Tooth Development II - King Salman International University Lecture Data

Faculty Of Dental Medicine Oral Biology Department Lecture: (Tooth Development – Part II ) Ass. Prof (Fatma Adel Saad)  By Dr. Fatma Adel Saad Associate Professor of Oral Biology  Stages of Tooth Development (odontogenesis) Are classif...

Faculty Of Dental Medicine Oral Biology Department Lecture: (Tooth Development – Part II ) Ass. Prof (Fatma Adel Saad)  By Dr. Fatma Adel Saad Associate Professor of Oral Biology  Stages of Tooth Development (odontogenesis) Are classified according to: 1- Morphological stages: Changes in the morphology of the enamel/dental organ (epithelial part of the developing tooth germ). 2- Histo-physiological processes: During each morphological stage  histological & physiological changes (processes).  Morphological stages Crown formation Dental lamina 1- DENTAL LAMINA. (Initiation of Odontogenesis) 2- BUD-STAGE. 3- CAP-STAGE. 4- BELL-STAGE (early bell). 5- Appositional/ late bell stage Appositional/ late bell stage Bud Cap Bell 2- Bud Stage  At 8th WIU of development, *At facial aspect of the main dental lamina;  Localized epithelial proliferations (enlargements/outgrowths) into surrounding ecto- mesenchyme at certain sites (sites of developing deciduous teeth)  bud enamel /dental organ s *(5 bud dental Dental organs in each quadrant / 10 in each jaw). lamina How? Under the influence of the ecto-mesenchymal neural crest cells  the basal cells of oral epithelium divide & proliferate. Dental lamina (Induction) Lip Lip Tongue * * Lip Lip Lip Lip Chin Chin Dental lamina (sheet) Tongue Tongue Tongue  Dental lamina Bud Note: The bud dental organs of teeth will not develop at the same time Histologically: Histologically: Central 1-Peripheral cells (Cuboidal or cells Peripheral cells Short columnar). 2-Central cells (polyhedral) secrete glyocsaminoglycans extracellulary. Dental papilla 3-Dental papilla: condensed ectomesenchyme below bud dental organ  Shows increase in cells and fibrous tissue. 4- Dental folicle/sac: Inner zone: Dense & more fibrous ectomesenchyme Dental papilla surrounding both dental organ & dental papilla  Dental forming a follicle. follicle Outer zone: Loose ectomesenchyme. Histophysiological processes in bud stage: The main physiological processes in bud stage : 1- Induction. 2- Proliferation. Dental Dental lamina lamina How? *Teeth buds are formed under the influence of neural crest cells Bud (Induction). * Neural crest cells (ectomesenchymal cells) induced the formation of localized epithelial proliferations on facial aspect of the dental lamina. 3- Cap Stage  3- Cap stage. -The bud dental organ shows unequal growth under the influence of neural crest cells leading to the formation of a cap shape which is called enamel/dental organ. Cap Stage Dental lamina Bud  Cap Stage Dental organ Dental Dental Dental follicle follicle / sac papilla / sac Dentalfollicle / sac  Enamel organ Tooth germ Dental papilla Dental sac Enamel organ, dental papilla and dental sac are called Tooth Germ. gives Enamel organ Enamel gives Dentin and pulp Dental papilla gives cementum, alveolar bone and PDL Dental sac Histologically: Stellate R Components of the tooth germ O.E.E. 1- Outer enamel /dental epithelium (OEE)  A layer of cuboidal cells rested on outer basement membrane. 2- Stellate reticulum I.E.E. 3-Inner enamel /dental epithelium (IEE)  (A layer of short columnar cells rested on inner basement membrane) Cell free zone (temporary structure) Note: Two Broad connections Oral Oralepithelium epithelium Dental Dentallamina lamina *Inner & outer basement membrane Enamel separates the dental /enamel organ organ (epithelium) from surrounding ectomesenchyme. -The ectomesenchyme surrounding dental organ gives: 4- Dental papilla (inside concavity) of condensed ectomesenchyme with an Dental sac Dental increase in cells and fibrous tissue. papilla Thers is a cell free zone (temporary structure) at the periphery of dental papilla beneath the inner basement memebrane. 5- Dental sac surrounds both dental organ & dental papilla & formed of inner & outer zones. Histophysiological processes in cap stage: The main physiological processes in cap stage : 1-Proliferation: growth of enamel organ, dental papilla and dental sac. 2-Differentiation: a. Morpho-differentiation : Is the change in the shape of the dental organ from bud to cap. Outer D. E. Stellate R. Inner D. E. b. Histo-differentiation : Appearance of different types of cells, outer and inner enamel epithelium and stellate reticulum. c. Cyto-differentiation :Total and gradual transformation from an undifferentiated embryonic cells to a fully differentiated state for specialization). 