Tooth Formation Stages PDF

When does the tooth formation start? At 5 – 6 W.I.U. The primitive oral cavity or stomodeum is lined by ectoderm of two or three layers. The basal layer is columnar and the superficial layer is flattened cells. The ectoderm is separated from mesoderm by basement membrane....

When does the tooth formation start? At 5 – 6 W.I.U. The primitive oral cavity or stomodeum is lined by ectoderm of two or three layers. The basal layer is columnar and the superficial layer is flattened cells. The ectoderm is separated from mesoderm by basement membrane. Ectoderm Mesoderm Basement membrane Basal cell layer Neural crest cells migrate from developing central nervous system to be present in the stomodeum mesoderm so it is called ectomesenchyme and they initiate the morphological stages of tooth development. Crest area Dental Lamina Bud Stage Cap Stage Bell Stage  1-Dental Lamina Flat cells ECTODERM ( Stratified squamous epith. ) Columnar cells Basement membrane Ectomesenchym Mesoderm+neural crest cells  By the influence of the neural crest cells, the basal columnar cells of ectoderm will proliferate downward forming ingrowth of ectoderm in the underlying ectomesenchyme. How many dental laminae in each arch? 1 dental lamina in each arch  Fate & function of the dental lamina 1- Initiation Of The Entire Deciduous Dentition at 7 w.i.u. 2- Initiation Of The Permanent Successors by deep proliferation to give successional lamina at 5 m.i.u. 3- Initiation Of The Permanent Molars by growing distally into the jaw at 4miu and 1 ,4 years. The activity of the dental lamina extends over a period of about five years and disintegrates completely or remains as epithelial rests of Serres. Develops at 6 W.I.U: as an ectodermal proliferation facial to the dental lamina. The cells will rapidly proliferate and then the central cells degenerate to form cleft which become the vestibule between cheek, lip and the jaws Tongue Dental lamina Vestibular lamina  Oral ectoderm Dental Vestibular lamina lamina will grow down and split on the tooth’s facial side creating alveolar & labial/buccal mucosae 2-The Bud Stage  From the facial side of the dental lamina ;10 ectodermal swellings for deciduous teeth in each jaw appear having the bud shape Facial side which is called the dental (enamel) organ. Lingual side The supporting ectomesenchymal cells aggregate beneath the epithelial bud and are called dental papilla Dental sac (dental follicle) encircles the enamel organ and dental papilla. Dental organ + Dental papilla + Dental sac = Tooth germ.  The dental organ is responsible for the formation of ENAMEL. The dental papilla is responsible for the formation of DENTINE and PULP The dental sac is responsible for the formation of ALVEOLAR BONE PROPER, CEMENTUM & PERIODONTAL LIGAMENTS 3-The Cap Stage  By differential growth of the dental organ the bud will change its shape to cap : a) Outer convex facing the dental sac and inner concave surface which faces the dental papilla. b) The enamel organ has short and broad connection to the dental lamina Cap Stage is formed of: A) Enamel organ 1- Outer dental epithelium (O.D.E.) : single layer of cuboidal cells with deeply stained round nuclei 2- Inner dental epithelium (I.D.E.) : single layer of columnar cells with deeply stained round nuclei. 3- Stellate reticulum star shaped cells attaches to each other and with both outer and inner dental epithelia by desmosomes with mucopolysaccharides fluid in the intercellular space occupying the center of the enamel organ between (O.D.E.) and (I.D.E.) 4- Condensation of cells of the I.D.E are called enamel knot. 5- From the enamel knot polyhedral cells extend to the (O.D.E.) which is called enamel cord. These two structures are transient and may disappear before enamel formation Their Functions : 1- Enamel cord may give stratum intermedium in the early bell stage. 2- Enamel Knot determine the position of cusp tips and incisal edge B) Dental papilla 1-Formed of condensation of ectomesenchymal cells. 2- Separated from the enamel organ by a cell free zone which contain no cells but contains cytoplasmic process of ectomesenchymal cells and argyrophilic fibers Dental papilla Cell free zone C) Dental sac Formed of condensation of ectomesenchymal cells and more fibers around the enamel organ and dental papilla. The Dental Lamina. Outer Dental Epith. Stellate reticulum. Inner Dental Epith. Dental sac. Dental papilla.  