The document discusses impression techniques for complete dentures. It defines key terms like impression, complete denture impression, and preliminary impression. It explains the objectives of impression making including retention, stability, support, esthetics, and preservation of remaining structures. It also covers different classification systems for impressions based on theories, materials used, technique, purpose, and tray type. Specific impression techniques like open mouth, closed mouth, and selective pressure are described.

1. IMPRESSION TECHNIQUES IN
COMPLETE DENTURE
Presented by:
AKANKSHA ARYA

2. CONTENTS
• INTRODUCTION
• DEFINITIONS
• PRINCIPLES OF IMPRESSION MAKING
• CLASSIFICATION OF IMPRESSIONS
• IMPRESSION TECHNIQUES
• IMPRESSION PROCEDURES
• IMPRESSION TECHNIQUES IN COMPROMISED
SITUATIONS
• SUMMARY
• BIBLIOGRAPHY.

3. INTRODUCTION
IMPRESSION
A negative replica or copy in reverse of the surface of
an object .
– gpt 8
• An impression can also be defined as an imprint of
the teeth and adjacent structures for use in dentistry.
- gpt 4

4. • COMPLETE DENTURE IMPRESSION
A complete denture impression is a negative registration
of the entire denture bearing, stabilizing and border seal
areas present in the edentulous mouth
• PRELIMINARY IMPRESSION
A preliminary impression is an impression made for the
purpose of diagnosis or for the construction of a tray

5. BASIC REQUIREMENTS FOR
IMPRESSION MAKING
• Knowledge of Basic anatomy
• Knowledge of basic reliable technique
• Knowledge and understanding of impression
materials
• Skill
• Patient management

6. OBJECTIVES OF IMPRESSION
MAKING
1) RETENTION
2) STABILITY
3) SUPPORT
4) ESTHETICS
5) PRESERVATION OF REMAINING
STRUCTURES
6

7. RETENTION
Retention is defined as the ability of denture to resist
the displacement against vertical forces
Retention resists the adhesiveness of food, the force
of gravity, & the forces associated with the opening
of jaws.
Retention begins with the impression. It depends
upon factors that produce attachment of the denture
to the mucosa.

8. Factors affecting Retention
Anatomical factors
 Physiological factors
 Physical factors
 Mechanical factors
 Muscular factors
8

9. Factors affecting Retention
Anatomical factors
 Size of the denture bearing area
 Quality of the denture bearing area.
9

10. Factors affecting Retention
Physiological factors
 Saliva and its quality
10

11. Factors affecting Retention
Physical factors
 Adhesion
 Cohesion
 Interfacial surface tension
 Capallarity and capillary attraction
 Atmospheric pressure and peripheral seal
11

12. Adhesion :-
It is the physical attraction of unlike molecules
• It acts when saliva sticks to the denture base & to
the mucous membrane of basal seat .

13. • Adhesion is achievied by ionic forces between
charged salivary glycoproteins & surface epithelium
or acrylic resin.
• Quality of adhesion depends on :-
Close
adaption Size of
of denture Type of
denture bearing saliva
area

14. • The most adhesive saliva is thin serous but contains
some mucous components.
• Thick & ropy saliva is very adhesive but tends to build
up so that it is too thick in palatal area & interferes
with oral adaptation .
• In this situation patient should rinse out the ropy
saliva every two to three hours

15. • The amount of retention provided by adhesion is
directly proportional to the area covered by denture.
• Mandibular dentures cover less surface area than
maxillary prosthesis & therefore are subject to a
lower magnitude of adhesive retentive forces.
• Similarly patients with small jaws or very flat alveolar
ridges cannot expect retention to be as great as can
patients with large jaws or prominent alveoli.

16. Cohesion:-it is the physical attraction of like molecules
for each other .
• it occurs within the layer of fluid (usually saliva ) that
is present between the denture base & the mucosa.

17. • Normal saliva is not very cohesive , therefore most of
the retentive forces of denture –mucosa interface
comes from adhesive & interfacial surface tension
factors.

18. Interfacial surface tension :-it is the resistance to
separation of two parallel surfaces that is imparted
by a film of liquid between them .
• It is dependent on the ability of the fluid to wet
the rigid surrounding material .

19. • If the surrounding material has low surface tension ,
as oral mucosa does ,fluid will maximize its contact
with the material, thereby wetting it readily &
spreading out in a thin film.
• If the material has high surface tension ,fluid will
minimize its contact with the material , resulting in
formation of beads on the material surface.

