FIGURE 9.

Micro-computed tomography of hemimandibles at 7 weeks. Row A, 18-μm section through the mandibular first and second molars. The enamel layers of the wild-type and Klk4 heterozygous mouse molars have similar intensities, which sharply contrast with dentin. The enamel is largely abraded from the molars of the null mouse. Row B, three-dimensional micro-computed tomography reconstruction of the hemimandibles. Row C, 18-μm sections through the mandibular incisor. As in the molars, the enamel layers of the wild-type and Klk4 heterozygous mouse have similar intensities that sharply contrast with dentin. The incisal edges are sharp and unbroken. The incisor enamel of the Klk4 null mouse does not contrast well with dentin and is abraded at the incisal edge. Row D, three-dimensional micro-computed tomography reconstruction of the hemimandibles as in row B, but using a threshold cutoff so that only highly mineralized structures are seen. The enamel crowns of the three molars and the incisor in the wild-type hemimandible are uniquely above the threshold. Dentin and bone are both below threshold. The area and volume of the supra-threshold signal (enamel) of Klk4 heterozygous mouse was reduced by ∼10% from the wild type. In the molar region of the heterozygote, only the thin enamel near the cemento-enamel junction of the first molar appeared to drop below threshold, whereas virtually the entire enamel layer of the molars from the null mouse dropped below threshold.