Amelogenesis And Enamel Flashcards
what are enamel rods
large slightly flexible, highly oritented calcium hydrozyapatite crystal
what is enamel composed of
-96% inorganic (calcium hydroxyapatite)
-3% organic compounds (TRAP)
-1% water
what constitues 90% of protein in enamel
amelogenin
describe amelogenin
thixotropic- ability to flow under pressure
-labile and exhibits both quantitative and qualitative changes
describe enamelin
phosphorylated-plays a role in crystal growth and nucleation
where is tuftelin located
in DEJ in enamel tufts
where is sheathlin found
located in rod sheathes
what happens in reciprocal induction
-pre-tooth bud stage ectoderm specifies the dental naure of the underlying mesenchyme
-neural crest cells then induce formation and proliferation of the dental lamina
-dental lamina eventually separated into the outer and inner dental epithelium
-inner enamel epithelium induces differentation of odontoblasts
-odontoblasts secrete mantle layer of dentin and ameloblast differentiation is initated and amelogenesis begins
where does amelogenesis occur
anterior -> posterior and coronal -> apical
what is the function of the morphogenic stage
cuboidal inactive cell
what is the function in the differentation stage
-cell increases in size and becomes tall and columnar
- junctional complexes occur
-induction of odontoblasts and mantle dentin
what is the function in the secretory stage
tomes processes and secretory granules
what is the function of the maturation stage
-height decreases
-ruffled border occurs
what is the function of the protective stage
hardening phase
- squishing together of the layers and form reduced enamel epithelium
what are tonofibrils
what the terminal web region in fully differentiated ameloblasts comprised
what do horizontal enamel rods represent
24 hour period of enamel production
how often do tomes processes constrict and change the angle at which the enamel is produced
every 4-8 days
what is the striae of retizius
angled enamel rods
-incremental lines produced by periodic constriction of tomes process associated with corresponding increase in the face forming the interrod enamel
how big are enamel rods
-takes 4 ameloblasts to contribute to
- about 60 nm in width and 100 microns long
what are perikymata
external manifestations of the striae of retzius
what are hunter schreger bands
optical phenomenon produced by changes in direction of the enamel rods
what is gnarled enamel and where is it found
found in cusp tips
- enamel rods appear to be twisted in a complex arrangement, resistant to fracture and abrasion
what is enamel lamellae
hypomineralized area of enamel extending from DEJ for considerable distances into the enamel
what are enamel tufts
hypomineralized areas of enamel at the DEJ that are rich in enamelin and tuftelin
