Dental pt3 Flashcards
Steps gypsum application
impression - (-) replica
gypsum models - (+) replica
ISO classification types
- impresssion plaster (based on ordinary gypsum plaster)
- plaster (based on ordinary gypsum plaster)
- stone (based on high strength gypsum plaster) - prep models imprints
- stone, high strength, low expansion (based on high strength gypsum plaster) - aka die stones
- stone, high strength, high expansion(based on high strength gypsum plaster) - aka die stones
Formation rxn
CaSO4 +2H2O <-> CaSO4 + 1/2H2O (hemihydrate)
anhydrid <-> y CaSO4 (hexagonal - soluble)
anhydrid <-> b CaSO4 (orthrombic - insoluble) (Beta -> orthromBic - beta -> cant swim -> non soluble)
Types procedure
Calcination aka prolonged heating below melting point sulfate dihydrate -> partial/complete dehydration -> when use mix w/ water
Dry calcination (hemihydrate)
Wet calcination
Wet calcination def
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))
Dry calcination def
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)
Charac dry calcination
slow
quality plaster low
Steps, charac dry calc
gypsum in open container 120-140celcius
loss water -> form channels w/in gypsum
-> low density
-> poor compatibility
-> high SA
Why use wet calcination
material high strength
(wet - swimming - high strength)
Steps wet calcination
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
Charac type 1 plaster
medium strength
hydrocal - dental stone
Steps manufacture type 1 plaster
autoclaving gypsum lump (after dry calc) - 123celcius 117kiloPa -> drying 100celcius 5-7hr
Charac manufacture type 2 plaster
high strength - type 3-4 ISO
die stone
Steps manufacture type 2 plaster
wel calc + modifiers (CaCl2; NaSuc)
form short, thick crystal
Effect high, low W/p
low w/p -> stronger product, faster rxn (b/c less water aka less water residues btw crystals)
high w/p -> weaker product, longer rxn
Apparen density def
apparen density = 1/bulkiness -> packing ability
Setting process, name gypsum
2CaSO40.5H2O (hemihydrate) + H2O -> 2CaSO42H2O (dihydrate)
Solubility hemihydrate
6.5g/l at 20 celcius
(dihydrate - 2.4g/l 40 celcius -> x3 :2 -> 6.5g/l 20 celcius)
Solubility dihydrate
< soluble in water
-> powder in water -> hemihydrate rxs w/ water -> form dihydrate
2.4g/l at 40 celcius
Saturation
aq dihydrate supersaturated
crystallizes at nucleation centers in suspension
check again
Formation gypsum crystals
radiate from nucleation centers
spherulitic aggregates
Water requirement gypsum diff b/c
diff apparent density
Water/powder W/P def
how many g water need to give 100g powder workable viscosity
Stages setting
- fluid
- plastic
- friable
- carvable
- Fluid setting charac
cont aq phase
viscous liquid mix
glossy
pseudoplasticity
- plastic setting charac
grow gypsum
growing gypsum interxs -> plastic
vibration - NO flow
can be molded
NO glossy
- friable setting charac
cont crystal growth -> plastic into rigid solid
1st: weak, friable
-> amount solid phase increase -> increase strength
- carvable stage charac
rigid mass carvable
Def setting time
amount time takes for all 4 stages complete
modify by:
w/p
add. accelerators/ retarders (also effect isotropic expansion)
Changes during setting
aq phase: setting contraction
-> gain rigidity (gypsum growth) -> isotropic expansion
Types additives
Accelerators
Retarders
Accelerators
provide seeds for nucleation
increase rate solution hemihydrate
Retarders
poisons seeds for nucleation
salts of low solubility
NaCl, NaS, acetates, borates
How low solubility salt acts as retarders
setting proceeds -> conc additives increase -> exceed limit solubility -> salts ppt on nuclei crystallization -> poisoning
Effect additives
reduce setting expansion (complete faster) by changing crystal habit
Effect inherent porosity
weakens gypsum
What cause inherent porosity
water residuals btw crystal
triangular voids btw crystal
Gypsum structure
tangled aggregation monoclinic gypsum crystal
5-20um length
Phases gypsum cast
- Manipulstion time
- Molding time
- Setting time
Manipulation time of gypsum cast stages
casting/ impression: must complete b4 loses fluidity (aq phase)
Molding time of gypsum cast stages
molding: must complete b4 loses fluidity -> friable stage (plastic phase)
Setting time of gypsum cast stages
when rigid material strong enough to carved (until carvable stage complete)
How to ID setting time over
Vcat/ Gillmore needles
Control rate setting by
additives (KS, tartrate, Na tartrate)
change W/P ratio
Hygroscopic expansion
additional H2O -> greater expansion
effect of immersion
Control setting expansion by
additives (accelerator + retarder + raw hemihydrate)
