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o Uses
Make an accurate replica of
tissues.o Impression
Single tooth.
Whole dentition.
Partially or
completely
edentulous mouth.
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• 1-Biocompatible: non toxic- non irritant.
o 2-Acceptable to the patient: pleasant
odour, taste, esthetic colour.
o 3-Ease of manipulation, reasonable
cost.
o 4-Reasonable setting time.
o 5-Adequate shelf life.
o 6-Adequate strength: not tear or break
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o 7-Compatible with model materials.
o 8-Dimensionally stable: neither expands
nor contracts.
o 9-Adequate flow properties: to register
fine details.
o 10-Readily disinfected without loss of
accuracy.
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Elastic Non Elastic
Non
Elastic
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Sets by a physical
reaction due to
temperature
changes
Sets by achemical reaction.
Reversible
Irreversible
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Impre
ssion
Ma
terials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible
Alginate (irreversible
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection
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o Thermoplastic material.
o Composition:
Natural resins e.g., shellac & carnuba
wax.
Fillers: soap or talc.
Lubricants: stearic acid.
Colouring agent: e.g., rouge.
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Type I: Type I: low fusing compoundlow fusing compound softens at 53-softens at 53-60°C60°C
Supplied in the form of sheets, or cakesSupplied in the form of sheets, or cakes
used as:used as: impression for edentulous patients.impression for edentulous patients.
OrOr in the form of sticks or cones orin the form of sticks or cones or
cylinders.cylinders.Used as:Used as: impression for a single toothimpression for a single tooth
preparation as in (crowns), known aspreparation as in (crowns), known as
Copper Band ImpressionCopper Band Impression..
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Type II: Type II: High fusing compoundHigh fusing compound softens atsoftens at
70°°C.70°°C.
Used as tray material to hold a secondaryUsed as tray material to hold a secondaryimpression materialimpression material
Heating:Heating:
o In a water bath-soaking in water in casesIn a water bath-soaking in water in casesof sheets and cakes.of sheets and cakes.
o Over a flame in case of sticks.Over a flame in case of sticks.
o Avoid over heating.Avoid over heating.o KneadingKneading: with the fingers.: with the fingers.
o Importance: assures uniform heatingImportance: assures uniform heating
Increases the flow.Increases the flow.
Gives workability.Gives workability.
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Cooling:Cooling:
o Assure uniform cooling byAssure uniform cooling by
spraying with water at 16-18°Cspraying with water at 16-18°C
before removal from the mouth.before removal from the mouth.
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Flow:Flow: Type 1 Type 1: 85%: 85% at 45°Cat 45°C
less than 6% atless than 6% at
37°C.37°C.
Type II: Type II: 70% at 45°C70% at 45°C
less than 2% at 37°C.less than 2% at 37°C.
Viscous material does not record fineViscous material does not record fine
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• Low thermal conductivity.Low thermal conductivity.
• High expansion and contractionHigh expansion and contraction
coefficients.coefficients.
• Linear contraction on cooling fromLinear contraction on cooling from
mouth temperature to roommouth temperature to room
temperaturetemperature
(0.3%-0.4%).(0.3%-0.4%).
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o Dimensional Changes: due to relief of Dimensional Changes: due to relief of
internal stresses (relaxation)internal stresses (relaxation) →→ WarpageWarpage
→→distortion of the impression.distortion of the impression.
o Model should be poured as soon asModel should be poured as soon as
possible.possible.
o No separating medium.No separating medium.
o Separation of model.Separation of model.
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Uses:Uses:
Secondary impression or final wash in aSecondary impression or final wash in a
special tray.special tray.
Composition of powder:Composition of powder:1. Calcium sulphate hemihydrate.(main
ingredient)
2. Potassium sulphate or nitrate:
Accelerator
3. Flavouring agent.
4. Colourin a ents.
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Reaction:Reaction:
Chemical reaction:Chemical reaction: crystalization andcrystalization and
exothermicexothermic
CaSOCaSO44 ½ H½ H22O + HO + H22OO →→CaSOCaSO44.2H.2H22O + heatO + heat
Dimensional changes:Setting expansion can be reduced to + 0.06%
by presence of K 2SO4.
Soluble impression plaster:
Contains starch to facilitate the separation of
impression from model by softening when
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Manipulation:Manipulation:
Water / powder ratio.55 to 60ml water to 100gm of powder.
Separating medium alcoholic solution of
varnish. Or soap suspensions.
Properties.
o Storage problems:
o kept in sealed containers.
