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Primary and Secondary ImpressionsFatima A. Elmahgoub

Primary ImpressionSelection of stock traySelection of Impression materialMixing and manipulationImpression makingLoadingInsertionMuscle mouldingRemoval of impressionStoring

Selection of stock traySizeArbitrary methodMeasuringPlace divider from hamular notch to hamular notch for posterior widthPlace divider from hamular notch to incissive papilla for anterior width

What should the tray cover?Upper tray: Posteriorly beyond the hamular notchAnteriorly to the anterior sulcusPalatally to vibrating lineLower tray: Posteriorly to retromolar padLingually to lingual pouchBuccaly to buccal and labial sulcus

Material:Stock tray is influenced by materialPerforated tray: AlginateNon-perforated tray: CompondWater cooling tray: Agar agar

Selection of Impression materialElastic Impression materialsHydrocolloidsReversible: AgarIrreversible: AlginateElastomersPolysulphidePolyetherSiliconNon-elastic impression materialsImpression compoundZOEImpression waxBlack GP

Selection of Impression material depends on:Presence of teethPresence/absence of severe bony undercutPresence/absence of flabby tissue

Alginate OR Compound

Impression taking proceduresMucostaticObjective is to obtain an impression of tissue in their rest stateUse a less viscous material with minimal application of pressure on tray (Alginate) Denture fits accurately at restWill tend to rotate during mastication on most incompressible areas and may lose retentionMucocompressive:Denture bearing tissues are compressed during impression taking and will subsequently be compressed during denture wearingDenture is maximally retentive during functionReduced retention when not under loadHigh viscosity impression material (compound) and close fitting tray

Mixing and/or ManipulationMixing of AlginateMeasure waterMeasure powderMix in rubber bowl beginning in the centre and then against the wallsLoad onto trayLower in 2 halvesUpper in 1 unit

Manipulation of CompundPut in controlled water temperature 60-70 degrees CelsiusKnead the compoundUpper tray: Shape into ballLower tray: Shape into rodDistribute over tray

InsertionUpper jaw: Patient position: upright, maxilla at operators elbow levelOperator position: Behind the patient to the right

Lower jaw:Patient position: upright, maxilla between elbow and shoulder of operatorOperator position: Anterior and to the right of the patient

Seating of impression:Press posteriorly first and then the anterior position

Muscle moulding:Upper at the area of the tuberosity by movement of the mandible left and right.Lower by the tongue

RemovalUpper: Remove posterior portion first to break sealBreak seal with fingersAsk patient to say ahh allowing air to enter

Lower: Pull lower lip allowing air to enterRemove tray posteriorly first

Storing the impressionUpperAlginate:Wash under running waterRopey saliva in palate can be removed using a soft toothbrushWrap alginate in wet napkinWet with disinfectant NaOCl or Gluteraldehyde (Sidex)Dip in potassium sulphate before casting to impreve surface quality

CompoundWash and disinfect with SidexNo dimensional change

LowerWash and scrub retromolar area with a soft toothbrushReinforce retromolar area by applying a few drops of wax outside the fitting surfacePosterior region shouldnt be lying on anything

Secondary Impression MakingCheck special tray on cast Should be 2mm less than outlineShould be fittingCheck out of castShould be smooth, with round borders and notchesCheck in patients mouthBorder mouldingRemove half a mm of compund from border and clear inner surface with scalpelTake secondary impressionZOEAlginate

Means of adhesion of impression material to trayPerforationAdhesive

ZOE doesnt require the aboveIf perforations are done, they should be done after border moulding

Border MouldingTracing of the tray border by impression material to get the most accurate length and width of future denture flange for retention

Seal is achieved by border moulding which creates a vaccuumRetention is by partial vaccuum and muscular activity (lip and tongue and buccinator)

If not properly controlled, muscles will displace rather than retain it.If too thick, coranoid pushes the denture

Seal is maintained by denture and bone with soft tissue in betweenThe soft palate seal is by the posterior palatal seal.

Steps for border mouldingGreenstick compoundDone in at least 5 increments for each jawGreenstick compoundStart by lower and be systemic. Leave frenal attachment areas lastShould be 3mm thick at leastShould not be glossyShould be removed from fitting surface (pressure area)

Border moulding in maxillary tuberosity area is by coranoid process (bilateral movement)

Remove half a mm of compound on border to allow room for impression material, otherwise secondary impression will also be overextended.

Techniques for taking impression1) Pressure (Closed mouth) MucocompressiveNo perforation on trayUse ZOEPatient bites on a wax rim of the opposite arch

2) Selective pressure (Open mouth)Use fingers to create pressure on certain areas of the mouth (areas of support: stress bearing areas)Upper: Primary SBA- Hard palateSecondary SBA- Entire ridgeLower: Primary SBA -Posterior ridge and external oblique ridgeSecondary SBA- anterior ridge

No pressure (Anatomical)Indicated in flabby tissueUsually seen in combination syndromePrimary impression taken with alginate to decrease pressure anteriorly

Secondary impression done using window techniqueAnterior area of the tray is open to clear room for redundant tissueBorder moulding is done all around conventionallyZOE secondary impression is taken posteriorlyWait until it setsAnterior redundant tissue is covered by painting with PlasterDentate stock tray is selected to cover the special tray and plasterMake alginate mix and load onto stock tray taking an overall impressionRemove trays Wash

Thank You