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8. Impression Materials

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Impression materials

Text of 8. Impression Materials

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WRSuarez, DMD, MPHIMPRESSION MATERIALSDiagnostic castsWorking casts for indirect reconstructionBite registration

2Indications

23

Poly sulfides34TypesNon-elastic*Impression compound*Impression plaster*Zinc oxide eugenol *impression wax

Must not have undercuts45TypesElastomer impression materials

Hydrocolloids aqueous impression (contain water) *reversible (agar)*Irreversible (alginate)

Non-aqueous elastomers*Polysulfides (PS)*Silicon rubber Additional (AS, HAS)Condensation (CS)*Polyethers (PE)Can be used in undercuts

(Sol gel) temperature(Sol gel)

Set by polymerisation

56

Trays

Individual, special tray Stock trays

67Choice and use of traysThe tray should have enough spacerAvoid flexible traysUse perforated traysMake sure the tray is cleanApply only a thin layer of adhesiveWait appropriate time before taking impressionDont mix adhesives and impression materials

78Mixing techniquesManual:Low viscosityLess viscous is easierSilicones are easiest to mix followed by polyethers and polysulphides

89Mixing techniquesAutomatic mixingReduces mixing timeReduces bubblesHomogenous mixUse correct mixing proportions

2x2x2x2x2x2x2x2 = 256 folds910Layering techniques Single stage: One material, one settingTwo stage (double impression): First material set then another material added as a second layerTwin mix (two phase impression): Two material layers are put together and set together

1011Requirements of impression materials

Accuracy = ability to replicate the intraoral surface details.Dimensional stability = ability to retain its absolute dimensional size over time.Tear resistance = ability to resist tearing in thin sections (such as through the feather-edged material within the gingival sulcus.

1112Whats important?PatientNeutral taste and odourShort setting timeSmall trayEasily removed impressionNo retakesNon-toxicCostLowest to highestAlginate < agar = polysulfide >PE>CCS=ACS39Relative merits of elastomeric impression materials

SURFACE DETAILAll show excellent reproduction of surface detail on dry surfaces.Polyethers are generally best as these are more hydrophilic than the other impression materials.Surfactants have been added to the addition-cured silicones to improve their wettability.40Relative merits of elastomeric impression materials

DIMENSIONAL ACCURACY AND STABILITYSetting shrinkagePE=ACS

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