Enamel Flashcards
State 3 Properties of Enamel
brittle - if not supported by dentine, it fractures = cavitation
withstands shearing hard forces
highly mineralised
Consituents of Enamel
95% pure mineral - hydroxyapatite
4% water
1% organic material - mainly non-collagenous protein
Hydroxyapatite - structure and length
prisms and rods
- perpendicular to ADJ
5micrometer diameter
What Pattern does the Daily Incremental Lines Follow?
Cross-striations in a circadian rhythm
- dark and light lines in intervals of 3-6micrometer
What is the Brown Striae of Retzius?
less frequent incremental lines
- irregularly spaced at the cusp
- associated with perikymata depressions
= able to provide space for diffusion pathways
What are Hunter-Shreger Bands?
banding pattern when there are periodic changes in direction of prism sheets
-diazones = prisms are sectioned transverse
- parazones = prisms are sectioned longitudinally
What is the Appearance of the ADJ, and two characteristics?
scalloped appearance
- aids retention of enamel on dentine
- resist shearing by forces
Give 3 other Structural Features of the Enamel
Spindles
Tufts
Gnarled Enamel
Describe Spindles and how they Relate to Enamel Tubules
where does it originate? appearance? penetrations?
originate at ADJ around cusps - where there is a lot of odontoblast crowding
- dark, club shaped
- penetrate 25micrometer in enamel
- not aligned with prisms
enamel tubules
= when odontoblast processes disrupt spindle and elongate into enamel
= creates a void
Describe Tufts
what is it? where does it orginiate? appeareance? protein? thickness?
- when residual enamel protein has collected between prisms
- originate at ADJ
- appears like tuft of grass
- sinusoidal path to the surface
- contain tuftelin enamel protein - high content of mature enamel
- 1/3 thickness of enamel
What is Gnarled Enamel? What are 2 Benefits?
when prisms are disordered at cusps
= increase resistance to fracture and occlusal masticatory forces
= regular changes of direction
What are the Zones of Enamel Caries from surface to pulpal
**surface zone - under the plaque biofilm
- lacks fluoride concentration
- 1-10% mineral loss - partial demineralisation
- calcium and phosphate ions release here to encourage remineralisation
- disrupted when lesions penetrate into dentine
**Body of lesion
- highest porosity
- most affected
- 60-70% mineral loss before cavitation
**Dark zone
- remineralisation, high protein = 5-20% mineral loss
- reflects light - appears unequal
** Transulcent zone
- least affected
- less than 1% mineral loss
- ions dissolve out - allows re-precipitation
- uniform pore size
Describ the Outermost Enamel
Porous
What are some Developmental Defects of Enamel
irregular fissures and micro-pores
How does the Microstructure Affect Carious Process? (4)
- outmost enamel = porous
- developmental defects - fissure and pores
- opening striae of Retzius at surface via perikymata grooves = diffusion pathway
- inter-crystalline spaces - filled with water - diffusion pathway
The Mechanism of Caries Progression through Enamel and Dentine
1.plaque layer forms on enamel
2.release of organic acids by bacteria
3.dissolution - exposure by acid
= irregular crystal outline
= demineralisation
= destruction in prism cores
4.spreads along ADJ
5. dentinal tubules become narrow and sclerosed
6. reactionary dentine on pulpal wall
7. enamel surface cavities
8. bacteria invades lesion and penetrate dentinal tubules
- EQM between ions in plaque and hydroxyapatite
- acid favours plaque
Define Caries
A localised, chemical dissolution of tooth surface brought about by metabolic activity in a microbial deposit/dental biofilm, covering a tooth surface at any given time
In an Enamel Caries Lesion, How does the Early Stage, Later Stage Appear, and What is the Name of the Stain?
Early = opaque white spots
- subsurface loss of mineral due to acid dissolution
Later = cavity and exposed dentine
Stain = brown spot lesions
What is Occult/Hidden Caries, why does it happen?
occlusal surface appears to be intact but shows radiolucencies in dentine, it derives from occlusal/pit caries
- enamel has a higher fluoride conc, which increases resistance to carious breakdown
How does Occlusal/Pit Enamel Caries Lesion Occur and Proceed?
- food debris and plaque accumulation in fissure
- acid
- dissolution begins on walls rather than the base
- penetrates perpendicular towards ADJ
= cavitation - occurs without apparent break in enamel surface
