Impression making

1. THEORIES,
OBJECTIVES AND
PRINCIPLES OF
IMPRESSION MAKI NG
JIBI SARA VARGHESE
1st year PG

2. CONTENTS
DEFINITIONS
PRINCIPLES OF IMPRESSION MAKING
OBJECTIVES OF IMPRESSION MAKING
THEORIES OF IMPRESSION MAKING
CONCLUSION
REFERENCES

3. DEFINITIONS
IMPRESSION: A NEGATIVE LIKENESS OR COPY IN REVERSE OF THE SURFACE OF AN
OBJECT.
DENTAL IMPRESSION: A NEGATIVE IMPRINT OF AN ORAL STRUCTURE USED TO
PRODUCE A POSITIVE REPLICA OF THE STRUCTURE TO BE USED AS A PERMANENT
RECORD OR IN THE PRODUCTION OF A DENTAL RESTORATION OR PROSTHESIS.
COMPLETE DENTURE: A REMOVABLE DENTAL PROSTHESIS THAT REPLACES THE
ENTIRE DENTITIONAND ASSOCIATED STRUCTURES OF THE MAXILLAE OR MANDIBLE
Glossary of Prosthodontic terms, 8th edition

4. PRINCIPLES OF IMPRESSION MAKING
CONCEPTS TO BE FOLLOWED FOR SUCCESSFUL IMPRESION ARE:
1 The oral tissues must be healthy
2Impression should include all of the basal seat within the limits of health and function of
the supporting and limiting tissues.
3The borders must be in harmony with the anatomical and physiological limitation of the
oral structures.
4 Physiological type of border moulding should be performed.
5 Sufficient space should be provided within the impression tray for the selected
impression material.

5. 6Impression must be removed from the mouth without
damaging the mucosa.
7Selective pressure should be applied on the basal seat
during impression making
8-A guiding mechanism should be provided for correct
positioning of the tray within the mouth.
9The tray and impression material should be made of
dimensionally stable materials.
10The external shape of the impression should be similar
to the external form of complete denture

6. OBJECTIVES OF IMPRESSION MAKING
• In an impression technique for complete dentures, the procedures
must strive for five primary objectives.)-: PRESS
1 PRESERVATION
2 RETENTION
3 ESTHETICS
4 STABILITY
5 SUPPORT

7. PRESERVATION-
M. M. De Van’s dictum, “It is more important to preserve what already exists than to replace what
is missing” has never been challenged or disapproved.
Preservation of the remaining residual ridges is one objective. It is physiologically accepted that
with the loss of stimulation of the natural teeth the alveolar ridge will atrophy or resorb. This
process varies in individual.
This process can be hastened or retarded by local factors.
Pressure in the impression technique is reflected as pressure in the denture base and results in
soft tissue damage and bone resorption.
– Syllabus of Complete denture, Charles M. Heartwell, 4th edition
Hence, in impression making, this rule is followed by not using heavy pressure and by not covering
as much of the supporting areas as possible to minimize the possibility of the soft tissue abuse and
bone resorption.
– Bernard Levin, Impressions for Complete Dentures

8. • Retention
Definition:). That quality inherent in the dental prosthesis acting to
resist the forces of dislodgment along the path of placement (GPT8)
•It is related to forces that resist the forces of gravity, adhesiveness of
food and opening of the jaws.
• The process of obtaining denture retention begins with impression
making. Factors that attach the denture to the mucosa affect retention.

9. Factors affecting retention
1. Anatomical factors
(i) ) Size of the denture-bearing area
• Retention increases with increase in the size of the denture -bearing area .
• The average size of the maxillary denture-bearing area is around 24 cm2 and that of
the mandibular denture- bearing area is around 14 cm2.
(ii) Tissue displaceability
• The displaceability of the tissues affects the retention of the denture.
• Tissues displaced during impression making will rebound during function and lead to loss
of retention.

10. (A)Maxillary edentulous ridge and (B) mandibular edentulous ridge.
Both ridges are well formed but size of denture-bearing area is smaller in the lower jaw.

11. 2. Physiological factors
• The amount and consistency of saliva affects retention.
• Thin, watery saliva affords best retention.
• Excessive saliva that is thick and ropy accumulates between the tissue
surface of the denture and the palate leading to loss of retention.
• The absence of saliva (xerostomia) affects retention and can also cause
irritation and soreness of the denture- bearing tissues

12. 3. Physical factors
(i) Adhesion
•Adhesion is defined as the physical attraction of unlike molecules to one
another.
•Saliva is present in between the denture base and the mucosa, and its contact
with both these surfaces creates adhesion. It is achieved by ionic forces
between the salivary glycoproteins and surface epithelium or acrylic resin .
• It depends on:
○ Close adaptation of denture.
○ Size of denture-bearing area.
○ Type of saliva.
Adhesion also takes place directly between the denture base
and mucosa in case of xerostomia (lack of saliva), but this leads
to ulcerations and abrasions in the mucosa.

