In this presentation different types of rpd impression techniques are discussed

1. Impression
Procedure for
RPD’s

2. INTRODUCTION
Believe it or not,
partials can provide
predictable service,
acceptable esthetics,
and good function at
a moderate cost .

3. In removable partial dentures that are completely
tooth supported, the occlusal forces transmitted to the
abutment teeth are directed vertically down the long
axes of the teeth through the occlusal, incisal, or
lingual rests.
The edentulous ridges will not contribute to the
support of the partial denture , because the teeth
absorb these forces before they are transmitted to the
residual ridge.

4. A tooth-tissue supported RPD constructed on such
a cast, however, will exert excess pressure on the
teeth that help support the denture as the soft
tissue under the denture base compresses.
A dual impression technique is used to equalize as
much as possible as the support derived from the
edentulous ridges and that received from the
abutment teeth.

5. What is an Impression
A negative reproduction of dental structures from
which a positive cast can be made.
It is one of the important steps in denture
construction as all steps depend on it.
“a negative likeness or copy in reverse of the surface
of an object ; an imprint of teeth and adjacent
structures for use in dentistry.”

6. An impression of partially edentulous arch must
record accurately the teeth in anatomic form and
surrounding tissues in a functional form.

7. TWO TYPES OF IMPRESSION
1. Primary impression
 Used to make a reproduction of the teeth and
surrounding tissues.
 It is made in a stock tray for making a study cast
on which custom tray is constructed.
2. Final Impression
 It is an impression made in custom tray.
 Done after mouth preparation.
 Used for making the master cast on which the
denture is constructed.

8. IMPRESSION TRAY SELECTION
Stock trays used for dentulous & partially
edentulous arches are of 3 types:
 Rimlock trays
 Perforated metal trays
 Plastic disposable trays

9. CHECKING TRAYSIZE
 There should be a clearance of 4-5 mm between teeth
and inner flanges of tray
 It should cover the desired anatomic areas
 Too Large tray may be difficult to insert & may interfere
with the coronoid process of the mandible while making
maxillary impression
 In case of mandibular impression ,if the tray extends too
far lingually , there is a tendency to trap the tongue or
floor of mouth.

10.  Record and relate the
tissues under the same
loading.
 Distribute the load over
as large area as
possible, and
 Delineate accurately
the peripheral extent of
the denture base.
The Impression must

11. Impression Techniques In Older
Adults
Problems associated:
 Rebound of soft tissues
 Protection of lips
 Tray selection and modification
 Maintenance of airways
 Stabilization of the loose teeth

12. DIAGNOSTIC IMPRESSIONS
 Stock Trays (Perforated)
 Irreversible hydrocolloid
impression material
(alginate)

13. MAKING IMPRESSIONS
 The tray is carefully seated
so that its flanges are
below the gingival margin
of the teeth.
 The syringe is used to
inject the impression
material over the occlusal
surface of the teeth and
into the vestibular and
alveololingual sulcus areas.
 Layer of alginate applied
with the syringe should be
3-4mm thick.

14. MAKING IMPRESSIONS
 In maxillary impression
alginate is injected over
the occlusal surfaces and
in all vestibular areas like
in mandibular impression.
 A fairly large amount of
alginate should be wiped
onto the palate.

15. Making The Final Impression For
The Master Cast
Materials used for making final
impressions are as follows:
Irreversible hydrocolloid
Reversible hydrocolloid (Agar Agar)
Polysulphide rubber
Silicon rubber

17. Type And Accuracy Of The
Impression Registration
The residual ridge may be said to have two
forms:-
1)The anatomic form.
2)The functional form.
 The anatomic form is the surface contour of the
ridge when it is not supporting an occlusal load.
 The functional form of the residual ridge is the
surface contour of the ridge when it is
supporting a functional load.

18. Type and Accuracy of Impression
Registration

19. Type and accuracy of the
impression registration
 McLean and others recognized the need to
record the tissues that support a distal extension
partial denture base in their functional form, or
supporting state, and then relate them to the
remainder of the arch by means of a secondary
impression.
 Anatomic ridge form for the partial denture need
some mechanical stress-breaker to avoid the
possible cantilever action of the distal extension
base against the abutment teeth.

20. Anatomic Form Impression
 It represents all the hard and soft tissues at rest.
 When the denture is positioned in the mouth, the rests in
the direct retainer will fit on to the abutments and the
denture base will contact the mucosa during the rest
position.
 When masticatory load is applied to extension saddle, the
rest in the direct retainer will act as definite stop, and
prevent the saddle near the abutment tooth from
transmitting the load to underlying anatomic structures.

21.  The distal end of saddle, which is able to move
freely will transmit the full masticatory load. The
result will be traumatic load to the base
underlying the distal end of saddle and to the
abutment tooth which in turn will result in bone
loss and loosening of abutment tooth.

