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Dental material > Dental pt3 > Flashcards

Dental pt3 Flashcards

1
Q

Steps gypsum application

A

impression - (-) replica
gypsum models - (+) replica

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2
Q

ISO classification types

A
  1. impresssion plaster (based on ordinary gypsum plaster)
  2. plaster (based on ordinary gypsum plaster)
  3. stone (based on high strength gypsum plaster) - prep models imprints
  4. stone, high strength, low expansion (based on high strength gypsum plaster) - aka die stones
  5. stone, high strength, high expansion(based on high strength gypsum plaster) - aka die stones
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3
Q

Formation rxn

A

CaSO4 +2H2O <-> CaSO4 + 1/2H2O (hemihydrate)
anhydrid <-> y CaSO4 (hexagonal - soluble)
anhydrid <-> b CaSO4 (orthrombic - insoluble) (Beta -> orthromBic - beta -> cant swim -> non soluble)

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4
Q

Types procedure

A

Calcination aka prolonged heating below melting point sulfate dihydrate -> partial/complete dehydration -> when use mix w/ water

Dry calcination (hemihydrate)
Wet calcination

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5
Q

Wet calcination def

A

low surface free E - crytsal with less imperfections
particles smooth, dense -> less crystallographic strain -> lower surface E -> better packing ability -> high apparent density

(wet -> swimming -> less free E -> swim smooth, dense -> better swim in packs (packing ability) -> high apparent results (high apparent density))

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6
Q

Dry calcination def

A

high surface free E - crystal imperfections
particles more likely stick tgt -> more bridges -> more voids -> low apparent density

(dry -> opposite to swimming -> high surface E -> can hug -> more likely to stick -> bonding aka more bridges -> more voids -> low apparent density)

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7
Q

Charac dry calcination

A

slow
quality plaster low

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8
Q

Steps, charac dry calc

A

gypsum in open container 120-140celcius
loss water -> form channels w/in gypsum
-> low density
-> poor compatibility
-> high SA

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9
Q

Why use wet calcination

A

material high strength

(wet - swimming - high strength)

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10
Q

Steps wet calcination

A

sufficient water -> conversion in solution -> recrystallization beta form (hexagonal CASO4) -> cooling air - rehydrate hemidrate but remain hexagonal -> grinded (imprrove packing ability, increase density, strength) -> modifications: add crystal shape modifiers (CaCl2, NaSucconate) -> short, thick crystal

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11
Q

Charac type 1 plaster

A

medium strength
hydrocal - dental stone

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12
Q

Steps manufacture type 1 plaster

A

autoclaving gypsum lump (after dry calc) - 123celcius 117kiloPa -> drying 100celcius 5-7hr

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13
Q

Charac manufacture type 2 plaster

A

high strength - type 3-4 ISO
die stone

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14
Q

Steps manufacture type 2 plaster

A

wel calc + modifiers (CaCl2; NaSuc)
form short, thick crystal

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15
Q

Effect high, low W/p

A

low w/p -> stronger product, faster rxn (b/c less water aka less water residues btw crystals)
high w/p -> weaker product, longer rxn

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16
Q

Apparen density def

A

apparen density = 1/bulkiness -> packing ability

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17
Q

Setting process, name gypsum

A

2CaSO40.5H2O (hemihydrate) + H2O -> 2CaSO42H2O (dihydrate)

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18
Q

Solubility hemihydrate

A

6.5g/l at 20 celcius
(dihydrate - 2.4g/l 40 celcius -> x3 :2 -> 6.5g/l 20 celcius)

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19
Q

Solubility dihydrate

A

< soluble in water
-> powder in water -> hemihydrate rxs w/ water -> form dihydrate
2.4g/l at 40 celcius

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20
Q

Saturation

A

aq dihydrate supersaturated
crystallizes at nucleation centers in suspension

check again

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21
Q

Formation gypsum crystals

A

radiate from nucleation centers
spherulitic aggregates

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22
Q

Water requirement gypsum diff b/c

A

diff apparent density

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23
Q

Water/powder W/P def

A

how many g water need to give 100g powder workable viscosity

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24
Q

Stages setting

A
  1. fluid
  2. plastic
  3. friable
  4. carvable
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25
Q
  1. Fluid setting charac
A

cont aq phase
viscous liquid mix
glossy
pseudoplasticity

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26
Q
  1. plastic setting charac
A

grow gypsum
growing gypsum interxs -> plastic
vibration - NO flow
can be molded
NO glossy

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27
Q
  1. friable setting charac
A

cont crystal growth -> plastic into rigid solid
1st: weak, friable
-> amount solid phase increase -> increase strength

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28
Q
  1. carvable stage charac
A

rigid mass carvable

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29
Q

Def setting time

A

amount time takes for all 4 stages complete
modify by:
w/p
add. accelerators/ retarders (also effect isotropic expansion)

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30
Q

Changes during setting

A

aq phase: setting contraction
-> gain rigidity (gypsum growth) -> isotropic expansion

