Therefore, the variation observed in the absorption band intensities for different thicknesses of the dentin reveals that the PS that has penetrated the dentin is distributed throughout it with some type of gradient profile. The area of each spectrum in Fig. 2(a) was plotted against the dentin thickness as shown in Fig. 2(b). Coordinate was plotted with correction made by means of averaging the exponential decay of the thermal diffusion length, , for each dentin thickness used, and coordinate was normalized in relation to the absorption at the surface, which figures 100%. Amazingly, data in Fig. 2(b) show a typical exponential decay that fits the model , in which represents the normalized PS absorption band areas through the dentin, is the relative sample thickness, is the saturation level for , is the relative amplitude in %, and is the characteristic decay parameter in the x direction, correlated to the percentage of PS as a function of the dentin thickness. The fitting provided as () μm. This means that at a depth of about 43 μm down from the occlusal surface, the relative attenuation of the amount of PS is 37%. The depth where the amount of PS is reduced to 5% is estimated to be , about .