20. • All denture base material have higher surface tension
than oral mucosa ,but once coated by salivary pellicle
,their surface tension is reduced ,which promotes
maximizing the surface area between liquid & base.
• Role of surface tension is through capillary attraction
or capillarity.
• When the adaptation of denture base to mucosa is
sufficiently close ,the space filled with a thin film of
saliva act like a capillary tube in that the liquid seeks
to increase its contact with both denture & mucosal
surface.

21. • It plays a major role in retention of maxillary denture.
It is totally dependent on presence of air at the
margin of liquid & solid contact (liquid air interface).
• As there is excess saliva along the lower border of
mandibular denture, Surface tension is lost in
mandibular denture due to loss of liquid air interface
at denture border .

22.  Mucostatics dismiss adhesion and cohesion as
factors in retention, the entire phenomenon being
attributed to interfacial surface tension.
 But an analysis has proved that if it was not for the
forces of adhesion and cohesion, the forces of
interfacial surface tension wont exist. Attachment of a
denture is possible because both tissue and denture
base material can become wet which means its
molecule will adhere to water molecules.

23. Oral & facial musculature :-supplement retentive forces
, provided :-
a)Teeth are positioned in “neutral zone “between the
cheeks & tongue
b)The polished surface of the denture are properly
shaped.
• If the buccal flange of maxillary denture slope up &
out of occlusal surface of teeth & the buccal flange of
mandibular denture slope down & out from the
occlusal plane, the contraction of buccinator will
tend to retain both denture on basal seat.

24. Atmospheric pressure:-
• Act to resist dislodging forces applied to the denture
,if the denture have an effective seal around their
borders.
• Retention due to atmospheric pressure is directly
proportional to the area covered by the denture
base.

25. In function, atmospheric pressure is superior to
interfacial surface tension as a retentive force, for
forces horizontal as well as parallel to the mean of
mucosal plane are resisted.
Interfacial surface tension will resist only forces
perpendicular to the axis of surface tension forces.

26. Factors affecting Retention
Mechanical factors
 Undercuts
 Retentive springs
 Magnetic forces
 Denture adhesive
 Suction chambers and
suction discs
26

27. Factors affecting Retention
Muscular factors
The muscles apply supplementary retentive
forces on the denture.
It is most effective in the neutral zone.
27

28. STABILITY
The quality of a denture to be firm, steady, or
constant, to resist displacement by functional
stresses and not to be subject to change of position
when force is applied. It is the ability of the denture
to withstand horizontal forces.
28

29. Factors Affecting Stability
 Vertical height of the residual ridge.
 Quality of soft tissue covering the ridge.
 Occlusal plane
 Quality of the impression.
 Teeth arrangement.
 Contour of the polished surfaces.
29

30. SUPPORT
• It is the resistance to vertical forces of mastication &
to occlusal or other forces applied in a direction
toward the basal seat .
• When the natural teeth are missing ,the alveolar
ridge & their covering of mucosal tissue become the
supporting elements.

31. • Unfortunately , they were never meant to endure the
forces of mastication & other constant occlusal
pressure that result from swallowing , clenching ,or
bruxing.
• To make the best of bad situation , it is necessary to
enhance the available support by utilizing maximum
coverage of all usable ridge bearing areas.

32. Areas of support are divided into:-
secondary
pimary
slight

33. Primary support area:- area of edentulous ridge that
are at right angle to occlusal forces & usually do not
resorb easily .
• Maxillary:-
a)posterior ridge
b) flat areas of the palate
• Mandibular:-
a)buccal shelf area
b)Posterior ridge
c)pear shaped pad

34. Secondary supporting area:- area of edentulous ridge
that are greater than at right angle to occlusal forces
; also the area of dentulous ridge that are at right
angle to occlusal forces but tend to resorb under
load.
• Maxillary :- anterior ridge ,rugae & all ridge slopes
• Mandibular:- anterior ridge & all ridge slopes

35. ESTHETICS
 The thickness of the denture flanges is one of the
important factors that govern esthetics.
 Thicker denture flanges are preferred in long-term
edentulous patients to give required labial fullness.
 Impression should perfectly reproduce the width and
height of the entire sulcus for the proper fabrication of
the flanges.
35