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Slide 9 of 33
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Advantages and
DisadvantagesAdvantages Disadvantages
Accurate
reproduction of fine details
Minimal dimensionalchanges
Patient may
experiencedry sensation
Material is brittle(fracture If undercuts arepresent)
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Uses: as a secondary impression, correctivewash.
Composition
1. Base materials
• zinc oxide• Inert oils: mineral oil.
2. Accelerator:
a. Oil of cloves or eugenol.b. Gum rosin.
c. Fillers: talc, kaolin.
d. Accelertor: MgCl2 and moisture.
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Other products: NON Eugenol type
Eugenol free: chlorothymol or
carboxylic acid or lauric acid
substituted for eugenol.
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Setting reactionSetting reaction
Acid – base reaction.
Zinc oxide + water zinc hydroxide
Zinc hydroxide + 2 eugenol
Acid base
zinc eugenolate (chelate) (salt)
Chelation reaction
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Chelation:
Is the attachment of a molecule or ion to
metal atom at more than one point.
The term is derived from the Greek word
meaning “crab’s claw” indicating two pronged
attachment.• A central zinc atom is held by two eugenol
“claws”.
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Setting timeSetting time
Types: S.T Type I: hard 10 minutes
Type II: soft 15 minutes
Factors Controlling the setting time:
Accelerators: water, magnesium
chloride, zinc acetate or alcohol.
Retarders: inert oils such as olive oils,
mineral oil.
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Ratio of zinc oxide paste to eugenol
paste.
Cooling spatula and mixing slab.
Effect of high temperature and
humidity:
sets more quickly at high temperature
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o Manipulation.
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Pouring and separating cast.
Dimensional changes:
Shrink less than 0.1% after 30
minutes.
Delayed pouring of impression – tray
should be stable.
o Do not use base plate (shellac) special
tray →warpage on standing →distortion
of impression
Plaster
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Im
pres
sion
Materials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible
Alginate (irreversible
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection
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Solution: homogenous mixture:
one phase system.
Suspension: hetrogenous mixture:
two phase system.
Colloids: hetrogenous, particle size of the
particles are smaller than in suspension:
two phase system.
Dispersed phase.
Dispersion medium →water →Hydrocolloid
• Sol stateSol state: viscous liquidviscous liquid
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• Sol state:Sol state: viscous liquid.viscous liquid.
• Gel state:Gel state: jelly like jelly like
solsol
→→ fibrils in a network pattern.
→Brush heap structure.Brush heap structure.
•
reversible hydrocolloidreversible hydrocolloid
Or by: chemical reaction:Or by: chemical reaction:
irreversible hydrocolloidirreversible hydrocolloid..
Agglomeration of molecules
SolSol reduction in temperature
gel
gel
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Reversible hydrocolloids: Agar-AgarReversible hydrocolloids: Agar-Agar
Liquefaction temperatureLiquefaction temperature: 71°C-100°C.: 71°C-100°C.
Gelation temperatureGelation temperature 37°C-43°C.37°C-43°C.
• Hysteresis:Hysteresis: temperature lag or differenttemperature lag or different
liquefaction and gelation temperatureliquefaction and gelation temperature
• SolSol gel: physicalgel: physical
change.change.
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agar hydrocolloid (hot agar hydrocolloid (cold
(sol
cool to 43 C
heat to 100 Cgel
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UsesUses
Composition:Composition: AgarAgar 12.5% by wt.(extracted from12.5% by wt.(extracted fromsea weeds)sea weeds)
Borax(strengthener)Borax(strengthener)
Potassium sulphatePotassium sulphate
Alkyl benzoate(anti fungal )Alkyl benzoate(anti fungal )
WaterWater 85.5% by wt.85.5% by wt.
Syringes:Syringes: low viscosity – high flow.low viscosity – high flow.
Tubes: Tubes: high viscosity – heavy body: low flow.high viscosity – heavy body: low flow.
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ManipulationManipulation
• Heating and Conditioning BathHeating and Conditioning Bath
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Manipulation3chamber conditioning unit
)1(liquefy at 100°C for10 minutes
converts gel to sol
)2(store at 65°C
place in tray
)3(temper at 46°C for 3 minutes
seat tray
cool with water at 13°C for 3
minutes
converts sol to gel
G l tiG l ti U f t li t tU f t li t t
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Gelation:Gelation: Use of water cooling system trayUse of water cooling system tray
with means of retention (perforations).with means of retention (perforations).
Avoid iced H2O: concentration of
stresses.
A id ti th t
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Avoid exerting pressure on the tray or
moving it.
Removal impression: one single stroke
or sudden pull.