13. (ii) Cohesion
Cohesion is defined as the physical attraction of like molecules to one another.
• This occurs within the film of saliva and aids in retention
•Normal saliva is not very cohesive; hence, retention from mucosa interface is
more dependent on adhesion and surface tension.
• As viscosity of saliva increases, greater is the cohesion but very thick, mucous
saliva can physically push the denture out, resulting in loss of retention.
Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition.

14. (iii)Interfacial surface tension
defined as the tension or resistance to separation possessed by a film of liquid
between two well adapted parallel surfaces.
• It is dependent on the ability of the liquid to ‘wet’ the surfaces. The
‘wettability’ of the fluid is inversely proportional to the surface tension of the
surfaces.
•These forces are found within the thin film of saliva that is present between
the denture base and tissues. Saliva ‘wets’ the denture surface, to aid in
retention. The oral mucosa has low surface tension and hence the saliva ‘wets’
it well, spreading out in a thin film.
Denture base materials demonstrate less wettability than oral mucosa, with
heat- cured resins showing better wetting than autopolymerized resins. But
once coated with salivary pellicle, the surface tension of the denture base
material decreases and contact increases. This is similar to trying to separate
two glass plates with intervening liquid between them

15. Interfacial surface tension acts only when the two glass plates are
pulled apart. The cohesive forces between the molecules of the
liquid, (intermolecular
attraction) and the adhesive forces between the plate and the liquid
will result in preventing the plates to move away from each other
forming a concave meniscus

16. • Interfacial surface tension is also dependent on existence of a l iquid/ air interface at
the boundary of the liquid/ solid contact. If two plates with a fluid between them are
immersed in the same fluid, then there is no interfacial surface tension and they can
be separated easily. The external boundary of the mandibular denture is always
filled (immersed) in saliva, thereby reducing the surface tension effect .Hence,
interfacial surface tension plays a significant role in retention of only the maxillary
denture.

17. (iv) Capillarity
That quality or state, which because of surface tension causes elevation or
depression of the surface of a liquid that is in contact with a solid.
• Capillarity causes the thin film of saliva to rise and increase its contact with
the denture base and the mucosa.
• Close adaptation of the denture base to mucosa is important for capillarity
to provide effective retention
Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition.

18. (v) Atmospheric pressure
•This can help resist dislodging forces if the dentures have aneffective border
seal. Peripheral seal or border seal is defined as the contact of the denture
border with the underlying or adjacent tissues to prevent the passage of air or
other substances (GPT8).
•When a force is exerted perpendicular to and away from the basal seat of a
denture which is properly extended and fully seated, pressure between the
prosthesis and mucosa drops below the ambient pressure, resisting
displacement. This has been previously referred to as ‘suction’
•Retention due to atmospheric pressure is proportional to the denture base
area. Proper border moulding is essential for this retention mechanism to
function

19. When dislodging forces act on a properly
extended denture, pressure between the prosthesis and
mucosa drops, contributing to retention.

20. (vi) Gravity
This natural force can aid in the retention of the mandibular denture
especially when there is more weight and other retentive forces and
factors are marginal
Gravitational force helps seat the mandibular
denture (a), while it acts against the maxillary denture (b).

21. Undercuts on one side can help in retention, but bilateral undercuts would
require surgical correction as they can interfere with denture insertion.
Intramucosal magnets can be placed for retention in highly
resorbed ridges.
Denture adhesives can be used where retention is needed, and should be
coated on tissue surfaces before wearing the dentures.
Suction chambers creates areas of negative pressure, which help in
retention (these are avoided now, as they are found to creating palatal
hyperplasia).
retentive springs like the adam’s clasp, circumferential clasps, etc
ainds in retention in partially edentulous cases
4.MECHANICAL FACTORS
Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition.

22. 5. Muscular factors
The oral and facial musculature and tongue supply supplementary retentive
forces. For this to be effective:
• Teeth must be positioned in the ‘neutral zone’ between the tongue and cheeks.
• Polished surfaces of the dentures should be properly contoured.
• Denture bases must be extended to cover maximum area.
• Occlusal plane must be at correct level.
– Bernard Levin, Impressions for Complete Dentures

23. Stability
Definition: The quality of a removable dental prosthesis to be firm, steady, or
constant, to resist displacement by functional horizontal or rotational stresses
(GPT-8).
• Factors affecting stability
1. Vertical height of the residual ridge
Stability deceases with loss of vertical height of the ridges
2. Quality of soft tissue covering the ridge
Flabby ridges provide poor stability.
3. Adaptation of denture to the tissues
Close adaptation of the denture to the basal seat tissues is very important to ensure
proper stability. An accurate impression is essential to achieve this.

