IMPRESSION TECHNIQUE AND MATERIALS

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IMPRESSION TECHNIQUE

AND MATERIALS

DR ZURYATI AB GHANI DR 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). 24.06.07

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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 another

into the surface of another’’

Active rather than passive roleActive rather than passive role

Making rather than taking Making rather than taking

Flawed impressions account for the Flawed impressions account for the

majority of denture problems majority of denture problems

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PRIMARY 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 tray

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Tray selection

stock trays: dentate

metal or plastic

2

2 -

-

3 mm clearance between stock

tray and ridge

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Stock tray

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Materials for primary

impression

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Secondary or definitive

impression

DefinitionDefinition ¾

¾An imprint that record the entire functional An imprint that record the entire functional denture

denture--bearing area to ensure maximum bearing area to ensure maximum

support, retention and stability for the denture

during use

Primary purposePrimary purpose

¾

¾To 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

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Secondary impression

Conventional techniques Conventional techniques

Selective pressure techniquesSelective pressure techniques

Functional techniquesFunctional techniques

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Conventional technique

Also known as Also known as Anatomical orAnatomical or MucostaticMucostatic

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

occlusal

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Special trays

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Conventional 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

tissueward

tissueward movement under movement under occlusalocclusal load

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Conventional technique

recommended for tooth supported recommended for tooth supported

partial dentures partial dentures

--KennedyKennedy’’s class III and IVs class III and IV

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Functional impression

technique

Impressions are recorded under Impressions are recorded under

functional load (pressure) i.e. Record functional load (pressure) i.e. Record

tissue in a compressed form tissue in a compressed form

Also known as: Also known as: MucocompressiveMucocompressive

impression impression

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Selective pressure

technique

Mucostatioc

impression

_impression

AND

Mucocompressive

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Support in free end

saddle

Support from tooth (rest seat) and soft tissue Support from tooth (rest seat) and soft tissue

(mucosa)

Tooth is rigid, mucosa is soft and displaceableTooth is rigid, mucosa is soft and displaceable

During 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

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 function

Therefore, selective pressure technique may be Therefore, selective pressure technique may be

used to achieve this.

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Selective pressure

technique

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2 Techniques to achieve

selective pressure

impression

Functional dual impression techniqueFunctional dual impression technique

Altered cast technique or Applegate Altered cast technique or Applegate

technique technique

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Functional dual

impression

A functional A functional impression of the impression of the edentuluos

edentuluos 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 form their anatomic form

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Altered cast technique

Anatomical master impression of oral Anatomical master impression of oral

structure is made structure is made

Construct master cast and refractory Construct master cast and refractory

cast cast

Construct metal framework with Construct metal framework with

temporary self

temporary self--cured acrylic resin cured acrylic resin saddles

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

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A viscous impression A viscous impression egeg impression impression

wax heated to 65

wax 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 ridge of the ridge

Other viscous impression material is Other viscous impression material is

compound compound

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Altered cast technique

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

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The metal frame is The metal frame is

located onto the located onto the

abutment teeth abutment teeth

The saddle area is The saddle area is

beaded and boxed beaded and boxed

The saddle area is The saddle area is

cast (2

cast (2--part stone part stone cast)

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Disadvantages of selective

pressure 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

osteoclasts osteoclasts

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 occlusalocclusal to normal

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Technique to be practiced in PPSG Technique to be practiced in PPSG

Dental Clinic for free end saddle Dental 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.

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

pressure

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References

Textbook of Textbook of ProsthodonticsProsthodontics. Deepak . Deepak

Nallaswamy

Nallaswamy. . JaypeeJaypee brothers medical brothers medical publishers (p) LTD. 2003

publishers (p) LTD. 2003

Notes 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

prosthodontics

prosthodontics. 11. 11thth _{edition. Elsevier,}_{edition. Elsevier,}

Mosby Mosby