The document discusses impression materials and procedures for removable partial dentures. It describes the different types of impression materials including reversible hydrocolloid (agar), irreversible hydrocolloid (alginate), and custom trays. The key steps for making primary impressions with alginate are also summarized, including preparing the tray, mixing and loading the impression material, and seating the tray in the mouth. Maintaining even pressure on the tray during setting is important to avoid distortions.

1. IMPRESSION MATERIALSIMPRESSION MATERIALS
ANDAND
PROCEDURES IN REMOVABLE PARTIAL DENTUREPROCEDURES IN REMOVABLE PARTIAL DENTURE
Presented by:Presented by:
Dr. Kamleshwar SinghDr. Kamleshwar Singh
BDS, MDS, ICMR-IF(Japan)BDS, MDS, ICMR-IF(Japan)
Assistant ProfessorAssistant Professor
Department of ProsthodonticsDepartment of Prosthodontics
King George’s Medical University, LucknowKing George’s Medical University, Lucknow

2. INTRODUCTIONINTRODUCTION
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

3.  An impression of partially edentulous arch
must record accurately the anatomic form
of teeth and surrounding tissues.
 Unless the cast upon which the prosthesis
is to be constructed is an exact replica of
mouth, the prosthesis can‘t be expected to
fit properly and accurate cast can be
obtained only from an accurate
impression.

4. Impression trays
A receptacle in to 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.

6. Impression trays can be classified broadly into
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.
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. Modified stock tray (individual tray)
Robert R Renner’s technique
The stock tray can be modified with
modeling composition and with wax to
create an accurately fitting tray.
This technique can be employed in class I
and class II cases.
Technique:
Softened modeling compound is placed in
the stock impression tray in such a way that
it may capture the edentulous areas of
mouth and include one or two teeth
adjacent to the space.

9. Modified stock tray (individual tray)
Robert R Renner’s technique
The stock tray can be modified with
modeling composition and with wax to
create an accurately fitting tray.
This technique can be employed in class I
and class II cases.
Technique:
Softened modeling compound is placed in
the stock impression tray in such a way that
it may capture the edentulous areas of
mouth and include one or two teeth
adjacent to the space.

10. The tray is positioned in the mouth and compound
is allowed to cool but it not permitted to harden
completely, so that it is prevented from becoming
hard when in contact with the adjacent teeth.
When it is hardened sufficiently to contour it is
removed from the mouth and thoroughly chilled.

11. The compound is trimmed so that it does not
contact the adjacent teeth and surface of
compound in the edentulous areas is scraped
to a depth of 2 - 4 mm to provide space for a
uniform layer of impression material.
In maxillary impression the compound should
cover the edentulous ridges and the palate and
should accurately fit to post dam area.

12. Modification of the tray to make it adhesive
If Impression material to be used is either
alginate or agar, we can heat surface of
compound with a flame.
An alternate method Is to paint the surface of
compound with a solvent such an chloroform to
make it tacky and then to embed cotton fibers in
it, the impression material will become enmeshed
in cotton fiber. And if rubber base material is to
be employed rubber adhesive is painted on the
compound

13. Advantages over custom tray:
1. Impression can be accomplished in one
appointment.
2. Can be used inpatient with tendency to gag.
Advantages over conventional use of stock stray:
Especially useful for mouth that is either
exceptionally large or small or the one with
anomalous contour which cannot be accurately fitted
with conventional stock tray.

14. Disadvantages: STOCK TRAY
a. The peripheral borders cannot be
accurately recorded.
b. Considerably more bulkier than a custom
tray.

15. Custom impression trays:
a. Peripheral borders can be precisely
recorded in the impression
b. Thickness of impression material can be
controlled. This is important consideration
when using rubber base type material,
which should not exceed thickness of 2-4
mm because a section thicker than this is
subject to distortion.

