Fig. 4From: Tooth whitening with an experimental toothpaste containing hydroxyapatite nanoparticlesThe nano-HAP adhesion on the enamel surface. a–d: water group; e–h toothpaste without nano-HAP; i–l: 1 wt% nano-HAP toothpaste; m–p: 10 wt% nano-HAP toothpaste. The sample was imaged with FE-SEM at the magnification of 5000 ×Back to article page