FIG. 8.

Incisor enamel defects in peri^lacZ null mice. (A) Incisor phenotype. A mandibular facial view of young 3-week-old incisor teeth from the wild type shows the typical translucent appearance of enamel that is reflected through the enamel layer on its surface. The dentin has a yellowish color. In contrast, the null incisors appear thinner and present a mesial interproximal gap (arrow), and their enamel layer appears less translucent, which gives a mild opacity to its surface. Brackets indicate reduced incisor width. (B) Radiographic view of the mandibular periapical region shows the progression of the enamel defect from day 7 to 5 months of age. (C) Radiographic view of the maxillary incisor at day 7, where no apparent defect is detectable in the peri^lacZ null mice, and of that of the 5-month-old (5m) peri^lacZ null mice, which displays a complete deformation of the enamel surface that affects the incisor from the apex to the incisal edge. Notice the anterior progression of the defect that is initially detected at 1 month. (D) Backscatter SEM images of 3-month-old maxillary incisors show clefting of the enamel surface in the periostin null incisors (indicated by arrows). E, enamel surface; D, dentin surface; WT, wild type; KO, knockout. (E) Coronal sections from the wild-type incisor show the typical enamel prism structure pattern. (F) In contrast to the wild type, the peri^lacZ null mice exhibit an abnormally thin enamel layer with an apparent amorphous and irregular prism pattern. For panels D, E, and F, boxed regions in left panels are shown at higher magnification to the right.