22. F u n c t i o n a l i m p r e s s i o n
“recording the functional form of
residual ridge to obtain uniformity of
support when the functional load is
applied”

23. Indications for Functional
impression:
Mandibular distal extension
partial dentures
Mainly Kennedy's class I & II
edentulous arches.

24. Materials Used
ANATOMIC IMPRESSION
 Irreversible hydrocolloid
 Elastomeric impression materials
 reversible hydrocolloid
FUNCTIONAL IMPRESSIONS
 fluid waxes
 metallic pastes
 elastomeric impression materials
 soft liners

25. IMPRESSION METHODS
There are basically two dual impression
techniques-
1) The physiologic or functional
impression technique
2) The selective pressure impression
technique.

26. Physiologic Or Functional
Impression Technique
It records the ridge portion of the arch in its physiologic or
functional form by placing an occlusal load on the
impression tray as the impression is being made.
There are physiologic impression techniques-
1) McLean’s Technique
2) Hindel’s modification of McLean's method.
2) The functional relining method
3) The fluid wax method

27. McLean’s Technique
 McLean realized the need of
recording the tissues of the
residual ridge that would
eventually support a distal
extension denture base in
the functional or supporting
form and then relating this
functional impression to the
remainder of the arch by
means of a second impression
(Dual impression).
Custom tray for McLean's functional
Impression technique has modeling plastic
Occlusal rims.

28. McLean “The basic problem of partial
denture stabilization is to equalize the
resilient and non resilient support”
McLean’s
Physiologic Method

29. 1. Custom tray over a primary cast
2. Functional impression of impression area under
load.

30. 3. Hydrocolloid impression over the first impression
made under finger pressure.

31. Disadvantages-
• Finger pressurenot equal to biting pressure.
• Closely affect the direct retention.

32. Hindel’’s MODIFICATION
 Hindel and others
developed irreversible
hydrocolloid trays for
second impression that
were produced with
holes so that finger
pressure could be
applied through the tray
as the hydrocolloid
impression was made.
Hindels impression tray . Holes are
used by dentist to apply finger
pressure
to underlying impression of the ridge
area.

33. HINDEL’S MODIFICATION
Impression is made with a modified tray applying
finger pressure.

34. DIASADVANTAGES OF MCLEANS’S AND
HINDLE’S METHOD
 Constantly compressed residual ridge is prone
to excessive bone resorption.
 If the clasp do not hold the denture, the
denture will be pushed slightly occlusally by
the tissue causing premature contacts (tissue
rebound )

35. The Functional Relining Method
It consists of adding a new surface to the inner, or
tissue, side of the denture base.
Technique- The partial denture is constructed on a
cast made from a single impression, usually
irreversible hydrocolloid.
 This is an anatomic impression, and no attempt is
made to alter it or produce a functional impression of
the edentulous ridge.

36. The Functional Relining Method
The patient must maintain the mouth in a
partially opened position while the border
molding and impression are being accomplished
because:-
1)The border tissues, cheek, and tongue are
thus best controlled and
2)The relationship between the partial denture
framework and the teeth must be observed.

37. The Functional Relining Method
Correcting Peripheral Extensions of Tray.
 The buccal extension of the tray should be
observed as the cheek is moved downward,
outward, and upward.
 The posterior extension of the tray should end at
two thirds coverage of the retromolar pad.
 The disto-lingual tray extension is determined by
the patient protruding the tongue so that the tip of
tongue contacts the upper lip.

38. The Functional Relining Method
 The remainder of the
lingual flange extension
is checked in a similar
manner.
 If the tray moves during
right and left movement
of the tongue,the lingual
flange opposite the
cheek toward which the
tongue moves should
be shortened.
Modeling plastic is put on the
Tissue surface of the denture base.

39. The Functional Relining Method
Border Molding The
Impression Tray
The mandibular distal extension
tray may be border molded in
two steps:
 From the anterior extent of the
buccal flange to the most
posterior extent of the tray and
 The remainder of the lingual
and distal lingual flange.
Modeling plastic over ridge
is relieved before final
impression is made.

40. DISADVANTAGE
 OCCLUSION MAY BE ALTERED SLIGHTLY .
 FINE LINE OF DEMARCATION EXIST BETWEEN THE
NEWLY ADDED & OLD RESIN .

41. Fluid Wax Functional Impression
The fluid wax
impression may be
used to make a reline
impression for an
existing partial
denture or to correct
the distal extension
edentulous ridge
portion of the original
master cast.

42. Fluid Wax Functional Impression
The objectives of the technique are:
1)To obtain maximum extension of the
peripheral borders of the denture base
while not interfering with the function of
movable border tissue.
2)To record the stress bearing areas of the
ridge in their functional forms.
3)To record non-pressure-bearing areas in
their anatomic form.

