We examined the importance of PpIX in P. gingivalis and the fluorescence wavelength of PpIX. The P. gingivalis suspension of each optical density (OD) was measured at the fluorescence wavelength (excitation 460 nm and emission 703 nm) of PpIX. We performed statistics using Spearman’s rank correlation coefficient, and there was a strong correlation (r = 0.9727, p < 0.001) between the OD of P. gingivalis and the relative fluorescence intensity (Fig. 3A). We converted the relative fluorescence intensity of each P. gingivalis concentration into a quantity of PpIX. Figure 3B shows the results of linear regression analysis after using Spearman’s rank correlation coefficient to prove the significant correlation between P. gingivalis concentration and PpIX level.Figure 3PpIX quantity in P. gingivalis. (A) Correlation of the relative fluorescence units and P. gingivalis concentration change (n = 3). (B) Linear regression between the concentration of P. gingivalis and PpIX (n = 3). Dots represent the 95% confidence curve.