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31
Q

Types additives

A

Accelerators
Retarders

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32
Q

Accelerators

A

provide seeds for nucleation
increase rate solution hemihydrate

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33
Q

Retarders

A

poisons seeds for nucleation
salts of low solubility
NaCl, NaS, acetates, borates

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34
Q

How low solubility salt acts as retarders

A

setting proceeds -> conc additives increase -> exceed limit solubility -> salts ppt on nuclei crystallization -> poisoning

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35
Q

Effect additives

A

reduce setting expansion (complete faster) by changing crystal habit

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36
Q

Effect inherent porosity

A

weakens gypsum

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37
Q

What cause inherent porosity

A

water residuals btw crystal
triangular voids btw crystal

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38
Q

Gypsum structure

A

tangled aggregation monoclinic gypsum crystal
5-20um length

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39
Q

Phases gypsum cast

A
  1. Manipulstion time
  2. Molding time
  3. Setting time
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40
Q

Manipulation time of gypsum cast stages

A

casting/ impression: must complete b4 loses fluidity (aq phase)

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41
Q

Molding time of gypsum cast stages

A

molding: must complete b4 loses fluidity -> friable stage (plastic phase)

42
Q

Setting time of gypsum cast stages

A

when rigid material strong enough to carved (until carvable stage complete)

43
Q

How to ID setting time over

A

Vcat/ Gillmore needles

44
Q

Control rate setting by

A

additives (KS, tartrate, Na tartrate)
change W/P ratio

45
Q

Hygroscopic expansion

A

additional H2O -> greater expansion
effect of immersion

46
Q

Control setting expansion by

A

additives (accelerator + retarder + raw hemihydrate)
ex: NaSuc + Borax

47
Q

Relationship setting expansion, W/P

A

inversely proportional

reduce aq phase -> more interxn growing gypsum crystal

48
Q

Relation strength, W/P

A

inversely proportional
low W/P -> max strength - increase setting expansion

49
Q

When to use high, low W/P

A

low: need strength
high: need accuracy

50
Q

Charac cast gypsum

A

brittle
tension < compression

51
Q

What does tensile strength indicates

A

fracture resistance

52
Q

What does compressive strength indicates

A

surface hardness

53
Q

Use of gypsum

A
  1. impression material (impression plaster)
  2. prep models/ dies
  3. gypsum bonded investments (mold materials in casting dental gold alloy)
54
Q

Pos effect of gypsum drying

A

water evaporates -> less water residues -> x2 strength (only happen if <2% water remains)

55
Q

Effect of gypsum drying

A

stable below 40
>100 -> shrinkage, strength reduction
soak dried cast in saturated solution CaSO4
if dried -> put in water -> og prop b4 drying

56
Q

Disinfection gypsum cast

A
    • disinfectants to mixing water (5% phenol, 2%glutaraldehyde) - sometimes skin irritants
  2. immersion in disinfecting solution after each clinical stage
  3. autoclave sterilization
57
Q

Types thermoplastic materials

A

dental impression compound
waxes
guttapercha

58
Q
A
59
Q

Types dental impression

A
  1. used for impression
  2. used for tray preparation
60
Q

Charac dental impression

A

NOT elastic/ fragile

61
Q

Dental impression prep

A

in cakes, sticks

62
Q

Compostion thermoplastic

A

40% natural resins (ex: shallac)
waxes
stearic acid - lubricant, plasticizer
50% fillers, inorg pigments

(thermoplastic -> plastic -> think of plasticity stuff: natural resins, waxes -> what destroy them: stearic acid - inorg)

63
Q

Thermoplastic material handling temp

A

use at 40 -> cooled at oral temp 37 (rigid)

64
Q

Flow ability Type 1

A

85% at 45
79% at 37 degree

(no.1 -> flow faster)

65
Q

Flow ability Type 2

A

70% at 45
68% at 37

66
Q

Thermal conductivity thermoplastic materials

A

low
time needed for temp to become uniform

67
Q

Thermal expansion, contraction coeff, viscosity thermoplastic material

A

high thermal expansion, contraction coeff -> high dimensional changing
high viscosity -> diff w/ details

68
Q

Manipulation thermoplastic

A

flame/ water bath -> softened (reversible process)
NO direct flame, NO kneading in water
NO too cold cooling water spray -> prevent thermal shock

69
Q

Disinfection by immersion in

A

Phenolic glutaraldehyde
Iodophors
Na hypochloride
Manufacturers recommened

(thermal plastic disinfection - think of hot stuff -> PIN)

70
Q

Use of type 1 thermoplastic

A

border modelling
full crown/ partially/ edentulous impression

71
Q

Use type 2 thermoplastic

A

impression edentulous arch
impression trays which final impresison taken w/ another material
NO elastic -> NO record undercuts

72
Q

Ad, disad impression compound

A

ad:
compatible w/ die, cast material
electroplated -> accurate abrasion resitant dies

(impression -> impressive -> electroplated -> abrasion resistance)
disad:
sensitive handling
rxs w/ water -> change comp -> lost low MW during heating

