enamel structure Flashcards
3 components of hard tissues
- in-organic component –> calcium hydroxyapatite
- organic component aka ECM –> non-fibrous and fibrous proteins (type 1 collagen)
- enzymes and minerals required for mineralization
t/f type 1 collagen is found in ALL hard tissues
FALSE. NOT enamel!!
percentages of in-organic materal in enamel, dentin, cementum and bone
enamel 92-97%
dentin 72-68%
bone 65-55%
cementum 50-45%
does enamel have stem cells?
NO! cannot repair itself
what is the general function of ECM
-Non-fibrous proteins facilitate mineral formation
* ECM proteins provides support and orientation for mineral deposition
* Regulates the shape and size of crystal formation (enamel has largest crystals
what is the anatomical crown vs the clinical crown?
- Anatomical crown: Part of tooth covered with enamel
- Clinical crown: Part of tooth exposed in the oral cavity. *May or may not be the same as the anatomical crown.
germ layer for enamel
ECTODERM!!! it is the only hard tissue that comes from ecto (enamel organ)
does enamel have cells, innervation and vascularization?
NO none
is enamel super brittle but resistant to wear?
yes
rank thickness of enamel LEAST to GREATEST
- Cervical margin
- Lateral edge
- Incisal edge
THINNEST -> cervical margin then –>
lateral edge
THICKEST -> incisal edge
T/F dentin is MORE translucent than enamel
FALSE! enamel is more translucent!
what is the permeability of enamel like?
semipermeable to some substance; small micropores exist between crystals allows form diffusion of some substances – subsurface is more porous
% of in-org and org of enamel
mature enamel is
96 % inorganic
4 % organic
can Crystal surface undergo ion exchange with other ions – may occur during mineralization process and after tooth emerges into oral cavity?
yes! Ion substitution may influence the apatite properties including:
o Crystal growth or shape
o Crystal structure / stability
o Solubility of apatite crystals
instead of Ca2+, you sub magnesium or sodium … whta happens to apatite
changes crystals SIZE = more spread out! affects stability and leads to an INCREASE in solubility. usually happening at DEJ
instead of OH- and PO4, you sub carbonate, what happens to apatite
INCREASE crystal solubility. not as stable! usually happens at DEJ
instead of OH-, you sub fluoride or chloride, what happens to apatite
DECREASE crystal solubility. MORE resistant to caries!! crystal structure is much tighter
what is the org component of mature enamel
3% water and 1% organic proteins
what are the functions of the 1% organic proteins in enamel and the two classes of them
Two classes of organic enamel matrix proteins:
* Amelogenins
* Non –Amelogenins –> Enamelins, Metalloproteinases (-> removes organic matrix)
Function: aid in crystal growth, orientation, packing of crystals, or breakdown organic matrix during maturation
what happens during the maturation phase in amelogenesis
water and organic proteins get removed
how are the crystals orientated
apatite crystals are interlocked together and organized as rods and inter-rods
are rods prismatic or interprismatic
PRISMATIC
are INTER-rods prismatic or interprismatic
INTER-prismatic
What are secreted by tomes process
rods - prismatic
do rods or inter-rods have their crystals pack more tightly
rods! crystals tightly packed parallel to
long axis of rods
what are secreted from region BETWEEN adjacent ameloblasts
inter-rods
their crystals are loosely packed and crystal orientation diverges from the long axis of rods
also Contain slightly more organic material –more porous
what is Aprismatic enamel
Caused by decreased activity in Ameloblast and absence of Tome’s process.
also contain tightly packed crystals aligned parallel to each other. Less porous
where can you find aprismatic enamel
DEJ, surface, cervical margin
**this is what we take off when we etch
what are DAILY enamel deposits called and how do they run
CROSS-STRIATIONS!!
transverse lines run perpendicular to long axis of each rod (prism)
* reflect variation in structure and mineralization of the rods,
either hypo or hyper mineralization.
T/F: Enamel is deposited incrementally with each new successive layer laid down on top of the next
TRUE
what are WEEKLY enamel deposits called and how do they run
STRIAE OF RETZIUS!!
-Stria run at oblique angles to enamel prisms and cross striations
-Stria terminate on surface as perikymata
-Look different in longitudinal section vs cross section
what are lines of imbrication that represent the surface terminations of the lines of retzius
perikymata!
