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1
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
2
CONTENTS
• Factors influencing support of distal extension base• Materials used for functional impression• Impression methods• Altered Cast Technique• Modifications of altered cast technique
3
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.
4
ACCORDING TO THE METHOD OF IMPRESSION MAKING
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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.
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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 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.
9
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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
11
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.
12
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.
13
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.
14
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
16McCracken’s Removable Partial Prosthodontics
•Type & Accuracy of impression registration
17McCracken’s Removable Partial Prosthodontics
•Accuracy of fit of denture base
18McCracken’s Removable Partial Prosthodontics
•Design of partial denture framework
19McCracken’s Removable Partial Prosthodontics
•Total Occlusal load applied
20McCracken’s Removable Partial Prosthodontics
IMPRESSION MATERIALS
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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
22
The master cast may be altered to accommodate the new ridge impression it is
referred as Altered Cast Technique Or Corrected Cast Impression Technique
23
McLean’s Physiologic Method
24Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
Custom tray over a preliminary cast
25
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Custom tray over a preliminary cast
Occlusal rim over a distal extension base is made
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Functional impression of extension area under occlusal load
Hydrocolloid impression over the first impression made under finger pressure.
29
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.
30
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.
31Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
32
Hindel’s special tray with holes to apply pressure
33
HINDLE’S FINGER LOADING
34
HINDLE’S FINGER LOADING
• Tissues are in constant stage of compression
• Ischemia and bone resorption
• Premature contacts at rest.
Disadvantage
Functional Reline Method
35Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
Layer of relief given
36
The denture is processed & fitted in the mouth in customary manner, except that the relief metal is
left in place.
37
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.
38
low fusing modeling compound is added in increments
39
Border molding done.
40
1 mm Modeling plastic is removed from the intaglio surface.
41
Impression made using one of the corrective materials : fluid wax, Zinc-oxide Eugenol pastes or
any elastomeric impression material.
42
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
43
FLUID WAX TECHNIQUE
44Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
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
45
The armantarium for fluid wax technique. (51- 54 degree Celsius)
46
Undercuts eliminated using baseplate wax
47
Separating medium applied to the cast.
48
Framework seated on the cast.
49
Tray material adapted 1-2 mm relief between
residual ridge and intaglio surface of tray.
50
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)
51
Completed impression.Check for proper tissue contact.(final insertion for 12
mins)
52
FLUID WAX TECHNIQUE
• The finished impression must be handled carefully & the new cast poured as soon as the wax is fragile & subject to distortion
53
SELECTIVE TISSUE PLACEMENT IMPRESSION METHOD
54
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.
55
Framework tried on the cast Tray outline marked for extension
56McCracken’s Removable Partial Prosthodontics
Framework with tray fabricated on it with holes on its ridge.
57McCracken’s Removable Partial Prosthodontics
Areas in which relief is to be provided is marked
58
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
59
ALTERED CAST TECHNIQUE
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
60
• 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.
61
ALTERED CAST TECHNIQUE
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
63
Framework with attached impression seated on the master cast
It is imperative that all the rests occupy their proper position on the cast
64
Assembly from underside of the cast
Peripheral borders of the impression are protected with
utility wax & the assembly wrapped with boxing wax
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The newly obtained altered cast with newly added stone
66
67
Alternate techniques
68
Alternate technique to separate the edentulous cast
69
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.
70
Mix of properly proportioned dental stone vibrated into three compartments of impression. Impression must be overfilled to
make solid base to prevent premature separation
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.
71
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.
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.
72
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
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.
73
View from bottom of master cast after base has been trimmed to expose separating
wax and wax dovetails.
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.
74
Edentulous portions separated from rest of master cast when removed from boiling clear slurry water. Appearance of dovetails for additional
retention for dental stone.
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.
75
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
76
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.
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
77
Protection of teeth in master cast with irreversible hydrocolloid.
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
78
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.
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
79
• 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
80
• 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
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Boxing wax placed around plaster base and cast leaving at least 20 mm from top of wax to highest point on
impression.
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
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• Completed altered cast.
Completed altered cast.
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
83
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
84
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.
85
Tissue surface of distal-extension irreversible hydrocolloid pickup
impression. Irreversible hydrocolloid is purposely
overextended 3 to 5 mm arounddistal-extension region.
86
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.
87
Tissue surface of final impression is surrounded
by a uniform land of irreversible hydrocolloid.
88
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
89
Master cast obtained by this method. Note uniform
stone land transition in distal-extension regions.
90
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
91
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.
92
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
Custom tray fabricated with extensions reduced 2 mm
short of vestibule.
93
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
Custom tray with softened modeling compound
reseated on diagnostic cast. Modeling compound over
residual ridges shaped appropriately before intraoral
placement.
94
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
Border molding procedure completed.
95
Trial of metal framework,altered cast technique and interocclusal record in one appointment
96
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
97
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
100
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.
101
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.
102
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.
103
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.
104
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.
105
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.
106
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.
107
Completed impression seated on cast from which
edentulous ridges have been removed.
Impression is boxed, in this case with plasticine.
108
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.
109
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
92
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
110
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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