Fig. (3) The acoustic modes of 4 different CAD/CAM chairside materials: A) Oscillogram (A-scan) 1 - the signal reflected from the sample surface,2 - the signals from the elements of the internal structure,3 - the signal from the lower limit of the sample;B) Vertical cut of the sample (B-scan); 1 - the surface of the sample; 2 - focus of acoustic lens;3 - The pores in the internal structure of the material