Intro to Hard Dental Tissue Flashcards
What is the hardest substance of the body?
enamel
Where is enamel thickest?
at the cusp tips (up to 2.5 mm)
Where is enamel thinnest?
as it tapers to knife edge at CEJ
What is the color of enamel?
yellow-white, grayish-white or transclucent
As enamel approaches the DEJ how is its texture and hardness affected?
it becomes extremely brittle and its hardness decreases as get closer to dentin
what is the purpose of enamel?
a protective layer over the entire surface of the crown
How is enamel’s permeability affected with age?
enamel is permeable, but its permeabilty decreases with age
What are the chemical components of enamel?
- 96% Inorganic
- Hydroxyapatitie (calcium phosphate)
- 3% Water
- 1% Organic
Describe retizius lines.
- estria of retzius (alt. name)
- reflect appositional growth of enamel during the formation of the crown
- only seen microscopically
- newly errupted teeth
- cervical retizius lines end in a surface groove: perikymata
- perikymata
- surface groove
- with wear become less defined
- more prevalent in incisors/anterior teeth
- can be seen macroscopically
what are perikymata and how are they affected by wear?
- incremental growth lines that appear on the surface of enamel as a series of grooves
- indicate the termination of striae of Retzius at the surface of enamel
- found on all teeth, but easiest o notice on canines (anterior teeth)
- with wear/over time, become less defined
What is the neonatal line?
- accentuated line of Retizius
- marks the division between enamel formed before birth vs after birth
- found in deciduous teeth and the cusps of first permanent molars
- with wear become less defined
- application in forensic dentistry
What are enamel rods (include structure, fucntion and location)?
- thin rod or prisms
- fundamental morphologic unit of enamel
- each rod transverses uninterrupted through the thickness of enamel
- perpindicular to enamel surface at every point on the crown
- stand upright on the surface of dentin
- dentin= enamel support
- formed in increments by ameloblasts
- ~5-12 million rods per crown
- rods increase in diameter as they flare out from DEJ (4-8 microns)
- composed of body and tail in cross section (see image)
Compare and contrast pits and fissures.
- PIts
- non-coalesced enamel
- at the deepest point of a fossa
- Fissure
- non-coalesced enamel
- marks location of the union between developmental lobes
- fissure = union is incomplete forms narrow, inaccessible canal of varying depths (if shallow termed a groove)
- invagiantions of the surface of a tooth
- highly susceptible to caries
how does lack of dentin support affect enamel rods?
dentin rods begin to fracture when dentin support lacking
How does acid affect enamel and why?
- enamel is extremely vulnerable to acid
- when exposed to acid
- enamel surface is demineralized ( loses calcium, potassium and fluoride ions)
- causes tooth softening and loss of structure
- enamel surface is demineralized ( loses calcium, potassium and fluoride ions)
- Reason:
- enamel contains high mineral content (96% inorganic)
What are the chemical components of Dentin?
- 70% hydroxyappatite
- 20% type 1 collage (organic material)
- 10% water
*Dentin-pulp complex derived from same tissue
