Week 3 - Amelogenesis & Enamel Flashcards
Is enamel cellular?
Acellular tissue
Does enamel have collagen?
No collagen in matrix
What does the formation of enamel involve?
Both secretory and resorptive activities of ectodermally derived cells
What is enamel harder than?
5x harder than dentin
What is the hardest tissue in the body?
Enamel
Describe the make-up of enamel?
Ca hydroxyapatite crystals that are large, highly oriented, and packed into rod-like structures i.e., the “enamel rod”
Is enamel flexible?
Although 96% mineral, the basic rod structure of enamel has some degree of flexibility
What is the composition of enamel?
1% water
3% organic components
96% inorganic
What are the organic components that make up enamel?
Tyrosine-rich amelogenin protein (TRAP)
- amelogenin constitutes 90% of the protein in enamel
- enamelin (5% of the protein)
- tuftelin (found in enamel tufts at DEJ)
- sheathlin
What is the inorganic component of enamel?
Calcium hydroxyapatite
What properties does amelogenein exhibit?
Thixotropic properties i.e., the ability to flow under pressure (thixotropy)
What happens as the enamel crystal size increases?
The amelogenin flows away from between the crystals and back towards the ameloblasts where it is degraded by proteolytic enzymes
Unlike other hard tissue proteins in which the organic matrix
remains stable (e.g., bone, cementum, dentin), in the case of enamel the organic protein is _______ and exhibits both ___________ and __________ changes
Labile; quantitative; qualitative
What kind of protein is enamelin?
An acidic, phosphorylated and glycosylated protein
What is the largest of the enamel matrix proteins?
Enamelin
Where is enamelin ristricted to?
The enamel rod area
What do the phosphorylated nature and initial accumulation near the growing ends of crystals suggest?
Enamelin plays a role in crystal growth and nucleation
Where is tuftelin restricted to?
The DEJ in enamel tufts
What does tuftelin play a role in?
induction, the initiation of mineralization, and possibly
functions as a junctional protein linking enamel
and dentin
Where is sheathlin found?
Throughout the rod and and interrod enamel
- However, it is preferentially located in the rod sheaths.
What stage specifies the “dental nature” of the underlying mesenchyme (neural crest cells)?
Pre-tooth bud stage
What do neural crest cells (ectomesenchyme) induce?
Formation and proliferation of the dental lamina
What does the dental lamina separate into/
Outer and inner dental epithelium
A. Stellate reticulum
B. Stratum intermedium
C. Ameloblasts
D. Mantle dentin
E. Odontoblasts
F. Pulpal cells
What does the inner enamel epithelium induce?
Differentiation of odontoblasts
What do odontoblasts secrete?
The mantle layer of dentin
What happens once the mantle layer of dentin is formed?
Ameloblast differentiation is initiated and amelogenesis begins shortly thereafter
The gradient of cellular differentiation, matrix secretion, and mineralization during tooth development is __________ to posterior (dentition) and _________ to apical (individual teeth).
Anterior; coronal
What are the stages of ameloblast function?
Morphogenic stage
Differentiation stage
Secretory stage
Maturation stage
Protective stage
A. Stellate reticulum
B. Stratum intermedium
C. Ameloblasts
D. Tome’s process
E. Enamel
Solid arrow points to enamel rods (running left to
right). Striae of Retzius (a.k.a. incremental lines of
Retzius) run from top left towards the bottom right
How many individual ameloblasts contribute to one enamel rod?
Four
Enamel rods
Enamel rods
What are structural features of enamel?
Striae of Retzius
Perikymata
Hunter-Schreger Bands
Gnarled Enamel
Enamel Lamellae
Enamel Tufts
Enamel Spindle
What are striae of retzius?
Incremental lines produced by periodic constriction of Tomes process associated with corresponding increase in the face forming the interrod enamel.
What do striae of retzius represent?
4-8 days of rhythmic enamel matrix apposition
What do cross striations on each rod represent?
24 hours of enamel matrix production
What are perikymata?
External (surface) manifestations of the striae of retzius
Perikymata
What are hunter-schreger bands?
an optical phenomenon
produced by changes in direction of the enamel rods.
- Seen only in ground histologic sections viewed by reflected light
Where is gnarled enamel most commonly found?
On cusp tips
What is gnarled enamel?
Enamel rods appear to be twisted in a complex arrangment
What is gnarled enamel resistant to?
Fracture and abrasion
What is enamel lamellae?
Hypomineralized areas of enamel extending from the DEJ for considerable distances into the enamel
What can enamel lamellae be involved with?
Smooth surface caries
What is an enamel crack?
Crack extend from the enamel surface to variable distances into the enamel
- may extend into the dentin
What are enamel tufts?
Hypomineralized areas of enamel at the DEJ that are rich in enamelin and tuftelin
What do enamel spindles represent?
extensions of odontoblastic processes and tubules across the basal lamina during initial stages of matrix formation
What is hypomineralization of enamel related to?
A delay in the removal of amelogenin during maturation
- Birthing difficulties and nutritional deficiencies also commonly disturb development
What is hypoplasis of enamel generally induced by?
Infectious diseases of childhood, e.g., measles, rheumatic fever, mumps, etc which leave a defect in those parts of the teeth actively developing the time of the infection
What does mottled enamel occur as a result of?
A diet containing relatively high levels of fluoride
What does severe enamel fluorosis manifest as?
Opaque areas, light-brown mottling, and surface pitting
What is amelogenesis imperfecta?
Defective enamel matrix
deposition which, in turn, voids the possibility of
enamel mineralization
What is the more common type of amelogenesis imperfecta?
Autosomal dominant inherited
What is enamel pearls and cervical enamel projections (CEP)?
Defects that occur during apposition and maturation stages of tooth development due to displacement of ameloblasts to root surface
What teeth do enamel pearls and CEPs most often involve?
Pearls: maxillary molars
CEPs: mandibular molars
What is dens-in-dente?
A deep invagination of the
crown or root that is lined
with enamel
What is the prevalence of dens-in-dente and what tooth is it most commonly in?
Prevalence rate of 0.4% to
10% of all patients.
Most commonly involves the
maxillary incisor
What is the enamel thickness range over cusps?
2-2.5mm
What does the neonatal line represent?
an exaggerated hypomineralized striae of Retzius that forms at birth
What is the perikymata?
Enamel surface manifestations of the striae of retzius AKA imbircation lines of pickerill
What is the enamel cuticle comprised of?
Remnants of the reduced enamel epithelium
What is the enamel pellicle comprised of?
Glycoprotein precipitates derived from saliva
and/or gingival crevicular fluids
