Amelogenesis Flashcards
What are the characteristics of enamel?
acellular tissue
no collagen
hardest tissue in body
Enamel is ___ times harder than dentin
5
What does formation of enamel involve?
both secretory and resorptive activities of ectodermally derived cells
What are the calcium hydroxyapatite crystals that are extremely large, highly oriented, and packed into rod-like structures called?
enamel rods
What percent of the enamel rod is mineral?
96%
What is the composition of enamel?
- 1% water
- 3% organic components (tyrosine-rich amelogenin protein or TRAP)
- 96% inorganic (calcium hydroxyapatite)
What unique property does amelogenin exhibit?
thixotrophic properties (ability to flow under pressure)
What happens to the amelogenin in the enamel crystals?
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
What are the characteristics of enamelin?
acidic
phosphorylated
glycosolated protein
What is the largest enamel matrix protein?
enamelin
What is the possible role of enamelin?
crystal growth and nucleation
What is the possible role of tuftelin?
induction, the initiation of mineralization, and possibly functions as a junctional protein linking enamel and dentin
Where is tuftelin restricted to?
DEJ in enamel tufts
Where is sheathlin located?
throughout the rod and interrod enamel but it is preferentially located in the rod sheaths
What is the process of reciprocal induction?
- Pre-tooth bud stage ectoderm specifies the “dental nature” of the underlying mesenchyme (neural crest cells)
- Neural crest cells (ectomesenchyme) then induces formation and proliferation of the dental lamina
- The dental lamina eventually separates into an outer and inner dental epithelium
- The inner enamel epithelium induces differentiation of odontoblasts
- Odontoblasts secrete the mantle layer of dentin
- 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 mineralizationduring tooth development is…
anterior to posterior (dentition) and coronal to apical (individual teeth)
What are the stages of ameloblast function?
Morphogenic Stage
Differentiation Stage
Secretory Stage
Maturation Stage
Protective Stage
What are the striae of retzius?
Incremental lines produced by periodic constriction of Tomes process associated with corresponding increase in the face forming the interrod enamel
How many individual ameloblasts contribute to the composition of one enamel rod?
four
Each striae of retzius represents about _______ days of rhythmic enamel matrix apposition
4-8 days
What are perikymata?
External (surface) manifestations of the Striae of Retzius
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
What is gnarled enamel?
most commonly found in cusp tips. Enamel rods appear to be twisted in a complex arrangement. Very resistant to fracture and abrasion
What are enamel lammellae?
Hypomineralized areas of enamel extending from the DEJ for considerable distances into the enamel. May be involved with smooth surface caries.
What is an enamel crack?
Cracks 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 are enamel spindles?
Represent extensions of odontoblastic processes and tubules across the basal lamina during initial stages of matrix formation
What is hypomineralization of enamel primarily related to?
delay in the removal of amelogenin during materation
What is hypoplasia of enamel usually induced by?
infectious diseases of childhood
What causes mottled enamel?
diet containing high levels of fluoride
What is amelogenesis imperfecta?
Defective enamel matrix deposition which, in turn, voids the possibility of enamel mineralization
What are enamel pearls and cervical enamel projections?
Defects that occur during apposition and maturation stages of tooth development due to displacement of ameloblasts to root surface
Where are enamel pearls most often?
maxillary molars
Where are cervical enamel projections most often?
mandibular molars
What is dens-in-dente?
A deep invagination of the crown or root that is lined with enamel
What is the prevelence of dens-in-dente?
0.4-10% of all patients
Where is dens-in-dente most common?
maxillary incisors
Enamel thickness ranges from _____ mm over the cusps
2 – 2.5 mm
The _______________ _________ represents an exaggerated hypomineralized striae of Retzius that forms at birth
neonatal line
The perikymata (enamel surface manifestations of the striae of Retzius) are also known as the…
imbrication lines of Pickerill
What is the enamel cuticle (nasmyth’s membrane) composed of?
comprised of the remnants of the reduced enamel epithelium
What is the enamel pellicle composed of?
comprised of glycoprotein precipitates derived from saliva and/or gingival crevicular fluids
