Distribution and structure of the initial dental enamel formed in incisors of young wild-type and Tabby mice.

Mouse incisor enamel can be divided into four layers: an inner prism-free layer; an inner enamel with prism decussation; outer enamel with parallel prisms; and a superficial prism-free layer. We wanted to study how this complex structural organization is established in the very first enamel formed in wild-type mice and also in Tabby mice where enamel coverage varies considerably. Unworn incisors from young female wild-type and Tabby mice were ground, etched, and analyzed using scanning electron microscopy. In both wild-type and Tabby mice, establishment of the enamel structural characteristics in the initially formed enamel proceeded as follows, going from the incisal tip in an apical direction: (i) a zone with prism-free enamel, (ii) a zone with occasional prisms most often inclined incisally, and (iii) a zone where prism decussation was gradually established in the inner enamel. The distribution of enamel in Tabby mice exhibited considerable variability. The sequence of initial enamel formation in mouse incisors mimics development from a primitive (prism-free) structure to an evolved structure. It is suggested that genes controlling enamel distribution are not associated with genes controlling enamel structure. The control of ameloblast configuration, life span, organization in transverse rows, and movement is important for establishing the characteristic mature pattern of mouse incisor enamel.