73
Q

Waxes charac

A

high flow
distort on withdrawal from undercuts
use only in edentulous reg

74
Q

Classification waxes based on application

A
  1. Pattern
    a. inlay -1,2
    b. resin
    c. casting
    d. base plate
  2. Processing
    a. boxing
    b. blockout
    c. carding
    d. white
    e. utility
  3. Impression
    a. corrective (record detail, displace selected reg soft tissue in edentulous impression)
    b. bite registration (how max, man intercuspate)

(pattern -> bcri - 1st category -> foundation - base: BAse plate, CAsting, resin, inlay
processing - long name -> 2bc2w: boxing, blackout, carding, white, utilities
impression -> bc: bite registration, corrective

75
Q

Charc inlay waxes - kerr dental (pattern)

A

use: inlay, crown, pontics replicas
types inlays:
1. soft - use: indirect technique
2. hard - use: prep direct patterns in mouth
inlay in geometric, n anatomic, bulks form

76
Q

Resin waxes (pattern) charac

A

high strength
resistance flow
dimenstional stability
burnout w/o residues

steps: 3-5mm resins -> light chamber -> cure -> resin remove from mold -> heat casting 690celcius - 45min

full crown patterns of pattern resin, inlay waxes - similar marginal discrepancies

77
Q

Casting wax (pattern) charac, use

A

use: thin section removable, fixed partial denture patterns
convenient in prep copins/clasps - thin reg, supplied in sheets, rods, bulk

78
Q

Base plate wax charac, use

A

use: full denture patterns ; occlusal rims (base -> imp foundation -> full denture, occlusal rims)
types base plate:
1. soft base plate - veneers, contours
2. medium hardness base - temperate climates
3. hardes - tropical climates

79
Q

Use processing waxes

A

Boxing - containers for pouring casts ; fabricate replacement pontics for provisional fixed partial dentures
Blackout - fill voids for removable partial denture fabrication
Carding - attaching parts in soldering tech
White - patterns stimulate veneer facing
Utilities - lab

(boxing -> blackout -> needs (carding) -> white washed (white) -> utilities)
(boxing -> injured
-> need to pour cast -> container for pouring cast
-> replacement permanently -> replacement pontics fixed partial dentures)
(blackout -> feels guilty temporarily -> avoiding -> fill voids removable partal denture)
(carding -> attach a face to some name in soldier -> attaching parts in soldering tech)
(white -> white wash -> veneer is white -> stimulate veneer facing)
(utilities -> lab)

80
Q

Composition waxes

A

org polymers
natural waxes (resins, oils, fats)
(wAx -> ao -> org poly, natural wax)

81
Q

Types waxes is used in waxes

A

Natural waxes (beeswax)
Synthetic wax

82
Q

Func adding natural waxes in waxes

A

modify melting ranges wax blends

83
Q

Charac synthetic wax

A

specific melting points
blended/ mixed with natural waxes
low molecular weight polyethylene

84
Q

Prop waxes

A

crystalline + amorphous component - diff distribution molecular weight
-> melt over range 5-30 celcius

85
Q

Prop waxes thermal expansion

A

highest coeff thermal expansion
-> poor fitting if no compensating factors

86
Q

Wax shrinkage

A

0.4%

87
Q

Wax flow ability, def

A

increase temp
increase force
-> increase flow

measure ability deform under light forces, analogous to creep (flow)

88
Q

Wax distortion

A

partly elastic
memory effect: deform -> return to og shape
residual stress -> distortion

89
Q

Min pattern distortion by

A

Direct tech wax heat uniformly 50celcius - 15min
Quick pattern application
Store in fridge if delay application (low temp -> elastic recover slower)
NO wax residues left in mold after burnout in lost wax process

90
Q

Use of corrective waxes

A

record details soft tissue in edentulous impression

91
Q

Use of bite waxes

A

in bite registration

92
Q

Gutta percha charac

A

non elastic
> brittle
harder
than natural rubber

(tree -> non elastic, brittle)

93
Q

Gutta percha chem structure

A

isomer of natural rubber: trans polyisoprane

94
Q

Forms of gutta percha

A

alpha:
natural
use in heat softened gutta percha

beta:
in gutta percha cones
use in cold compaction root canal filling (small cone gutta percha + edodontic sealer)

95
Q

States of gutta percha

A

interchangable depends on temp

96
Q

Composition gutta percha

A

59-75% ZnO
19-28% Gutta percha
additives: coloring agents, anitoxidants, metllic salts

(composition: name: gutta percha -> composed most - ZnO -> gutta percha)
(gutta percha tree -> additives to make it -> antioxidants, leaves green colour -> coloring agent, to cook -> season with salts -> metallic salts)
VERY IMP: ZnO

97
Q

chem formula gypsum in nature (calcination process)

A

dihydrate

98
Q

Thermodynamic changing gypsum

A

heat production

99
Q

Steps dry calc

A

gypsum in open container 120-140celcius
loss water -> form channels w/in gypsum
->

100
Q

Additional use of gutta percha

A

probes
radiography -> ID dept, topographic charac periodontic pockets, fistulas

Dental material (7 decks)

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