enamel Flashcards
describe enamel composition
- almost entirely mineral
- 95% = organic HAP crystals
- 5% = unique enamel proteins, H2O, lipid material
- mature enamel = 1-3% organic matrix and 2% H20
- presence of H2O related to porosity of enamel
what does the organic matrix of enamel contribute
mechanical properties of enamel like fracture toughness
explain the physical properties of enamel
1) HARDEST biological tissue
2) highly mineralised and withstands both shearing + impact forces well
3) high abrasion resistance so wears down only slowly
4) low tensile strength
5) brittle
6) BUT high modulus of elasticity
what is the important of high abrasion resistance of enamel
means it wears down only slowly
imp bc enamel cannot undergo repair or replacement
what is the important of high modulus of elasticity of enamel
together w support of underlying dentine minimises possibility of fracture
explain the chemical properties of enamel
- calcium HAP crystallites containing impurities in tiny amounts (ie carbonates)
- larger crystallites than other mineralised tissues (30nm thick, 70nm wide = ADJ to tooth surface)
- pores (occupied by organic matrix +/or h2o) of <5nm between them
- NO CELLS in/on its surface
what is the origin of enamel
ECTODERMAL
- develops from IEE of tooth germ
what do enamel proteins do and what do they account for
- most imp components comprising organic matrix
- less than 1% of mature enamel weight BUT 25-30% of early developing enamel
what are the most abundant proteins in developing enamel and their %
1) amelogenin = 90-95%
2) ameloblastin = 5%
3) enamelin
what are the proteins in mature enamel and why
remaining 1% by weight of proteins is comprised of non-amelogenin proteins
bc amelogenins are selectively reabsorbed during enamel maturation (removal + modification of initially formed protein rich matrix)
- tuftelin and tuft proteins
explain the role of AMELOGENIN
- stabilisation of amorphous Ca-P phase
- controls crystal morphology + organisation
- control enamel thickness
explain the role of AMELOBLASTIN
- cell adhesion protein
- controls cell differentiation
- maintains enamel rod / prism integrity
explain the role of ENAMELIN
- controls mineral nucleation + elongated growth (possibly w amelogenin)
explain the role of TUFTELIN
- cell signalling
- enamel protein which persists in mature enamel
what is amelogenesis
process of enamel formation
secretory stage of amelogenesis:
all secretion + modification of matrix occurs via what
TOMES PROCESSES
secretory stage of amelogenesis:
what happens with the development of tomes processes
mineralising surface of enamel has pit like appearance (pits surrounded by inter-prismatic / interrod enamel)
secretory stage of amelogenesis:
why are BOUNDARY AREAS of prisms formed first
because crystallites are formed at surfaces of tomes processes at different rates
secretory stage of amelogenesis:
which areas secrete first and what does this mean
proximal regions between two processes (deep in junctional regions)
ALWAYS SECRETE AHEAD OF
more distal regions
forms walls that represent the periphery of the prism + interprismatic regions and outlines pits occupied by tomes processes
secretory stage of amelogenesis:
what happens to central pits
infilled by tomes processes as ameloblasts retreat to form main core of enamel prism
gives enamel its PRISMATIC STRUCTURE
secretory stage of amelogenesis:
what do ameloblasts have that accounts for variation in crystal orientation
2 secretory sites
secretory stage of amelogenesis:
what are inter-rod regions
regions between enamel rods and have different crystallite orientations and a higher organic content than them
what is the basic structural unit of enamel
this prism (rod)
why do we see prism boundaries and what happens at these boundaries
reflect sudden changes in crystallite orientation between prism core (head) and interprismatic enamel (tail) of ADJACENT prisms
crystallites deviate by 60 degrees from those in the prism core
more organic material + h20 (bc larger pores produced by abutment of HAP crystallites)