4- Early Bell Stage  4- Bell stage (early bell) The cap shape of the dental organ changed into bell shape due to continuous unequal growth of the dental organ. During this stage, The main dental lamina is elongated and due to the mesenchymal invasion, it gives: Main DL Successional DL Lateral DL *Lateral dental lamina: Connects the deciduous dental organ to main dental lamina. *Successional dental lamina: Connects the dental organ of permanent successor to main dental lamina. B L -It is lingual to deciduous dental organ. Histologically: Bell stage  (from outside directed inward): 0- Dental laminae 1- Dental sac 2- Outer enamel epithelium 3- Stellate Reticulum (SR) 4- Stratum Intermedium (SI) Dental organ Note: 5- Premeloblasts 1-cervical loop is a part of the dental organ 6- Odontoblasts 2- tooth germ: dental organ + 7- Dental papilla D.papilla + D.sac Lateral Successional D.L D.L Dental sac Dental sac Dental papilla Cervical loop  9- Successional Dental lamina od 7. Preameloblasts 11- Cervical loop Histologically: Components of the tooth germ 1-Dental follicle (sac) Inner zone: dense & more D.Sac fibrous ectomesenchyme surrounding both dental organ & D.Sac dental papilla forming a follicle. Outer zone:Loose ectomesenchyme. Function : - Provide nutrition & support - Give rise to cells that form cementum, periodontal ligament & alveolar bone. 2- Outer enamel epithelium (OEE) A layer of cuboidal cells rested on outer basement membrane Function: Protection and nutrition transport 3-Stellate reticulum -These cells secrete extracellular glycosaminoglycan (hydrophilic)  so pulls water into enamel organ. - The cells are forced apart but retain their connections (desmosomal junctions). Thus, they become star shaped forming a network -These cells contain alkaline phosphatase. Function: -Acts as a store house for nutrient materials. -Acts as a cushion for mechanical protection. -Maintenance of tooth shape. -Support enamel production. - Keeps space for enamel matrix. 4-Stratum intermedium *2-3 layers of flattened cells firstly appears in bell stage (on preameloblasts). *Cells have desmosomal junctions between each other & other cells. *Contain much alkaline phosphatase. Function: - Synthesis of enzymes (alkaline phosphatase, Ca-Mg ATPase) -Supports enamel mineralization. -Nutrients& minerals transport from & to pre/ameloblasts 5- Pre-ameloblasts (From IEE)  Cap Bell stage stage Outer ectomesenchymal cells of dental papilla induce IEE to differentiate into preameloblasts. IEE Pre-ameloblasts Preameloblasts IEE 5- Pre-ameloblats (from IEE): Under the influence of ectomesenchymal cells found in the outer dental papilla (at periphery) * IEE increase in number  folding & map out the crown outline. * IEE increase in size  become tall columnar. *IEE increase in volume & in protein synthesis organelles. *Celluar repolarization nuclei move to apical end away from BM. *So, IEE differentiate into preameloblasts. Preameloblasts IEE  Cell repolarization in pre-ameloblasts preameloblasts. Inner dental epith. Apical end Basal end Cell free zone Nuclei move from basal end to apical end (Cellular repolarization in preameloblasts)  NOTE: Cell polarity preameloblasts. Inner dental epith. Apical/proximal end Basal/distal end Cell free zone Cell end (pole) is named according to: - Basement membrane  ( Basal end & Apical end) - Site of nucleus  ( Proximal end & Distal end) Partial disintegration of basement membrane preameloblasts. Inner dental epith. Proximal end Distal end Cell free zone Dental papilla Dental papilla  Preameloblasts -Preameloblasts secrete enzymes that partially degrade the underlying basement membrane. Dentin. Note: All these changes occur at first at the future incisal / cuspal region then proceed cervically. 