measurement of enamel thickness would be useful for early diagnosis of enamel loss and for monitoring progression. Ultrasound has been identified by several researchers as a potential tool suitable for enamel thickness measurement. However, in vitro studies have shown that while the method is feasible, it suffers from wide variability. The methods proposed to date rely on the measurement of the time of flight of an ultrasonic pulse through the enamel layer. This requires the operator to locate the enamel-dentine junction. In this work, three methods are evaluated to try to reduce this variability and to investigate some practicalities of the approach. Time-of-flight methods using both contact and immersion transducers were used. Immersion transducers gave the most accurate results, within 10-15 per cent of values deduced from tooth sections, but would be harder to arrange for in vivo measurements. Preliminary studies have also shown that it is possible to achieve a resonance in the enamel layer and to measure thickness that way. While this approach needs further experimental refinement, it has the potential to be used for much thinner enamel layer thicknesses.