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50 Cards in this Set

  • Front
  • Back
what forms enamel?
ameloblast cells
what is the fundamental unit of enamel?
enamel rod or prism
does dentin or enamel begin to form first?
dentin and then enamel begins to form on top of it
is it correct to say that enamel covers and protects the clinical crown or the anatomical crown?
anatomical crown
is the peripheral enamel or deeper enamel harder?
peripheral enamel is harder
what is the MOH's hardness of enamel
5-8 as compared to a diamond of 10
what is the knoop hardness (KHN) of enamel
300 while dentin is 65, pure gold is 32, amalgam is 90, and composite is 60
does the density of enamel increase from the DEJ to the surface or from the surface to the DEJ?
increases from DEJ to surface
where is enamel thicker and where is it thinner?
thicker in cusp and incisal areas and thinner towards cervical areas
what color is enamel? what does it depend on?
semi-translucent, partly dependent on enamel thickness and underlying dentin; thinner enamel is yellow white and thicker enamel is blue-grayish white
enamel is cushioned by what?
dentin
enamel is hard but unfortunately what?
brittle - prone to splitting and chipping; high compressibility but very low tensile strength - like glass
1)what dissolves enamel and 2) what reduces its solubility?
1) acid - demineralization
2) flouride - increases hardness
is surface enamel or deep enamel less soluble?
surface enamel is less soluble
what acts like a molecular sieve in enamel?
submicroscopic pores, water and ions pass via osmosis
what is the chemical composition of enamel?
inorganic = 96%
organic = 1%
water = 3-4%
what is the inorganic content of enamel?
hydroxyapatite crystal - Ca10(PO4)6(OH)2
calcium + phosphate + hydroxyl ions = hydroxyapatite
how is fluorapatite different from hydroxyapatite?
it is harder and less soluble; Fl combines with Ca
what is the organic content of enamel?
various AAs, carbohydrates, and lipids
what does the water content in enamel form?
hydrated shell or covering around the apatite crystal
what is the cross-section of enamel rods described as?
key hole, interlocking
primary enamel rods are perpendicular to what?
DEJ*
how do enamel rods run?
from DEJ to surface
enamel rods are essentially ________ to the surface
perpendicular
what is perikymata?
wave-like surface characterization of enamel
what are the lines of retzius?
incremental growth lines in enamel: concentric series of brown lines (tree rings) that have an arc-like pattern
what are the hunter-schreger bands?
alternating light and dark bands of enamel (they bifurcate too): dark bands are diazones and light bands are parazones
what is the chemical composition of dentin?
75% inorganic
20% organic
5% water
what is the inorganic composition of dentin
-calcium phosphate as hydroxyapatite
-fluoride presence is 2-3X that found in enamel
-higher in permanent teeth than primary
-more concentrated closer to pulp
-concentration increases w/ age
knoop hardness of dentin
65, greater than bone or cementum but less than enamel
color of dentin
yellowish white
why is dentin elastic
to support the brittle enamel
describe dentin's permeability
highly permeable - decreases w/ age becoming more brittle; ex. tubules get plugged up
what are odontoblast processes?
extensions of odontoblast cells w/in dentinal tubules
what are dentinal tubules?
microscopic tubes that radiate outward from the pulp
what is the main component of tooth structure?
dentin
dentin is formed by what?
odontoblast cells (dentinogenesis)
how long do odontoblasts and ameloblasts live?
odontoblasts are alive as long as the tooth is, but ameloblasts die off so enamel can't be regenerated
organic composition of dentin
*mainly collagen (protein)
-glycine, alanine, proline, hydroxyproline
-thought to be a seeding agent in apatite crystal formation
*some lipids - cholesterol
structural components of dentin
odontoblasts and their processes located w/in dentinal tubules; tubules bigger towards pulp and narrows towards DEJ
what 2 forms of dentin make up the dentinal matrix? distinguish between the 2
intertubular dentin and peritubular dentin; peritubular dentin is more mineralized than intertubular dentin, intertubular dentin is mainly collagenous fibers criss-crossing between tubules
what are imbrication lines?
(lines of owen) incremental lines of growth in dentin, similar to lines of retzius (tree rings)
what is the neonatal line?
demarcation between prenatal and postnatal dentin, separates formation of dentin between pre and post birth, in primary teeth and permanent first molars
what are the 5 types of dentin and describe each?
1)primary dentin- initial formation (as tooth is forming)
2)secondary dentin- next to pulp, lifelong, aka physiologic secondary dentin, after tooth is formed
3)tertiary dentin- aka reparative secondary dentin, in response to an irritant or stimulus
4)sclerotic dentin- tubules obliterated by minerals, hardened
5)dead tracts- tubules w/ dead odontoblast processes
what are 2 main functions of the cementum?
protects root dentin, provides for attachment to alveolus via sharpey's fibers
cementum formed by what?
cementoblast cells (cementogenesis)
chemical composition of cementum
50% organic material and water
50% inorganic-hydroxyapatite
what are the 3 types of cementum and describe each?
1)acellular cementum- cervical 2/3 of root, mainly calcified substance
2) cellular cementum- apical 1/3 of root, mainly cementocytes
3)secondary cementum- forms as a result of trauma or pathology
how is bonding attached to enamel
acid etching to remove microscopic amounts of enamel hydroxyapatite and then resin flows into roughened crevices and bonds mechanically
how is bonding attached to dentin?
more complex than enamel;
etch removes mineral components leaving collagen matrix, resin primer infuses between collagen matrix and into dentinal tubules - collagen/resin hybrid layer