6- Odontoblasts (From dental papilla)  Cap Bell stage stage Under the influence of preameloblasts Peripheral cells of dental papilla Odontoblasts IEE Preameloblasts Dental papilla Odontoblasts  Induce the outer cells of dental papilla. Odontoblasts Preameloblasts (cell repolarization) Preameloblasts Preameloblasts Dental papilla Odontoblasts 6- Odontoblasts: Under the influence of preameloblasts  the peripheral cells of dental papilla will: * Increase in number. * Increase in size  become tall columnar. *Increase in volume & in protein synthesis organelles. *Celluar repolarization  nuclei move to apical end away from B.M. *So, these cells differentiate into odontoblasts. IEE Preameloblasts Dental papilla Odontoblasts  Pre-ameloblasts How? Odontoblasts -Preameloblasts induce outer cells of dental papilla which differentiate into odontoblasts. -Then, preameloblasts release enzymes that fully degrade basement membrane separating them from odontoblasts. Function of odontoblasts: - Deposit dentin matrix and mineralize it.  7- Dental papilla (inside concavity) Condensed ectomesenchyme with an increase in cells and fibrous tissue. Function : - Provide nutrition & support. - Give rise to odontoblasts & pulp. 8- Cervical loop At cervical rim of enamel organ Histologically; It is formed of : A- Outer enamel epithelium B- Stellate reticulum C- Stratum intermedium D- Inner enamel epithelium Function: 1-At this region , the cells IEE continue to proliferate till crown SR attains full size (Growth center). SI 2- It will give rise to epithelial OEE component needed for root formation. All these changes start from incisal/cuspal region & then progress cervically (toward cervical loop) Bell Stage 9-Transient structures (in cap & bell stages) Enamel cord  Enamel knot Enamel cord Oral Oralepithelium epithelium Dental Dentallamina lamina  Transient structures a- Cell free zone (Acellular zone) The peripheral layer of the dental papilla is free of cells but contains their cytoplasmic processes and fine collagen argyrophilic fibers. It appears as a clear light zone beneath IEE in cap stage. It also gradually disappears with the differentiation of preameloblasts & odontoblasts. b-Enamel knot -A localized condensation of non dividing polyhedral epithelial cells at the center of the enamel organ in the region of the IEE. It appears at cap stage & disappear in bell stage by apoptosis. Function: -Crown patterning and cuspal morphogenesis. c- Enamel cord - A strand of non dividing polyhedral epithelial cells extending from enamel knot to OEE, over the incisal edge/cusp tip, dividing the stellate reticulum. Function: -Involved in the transformation of cap stage into bell stage (acts as a mechanical tie). -origin of stellate reticulum cells. Both enamel knot & cord disappear before beginning of enamel formation. Histophysiological stages of bell stage: The main physiological processes occur in early bell stage : 1-Proliferation (growth). 2-Morpho-differentiation : -The enamel organ changed from cap to bell shape. 3-Histo-differentiation -In addition to the previous three layers (outer enamel epithelium, inner enamel epithelium (preameloblasts) and stellate reticulum), a stratum intermedium appeared as well as odontoblasts in dental papilla. 4- Induction (Reciprocal induction) A- Outer cell layer of D.P induce IEE. SO, IEE Pre-ameloblasts B- Preameloblasts induce outer cell layer of D.P. SO, Outer cell layer of D.P Odontoblasts  Sample of Questions with model answers  Match the following columns with suitable answers 1. Dental organ a. Dentin 2. Dental papilla b. Periodontal ligament 3. Dental sac c. Enamel d. Dentin & pulp e. PDL,Cementum, alv. bone 1…….c 2……..d 3……….e Put √ or X and correct the wrong answers: 1- Induction by neural crest cells exists only in the bud stage. 2- Proliferation means change from one shape to another. 3- Morpho-differentiation presents in the stage of dental lamina formation. 4- Histo-differentiation in the cap stage results in the formation of the dental sac. 5- Neural crest cells have no role in tooth development.  Answers 1-Induction by neural crest cells is a characteristic physiological process in dental lamina formation and bud stage. 2- proliferation means growth in the tooth germ accompanied or not by change in the shape of enamel organ. 3-Morpho-genesis means change in the shape of the dental organ, thus it is a characteristic physiological process in cap and bell stages. 4-Histo-differentiation means changes in the cells shape. This physiological process is thus predominated in the cap, bell, appositional and maturation stages. 5-Neural crest cells play a great role in initiation of the tooth. First, they have the main role in dental lamina initiation. Second, they have the main role in bud formation. Identify the following histological sections: