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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
1. Fluid setting charac
cont aq phase viscous liquid mix glossy pseudoplasticity
26
2. plastic setting charac
grow gypsum growing gypsum interxs -> plastic vibration - NO flow can be molded NO glossy
27
3. friable setting charac
cont crystal growth -> plastic into rigid solid 1st: weak, friable -> amount solid phase increase -> increase strength
28
4. carvable stage charac
rigid mass carvable
29
Def setting time
amount time takes for all 4 stages complete modify by: w/p add. accelerators/ retarders (also effect isotropic expansion)
30
Changes during setting
aq phase: setting contraction -> gain rigidity (gypsum growth) -> isotropic expansion
31
Types additives
Accelerators Retarders
32
Accelerators
provide seeds for nucleation increase rate solution hemihydrate
33
Retarders
poisons seeds for nucleation salts of low solubility NaCl, NaS, acetates, borates
34
How low solubility salt acts as retarders
setting proceeds -> conc additives increase -> exceed limit solubility -> salts ppt on nuclei crystallization -> poisoning
35
Effect additives
reduce setting expansion (complete faster) by changing crystal habit
36
Effect inherent porosity
weakens gypsum
37
What cause inherent porosity
water residuals btw crystal triangular voids btw crystal
38
Gypsum structure
tangled aggregation monoclinic gypsum crystal 5-20um length
39
Phases gypsum cast
1. Manipulstion time 2. Molding time 3. Setting time
40
Manipulation time of gypsum cast stages
casting/ impression: must complete b4 loses fluidity (aq phase)
41
Molding time of gypsum cast stages
molding: must complete b4 loses fluidity -> friable stage (plastic phase)
42
Setting time of gypsum cast stages
when rigid material strong enough to carved (until carvable stage complete)
43
How to ID setting time over
Vcat/ Gillmore needles
44
Control rate setting by
additives (KS, tartrate, Na tartrate) change W/P ratio
45
Hygroscopic expansion
additional H2O -> greater expansion effect of immersion
46
Control setting expansion by
additives (accelerator + retarder + raw hemihydrate) ex: NaSuc + Borax
47
Relationship setting expansion, W/P
inversely proportional reduce aq phase -> more interxn growing gypsum crystal
48
Relation strength, W/P
inversely proportional low W/P -> max strength - increase setting expansion
49
When to use high, low W/P
low: need strength high: need accuracy
50
Charac cast gypsum
brittle tension < compression
51
What does tensile strength indicates
fracture resistance
52
What does compressive strength indicates
surface hardness
53
Use of gypsum
1. impression material (impression plaster) 2. prep models/ dies 3. gypsum bonded investments (mold materials in casting dental gold alloy)
54
Pos effect of gypsum drying
water evaporates -> less water residues -> x2 strength (only happen if <2% water remains)
55
Effect of gypsum drying
stable below 40 >100 -> shrinkage, strength reduction soak dried cast in saturated solution CaSO4 if dried -> put in water -> og prop b4 drying
56
Disinfection gypsum cast
1. + disinfectants to mixing water (5% phenol, 2%glutaraldehyde) - sometimes skin irritants 2. immersion in disinfecting solution after each clinical stage 3. autoclave sterilization
57
Types thermoplastic materials
dental impression compound waxes guttapercha
58
59
Types dental impression
1. used for impression 2. used for tray preparation
60
Charac dental impression
NOT elastic/ fragile
61
Dental impression prep
in cakes, sticks
62
Compostion thermoplastic
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
Thermoplastic material handling temp
use at 40 -> cooled at oral temp 37 (rigid)
64
Flow ability Type 1
85% at 45 79% at 37 degree (no.1 -> flow faster)
65
Flow ability Type 2
70% at 45 68% at 37
66
Thermal conductivity thermoplastic materials
low time needed for temp to become uniform
67
Thermal expansion, contraction coeff, viscosity thermoplastic material
high thermal expansion, contraction coeff -> high dimensional changing high viscosity -> diff w/ details
68
Manipulation thermoplastic
flame/ water bath -> softened (reversible process) NO direct flame, NO kneading in water NO too cold cooling water spray -> prevent thermal shock
69
Disinfection by immersion in
Phenolic glutaraldehyde Iodophors Na hypochloride Manufacturers recommened (thermal plastic disinfection - think of hot stuff -> PIN)
70
Use of type 1 thermoplastic
border modelling full crown/ partially/ edentulous impression
71
Use type 2 thermoplastic
impression edentulous arch impression trays which final impresison taken w/ another material NO elastic -> NO record undercuts
72
Ad, disad impression compound
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
Waxes charac
high flow distort on withdrawal from undercuts use only in edentulous reg
74
Classification waxes based on application
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
Charc inlay waxes - kerr dental (pattern)
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
Resin waxes (pattern) charac
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
Casting wax (pattern) charac, use
use: thin section removable, fixed partial denture patterns convenient in prep copins/clasps - thin reg, supplied in sheets, rods, bulk
78
Base plate wax charac, use
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
Use processing waxes
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
Composition waxes
org polymers natural waxes (resins, oils, fats) (wAx -> ao -> org poly, natural wax)
81
Types waxes is used in waxes
Natural waxes (beeswax) Synthetic wax
82
Func adding natural waxes in waxes
modify melting ranges wax blends
83
Charac synthetic wax
specific melting points blended/ mixed with natural waxes low molecular weight polyethylene
84
Prop waxes
crystalline + amorphous component - diff distribution molecular weight -> melt over range 5-30 celcius
85
Prop waxes thermal expansion
highest coeff thermal expansion -> poor fitting if no compensating factors
86
Wax shrinkage
0.4%
87
Wax flow ability, def
increase temp increase force -> increase flow measure ability deform under light forces, analogous to creep (flow)
88
Wax distortion
partly elastic memory effect: deform -> return to og shape residual stress -> distortion
89
Min pattern distortion by
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
Use of corrective waxes
record details soft tissue in edentulous impression
91
Use of bite waxes
in bite registration
92
Gutta percha charac
non elastic > brittle harder than natural rubber (tree -> non elastic, brittle)
93
Gutta percha chem structure
isomer of natural rubber: trans polyisoprane
94
Forms of gutta percha
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
States of gutta percha
interchangable depends on temp
96
Composition gutta percha
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
chem formula gypsum in nature (calcination process)
dihydrate
98
Thermodynamic changing gypsum
heat production
99
Steps dry calc
gypsum in open container 120-140celcius loss water -> form channels w/in gypsum ->
100
Additional use of gutta percha
probes radiography -> ID dept, topographic charac periodontic pockets, fistulas

Dental material (7 decks)

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