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spl imp tech.pptx
1. SPECIAL IMPRESSION TECHNIQUES FOR
DISTAL EXTENSION RPD/CPD
BY DR PUTTARAJ.T.K.
Prof.& H.O.D.
Dept of Prosthodontics & D.M.
2. 1. INTRODUCTION
2. DEFINITIONS
3. RPD IMPRESSION Vs C D IMPRESSION
4. PRIMARY IMPRESSION FINAL IMPRESSION METHODS
5. Mc LEAN’S TECHNIQUE
6. HINDEL’S TECHNIQUE
7. SELECTIVE PRESSURE TECHNIQUE
8. FUNCTIONAL RELINING TECHNIQUE
9. FLUID WAX TECHNIQUE
10. ALTERED CAST TECHNIQUE MODIFICATION
11. CONCLUSION
12. REFERENCES
3. INTRODUCTION
The construction of a removable partial denture in
distal extension cases is a delicate procedure since the
prosthesis is supported by two different tissues,
namely teeth and mucosa.
The different resiliency of these supporting tissues
may lead to the instability of the prosthesis.
The viscoelastic reaction of ridge mucosa and
abutment teeth, by virtue of their periodontal
ligaments are not the same.
4. The possible modalities are
(1) removable partial dentures with flexible denture
bases (stressbreakers),
(2) use of a floating denture base impression
technique,
(3) use of a mucofunctional impression
technique to relate the denture base to
the framework, and
(4) use of an end osseous implant. An evaluation of
each modality is utmost important
INTRODUCTION
5. Definitions of 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 – 8
Partial denture impression .
A negative likeness of a part or all of a partially
edentulous arch - GPT – 8
6. IMPRESSION TRAYS
A receptacle into which suitable impression material
is placed to make negative likeness
OR
A device that is used to carry, confine and control
impression material while making an impression.
7. Impression trays can be classified broadly in to stock
trays and custom trays
Stock trays for partially edentulous patients may be
perforated to retain the impression material or they
may be constructed with a rimlock for this purpose.
Rim lock TRAY-- Another type of stock tray designed
for the reversible type of hydrocolloid is water cooled
trays. It contains tubes through which water can be
circulated for purpose of cooling the tray.
8. Disadvantages: STOCK TRAY
A. The peripheral borders cannot be accurately
recorded.
b. Considerably more bulkier than a custom tray.
9. Custom impression trays:
A. Peripheral borders can be precisely recorded in the
impression
B. Thickness of impression material can be controlled.
10. Well fitted tray will better support the impression in
the palate, then avoiding even present danger of
material slumping in vital areas.
Custom trays are sometimes needed for mouths that
are abnormally or of unusual configuration
12. RPD IMPRESSION V/s COMPLETE DENTURE IMPRESSION
Partial denture impression records relative soft yielding
tissues (the oral mucosa) as well as a hard unyielding
substance (the remaining teeth).
The complete denture impression records the edentulous
mucosa with underlying bone only
13. Removable partial denture impression need to record
the teeth that are irregular in contour as well as
varying in their vertical relations to occlusal plane.
The chosen impression material must be capable of
recording the tissue contours as accurately as possible
without distortion, which occurs as impression is
withdrawn.
14. PRIMARY IMPRESSION
Objective:
To obtain an impression of all the standing teeth and
denture - supporting tissues of each jaw from which
study casts may be prepared.
15. study casts
The purpose of the study casts are:
To enable special trays and occlusion rims to be
constructed if necessary.
To examine the occlusion in detail on an articulator.
By use of a surveyor, to plan the path of insertion of
the proposed denture, arrive at a tentative design and
plan any mouth preparation.
17. Factors Influencing Support of Distal
Extension Base
Contour and Quality of Soft tissue covering edentulous
ridge
Type of bone making up denture-bearing area
Design of partial denture
Amount of tissue coverage of denture base
Amount of occlusal forces
Denture bearing area
Fit of the denture base
28. Impression Methods
There are basically two dual impression techniques.
1.The physiologic impression techniques are as follows:
A. McLean’s and B. Hindel’s methods,
2.The functional relining method, and
3.The fluid wax method.
4.Selected pressure impression
30. Physiologic impression techniques
The need for physiologic impressions was first recognized
by McLean
For this dual impression a custom impression tray was
constructed over a preliminary cast of the arch
A functional impression of the distal extension ridge
was made, and then hydrocolloid impression was made
with the first impression held in its functional position
with finger pressure
Its an over impression or pick up impression
31. The greatest weakness of the technique
was that finger pressure could not produce the same
functional displacement of the tissue that biting force
produced.
Many variations of this technique have been
developed and advocated, but all require some form of
finger loading pressure as the second impression is
made.
Physiologic impression techniques
32. Hindels and other developed irreversible hydrocolloid
trays for the second impression that were provided with
holes so that finger pressure could be applied through the
tray as the hydrocolloid impression was made.