→reduce permanent deformation and
tearing of impression
Dimensional changes:Dimensional changes:
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g
Loss of water by EvaporationLoss of water by Evaporation
Synersis:Synersis: Exuding of fluid at surfaceExuding of fluid at surface
of the gel (fibrils cross link continuesof the gel (fibrils cross link continues
..
Imbibition:Imbibition:
If the gel absorbs water If the gel absorbs water
expansion or swelling.expansion or swelling.
Stresses:Stresses:
Pressure on tray during gelation.
Use of iced H2O during initial stages
Shrinkage
Syneresis
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60
Syneresis
Imbibition
contract or expand by water loss or gain
H2O
H2O
Ad d
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Advantages and
Disadvantages of AgarAdvantages:Detail reproduction is very
good.
Can record undercut areascorrectly.
Distortion on removal isprevented due to elasticrecovery.
Well tolerated by thepatient.
Can be reused.
Disadvantages:Can not be electroplated.
Thin sections of impression
tears easily.Multiple models can not be
poured like elastomericimpression materials.
Special armamentarium
(equipments) required.Gypsum hardener required.
Sterilization of impressionis difficult.
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Advantages:Advantages:
Easy to manipulate.
Does not require
special equipment.
Relatively
inexpensive.
Comfortable for the
UsesUsesSolSol gel by chemical reactiongel by chemical reaction
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Composition:Composition:
Potassium alginate.(salt of alginic acid)
Calcium sulphate dihydrate.(reactor)
Potassium sulphate.(improves gypsum
surface)
Sodium phosphate: retarder.
Diatomaceous earth: filler.
Glycols: dustless. Pigments.
Flavours.
Quaternary ammonium salts:
i
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Reaction:Reaction:
1.1. CaSOCaSO44.2H.2H
22O + NaO + Na33POPO
44
2.2. CaSOCaSO44.2H.2H
22O+k Alginate K O+k Alginate K 22SOSO
44 + calciu+ calciu
alginatealginate
(insolubl(insolubl
gel)gel)
Types:Types: amount of Naamount of Na33POPO44
Fast set: less amount of retarder.
Regular set.
+ H2O CaCa33POPO
44 + 3Na+ 3Na22SOSO
Concentration of filler:Concentration of filler:
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Concentration of filler:Concentration of filler:
Controls flexibility of set impression.Controls flexibility of set impression.
Soft set: less amount of filler. Hard set.
Manipulation:
Proportioning.
Mixing: vigorous mix – against sides of
the rubber bowl. Mixing time: 45 seconds (fast set).
One minute (regular set).
G l ti tiG l ti ti
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Gelation time:Gelation time:
1.5-5 minutes from the start of mix till1.5-5 minutes from the start of mix till
material is no longer tacky when touchedmaterial is no longer tacky when touched
with finger.with finger.
Avoid movement of the tray during
setting.
Remove the tray after additional/2-3
minutes as elasticity is improved with
time and permanent deformation is ↓↓.
Control of the S T:
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Control of the S.T:
• Do not reduce powder/H2O ratio as
this affects consistency, accuracy and
↓strength.• To prolong S.T: reduce temperature
of H2O *not below 18°C.
temperature of water should be
between 18-24°C.
• Better to choose the suitable type of
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H t id di i l hHow to avoid dimensional changes
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How to avoid dimensional changesHow to avoid dimensional changes
1.Immediate pouring of the impression.
2.Storing in a humidor: 100% relative
humidity or wrapping in paper towel
saturated with water.
• This does not prevent
synersis.
• Done only for one
hour maximum.
Surface Hardness Of The CastSurface Hardness Of The Cast
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Surface Hardness Of The CastSurface Hardness Of The Cast
Gypsum casts poured against
hydrocolloids sometimes have rough or
chalky surface which causes inaccuracy
or lack of sharp details.
Causes:Causes:
• Impression not washed from blood or
saliva after removal from the mouth as
blood and saliva retard the setting of
gypsum.
E H O l ft i i i f b f
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• Excess H2O left in impression surface before
pouring dilute surface of the model.
• Impression stored in humidor for ½ or 1
hour, not washed to remove exudate.
• Removal of the model after a long time(several hours)…contact of the gel
containing H2O with gypsum which is
slightly soluble. CaSO4.2H2O chalky
surface.
• Premature removal of the model: not before
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Syringed agar: boiled for 8 minutes cooledSyringed agar: boiled for 8 minutes cooled
to 65°C for 10 minutes, injected aroundto 65°C for 10 minutes, injected around
preparation.preparation.
Alginate: mixed inAlginate: mixed in
tray over agar.tray over agar.
Setting time: 4Setting time: 4
minutes.minutes.
