Enamel Morphology Flashcards
physical characteristics of enamel
- hardest tissue in the body
- resists abrasion
- brittle
- supported by dentine
- covers tooth crown
- varies in thickness
- translucent
- transparency increases with mineralisation
why does enamel need to be supported by dentine?
in order for enamel to act properly
if unsupported becomes too brittle and fails
what are the shape of dentine tubules?
S shape (sinusoidal)
which class of teeth has thinner enamel?
decidous
what is enamel thickness mainly based upon?
function (worn enamel at tip of incisor because of tooth wear, deciduous teeth have thinner enamel as less time in oral cavity)
enamel regional variations
- surface enamel more mineralised and harder than deeper enamel
- hardness decreases from cusp tip/incisal edge to cervical region
have functional and clinical significance
where is enamel is more mineralised?
surface enamel more mineralised and harder than deeper enamel
what is the basic unit of enamel?
enamel rod/prism
what is the dimensions of an enamel rod?
5um x 2.5 mm
length of enamel
where to rods run from?
ADJ to surface
how are rods arranged?
enamel rods orientation varies within and along rod
- some crystallites are parallel and some perpendicular
- some have inclination
what dictates the arrangement of the rod?
crystallite orientation
what causes cross striations in enamel?
daily growth
- see long parallel rods
- approx. 4um
what caused brown transverse striae in enamel?
weekly intervals of growth
- 25-35um apart
why do we use acid etch on enamel?
make enamel structure more gripping, increase in Surface area - makes more uneven
what basic shape are enamel rods?
key hole
- with head and tail
what are enamel rods composed of mainly?
crystallite (hydroxyapatite)
SEM is
scan electron microscopy
breakdown of enamel content
hydroxyapatite - 95% weight (90% volume) water - 4% weight (5-10% volume) organic matrix - 1% weight (1-2% volume)
in healthy enamel
what proteins are in the organic matrix of enamel?
amelogenins
enamelins
peptides
amino acids
what causes the changes in weight and volume % for HA, water and organic matrix?
density
what happens to composition of enamel after restoration?
changes - lose water and organic matrix
significant change for the ability of enamel to withstand forces
what is in dentine but not in enamel?
collagen
why does enamel require organic component?
to withstand forces
- nanomechanical properties
otherwise too brittle
when is crystallite orientation determined?
during enamel formation
- the matrix itself established lay out of crystallites
how are crystallites deposited in relation to ameloblast membrane?
at right angles
what other process also influences crystallite orientation?
tommes process
what are the 2 stages in enamel maturation?
mineralisation at first stage is approx. 30%
need break down of amelogenins
crystal can then grow to full potential
what condition occurs if no breakdown of amelogenins?
amelogenins imperfecta
what is supersaturation?
proteins in enamel matrix allow hypersaturation of Ca and PO4 in a very specific arrangement, that creates the perfect form for crystallite formation
hydroxyapatite formula
Ca10(PO4)6(OH)2
what shape are hydroxyapatite crystals?
hexagonal
dimensions of HA crystals
70nm x 25nm x up 1um long
not all the way through rod
what ions can be substituted into HA
Mg2+
CO3 (2-)
F-
when is carbonated apatite more common? CO3 (2-)
when tooth erupting, as enamel matures carbonated apatite decreases
ground sections contain
minerals (no soft tissue)
decalcified sections contain
soft tissues only (no mineral)
enamel rods shape characteristics
- run in sinusoidal shape
- adjacent groups of rods have different orientations
- periodic orientation causes banding patterns (Hunter-Schreger bands; not parallel)
what causes Hunter-Schreger bands in enamel?
periodic orientation in enamel rods
- not parallel
- absent in outer enamel
what is gnarled enamel?
- optical effect at cusps
- greater concentration of rods in cusps regions as distribution of forces requires it
what are 2 types of incremental lines you can see in enamel?
