Figure 1. (a) SEM image of a fixed, demineralized dentin specimen showing the collagen fibrils that are randomly oriented in the plane perpendicular to the tubule lumens (after Marshall et al., 1997). (b) A higher-resolution AFM image of an unfixed specimen obtained in water. The AFM image shows the periodic 67-nm hole and overlap zones characteristic of the Type I collagen fibrils found in dentin and bone (after Marshall et al., 2001; Habelitz et al., 2002b).