2. IMPRESSION MATERIALS
&
PROCEDURES FOR R.P.D
Presented by
Jean Michael
Final Year Part 2

3. INTRODUCTION
• An impression is defined as a negative likeness
of the teeth and/or edentulous areas where
the teeth have been removed, made in a
plastic material which becomes relatively hard
while in contact with these tissues

4. CLASSIFICATION OF IMPRESSION
MATERIALS
RIGID MATERIALS
Plaster of Paris
Metallic Oxide Paste
THERMOPLASTIC MATERIALS
Modeling plastic
Impression Waxes & Natural Resins

5. ELASTIC MATERIALS
Reversible Hydrocolloids
Irreversible hydrocolloids
Mercaptan Rubber-base materials
Polyether Impression Material
Silicone Impression Materials
Condensation SIM
Addition SIM

6. IRREVERSIBLE HYDROCOLLOIDS
(ALGINATE)
Indicated for diagnostic casts,
orthodontic treatment casts &
master casts for R.P.D.
Can be used in presence of saliva
Hydrophilic
Pleasant taste and smell
Nontoxic, nonstaining & inexpensive

7. Can be disinfected with 2% Gluteraldehyde
Should be stored in 100% moisture & poured within
1 Hour
Low tear strength
Surface details - less than elastomeric impression
materials
Dimensional stability – less than elastomeric
impression materials

8. POLYSULFIDE IMPRESSION MATERIALS
High tear strength
Long working and setting time (8 to 10 minutes)
Can be disinfected
Cast poured will have smoother texture & will be
harder as they do not retard or etch the surface of
the setting stone
Should have a uniform thickness that does not
exceed 3mm

9. Medium and heavy body should not be used in case
of large/multiple undercuts
Long term dimensional stability is poor due to
water loss after setting
Should be held still during the impression making
procedure
Allow to rebound for 7 to 15 minutes after removal
from mouth and pour immediately
Unpleasant odor & Stains clothes

10. POLYETHER IMPRESSION MATERIALS
Good surface details
Hydrophilic – good wettability for easy cast forming
Shorter working and setting time
Flow characteristics and flow - lowest among others
Stiffness – cast breakage of while removal from tray

11. Unpleasant taste
Absorbs water
Cannot be immersed in disinfecting solutions
Pour within 2 hours for better results

12. CONDENSATION SILICONES
Moderate working time (5 to 7 minutes)
Pleasant odor
Good tear strength
Excellent recovery from deformation
Can be disinfected with disinfecting solutions without
any alternation in accuracy
Hydrophobic
Ideally pored within 1 hour

13. ADDITION SILICONES
Most accurate among elastic
impression materials
Low polymerization shrinkage &
distortion
Fast recovery from distortion
Good tear strength
Working time – 3 to 5 minutes

14. Both hydrophilic & hydrophobic forms are available
Available in automixing devices
Pouring can be delayed up to 1 week
Stable in sterilizing solutions
Sulfur in latex gloves – retards the setting reaction

15. IMPRESSION OF PARTIALLY
EDENTULOUS ARCH
Elastic impression materials are used for making
impression of partially edentulous arch
This is due to the presence of undercuts in the
partially edentulous mouth

16. MATERIALS AVAILABLE FOR MAKING
IMPRESSION
Reversible hydrocolloids (agar-agar)
Irreversible hydrocolloids (Alginate)
Elastomeric impression materials

17. STEPS IN IMPRESSION MAKING
Position of patient & dentist
Tray selection
Mixing the material & loading into the tray
Impression making & removal
Inspecting, cleaning & disinfecting the impression

18. POSITION OF PATIENT & DENTIST
Dentist should stand & patient should sit upright
Occlusal plane should be parallel to the floor
MAXILLARY IMPRESSION- dentist should stand at
the right rear of the patient
MANDIBULAR IMPRESSION- dentist should stand at
the right front of the patient

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

21. CHECKING MAXILLARY TRAY SIZE
There should be a clearance of 5-7mm between the
inner flanges of the tray & facial surface of teeth &
edentulous ridge
Tray should cover the desired anatomic areas
Too large a tray may be difficult to insert & may
interfere with the coronoid process of mandible

22. CHECKING MANDIBULAR TRAY SIZE
There should be a clearance of 5-7mm between the
tray and tooth surface and ridge
If the tray extends too far in the lingually, there is a
tendency to trap the tongue or floor of the mouth.
Tray is held in the right hand
Left thumb & index fingers are used to manipulate
the right corner of the mouth

23. As the right flange of tray is rotated toward
mouth, depress the lower lip & stretch the right
corner of mouth with the left thumb & index finger

24. EXTENDING AN IMPRESSION TRAY
Some times impression
tray of adequate width
may not cover the
desired impression area
In such cases, the tray is
lengthened using
modeling wax

25. MIXING IMPRESSION MATERIAL

26. LOADING IMPRESSION TRAY
Place impression material in small amounts.
Tray should be filled in level with the flanges
Overfilling should be avoided

27. Mandibular Impression Technique
Inject some material over occlusal surface of
teeth, into vestibular areas & alveolo-lingual sulcus
Then tray is rotated into mouth & is carefully seated
The patient is asked to keep the tip of tongue in
contact with the upper surface of tray during
gelation
Maintain the position of tray by placing the
forefinger of each hand on top of tray on premolar
area & thumb under patient’s chin

29. Maxillary Impression Technique
Inject alginate into occlusal surface & vestibular areas
& wipe some amount on the palate
Tray must be centered & properly aligned & verify the
position by looking at the patient’s face from above
It should protrude straight from the center of the
mouth.
After this, the tray is seated by using fingers of both
hands over the premolar areas & stabilize the tray

