Fig. 1

Scanning electron microscopic images of human dentin disks at 2500x magnification, after brushing for 2 or 4 weeks. The upper row presents the disks after 2 weeks of toothpaste application, and the lower row presents those after 4 weeks of application. In the negative controls (A and F), the dentin surface appeared free of smear layer, and the dentinal tubules were completely open. In the experimental disks (B–E and G–J), partial occlusion of dentinal tubules was observed