Ad tAd t
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Advantages:Advantages:
• Simple heating equipment.Simple heating equipment.
• No water cooling system trays.No water cooling system trays.
• Fine details of preparation.Fine details of preparation.
• Agar: more compatible with gypsumAgar: more compatible with gypsum
model materials than alginate, & hasmodel materials than alginate, & has
higher tear strength than algiantehigher tear strength than algiante
Plaster
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Impression
Materia
ls
Non-elastic
Elastic
AqueousHydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar
(reversible
Alginate (irreversible
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection
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Rubber-like in nature *polymers.
ADA No. 19: Non Aqueous Elastomers
Uses:
• Impression for crown and bridge.
• Partial denture.
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Non-Aqueous Elastomers• Synthetic rubbers
• mimic natural rubber• scarce during World War II
• Large polymers
• some chain lengthening• primarily cross-linking
• Viscosity classes• low, medium, high, putty
• monophasic
Phillip’s Science of Dental Materials
I- PolysulphidesI- Polysulphides
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I PolysulphidesI Polysulphides
BaseBase CatalystCatalyst
• Polysulphide polymer • Lead
dioxide.
•Dibutylphthalate
• Sulphur
• Copper carbonate
Titanium carbonate
Or silica as filler materials.
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Polymer with terminal and pendant mercaptan groups (-SH(
Byproduct H2O
Reaction: condensation polymerizationReaction: condensation polymerization
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Reaction: condensation polymerizationReaction: condensation polymerization
Terminal and pendant gps of polymer are
oxidized by lead dioxide →chain extension of
terminal SH gp and cross linking of pendant
gp.
Polysulphide polymer + lead dioxide →
polysulphide rubber + lead oxide + H2O …..
Exothermic 3-4°C.
↑↑ in molecular weight
Paste → rubber.
Base: three consistenciesBase: three consistencies
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Base: three consistenciesBase: three consistencies
low: syringe ------ light body
Medium ----------- regular
High: tray ----------- Heavy body
As % filler
increase
viscosity
increase
s
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--SH HS---------------------
SH
HS-
-
S
H
O=
Pb
=
O
O=
Pb
=
OO = Pb =
OHS
-S-S---------------S-S-
S
S
+3PbO + H2O
mercaptan + lead dioxide polysulfide rubber + lead oxide +water
O’Brien Dental Materials & their Selection
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Lead dioxide: is dark brown to
gray brown in colour and toxic.
So substituted by hydrated
Cu(OH)2
→green mix
Sili i i t i l
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Silicone impression material
I- Condensation SiliconeI- Condensation Silicone
Polymer: hydroxy-terminated polyPolymer: hydroxy-terminated poly
(dimethyl siloxane)(dimethyl siloxane)
BaseBase CatalystCatalyst
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Dimethyl siloxane polymer withDimethyl siloxane polymer with
terminal OH gpterminal OH gp
Copper carbonate, silica as fillers.Copper carbonate, silica as fillers.
Stannous octoate + alkylStannous octoate + alkyl
silicate assilicate as
Tetra ethyl silicate Tetra ethyl silicate
ReactionReaction →→ silicone rubber + alcoholsilicone rubber + alcohol
exothermicexothermic 1°C1°CCondensation polymerizationCondensation polymerization →→ largestlargest
dimensional change.dimensional change.
ShrinkageShrinkage -0.6%-0.6%
ConsistenciesConsistencies: only two: only two
LowLow putty very highputty very high
Limited shelf life due to oxidation of stannousLimited shelf life due to oxidation of stannous
octoate and ethyl silicate is not stable in presenceoctoate and ethyl silicate is not stable in presence
++
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Hydroxyl terminated polydimethyl
siloxane
Crosslinking reaction
Tin compound
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Vinyl terminated polydimethyl siloxane
Crosslinking reaction (no byproduct(
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Reaction:Reaction: Ionic PolymerizationIonic Polymerization
Addition type --- no by products.Addition type --- no by products.
If proper balance between two polymers isIf proper balance between two polymers is
not maintainednot maintained →→ 22ryry reaction occurs.reaction occurs.
EvolutionEvolution of the hydrogen gasof the hydrogen gas
→→ bubbles on surface of bubbles on surface of
impressionimpression →→
voids in stone model.voids in stone model.
∴∴ Manufacturers add finely dividedManufacturers add finely divided PlatiniumPlatinium
oror palladiumpalladium to absorbto absorb Hydrogen.Hydrogen.
C i t iC i t i ll didi hi hhi h
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Consistencies:Consistencies: lowlow mediummedium highhigh
lightlight regularregular heavyheavy
and a very high (putty).and a very high (putty).
