Fig. 3
From: Tooth whitening with an experimental toothpaste containing hydroxyapatite nanoparticles
The average color changes (expressed as △E values) at each experimental time point (HAP 1: the first circle of nano-HAP application; HAP 2: the second circle of nano-HAP application; HAP 3: the third circle of nano-HAP application; HSF: application of hydrodynamic shear force). Lowercase letters indicate the differences between different groups at the same experiment time point. Capital letters indicate the differences of the same group between different experiment time points. Different superscripts indicate groups that statistically differed from any other group (P < 0.05). Same superscripts suggest that groups showed no significant differences (P > 0.05). From a (A) to c (C), the mean value is decreased. * indicates the significant differences between HAP 3 and HSF (P < 0.05)