<P> A residue may form on newly erupted teeth of both dentitions that may leave the teeth extrinsically stained . This green - gray residue, Nasmyth membrane, consists of the fused tissue of the reduced enamel epithelium and oral epithelium, as well as the dental cuticle placed by the ameloblasts on the newly formed outer enamel surface . Nasmyth membrane then easily picks up stain from food debris and is hard to remove except by selective polishing . The child's supervising adults may need reassurance that it is only an extrinsic stain on a child's newly erupted teeth . </P> <P> Patients with osteopetrosis display enamel abnormalities, suggesting that the a3 gene mutation found in V - ATPases also plays a role in the development of hypomineralized and hypoplastic enamel . </P> <P> Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development . The formation of dentin must always occur before the formation of enamel . The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin . </P> <P> Odontoblasts, the dentin - forming cells, differentiate from cells of the dental papilla . They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth . The organic matrix contains collagen fibers with large diameters (0.1--0.2 μm in diameter). The odontoblasts begin to move toward the center of the tooth, forming an extension called the odontoblast process . Thus, dentin formation proceeds toward the inside of the tooth . The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix . This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick . </P>

When does the first permanent molar begin to mineralize