Tooth development

The primitive oral cavity or stomodaeum is lined by stratified squamous epithelium called oral ectoderm which contact the endoderm of the foregut to form the bucco-pharyngeal membrane which rupture at about 27 days of gestation and the primitive oral cavity establish as connection with foregut. So the process of tooth development is related to the rupture of this membrane and starts after rupturing by 2-3 weeks when embryo about 6 weeks old. Most of the connective tissue cells underlying oral ectoderm are neural crest cells are ecto-mesoderm in origin.

Tooth development begins in anterior portion of maxilla and mandible and proceeds posteriorly. Certain areas of buccal cells of oral ectoderm proliferate more rapidly than the cells of adjacent areas which are 10 in number in each jaw for deciduous teeth. This lead to the formation of primary epithelium band that has invaded underlying ecto-mesenchymal tissue. Along each of horse shoe-shaped future dental arches ; from which dental lamina arise as a band of epithelium and serves as primordial for ectodermal portion of deciduous teeth. It developed as little knobs which represent the beginning of enamel organ as tooth bud. While the successors of the deciduous teeth are developed from lingual extension of the free end of dental lamina opposite to enamel organ of each deciduous tooth. The lingual extension of dental lamina is named the successional lamina which begin in development from 5th month in utro (permanent central incisor) to 10 month of age (second premolar) . Later on during development of the jaw ;permanent molars arise directly from a distal extension of dental lamina. The first molar is initiated at 4th month in utro; the second at about 1 year after birth; while the third molar at 4-5 year. ) .

Dental lamina and tooth bud

Vestibular lamina: An epithelial thickening developed independently labial and buccal to dental lamina in each arch. It is called lip furrow band). They subsequently hallow and forms oral vestibule between alveolar portion of jaw and lip and cheeks. Enamel organ: Is an epithelial structure arise from dental lamina as round swelling. Not all enamel organs starts to develop at same time . it starts in anterior mandibular region. Tooth development stages named after the changes in enamel organ shape as bud,cap and bell stage. Dental papilla: Is a mesenchymal cells condensation under enamel organ basement membrane which responsible for the change of enamel organ shape during tooth development. It shows active budding of capillaries and mitotic figures and its responsible for dentin and pulp formation Dental sac(D.F.S): Is a marginal condensation in ectomesnchymal tissue surrounding the enamel organ and dental papillae. It is composed of dense fibrous layer ;it protect tooth bud and give rise cementum and periodontal ligament.

Fate of dental lamina: Total activity of dental lamina extends over period of at least 5 year . still active in third molar region after it has disappeared except for occasional epithelium remnant. These remnants may give rise a discrete clusters of epithelial cells persists in the jaw called epithelial pearls. These clusters of cells may form small cysts over the developing tooth called eruption cysts which may delay eruption. Developed teeth lose their connection with dental lamina by degeneration due to mesenchymal invasion.

Histophysiological events (stages) of tooth development 1-intiation: It is the beginning of tooth development from the dental lamina (bud stage). Lack of initiation results in absence of either single or multiple teeth,most frequent missing teeth are permanent upper,lateral incisors,third molar and lower second premolars. Abnormal initiation results in development of single or multiple supernumerary teeth. 2-proloferation: Its capacity of cells to multiply, the proliferated cells will lead to change in size of the growing tooth germ.

3-histodifferention: The proliferated cells assume a definite shape and function, capable to multiply, this phase is seen in bell stage. 4-morphodifferention: The morphologic pattern or basic form and relative size of the future tooth, is established by morphodifferention this by differential growth. Disturbances in this phase may affect the form and size of the tooth, without impairing the functions of the cells. 5-appostion: Is the deposition of the matrix of the hard dental structures, apposition growth of enamel and dentin is a layer like deposition of an extracellular matrix. This type of growth is therefore additive. The basic developmental process is similar for all teeth but each developing tooth develops as anatomically distinct unit. Vitamins, minerals and hormones affect tooth development. Vitamin A is important for epithelial growth. Vitamin C for connective tissue development. Vitamin D is essential for calcification.  

2 1 4 3 5 Tooth germ in advanced bell stage Primordium of permanent tooth. Outer enamel epithelia. Stellate reticulum. Dental papilla. bone 1 4 3 5