Impression Materials PPT

December 15, 2011 | By | Reply More

Impression Materials PPT

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Impression Materials

—  Non-elastic

—  Elastic

¡  Aqueous hydrocolloids

÷ Agar

÷ Alginate

¡  Non-aqueous elastomers

÷ Polysulfide

÷ Silicones

¢ Condensation

¢ Addition

÷ Polyether

—  Indications

—  Diagnostic casts

¡  preliminary

¡  opposing

—  Indirect
reconstruction

¡  fixed

¡  removable

—  Bite registration

—  Elastomeric Impression Materials

—  Viscoelastic

¡  physical properties vary

÷ rate of loading

—  Rapidly remove

¡  decreases permanent
deformation

÷ chains recoil from a recoverable distance

¡  increases tear strength

—  Aqueous Hydrocolloids

—  Colloidal suspensions

¡  chains align to form fibrils

¡  traps water in interstices

—  Two forms

¡  sol

÷ viscous liquid

¡  gel

÷ elastic solid

—  Placed intra-orally as sol

¡  converts to gel

÷ thermal or chemical process

—  Aqueous Hydrocolloids

—  Semi-permeable membranes

¡  poor dimensional stability

—  Evaporation

—  Syneresis

¡  fibril cross linking continues

÷ contracts with time

÷ exudes water

—  Imbibition

¡  water absorption

÷ swells

 

—  Reversible Hydrocolloid
(Agar)

—  Indications

¡  crown and bridge

÷ high accuracy

—  Example

¡  Slate Hydrocolloid (Van R)

 

 

—  Composition

—  Agar

¡  complex polysaccharide

÷ seaweed

¡  gelling agent

—  Borax

¡  strength

—  Potassium sulfate

¡  improves gypsum surface

—  Water (85%)

 

—  Manipulation

—  Gel in tubes

¡  syringe and tray material

—  Manipulation

—  3-chamber conditioning unit

¡  (1) liquefy at 100°C for
10 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

—  Advantages

—  Dimensionally accurate

—  Hydrophilic

¡  displaces moisture, blood, fluids

—  Inexpensive

¡  after initial equipment

—  No custom tray or adhesives

—  Pleasant flavor

—  No mixing required

—  Disadvantages

—  Initial expense

¡  special equipment

—  Material must be prepared in advanced

—  Tears easily

—  Dimensionally unstable

¡  Must be poured immediately

¡  Can only be used for a single cast

—  Difficult to disinfect

—  Irreversible Hydrocolloid (Alginate)

—  Most widely used
impression material

—   Indications

¡  study models

¡  removable fixed partial dentures

÷ framework

—  Examples

¡  Jeltrate (Dentsply/Caulk)

¡  Coe Alginate (GC America)

 

 

—  Composition

—  Sodium alginate

¡  salt of alginic acid

÷ mucous extraction of seaweed (algae)

—  Calcium sulfate

¡  reactor

—  Sodium phosphate

¡  retarder

—  Filler

—  Potassium fluoride

¡  improves gypsum surface

 

—  Manipulation

—  Weigh powder

—  Powder added to water

¡  rubber bowl

¡  vacuum mixer

—  Mixed for 45 sec to 1 min

—  Place tray

—  Remove 2 to 3 minutes

¡  after gelation (loss of tackiness)

 

—  Advantages

—  Inexpensive

—  Easy to use

—  Hydrophilic

¡  displace moisture, blood, fluids

—  Stock trays

 

—  Disadvantages

—  Tears easily

—  Dimensionally unstable

¡  immediate pour

¡  single cast

—  Lower detail reproduction

¡  unacceptable for fixed pros

—  High permanent deformation

—  Difficult to disinfect

 

—  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

—  Polysulfide

—  First dental elastomers

—  Indications

¡  complete denture

¡  removable fixed partial denture

÷ tissue

¡  crown and bridge

—  Examples

¡  Permlastic (Kerr)

¡  Omni-Flex (GC America)

—  Composition

—  Base

¡  polysulfide polymers

¡  fillers

¡  plasticizers

—  Catalyst

¡  lead dioxide (or copper)

¡  fillers

—  By-product

¡  water

—  Polysulfide Reaction

—  Manipulation

—  Adhesive to tray

—  Uniform layer

¡  custom tray

—  Equal lengths of pastes

—  Mix thoroughly

¡  within one minute

—  Setting time 8 – 12 minutes

—  Pour within 1 hour

 

—  Advantages

—  Lower cost

¡  compared to silicones and polyethers

—  Long working time

—  High tear strength

—  High flexibility

—  Good detail reproduction

 

—  Disadvantages

—  Poor dimensional stability

¡ water by-product

¡ pour within one hour

¡ single pour

—  Custom trays

—  Messy

¡ paste-paste mix

¡ bad odor

¡ may stain clothing

—  Long setting time

—  Condensation Silicone

—  Indications

¡  complete dentures

¡  crown and bridge

—  Examples

¡  Speedex (Coltene/Whaledent)

¡  Primasil (TISS Dental)

 

—  Composition

—  Base

¡  poly(dimethylsiloxane)

¡  tetraethylorthosilicate

¡  filler

—  Catalyst

¡  metal organic ester

—  By-product

¡  ethyl alcohol

—  Manipulation

—  Mix thoroughly

¡  paste – paste

¡  paste – liquid

—  Putty-wash technique

¡  reduces effect of polymerization shrinkage

¡  stock tray

÷ putty placed

÷ thin plastic sheet spacer

÷ preliminary impression

¢ intraoral custom tray

÷ inject wash material

 

