Figure 3: Scanning electron microscopy of the mandibular molars (a and b) and mandibular incisor (c–e) of a Klk4 null mouse at 7 weeks. The enamel of all molars showed a significant loss of enamel from all working surfaces (buccal cusps, occlusal surface, and marginal ridges) (a and b). Similarly, the enamel layer was abraded at the working (buccal) surface of the mandibular incisor at its tip (c). Higher magnification of the chipped area near the tip of the incisor showed that the break was in the enamel layer, close to, but not at the DEJ. The broken surface appears to be composed of interrod (ir) enamel with holes where enamel rods (r) had pulled out and separated (d) from the initial deposit of interrod enamel near the DEJ. The holes are too numerous to be made by odontoblastic processes penetrating the enamel (enamel spindles). The orientation of the crystallites on the walls of the holes is parallel to the direction of the tubular holes and to the crystallites between the holes (e). This figure was originally published in: Simmer et al. J. Biol Chem. 284 (28):19110-19121, 2009. The American Society for Biochemistry and Molecular Biology. DOI 10.1074/jbc. M109.013623.