Tooth Development

• epithelium is derived from the ectoderm
• neural crest cells give rise to ecto-mesenchymal cells
• the enamal organ is derived from the ectoderm
• cementum, periodontal ligament and alveolar bone are derived from the dental follicle
• dentine and pulp are derived from the dental papilla
• the dental follicle and papilla are derived from the ecto-mesenchyme
• tooth development starts at six weeks
• the primary epithelial band divides into the dental lamina and vestibular lamina
• the laminae give rise to 52 buds, with 20 deciduous and 32 permanent
• the significance of the bud stage is it forms the future crown shape
• in the bud stage the enamel organ proliferates, forming a bud shape
• in the cap stage, the dental papilla surrounds the enamel organ
• in the late cap stage, the inner enamel organ becomes stellate reticulum
• in the bell stage, the inner enamel epithelial cells elongate and become pre-ameloblasts
• remnants of the dental lamina are called pearls of Serres
• the outer enamel epithelium are cuboidal cells and communicate via desmosomes and gap junctions
• the stellate reticulum are star-shaped cells and its function relates to protection
• the stratum intermedium are flattened cells, contains alkaline phosphatase and is concerned with protein synthesis and transport to the ameloblasts
• the inner enamel epithelium are columnar cells, rich in RNA, do not contain alkaline phosphatase
• the late bell stage or appositional stage, is the formation of hard tissues
• the pre-odontoblasts lay down the first layer of dentine
• the transitory structures are the enamel knot, cord and nihe
• the enamel knot is a mass of cells in the inner enamel epithelium and disappears in the bell stage
• the enamel cord extends from the stratum intermedium to the stellate reticulum, when it completely divides the two it is called the enamel septum
• the enamel niche is found between the strands attached to the dental lamina
• the cervical loop is where the outer enamel epithelium meets the inner enamel epithelium
• cell proliferation at the cervical loops creates Hertwig's epithelial root sheath
• the bending of the root sheath at 90 degrees makes the epithelial diaphragm
• the remnants of Hertwig's root sheath become the cell rests of Malassez
• hypodontia is absence of less than 6 teeth, not including third molars
• oligodontia is the absence of more than 6 teeth
• anodontia is the complete absence of teeth
• gemination is the partial division of a tooth germ