IMPRESSION TECHNIQUE IMPRESSION TECHNIQUE AND MATERIALSAND MATERIALS

DR ZURYATI AB GHANIDR ZURYATI AB GHANI

BDS (WALES), Grad Dip BDS (WALES), Grad Dip ClinClin Dent (Adelaide), Dent (Adelaide), Doctor in Clinical Dentistry (Doctor in Clinical Dentistry (prosthodonticsprosthodontics), ),

Adelaide, FRACDS (Australia).Adelaide, FRACDS (Australia).

24.06.0724.06.07

Impressions Impressions

An impression An impression –– an imprint produced an imprint produced by by ‘‘the pressure of one thing upon or the pressure of one thing upon or into the surface of anotherinto the surface of another’’Active rather than passive roleActive rather than passive roleMaking rather than taking Making rather than taking Flawed impressions account for the Flawed impressions account for the majority of denture problemsmajority of denture problems

PRIMARY IMPRESSIONPRIMARY IMPRESSION

DefinitionDefinition--an impression made for the an impression made for the purpose of diagnosis or for the construction purpose of diagnosis or for the construction of a trayof a tray

Tray selectionTray selection

stock trays: dentatestock trays: dentatemetal or plasticmetal or plastic22--3 mm clearance between stock 3 mm clearance between stock tray and ridgetray and ridge

Stock trayStock tray

Materials for primary Materials for primary impressionimpression

AlginateAlginate

Secondary or definitive Secondary or definitive impressionimpression

DefinitionDefinitionAn imprint that record the entire functional An imprint that record the entire functional denturedenture--bearing area to ensure maximum bearing area to ensure maximum support, retention and stability for the denture support, retention and stability for the denture during useduring use

Primary purposePrimary purposeTo record accurately the tissues of the denture To record accurately the tissues of the denture bearing areas, in addition to recording the bearing areas, in addition to recording the functional width and depth of the sulci functional width and depth of the sulci

Secondary impressionSecondary impression

Conventional techniques Conventional techniques Selective pressure techniquesSelective pressure techniquesFunctional techniquesFunctional techniquesReline and rebases techniquesReline and rebases techniques

Conventional techniqueConventional technique

Also known as Also known as Anatomical orAnatomical orMucostaticMucostatic

The surface contour of the ridge is The surface contour of the ridge is recorded at its resting form (no recorded at its resting form (no occlusalocclusal load)load)

Special traysSpecial trays

Conventional techniqueConventional technique

Material of choice (soft or less viscous Material of choice (soft or less viscous impression material)impression material)alginate, alginate, Disadvantages: In freeDisadvantages: In free--end saddle end saddle dentures, distal end will show dentures, distal end will show tissuewardtissueward movement under movement under occlusalocclusalloadload→→ridgeridge resorptionresorption

Conventional techniqueConventional technique

recommended for tooth supported recommended for tooth supported partial denturespartial dentures--KennedyKennedy’’s class III and IVs class III and IV--These are bounded saddlesThese are bounded saddles

Functional impression Functional impression techniquetechnique

Impressions are recorded under Impressions are recorded under functional load (pressure) i.e. Record functional load (pressure) i.e. Record tissue in a compressed formtissue in a compressed formAlso known as: Also known as: MucocompressiveMucocompressiveimpressionimpression

Selective pressure Selective pressure techniquetechnique

MucostatiocMucostatioc impressionimpressionANDAND

MucocompressiveMucocompressive impressionimpression

Support in free end Support in free end saddlesaddle

Support from tooth (rest seat) and soft tissue Support from tooth (rest seat) and soft tissue (mucosa)(mucosa)Tooth is rigid, mucosa is soft and displaceableTooth is rigid, mucosa is soft and displaceableDuring function, the free end saddle will be pushed During function, the free end saddle will be pushed towards the tissue and then bounces back. This towards the tissue and then bounces back. This movement may cause loosening of abutment tooth movement may cause loosening of abutment tooth and and resorptionresorption of alveolar bone.of alveolar bone.The aim is to create minimum movement of the The aim is to create minimum movement of the denture base during functiondenture base during functionTherefore, selective pressure technique may be Therefore, selective pressure technique may be used to achieve this.used to achieve this.

