altered casts technique

ALTERED CAST TECHNIQUE

ByDr. Saili Chandavarkar

MDS II

CONTENTS

• Introduction• Support of distal extension based

partial denture• Concept of functional impression• Need of functional impression• Indication for functional impression• Objectives of functional impression

CONTENTS

• Factors influencing support of distal extension base• Materials used for functional impression• Impression methods• Altered Cast Technique• Modifications of altered cast technique

SUPPORT OF DISTAL EXTENSION BASED PARTIAL DENTURE

• A minor support comes from the abutment teeth• The major support comes from elastic fibrous

connective tissue pad overlying the alveolar process

• Residual ridge: It is the remnant of the alveolar process together with the fibrous connective tissue covering (& included structures) in an edentulous area of the dental arch.

ACCORDING TO THE METHOD OF IMPRESSION MAKING

RESIDUAL RIDGE

Anatomic form Functional form

ANATOMIC FORM

• The surface of the residual ridge at rest.

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

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.

Anatomic or Resting form Supporting or Functional form

McCracken’s Removable Partial Prosthodontics 3rd edition

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.

HISTORY

• Applegate used impression wax to load functionally the residual ridge

• Hindel felt that 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 technique

• Leupold & Kratochvil used Zinc-oxide Eugenol paste to record the shape of residual ridges

HISTORY

• Kramer & Singer used a double impression technique based on load distribution by Hindel

• McCracken concluded that a functional technique should be used when constructing mandibular distal extension based partial denture

NEED OF FUNCTIONAL IMPRESSION• The displaceability of the mucosa of residual ridge is

not uniform.• The need of functional impression arises in cases of

distal extension based partial denture.• Some mouth does not exhibit significant difference in

anatomical and functional form of ridge.• Short span distal extension bases.

INDICATIONS FOR FUNCTIONAL IMPRESSION

• Mandibular distal extension partial dentures –Only a limited ridge area can be used as a stress bearing site.

• Mainly Kennedy’s class I & II edentulous arches.

OBJECTIVES OF FUNCTIONAL IMPRESSION(O.C. Applegate)

• To obtain the maximum area of coverage • Traumatic impact on any area must be avoided• At rest there must be no islands of ischemia• Under work loads all areas must receive massage

stimuli.

Factors influencing the support of distal extension base

• Contour & Quality of residual ridge

15McCracken’s Removable Partial Prosthodontics

•Extent of residual ridge coverage by the denture base

•Type & Accuracy of impression registration

•Accuracy of fit of denture base

•Design of partial denture framework

•Total Occlusal load applied

IMPRESSION MATERIALS

ANATOMIC IMPRESSIONS • IRREVERSIBLE

HYDROCOLLOID• ELASTOMERIC IMPRESSION

MATERIALS• REVERSIBLE HYDROCOLLOID

FUNCTIONAL IMPRESSIONS• FLUID WAXES• METALLIC PASTES• ELASTOMERIC IMPRESSION

MATERIALS• SOFT RELINERS

METHODS OF FUNCTIONAL IMPRESSION

PHYSIOLOGIC OR FUNCTIONAL IMPRESSION

SELECTED PRESSURE IMPRESSION TECHNIQUE

McLean's method

Functional relining method

Hindel’s modification for McLean's method

The Fluid wax technique

The master cast may be altered to accommodate the new ridge impression it is

referred as Altered Cast Technique Or Corrected Cast Impression Technique

McLean’s Physiologic Method

24Clinical Removable Partial Prosthodontics – Stewart. 3rd edition

Custom tray over a preliminary cast

Occlusal rim over a distal extension base is made

Functional impression of extension area under occlusal load

Hydrocolloid impression over the first impression made under finger pressure.

McLean’s Physiologic Method

• Finger pressure not equal to biting pressure• Alginate between stock tray and occlusal rim

acts as buffer. May not transfer entire load to special tray.

Disadvantages-

Hindel’s Modification

• First anatomic impression in alginate is made

• Acrylic resin tray over saddle area is prepared

• Impression of saddle area is made in zinc oxide eugenol paste without pressure

• Super impression is made with a modified tray applying finger pressure.