- brown striae of Retzius
- Perikymata
what is a neonatal line?
particular band of incremental growth lines
- Consequence in changes in diet and physiological changes at birth
what are perikymata?
incremental growth lines that appear on the surface of tooth enamel as a series of linear grooves.
- Can disappear over time due to abrasion
what are enamel tufts?
hypominerlised regions due to residual matrix protein at prism boundaries
- at ADJ
- can see projection into rods
what are enamel lamella?
incomplete maturation of groups of prisms
- ‘fault’ line extending through enamel thickness
- goes all the way into rods unlike tufts
what are enamel spindles?
odontoblasts process extending into enamel
- projections are clearer, like fingers
- odontoblasts leave projections there after early stage - rare
what can you not see in a ground section?
any cells or organic materials
where is enamel thinnest?
cervical region where it usually tapers gradually
where is enamel thickest?
at the incisal edge or under the cusp.
In the absence of any tooth wear, the enamel is around 2 mm thick.
The exact amount will vary between different teeth.
what are the set of lines in enamel that run at right angles to the enamel surface and ADJ?
enamel prisms/rods
alternating light and dark lines
Another set lie almost parallel to the outer surface and are broader
what are the brown striae of Retzius?
Thicker brownish lines that run obliquely from outer surface to the EDJ
external representation is perikymatas
- lines on tooth surface
where can you see evidence of scalloped ADJ?
below cuspal edges and incisal edges, compared with the side of the crown
advantages of scalloping in ADJ
Advantage as be able to withstand high shearing forces
- More mechanical retention against strong occlusal forces between enamel and dentine
- Shearing forces less at cervical region of the tooth as scalloping less
why can you get abfraction at cervical portion of tooth?
lose portion of enamel,
does need caries, needs external shearing forces and enamel detaches from dentine (occlusal lesions)
- Reduced density of enamel and reduction of scallops
- Usually on upper premolars
Bending forces on teeth – like flex ruler almost
what do cross striations indicate?
daily growth of tissue
0.004mm (4um) apart
where is the thickest enamel on posterior teeth?
Enamel is thickest under the cusps.
In the absence of any tooth wear, the enamel is around 2.5 mm thick.
how do enamel prisms lie and run?
prisms lie perpendicular to the EDJ
run from EDJ to the tooth surface
do the enamel prisms extend to the outer surface of enamel?
No. The outer 20-70 μm of enamel has no prisms (aprismatic enamel), where crystallites lie parallel to each other.
prism orientation in regards to cavity prepartions
important
want to be perpendicular to ADJ cut so no unsupported enamel (will be brittle and break off, no resistance to occlusal forces)
Enamel is inherently brittle and can fracture along the prism boundaries.
- supported by dentine is less likely to fracture.
When a tooth is prepared for a restoration, it is essential to make sure that there is no unsupported enamel, especially at the cavity margins.
advantages of gnarled enamel cusps
Give more resilience to the enamel on top of it to withstand occlusal forces
- Hence why under cups tips
why are dentinal tubules closer together at pulp?
Odontoblast start ADJ and go inwards to pulp
- Come closer together
- Don’t increase in number (if die, stem cells will replace them)
where is the good dentine to bond to?
at the ADJ outskirts – more to bond as more intertubular space
- Large cavity harder to bond to
More moisture towards pulp as tubules closer together – adversely affect resin bonds (also spaces between tubules advantages for etch
- Increased tag spaces – good for chemical retention
what happens to tubules SA as they migrate?
occupy a smaller surface area as they migrate in hence, they are wider at the periphery
Smaller diameter and wider apart at ADJ
Closer together and wider diameter at pulp
where is dentine formation?
inside the tubules
- intratubular dentine
pits and fissure caries
base wider at EDJ and top of pyramid at exterior of tooth
- when invades dentine - pyramid reversed (base at ADJ and tip at deeper part of lesion/ towards the pulp) 2 pyramids back to back
can have fissure in palatal surface of tooth
smooth surface caries
lesion will have base towards the exterior (reverse of enamel lesion of pits & fissures)
enamel that is not fully supported by dentine common especially trying to Hall technique
how can a fissure increase the tooth’s susceptibility to caries?(3)
- The fissure is difficult to clean, and becomes a plaque trap.