24. 4.Occlusal plane
The occlusal plane should be oriented parallel to the ridges and
should divide the interarch space equally. Inclined occlusal planes
will promote sliding forces and cause instability
5. Teeth arrangement
•Setting teeth in ‘balanced occlusion’ and in the ‘neutral zone’ promotes stability.
6. Contour of polished surface
•The polished denture surface should be in harmony and with the functioning of oral muscles
to promote stability

25. Support
Definition: The resistance to the vertical forces of mastication, occlusal forces and
other forces applied in a direction towards the basal seat tissues.
• To provide adequate support, the denture base should cover as much denture-
bearing area as possible. This distributes the forces over a large area and is known
as snowshoe effect
Forces distributed over a large area, by
maximum extension of denture base, known as snowshoe
effect.

26. Aesthetics
• Denture border and flange thickness are dependent on the amount of
residual ridge loss and varies with each patient.
• Reducing or increasing the thickness of this area leads to poor
aesthetics.
• Border moulding ensures adequate thickness in the region.

27. • Theories of Impression Making
•Most of the impressions of the twentieth century are made with a view to functional
movement of the musculature.
• Theoretically, the impressions are so formed that the complete denture will require
no change in contour. This happens often with upper dentures but no so often with
lower dentures.
– C O M P L E TE D E N T U R E P R O S TH O D O N TI C S , J O H N J . S H A R R Y , 3 R D E D I T I O N T H E O R I E S , P R I N C I P L ES A N D O B J E C T I V ES O F
I M P R E S S I O N M A K I N G

28. • MUCOCOMPRESSIVE TECHNIQUE
The muco compressive technique was initiated by Greene Brothers.
The main objective of this technique was to attain better retention of the dentures.
The typical technique by Greene brothers was as follows .
• A preliminary impression was made in impression compound and
• a custom tray was constructed using baseplate with its periphery 1/8 th inch shorter
than the denture outline.
• With this tray another impression with compound was taken.
• Well fitting rinse with uniform occlusal surface were made and the height of the bite
adjusted against a similar bite rim on the mandibular ridge.

29. • Areas to be relieved like median raphe was softened on the impression and was
again inserted in the mouth and was held under biting pressure for one / two
minutes.
• The peripheral margins of the impression was then softened and border molding
was done by asking the patient to give various cheek and lip movement as in
whistling and smiling.
• The posterior palatal seal was obtained by swallowing movements by the patient
under biting pressure.
• The claims made by the advocates of this technique was that since border molding
was done in their functional positions, the final dentures would retain well and
cannot be dislodged during functional movements of the jaw.

30. APPLIED ASPECT
• 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

31. Advantages
• Better retention and support
Disadvantages
• Excess pressure - increase alveolar bone resorption.
• Excess pressure on peripheral tissues and the palate - transient
ischaemia.
• Tissue rebound when the tissue resume their normal resting state.
• Pressure on sharp bony ridges - pain

32. Minimal-pressure impressions
• Main point of the mucostatic principle concerned Pascal’s law, which
states that pressure on a confined liquid, will be transmitted
throughout the liquid in all directions.
• According to this concept, the mucosa, being more than 80 % water,
will react like liquid in a closed vessel and thus cannot be
compressed.
• This is not true, as tissue fluids can easily escape under the border
of a denture. Hence mucosa is not a closed vessel.
– COMPLETE DENTURE PROSTHODONTICS, JOHN J. S HARRY, 3R D EDITION THEORIES, PR IN CIPLES AN D
OBJECTIVES OF IMPR ESSION MAKING

33. A typical impression method representing this technique was as
follows.
-A compound impression was made in a suitable tray and a cast was made.
-On this base plate wax was adapted which acted as a spacer according to denture outline.
Custom tray was fabricated over this spacer.
-A soft ribbon of carding wax was applied at the posterior margin of the maxillary tray and it was
placed in the mouth under light pressure and patient was asked to do swallowing movements
inorder to obtain a posterior palatal seal.
-A small amount of impression plaster mixed into a smooth consistently was placed in the tray,
introduced in the mouth and was slowly raised to position and held with as little pressure as
possible.
-No border molding was advocated but the soft plaster was expected to mold itself to the relaxed
vestibular tissues.
-The impression was held till the impression hardened and was then removed

34. APPLIED ASPECT
The technique holds good in the sense it helps in preservation of tissue
health. In practice which 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.

