Tooth Development Flashcards
What is the Crown?
Part of tooth covered w/enamel
Provide chewing surface
What is the Root?
Part of tooth covered with cementum and embedded in the jaw
Supports the crown
Periodontium includes?
Cementum
Alveolar bone
Periodontal Ligament
List the Crown Formation Stages
- Dental Lamina Stage
- Bud stage
- Cap stage
- Bell stage
- Apposition stage
- Maturation stage
What is Proliferation?
Cell dividing
What is Differentiation?
Cells stop dividing (if still dividing it won’t specialize!)
Undergo morphological changes, then acquire functional assignments
Ex. a cell becoming an odontoblast
What is Morphogenensis?
Establishment of shape and size of future tooth
Achieved by differential growth
Explain the Dental Lamina Stage
- Ectomesenchyme cell induce oral epithelium which creates horseshoe-shaped ridges along both jaws
- Successional dental lamina
Explain the Bud Stage
- Proliferation of DL epithelial cells at 10 locations on each ridge, which makes tooth buds
* Tooth buds: early enamel organs - Ectomesenchyme begins to condense around epithelial bud
Explain the Cap Stage:
- Morphodifferentiation
- unequal proliferation of bud cells (cap) - Ectomesenchymal cells become dental papilla (DP) and dental sac (DS)
- Creation of the tooth germ
- Succesional dental lamina forms on LINGUAL side of DL
- Cytodifferentiation
- four layers of enamel organ
What is a tooth germ?
Present in Cap Stage
enamel organ + dental papilla + dental sac
What does the enamel organ form?
Forms Enamel
Epithelial component of tooth germ
What does the dental papilla form?
Forms Dentin and Pulp
Derived from neural crest cells
What does the dental sac form?
Forms cementum, alveolar bone and periodontal ligament (basically forms the periodontium!)
Derived from neural crest cells
Explain the Bell Stage:
- Cont. differentiation of enamel organ that produces 4 distinct layers with different functions
- Creation of cervical loop
- Dental papilla cells continue to proliferate & they develop into the OUTER and INNER dental papilla cells
- Dental sac cells continue to proliferate & they develop into periodontal tissues
What are the 4 distinct layers the enamel organ produces in the Bell Stage?
Inner enamel epithelium
Stratum intermedium
Stellate reticulum
Outer enamel epithelium
Inner enamel organ (IEE) function
- Differentiate into ameloblasts (enamel forming cells)
- Induce the differentiation of adjacent cells of dental papilla into odontoblasts
Stratum Intermediate function
A layer of spindle-shaped cells adjacent to IEE cells.
Supports enamel mineralization - alkaline phosphatase
Stellate reticulum function
- Cells secrete glycosaminoglycans (GAG).
- GAG’s draw water into enamel organ increasing its volume.
Outer enamel epithelium (OEE) function
- Protective outer barrier for enamel organ.
- Associated with** capillary plexus**.
What is the cervical loop?
Junction of OEE and IEE
Explain the Apposition Stage:
- Matrix of enamel and dentin are laid down followed by initial calcification
- Reciprocal inductions between enamel organ and dental papilla occur in specific order (1-7)
Apposition/Ameloblast Functional Phases (in order!!!)
- Morphogenetic (IEE)
- IEE to preameloblasts - Differentiation
- Preameloblasts to preodontoblasts to odontoblasts - Initial Secretory ameloblast
- Odontoblasts to predentin and signals preameloblasts to create secretory ameloblasts - Secretory ameloblast
- Secretory ameloblasts begin secreting enamel matrix which calcifies to 30% ASAP - Ruffle-ended Maturation Ameloblast
- Smooth-ended Maturation Ameloblast
- Protective ameloblast
What is Reduced enamel epithelium? (REE)
-
Composed of the ISSO parts from Bell Stage!!