16. C. 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.

17. Impression MaterialsImpression Materials

18. Factors that influence the selection of
impression materials are:
 Convenience of use
 Time of manipulation and set
 Cost
 Need for special trays
 Operator training and preference

19. Impression Materials

20. Impression
Materials
Non-elastic
Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
Plaster
Compound
ZnO - Eugenol
Waxes
O’Brien Dental Materials & their Selection 1997

21. Reversible Hydrocolloid
(Agar)
• Indications
– crown and bridge
• high accuracy
• Example
– Slate Hydrocolloid (Van R)

22. Composition
• Agar
– complex
polysaccharide
• seaweed
– gelling agent
• Borax
– strength
• Potassium sulfate
– improves gypsum
surface
• Water (85%)
agar hydrocolloid (hot) agar hydrocolloid (cold)
(sol) (gel)
cool to 43 C
heat to 100 C
O’Brien Dental Materials & their Selection 1997

23. Manipulation
• Gel in tubes
– syringe and tray material

24. Manipulation
• 3 chamber conditioning unit
– (1) liquefy at 100°C for
10 minutes
• converts gel to sol
– (2) store at 65°C
– place in tray
– (3) temper at 46°C for 3 minutes
– seat tray
– cool with water at 13°C for 3 minutes
• converts sol to gel
O’Brien Dental Materials & their Selection 1997

25. Advantages
• Dimensionally accurate
• Hydrophilic
– displace moisture, blood, fluids
• Inexpensive
– after initial equipment
• No custom tray or adhesives
• Pleasant
• No mixing required
Phillip’s Science of Dental Materials 1996

26. Disadvantages
• Initial expense
– special equipment
• Material prepared in advance
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Difficult to disinfect
Phillip’s Science of Dental Materials 1996

27. Irreversible Hydrocolloid
(Alginate)
• Most widely used
impression material
• Indications
– study models
– removable fixed partial dentures
• framework
• Examples
– Jeltrate (Dentsply/Caulk)
– Coe Alginate (GC America)
Phillip’s Science of Dental Materials 1996

28. Composition
• Sodium alginate
– salt of alginic acid
• mucous extraction of
seaweed (algae)
• Calcium sulfate
– reactor
• Sodium phosphate
– retarder
• Filler
• Potassium fluoride
– improves gypsum
surface
2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O
O’Brien Dental Materials & their Selection 1997

29. Manipulation
• Weigh powder
• Powder added to water
– rubber bowl
– vacuum mixer
• Mixed for 45 sec to 1 min
• Place tray
• Remove 2 to 3 minutes
– after gelation (loss of tackiness)
Caswell JADA 1986

30. Advantages
• Inexpensive
• Easy to use
• Hydrophilic
– displace moisture, blood, fluids
• Stock trays
Phillip’s Science of Dental Materials 1996

31. Disadvantages
• Tears easily
• Dimensionally unstable
– immediate pour
– single cast
• Lower detail reproduction
– unacceptable for fixed prosthodontics
• High permanent deformation
• Difficult to disinfect
Phillip’s Science of Dental Materials 1996

32. RPD IMPRESSION Vs COMPLETE DENTURE
The complete denture impression records the
edentulous mucosa with underlying bone only,
whereas partial denture impression records not
only relative soft yielding tissues (the oral
mucosa) as well as a hard unyielding
substance (the remaining teeth).

33. 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.

34. PRIMARY IMPRESSION
Objectives:
To obtain an impression of all the standing
teeth and denture - supporting tissues of
each jaw from which study casts may be
prepared.
The purpose of the study casts are:

35. 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.

36. Checking Maxillary Tray For Correct Size
Checking Mandibular Tray for Correct Size

37. Mixing Impression Material
Alginate may be mixed by hand spatulation,
mechanical spatulation, or mechanical
spatulation under vacuum.
The objective is to obtain a smooth, bubble-
free mix of alginate. In hand spatulation a
measured amount of distilled water at
approximately 22 °C is placed in a rubber
mixing bowl The pre-weighed alginate
powder is sifted from its container into the
water.

38. The mixing should begin slowly using a
stiff, broad - bladed spatula.When the
powder is thoroughly wet, the speed of the
spatulation should be increased The
spatula should crush the material against
the sides of the bowl to ensure that the
material is completely mixed. The
spatulation should continue for a minimum
of 45 seconds.

