Various impression techniques for partially edentulous PTs.

1. IMPRESSION PROCEDURES FOR
REMOVABLE PARTIAL
DENTURES
PRESENTED BY:
DR.CHHAVI
RANA

2. INTRODUCTION
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 – 9
Partial denture impression
A negative likeness of a part or all of a partially
edentulous arch - GPT – 9

3. The occlusal forces applied to tooth supported RPD, they are
directed through rest and transmitted to the abutments.
Abutments tooth absorb forces and distribute to the tissues of
residual ridge.
So these forces should be equally distributed to the
abutment and the tissues of ridges.

4. Dual impression
technique is
used in which a
corrected cast is
generated

5. •Impression of
residual ridge must
1. Record and relate the
tissue under uniform
loading
2. Distribute the load over a
large area
3. Accurately delineate the
peripheral extent of
denture base.

6. Factors influencing support
for distal extension

7. 1.Quality of soft tissue
• Soft tissue displaceablity vary from patient to patient
• Soft tissue with thick and dispalacable tissue provide less
support for denture base.
• Firm and tightly attached mucosa displaying moderate
thickness ( 2-3mm) provide greatest support.

8. 2.Type of bone in
denture bearing area
Cancellous bone campared with cortical bone, is less able
to resist vertical forces because of its irregular surface act
as an irritant to overlying soft tissue if vertical stresses
occure.
So area of cancellous bone should not be considered the
primary stress bearing area.

9. 3.Design of prosthesis
• Mechanical principles guides the management of the functional
forces.
• Rotational forces passing through the distal abutment clasp can be
controlled by using other components.

10. 4.Amount of tissue coverage of
denture base
Broader the coverage of edentulous ridge
Greater distribution of the load
Smaller the force per unit area
Overextension may cause rotation of RPD this
may result in torquing of the clasped abutment &
orthodontic movement of teeth on opposite side
of fulcrum line.

11. 5. Anatomy of denture bearing area
Forces must be directed to the ridge that are most capable to
withstand those forces.
Maxillary edentulous ridges:
• Except the crest of the arch
are capable of serving as
primary stress bearing area,
as they are covered by layer of
cortical bone.
• Some resistance derived from
the horizontal portion of hard
palate from vertical forces

12. Mandibular edentulous ridges:
•Buccal shelf area makes excellent
stress bearing site.
•Areas with cortical bone has firm and
dense soft tissue coverage.
•Resistance to horizontal forces is
provided by the buccal and lingual
slopes of residual ridge.

13. 6.Fit of Denture Base
Denture base must be made to fit the area
that can serve primary stress bearing
reason.

14. INDICATIONS FOR FUNCTIONAL
IMPRESSION
•Mandibular distal extension partial dentures –Only a limited ridge area
can be used as a stress bearing site.
•Maxillary extension ridges is covered with firm and well attach mucosa ,
stress bearing area are buccal slopes and crest .Therefore dual impression
technique doesn’t improve stress distribution
• Mainly Kennedy’s class I & II edentulous arches.
•During depression the indirect retainers lifts away from the teeth dual
impression technique is indicated.

15. Impression
Methods
Physiologic
Impression
Techniques
McLean’s
technique
Hindel’s
technique
Fluid wax
technique
Functional
reline
technique
Selected
pressure
technique-

16. Physiologic
Impression
Techniques
• This technique records the ridge
portion of the cast in its functional
form by placing an occlusal load.

17. McLEAN’S
Physiologic
Impression
Aim :To record the tissues of the residual ridge in a
functional form while capturing the remaining teeth
in the anatomic form.
Methods :They constructed a custom tray on a
diagnostic cast. Spacer is not adapted. A functional
impression was made using custom tray and a
suitable impression material.
A hydrocolloid "over-impression" was then made
while maintaining the functional impression in its
intended position.
Disadvantages:The greatest weakness of the technique was that
practitioners could not produce the same functional displacement
generated by occlusal forces.

18. Hindel’s
Method
In response to the shortcomings in McLean’s
technique.
Aim: The residual ridge recorded in its normal or rest
state, but is related to the anatomic structures like
teeth in a functional form.
Hindel modified the impression procedure which
records the tissues under rest. They also developed
modified impression trays for the second impression
procedure.
The trays had large holes in their posterior segments.
For applying finger pressure to the functional
impression as the hydrocolloid impression was being
made.
The finished impression was a reproduction of the
anatomic surface of the ridge and the surfaces of the
teeth.
Disadvantages
Finger pressure does not simulate masticatory load.
Premature contacts at rest.

20. Functional
Reline
Method
It consists of adding a new surface to the intaglio of
the denture base.
Anatomic impression: The partial denture is
constructed on a cast made from a single impression,
usually irreversible hydrocolloid.
functional impression: An impression is made with a
free-flowing zinc oxide-eugenol paste or a light-bodied
elastomers. With spacer.
This is accomplished before insertion or it may b done in later stages if denture has no longer fits the ridges.
Problem: cause failure to maintain the correct relationship between framework and abutment during
impression procedure and fail to achieve accurate occlusal contact following the reline procedure.

21. Metal spacer (Ash’s No.7 metal
USA) is placed on dental cast to
provide spacer for functional reline
After denture base has
been processed the
metal spacer is removed
Heated modeling plastic is
carefully applied to the
intanglio of denture base
Modelling plastic
impression is complete

22. Modelling plastic is removed from
the ridge crest before the final
impression
Impression made using one of the
corrective materials : fluid wax,
Zinc-oxide Eugenol pastes or any
elastomeric impression material.