Physiologic impression techniques
33. The main change that Hindels introduced to McLean ‘s
original technique was that
The impression of the edentulous ridge was not made
under pressure but was an anatomic impression of the
ridge at rest made with a free flowing zinc oxide eugenol
paste.
34. As the hydrocolloid second
impression was being made,
finger pressure was applied
through the holes in the tray
to the anatomic impression.
The pressure had to be
maintained until the alginate
was completely set
By Hindels
35. the main purpose of these techniques was to relate an
impression of the edentulous ridge to the teeth under
a form of functional loading.
37. ii. FUNCTIONAL RELINE TECHNIQUE.
Most methods of obtaining a physiologic impression
for support of a distal extension denture base
accomplish the impression procedure before
completion of the denture, usually following the
construction of the framework.
It is possible, however, to obtain the same results after
the partial denture has been completed.
The technique is referred to as a functional reline. It
consists of adding a new surface to the inner, or tissue,
side of the denture base.
38. the procedure may be accomplished before the insertion
of the partial denture, or it may be done at a later date
because of bone resorption, the denture base no longer
fits the ridge adequately.
Although the functional reline has many advantages,
and for correcting the fit of denture base that has been
worn for a period of time is essential, it does present
many difficulties.
FUNCTIONAL RELINE TECHNIQUE.
39.
40. To allow room for the impression material between the
denture base and the ridge, space must be provided.
One of the most accurate methods of ensuring
uniform space for the impression is to adapt a soft
metal spacer over the ridge on the cast before
processing the denture base.
After processing, the metal is removed leaving an even
space between the base and the edentulous ridge.
FUNCTIONAL RELINE TECHNIQUE.
41. The patient must maintain the mouth in a partially
open 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 frame
work and the teeth must be observed.
FUNCTIONAL RELINE TECHNIQUE.
42. The functional reline method has the advantage that
the amount of soft tissue displacement can be
controlled by the amount of relief given to the
modeling plastic before the final impression is made.
The greater the relief the less will be the tissue
displacement.
FUNCTIONAL RELINE TECHNIQUE.
44. OBJECTIVES
To obtain maximum extension of the peripheral
borders of the denture base while not interfering with
the function of movable border tissues.
To record the stress bearing areas of the ridges in their
functional form.
To record non pressure bearing areas in their anatomic
form
45. Fluid wax technique
The term fluid wax is used to denote waxes that are
firm at room temperature and have the ability to flow
at mouth temperature.
46.
47. 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--1 to 2
mm is desired.
Each time the tray is introduced into the mouth, it
must remain in place 5 to 7 minutes to allow the wax to
flow and to prevent build-up of pressure under the tray
with resulting distortion or displacement of the tissue.
Fluid wax technique
48. The water bath maintained at
51° to 54° C into which a
container of the wax is placed.
At this temperature the wax
becomes fluid.
The wax is painted on the
tissue side of the impression
tray with a brush.
Fluid wax technique
49. The tray is seated in the mouth.
The patients must remain with the mouth approximately
half open for about 5 minutes.
The tray is removed, and the wax examined for evidence
of tissue contact,
Where tissue contact
is present the wax
surface will be dull.
Fluid wax technique
50. If needed additional wax is painted on those areas not
in contact with the tissue.
For the buccal and distobuccal extension in a
mandibular impression the patient must move to a
wide- open-mouth position.
This will activate the buccinator muscle and
pterygomandibular raphe and produce the desired
border anatomy.
Fluid wax technique
51. For the proper lingual extension for a mandibular
impression the patient must thrust the tongue into the
cheek opposite the side of the arch being border
molded.
The distolingual extension is obtained by having the
patient press the tongue forward against the lingual
surface of the anterior teeth.
Fluid wax technique
52. These movements must be repeated a number of times
after the impression has been in the mouth long
enough for the wax to have softened sufficiently to
flow.
Fluid wax technique
53. When the impression evidences complete tissue
contact and when the anatomy of the limiting border
structure is evident, the impression should be replaced
in the mouth for 12 minutes.
This final time to be certain that the wax has
completely flowed and released any pressure that may
be present.
Fluid wax technique
54.
55. T he fluid wax impression technique can produce an
accurate impression if the technique is properly
executed
The procedure is time consuming, but if the time
periods are not followed accurately, an impression
with excessive tissue displacement will result.
Fluid wax technique Limitations
57. Impression technique
Border molding
Making impression with the ZOE or Rubber base
materials
The critical point is to determine visually that all rest and
indirect retainers
are completely seated
65. conclusion
Partially edentulous mouths with distal-extension ridges
present the challenge of correctly registering two tissues as
dissimilar as teeth and edentulous ridges
.
In removable partial denture, impression need to consider
into the harmony between uncompressible hard tissue and
delicate structures with variable compressibility's.
