Figure 2 is representative of the Boltzmann function, which is described by , where and are the initial and final plateau of the peak band intensity at , which corresponded to the dentin and cement region of the sample, respectively. is the displacement across the interface formed by the adhesive cement and dentin, while represents the midpoint of the resin cement–dentin diffusion zone. The axis is the Raman signal intensity. The diffusion zone is the region delimited by a straight-line tangent to the midpoint . The straight tangent line is mathematically described by a linear equation, i.e., , where and are constants. The is obtained by the first derivate of the Boltzmann function at , and the is obtained by replacing the values and in the linear function. By replacing and values in , it is possible to obtain the distance between and the two intersection points and that correspond to , which represents the width of the resin cement–dentin diffusion zones. Thus, by fitting the experimental Raman data collected from the scanned lines to the Boltzmann function, the authors could acquire the parameter and determine the width of the resin cement–dentin diffusion zone.