Hindel’s special tray with holes to apply pressure

HINDLE’S FINGER LOADING

• Tissues are in constant stage of compression

• Ischemia and bone resorption

• Premature contacts at rest.

Disadvantage

Functional Reline Method

Layer of relief given

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

left in place.

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

The relief metal is stripped off from the acrylic.

low fusing modeling compound is added in increments

Border molding done.

1 mm Modeling plastic is removed from the intaglio surface.

Impression made using one of the corrective materials : fluid wax, Zinc-oxide Eugenol pastes or

any elastomeric impression material.

Functional Reline Method

• Disadvantage – a) Occlusion may be altered slightly by reline

procedures & may require adjustments b) There remains a fine line of demarcation between

the newly added & old resin of the denture

FLUID WAX TECHNIQUE

• The most frequently used waxes are – Korrecta wax no. 4 - Dr. O.C.& S.G. Applegate at University of

Michigan IOWA wax -Developed by Dr.Smith at University of IOWA • Korrecta wax no. 4 is slightly more fluid than IOWA wax

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

Undercuts eliminated using baseplate wax

Separating medium applied to the cast.

Framework seated on the cast.

Tray material adapted 1-2 mm relief between

residual ridge and intaglio surface of tray.

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

Completed impression.Check for proper tissue contact.(final insertion for 12

FLUID WAX TECHNIQUE

• The finished impression must be handled carefully & the new cast poured as soon as the wax is fragile & subject to distortion

SELECTIVE TISSUE PLACEMENT IMPRESSION METHOD

• The technique attempts to direct more force to those portions of ridge able to absorb stress without adverse response & to protect the areas of ridge which are least able to absorb forces.

Framework tried on the cast Tray outline marked for extension

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

Areas in which relief is to be provided is marked

Tray is being relieved before the final

impression is made

Clinical Removable Partial Prosthodontics – Stewart. 3rd edition

Acrylic resin impression trays

with holes

Framework with tray tried in

patient’s mouth

Functional impression made

Altered cast \oˆ l#terd ka˘ st\: a final cast that is revised in part before processing a denture base—called also corrected cast, modified cast

Altered cast partial denture impression \oˆ l#terd ka˘ st pa¨r#shal de˘n#cher ı˘m-pre˘sh#an\: a negative likeness of a portion or portions of the edentulous denture bearing area(s) made independent of and after the initial impression of the natural teeth. This technique employs an impression tray(s) attached to the removable dental prosthesis framework or its likeness

• Also known as Corrected cast or Split cast Technique.• It is mainly a modification of functional impression

through laboratory procedure. • Functional impression for this technique can be made

using any of the above mentioned materials and techniques.

Robert J. Leupold And Frank J. Kratochvil:An Altered-cast Procedure To Improve Tissue SupportFor Removable Partial Dentures .J Prosthet Dent 1965:672-679

Functional impression made

Final impression

62McCracken’s Removable Partial Prosthodontics 12thedition

Edentulous area cut from the master cast

Framework with attached impression seated on the master cast

It is imperative that all the rests occupy their proper position on the cast

Assembly from underside of the cast

Peripheral borders of the impression are protected with

utility wax & the assembly wrapped with boxing wax

The newly obtained altered cast with newly added stone

Alternate techniques

Alternate technique to separate the edentulous cast

Boxed elastomeric final impression in which edentulousridges have been separated with contoured baseplate

wax (A arrows) and sealed to anatomic contour ofimpression at base. Triangular wax bars (B arrows) are attached

to make dovetails (three separate compartments ofimpression).

Izharul Haque Ansari: A new procedure for separating the edentulous distal extension portion from the master cast when an altered cast is made. J Prosthet Dent 1994;72:666-9.

Mix of properly proportioned dental stone vibrated into three compartments of impression. Impression must be overfilled to

make solid base to prevent premature separation

Master east ready for duplication. Three to 5 mm thick base (line shown by arrow) below level of

separating wax to prevent premature separation while cast is handled to make the framework.

Base of the cast has been trimmed to line shown by arrows in previous dgm

and cast is ready for immersion in boiling slurry water. Portions of old cast may require trimming (arrow)

before new impression is poured

View from bottom of master cast after base has been trimmed to expose separating

wax and wax dovetails.

