Impression techniques in rpd

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Impression techniques in RPD

Good technique pays off is not merely a motto to hang on a wall but these are words of wisdom

Impression techniques in RPDPresented by:Apurva Thampi1st yr PG

CONTENTSIntroductionterminologiesComplete denture impression v/S RPD impression Impression materialsAnatomic form and functional formConcept of functional impressionNeed of functional impressionIndication for functional impressionObjectives of functional impressiondistal extension based partial denture

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1/28/2016FUNCTIONAL IMPRESSION

CONTENTSMcLeans physiologic impression techniqueHindels modificationsFunctional relining methodFluid wax techniqueSelective pressure impressionAltered cast techniqueModifications of altered cast techniqueReview of literatureSummaryConclusionbibliography

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introduction

Based on tissue borne/ tissue tooth borne the stress over the underlying tissues5

Impression

A negative likeness or copy in reverse of the surface of an object ; imprint of teeth and adjacent structures for use in dentistry. GPT 8

Partial denture impression

A negative likeness of a part or all of a partially edentulous arch GPT 8

Terminology

A receptacle in to which suitable impression material is placed to make negative likeness ORA device that is used to carry, confine and control impression material while making an impression. Impression trays

RPD IMPRESSION Vs COMPLETE DENTURE

complete denture impression the edentulous mucosa with underlying bone onlypartial denture impression relative soft yielding tissues (the oral mucosa) + hard unyielding substance (the remaining teeth).

Impression MaterialsNon-elasticElasticAqueous hydrocolloidsAgarAlginateNon-aqueous elastomersPolysulfideSiliconesCondensationAdditionPolyether

Impression Materials

Non-elasticElastic

Aqueous HydrocolloidsNon-aqueous Elastomers

PolysulfideSiliconesPolyether

CondensationAddition

Agar (reversible)Alginate (irreversible)

PlasterCompoundZnO - Eugenol

Waxes

OBrien Dental Materials & their Selection 1997

Factors that influence the selection of impression materials are

Based on THE METHOD OF IMPRESSION MAKING13

ANATOMIC FORMThe surface of the residual ridge at rest.

It is the shape of the ridge before functional load is applied.

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FUNCTIONAL FORM It means the shape of the residual ridge tissue when it is functioning to support the denture base.

It is the shape of the ridge after functional load is applied.

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Anatomic or Resting formSupporting or Functional form

McCrackens Removable Partial Prosthodontics 3rd edition

IMPRESSION MATERIALS ANATOMIC IMPRESSIONS

IRREVERSIBLE HYDROCOLLOIDELASTOMERIC IMPRESSION MATERIALSREVERSIBLE HYDROCOLLOID FUNCTIONAL IMPRESSIONS

FLUID WAXESMETALLIC PASTESELASTOMERIC IMPRESSION MATERIALSSOFT RELINERS17

CONCEPT OF FUNCTIONAL IMPRESSION The term functional impression means recording the functional form of the residual ridge tissue & to obtain uniformity of support when the functional load is applied.18

Occlusal forces must be equally distributed to the abutment and the tissues of the ridge cannot be accomplished by a single impression18

INITIALLY..Applegate impression wax to load functionally the residual ridgeHindel free end denture base under masticatory load should be related to metal framework when it is seated Holmes used four different materials with altered cast techniqueLeupold & Kratochvil used Zinc-oxide Eugenol paste to record the shape of residual ridges

Leupold RJ, A comparative study of impression procedures for distal extension removable partial dentures. J Prosthet Dent 1966; 16:708.20

Kramer & Singer used a double impression technique based on load distribution by HindelMcCracken functional technique should be used when constructing mandibular distal extension based partial denture Leupold RJ, A comparative study of impression procedures for distal extension removable partial dentures. J Prosthet Dent 1966; 16:708.21

NEED OF FUNCTIONAL IMPRESSIONThe displaceability of the mucosa of residual ridge is not uniform.in cases of distal extension based partial denture.Short span distal extension bases.

