Survey of enamel formation in presecretory, secretory and early maturation stages on maxillary and mandibular incisors from 7-week-old mice.

(A, B) Wild type incisors showed normal matrix deposition and enamel development. Matrix protein stained blue in the enamel space during secretory stage was absorbed in the maturation stage allowing crystal maturation to take place (arrowheads). (C) Maxillary incisors in Enam^+/− mice appear similar to wild type. (D) However, the mandibular incisors in these mice consistently demonstrated disturbed ameloblasts resulting in cyst formation within the enamel organ beginning in late secretory stage (arrow). (E) In Enam^−/− maxillary incisors, there was no apparent enamel matrix deposition; (F) in the mandibular incisors, soon after the onset of the secretory stage, ameloblasts showed pooling of secreted material at their apices and gradual loss of polarity and organization within the enamel organ (arrowheads). (G, H) In line 2^(M), Enam^−/−,tg incisors, ameloblasts were polarized and deposited matrix during early secretory stage. Soon after that ameloblast layer became detached and cystic formation was evident on both maxillary and mandibular incisors (arrows). These 0.5 µm thick toluidine blue stained sections of EDTA-decalcified incisors were obtained from mice perfused with 2.5% GA and embedded in Epon. Bar = 500 µm for all panels.