Latex or rubber gloves: containing
sulphur → cause retarded or no
polymerization of addition silicones Use: Vinyl gloves.
IV- Polyethers:IV- Polyethers:
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IV Polyethers:IV Polyethers:
BaseBase
Polymer with ethylenePolymer with ethyleneImine rings terminalImine rings terminal
groups.groups.
Silica fillerSilica fillerplasticizer: glycoetherplasticizer: glycoether
phthalatephthalate
CatalystCatalyst
Cross linking agentCross linking agentas dichlorobenzeneas dichlorobenzene
sulphonatesulphonate
Reaction:Reaction:
Cationic polymerization and opening of the iminerings.
Additional polymerization
exothermic 4°C
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Structure of polyether
crosslinking reaction with imine end groups
No byproduct
Consistencies: *medium consistency + thinner
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Consistencies: medium consistency + thinner
in a separate tube to ↓↓viscosity.
Recently low and high viscosity.
Hydrophilic must not be stored in H2O or
humid atmosphere.
Very short working time 2.5 minutes
↑↑by thinner
Stiff: difficult to remove from the patient’s
mouth and to separate from the cast.
Properties of elastomeric impressionProperties of elastomeric impression
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materialsmaterials
Setting timeSetting time
Polysulphide: longest S.T 7-10 min.
↓Condensation silicone 6-8 min.↓Addition silicone 6-8 min.
↓Polyethers 3-4.5 min.
W.T and S.T Decreases as viscosity increases from
low to high
W.T and S.T ↓↓ b ↑↑ in tem erature and
Dimensional Changes on SettingDimensional Changes on Setting
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Dimensional Changes on SettingDimensional Changes on Setting
Addition silicone: smallest change
-0.15%
Polyethers -0.2%
Polysulphides -0.4%
Condensation silicone: largest change
-0.6%
Causes of dimensional
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Causes of dimensional
changes:Continuation of the polymerization rxn
Thermal contraction
Volatile components
Elastic Recovery from Deformation:Elastic Recovery from Deformation:
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yy
Addition silicone: shows the best recovery
from deformation↓Condensation silicone.
↓Polyethers
↓Polysulfies shows greatest deformation
i.e., poorest recovery.
Visco elasticVisco elastic
Mechanical properties are time dependent,
higher rate of deformation → higher tear
strength (sudden pull).
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Detail Reproduction:Detail Reproduction:
All reproduce 0.02mm wide line except
the very high viscosity 0.075mm line.
Compatible with gypsum.
St i i iSt i i i
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Strain in compressionStrain in compression
Measure of flexibility.Low consistency more flexible than high
consistency.
Polyethers highest stiffness
Addition silicone
Condensation silicone
Polysulfides lowest
Lowest strain(flexibility)
Highest strain
Shore A HardnessShore A Hardness
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Shore A HardnessShore A Hardness
Highest: polyethers.
Lowest: polysulfides
Hardness and flexibility (strain) affect
the force necessary for removal of
impression from mouth.
Tear strength:Tear strength: withstand tearing in thin
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Tear strength: Tear strength: withstand tearing in thin
interproximal areas.
Much higher than hydrocolloids 350-700
g/cm.
Elastomers:Elastomers: 2000-4000g/cm.
Polysulfides:Polysulfides: shows the highest tear
strength.
But due to high permanent deformation
→ inaccurate impression
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Double mix technique-single impression
• Syringe or light bodied material is
injected in and around preparation.• Heavy body is mixed, inserted in tray
and placed over syringed material.
Two materials bond, set at about the
same time.
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1- Automatic mixing systems (mixing
gun).
Advantages
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• Uniform dispensing of catalyst and
base.
• Fewer bubbles.
• Less waste than in hand mixed.
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2- Hydrophilic Addition Silicone:
Hydrophobic materials has poor
wettability: high contact angle: casts with
voids (water repellent).
In hydrophilic: surfactants (wetting
agents) added → ↓↓contact angle, improve
wettability, simplify pouring of gypsummodels.
Di d b l l d
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Disadvantage: cannot be electroplated as
metallizing powder does not adhere to
surface of hydrophilic silicone.
3-Addition Silicone Containing Hydrogen
Absorbers
So that dies can be poured as
soon as desired without bubbles.
4 Single viscosity (Monophase) addition
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4- Single viscosity (Monophase) addition
silicone with sufficient shear thinning
qualities
So they can be used as both syringe and
tray material.
Decrease in viscosity at high shear stress
as during syringing or mixing, highviscosity at low stress as when inserted
in the tray.
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