 

—  Advantages

—  Better elastic properties

—  Clean, pleasant

—  Stock tray

¡  putty-wash

—  Good working and setting time

 

 

—  Disadvantages

 

—  Poor dimensional stability

¡  high shrinkage

÷ polymerization

÷ evaporation of ethanol

¡  pour immediately

÷ within 30 minutes

—  Hydrophobic

¡  poor wettability

 

—  Addition Silicones

—  AKA:  Vinyl polysiloxane

—  Indications

¡ crown and bridge

¡ denture

¡ bite registration

—  Examples

¡ Extrude (Kerr)

¡ Express (3M/ESPE)

¡ Aquasil (Dentsply Caulk)

¡ Genie (Sultan Chemists)

¡ Virtual (Ivoclar Vivadent)

—  Composition

—  Improvement over condensation silicones

¡  no by-product

—  First paste

¡  vinyl poly(dimethylsiloxane)
prepolymer

—  Second paste

¡  siloxane prepolymer

—  Catalyst

¡  chloroplatinic acid

—  Manipulation

—  Adhesive to tray

—  Double mix

¡  custom tray

÷ heavy-body

¡  light-body to prep

—  Putty-wash

¡  stock tray

 

—  Advantages

—  Highly accurate

—  High dimensional stability

¡  pour up to one week

—  Stock or custom trays

—  Multiple casts

—  Easy to mix

—  Pleasant odor

—  Disadvantages

—  Expensive

—  Sulfur inhibits set

¡ latex gloves

¡ ferric and Al sulfate
retraction solution

—  Pumice teeth before
impressing

—  Short working time

—  Lower tear strength

—  Possible hydrogen gas release

¡ bubbles on die

¡ palladium added to absorb

 

 

 

—  Addition Silicones

—  Surfactants added

¡  reduce contact angle

¡  improved

÷ castability

¢ gypsum

÷ wettability??

¢ still need dry field clinically

 

—  Polyether

—  Indications

¡  crown and bridge

¡  bite registration

—  Examples

¡  Impregum F (3M/ESPE)

¡  Permadyne (3M/ESPE)

¡  Pentamix (3M/ESPE)

¡  P2 (Heraeus Kulzer)

¡  Polygel (Dentsply Caulk)

 

—  Composition

—  Base

¡  difunctional epimine-terminated prepolymer

¡  fillers

¡  plasticizers

—  Catalyst

¡  aromatic sulfonic acid ester

¡  fillers

—  Cationic polymerization

¡  ring opening and chain extension

 

—  Polyether Reaction

—  Manipulation

—  Adhesive to tray

¡  stock or custom tray

÷ very stiff

—  Paste-paste mix

—  Auto-mixing

¡  hand-held

÷ low viscosity

¡  mechanical dispenser

÷ high viscosity

 

 

—  Advantages

—  Highly accurate

—  Good dimensional stability

—  Stock or dual-arch trays

—  Good surface detail

—  Pour within one week

¡  kept dry

—  Multiple casts

—  Good wettability

—  Disadvantages

—  Expensive

—  Short working time

—  Rigid

¡  difficult to remove from undercuts

—  Bitter taste

—  Low tear strength

—  Absorbs water

¡  changes dimension

 

—  Impression Material Usage*
Civilian General Dentists

—  Crown & Bridge

¡  vinylpolysiloxane        81%

¡  alginate                  38%

¡  polyether               28%

—  Inlays and Onlays

¡  vinylpolysiloxane        71%

¡  polyether               22%

¡  alginate                  20%

—  Impression Material Usage*
Civilian General Dentists

—  Complete dentures

¡  alginate                  58%

¡  vinylpolysiloxane        55%

¡  polyether               27%

—  Partial dentures

¡  alginate                  78%

¡  vinylpolysiloxane        43%

¡  polyether               15%

 

—  Handling Properties

—  Handling Properties

—  Properties

—  Comparison of Properties

—  Working time

¡  longest to shortest

÷ agar > polysulfide > silicones > alginate = polyether

—  Setting time

¡  shortest to longest

÷ alginate < polyether < agar < silicones < polysulfide

 

 

—  Comparison of Properties

—  Stiffness

¡  most to least

÷ polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids

—  Tear strength

¡  greatest to least

÷ polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids

—  Comparison of Properties

—  Cost

¡  lowest to highest

÷ alginate < agar = polysulfide <condensation silicone < addition silicone < polyether

—  Dimensional stability

¡  best to worst

÷ addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid

 

 

 

—  Comparison of Properties

—  Wettability

¡  best to worst

÷ hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic addition silicone = condensation silicone

—  Castability

¡  best to worst

÷ hydrocolloids > hydrophilic addition silicone > polyether > polysulfide > hydrophobic addition silicone = condensation silicone

 

— Regularly-Used Impression Materials*
Civilian Practitioners

—  Alginate                    88%

—  Polyvinyl Siloxane       85%

—  Polyether            27%

—  Other                   6%

—  Summary

—  Study models

¡  Alginate most widely used

÷ inexpensive

÷ displaces moisture

÷ lower detail reproduction

÷ dimensionally unstable

 

—  Summary

—  Prosthodontics

¡  Addition silicones most popular

÷ accurate

÷ dimensionally stable

÷ user friendly

÷ expensive

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