43. Fluid Wax Functional Impression
 The term fluid wax is used to denote waxes
that are firm at room temperature and have
the ability to flow at mouth temperature.
 The key to the use of fluid wax lies in two
areas: space and time.
 Space refers to the amount of relief
provided between the impression tray and
the edentulous ridge.

44. Fluid Wax Functional Impression
 Relief between the
tray and the ridge of 1
to 2 mm is the desired
amount.
 Each time the tray is
introduced into the
mouth, it must remain
in place 5 to 7
minutes.

45. A container of wax is placed in water
bath maintained at 51 to 54 degree
Celsius.
The wax is painted onto impression
surface with brush. Tray borders should
not more than 2mm short because the
fluid wax does not have sufficient
strength beyond that distance.

46. The tray is then seated in the
mouth and the patient must hold
his mouth half open for about 5
min. When tissue contact is
present, wax will be glossy and
where tissue contact is not present
it will be dull.
When complete tissue contact and
anatomy of limiting border
structure has been established, the
impression is left in the mouth for
12 min. This is to ensure that wax
had flown completely.

47. Selective Pressure Impression
Technique
The selected pressure
impression attempts to direct
more force to those portions
of the ridge able to absorb the
stress without adverse
response and to protect the
areas of the ridge least able
to absorb force.

48. Selective Pressure
Impression Technique
For the mandibular posterior ridge:-
 The crest of the ridge is not considered to
be a pressure-bearing area, so the
undersurface of the tray is relieved down
to the metal retention struts.
 This will usually be at least 1 mm.
 The buccal shelf is the primary stress-
bearing area, so only slight relief.

49. Altered Cast Procedure
Altered cast impression in
case of distal extensions or
Kennedy class I or II arch
form
Tray fabrication
Border molding

50. Primary Impression
Stone Model Preparation
Preparation of Metal Framework
& Tray for Border Molding

51. Extension of Tray Checked In
Mouth
Tissue Surface Bearing
Area
Sectioning Of Master Cast

52. ZOE Impression Paste On Distal
Extension Edentulous Tray
ZOE Loaded Tray Placed In
Mouth
After Setting Of ZOE

53. After Removal Of Edentulous
Region
Sectional Impression & Metal
Framework Adjusted On To
Master Cast

54. After removal of the custom tray
from the metal framework, the
latter can then be positioned on
the new master cast and the
remaining stages in the
construction of a lower distal
extension partial denture carried
out
A new base poured into the
sectional impression to
give a new (or modified, to
be strictly accurate) master
cast when making a lower
partial denture for a distal
extension case

55. Master Cast Before Altered
Cast Procedure
Master Cast After Altered Cast
Procedure

56. Impression Technique For Relining
The RPD
 In order for a RPD reline to be
successful the denture base must
extend to cover the denture space.
 If the existing denture is short of ideal
coverage, a rebase should be used
instead of reline.

57. Impression Technique For Relining The RPD
The resin should be removed for two important reasons:
1) Space must be created so that there is no possibility
that semi-contained impression material might displace
soft tissue an distort the supporting structures and
2) The resin that has been in continuous contact with
the oral cavity must be removed so that the new
resin will interface with the material that is dense and
uncontaminated.
Under no circumstances can the patient be allowed to bring
his teeth in contact during impression making.

58. Intraoral Reline
There are commercially
available auto
polymerizing resins that
are intended to be cured
in the mouth.
External surface of partial denture
prepared for intraoral reline.

59. Impressions for Denture Base
Repair
 If the section is available and can be
accurately positioned on the fracture site, the
repair is a simple matter of luting the pieces
with sticky wax.
 If the broken segment(s) cannot be positively
related, they should be discarded and the
repair undertaken in the following manner
(the same approach is indicated if the
segments have been lost).

60.  If only a small segment is missing, it may be
sufficient to simply adapt modeling plastic to the
denture base and reconstruct that area in the
mouth.
 The modeling plastic is added to the denture
base with dry heat so that it will stick to the
base.
 It is molded by hand to approximate with soft
tissue contours, flamed, tempered in the water
bath, and seated in the mouth.
 The plastic will need to be refined by scraping
and reheating one or two times to achieve an
impression that does not displace the tissues.

61. If the defect is large, it is advisable to first
approximate the contour with modeling
plastic and then reline both the plastic and
the remainder of the denture base by
making a rebasing “wash” impression.

62. CONCLUSION
Various techniques used for the construction of
removable partial dentures are based on the
characteristics and behavior of hard and soft tissues.
The prosthesis thus designed should be constructed
to preserve the oral structures as well as restore
function.

63. THANK YOU