Amelogenesis and Enamel Flashcards
characteristics of amelogenesis and enamel (5)
Acellular tissue
No collagen in matrix
Formation involves both secretory and resorptive activities of ectodermally derived cells
Enamel is 5x harder than dentin
Enamel is the hardest tissue in the body
Compared to other mineralized tissues, the
Ca hydroxyapatite crystals are extremely
—, highly oriented, and packed into
rod-like structures, i.e., the —
large
“enamel rod”
Although 96% mineral, the basic rod structure of enamel exhibits some degree of
flexibility
Composition of Enamel (3)
1% Water
3% Organic Components
96% Inorganic
organic components include
• 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
inorganic component include
Ca hydroxyapatite
Amelogenin exhibits — properties
thixotropic
i.e., the ability to flow under pressure (thixotropy)
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 (2) changes
labile
quantitative and qualitative
Enamelin is an (3) protein
acidic, phosphorylated, and glycosolated
The largest of the enamel matrix proteins
enamelin
enamelin is preferentially restricted to the
enamel rod area
enamelin’s phosphorylated nature and initial accumulation
near the growing ends of crystals suggest that enamelin plays a role in (2)
crystal growth and nucleation
Tuftelin
appears restricted to the DEJ in enamel
tufts. It is thought to play a role in induction,
the initiation of mineralization, and possibly
functions as a junctional protein linking enamel
and dentin.
Sheathlin
is initially found throughout the rod and
and interrod enamel. However, it is preferentially
located in the rod sheaths.
Reciprocal Induction (6)
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 mineralization
during tooth development is (2)
anterior to posterior
(dentition) and coronal to
apical (individual teeth)
Stages of Ameloblast Function (5)
Morphogenic Stage Differentiation Stage Secretory Stage Maturation Stage Protective Stage
— individual ameloblasts contribute to the composition of one enamel rod
Four
Structural Features of Enamel (7)
Striae of Retzius Perikymata Hunter-Schreger Bands Gnarled Enamel Enamel Lamellae Enamel Tufts Enamel Spindle
Striae of Retzius
Incremental lines produced by periodic constriction of Tomes process associated with corresponding increase in the face forming the interrod enamel. Represents about 4-8 days of rhythmic enamel matrix apposition.
Cross striations
on each rod
represent 24 hours of enamel
matrix production, about
4 m/day.
Perikymata:
External (surface) manifestations of
the Striae of Retzius.
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.
Gnarled Enamel –
most commonly found in cusp tips.
Enamel rods appear to be twisted in a complex
arrangement. Very resistant to fracture and abrasion.
Enamel Lamellae:
Hypomineralized areas of enamel
extending from the DEJ for considerable distances
into the enamel. May be involved with smooth
surface caries.
Enamel Crack:
Cracks extend from the enamel
surface to variable distances into the enamel.
May extend into the dentin.
Enamel Tufts:
Hypomineralized areas of enamel at
the DEJ that are rich in enamelin and tuftelin.
Enamel Spindles:
Represent extensions of
odontoblastic processes and tubules across the basal
lamina during initial stages of matrix formation.
Hypomineralization
of enamel is primarily related to a delay
in the removal of amelogenin during maturation. Birthing
difficulties and nutritional deficiencies also commonly disturb
development.
Hypoplasia of enamel is 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 at
the time of the infection.
Mottled enamel
occurs as a result of a diet containing
relatively high levels of fluoride. Severe enamel fluorosis
may manifest as opaque areas, light-brown mottling, and
surface pitting.
Amelogenesis Imperfecta:
Defective enamel matrix
deposition which, in turn, voids the possibility of
enamel mineralization. Although there are multiple
types of amelogenesis imperfecta, the more common
types are autosomal dominant inherited.
Enamel Pearls & Cervical Enamel Projections (CEP):
Defects
that occur during apposition and maturation stages of tooth
development due to displacement of ameloblasts to root surface.
Enamel pearls most often involve maxillary molars and CEPs
most often involve the mandibular molars.
Dens-In-Dente
A deep invagination of the
crown or root that is lined
with enamel.
Dens-In-Dente prevalence rate
0.4-10% of all patients
Dens-In-Dente most commonly involves the
maxillary incisor
Enamel thickness ranges from – mm over the cusps
2 – 2.5
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
— is comprised of the remnants of the reduced enamel epithelium.
Enamel cuticle (a.k.a. primary enamel cuticle or Nasmyth’s membrane)
— is comprised of glycoprotein precipitates derived from saliva
and/or gingival crevicular fluids.
Enamel pellicle (a.k.a. acquired pellicle or salivary pellicle)