User:Ulkulk4a/sandbox

How does the enamel organ determine the shape of tooth?

The shape of the enamel layer covering the crown is determined by five growth parameters : 1. The appositional growth rate 2. Duration of appositional growth (at the cusp tip) 3. Ameloblast extension rate 4. Duration of ameloblast extension 5. Spreading rate of appositional termination. The appositional growth mechanism establishes the thickness of the enamel layer and it is determined by ribbon-like carbonate apatite crystals which are present in the rods (or prisms) and interrods. They are produced by the ameloblast in the bell stage of tooth development. As the crystals are long and closely packed, the thickness depends on the abundance of the crystals in the tooth.Crown shape or morphology is determined by the epithelial-mesenchymal interaction, which occurs at the dentinoenamel junction (DEJ).

Firstly, the pre-ameloblasts differentiate from the inner enamel epithelia on the dentine surface covering the pulp horn. A wave of ameloblasts will then differentiate from the cusp tip and move through the inner enamel epithelia down the slope of the mineralised dentine surface. The differentiation will extend down the slope of the dentine surface and reaches its limit, where the inner epithelium is fused with the outer enamel epithelium to form Hertwig’s epithelial root sheath. Enamel mineral will increase daily (apposition growth) during the secretory stage of amelogenesis (enamel formation). Ultimately, the secretory stage will end and they will transition into maturation stage ameloblasts. These ameloblasts will move down to the enamel surface of the tooth and the shape of the crown and tooth is then established.