OB D8 - Enamel histology Flashcards
why can you not study enamel by a decalcified section?
- mineral removed
- 7-10 microns thick
- no enamel
How do you study enamel histologically?
Ground section:
- cut with a diamond saw
- 150microns
- mineral present
when does enamel appear darker?
- contain less mineral
- light doesnt pass through as well
- demineralised due to caries
what is the enamel structure?
tightly packed hydroxyapatite crystals
what is the basic unit of enamel?
enamel prism (or rod)
what are prisms visible in?
- ground sections
- SEM’s of acid etched enamel (Scanning electron micrograph)
what are the two parts of enamel in cross section?
- prism core
- prism sheath
what does every dash cross sectionally represent?
hydroxyapatite crystal
what is the shape of enamel prisms?
complex “key hole” shape
what gives the prisms their key hole shape?
from different orientations of the hydroxyapatite crystals
what is the structure of prism core?
tightly packed hydroxyapatite crystals
what is the structure of prism sheath?
– boundary of clearly different crystal orientations – crystals less tightly packed
– more space for organic components
what is the significance of the prism sheath structure?
more vulnerable to acid attacks
what is the enamel prisms shape governed by?
– The presence of the Tomes process
– The shape of the Tomes process
– The direction of movement of the ameloblast
what are regions formed without a tomes process?
aprismatic
what areas are aprismatic?
– 1st formed (i.e. innermost) 5μm
– last formed (i.e. outmost) 30μm
what is the significance of acid etch/conditioning?
- remove top prism sheath or core
- get grooves - put resin/fissure sealant on tooth
- capillary action- sucked into grooves- gives micro mechincal attachement /retentition
- resin flows in crevices between prisms and locks it on
what size are enamel prisms?
3-6microns in diameter
what path of enamel prisms follow?
ameloblasts so 90 degrees to ADJ
what course to the enamel prisms take?
although they look straight in longitudinal section - they take an undulating course
what type of enamel is at the cusps of the tooth and why?
- Gnarled enamel
- the prisms appear twisted around each other
- give strength due to most forces at the cusps
what is striae of retzius?
incremental growth lines
what is the appliance of striae of retzius?
brown lines
what does striae of retzius represent?
weekly growth
what results from systemic disturbances ( e.g. illness) / birth (neonatal line) ?
accentuated lines
which teeth have neonatal line?
- all primary teeth
- permanent 6’s
what is perikymata?
shallow furrow where the striae reach the surface?
what is imbrication lines of peckerill?
ridges between perikymata
why is perikymata important?
aesthetically - difference in crown
what are hunter-schreger bands?
An optical effect reflecting the sinusoidal path of enamel prisms in alternating sheets
what are enamel spindles?
dentinal tubules in enamel
what are enamel tufts?
hypomineralised
what are enamel lamellae?
- developmental
- acquired
- preparation artefact
what are the 3 type of amelogenesis imperfecta (enamel anomalies)?
- type I -hypoplastic
- type II - hypomaturation
- type III- hypocalcified
Describe type I - hypoplastic.
Features - less matrix formed
Clinical :Small crown or pitted/grooved enamel Small–normal crown
Colour: Normal or white or yellow/brown
Describe type II - hypomaturation.
Features- reduced crystal growth
Clinical :
Opaque cream to yellow brown
Surface soft and rough – easily chips/abrades
Describe type III - hypocalcified.
Features - reduced crystal formation
Clinical :
Opaque white – yellow brown
Surface soft and rough - easily chips/abrades
what results from molar incisor hypomineralisation (enamel anomalies)?
- Discrete opaque white soft enamel
- Altered localised ameloblast function
- ?Due to systemic childhood illness
what results from fluororosis (enamel anomalies)?
- Ameloblasts susceptible to environment
- Reduced enamel matrix protein degradation
-Incomplete crystal growth
what can cause trauma to primary incisors (enamel anomalies)?
- Intrusion of primary incisors
- Damage to successional tooth germ
- Damage to reduced enamel epithelium