T/F : Shift in orientation of rods believed to WEAKEN enamel, making it more likely to fracture under the stress of mastication.
FALSE
Shift in orientation of rods believed to STRENGTHEN enamel, making it more resistant to fracturing under the stress of mastication.
what is an optical phenomenon as the ameloblast moves outward from the DEJ the rods shift direction. There is less shifting farther from the DEJ. DOES NOT reach the surface
Hunter-Schreger Bands
what are rods in the tip of the cusps region appear to become very irregular and twisted called?
**Caused by the small radius of ameloblasts during development. This extends from DEJ all the way to the surface. Usually visible when the section is not taken through the cusp
GNARLED enamel
what are the 2 structures near the DEJ
enamel tufts and enamel spindles
T/F:
ENAMEL TUFTS:
* hypercalcified space near the DEJ extends 1/3 to 1/2 into enamel surface
* result from spatial adaptation in enamel
* Best seen in X-section
FALSE
ENAMEL TUFTS:
* HYPOcalcified space near the DEJ extends 1/3 to 1/2 into enamel surface
* result from spatial adaptation in enamel
* Best seen in X-section
T/F:
ENAMEL SPINDLES:
* Appear as short dark lines
* Tubular spaces in enamel at the DEJ – continuation of dentin tubule into enamel
* Most often seen below cusps
* Best visualized in longitudinal prep
TRUE
what are the two junctions we should know for enamel
DEJ and CEJ
which junction has a scalloped looked
DEJ (better bonding)
3 variations of CEJ
OMG
overlapping most common
2 structures associated with surface enamel
enamel lamella and enamel crack
T/F: enamel lamella is a PRE-eruptive thing
true
T/F: enamel crack is a PRE-eruptive thing
FALSE. POST-eruptive!
is enamel lamella hypo or hyperminerzliaed
HYPO
what are the Developmental Organic Coverings
- Unerupted tooth –REE (Nasmyth’s membrane; primary enamel cuticle)
- Fully erupted tooth – remnants of primary enamel cuticle
-Acquired Pellicle (secondary pellicle-salivary protein)
-Plaque –colonization of pellicle
-Calculus (tartar) –mineralization of plaque
what is the point of etching
removes contaminants and creates microscopic spaces/pores between crystals by dissolving enamel rods. Roughened surface increases mechanical retention of resin sealant/composite material
2 stages of etching
- Removal of plaque and organic debris
- Removal of thin aprismatic surface layer of enamel to expose prismatic enamel
MOA of etching
increases the porosity of exposed surfaces through selective dissolution of crystals. Rods dissolve more readily on ends than on the sides.
2 patterns acid etching
- Occlusal: Enamel rods aligned perpendicular to surface (STRONG bond)
- Lateral surface (buccal and lingual): sight inclination to enamel surface – the side of the crystal more exposed (not as strong!)
what is a type 1 etching pattern
characterized by preferential removal of rods. Due to how the enamel is deposited during tooth formation. The acid works more on crystals in the central rod, commonly found in occlusal surface
what is a type II etching pattern
characterized by dissolving the peripheral inter-rod enamel is removed preferentially and the rod remains intact
majority of enamel loss is due to :
attrition, erosion and abrasion
what is attrition
excessive occlusal wear. GRINDING
what is enamel loss or wear due to abnormal occlusal load on tooth (i.e bruxism)
abfraction
T/F
root caries spread SLOW
FALSE!! spread super fast
what shape do smooth surface/inter proximal caries form
forms a triangular pattern - however, the base faces the surface of the tooth and the apex faces the DEJ.. Interproximal may created greater damage if it goes undetected
what shape do pit caries form
triangular pattern or cone shape of lesion with the base towards DEJ and apex towards the tooth surface. The enamel is very thin in the region of the pit and so it progresses rapidly into the dentin.
what are the 4 zones of a carious lesion
DEEP -> superficial
translucent -> dark zone -> body of lesion -> surface zone
which zone has largest extent of demineralization
body of lesion
what is the first change seen when talking about non-cavitated carious enamel lesion
The first change seen histologically is the loss of inter-rod substance of enamel with increased prominence of the rods in the region below the surface.