31. Removal of Impression From Mouth
Clinically the initial set of alginate is determined by
loss of surface tackiness
Release seal by retracting lips & cheek
Then impression is removed by a sudden jerk

32. INSPECT THE IMPRESSION FOR DEFECTS

33. CLEAN & DISINFECT THE IMPRESSION

34. Preparation Of Custom Tray

35. Marking the outline on the cast

36. Wax spacer adaptation

37. Self Cure Acrylic

38. Apply self cure acrylic over wax spacer

39. Attaching the Handle and polishing

40. Wax spacer scraped and tray perforated

41. Secondary Impression
• Same as that for diagnostic impression.
• In this procedure paint or inject impression
material in critical areas:
Rest preparation
Hard palate
Peripheral extensions

42. SPECIAL IMPRESSION PROCEDURES

43. Anatomic and Functional
Form of Ridge

44. Anatomical form of Ridge
The anatomic form is the
surface contour of the ridge
when it is not supporting an
occlusal load

45. Functional form of Ridge
The functional form of the
residual ridge is the surface
contour of the ridge when it
is supporting a functional
load

46. SPECIAL IMPRESSION PROCEDURES
1. Physiologic or functional impression technique
Functional Relining method
Mc Lean’s and Hindel’s methods
Fluid Wax method
2. Selected Pressure technique

47. Mc LEAN’S PHYSIOLOGIC IMPRESSION
Procedure
A custom impression tray is constructed over a
preliminary cast
Functional impression of distal extension ridge is
made. Patient applies some biting force with
occlusion rims
Then an Alginate impression is made with the 1st
impression held in it’s functional position with
finger pressure

50. HINDEL’S MODIFICATION
Main difference of this with Mc Lean’s is that
impression of edentulous ridge is not made under
pressure but is an anatomic impression made at rest
with ZOE paste.
As the hydrocolloid impression was being made
finger pressure was applied through holes in the tray
to the anatomic impression.

51. Disadvantages of these methods
Constantly compressed residual ridge is prone to
excessive bone resorption.
If the clasp do not hold the partial denture, the
denture will be pushed slightly occlusally by the
tissue causing premature contacts (TISSUE
REBOUND)

52. FUNCTIONAL RELINING METHOD
Here a new surface is added into the inner, or tissue
side of the denture base
The partial denture is made from a cast made from
impression made with alginate
A space is provided by adapting a metal spacer over
the ridge on the cast before processing the denture
base.
A functional impression of the edentulous area is
made using the cast partial denture framework.

53. The patient must maintain the mouth in a partially
opened position
Border moulding is carried out.
Then a low fusing modeling plastic/green stick
compound is allowed to flow over the tissue side of
the denture base.
It is tempered in water bath & seated in patient’s
mouth.

54. To provide space for the impression
material, modeling plastic is scraped to a depth of
1mm
The modeling plastic serves a s a tray material for the
secondary impression material
The final impression is made with a Zinc Oxide
Eugenol impression paste
If undercuts are present, light bodied rubber based
impression materials can be used

56. Advantages
The amount of soft tissue displacement is controlled
by the amount of relief given to the modeling plastic
before final impression is made
Greater the relief, the less will be the tissue
displacement.
Tissue surface of metal frame work can be relined
after insertion
Disadvantage
Since open mouth technique is used it is difficult to
maintain the previous occlusal contact

57. FLUID WAX FUNCTIONAL IMPRESSION
• Make an anatomic impression of the arch using
alginate
• Fabricate a refractory cast using this impression
• Fabricate the partial denture framework over the
refractory cast

59. Draw the outline of the denture base
Cast is coated with separating medium
Wax Spacer is adapted over the crest of the
edentulous ridge

63. Framework is placed over the spacer
Auto-polymerizing resin is mixed to dough
stage and is adapted and contoured over the
framework along the length of the ridge
Borders of the tray are trimmed

65. Impression Procedure
Wax is softened at 51 ̊ to 54 ̊
Softened wax is painted on the tissue surface with a
brush
Wax is painted in excess near the border to record
the sulcus
Tray is seated and held in position
It takes at least 5 minutes for the wax to set

66. The tray is removed and the impression is examined
The wax surface that has contacted soft tissue
appears glossy and the other areas that has not
contacted the tissues will appear dull
The impression should be placed in the mouth finally
for 12 minutes

68. SELECTIVED PRESSURE IMPRESSION
More force are applied to areas that can absorb
stress without adverse response & protect that areas
that is least able to absorb force
Stress bearing areas are the buccal shelf area & the
lingual slopes of residual ridge stress bearing areas
The denture base made from this impression will be
closely adapted to & in firm contact with the tissues
in buccal shelf area

69. Custom Trays

70. The tissue surface if the tray is trimmed with burs to
provide adequate relief

72. Impression material is loaded on the prepared
special tray and inserted into the patient’s mouth
Impression is made with the patient with his mouth
open under finger pressure
Only the stress bearing areas will be compressed
during impression making

73. Materials used for Secondary Impression
Zinc Oxide Eugenol impression paste
Rubber base material

74. Altering The Master Cast
This procedure is done to obtain a ‘Hybrid Cast’
which records the edentulous areas in the functional
form and the dentulous areas in the anatomic form

83. Conclusion
• An accurate impression is vital for the success
of a cast partial denture. So proper selection
of material, impression technique and the skill
of the dentist plays a key role in the success of
the overall treatment.

84. REFERENCE
Mc Cracken’s Removable Partial Prosthodontics
Clinical Removable Partial Prosthodontics