39. The strength of the gel can be reduced to
50 % if the mixing is not complete.
Insufficient spatulation can result in failure
of the ingredients to dissolve sufficiently.
Then the chemical reaction of changing
from sol to gel will not proceed uniformly
throughout the mass of alginate. An
incompletely spatulated mix will appear
lumpy and granular and will have
numerous areas of trapped air.

40. Complete spatulation will result in a
smooth, creamy mixture. The mixing
should be completed by wiping the
alginate against the side of the bowl with
the spatula to remove any trapped air. The
most consistent method of making a
smooth, bubble- free mix is mechanical
spatulation under vacuum.

41. The pre-weighed powder is added to the
pre-measured water in the mechanical
mixing bowl .The powder is thoroughly
incorporated into water by hand
spatulation. The mix is then mechanically
spatulated under 20 pounds of vacuum for
15 seconds.

42. Longer spatulation will result in a greatly
reduced setting time of the alginate and
could affect the strength of the gel.

43. Loading the Impression Tray
Small increments of the impression material
should be placed in the tray and forced under
the rim lock. Placing too large a portion of
alginate at one time increases the possibility of
trapping air The tray should be filled to the level
with the flanges of the tray.
Overfilling should be avoided.

44. Making the Impression
The mandibular impression is made first
because it usually entails less patient
discomfort patient confidence is increased
when an impression has been
successfully completed while holding the
tray with the left hand the dentist uses the
right hand to remove the gauze pads from
the patient’s mouth.

45. The syringe is used to inject the
impression material over the occlusal
surface of the teeth and into the vestibular
and alveolingual sulcus areas. The
impression material will remain in place if
the tissues are fairly dry. A tendency for
the alginate to form a ball and not remain
where placed indicates that the tissues are
too moist and that voids are likely to be
present in the impression.

46. There is not enough time to repack the
mouth before gelation begins, so the
impression procedure should be completed.
The impression should be carefully inspected
and if voids are present in critical areas, the
impression procedure should be repeated.
Packing the mouth with more or larger gauze
pads and avoiding removal of the gauze until
ready to apply the alginate will usually
prevent this problem.

47. The layer of alginate applied with the syringe
should be 3 to 4 mm thick; If it is too thin, the
heat of the tissues of the oral cavity may
cause the material to set before the tray is
seated, resulting in a layered impression.

48. The fingers of the left hand that are
retracting the right cheeks should depress
the lower lip to provide good visibility.
When the tray is correctly lined up over
the teeth, the patient is asked to protrude
the tongue. The tray is carefully seated so
that its flanges are below the gingival
margins of the teeth.

49. The tray should not be over seated
because this could result in the cusps of
the teeth contacting the tray, causing an
inaccurate impression. Great care must be
exercised in seating the tray if the patient
has mandibular tori or other exostoses, or
the making of this impression can be a
very painful experience for the patient.

50. As the tray is being seated, the cheeks are
pulled out to prevent the trapping of buccal
tissues under the tray. The patient is
asked to keep the tip of the tongue in
contact with the upper surface of the tray
during the gelation of the impression
material.

51. The dentist must maintain the position of
the tray during the entire gelation period.
This can be accomplished most
conveniently and effectively by placing the
forefinger of each hand on the top of the
tray in the premolar area and by placing
the thumbs under the patient ‘s chin.

52. The dentist through tactile sense can maintain an
even amount of pressure on the tray even if the
patient swallows or opens or closes the mouth.
Any movement of the tray during the gelation
period will result in an inaccurate impression.
Allowing the patient or the assistant to hold the
tray or leaving the patient unattended must be
avoided.
Within 3 to 4 minutes the alginate should be set.

53. For maxillary impression, the patients is
prepared by using the rinses and placing
the gauzes pads described for making the
mandibular impression. While holding the
loaded tray with the left hand the dentist
uses the right hand to remove the gauze
pads.

54. Alginate is injected onto the occlusal
surfaces and in all vestibular areas as for
the mandibular arch. In addition, a fairly
large amount should be wiped onto the
palate. Failure to accomplish this step will
usually result in an impression with a large
void in the palatal area.