Edentulous portions separated from rest of master cast when removed from boiling clear slurry water. Appearance of dovetails for additional

retention for dental stone.

Alternate boxing technique

Leila Jahangiri, Patrick Mascarenhas and Donald Kitzis: A simple technique for boxing impressions for fabrication of altered casts. J Prosthet Dent 2001;85:519-20Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent 1982;47:573-575

Replacement of impression and framework on master cast after

removal of edentulous distal extension areas of cast.

Framework is luted to master cast with sticky wax.

Protection of teeth in master cast with irreversible hydrocolloid.

Immersion of master cast and frame assembly within

supporting base.

Framework with corrected impression

is seated into a plaster mix contained bv wax boxing sheet.

• Make a support base mix with an Accu-Dent (Buellton, Calif.) water measure. Mix 2 parts (26 mL) cornstarch (Argo Cornstarch, Best Foods Div, CPC International Inc, Englewood Cliffs, N.J.), 1 part (13 mL) fine pumice, and 1 part (13 mL) plaster. Mix the dry powders and add to 115 mL water. Pour the material into a denture flask.

• Let set for 15 minutes. Pour a base with a compatible stone to that of the master cast, filling up the denture flask. Once set, remove from flask.

• Separate master cast from the supporting base and irreversible hydrocolloid (this supporting base is easy to remove with one’s fingers). Trim the cast to the desired dimensions

Leila Jahangiri, Patrick Mascarenhas and Donald Kitzis: A simple technique for boxing impressions for fabrication of altered casts. J Prosthet Dent 2001;85:519-20

• Mix 50% cornstarch (Argo Cornstarch, Best Foods Div. C.P.C. International Inc., Englewood Cliffs, N.J.) and 50% white modeling plaster by volume with water to a creamy consistency. Pour this into the boxing wax form. Place the impression in the mixture.

• Allow the mixture to set for 10 minutes. Remove and save the boxing wax.

• Seal the previously used boxing wax to the trimmed base leaving at least 20 mm from the top of the boxing wax to the highest point on the impression.

• Soak the master cast in slurry water for 5 minutes. Pour the cast using the same stone as the original master cast. No separating medium is needed

• When the stone is set, remove the boxing wax and place the cast in a water bath of 110” F to facilitate removal of the plaster/cornstarch mixture and the Framework. Separate the plaster/cornstarch mixture with plaster pliers and your fingers.

Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent 1982;47:573-575

Boxing wax placed around plaster base and cast leaving at least 20 mm from top of wax to highest point on

impression.

• Completed altered cast.

Completed altered cast.

Alternative to altered cast technique

Ming-Sheh Chen, W.A. Eichhold, Chao-Chin Chien and D.A. Curtis : An altered-cast impression technique that eliminates conventional cast dissecting and impression boxing. J Prosthet Dent 1987;57:471-474

Tissue surface of final impression. Note excess rubber base

impression material has been trimmed to internal finish line (arrows) of metal framework.

Lingual surface of custom tray. Most of excess

final impression material has been trimmed. Only 3 mm of impression

material is left over and above border flange. This residual final

impression material is later used as a guide to develop ledge of an irreversible hydrocolloid land.

Tissue surface of distal-extension irreversible hydrocolloid pickup

impression. Irreversible hydrocolloid is purposely

overextended 3 to 5 mm arounddistal-extension region.

Irreversible hydrocolloid pickup impression after trimming is completed. Note a land of irreversible hydrocolloid

impression material that is 3 mm in width and 3 mm below crest of

border flange.

Itshows relationship

between final impression, irreversiblehydrocolloid land, and

stock metal tray.

Tissue surface of final impression is surrounded

by a uniform land of irreversible hydrocolloid.

Tissue surface of pickup impression. Note wax

blockout (arrows) of all undesirable mechanical undercuts.

There is no blockout of major connectors, rests, andreciprocal clasp arms

Master cast obtained by this method. Note uniform

stone land transition in distal-extension regions.