- There is reduced thickness of enamel at the base of the fissure, so a carious lesion can spread rapidly into dentine.
- A fissure will reduce access of salivary buffering to the deeper regions of the dental plaque and make cleansing by brushing more difficult
implication on dental practice on the orientation of prisms
spatial arrangement of prisms may provide some resilience so that the enamel ‘gives’ very slightly during application of occlusal loads
how to differentiate between enamel lamella and artefacts?
lamella will stay when demineralised whereas artefact will disappear
Artefacts would not be embedded onto the general structure of the tooth.
enamel spindle
spindles are thought to be formed by odontoblast processes that extend for a short distance into the Internal Enamel Epithelium layer of the enamel organ from the ADJ. – round corner (projection of odontoblast)
gnarled enamel is…
When enamel rods/prisms intertwine, complex arrangement
enamel tuft
represent regions of incompletely (hypomiineralised) mineralised enamel matrix.
Tufts extend a short distance from the ADJ, and resemble tufts of grass.
Failed production of enamel structure
enamel lamellae
represent regions of incompletely mineralised enamel matrix. Lamellae extend through the full thickness of enamel.
dead tracts
Black coloured dentinal tubules under transmitted light– air filled
The tubules are empty and are sealed at the pulpal end by the deposition of tertiary dentine.
Tertiary dentine is laid down in response to wear of the overlying enamel and dentine. (What types of ‘wear’ might be involved?)
primary dentine
refers to dentine laid down while the tooth is forming. It is completed when the root apex is fully formed.
secondary dentine
dentine is laid down during the life of the tooth, after the tooth is fully formed.
how to find the boundary between primary and secondary dentine?
Often, it is difficult to see the boundary between primary and secondary dentine, but sometimes there is a change in orientation/direction of the dentinal tubules. (not always seen)
tertiary dentine
laid down as a result to insult to the tooth
dentinal tubules permeabilty
increase with depth
size of tubules accomodated permeability
- deeper the cavity the larger need for cavity lining
can tertiary dentine have dead tracts?
no
- missing tubules
Makes sense as forms a plug against irritants that are trying to invade
Made by odontoblast or recruited stem cells (to make dentine as dead/damaged odontoblasts)
- Reactionary – primary odontoblasts
- Reparative – recruited stem cells
reactionary tertiary dentine is made by
primary odontoblasts
reparative tertiary dentine is made by
recruited stem cells
inner and outer dentine tubule density comparison
Inner dentine has higher density and outer dentine has smaller diameter tubules
what is the change in orientation of tubules nearer the pulp mark?
This marks the onset of secondary dentine formation.
if there is a substantial amount of secondary dentine, suggests that the tooth has been in function for several decades
why can the apex of a tooth be wider when the tooth erupts?
tooth not fully formed yet
rate of secondary dentine formation compared to primary dentine
slower
predentine is
unmineralised
Pale pink stained zone at pulpal aspect of dentine
describe tubules at the dentine pulpal interface
Tubules come closer together nearer the pulp because the surface area of the pulp-dentine interface is less than that of the original ADJ.
So the odontoblasts are forced together, as more dentine is laid down.
The result is that the odontoblast cell layer has a pseudostratified appearance.
calcospherites
Darker red ‘blobs’ in the predentine (pale pink staining tissue) represent centres of minerlisation (calcification)
structures in the inner part of dentine
an odontoblast process
unmyelinated nerve terminal (especially in dentine under the cusps),
perhaps also the process of a dendritic cell (an antigen presenting cell).
structures in the outer part of dentine
no vital cells