36. PRESERVATION OF REMAINING STRUCTURES
 De Van (1952) stated that, “the preservation of that
which remains is of utmost importance and not the
meticulous replacement of that which has been lost.
 Impressions should record the details of the basal
seat and peripheral structures in an appropriate form
to prevent injury to the oral tissues.
36

37. IMPRESSIONS

38. CLASSIFICATION
Depending
on the
theories of
impression
making.
Depending Depending
on the on the
material used technique
classification
Depending
on the Depending
purpose of on the tray
the type
impression

39. Depending on theories of impression making
Mucostatic
Mucocompressive
Selective pressure
39

40. Mucostatic or Passive Impression
 First proposed by Richardson and later popularised by
Harry Page.
 The impression is made with the oral mucous
membrane and the jaws in a normal, relaxed condition.
Border moulding is not done here.
 The impression is made with an oversized tray.
40

41.  Impression material of choice is impression plaster.
 Retention is mainly due to interfacial surface tension.
The mucostatic technique results in a denture, which
is closely adapted to the mucosa of the denture-
bearing area but has poor peripheral seal.

42. Mucocompressive Impression
(Carole Jones)
 Records the oral tissues in a functional and displaced form.
The materials used for this technique include impression
compound, waxes and soft liners.
 The oral soft tissues are resilient and thus tend to return to
their anatomical position once the forces are relieved.
Dentures made by this technique tend to get displaced due to
the tissue rebound at rest. During function, the constant
pressure exerted onto the soft tissues limit the blood
circulation leading to residual ridge resorption.
42

43. Selective Pressure Impression (Boucher)
 In this technique, the impression is made to extend over as
much denture-bearing area as possible without interfering
with the limiting structures at function and rest.
 The selective pressure technique makes it possible to confine
the forces acting on the denture to the stress-bearing areas.
This is achieved through the design of the special tray in
which the non stress-bearing areas are relieved and the
stress-bearing areas are allowed to come in contact with the
tray.
43

44. Depending on the technique
Open-
mouth
Closed-
mouth
44

45. Open mouth impressions
The open mouth impression is built in a tray which carries
the impression material of choice into the desired
contact with the supporting tissues and into an
approximate relation to the peripheral tissues when the
mouth is opened and without applied pressure.
The rationale behind this method is that the dentures do
not dislodge when subjected to biting force.

46. The open mouth methods provide clearance for the
tissues that are pulled over the edges of the
dentures as in function of speech.
It develops a contour of impression surface which is
in harmony with the relaxed supporting tissues, and
which may be out of perfect adaptation with these
tissues when the denture is subjected to occlusal
loading.

47. Closed mouth impression technique
These require wax occlusal rims to be fabricated on
the preliminary cast .
The patient is made to close on these rims and a
generous clearance is made for the various frenula so
that the patient can manipulate his tissues by
closing, grimacing, sucking and swallowing to form
peripheral borders.

48. Depending on the tray type
Stock tray
Custom
tray
48

49. Type of tray
Some dentists use a stock tray and an impression
material such as alginate , impression plaster or
impression compound is used .However such
impressions are generally overextended and serve as
primary impressions.

50. Edentulous stock trays

51. On casts made from these primary impressions,
special/custom trays are fabricated. The tray is tried
in the mouth and modified and the final impressions
are made using zinc oxide eugenol or other such
materials.

52. Depending on the purpose of the
impression
Diagnostic
Secondary Primary
52

53. Diagnostic Impression
 The negative replica of the oral tissues used to prepare a
diagnostic cast.
 Used for study purposes like measuring the undercuts,
locating the path of insertion.
 Is made as a part of treatment plan and to estimate the
amount of pre-prosthetic surgery.
 Articulate the casts on tentative jaw relation and evaluate
the inter-arch space.
53

54. Primary Impression
(PRELIMINARY IMPRESSION)
 An impression made for the purpose of diagnosis or for the
construction of a tray.
 There should be at least 5mm clearance between the
stock tray and the ridge.
 The tray should extend over hamular notch and maxillary
tuberosity. Mandibular tray should cover retromolar pad.
 Tray can be extended using modelling wax.
Impression compound, Alginate, Impression plaster
54

55. Secondary Impression
(WASH IMPRESSION)
Involve:
 Fabriction of custom tray.
 Border molding.
 Developing the posterior palatal seal.
 Making the wash impression.
55

56. Depending on the material used
Reversible
hydrocolloid
impression.
Irreversible
hydrocolloid
impression.
Modeling
plastic
impression.
Plaster
impression.
Wax
impression.
Silicone
impression.
Thiokol rubber
impression.
(Polysulphide) 56

