Vibhor Tyagi presented on impression materials and procedures for removable partial dentures. The presentation covered classification of impression materials including rigid, thermoplastic and elastic materials. Specific elastic materials discussed included reversible and irreversible hydrocolloids, polysulfide and polyether impressions. Techniques for maxillary and mandibular impressions were outlined. Special impression procedures for edentulous ridges including functional, McLean's, Hindel's and fluid wax methods were also presented. The importance of custom trays, border molding and selective pressure techniques were emphasized for accurate impressions.

1. IMPRESSION MATERIALS
&
PROCEDURES FOR
R.P.D
PRESNTED BY :
VIBHOR TYAGI
(FINAL YEAR )

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

3.  Classification of impression materials
 Rigid materials
 Plaster of paris
 Metallic oxide plaster
 Thermoplastic materials
 Modelling plastic
 Impression waxes and natural resins

4. Elastic material
 Reversible hydrocolloid
 Irreversible hydrocolloid
 Silicone impression material
 Condensation
 Addition

5.  Indicated for diagnostic casts,orthodontic
treatment casts and master cast for R.P.D
Can be used in presence of saliva
>Hydrophilic
>Pleasant taste and smell
>Nontoxic,nonstaining &inexpensive
IRREVERSIBLE HYDROCOLLOID

6. 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
material
Dimensional stability-less than elastomeric impression
material

7. Polysulfide impression materials
• High tear strength
• Long workin and setting time(8 to 10 min)
• Can be disinfected
• Cast poured will have smoother texture & will be
harder as they do not retard or etch
the surface of setting stone
• Should have a uniform thickness that does not
exceed 3mm

8. • Medium and heavy body should not be used in case of large
multiple undercuts
• Long term dimension 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
• Unplaesant odour & stains clothes

9. Polyether impression materials
Good surface details
Hydrophilic-good wettability for easy cast forming
Shorter working and setting time
 flow characteristic and flow-lowest among others
 Stiffness -cast removal of while removal from tray

10. Unpleasant taste
Absorb water
Cannot be immersed in disinfecting solutions
Pour within 2 hours for better results

11.  Condensation silicones
 Moderate working time(5-7minutes)
 Pleasant odor
 Good tear strength
 Excellent recovery from deformation
 Can be disinfected from disinfecting solutions without any
alternation in accuracy
 Hydrophobic
 Ideally poured within 1 hour

12.  ADDITION SILICONES
• Most accurate among elastic impression
material
• Low polymerisation shrinkage and
distortion
• Fast recovery from distortion
• Good tear strength
• Working time-3 to 5 minutes

13. • Both hydrophilic an hydrophobic forms are available
in automixing devices
• Pouring can be delayed upto 1 week
• Stable in streilising solutions
• Sulphur in latex gloves-reatards the setting reaction

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

15.  MATERIALS AVAILABLE FOR MAKING IMPRESSION
 Reversible hydrocolloids (agar-agar)
Irreversible hydrocolloids (alginate)
Elastomeric impression materials

16. Steps in impression making
 Position of patient and dentist
 Tray selection
 Mixing the material &loading into the tray
 Impression making & removal
 Inspecting,cleaning &disinfecting the impression

17. Position of patient and 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 shold stand at the right front of
the patient

19. Impression tray selection
Stock trays fordentulous & partially edentulous arches
are of 3 types:
 Rimlock trays
 Perforated metal trays
 Plastic disposable trays

20. Checking maxillary tray size
There should be a clearance of 5-7 mm 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

21. Checking mandibular tray size
 There should be a clearance of 5-7 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
 As the right flange of tray is rotated toward mouth , depress the lower lip
and stretch the right corner of mouth with the left thumb and index finger

22. Extending an impression tray
o Sometimes impression tray of adequate width may not cover the
desired impression area
o In such cases,the tray is lengthened using modelling wax

23. MIXING IMPRESSION MATERIAL

24. Loading impression tray
• Place impression material in small amount
• Tray should be filled in level with the flangers
• Overfilling should be avoided

25. Mandibular impression technique
• Inject some material over occlusal surface of teeth,into vestibular
area& alveolo-lingual sulcus
• Then tray is rotated into mouth & carefully seated
• The patient is asked to keep the tip of tounge 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 & thum under patient’s chin

27. Maxillary impressIon technique
Inject alginate into occlusal surface &vestibular areas & wipe some
amount pn the palate
Tray must be centered & properly alginate and 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 & stabilise the tray

29. Removal of impression from mouth
 Clinically the initial set of alginate is determined by loss of
surface tackiness
 Release seal by retracting lips 7 cheek
 Then impression is removed by a sudden jerk

30. INSPECTTHE IMPRESSION FOR DEFECTS

31. CLEANANDDISINFECT THE IMPRESSION

32. Preparation of custom tray

33. MARKING THE OUTLINE OF THE CAST

34. WAXSPACER ADAPTATION

35. SELF CURE ACRYLIC

37. Attaching the Handle And Polishing

38. Wax spacer scraped and tray perforated

39. 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

40. SPECIAL IMPRESSION PROCEDURES

41. ANATOMIC AND FUNCTIONAL FORM
OF
RIDGE

42. ANATOMICAL FORM OF RIDGE
The anatomic form is surface contour of the
ridge when it is not supporting an occlusal load

43. 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

44. 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

45. 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.

48. HINDEL’SMODIFICATION
Main difference of this Mc leans’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

49. Disadvantage of these methods
 Constantly compressed residual ridge is prone to excessive bone resorption
 If the clasp do not hold the partial denturethe denture will be pushed slightly
occlusally by the tissue causing premature contacta(TISSUE REBOUND)

50. FUNCTIONALRELININGMETHOD
Here a new surface is added into the inner or tissue side of the denture base
The partial denture is made fro a cast made from impression made with alginate
A space is provide by adapting a metal spacer over the ridge on
the cast before processing the denture base
A functional impression impression of the edentulous area is
made using the cast partial denture framework

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

52. • To provide space for the impression material plastic is scraped to a depth of
1mm
• The modelling plastic serves as 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 impressin material can be
used

54. Advantages
 The amount of soft tissue displacement is controlled by the amount of relief given
to modelling plastic before the 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 oocclusal contact

55. FLUIDWAX FUNCTIONAL IMPRESSION
 Make an anatomic impression of the arch using aliginate
 Fabricate a refractory cast using alginate
 Fabricate the partial denture framework over the
refractory cast

57.  Draw the outline of the denture base
 Cast is coated with separating medium
 Wax spacer is adapted over the crest of the edentulous ridge

60.  Framework is placed over the spacer
 Auto-polymerisation 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

62. IMPRESSIONPROCEDURE
• 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 5min for the wax to set

63. • The tray is removed and the impression is examined
• The wax surface that has contracted soft tissue appers 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 min

65. SELECTIVEDPRESSURE 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 and lingual slopes pf residual ridge
stress
bearing areas
 The denture base made from this impression will be closely adapted & in firm
contact with tissues in buccal shelf area

66. CUSTOM TRAYS

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

69.  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 the impression
making

70. Materials used for secondary impression
Zinc oxide eugenol impression Paste
Rubber base material

71. 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

77. Conclusion
An accurate impression is vital for the success of a cast partial denture.
So proper selection of material , impression technique and the skills of
the dentist plays a key role in the success of the overall treatment
REFERENCE:
• Mc Cracken’s R.P.D
• Stewart textbook of RPD
• Nallaswami textbook of
prosthodontics
• www.google.co.in

78. THANK YOU
PRESENTED BY :
VIBHOR TYAGI (FINAL YEAR)