Lateral distribution of ultrasound velocity in horizontal layers of human teeth

The speed of ultrasound at 20 MHz differs inside human teeth depending on which tissues are involved. At least two out of four dental tissues exhibit variations in the longitudinal velocity (CL). The aim of this in vitro study is to describe the laterally varying propagation velocity of tangentially propagating longitudinal waves. At a distance of 5 mm from the crown reference, the CL is determined using longitudinal sections and a pulse-echo technique. Several graphs are combined to account for the corono-apical decrease in CL and the laterally varying CL distribution along horizontally adjacent relative tooth width portions. The laterally increasing CL of 21 specimens at radial locations rises from 2900 to 4000 m/s. A mathematical evaluation reveals an optimal horizontal formula of the form CL(5 mm) = a + bX2 ln(X), where X is the standardized lateral parameter relative to individual tooth width w, which is compensated for offsets. Individual residuals and a, b coefficients of the corresponding approximations are provided. Individual mean errors range from 7 m/s (SD=6 m/s) to 92 m/s (SD=79 m/s). The lower contour of the envelope curve of all CL distributions is described by taking up a formerly introduced equation [J. Acoust. Soc. Am. 116, 545 (2004)].