Alternative to altered cast technique

Herman B. Dumbrigue and Josephine F. Esquivel: Selective-pressure single impression procedure for tooth-mucosa–supported removable partial dentures. J Prosthet Dent 1998;80:259-61

Aluminum foil and two sheets of baseplate wax over

diagnostic cast before tray fabrication.

Custom tray fabricated with extensions reduced 2 mm

short of vestibule.

Custom tray with softened modeling compound

reseated on diagnostic cast. Modeling compound over

residual ridges shaped appropriately before intraoral

placement.

Border molding procedure completed.

Trial of metal framework,altered cast technique and interocclusal record in one appointment

Technique 1• Richard Bauman and James DeBoer :A modification

of the altered cast technique. J Prosthet Dent 1982;47:212-213

A custom tray was fabricated over the metal framework in the edentulous portion.

A wax occlusal rim was fabricated over the custom tray

Border molding is completed. Final impression is completed in

material of choice

Richard Bauman and James DeBoer :A modification of the altered cast technique. J Prosthet Dent 1982;47:212-213

98Richard Bauman and James DeBoer :A modification of the altered cast technique. J Prosthet Dent 1982;47:212-213

Interocclusal record is made by placing low fusing modelling compound over the wax rim to record the interocclusal relationship

99Richard Bauman and James DeBoer :A modification of the altered cast technique. J Prosthet Dent 1982;47:212-213

An over impression of the entire assembly in

irreversible hydrocolloid

Technique 2

• Lih-Shou Lay,Wing-Hong Lai and Chen-Tsye Wu :Making the framework try-in, altered-cast impression, andocclusal registration in one appointment. J Prosthet Dent 1996;75:446-8.

Wax used to block out undercuts around framework over edentulous portion of cast. Autopolymerizing acrylic resin tray material formed over

edentulous ridge portion of framework. Trays detached from framework. Custom-made trays attached to framework with acrylic

resin.

Index grooves on occlusal surface of trays. Jaw relation record (yellow) made in mouth with framework and record base in place. Altered cast

poured without removal of jaw registration material.

Technique 3

• U. Santana-Penín and J. Gil Lozano: An accurate method for occlusal registration and altered-cast impression for removable partial dentures during the same visit as the framework try-in. J Prosthet Dent 1998;80:615-8.

Light-cured acrylic resin tray formed over edentulousridge portion of framework. Holes are made in tray to allowresin columns to be built up through it. Position of holes can

be marked with pencil so that it is clear where to locatebases of columns (arrows).

U. Santana-Penín and J. Gil Lozano: An accurate method for occlusal registration and altered-cast impression for removable partial dentures during the same visit as the framework try-in.J Prosthet Dent 1998;80:615-8.

Acrylic resin trays (with holes for resin columns)

detached from framework

Framework in mouth showing 1 inch resin column built up

as jaw relation index.

Acrylic resin tray in position on framework after building up resin

column (a) that acts as jaw relation index. In addition, stone index beneath major connector

(b) will facilitate accurate repositioning of framework on

altered cast.

Framework in mouth showing 1 resin column built upas jaw relation index.

Completed impression seated on cast from which

edentulous ridges have been removed.

Impression is boxed, in this case with plasticine.

Finished altered master cast, with impression and jaw

relation indexes (arrows) in place.

Resin columns are used to relatemandibular cast to previously mounted maxillary cast, andare attached to lower arm of

articulator with stone.

Richard P. Frank et al :Clinical Outcome Of Altered Cast Impression Procedure Compared With Use Of A

One Piece CastJ Prosthet dent 2004;91:468-76

Altered cast procedure does not offer significant advantages over one piece cast if the following standards

are met :• Complete extension of impression

• Use of magnification to adjust and ensure complete seating of the framework.

• Coverage of retromolar pad and buccal shelf area by the base

REFERENCES • Essential of Removable partial denture –

Applegate• Removable Partial Prosthodontics – Miller• Partial dentures – Osborne & Lamiae• Advanced removable partial dentures –

Brudvik • Clinical dental prosthetics –Fenn ,Liddelow

and Gimson’s

REFERENCES

• Treatment of partially edentulous patients – Louis Boucher

• J.Pros.Dent. July,2004 :volume 24;number1

• J.Pros.Dent May – June 1992 : Volume 15;number 3

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