L11 Flashcards
The periodontium: “Around the tooth” - The support system for the tooth
Cementum
Alveolar bone
Periodontal ligament (PDL)
Gingiva: Tooth-associated and gingival ligaments
Hertwig’s epithelial root sheath (HERS)
what is it?
Extension of enamel organ, transforms from cervical loop
Bilayer structure of IEE and OEE
Hertwig’s ERS
What does it do?
“Architect” of the root defining size and shape (morphogenesis)
Induces root odontoblast differentiation
But how do you get multiple roots?
Epithelial growth – epithelial interradicular process(es) = tongues of epithelium growing toward one another
Apical foramina (plural
Hertwig’s epithelial root sheath (HERS):
Differentiation of the root
Differentiation of root odontoblasts
Epithelial-mesenchymal signaling
Dental papilla:
Undifferentiated ectomesenchymal cells
HERS induces dental papilla cells to
differentiate to pre-odontoblasts, then odontoblasts
Root dentin forms in step with
HERS proliferation
HERS is a
transient structure
HERS disintegrates shortly after
inducing root odontoblast differentiation
Some HERS cells become
epithelial rests of Malassez (ERM)
Epithelial rests of Malassez (ERM)
ERM appear as clumps, strands, or networks of cells in the PDL
Surrounded by basement membrane
Sometimes close to root, sometimes several cell layers away
Function(s)? Can cause cysts. Also speculated to be involved with periodontal homeostasis or regeneration, but not proven…
Root dentin
continuous with
crown dentin
Dentinogenesis largely the same as crown
(exception: Interacting with IEE of HERS instead of IEE of enamel organ)
Cells:
Ectomesenchyme»_space; Dental papilla»_space; Pre-odontoblasts»_space; Odontoblasts
Types: Mantle dentin, circumpulpal dentin, predentin, primary/secondary/tertiary dentin, etc.
Epithelial-mesenchymal signaling in root
HERS
Smad4 transcription factor (TF) Sonic hedgehog (SHH) secreted signal → papilla cells
Dental papilla
Induces Gli1 TF
Downstream Nfic TF
Odontoblast differentiation
Without Nfic, dental papilla cannot respond to
HERS signaling and cells do not differentiate into odontoblasts
Result: Rootless teeth!
Developmental root defects
Defects of HERS growth and/or root dentin formation
Can make teeth prone to breakage, exfoliation, ankylosis, or cause difficult extraction and other issues
Dilaceration: deformity in shape/direction
“Rootless teeth”
Taurodontism: large pulp chamber at expense of root/furcation
Cementum comes in two main types
Defined by:
Presence/absence of cells within its matrix
Origin of collagen fibers of the matrix
Major types you need to be familiar with:
Acellular cementum = Acellular extrinsic fiber cementum (AEFC) = Primary cementum
Cellular cementum = Cellular intrinsic fiber cementum (CIFC) = Secondary cementum
Acellular cementum =
Acellular extrinsic fiber cementum (AEFC) = Primary cementum
Cellular cementum =
Cellular intrinsic fiber cementum (CIFC) = Secondary cementum
Cellular mixed stratified cementum (CMSC): A mix of =
alternating acellular and cellular layers
2 major types of cementum:
primary accellular cementum (covers 2/3rds of root).
Secondary Acellular cementum (covers apical 1/3rd of root)