Exam 3 - Enamel Davenport Flashcards
Hardest substance in the human body
Enamel
Hard as mild steel
Physical characteristics of enamel
- elicit sparks when struck with flint
- withstands tremendous mechanical forces
- brittle
- translucent (light yellow to grayish white)
- variable thickness (max 2.5mm)
- acellular/avascular
- no collagen
True or false: enamel is considered an active chemical system
True - participates in a variety of chemical reactions
Most highly mineralized tissue
Enamel (96% inorganic material)
Enamel - inorganic material
Hydroxyapatite (crystalline calcium phosphate)
___ can strengthen hydroxyapatite
Fluoride (fluorapatite)
During maturation of enamel, some organic material is:
Reabsorbed
True or false: apatites are precipitated on a fibrillar substrate
False - they are not
Enamel is made of 4%:
water and organic material (1% protein)
Enamel is a ____ substance
Interprismatic
Enamel rod is thought to be ____ shaped
Cylindrical (keyhole shape discontinued)
Initial layer of enamel is:
Aprismatic
Rod crystals are oriented in:
The same direction
The long axis of the crystals is ____ to the long axis of the enamel rod
Parallel
Does interrod substance have a specific orientation?
Does not appear so, but slightly perpendicular to the long axis of the enamel rod
Rod sheath
optical/refractive phenomenon between the interrod substance and the enamel rod caused by the differences in hydroxyapatite crystal orientation
Crystallites are ____ in the rod than the interrod substance
Larger and more compact
Interrod substance looks like:
Honeycomb; crystals more haphazard
Successive enamel rods are off by _____ which contributes to a stacking in a structurally sound manner
2 or 4 degrees
Enamel rods are more ____ at cusps and _____ at cervix
Vertical; horizontal
Enamel rods run generally ____ to long axis of the tooth
Perpendicular
Enamel rods ____ as they run toward the surface
Undulate
Rod heads are always oriented:
Coronally
Rod structure allows:
Interlocking arrangement
Rate of enamel maturation depends on:
Nutrients available
Striae of Rezius
- Incremental growth lines (dark bands in longitudinal section, concentric rings in cross section)
- phasic episodes of mineral maturation
Accentuated lines of Striae of Retzius represents:
Systemic disturbances
Darker bands of Striae of Retzius means:
Less mineralized
What is the neonatal line?
Accentuated Stria of Retzius reflecting marked physiologic change at birth
How often is Striae of Retzius laid down?
Weekly (circaseptimanian)
Enamel cross striations
Indicates daily circadian variation in secretory activity of ameloblasts
Enamel cross striations result from:
- Temporary constriction of Tomes’ process
- corresponding increase in the secretory face forming interrod substance
Hunter Schreger bands
Optical phenomenon produced strictly by the change in orientation of rod direction
Gnarled enamel
- found at cusp tips
- rods appear twisted around each other in a complex pattern
Enamel tufts are analagous to
Geologic faults
Enamel tufts project from ___ for a ___ distance
DEJ; short (1/3-1/2 enamel thickness)
Enamel tufts are hyper or hypomineralized?
Hypomineralized - increased concentration of enamel protein
Enamel ____ can be microscopically confused with cracks
Lamellae
What are enamel lamellae?
Linear, longitudinally oriented defects which are highly organic (hypomineralized enamel)
True or false: enamel lamellae exacerbate caries development
False - do not
Enamel lamellae have a different _____ than the rest of enamel
refractive index
_____ are physical defects extending from surface for varying depths
Enamel cracks
True or false: Enamel cracks have a developmental origin
False - physical defect
What is the dentinoenamel junction?
Series of ridges that increases surface area and facilitates adhesion
What are enamel spindles?
Newly formed odontoblast process that push between adjoining ameloblasts, become entrapped in enamel matrix when it mineralizes
Carious lesion forms a ____ shape through the enamel and then ___ at the DEJ, then forms a _____ through the dentin
Conical; Spreads; Conical lesion
What are perikymata?
Extensions of Striae of Retzius from the DEJ to the outer surface of enamel
Perikymata run in what direction?
Circumferentially horizontal lines across the face of the crown (where Striae of Retzius ends on surface of tooth)
Surface structure of unerupted teeth
- Structureless cuticle of organic material
- Subsurface layer of loosely packed crystals
Surface structure of erupted teeth
- cuticle and subsurface layer is lost
- Salivary pellicle
Age changes of enamel
- Becomes worn
- Discoloration
- Reduced permeability
- Modifications of surface layer
Amelogenesis imperfecta causes:
Disruption to the structure and clinical appearance of tooth enamel
Amelogenesis imperfecta - phenotypic classifications
- hypoplastic
- hypocalcified
- hypomature
Amelogenesis imperfecta is acquired via:
- X-linked autosomal dominant
- Autosomal recessive
Best fix for amelogenesis imperfecta
Crown the teeth
What are some environmental effects that affect enamel?
- febrile diseases (bands of malformed enamel)
- Tetracycline induced disturbances
- fluoride concentrations over 5ppm can cause mottled enamel/toxic to secretory ameloblasts
Tetracycline can get incorporated into:
Bone, dentin, enamel
Fluoridation effects on enamel
- crystals more resistant to acid demineralization
- toxic to secretory ameloblasts in high concentrations (mottling of enamel)
- enhances calcium phosphate/remineralization
Acid etching
- involved in use of fissure sealants, orthodontics
- removes plaque and other debris
- increases porosity of exposed surface
Ionic substitutions to biological apatites may alter:
- chemical properties
- physical properties
- chemical reactivity
- hardness
What ionic substitutions can occur on apatites?
- substitution of calcium ions
- substitution of phosphate ions
- substitution of hydroxyl ions
Enamel is a dynamic system which participates in what kind of interractions?
- solute and ion transport from saliva to dentin
- ion exchange with saliva
- demineralization/remineralization
- reactions with bacteria and other surface organic compounds
____ is in equilibrium with oral fluid/saliva
Enamel
Saliva is super saturated with:
Calcium and phosphate