55. The loaded maxillary tray is grasped by
the thumb and forefinger of the right hand.
As the right posterior flange of the
impression tray stretches the right corner
of the mouth, the dentist ‘s left arm should
be behind the patient’s head and headrest
so that the thumb and index finger may
grasp the left corner of the mouth and
distend it slightly to allow the impression
tray to enter the mouth in a straight line.

56. No attempt should be made to seat the
tray until the tray is in its correct
anteroposterior position. Once the tray is
in the mouth, the thumb and forefinger of
the left hand should raise the upper lip to
allow the dentist to see the relationship
between the labial flange of the tray and
the anterior teeth or the residual ridge.

57. The tray must be centered and properly
aligned. This position can best be verified
by looking at the patient ‘s face from
above and observing the position of the
handle of the tray.

58. It should protrude straight from the center of
the mouth. After the proper position has
been verified the tray is seated by using the
fingers of both hands over the premolar
areas. As the tray is being seated the cheeks
must be lifted outward and upward to prevent
the buccal tissues from being trapped under
the flanges of the tray.

59. The lip must also be lifted up and out to allow
good visibility and to avoid trapping the lip
between the flanges of the tray and the anterior
teeth. Care must be taken not to over seat the
tray to avoid. contact between the tray and cusp
tips of incisal edge of the teeth.

60. The tray should be stabilized throughout
the set of the impression material by
keeping light pressure over the premolar
areas on both sides of the arch The
alginate should set in 3 to 4 minutes.

61. Effect of movement of tray:
Gelation of alginate occurs by a chemical
reaction. When mixed with water, the sodium
alginate and calcium sulfate in the powder react
to form a lattice work of fibrils of insoluble
calcium alginate. The heat of the oral tissues
accelerates the chemical reaction, causing the
alginate next to the tissues to gel first .

62. If the dentist exerts pressure or allows the
tray to move during gelation of the
remainder of the alginate, internal
stresses are created that can distort the
impression as it is removed from the
mouth.

63. Removal of Impression from Mouth:
Clinically, the initial set of alginates is determined
by a loss of surface tackiness. The impression
should be left in the mouth for an additional 2 to 3
minutes to allow the development of additional
strength. Early removal of the weak alginate may
lead to unnecessary tearing of the impression.

64. The gel strength doubles during the first 4-
minutes after initial gelation. No further
strengthening is found after that time. In
fact, Impression is left in the mouth for 5
minutes rather than the recommended 2
to 3 minutes after initial gelation exhibits
definite distortion.

65. Most alginates improve their elasticity with
time, providing a better opportunity for
accurate reproduction of undercuts.
Impressions removed too early after initial
gelation produce a rough surface of the
poured cast. These data indicate the
alginate impressions should not be removed
from the mouth for at least 2 to 3 minutes
after initial gelation.

66. There are two reliable methods of determining the
correct time for removal of the impression
1. A timer can be used to measure the 2 to 3 minute
period after initial gelation or
2. A small mound of the original mix of alginate can
be placed on a glass or metal surface; when this
alginate will fracture cleanly with finger pressure,
the impression is ready to be removed from the
mouth.

67. Impression Methods:
There are basically two dual impression
techniques. The physiologic, or functional,
impression technique records the ridge
portion by placing an occlusal load on the
impression tray as the impression is being
made.

68. For this dual impression a custom
impression tray was constructed over a
preliminary cast of the arch, a function
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.

69. The underlying s tissues will be displaced
because displacement will normally occur
under function.
The physiologic impression techniques
that discussed are as follows: Mc Lean’s
and Hindel’s methods, the functional
relining method, and the fluid wax method.

70. The selected pressure impression technique not
only equalizes the support between the abutment
teeth and the soft tissue, but has the added
advantage of directing the force to the portions of
the ridge that are most capable of withstanding
the force.
This is accomplished by providing relief in the
impression tray in selected areas and permitting
the impression to be recorded.

71. The need for physiologic impressions was
first recognized by McLean and others
They 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.

73. For the production of accurate master cast
the impression technique far out weights the
selection of the impression material.
No available knowledge of the person
making the impression material will produce
results greater than the skill and knowledge
of the person making the impression.