- Composed of flattened ameloblasts and the leftover 3 layers from enamel organ
- Covers and protects enamel
List and Explain Stages of Dentinogenesis
-
Mantle Dentin
*1st formed layer of dentin from newly differentiated odontoblasts
*Collagen fibers are perpendicular to DEJ -
Circumpulpal Dentin
* Dentin beneath the mantle dentin
* Collagen fibers are smaller in diameter and randomly oriented
List and explain the 2 types of dentin (phases) in Dentinogenesis
-
Pre-dentin
* Layer of organic collagen matrix
* Unmineralized (if unmineralized ALWAYS pre-dentin) -
Dentin
* Organic collagen matrix
*Hydroxyapatite crystals
Patterns of Dentin Mineralization
Globular Mineralization
Linear Mineralization
What is Globular Mineralization?
Calcophospherites grow and coalesce (unite)
Irregular mineralization front
Rate of dentin deposition is FAST
Calcophospherites are what?
Spherical foci of hydroxyapatite
What is Linear Mineralization?
More uniform mineralization front
Rate of dentin deposition is SLOW
What 2 things need to happen in order for root formation to occur?
Dentinogenesis
Cementogenesis
Root Formation (Maturation)
What does the Reduced Enamel Epithelium grow into after apical growth? How is it formed and what is it’s purpose?
Hertwig’s Epithelial Root Sheath
- Formed by: the joining of the IEE and the OEE
- Purpose: Shapes the root of the tooth and the formation of root dentin from odontoblasts
Root Formation (Maturation)
At what angle does the epithelial root sheeth proliferate?
Coronally at the angle of the epithelial diaphragm, but NOT at its tip because at the end is where proliferation is still occuring!
Root Formation (Maturation)
T/F: The epithelial diaphragm does NOT maintain a constant size during root formation
False!
The epithelial diaphragm DOES maintain a constant size
Root Formation (Maturation)
What does the remnants of HERS become?
Malassez’s epithelial rests
What is the difference between cementoid and cementum?
Cementoid: NOT mineralized
Cementum: mineralized
What is multiple root formation?
- Occurs when medial ingrowths or invaginations of the HERS
- The number of roots is determined by the number of medial ingrowths!
What is cementogenesis?
- Creation of cementum
- Occurs after the first layer of dentin is depositied and the cervical portion of Herwig’s root sheath breaks down
- Cementum is then deposited incrementally
- Creation order goes like this:
- Ectomesenchymal cells (dental sac cells) & new dentin contact
- Ectomesenchymal cells form cementoblasts, which then form cementum
What are the 2 types of fiber cementum formed during Cementogenesis? List their characteristics
Cellular intrinsic fiber cementum
- Secondary cementum: deposited AFTER tooth eruption
- Contains cementocytes
- Forms RAPIDLY
Acellular extrinsic fiber cementum
- Primary cementum: deposited during tooth eruption
- NO cementocytes
- Forms SLOWLY
What are the 3 types of Root Anomalies?
Exposed root dentin
Enamel pearls
Accessory root canals
Root Anomalies
Explain what exposed root dentin is
- An area of root dentin lacking cementum
- Occurs when epithelial root sheath remains attached to root dentin surface
- Ectomesenchymal cells won’t come into contact with root dentin so no cementoblasts will be created!
- Can be found anywhere along the root surface, particularly the cervical zone
Root Anomalies
Explain what enamel pearls are!
- An enamel droplet often found between the roots of permanent molars
- Formed when the epithelial root sheath remains attached to the root dentin surface
- Cells of the inner layer of the root sheath can differentiate into ameloblasts and form this
Root Anomalies
Explain what accesory root canals are!
- A small lateral canal (connecting PDL to main root canal)
- Formed if epithelial root sheath breaks down before root dentin is formed
- No ectomesenchymal cells (epithelial root sheath) to differentiate into odontoblasts= no root dentin formation
- Can be found anywhere along the root, particularly in the apical third or furcation area of multirooted teeth
