Amelogenesis Flashcards
Characteristics of amelogenesis and enamel
Acellular tissue. No collagen in matrix. Formation involves both secretory and resorptive activates of ectoderm ally derived cells. Enamel is 5x harder than dentin. Enamel is the hardest tissue in the body
Enamel rod compared to other mineralized tissues
the Ca++ hydroxyapatite crystals are extremely large, highly oriented, and packed into rod-like structures.
The basic rod structure of enamel exhibits some degree of
flexibility
Composition of enamel
1% of water.
3% organic components
96% Inorganic - Ca++ hydroxyapatite
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
Amelogenin exhibits thixotropic properties
The ability to flow under pressure (thixotropy)
As the enamel crystal size increases
The amelogenin flows away from btw the crystals and back towards the ameloblasts where it degraded by proteolytic enzymes (serine proteases and enamelysin)
Unlike other hard tissue proteins in which the organic matrix remains stable (ex: bone, cementum, dentin)
in the case of enamel the organic protein is labile and exhibits both quantitative and qualitative changes
Enamelin is
an acidic, phosphorylated and glycosolated protein. The largest of the enamel matrix proteins. Preferentially restricted to the enamel rod area. Its prohsphorylated nature and initial accumulation near the growing ends of crystals suggest that enamelin plays a role in 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
Shealthlin
is initially found throughout the rod sheath and interrod enamel. It is preferentially located in the rod sheaths
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
Dental lamina eventually separates into
an outer and inner dental epithelium
Reciprocal induction
the inner enamel epithelium induces differentiation of odontoblasts.
Odontoblasts secrete
the mantle layer of dentin
What happens after the mantle layer of dentin is formed
ameloblast differentiation is initiated and amelogenesis begins shortly
The gradient of cellular differentiation, matrix secretion, and mineralization during tooth development is
anterior to posterior (dentition) and coronal to apical (individual teeth)
What are the stages of ameloblast function
Morphogenic stage Differentiation stage (increase in size) Secretory stage (alkaline phosphatase) Maturation stage (ruffles border - increases surface area so it can remove excess proteins and water to harden the enamel) Protective stage
Enamel rods and ____ _ _____ run in different directions bc the different angles of enamel production
Striae of retries (incremental lines of retzius)
Four individual ameloblasts contribute to the composition of what
1 enamel rod - a key hole structure
what are the structural features of enamel
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 4-8days of rhythmic enamel matrix apposition
Cross striations
on each rod represents 24 hours of enamel matrix productions about 4mM/day