ex: NaSuc + Borax
Relationship setting expansion, W/P
inversely proportional
reduce aq phase -> more interxn growing gypsum crystal
Relation strength, W/P
inversely proportional
low W/P -> max strength - increase setting expansion
When to use high, low W/P
low: need strength
high: need accuracy
Charac cast gypsum
brittle
tension < compression
What does tensile strength indicates
fracture resistance
What does compressive strength indicates
surface hardness
Use of gypsum
- impression material (impression plaster)
- prep models/ dies
- gypsum bonded investments (mold materials in casting dental gold alloy)
Pos effect of gypsum drying
water evaporates -> less water residues -> x2 strength (only happen if <2% water remains)
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
Disinfection gypsum cast
- disinfectants to mixing water (5% phenol, 2%glutaraldehyde) - sometimes skin irritants
- immersion in disinfecting solution after each clinical stage
- autoclave sterilization
Types thermoplastic materials
dental impression compound
waxes
guttapercha
Types dental impression
- used for impression
- used for tray preparation
Charac dental impression
NOT elastic/ fragile
Dental impression prep
in cakes, sticks
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)
Thermoplastic material handling temp
use at 40 -> cooled at oral temp 37 (rigid)
Flow ability Type 1
85% at 45
79% at 37 degree
(no.1 -> flow faster)
Flow ability Type 2
70% at 45
68% at 37
Thermal conductivity thermoplastic materials
low
time needed for temp to become uniform
Thermal expansion, contraction coeff, viscosity thermoplastic material
high thermal expansion, contraction coeff -> high dimensional changing
high viscosity -> diff w/ details
Manipulation thermoplastic
flame/ water bath -> softened (reversible process)
NO direct flame, NO kneading in water
NO too cold cooling water spray -> prevent thermal shock
Disinfection by immersion in
Phenolic glutaraldehyde
Iodophors
Na hypochloride
Manufacturers recommened
(thermal plastic disinfection - think of hot stuff -> PIN)
Use of type 1 thermoplastic
border modelling
full crown/ partially/ edentulous impression
Use type 2 thermoplastic
impression edentulous arch
impression trays which final impresison taken w/ another material
NO elastic -> NO record undercuts
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
Waxes charac
high flow
distort on withdrawal from undercuts
use only in edentulous reg
Classification waxes based on application
- Pattern
a. inlay -1,2
b. resin
c. casting
d. base plate - Processing
a. boxing
b. blockout
c. carding
d. white
e. utility - 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
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
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
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
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
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)
Composition waxes
org polymers
natural waxes (resins, oils, fats)
(wAx -> ao -> org poly, natural wax)
Types waxes is used in waxes
Natural waxes (beeswax)
Synthetic wax
Func adding natural waxes in waxes
modify melting ranges wax blends
Charac synthetic wax
specific melting points
blended/ mixed with natural waxes
low molecular weight polyethylene
Prop waxes
crystalline + amorphous component - diff distribution molecular weight
-> melt over range 5-30 celcius
Prop waxes thermal expansion
highest coeff thermal expansion
-> poor fitting if no compensating factors
Wax shrinkage
0.4%
Wax flow ability, def
increase temp
increase force
-> increase flow
measure ability deform under light forces, analogous to creep (flow)
Wax distortion
partly elastic
memory effect: deform -> return to og shape
residual stress -> distortion
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
Use of corrective waxes
record details soft tissue in edentulous impression
Use of bite waxes
in bite registration
Gutta percha charac
non elastic
> brittle
harder
than natural rubber
(tree -> non elastic, brittle)
Gutta percha chem structure
isomer of natural rubber: trans polyisoprane
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)
States of gutta percha
interchangable depends on temp
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
chem formula gypsum in nature (calcination process)
dihydrate
Thermodynamic changing gypsum
heat production
Steps dry calc
gypsum in open container 120-140celcius
loss water -> form channels w/in gypsum
->
Additional use of gutta percha
probes
radiography -> ID dept, topographic charac periodontic pockets, fistulas
