Theories, Principles & Objectives of impression Making Of Completely Edentulous Patients

Presented By:-
Dr. Soham Prajapati,
1st Year PG,
Dept. of Prosthodontics
& Maxillofacial Prosthesis
Including Oral Implantology
29-05-14
Guided By:-
Dr. Dilip Dhamankar
Dr. Ravi Kumar C.M.
Dr. DRV Kumar
Dr. Manish Chadha
Dr. Devendra
THEORIES, PRINCIPLES AND
OBJECTIVES OF IMPRESSION
MAKING IN COMPLETELY
EDENTULOUS PATIENTS
THEORIES, PRINCIPLES AND OBJECTIVES OF
IMPRESSION MAKING

CONTENTS
• Introduction
• Definitions
• History of Complete Dentures
• Theories of Impression Making
• Principles of Impression Making
• Objectives of Impression Making
• Conclusion
• References
THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING

Introduction
• The beginning of a good denture starts with
making of a good impression, so a good
impression is a stepping stone.

• 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.
Definition
Glossary of Prosthodontic terms, 8th edition

• Complete denture is defined as a removable
dental prosthesis that replaces the entire
dentition and associated structures of the
maxillae or mandible
Definition
Glossary of Prosthodontic terms, 8th edition

History of Complete Dentures
• 1711 Matthian G. Purman introduced the use
of wax.
• 1844 Plaster of paris was first used as an
impression material.

• 1845-1899 concepts of atmospheric pressure,
maximum extension of denture bearing area,
equal distribution of pressure and close
adaptation of the denture bearing tissues
were stressed.

• 1928 Pierre Fauchard made
dentures by measuring the mouth
with compasses and cutting bone
into an approximate shape.
• 1896 Green brothers introduced
mucocompressive theory.
• 1900-1929 Concepts like Rebase
impressions, border molding and
techniques for flabby tissues were
introduced.

• 1930-1940 This era recognized the anatomy of
the denture bearing areas, and muscle physiology
as related to impression procedures. This is
evident by descriptions of border molding of
dentures. Several new impression materials were
introduced : reversible hydrocolloids, zinc oxide
eugenol and zinc oxide and oil of cloves

• 1950-1964 more emphasis on biologic factor
of impression making was given.
• 1951 Carl O Boucher introduced selective
pressure theory.

1965-1980 new techniques to manage
compromised situations were introduced.
New techniques are periodically been
formulated to overcome the drawbacks faced.

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.
– COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD
EDITION

• Impression are made with
– Definitive-pressure impressions
– Minimal-pressure impressions
– Selective-pressure impressions
• COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY, 3RD
EDITION
– Functional impression technique.
– Not discussed about definitive pressure
impressions.
– DCNA, Volume 40, January 1996.

• Because denture retention is tested most severely
during mastication, many dentist formerly considered it
essential for the tissue to remain in contact with the
denture during chewing.
• However, dentures did not fit well at rest, because of
» Tissue so distorted, tend to rebound.
» Tissues so abused will long maintain the shape that they
assumed on the day of impression.
EDITION

• Many of the proponents of this
group advocated the use of closed-
mouth techniques (Tryde et al.,
1965).
• Aside the disadvantages of pressure
impression technique mentioned
above, the closed mouth technique
do not allow adequate muscle
trimming of the periphery.
– COMPLETE DENTURE
PROSTHODONTICS, JOHN J. SHARRY,
3RD EDITION

• Very often dentures made with this technique are
over-extended and must be arbitrarily trimmed.
– COMPLETE DENTURE PROSTHODONTICS, JOHN J. SHARRY,
3RD EDITION
• Critics of this procedure point out that the dentures
are in actual contact for only a relatively short period
of time and the constant pressure, even if equal, may
overstress the tissue.
• Advocates were not always able to actually obtain
the desired pressure but tended to creat excessive
pressure.
– Bernard Levin, Impressions for Complete Dentures

• Dentures often resulted in good initial retention but
eventually bone resorption and loose dentures.