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INDICATIONS FOR FUNCTIONAL IMPRESSION23

OBJECTIVES OF FUNCTIONAL IMPRESSION(O.C. Applegate)24

SUPPORT OF DISTAL EXTENSION BASED PARTIAL DENTURE 25

Factors influencing the support of distal extension baseContour & Quality of residual ridge

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Stewarts clinical Removable partial denture prosthodontics 4th ed

Compressibility of tissue recognised vary from patient to patient and site to siteThick and displacable less support Firm and tightly attached 2-3mm moderate thickness greatest supportRedundant tissues over tuberosities surgically removed26

EXTENT OF RESIDUAL RIDGE COVERAGE BY THE DENTURE BASE27

Stewarts clinical Removable partial denture prosthodontics 4th ed

TYPE & ACCURACY OF IMPRESSION REGISTRATION28

Stewarts clinical Removable partial denture prosthodontics 4th ed

McCrackens Removable Partial Prosthodontics

ACCURACY OF FIT OF DENTURE BASE29Stewarts clinical Removable partial denture prosthodontics 4th ed

Made to fit the areas that serve as the primary stress bearing areas29

Design of partial denture framework30McCrackens Removable Partial Prosthodontics

TOTAL OCCLUSAL LOAD APPLIED

31McCrackens Removable Partial Prosthodontics

METHODS OF FUNCTIONAL IMPRESSION32

P record the ridge in its functional form place an occlusal load on the trayS equalize the support between the abutments and soft tissue relieve the tray in some areas32

McLeans Physiologic Method33Clinical Removable Partial Prosthodontics Stewart. 3rd edition

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As a result they developed a dual impression technique34

Custom tray over a preliminary cast35

36Functional impression of extension area under occlusal load

Hydrocolloid impression over the first impression made under finger pressure.37

Finger pressure not equal to biting pressureClosely affect the direct retention38Disadvantages-

Clasps sufficient to maintain the positiontissues of ridge in functional form compromised blood flowClasps not sufficient DB occlusally positioned premature contact38

impression is made with a modified tray applying finger pressure.39Clinical Removable Partial Prosthodontics Stewart. 3rd editionHindels Modification

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HINDLES FINGER LOADING

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HINDLES FINGER LOADINGTissues are in constant stage of compression

Ischemia and bone resorption

Premature contacts at rest.

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Disadvantage

The main purpose of these techniques was to relate an impression of the edentulous ridge to the teeth under a form of functional loading.

Functional Reline Method44Clinical Removable Partial Prosthodontics Stewart. 3rd edition

Layer of relief given

45Clinical Removable Partial Prosthodontics Stewart. 3rd edition

The denture is processed & fitted in the mouth in customary manner, except that the relief metal is left in place.

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It should be worn for a trial period of a week & all needed adjustments are done

Clinical Removable Partial Prosthodontics Stewart. 3rd edition

The relief metal is stripped off from the acrylic.

47Clinical Removable Partial Prosthodontics Stewart. 3rd edition

low fusing modeling compound is added in increments

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Border molding done.

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1 mm Modeling plastic is removed from the intaglio surface.

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Impression made using one of the corrective materials : fluid wax, Zinc-oxide Eugenol pastes or any elastomeric impression material.

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Functional Reline MethodDisadvantage

Occlusion may be altered slightly fine line of demarcation between the newly added & old resin of the denture52

FLUID WAX TECHNIQUE53Clinical Removable Partial Prosthodontics Stewart. 3rd edition

The most frequently used waxes are

54Korrecta wax no. 4 is slightly more fluid than IOWA wax

The armantarium for fluid wax technique. (51- 54 degree Celsius)

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Undercuts eliminated using baseplate wax

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Separating medium applied to the cast.

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Framework seated on the cast.

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Tray material adapted 1-2 mm relief between residual ridge and intaglio surface of tray.

59EXCESS MATERIAL REMOVED.

Tray border smoothed using laboratory bur.Should be 2 mm short of border extension required.

Fluid wax painted onto the intaglio surface of tray (1 -2 mm)

60Assembly seated in patients mouth.(5 -7 mins)

Completed impression.Check for proper tissue contact

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SELECTIVE TISSUE PLACEMENT IMPRESSION METHOD62

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Framework tried on the cast Tray outline marked for extension 64

McCrackens Removable Partial Prosthodontics

Framework with tray fabricated on it with holes on its ridge.

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McCrackens Removable Partial Prosthodontics

Areas in which relief is to be provided is marked66

TRAY IS BEING RELIEVED BEFORE THE FINAL IMPRESSION IS MADE

Clinical Removable Partial Prosthodontics Stewart. 3rd edition

Acrylic resin impression trays with holesFramework with tray tried in patients mouthFunctional impression made67

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