dentistry: functional impressions in cast partial dentures

1. ALTERED CAST
TECHNIQUE
By
Dr. Saili Chandavarkar
MDS II
1

2. 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

3. CONTENTS
• Factors influencing support of distal
extension base
• Materials used for functional impression
• Impression methods
• Altered Cast Technique
• Modifications of altered cast technique
3

4. 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

5. ACCORDING TO THE METHOD OF
IMPRESSION MAKING
RESIDUAL
RIDGE
Anatomic
form
Functional
form
5

6. ANATOMIC FORM
• The surface of the residual ridge at rest.
• It is the shape of the ridge before functional load is
applied.
6

7. 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.
7

8. Anatomic or Resting form
Supporting or Functional form
McCracken’s Removable Partial Prosthodontics 3rd edition
8

9. 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

10. 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
10

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
11

12. 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

13. 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

14. 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

15. Factors influencing the support of
distal extension base
• Contour & Quality of residual ridge
McCracken’s Removable Partial Prosthodontics15

16. •Extent of residual ridge coverage by the denture base
McCracken’s Removable Partial Prosthodontics
16

17. •Type & Accuracy of impression registration
McCracken’s Removable Partial Prosthodontics
17

18. •Accuracy of fit of denture base
McCracken’s Removable Partial Prosthodontics
18

19. •Design of partial denture framework
McCracken’s Removable Partial Prosthodontics
19

20. •Total Occlusal load applied
McCracken’s Removable Partial Prosthodontics
20

21. IMPRESSION MATERIALS
ANATOMIC IMPRESSIONS
FUNCTIONAL IMPRESSIONS
• IRREVERSIBLE
HYDROCOLLOID
• ELASTOMERIC IMPRESSION
MATERIALS
• REVERSIBLE HYDROCOLLOID
• FLUID WAXES
• METALLIC PASTES
• ELASTOMERIC IMPRESSION
MATERIALS
• SOFT RELINERS
21

22. METHODS OF FUNCTIONAL IMPRESSION
SELECTED PRESSURE
IMPRESSION TECHNIQUE
PHYSIOLOGIC OR
FUNCTIONAL IMPRESSION
McLean's method
Hindel’s modification for
McLean's method
Functional relining
method
The Fluid wax technique
22

23. 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

24. McLean’s Physiologic Method
Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
24

25. Custom tray over a preliminary cast
25

26. Custom tray over a preliminary cast
26

27. Occlusal rim over a distal extension base is made
27

28. Functional impression of extension area under
occlusal load
28

29. Hydrocolloid impression over the first impression made
under finger pressure.
29

30. McLean’s Physiologic Method
Disadvantages• 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

31. 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.
Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
31

32. Hindel’s special tray with holes to apply
pressure
32

33. HINDLE’S FINGER LOADING
33

34. HINDLE’S FINGER LOADING
Disadvantage
• Tissues are in constant
stage of compression
• Ischemia and bone
resorption
• Premature contacts at
rest.
34

35. Functional Reline Method
Clinical Removable Partial Prosthodontics – Stewart. 3rd edition
35

36. Layer of relief given
36

37. 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
37

38. The relief metal is stripped off from the acrylic.
38

39. low fusing modeling compound is added in increments
39

40. Border molding done.
40

41. 1 mm Modeling plastic is removed from the intaglio
surface.
41

42. Impression made using one of the corrective
materials : fluid wax, Zinc-oxide Eugenol pastes or
any elastomeric impression material.
42

43. 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

44. FLUID WAX TECHNIQUE
44
Clinical Removable Partial Prosthodontics – Stewart. 3rd edition

45. 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

46. The armantarium for fluid wax technique. (51- 54
degree Celsius)
46

47. Undercuts eliminated using baseplate wax
47

48. Separating medium applied to the cast.
48

49. Framework seated on the cast.
49

50. Tray material adapted 12 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.
50

51. Fluid wax painted onto the intaglio surface of tray (1 -2 mm)
Assembly seated in patients mouth.(5 -7 mins)
51

52. Completed impression.
Check for proper tissue contact.(final insertion for 12
mins)
52

53. 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

54. SELECTIVE TISSUE PLACEMENT
IMPRESSION METHOD
54

55. 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

56. Framework tried on the cast
McCracken’s Removable Partial Prosthodontics 56
Tray outline marked for
extension

57. Framework with tray fabricated on it with
holes on its ridge.
McCracken’s Removable Partial Prosthodontics
57

58. Areas in which relief is to
be provided is marked
Tray is being relieved
before the final
impression is made
58
Clinical Removable Partial Prosthodontics – Stewart. 3rd edition