Selective pressure Selective pressure techniquetechnique

Kennedy Class I

2 Techniques to achieve 2 Techniques to achieve selective pressure selective pressure impressionimpression

Functional dual impression techniqueFunctional dual impression techniqueAltered cast technique or Applegate Altered cast technique or Applegate techniquetechnique

Functional dual Functional dual impressionimpression

A functional A functional impression of the impression of the edentuluosedentuluos ridge is ridge is made.made.The 2The 2ndnd impression impression made over made over functional functional impression and impression and record structures in record structures in their anatomic formtheir anatomic form

Altered cast techniqueAltered cast technique

Anatomical master impression of oral Anatomical master impression of oral structure is madestructure is madeConstruct master cast and refractory Construct master cast and refractory castcastConstruct metal framework with Construct metal framework with temporary selftemporary self--cured acrylic resin cured acrylic resin saddlessaddles

Special tray construction for Special tray construction for selective pressure techniqueselective pressure technique

A viscous impression A viscous impression egeg impression impression wax heated to 65wax heated to 65°°C and painted onto C and painted onto surface of saddles, then placed inside surface of saddles, then placed inside mouth, to get satin finish impression mouth, to get satin finish impression of the ridgeof the ridgeOther viscous impression material is Other viscous impression material is compoundcompound

Altered cast techniqueAltered cast technique

In the lab, the saddle area is cut away from stone cast

The metal frame is The metal frame is located onto the located onto the abutment teethabutment teeth

The saddle area is The saddle area is beaded and boxedbeaded and boxed

The saddle area is The saddle area is cast (2cast (2--part stone part stone cast)cast)

Disadvantages of selective Disadvantages of selective pressure techniquespressure techniques

Tissues are constantly compressed, and Tissues are constantly compressed, and can cause bone can cause bone resorptionresorption due to 2 due to 2 reasons:reasons:

i)i) Constant pressure stimulate formation of Constant pressure stimulate formation of osteoclastsosteoclasts

ii)ii) Constant pressure reduces blood supply, Constant pressure reduces blood supply, which simulates formation of which simulates formation of osteoclastsosteoclasts..If retentive clasps do not hold denture in If retentive clasps do not hold denture in place, the denture will be slightly place, the denture will be slightly occlusalocclusalto normal to normal positionposition→→prematurepremature contact.contact.

Technique to be practiced in PPSG Technique to be practiced in PPSG Dental Clinic for free end saddleDental Clinic for free end saddle

Single traySingle tray--spaced in dentate area and closed spaced in dentate area and closed fitting in free end saddle area.fitting in free end saddle area.Dual impression materialsDual impression materials-- alginate in dentate alginate in dentate area and area and ZnOEZnOE in saddle area.in saddle area.To ensure ideal adaptation in free end saddle.To ensure ideal adaptation in free end saddle.Conventional technique rather than selective Conventional technique rather than selective pressurepressure

Courtesy of Sofia

Courtesy of Sofia

ReferencesReferences

Textbook of Textbook of ProsthodonticsProsthodontics. Deepak . Deepak NallaswamyNallaswamy. . JaypeeJaypee brothers medical brothers medical publishers (p) LTD. 2003publishers (p) LTD. 2003Notes on Notes on ProsthethicProsthethic dentistry.dentistry.MRY Dyer, BJ Roberts. Butterworth & Co MRY Dyer, BJ Roberts. Butterworth & Co 1989.1989.McCrackenMcCracken’’s Removable partial s Removable partial prosthodonticsprosthodontics. 11. 11thth edition. Elsevier, edition. Elsevier, MosbyMosby