• The popularization of this techniques in the early
forties.
• Idea was not new, however for Richardson in
1896 had advocated plaster because it least
disturbed the tissues.
• Addison (1944) descirbed the so called “muco-
static impression” and attributed to Page. This
was based on theories and were not applicable in
the oral cavity.
– COMPLETE DENTURE PROSTHODONTICS, JOHN J.
SHARRY, 3RD EDITION

• 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.
SHARRY, 3RD EDITION

• According to principle of mucostatics, impression
material should record, without distortion every detail
of the mucosa so that complete denture would fit all
minute elevations and depressions.
EDITION

• So much emphasis on recording detail was placed that
even seperating medium could not be used at any point
in the procedure.
• Needless to say, the impression materials and cast
exhibited sufficient dimensional change to render
worthless the care used to obtain the minute details of
the mucosal surface.
EDITION

• Mucostatics further demanded that a metal base be
used rather than the dimensionally unstable acrylic.
• Gold, one of the most accurate metals, was by passed
in favor of a chrome alloy. Thus another minor
inaccuracy was added.
EDITION

• Most Important of all, the mucosal
typography, is not static over a 24-hour period.
• There is difference between the mucosal
contours just after rising in the morning, and
that which exists after 12 hours in the upright
position. (Stephens et al, 1966)
• So all the infinite details achieved in the
impression would be altered by the time the
denture is finished.
SHARRY, 3RD EDITION

• The adherents of the mucostatic principle considered
interfacial surface tension as the only important
retentive mechanism in complete dentures.
EDITION

• Therefore, they did not use conventional flanges.
However, Dykins (1947) recommended a short lingual
flange in order to resist lateral displacement.
EDITION

• Mucostatic principle further ignores
» The value of dissipating masticatory forces over larger
possible basal seat area.
» The form of mucostatic denture minimized the retentive
role of the musculature. (Fish, 1948)
EDITION

• Reference in literature to negative pressure impressions
(Denen, 1944), but one recognize that non pressure or
negative pressure impression techniques do not exist.
• These are semantic devices to dramatize the minimal
amount of forces desirable in making impressions.
EDITION

• Thus it attempts to record the oral tissues “at rest”.
• Requires a material of high fluidity (low viscosity).
• Thus create a denture base that models the unloaded
tissues.

– 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).
EDITION

• Boucher advocated that this technique combines the
principles of both pressure and non pressure
procedures

• The technique utilizes a preliminary compound
impression that is generously relieved over the midline
and incisive papilla areas.
• The final impression is taken in plaster, which acts as a
wash and also records the relieved areas with minimal
pressure while the ridge areas are undergoing
considerable pressure.
EDITION

• Thus, the midline and papilla sections of the denture
will not make contact with the mucosa when the
denture is not in function, but by the same token, they
will not bear heavily when the patient is chewing.
EDITION

• Points to keep in mind:-
» Most fine dentures are made with this principle.
» This technique demands firm, healthy mucosal covering
over the ridge.
» If flabby ridge exist, it is preferable to use a minimal
pressure impression.
• COMPLETE DENTURE PROSTHODONTICS, JOHN J.
SHARRY, 3RD EDITION
» This technique optimizes the stability and retention of the
prosthesis
• DCNA, Volume 40, January 1996.

– Functional Impression Technique
• This technique uses a complete denture that is
delivered, relieved on its internal aspects, and filled
with a slow setting impression material(tissue
conditioning material).
• The patient wears the prosthesis for several days,
allowing the tissues to be recorded “in function”

– Functional Impression Technique
• The completed impression then is converted to and
reline material via laboratory processing.
• This technique seeks to create a denture base that
models the functionally loaded tissues.

Principles of Impression Making.
• The concepts to be followed to get successful
impression are:-
– The oral tissues must be healthy.
– Impression should include all of the basal seat
within the limits of health and function of the
supporting and limiting tissues.

– The borders must be in harmony with the
anatomical and physiological limitation of the oral
structures.
– Physiological type of border moulding should be
performed.
– Sufficient space should be provided within the
impression tray for the selected impression
material.

– Impression must be removed from the mouth
without damaging the mucosa.
– Selective pressure should be applied on the basal
seat during impression making.
– A guiding mechanism should be provided for
correct positioning of the tray within the mouth.
– The tray and impression material should be made
of dimensionally stable materials.

– The external shape of the impression should be
similar to the external form of complete denture.

