Odontogensis Flashcards
What two cells do teeth develop from?
Oral epithelial cells: ectoderm origin Mesenchyman cells: ectomesenchymal origin
What is the first stage of tooth development?
Initiation/ 6-7th week. Induction: Ectoderm lining stomodeum gives rise to oral epithelium and then to dental lamina; adjacent to deeper ectomesenchyme, which is influenced by the neural crest cells. Both tissue types are separated by a basement membrane
what is the second stage of tooth development?
Bud stage 8th week. Proliferation; Growth of dental lamina into bud shape that penetrates growing ectomesenchyme
What is the third stage of tooth development ?
CAP STAGE 9th-10th week: Prolifferation, differentiation, morphogensis. Formation of tooth germ as enamel organ, that forms into cap shape that surrounds inside mass of dental papilla, with an outside mass of dental sac, both from ectomesenchyme
What is the fourth stage of tooth development?
BELL STAGE. 11th-12th week; proliferation, differentiation morphogenesis. Differentiation of enamel organ into bell shape with 4 cell types dental papilla into 2 cell types
What is the fifth stage of tooth development?
Apposition; induction, proliferation. Dental tissue types secreted in successive layers as matrix
What is the sixth stage of tooth development?
Maturation, dental tissue fully mineralise to mature form
Describe initiation of tooth development
Thickened band of epithelium forms primitive jaws called the primary epithelial band, each band quickly gives rise to 2 sub divisions: vestibular lamina & dental lamina
PICDescribe dental lamina
Epithelial outgrows at the sites corresponding to the future deciduous teeth
What orientation do succesional dental lamina move in bud stage?
Lingual, or palatal
Describe the cap stage
Commencement of cell proliferation and the beginning of cell differenciation.
Enamel organ: future enamel.
Formation of the tooth bud in a cap shape with a deep central depression,
Dental papilla: condenses mass of ectomesenchyme within the concavity of enamel organ (future dentin & pulp)
Dental sac/follicle: ectomesenchyme surrounding the outside of the enamel organ (forms future cemntum, PDL, alveolar bone
Describe the bell stage
Further proliferation & histogensis. External enamel epithelium cubodial, stellate reticulum, strattim intermedium, internal enamel epithelum. Outer and central cells of dental lamina. Dental lamina break down
Describe the apposition and maturation stage of tooth development
During the apposition stage enamel dentine and cementum are initally secreted as a matrix in layer. Maturation is mineralisation of this matrix
Define apposition
Cells of the inner enamel epithelium differentitate into preameloblasts and undergo repolarisation. This stimulates the differentiation of odontoblasts from the mesenchyma cells of dental papilla. The enamel organ looses connection with oral epithelium due to the break down on the dental lamina, odontoblasts begin dentinogenesis secreting predentine
PICWhat is the process of Apposition?
Basement membrane between the preameloblasts and the odontoblast disintegrates, preameloblasts come into contact with newly formed predentine → triggering preameloblasts to differentiate into ameloblasts and commence amelogenesis → tomes process = mineralisation of the disintegrating basement membrane forms the DEJ
Describe crown maturation
Dentinogensis forms the foundation that proceeds amelogenesis. Bulk of crown is formed by dentinogenesis & amelogensis
Describe dentinogenesis
Process develops at proximal end of odontoblast, as cell secretes matrix in increments it moves pulpward this odontoblastic process elongates and is left in dentine.
Describe Amelogensis
Process starts at cusps, ameloblasts retreat & lay down incremental deposition of enamel matrix stretching from ameloblasts to the surface. Calcium phosphate crystals are deposited and matrix begins to mineralise. Resulting in maturation
Describe root formation
Occurs after crown completion, and eruption commencement. The cervical loop elongates moving away from the crown to enclose more of the dental papilla tissue and form Hertwig root sheath
PICDescribe Cementum Formation
Outer root sheath cells form acellular cementum covering dentine, on completion these cells disperse to form epithelial rests in the future PDL space. Ectomesenchymal cells of dental follicle differentiate into cementoblasts and secrete cementoid over the acellular cementum which later calcifies into cellular cementum.
How does periodontal ligament formation form?
Dental follicle cells differentiate into fibroblasts who form collagen fibers. → Fibers embed in cementum and other end embeds in alveolar bone, →Fibers bundles increase in density as teeth erupt into functional occlusion
What are the three phases of tooth eruption?
Pre-eruptive phase Prefunctional eruptive phase Functional eruptive phase
Describe what happens in Pre-eruptive phase?
Movements related to tooth eruption begin during crown formation. Phase is finished with early root formation.
Describe the prefunctional eruptive phase (root formation)
Root formation: Proliferation of epithelial root sheath that cause initiation of root dentin and pulp formation.
Describe the prefunctional eruptive phase (movement)
Occurs occlusally through bony crypt of jaws to reach oral mucosa.
Describe the prefunctional eruptive phase (Penetration)
Of tooth’s crown tip through the fused epithelial layers allowing entrance of crown to oral cavity
Describe the prefunctional eruptive phase - Intraoral insical/occlusal movement
Eruptive tooth continues until clinical contact with opposing crowns
Describe the prefunctional eruptive phase - tissues overlying the teeth
Tissues overlying the teeth: Degenerate resulting in eruption pathway. Gubernacular cord directed to mucosa. Osteoblastic and osteoclastic function to remodel bone as teeth enlarge and move. Resorption of roots of deciduous teeth, similar to the process of bone resorption for their eruprion
What are the elements of Prefunctional Eruptive phase?
Root formation Movement Penetration Intraoral incisal/occlusal movement Tissues overlying the teeth Tissue underlying the teeth
Describe the prefunctional eruptive phase - tissues underlying the teeth
As crown erupts more space is made to accomodate rooth lengthening. Root dentine and cementum development. Fine trabeculae form in fundic area fist, and gradually bone becomes denser until functional occlusion is reached
Describe Functional Eruptive Phase
Takes place after teeth are functioning and continues as long as teeth are present. During this period of root completion, height of alveolar process undergoes a compensating increase The fundic alveolar plates resorb to adjust for formation of the root tip apex. Increased mineral density of bone.
What is Anodontia?
Absence of teeth
What is Hypodontia?
Absence of 6 or fewer teeth?
What is hyperdontia?
Supernumerary teeth and supplemental teeth
What is the variation in tooth size?
Macrodontia, microdontia
What is Den Evaginatus?
Extra cusp due to effects on enamek organ (talon)
What is germination?
Occurs in a single tooth germ, tried to unsuccessfully to divide into two tooth germs
What is fusion?
Results form the union of two adjacent
What is Enamel Dysplasia?
Faulty development of enamel - hypoplasia, hypomineralisation, dentine dysplasia
What are some variations in root formation?
Enamel pearl, dilaceration. Cementun formation
When do the early stages of tooth development commence?
6th week in utero
