Tooth Development PDF

Oral Biology I Tooth Development Dr.Sara elbanna 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...

Oral Biology I Tooth Development Dr.Sara elbanna 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 The three germ layers 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. Tooth development starts at about 5-6 W.I.U. At first the development of the deciduous teeth then the permanent ones. Stages of tooth development for both deciduous and permanent teeth are classified according to morphology into: 1- Dental lamina. 2- Bud stage. 3- Cap stage. 4- Bell stage A- Early bell stage. B- Late bell stage. Bud. Cap. Early bell. Late bell. 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. Dental lamina  1-The Dental lamina Oral ectoderm Lining of Stomodeum Ectoderm Basement membrane (Ectomesenchyme) Mesoderm Neural crest cells 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. Vestibular Lamina 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  Bud stage L F I A N C G I U A A L L  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 The Bud stage: 1-Dental organ 2-Dental papilla 3-Dental sac  Bud stage Formation of a BUD from the dental lamina facial Next step - formation of a CAP from the bud 3-The Cap Stage  Cap stage “differential growth”  Oral epithelium Outer Enamel epithelium Dental Lamina Enamel Cord Enamel Knot Stellate Reticulum Cell Free Zone Dental Papilla Inner Enamel epithelium Dental Sac (Follicle)  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 Early bell stage  Stratum Intermedium Early Bell Stage Lateral Dental Lamina Cap Stage Odontoblasts Induction Membrana Prefrmativa Future Tooth shape (DEJ) Cervical Loop Deep Dental papilla  Early Bell Stage Oral Epithelium Outer Enamel Epithelium Stellate Reticulum Odontoblast Stratum intermedium D.P Inner Enamel Epithelium C.F.Z 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 Induction Proximal end I.D.E Distal end U.M.C Odontoblasts Centriol Golgi apparatus Nucleus Mitochondria Induction Proximal end I.E.E Distal end Centriol U.M.C Golgi apparatus Mitochondria Odontoblasts Nucleus 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  Oral epithelium Main Dental Lamina Lateral Dental Lamina Outer Enamel epithelium Successional Dental Lamina Preameloblasts Odontoblasts Stratum Intermedium Stellate Reticulum Dental Sac (Follicle) Cell Free Zone Inner Enamel epithelium Dental Papilla Cervical loop 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 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.  S.R. R.D.E S.I Reciprocal Induction RER Ameloblast Enamel matrix Dentine Dentine matrix (predentine) Odontoblast Induction & Reciprocal induction AMELOBLAST IEE Enamel matrix IEE Dentine Dentine D.P Odontoblast  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.  Ameloblasts Enamel matrix Dentine Predentine Odontoblasts 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. ROOT FORMATION Dental sac Cervical loop  + D.Papilla diaphragm epithelial Epithelial root sheath of Hertwig Epithelial root sheath of Hertwig  Dental Dental sac sac Rests of Malassez + D.Papilla Dental Dental sac sac Dental Dental sac sac And so on… Dental Dental sac sac 1- When enamel and dentine formation reached the future cemento-enamel junction, the cervical loop will proliferate to form epithelial root sheath of Hertwig without stellate reticulum or stratum intermedium. This part of Hertwig bends in horizontal plane and is called epithelial diaphragm. There is proliferation of the connective tissue of the dental papilla accompanying the proliferation of epithelial diaphragm. 2- The epithelial root sheath of Hertwig proliferates coronally to the epithelial diaphragm in coronal direction. 3- The inner enamel epithelium of the Hertwig sheath induces differentiation of odontoblasts from U.M.Cs. of dental papilla. 4- The differentiated odontoblasts will deposit dentine. 5- After dentine formation the connective tissue of dental sac proliferates and invade the epithelial sheath leading to its degeneration into strands of epithelial cells, which persist in periodontal ligament and called the epithelial rests of Malassez. 6- The cells of dental sac (U.M.Cs.) will be in direct contact with the formed dentine of the root and is differentiated into cementoblasts to form cementum. - The previous steps will be repeated till the all length of the root is formed, then the apical foramen will be reduced by apposition of dentine and cementum at the apex to form the normal apical foramen. MULTI-ROOTED TOOTH Root formation in multirooted teeth Tongue Like Extensions Their root will be formed as in single root i.e. 1- Epithelial diaphragm. 2- Epithelial root sheath of Hertwig. 3- Differentiation of odontoblasts. 4- Formation of dentine. 5- Degeneration of epithelial sheath. 6- Differentiation of cementoblasts. 7- Formation of cementum. This process is performed till it reach the level of bi- or trifurcation where the epithelial diaphragm will grow horizontally to form 2 tongue like projections in 2 rooted teeth and 3 tongue like projections in 3 rooted teeth. The tongue like projections will unit together to divide the wide apical foramen into 2 or 3 openings. On the pulpal surface, dentine will be formed and cementum from the other side of the united projections.  Functions of the Enamel Organ 1- Formation of the future crown shape. 2- Formation of enamel. 3- Induce the differentiation of odontoblasts to form dentine.  FUNCTIONS OF THE ENAMEL Organ's Cells 1- OUTER DENTAL EPITHELIUM. Active transport of materials from the dental sac to the dental organ specially, after hard dental tissues formation. Form the cervical loop with IEE 2- STELLATE RETICULUM. Act as a buffer against physical forces that may distort the configurations of the developing amelodentinal junction giving rise to gross morphological changes. It acts as a store house for the nutritive materials. It keeps room for the developing enamel. 3- STRATUM INTERMEDIUM. Control fluid diffusion into and out of the ameloblasts. It provides the enamel organ with alkaline phosphatase enzyme needed for mineralization. These cells plus the ameloblasts are considered a single functional unit responsible for enamel formation. 4- INNER DENTAL EPITHELIUM. Arranged in a pattern to determine the future morphology of the crown. Transport of the nutritive materials from the dental papilla to the enamel organ before dental hard tissues formation.  It exerts an organizing influence on the undifferentiated cells of the dental papilla to differentiate into odontoblasts. It lays down enamel matrix and helps in its mineralization. It shares with O.D.E.in the root formation. It Forms cervical loop with OEE  FUNCTIONS OF THE DENTAL PAPILLA AND DENTAL SAC The Dental Papilla Gives Rise To Dentin And Pulp & nutrition The Dental Sac Gives Rise The Cementum, Periodontal Ligament & Alveolar Bone Proper & nutrition  Function of the epithelial root sheath of Hertwig 1- To mold the shape of the root. 2- Initiate root dentine formation.  CLINICAL CONSIDERATIONS ACCESSORY ROOT CANAL Accessory root canal means that the pulp cavity is connected with periodontal tissue with an opening rather than the apical foramen. Mechanism of formation of accessory root canals 1- Early degeneration of the epithelial root sheath of Hertwig before the differentiation of the odontoblasts. 2- It occurs in areas, where the developing root meets a large blood vessel, where dentine will be formed around it. 3-Lack of complete union of the tongue like projections at the floor of the pulp chamber.  ENAMEL PEARL If the root sheath is not degenerated after dentine formation It may lead to: 1-Differentiation of I.D.E. into ameloblasts forming enamel pearl The most common site for it is the bifurcation of permanent molars. 2- No cementum well be formed and a bare dentin well result  INTERMEDIATE CEMENTUM If the epithelial sheath is degenerated after odontoblasts differentiation and before dentine formation this will lead to what is called intermediate cementum.  Premature degeneration of epith. Root sheath of Hertwig ( after odontoblasts differentiation and before dentin formation) Contains entrapped epithelial cells It occur at apical 2/3 of premolars and molars roots and rare in incisors and deciduous teeth