Objectives of Impression Making
• In an impression technique for complete
dentures, the procedures must strive for five
primary objectives. The objectives are:-
– Preservation
– Support
– Stability
– Esthetics
– Retention
THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING 40/100

• 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
– 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.
– Syllabus of Complete denture, Charles M. Heartwell, 4th
edition
42/100THEORIES, PRINCIPLES AND OBJECTIVES OF IMPRESSION MAKING

• Preservation
– 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.
edition

• Preservation
– 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.

• Preservation
– Other factors such as
• Occlusion
• Interocclusal distance
• Centric relation in harmony with centric occlusion are
of great importance.
edition

• Support
– Denture support is the resistance to vertical forces
of mastication and to occlusal or other forces
applied in a direction towards the basal seat.

• Support
– When the natural teeth are missing, the alveolar
ridge and their coverage of mucosal tissues
become the supporting elements.
– They were never meant to endure the forces of
mastication and other constant occlusal pressures
that result from swallowing, clenching and
bruxing.

• Support
– To make the best of a bad situation, it is necessary
to enhance the available support by utilizing
maximum coverage of all usable ridge bearing
areas.
– Must be accomplished without interference of
routine movements or function of the
stomatognathic system.

• Support
– Maximum coverage provides the “snowshoe”
effect, which distributes applied forces over as
wide an area as possible.
– This helps in preservation, stability and retention.
edition

• Support
– Areas of support
• Divided into
» Primary
» Secondary
» Slight

• Support
– Primary support
• Areas of edentulous ridge that are at right angles to
occlusal forces do not resorb easily.
• Maxillary:- Posterior ridges and flat areas of the palate.

• Support
– Primary support
• Mandibular:- Buccal shelf area, posterior ridges and the
pear shaped pad. The pear shaped pad is sometimes soft
and can be a poor area of support but must be covered
so the important retromylohyoid flange is complete and
the buccal shelf is covered.

• Support
– Secondary support
• Areas of the edentulous ridge that are greater than at
right angles to occlusal forces or are parallel to them;
also the areas of the edentulous ridge that are at right
angles to occlusal forces tend to resorb under load.
• For example, the anterior ridge is known to resorb at a
much faster rate than the posterior ridge areas where it
is subjected to load.
IMPRESSION MAKING 53/100

• Support
– Secondary support
• Maxillary:- anterior ridge and all ridge slopes
• Mandibular:- anterior ridge and all ridge slopes.

• Slight
– Areas of very displaceable tissues, i.e, all the
vestibular areas that provide very little support
but are needed for the the very important
peripheral seal.

• Importance of covering the buccal shelf
– Buccal shelf is the area of bone between the
extraction sites of the molars and the external
oblique line. The cortical plate over the site of the
extracted teeth is rarely intact and is usually
spiculated and rough.

• Importance of covering the buccal shelf
– It is intact cortical plate and tends not to resorb due to
stimulation of the attachment of the buccinator muscle.
– When the ridge is flat, the buccinator is often attached almost to
the centre of the ridge. This muscle can be covered by the
denture in this area because this muscle is flaccid and inactive,
and also its fibers function in a horizontal direction.

• Importance of covering the buccal
shelf
– Fortunately, in rare old patients,
buccinator is tense and active, then it
is more difficult to cover buccal shelf
area (tend to have flatter ridges).
– i.e., thin spiney, or flat, the buccal
shelf is usually the only available
area of support.
– Bernard Levin, Impressions for Complete
Dentures

• Importance of covering the
retromolar pad
– The reason the pear-shaped pads
so important for support is that it
is an area that rarely resorbs.
– Because the very large and active
temporalis muscle inserts on the
coronoid process and also on the
anterior border of the ramus with
the tendons ending on the alveolar
bone distal to the pad.
– Bernard Levin, Impressions for
Complete Dentures

• Importance of covering the retromolar
pad
– Bone responds to tensile stimulation by
growth and apposition, which cause areas
of muscle attachments not to resorb. E.g
genial tuberlce and mylohyoid ridges.
– Pad is on an area of bone that is relatively
stable.
– Important to include the pad in the
impression so that it can be used as a
landmark for the placement of the occlusal
plane.
– Bernard Levin, Impressions for Complete
Dentures

