After confirming that the gingival circulation had little effect on transmitted light plethysmography measurement in the upper central incisor in both in vivo experiments and numerical Monte Carlo simulation studies, a three-layer model comprising of a pulp chamber sandwiched between two dentin layers has been introduced to quantify the pulp chamber hematocrit from the measured optical density. Two-flux theory was utilized to derive a mathematical equation for transmitted intensity in terms of tooth dimensions, , and light-source wavelength. Each layer was assumed homogeneous so as to represent its optical properties by the bulk absorption and scattering constants. The mean error between the estimate based on the three-layer-model equation and the actual in the extracted model tooth was with standard deviation (SD) of 0.00733 at wavelength, while for and 0.02493. The estimate of the upper central incisor in 10 young volunteers at using the three-layer model ranged from 0.002 to 0.061 with the mean of 0.032. The change reflects blood volume shift in the pulp microcirculation to possibly indicate dental pulp vitality.