57. IMPRESSION TECHNIQUES

58. Impression techniques may be classified
depending on:
a) Amount of pressure used
1. Pressure technique
2. Minimal pressure technique
3. Selective pressure technique
b) Based on the position of the mouth while making
impression
1. Open mouth
2. Close mouth
c) Based on the method of manipulation for border
molding.
1. Hand manipulation
2. Functional movements

59. Pressure theory or mucocompressive
theory:
• This theory was proposed on the assumption that
tissues recorded under functional pressure provided
better support and retention for the denture.
• Greene in 1896 gave this concept

60. Primary impression made with impression
compound
Special tray made using shellac base plate.
Second Impression is made in this tray using
compound
Bite rims with uniform occlusal surfaces are then
made.
Areas to be relieved are softened and the
impression is inserted in mouth and held under
biting pressure for one or two minutes.
Borders are molded by asking the patient to
perform functional movements.

61. Demerits of the theory
1. Excess pressure could lead to increase alveolar
bone resorption.
2. Excess pressure was often applied to the peripheral
tissues and the palate.
3. Dentures which fit well during mastication tend to
rebound when the tissue resume their normal
resting state.
4. Pressure on sharp bony ridges results in pain.

62. Applied aspects:
• The technique tells that border tissues are recorded
in their functional positions and denture cannot be
dislodged during functional movements of jaws.
• The pressure applied is more and directed towards
the palate and peripheral tissues. So the retention
will be for short time and will be lost as soon as the
bone undergoes resorption.
• Usually this technique is used for preliminary
impression making as it gives a positive peripheral
seal and tissues are recorded in function. Amount of
pressure applied is for short duration and the areas
can be relieved during the final impression.

63. Minimal pressure or mucostatic theory –
The main advantage of this technique is its high regard
for tissue health & preservation.
• 1946 Page gave the concept of mucostatic based on
Pascal’s law.

64. Technique
• A compound impression is made.
• A baseplate wax space is adapted.
• A special tray is adapted over the wax spacer.
• Spacer is removed and an impression is made with a
free flowing material with little pressure.
• Escape holes are made for relief.

65. Demerits
• The short denture borders are readily accessible to the
tongue which might provoke irritation.
• The lack of border molding reduces effective peripheral
seal.
• The short flanges may reduce support for the face.
• The shorter flanges prevent the wider distribution of
masticatory stresses.
• The shorter flange would mean less lateral stability.

66. Applied aspect:
• The technique holds good in the sense it helps in
preservation of tissue health.
• In practice with short flanges the oral musculature is non
supported and stresses are not widely distributed.
• Food can slip beneath the denture and tongue can
readily access the denture borders.
• This technique is useful in impressions of flabby and
sharp or thin ridges.

67. Selective pressure theory
• Advocated by Boucher in 1950 it combines the
principles of both pressure and minimal pressure
technique.
• In this technique idea of tissue preservation is
combined with mechanical factor of achieving
retention, through minimum pressure which is
within physiologic limits of tissue tolerance.
• This theory is based on a thorough understanding
of the anatomy and physiology of basal seat and
surrounding areas.

68. Demerits
• Some feel that It is impossible to record areas with
varying pressure.
• Some areas still recorded under functional load, the
dentures still faces the potential danger of
rebounding and loosing retention.

69. Applied aspect:
• Inspite of some of its apparent drawbacks all the
impression techniques based on the selective
pressure technique are still popular.
• Final impressions using this technique are made
where relief areas are provided and pressure is
distributed on the stress bearing areas.

70. Open mouth technique
Made with tray held by dentist and mouth open
Muscle movements may be emphasized and
can be seen by the operator

71. Closed mouth technique
The rationale behind this technique is that the
supporting tissues are recorded in a functional
relationship.
Requires occlusal rims to be made
Border molding done and final impressions made

72. Hand manipulation
Dentist uses hand manipulation for movements of
lips and cheeks
Functional movements
Patient makes functional movements such as
sucking, swallowing, licking or grinning

73. STEPS IN MAKING AN IMPRESSION
Preliminary examination of the patient
Seating the patient
Selection of the tray
Selection of the material
Making impression-primary
border molding
secondary

74. Preliminary examination of the patient
• A complete case history and thorough clinical
examination is done.
• Factors that can complicate impression making are
identified.
• Patient education.