• Improving Support
– There are five basic Methods:-
• Surgical removal of pendulous
tissue
• Use of tissue-conditioning
materials
• Surgical reduction of sharp or
spiney mandibular ridge
• Surgical enlargement of ridge.
• Implants.
Complete Dentures

• Retention
– Retention of a denture is its
resistance to removal in a
direction opposite to that of its
insertion.
– Retention resist the
adhesiveness of foods, the force
of gravity, and the forces
associated with the opening of
the jaws.
Complete Dentures

• Retention
– FACTORS INVOLVED IN THE RETENTION OF DENTURES
• Interfacial force
• Adhesion
• Cohesion
• Oral and facial musculature
• Atmospheric pressure
• Adhesion, Rotation insertion paths and Parallel walls
• Gravity
– Prosthetic treatment for edentulous patients, Zarb, Bolender,
12th edition.

• Interfacial force
– “The tension or resistance to separation possed by the film
of liquid between two well-adapted surfaces” –GPT
– For better understanding, it is divided into:-
• Interfacial surface tension
• Interfacial viscous tension
– Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th
edition.

• Interfacial Surface Tension
– It results from a thin layer of fluid that is present
between two parallel planes of rigid material.
– It dependent on the ability of fluid to wet the rigid
surrounding material.
12th edition.

– If the surrounding material has a low surface tension,
as oral mucosa does, fluid will maximize its contact
with the material, thereby wetting it readily and
spreading it out in a thin film.
– Denture base material vary in their surface tension(
termed as wettability), with processed materials
displaying greater wettability than autocured resins.
edition.

– This factor may not play as important a role in
retaining the mandibular denture as it does for the
maxillary one.
– WHY?
• In many patients, there is sufficent saliva to keep the
external borders of the mandibular denture awash in saliva,
thereby eliminating the effect of interfacial surface tension.
edition.

– All the denture base materials have higher surface
tension than oral mucosa, but once by salivary
pellicle, their surface tension is reduced, which
promotes maximizing the surface area between liquid
and base.
– Thus the thin film furnishes retentive force by virtue
of the tendency of the fluid to maximize its contact
with both surfaces.
edition.

• Interfacial Viscous Tension
– It refers to the force holding two parallel plates
together that is due to the viscosity of the
interposed liquid.
– It is explained by Stefan’s Law
12th edition.

– F decreases with the increase in (h )width of the space
between the denture base and the mucosa.
– A slow and steady increase in V (velocity of the
displacing force) will have least resistance from
interfacial surface tension than a rapid V.
edition.

– To obtain maximum interfacial surface tension:-
• Saliva should be thin and even.
• Perfect adaptation between the denture base and the
tissue should be present.
• Denture base should cover a large area.
• There should be a good adhesive and cohesive forces,
which aid to enhance interfacial surface tension
12th edition.

• Adhesion
– “the physical attraction of unlike molecules to one
another” – GPT
– Saliva plays an important role in adhesion.
12th edition.

• Adhesion
– The amount of adhesion present is directly
proportional to the denture base area.
– In patients with Xerostomia, adhesion does not
play a major role.
12th edition.

• Adhesion and Xerostomia
– Denture base seem to stick to the dry oral mucosa
– It is not very retentive and predisposes to mucosal
abrasion and ulcerations, due to lack of salivary
lubrication.
– It is annoying for the patients to have stick the
denture base to the lips, cheek and tongue.
12th edition.

– Prescription
• An ethanol free rinse containing
aloe or lanolin, a water soluble
lubricating jelly, or a salivary
substitute containing
carboxymethylcellulose (CMC) or a
mammalian mucin can be helpful.
– Prosthetic treatment for edentulous
patients, Zarb, Bolender, 12th edition.

– Prescription
• In case or irradiation or autoimmune disorder, a prescription
of 5 to 10 mg of oral pilocarpine, 3 times a day can be
beneficial if a patient can tolerate the likely adverse effects
like increased perspiration and occasionally excess
lacrimation.
edition.

• Cohesion
– “the physical attraction of like molecules for each
other” – GPT
– It acts within the thin film of saliva.
12th edition.

• Cohesion
– The effectiveness of these forces increases with
increase in denture-bearing area.
– Watery serous saliva can form a thinner film and is
more cohesive than thick mucous saliva.
12th edition.

