Histology Of Enamel Flashcards
Embryonic origin of enamel
Ectoderm
Inorganic mineral content of enamel composition
96%
Majority - calcium hydroxyapatite
Minority - carbonate, fluoride
Components of calcium hydroxyapatite
Calcium
Phosphate
Hydroxyl
Organic mineral content of enamel composition
4%
Fibrous collagen material
Water
Some proteins
Overview of enamel structure
- Enamel rods (prisms)
- Interrods
- Crystallites (calcium hydroxyapatite)
- Link to amelogenesis
- Incremental lines
- Prismless enamel (rod-less)
- Dento-enamel junction and microscopic features.
Key structural unit of enamel
Enamel rods (prisms)
What does each enamel rod contain and how are they structured?
Millions of calcium hydroxyapatite crystallites.
Tightly packed with a head and tail in keyhole shape.
Orientation of head and tail of enamel rods
Head - usually towards occlusal/incisal surface.
Tail - usually towards cervical region.
Interrod
Tail of enamel rod
What surrounds each rod and interrod?
Sheath of organic material
What runs within the the enamel rods and what’s their orientation
Enamel crystallites
In the head runs parallel with long axis of rod
In the tail they diverge slightly.
What’s the significance of the pattern of crystallites within the rod
Adds to the strength of enamel
Amelogenesis
Process of enamel formation.
Results in incremental lines.
What forms the structure of enamel rods
Ameloblasts
1 ameloblast forms 1 enamel rod
Lifecycle of ameloblasts
Only live for as long as the enamel is forming. They move into function of protection during eruption, this ends their life cycle.
Strip of retzius
Growth rings in the ground sections on enamel under a microscope
Perkymata
Edge of the stria of retzius that is clinically visible on the enamel surface showing where the incremental lines reach the labial and buccal surfaces.
Structure of enamel rods at the cusps
Twisted forming gnarled enamel, adds to overall strength
Structure of rods at dentoenamel junction
Perpendicular to the dentine
Areas of princess/aprismatic enamel
Very first and last formed enamel usually has no prism structure where the crystals are parallel to surface.
Structure of prismless enamel
30 microns wide
Includes more fluoride and carbon
Seen in primary dentition and 70% of permanent dentition. (Greatest in cervical regions)
Clinical significance of primless enamel
Can interfere with optimal etching
When does the dentine enamel junction form and microscopic appearance
Once dentinogenesis and amelogenesis have started.
Scalloped appearance.
Microscopic features at the dentine-enamel junction
Enamel tuft
Enamel spindles
Structural features at enamel surface and how they form
Lamella.
Appear as cracks in enamel - developmental defects.
Result of ameloblast ceasing production of enamel.
Functions of enamel
Protect
Eating
Ion exchange
Inability to repair or feel injury
Smile
How does the function of enamel link to its structure?
- Protect tooth/pulp; covers entire tooth crown, hardest biological tissue.
- Eating; thickest at cusp/occlusal/incisal surfaces.
- Inability to repair or feel injury; inert tissue.
- Able to re/demineralise; highly mineralised tissue.
Smile; white translucent crystalline.
What does the exchange of ions cause in enamel over the life course?
Reduced permeability
The critical pH level of enamel
5.5
Acidic conditions the balance favours
Demineralisation
Alkaline conditions the balance favours
Remineralisation
Enables uptake of fluoride and calcium phosphate.
What substance in the mouth is alkaline and favours remineralisation?
Saliva
Critical pH level of fluorapatite and its relevance
4.5; lower than hydroxyapatite and therefore more resistant to acids and demineralisation.
How is the composition and structure of enamel in clinical prevention?
- Inert; no living cell, unable to feel injury, we need to be able to risk assess and detect early caries/changes.
Local disturbances
Affect individual teeth
(Trauma)
Systemic disturbances
Affect all teeth forming at the time
(Fluorosis, tetracycline exposure, MIH)
Genetic factors
May affect all teeth
(Amelogenesis imperfecta)
Neo-natal line in enamel
Exaggerated line that shows distinction between enamel that formed before and after birth.
(Usually reflects disturbance in amelogenesis at birth)
Other exaggerated lines in enamel
Reflect systemic disturbances during amelogenesis.
(Fever, tetracycline staining)
Defects during amelogenesis can result in?
Molar incisor hypomineralisation.
(Softer enamel, more prone to caries)
