Fig. 1.

Schematic drawing of the location of stages of amelogenesis and sites for enamel strip dissections on maxillary and mandibular mouse incisors, and radiograph of a mandibular incisor enlarged to a similar scale as the schematic drawing. In normal wild-type mice, three, and sometimes four, 1-mm-long strips of developing enamel can generally be dissected from maxillary incisors across the length of the tooth from the start of the secretory stage (EM, SEC) to about the midpoint of the maturation stage (MAT), where the enamel becomes so hard that it physically damages the scalpel blades used to partition the enamel layer into strips. On mandibular incisors, usually two strips can be obtained from the secretory stage and three strips from the maturation stage before the enamel is too hard to dissect by hand. Because the average strip number per series is not an integer on maxillary incisors (3.5 strips per series per tooth) unlike mandibular incisors (5.0 strips per series per tooth), data for the most incisally positioned strip on maxillary incisors tend to have higher variation than comparable strips on mandibular incisors. In the radiograph below the schematic drawing, the dotted line indicates the boundary between the presecretory stage (PS) and the beginning of the secretory stage (SEC) on the mandibular incisor. The numbered white lines correspond to imaginary strips spaced at 1-mm intervals. AL, apical loop; EM, the point marking the start of enamel matrix formation; GM, gingival margin where the erupted portion of the incisor starts; MAT, maturation stage; NTP, ‘no Tome’s processes’ visible on ameloblasts; PS, presecretory stage.