in the future incisal and cuspal areas. Amelogenesis will then follow. The cervical portion of the enamel organ then gives rise to the Hertwig Epithelial Root Sheath (HERS)- this outlines the future root and also is responsible for the size, shape, length and the number of roots. Determination of crown morphology The composition of the enamel organ does not vary greatly between incisors, canines, premolars, and molars. Although the quantity of odontoblasts, ameloblasts and cementoblasts present in premolars/molars and incisors/canines remains the same, the major difference between these morphological types of teeth is the rate of secretion and quantity of products secreted by the enamel organ (dentine, enamel, cementum). There has been no definite consensus as to what determines the differences between enamel organs in different teeth. However, it is a widely held view by dental professionals and biologists that genes and cell signaling between cells in the dental extracellular matrix/enamel matrix play a role. The shape of the enamel layer covering the crown is determined by five growth parameters: The appositional growth rate Duration of appositional growth (at the cusp tip) Ameloblast extension rate Duration of ameloblast extension 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