59. Acrylic resin
impression trays
with holes
Framework with
tray tried in
patient’s mouth
Functional
impression made
59

60. 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

61. ALTERED CAST TECHNIQUE
• 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 Support
For Removable Partial Dentures .J Prosthet Dent61
1965:672-679

62. Functional impression
made
Final impression
McCracken’s Removable Partial Prosthodontics 12thedition
62

63. Edentulous area cut from the master
cast
63

64. Framework with attached impression seated on
the master cast
It is imperative that all the rests occupy their proper
position on the cast
64

65. Assembly from underside
of the cast
Peripheral borders of the
impression are protected with
utility wax & the assembly
wrapped with boxing wax
65

66. The newly obtained altered cast with newly added
stone
66

67. Alternate
techniques
67

68. Alternate technique to separate the
edentulous cast
68

69. Boxed elastomeric final impression in which edentulous
ridges have been separated with contoured baseplate
wax (A arrows) and sealed to anatomic contour of
impression at base. Triangular wax bars (B arrows) are attached
to make dovetails (three separate compartments of
impression).
Izharul Haque Ansari: A new procedure for separating the edentulous distal extension portion
69
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
70
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
71
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
72
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
73
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
74
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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
75

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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
76

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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
77

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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
78

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
79

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
80

81. 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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
81

82. • 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;85:519-20
Kevin D. Plummer:Technique for boxing an altered cast impression. J Prosthet Dent
1982;47:573-575
82

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
83
1987;57:471-474

84. 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.
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
84
1987;57:471-474

85. Tissue surface of distal-extension
irreversible hydrocolloid pickup
impression. Irreversible
hydrocolloid is purposely
overextended 3 to 5 mm around
distal-extension region.
85

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.
It
shows relationship
between final
impression, irreversible
hydrocolloid land, and
stock metal tray.
86

87. Tissue surface of final impression is
surrounded
by a uniform land of irreversible
hydrocolloid.
87

88. Tissue surface of pickup
impression. Note wax
blockout (arrows) of all undesirable
mechanical undercuts.
There is no blockout of major
connectors, rests, and
reciprocal clasp arms
88

89. Master cast obtained by this
method. Note uniform
stone land transition in distalextension regions.
89

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
90

91. Aluminum foil and two sheets of
baseplate wax over
diagnostic cast before tray
fabrication.
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

92. Custom tray fabricated with
extensions reduced 2 mm
short of vestibule.
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
92

93. Custom tray with softened
modeling compound
reseated on diagnostic cast.
Modeling compound over
residual ridges shaped
appropriately before intraoral
placement.
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
93

94. Border molding procedure completed.
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
94

95. Trial of metal framework,altered cast
technique and interocclusal record in
one appointment
95

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 96

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
97
Dent 1982;47:212-213

98. Interocclusal record is made by placing low fusing modelling compound
over the wax rim to record the interocclusal relationship
Richard Bauman and James DeBoer :A modification of the altered cast technique. J Prosthet
98
Dent 1982;47:212-213

99. An over impression of the
entire assembly in
irreversible hydrocolloid
Richard Bauman and James DeBoer :A modification of the altered cast technique. J Prosthet
99
Dent 1982;47:212-213

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.
100

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
101
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.
102

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.
103

104. Light-cured acrylic resin tray formed over edentulous
ridge portion of framework. Holes are made in tray to allow
resin columns to be built up through it. Position of holes can
be marked with pencil so that it is clear where to locate
bases of columns (arrows).
U. Santana-Penín and J. Gil Lozano: An accurate method for occlusal registration and alteredcast impression for removable partial dentures during the same visit as the framework try-in.
104
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.
105

106. Framework in mouth showing 1
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.
106

107. Completed impression seated on
cast from which
edentulous ridges have been
removed.
Impression is boxed, in this case
with plasticine.
107

108. Finished altered master cast, with
impression and jaw
relation indexes (arrows) in place.
Resin columns are used to relate
mandibular cast to previously
mounted maxillary cast, and
are attached to lower arm of
articulator with stone.
108

109. Richard P. Frank et al :Clinical Outcome Of Altered
Cast Impression Procedure Compared With Use Of A
One Piece Cast
J 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
109

110. 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

111. 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
111