The Bell Stage Differential growth of the dental organ causes more deepening of concave surface giving the bell shape  Early bell stage: No hard dental tissues Late bell stage: Hard dental tissues are present 4-The Early Bell Stage Main dental lamina Lateral dental lamina Successional dental lamina 1- Dental lamina It will be divided into lateral dental lamina carrying the enamel organ of the deciduous tooth and the main dental lamina that grow deeply to give the permanent successor (the successional lamina). 2- Dental organ A) O.D.E.: It becomes low cuboidal cells. B) I.D.E.: 3 changes occur: 1- It is arranged on the basement membrane to give the pattern of the future dentino-enamel junction and so the morphology of the future crown. 2-It becomes tall columnar (40 microns) on the expense of the cell free zone, so it will come in contact with undifferentiated mesenchymal cells of the dental papilla which will be differentiated into odontoblasts. This process is called induction 3-Change in functional polarity i.e. the nucleus and mitochondria are proximal (facing the stratum intermedium) and the Golgi apparatus and centrioles are distal (facing the dental papilla). Induction means differentiation of UMC of the dental papilla into odontoblasts under the influence of the I.D.E. Inner dental epith. Proximal end Distal end Cell free zone Odontoblasts Centriol Golgi apparatus Nucleus Mitochondria C) Stellate reticulum. The mucoid fluid in the intercellular spaces is increased and the cells become further apart with smaller bodies and taller processes. D) Stratum intermedium. It is formed of 2-3 layers of squamous (flattened )cells between I.D.E. and stellate reticulum. These cells are rich in alkaline phosphatase enzyme which is essential for enamel mineralization. E) Cervical loop. The I.D.E. and O.D.E. meet each other in a stable rim where the I.D.E. covers the O.D.E.  Cervical Loop St.ret Inner dental epithelium Outer dental epithelium 3- Dental papilla. 1- Differentiation of odontoblasts. 2- Thickening of the basement membrane between IDE. and odontoblasts called membrana preformativa. 4- Dental sac. 1- The fibers show circular arrangement 2- The inner surface of it facing the dental papilla and enamel organ becomes more vascular. 5-The Late Bell Stage Starts by the formation of the 1st layer of dentine. The epithelial enamel organ (free of blood vessels) will not depend only on dental papilla for nutrition so, changes will take place in it to gain other source of nutrition (from dental sac).  1st layer of dentin formation Reciprocal induction Enamel Matrix Formation 1) Dental lamina. The lateral dental lamina will be degenerated and its remnants are called epithelial rests of Serres or (Serres' pearls) 2) Enamel organ. A) O.D.E. 3 changes occur: 1- The convex smooth surface will be folded to increase the surface area at the zone facing dentine formation, where there are more capillary loops in the dental sac. 2- The cells of O.D.E. will be flat 3-Cells will develop microvilli(to increase surface area for fluid exchange), cytoplasmic vesicles and increased number of mitochondria. B) I.D.E. The I.D.E. under the influence of the first layer of dentine formed (with a process called reciprocal induction) will be differentiated into ameloblasts.  outermost papilla cells have become Odontoblasts Odontoblasts make dentine, which signals inner epithelial cells to become ameloblasts C) Stellate reticulum. By the formation of enamel the stellate reticulum will be shrunken after fluid loss starting from the tip of the cusp cervically. D) Stratum intermedium. It is rich in alkaline phosphatase, acid mucopolysaccharides and glycogen. Dental papilla: becomes the dental pulp Dental sac: becomes more vascular and near the O.D.E. HISTO PHYSIOLOGICAL STAGES 1 – INITIATOIN. 2 – PROLIFERATION. 3 – HISTODIFFERENTIATION. 4 – MORPHODIFFERENTIATION. 5 – APPOSITION. 1- Initiation. Represented by the dental lamina and bud stage. 2- Proliferation. Represented by dental lamina, bud, cap, early bell stages just before hard dental tissue formation. 3- Histodifferentiation. Represented by early and late bell stages. There are differentiation of stratum intermedium, odontoblasts and ameloblasts. 4- Morphodifferentiation. Represented by early and late bell stages. 5- Apposition. Occurs at late bell stage.