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