23. 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

24. 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
Objective:
•Obtain maximum extension of borders with not
interfering with functional movements.
•Recording stress bearing areas in functional form
•Recording non-stress bearing area in anatomic form
•Can also be used for existing partial denture.

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

26. Undercuts eliminated using baseplate
wax
Separating medium applied to the
cast.
Framework seated on the cast.

27. 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.

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

29. Completed impression.
Check for proper tissue contact.(final insertion for 12 mins)
The finished impression must be handled carefully &
the new cast poured as soon as the wax is fragile &
subject to distortion

30. SELECTIVE
PLACEMENT
IMPRESSION
METHOD
This is intended to equalize the support
between the abutment and soft tissues
and to direct forces to the portion of
ridges that are most capable of
withstanding such forces.

31. Framework tried on the cast Tray outline marked for
extension

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

33. Areas in which relief is
to be provided is
marked
Tray is being relieved before the
final impression is made
mandibular impression tray is
selectively reduced at the ridge crest
– provides additional room for
impression material and minimizes
tissue displacement.

34. Acrylic resin
Impression trays
with holes to allow
escape of excess
impression material
Framework with tray
tried in patient’s
mouth
Borders of impression are shortened
by 1 to 1.5 mm and the whole inside
of the impression, with exception of
buccal shelf region is relieved by
1mm. Modeling plastic is removed
from holes in the tray. Final
impression is made with zinc oxide
eugenol impression paste.

35. A more viscous
impression material
results in greater
displacement of the soft
tissues
a less viscous impression
material provides
decreased tissue
displacement.
Overdisplacement of resilient
tissues should be avoided
because it may result in an
inflammatory reaction
beneath the denture base
Displaced tissues also have a
tendency to rebound to their
anatomic contours, resulting
in occlusal displacement of
the prosthesis and placing
additional stresses on the
abutments.

36. ALTERED
CAST
TECHNIQUE
Altered cast : a final cast that is revised in part
before processing a denture base—called also
corrected cast, modified cast
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.

37. Maxillary ridge Mandibular ridge
Chandrashekar Sajjan An Altered cast procedure to improve tissue support for RPD
contemporary Clinical Dentistry Apr-Jun2010 vom 1 issue 2

38. Fabrication of maxillary and mandibular metal
frameworks

39. line indicates the proposed
cast modifications for a
bilateral corrected cast
process.
Border moulding

40. Final impression with
ZOE paste

41. Sitting the framework with
the wax to prevent
distortion

42. The altered cast
is obtained

43. SingleTray
Dual
Impression
Technique
The anterior teeth on
the diagnostic cast are
blocked out with three
to four layers of
asbestos paper.
The cold-curing resin is
adapted on the
diagnostic cast to form
the custom tray
opening has been
made around the teeth
in the resin custom
tray.
The border has been
molded to be in harmony
with the surrounding
tissues. A zinc oxide and
eugenol impression is
made of the residual
ridges
occlusion rim is
constructed on the
resin tray containing
the final impression of
the residual ridges.

44. Lund PS &Aquilino SA in 1991
•Described a technique that allowed the
RPD framework try-in and the impression
for the altered cast to be efficiently
•Completed in a single appointment.
The method used prefabricated custom
impression trays that are readily attached
to the framework after the try-in
Prefabricated
Custom
Impression
Trays

45. Conclusion
• The method used to make impressions of the supporting and retaining anatomic
structures of the mouth is of basic importance for obtaining optimum distribution
of the masticatory load in the construction of removable partial dentures,
especially of the lower extension saddle type.
• That it records and relates the tissues under some loading
• That it distributes the load over as large an area as possible.
• The denture saddle should be related to the metal framework in such a way as to
be similar to the relationship existing between the supporting teeth and the
supporting mucosa when the latter is under a masticatory load.

46. The maxillary and
mandibular occlusion rims
are in contact at the
vertical dimension of
occlusion.The mandible is
in centric relation
anterior part of the
maxillary occlusion rim has
been removed
Irreversible hydrocolloid
impression material has
been forced through the
opening in the tray.
The single-tray dual
material impression is
completed

47. Individual tray with occlusal
rims surpassing the height of
residual teeth.
Impression of the edentulous ridges
without any compression soft
tissues are left in their passive state.
zinc oxide-eugenol impression
paste
Elie Daou Paul Boulos simplifies impression technique for distal extension RPD. A Case Report
IAJDVol. 3 – Issue 3

48. •When the material sets, the
tray is removed and the
impression inspected .
•The excess material is
trimmed away and teeth are
freed from any residual
impression paste.
•The tray is tested in the
mouth for stability

49. Metallic stock tray chosen to cover the
whole arch.The arrow indicates the site
of finger pressure over the edentulous
area.
The mucostatic impression
with the occlusal rims in
place.
metallic tray is being loaded with an alginate impression
material, this same material is used to fill the space
between the soft tissue impression and the remaining
teeth.

50. Loaded metallic tray with
a positive pressure
Pick-up impression relating
edentulous areas to residual
teeth.

51. References
•Stewart clinical removable partial prosthodontics
4Th edition
•Reeta Jain Impression techniques for removable
partial dentures: A review Annals of Prosthodontics
& Restorative Dentistry, April-June 2017:3(2):52-56
•Chandrashekar Sajjan An Altered cast procedure to
improve tissue support for RPD contemporary
Clinical Dentistry Apr-Jun2010 vom 1 issue 2
•Li QL, Cao Y A Novel Functional Pressure
Impression Procedure for Distal-Extension
Removable Partial Dentures. Int J Dentistry Oral
Sci. (2015) 2(11), 168-172
•Elie Daou Paul Boulos simplifies impression
technique for distal extension RPD. A Case Report
IAJD Vol. 3 – Issue 3