74. MCQSMCQS

75. 1.1. Which is true regarding maxillary residualWhich is true regarding maxillary residual
ridgeridge
a)a) Crest is cortical boneCrest is cortical bone
b)b) Crest is cancellous bone with firmCrest is cancellous bone with firm
mucosamucosa
c)c) Crest is cancellous bone without firmCrest is cancellous bone without firm
mucosamucosa
d)d) Preesure placed on the crest result inPreesure placed on the crest result in
irritation of these tissuesirritation of these tissues

76. 2. In a maxillary denture, relief must be2. In a maxillary denture, relief must be
providedprovided
a)a) Crestal regionCrestal region
b)b) Buccal slopesBuccal slopes
c)c) Palatal slopesPalatal slopes
d)d) Median palatal rapheMedian palatal raphe

77. 3. Which is correct?3. Which is correct?
a)a) AA
b)b) BB
c)c) Depends upon the residual ridgeDepends upon the residual ridge
d)d) nonenone
aa bb

78. 4. For a distal extension base, which should4. For a distal extension base, which should
be followed?be followed?
a)a) Make a functional impressionMake a functional impression
b)b) Make an anatomic impressionMake an anatomic impression
c)c) Make an anatomic impression with stressMake an anatomic impression with stress
breakersbreakers
d)d) Both a and cBoth a and c

79. 5. Functional form of the residual ridge is not5. Functional form of the residual ridge is not
recorded by which of the following means?recorded by which of the following means?
a)a) Under some loading, occlusal or fingerUnder some loading, occlusal or finger
b)b) By specially designed traysBy specially designed trays
c)c) By soft impression material, such as ZnO,By soft impression material, such as ZnO,
if the entire impressionn tray is uniformlyif the entire impressionn tray is uniformly
relievedrelieved
d)d) Maintaining the consistency of theMaintaining the consistency of the
recording mediumrecording medium

80. 6.In order to increase the amount of6.In order to increase the amount of
vertically directed forces on the residualvertically directed forces on the residual
ridgeridge
a)a) Move the rest posteriorlyMove the rest posteriorly
b)b) Move the rest anteriorlyMove the rest anteriorly
c)c) Reduce the number of restsReduce the number of rests
d)d) None is correctNone is correct

81. 7. Which is not outcome of reducing the7. Which is not outcome of reducing the
occlusal tableocclusal table
a)a) Reduces vertical and horizontal forcesReduces vertical and horizontal forces
b)b) Increases vertical and horizontal forcesIncreases vertical and horizontal forces
c)c) Reduces stress on the abutment teethReduces stress on the abutment teeth
d)d) Lessens stress on the residual ridgeLessens stress on the residual ridge

82. 8. Which is true about anatomic impression8. Which is true about anatomic impression
a)a) It is a one-stage impression method usingIt is a one-stage impression method using
elastic impression materialelastic impression material
b)b) Places more masticatory load on thePlaces more masticatory load on the
abutment teethabutment teeth
c)c) Places more masticatory loads on thePlaces more masticatory loads on the
residual ridgeresidual ridge
d)d) All of the aboveAll of the above

83. 9. To evaluate complete seating of the9. To evaluate complete seating of the
framework several types of disclosingframework several types of disclosing
media are used. Which one is wronglymedia are used. Which one is wrongly
written?written?
a)a) RougeRouge
b)b) ChloroformChloroform
c)c) Pencil correction fluidPencil correction fluid
d)d) WaxesWaxes

84. 10. Altered cast impression technique is10. Altered cast impression technique is
used inused in
a)a) Kennedy Class I maxillary residual ridgeKennedy Class I maxillary residual ridge
b)b) Kennedy Class II mandibular residualKennedy Class II mandibular residual
ridgeridge
c)c) Kennedy Class IV maxillary residual ridgeKennedy Class IV maxillary residual ridge
d)d) Kennedy Class III mandibular residualKennedy Class III mandibular residual
ridgeridge

85.  1. b1. b
 2. d2. d
 3. a3. a
 4. d4. d
 5. c5. c
 6. b6. b
 7. b7. b
 8. d8. d
 9. c9. c
 10. b10. b