Enamel Flashcards
what supports enamel?
dentine
needs this to work properly
without it will fail
give characteristics of enamel
- hardest tissue in body
- brittle
- resists abrasion
- variable thickness
- translucent
- transparency increases with mineralisation
why is enamel not as thick in primary teeth?
meant to be in the mouth for a shorter period of time
compare surface enamel to deeper enamel
surface enamel is more mineralised and harder than deeper enamel
[this is only true of a tooth that hasn’t just erupted as over time enamel becomes harder]
how does enamel thickness vary within a tooth
hardness decreased from cusp tip / incisal edge to cervical region
this makes sense as the incisal edge needs to be harder for biting etc
what is the basic unit of enamel
enamel rod / prism
what is the width x length of an enamel rod
5 micrometres x 2.5mm
where are rods in enamel?
they run from the ADJ to the surface
orientation varies within and along the enamel
c
how many hyrdoxyapattite crystals does 1 rod contain?
over 10 to the power of 6 crystals
what are long parallel rods
cross striations in rod due to a consequence of growth when created
due to daily growth [approx 4 micrometres]
what are brown transverse striae
25-35 micrometres apart
formed at weekly intervals
what is the purpose of acid etching the enamel
not intended to actually remove rods
want to make the surface uneven to help make a connection between the enamel and the material
what is the composition of enamel?
• Hydroxyapatite (HA) ○ 95% weight ○ 90% volume • Water ○ 4% weight ○ 5-10% volume • Organic matrix ○ 1% weight ○ 1-2% volume ○ Proteins § Amelogenins § Enamelins § Peptides §Amino acids % is for healthy enamel only
what regulates the nanomechanical properties of enamel?
minor protein components - part of the organic matrix
what ways can forces be organised?
vertically or horizontally
when is crystallite orientation determined
during enamel formation
how are crytallites deposited?
at right angles to ameloblast membrane
what is the proposed scheme for the development of crystallites?
• Ameloblasts will create a globular structure in which the inner portions can be hyperconcentrated in terms of calcium and phosphate = supersaturation
• Proteins allow supersaturation of calcium but allow it in a very specific arrangement that creates the perfect form for the formation of the crystallites
• You need to have access to calcium phosphate for the crystal to grow on its own
• Cocoon protecting the calcium phosphate needs to be removed for crystal to form
• 2 stages of maturation
○ Mineralisation in the first stage is around 30%
○ We require breakdown of amelogenins
○ Amelogenesis imperfecta is condition linked to lack of breakdown of amelogenins
• Then crystal grows to full potential
what are Hydroxyapaptite (HA) crystals?
- HA: Ca10(PO4)6(OH)2
- Hexagonal crystallites
- 70 nm x 25 nm x up to 1 micrometre long
- Larger in enamel that in dentine, cementum or bone
ion substitution in HA crystals happen by what?
• Ion substitutions by: Mg2+, CO32-, F- Mg = metal carbonate = phosphate arrangement F = negative arrangement mix of these
Carbonated apatite = not perfect HA
When tooth is erupted, substitution occurs over time
Enamel matures in the mouth to have carbonated part removed
= becomes proper HA
what does the maturation of enamel need?
fluoride to be present
demineralisation and remineralisation process occurring
what does traditional histology of enamel use?
- ground sections
> mineral present, no soft tissues - decalcified sections
> no mineral, soft tissues
what is the shape of enamel rods?
sinusoidal course
‘S’ shape
not straight
Adjacent groups of rods have different orientations
Periodic orientation causes banding patterns (Hunter-Schreger bands)
what are Hunter-Schreger bands?
○ Rod periodic orientation
○ Absent in outer enamel
○ Rods are not arranged in a parallel arrangement
where would you find gnarled enamel?
○ Cusps
§ Greater concentration of the rods
§ This is to withstand the distribution of forces
name incremental lines
brown striae of retzius
perikymata
neonatal line (not common)
what features can be found at the ADJ?
• Enamel tufts
○ Hypo-mineralised regions due to residual matrix protein at prism boundaries
• Enamel lamella
○ Incomplete maturation of groups of prisms - ‘fault’ line extending through enamel thickness
• Enamel spindles
○ Odontoblast processes extending into enamel
○ Rare to see
why are early lesions often found in fissures in the enamel?
limited ability to buffer in these areas
how does enamel structure influence caries?
- Concentration of rods cuspally
- Arrangement of rods
○ Caries is not a one fits all process
○ Shape of carious lesion depends on the type of arrangement of the rods
