enamel structure Flashcards by Korbyn Perpich

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

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t/f type 1 collagen is found in ALL hard tissues

FALSE. NOT enamel!!

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percentages of in-organic materal in enamel, dentin, cementum and bone

enamel 92-97%
dentin 72-68%
bone 65-55%
cementum 50-45%

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does enamel have stem cells?

NO! cannot repair itself

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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

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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.

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germ layer for enamel

ECTODERM!!! it is the only hard tissue that comes from ecto (enamel organ)

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does enamel have cells, innervation and vascularization?

NO none

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is enamel super brittle but resistant to wear?

yes

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rank thickness of enamel LEAST to GREATEST

Cervical margin
Lateral edge
Incisal edge

THINNEST -> cervical margin then –>
lateral edge
THICKEST -> incisal edge

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T/F dentin is MORE translucent than enamel

FALSE! enamel is more translucent!

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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

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% of in-org and org of enamel

mature enamel is

96 % inorganic

4 % organic

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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

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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

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instead of OH- and PO4, you sub carbonate, what happens to apatite

INCREASE crystal solubility. not as stable! usually happens at DEJ

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instead of OH-, you sub fluoride or chloride, what happens to apatite

DECREASE crystal solubility. MORE resistant to caries!! crystal structure is much tighter

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what is the org component of mature enamel

3% water and 1% organic proteins

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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

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what happens during the maturation phase in amelogenesis

water and organic proteins get removed

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how are the crystals orientated

apatite crystals are interlocked together and organized as rods and inter-rods

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are rods prismatic or interprismatic

PRISMATIC

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are INTER-rods prismatic or interprismatic

INTER-prismatic

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What are secreted by tomes process

rods - prismatic

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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

1. Unerupted tooth –REE (Nasmyth's membrane; primary enamel cuticle) 2. 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

1. Removal of plaque and organic debris 2. 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

1. Occlusal: Enamel rods aligned perpendicular to surface (STRONG bond) 2. 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.