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