75. Position of the operator for
Seating of the patient maxillary impression
Position of the operator for
mandibular impression

76. Selection of tray:
• The beginning of good impression starts with the
selection of the correct stock tray.
• Tray is a device that is used to carry, confine and
control impression material while making an
impression.
• The space available in the mouth for upper
impression is studied carefully by observation of the
width and height of the vestibular spaces with mouth
partly open.
• And in the lower the general form and size of basal
seat is studied.

78. IMPRESSION PROCEDURES
• First technique:- border- molded special tray:
 Preliminary impression:
 An edentulous stock metal tray that is approximately 6mm larger
than the outside surface of the residual ridge is selected.
 The borders of the stock tray are lined with a strip of soft boxing
wax so a rim is created to help confine the alginate material.
 The objective is to obtain a preliminary impression that is slightly
overextended around the borders.

79.  The tissue surface and borders of the tray, including
the rim of wax, are painted with an adhesive
material.
 The loaded tray is positioned in the mouth.
 The tray is left in the mouth for 1 minute after the
initial set. The impression is removed and inspected
to ensure all basal seat is included.
 The impression is poured in artificial stone.

80. Primary impression making
• With alginate (Maxillary)

81. (Mandibular impression with alginate)

82.  A wax spacer is placed within the outlined border to
provide space in the tray for final impression
material.
 A custom tray made using self- curing acrylic resin.
• Preparing the final impression tray:
 Border molding is the process by which the shape of
the borders of the tray is made to conform accurately
to the contours of the buccal and labial vestibules.
 It begins with manipulation of the border tissues
against a moldable impression material that is
properly supported and controlled by tray.

83. Border molding

84. Mandibular border molding

85.  Stick modeling compound is added in sections to the
shortened borders of the resin tray and molded to a
form that will be in harmony with the physiologic
action of the limiting anatomic structures.
 The final impression material is mixed according to
manufacturer’s directions and uniformly distributed
within the tray.

86. Secondary impression

87. Mandibular secondary impression

88. • Second technique:- one- step border- molded tray:
• A material that will allow simultaneous molding of all
borders has two general advantages:
1. The number of insertions of the tray for maxillary
and mandibular border molding is reduced.
2. Developing all borders simultaneously avoids
propagation of errors caused by a mistake in one
section affecting the border contours in another.

89. • The requirements of such a material are that it
should:
1. Have sufficient body to allow it to remain in
position on the borders during loading of the tray.
2. Allow some preshaping of the form of the borders
without adhering to the fingers.
3. Have a setting time of 3 to 5 min
4. Retain adequate flow while the tray is seated in the
mouth
5. Allow finger placement of the material into
deficient parts after the tray is seated

90. • Not cause excessive displacement of the tissues of
the vestibule.
• Be readily trimmed & shaped so excess material can
be carved & the borders shaped before the final
impression is made.

91. • The following procedure utilizes polyether
impression materials for border molding.
1. Place adhesive for polyether impressions on the
borders of tray.
2. Express a 3- inch strip of polyether material from
large tube onto a mixing pad. Next express 2.5
inches of catalyst to provide sufficient working time
to complete border molding.
3. Thoroughly mix material for 30 to 45 seconds using
a metal spatula.

92. 4. Position the polyether material on the borders, making
certain that a minimum width of 6 mm exists on inner
portion.
5. Quickly preshape material to proper contours with
fingers moistened in cold water
6. Place the impression tray in the mouth .
7. Inspect all borders to be sure that impression material is
present in the vestibule
8. Border molding is done

93. 9. Remove tray when impression material is set.
10. Examine border molding to determine that it is
adequate.

94. • Preparing the tray to secure the final
impression:
1. Reduce the borders on the tray that protrude
through the polyether.
2. Remove any material that extends internally within
the tray more than 6mm.
3. Remove the relief wax.
4. Reduce the thickness of labial flange to
approximately 2.5 to 3mm from one buccal frenum
to another.
5. Make the final impression in silicone, metallic oxide
paste, or rubber base.

95. • Third technique:- custom tray design based on
previously worn denture:
1. The denture is treated like a standard impression,
and a stone cast is poured.
2. An acrylic resin tray is made on the cast over a wax
spacer that is outlined just short of the borders of
the impression.
3. The tray is tried in the mouth and checked for
overextensions.
4. The spacer is removed, relief holes prepared, an
adhesive is applied and an impression is made in
the preferred material.