35. ADVANTAGE
• High regards for the tissue health and preservation
•Good stability due to close adaptation of denture bases
DISADVANTAGE
• Less tissue coverage
• Reduced retention
• Lack of border- moulding reduces effective border seal
• Lack of border seal permits food lodgment
• Compromised aesthetics due to short denture flanges
•Tissue variations at the time of impression making and insertion may affect
the results

36. Selective Pressure Technique
•This principle is based on the belief that the mucosa over the ridge is best able
to withstand pressure, whereas that covering the midline is thin and contains very
little submucosal tissues. (Boucher, 1951 ).
• Boucher advocated that this technique combines the principles of both pressure
and non pressure procedures
– Bernard Levin, Im pres sions for C om plete D entures THEORIES, PRINCIPLES AND OBJ ECTIVES OF IMPRESSIO N MAKING

37. • A well fitting tray with a uniform clearance of about 5mm was selected and a compound
impression was obtained with little border molding done on the peripheries.
• This compound impression was separated from the metal tray and its peripheral borders were
trimmed 1 – 2 mm short.
• The base portion of the impression was then scrapped evenly to a depth of about 2mm except
in the posterior seal area where no scraping was done.
• A sufficient amount of creamy mix of plaster was spread over this impression and was placed in
the mouth with little pressure. The cheeks and lips were lightly patted from outside while the
plaster was still soft.
This procedure gave sufficient value like seal without exaggerated pressure on soft tissues.

38. Advantages
• Technique considers the physiologic functions of the tissues of the basal
seat, and therefore appears more sound and appealing.
Disadvantages
• Some feel that it is impossible to record areas with varying pressure.
• Since some areas are still recorded under functional load, the denture still
faces the potential danger of rebounding and loosing retention

39. 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 .
“ Ye s t e r d a y ’ s controversies will become to d a y ’ s reality & to d a y ’ s reality
will become tomorrow’s controversy”

40. Impression by the use of subatmospheric pressure – Milo V. Kubalek,
Bert C. Buffington (1966)
• The objective of this technique is to reduce the stress on any given tissue by
increasing the load bearing area. To realize the ideal the form of tissues must be
recorded both vertically and laterally so that all surfaces can bear an equal load and
vacustatic technique is an attempt to achieve this. When a controlled partial vacuum
is established, an impression tray specially built for the patient is maintained in the
mouth without direct mechanical support of any kind. The difference between
subatmospheric pressure within the tray and atmospheric pressure outside is all that
retained the impression in a static position. It denotes the equilibrium of forces which
results when a controlled vacuum is established

41. The mucoseal technique was stated by Pryor in 1948 which was
introduced as a variation to the mucostatic technique.
• The anterior lingual border is molded by the floor of the mouth with
the tongue in repose.
• The tray is extended horizontally backward, over the sublingual
glands towards the tongue to effect a border seal.
• Thus this technique utilizes the benefit of minimal pressure and also
provides maximum extension of denture borders and maximum
coverage of denture bearing area

42. • The selective pressure maxillary impression: A review of the techniques
and presentation of an alternate custom tray design bySanath Shetty, P. Venkat
Ratna Nag, Kamalakanth K. Shenoy
• This article reviews the various ways of achieving selective pressure as seen by
different authors and also includes a custom tray design to achieve selective
pressure, which is based on the newer concepts of the stress bearing and relieving
areas in the maxillary edentulous impression procedures

43. CONCLUSION
The perpetual preservation of what remains is more important than the meticulous replacement of
what is lost.
“Ideal impression must be in the mind of the dentist before it is in his hand. He must literally make
the impression rather than take it” - M.M. De van

44. REFERENCES
• Boucher : Prosthodontic treatment for edentulous patients
• Filler W. H. : Modified impression technique for hyperplastic alveolar ridges. J. Prosthet.
Dent., 25 : 609 -612, 1971 .
• Glossary of Prosthodontics. J. Prosthet. Dent., Edition 7th, 81 : 48 -110, 1999.
• Heartwell Charles M. : Syllabus of complete dentures.
• Luin Bernard : Impressions for complete dentures.
• Lott F. and Luin B. : Flange technique : An anatomic and physiologic approach to increase
retention, function, comfort and appearance of dentures”. J. Prosthet. Dent., 13 : 394 -413 ,
1966.
• Milo V. Kubalek and Bert C. Bufington : Impressions by the use of substathmospheric
pressure. J. Prosthet. Dent., 16 : 213 -223 , 1966 .
• Page H.H. : Mucostatics, A principle not a technique by Harry L. Page, Chicago, 1946.
• Sharry J.J. :Complete denture prosthodontics.

45. Thank you