Appearance Of Human Teeth Structure Of The Laser Ultrasonic Propagation

This paper mainly studies the influence of laser ultrasonic transmission that is caused by the appearance of human teeth, a theoretical model of thermo-elastic generation of laser-ultrasound in the teeth surfaces which have different curvature has been studied and established. By using the finite element method, the temperature fields, the generation of laser ultrasonic wave, waveform characteristics, propagation characteristics and the dispersion of the phase velocity of Rayleigh wave are studied by numerical and calculation and theoretical analysis. In this paper Rayleigh wave and longitudinal wave are studied:Incisor's 2D double plate model. First the transient temperature fields in tooth surface by pulsed line-source laser producing are studied. The temperature rises in the direction of depth and the radius are analyzed. Then the time domain waveforms are studied, via FFT the frequency spectrum is gotten, calculated the dispersion of Rayleigh wave by phase spectrum method.The 2D tubular double model. First the transient temperature fields in the direction of radius and circumference are studied. The result is the bigger curvature of tooth surface, the higher the temperature rise in the tooth. Then the laser ultrasound time domain waveforms are analyzed. The numerical results denoted:in the tube the Rayleigh wave's pulse polarity happens the alternate transformation from single polarity to dual polarity. Because the model is double-deck, it makes effect of Rayleigh wave's frequency dispersion. The polarity transformation becomes more complicated than single model. The corresponding angles of pulse polarity transformation are different with different curvature models. Last the effect of the curvature to the speed of wave propagation analysis:by the same transmission distance, the bigger curvature of tooth surface, the higher the speed of the surface longitudinal wave and Rayleigh wave. The phase velocity dispersion of Rayleigh wave is gotten.Based above tow kinds of model, simulate 2D real incisors model and analyze the ultrasonic by laser stimulate in the near lip face and receive ultrasonic signals. Make the time-frequency analysis.Establish the 2D model of big spot laser irradiating the surface of incisor's double plate model and real incisors model. Through analyzing the ultrasonic's time domain waveform in the enamel model and the double plate model, get the path of longitudinal wave's propagation in incisor's double plate model. Based on the result, the path of longitudinal wave's propagation in the real incisors model is studied. The results in this paper can provide the theoretical foundation for the non-destructive evaluation of the tooth.