• Cohesion
– Actually, normal saliva is not very cohesive.
– Unless saliva is modifed (as it can be through the
use of denture adhesive)
12th edition.

• Oral and Facial Musculature
– It supply supplementary retentive forces, provided
• Teeth being positioned in the neutral zone
• Polished surface being properly shaped. This is not to
say that patient should hold their prosthetic teeth in
place by conscious effort but the shape of the buccal
and lingual flanges must make it possible for the
musculature to fit automatically against the denture
and thereby to reinforce the border seal.
12th edition.

• Oral and Facial Musculature
edition.

• Atmospheric Pressure
– When displacing forces act on a denture, a partial vacuum is
produced between the denture and soft tissues, which aid in
retention.
– This property is called natural suction of a denture.
– Hence atmospheric pressure is referred to as emergency-
retentive force or temporary restraining forces.
– Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition.

• Atmospheric Pressure
– Retention produced by an atmospheric pressure is
directly proportional to the denture base area.
12th edition.

• Undercuts, Rotation insertion paths and Parallel
walls
– The resiliency of the mucosa, submucosa overlying
basal bone allows for the existence of the modest
undercut that can enhance retention.
edition.

– Less severe undercuts of the lateral tuberosities,
maxillary premolar areas, distolingual areas and
lingual mandibular midbody areas can be extremely
helpful to the retention of the prosthesis.
edition.

• Undercuts, Rotation insertion paths and Parallel
walls
– Some “undercuts” are only undercut in relationship to
a linear path of insertion or presumed vertical path of
insertion.
– However, if the undercut is seated first and the
remainder of the denture base can be brought into
proximity with the basal seat on rotation of the
prosthesis around the undercut part that is already
seated; this rotational path will provide resitance
against vertical displacement.
edition.

• Undercuts, Rotation insertion paths and Parallel walls
– Prominent alveolar ridge with parallel and buccal walls may
provide significant retention by increasing the surface area
between denture and mucosa and thereby maximizing
interfacial and atmospheric forces.
– Prosthetic treatment for edentulous patients, Zarb, Bolender, 12th edition.

• Gravity
– When a person is in upright
posture, gravity acts as a retentive
force for the mandibular denture
and a displacive force for the
maxillary denture.
– Weight of the denture acts as an
important factor.

• Gravity
– Curiously, another report focusing
on maxillary denture base
materials in patients with
xerostomia found strong patient
preference for metal based
prothesis in the maxilla.

• Stability
– The stability of a denture is its
ability to remain securely in place
when it is subjected to horizontal
movements.
– The latter occurs during the
functional forces of chewing,
talking, singing, whistling, kissing,
etc – all the orofacial activities
needed for normal everyday
living.
Complete Dentures

• Stability
– To be stable, a denture requires
• Good retention
• Noninterferening occlusion
• Proper tooth arrangement
• Proper form and contour of the
polished surface
• Proper orientation of the occlusal
plane
• Good control and coordination of the
patient’s musculature.
Complete Dentures

• Stability
– Occlusion
• No matter how skillfully the impressions were made,
the dentures will eventually loosen and cause irritation
if there are interfering occlusal contacts.

• Stability
• A common occurrence is an interfering contact in the
second area that may cause the mandibular denture to
rotate upward and forward.

• Stability
– Occlussal plane
• Ideally the occlusal plane is parallel to and anatomically
oriented to the ridges.
• If the occlusal plane is tipped, there will be a shunting
effect and a loss of stability.

• Eshetics
– The role of esthetics in impression making refers to
the development of the labial and buccal borders so
that they are not only retentive but also support the
lips and cheeks properly.

Conclusion
• Muller De Van stated that the perpetual
preservation of what remains is more
important than the meticulous replacement of
what is lost.

References
• Complete Denture Prosthodontics, John J. Sharry, 3rd
edition
• Bernard Levin, Impressions for Complete Dentures
• Prosthetic treatment for edentulous patients, Zarb,
Bolender, 12th edition.
• Syllabus of Complete denture, Charles M. Heartwell, 4th
edition
• DCNA, Volume 40, January 1996.
• Glossary of Prosthodontic terms, 8th edition
• M. M. Devan, Basic principles in impression making,
JPD 2005, 503-508

Thank you

Theories, Principles & Objectives of impression Making Of Completely Edentulous Patients

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