impression making-theories and techniques in complete denture
P.G. 2nd Year
Dept of Prosthodontics 1
• Complete denture impression procedures are
perhaps one phase on which much has been
spoken about. The literature on the subject shows
a persistent disagreement ever since 1850.
• Much of this confusion results from the fact that
many impression procedures have been
developed on empirical basis.
• Many have used the available knowledge of
functional and histological anatomy for the
development of their procedures, but the variation in
these techniques indicate a wide difference in
interpretation of the foundation of dentures.
• Whatever the method used it is generally agreed that
good impressions are basic for the construction of a
“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. Devan
A negative likeness 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
• 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
A final impression is an impression for making the
master cast .
Any substance or combination of substances used for
making an impression or negative reproduction.
• Before the middle of the 18th century, no method
was available for producing an impression of the
alveolar ridge. A widely used method at that time
was the painting of the ridge with a dye , and the
pressing of a block of ivory or bone against the dyed
• Areas of contacts were scraped away from the block
until the best fit for the prosthesis was achieved
• 1756 – beeswax was apparently first used in making
impressions in the mouth.
Philip Pfaff(Berlin) made a sectional wax
impression of half of an arch at a time.
• 1782 -William Rae said that
“he got the measurement of the jaws in a piece of
wax pushed into the gum, afterwards making a cast
of it with plaster of paris”
• 1840 - Charles De loude (london) made one of the
earliest refrences to impression trays . He wrote
“for impressions, I use wax in tin cups or shapes, the
whole size of the upper and lower jaws, right or left, half
jaws and fronts.”
• 1842- Montgomery discovered gutta percha. It was
obtained from various sapotaceous trees in Malaysia. It
was introduced as an impression material in 1848 by
Colburn said it should be thoroughly soaked in boiling
water, kneaded and moulded in the same way as wax
and …. immediately place in the mouth, and firmly
pressed to the jaws.
• 1844- Plaster of paris
• Wescott, Dwinelle and Dunning have been credited
with this discovery.
• 1847 - Desirabode referred to an impression tray as
“ we place wax in a box, a kind of semi elliptical gutter
of tin or silver, upon the anterior part of which is a
shaft which forms a handle. The walls of this
receptacle offering some resistance, opposite the
deformation of the wax”.
Franklin described the first correct impression . He used
wax for the preliminary impression followed by a
Wescott described a similar technique using oversized
wax trays made by scooping out primary impressions
• 1874 - Use of impression compounds dates from
contributions of J.W.Greene, P.T.Greene and of
• The Greene brothers (about 1900) introduced a
modeling plastic , a method to manipulate it , and a
technique that is said to have been the first to utilize
all the surfaces of a mouth to advantage for denture
retention. They were probably the first to describe
the closed mouth all modeling plastic technique in
Furthermore, they were the first to use the word “ post
dam” in describing posterior palatal seal.
• 1915 - Rupert hall , perfected the first moderate heat
modeling plastic for making individual trays and
introduced the correctable modeling plastic-plaster
technique that became a standard method for
making an impression.
• Hall used a specially prepared hard black modeling
plastic for making a custom tray in which a very thin
mix of impression plaster was placed for correction.
• 1922- Everett described an early wax technique
around this time. He used fluid wax compound of
three consistencies: hard, medium and soft.
He said “ in every way possible represents the three
general tissues of the mouth on the bone”
• 1925- Alphous Poller (Vienna) described his elastic
material for “molding articles of all kinds, more
particularly, parts of a living body.
• He was most likely the first to suggest the use of agar
for dental impressions.
• Booth, however, described complete denture
impression technique using agar but found it
necessary to build custom water cooled trays and to
pre-medicate the patient with a drug to reduce
• During late 1920’s the idea became widely held that
uniform tissue support may be of value. It was
believed that this would be attained by controlled
placement of soft tissues.
• During this period, the first true functional
impression wax was developed. The waxes before
this (beeswax and parafinn wax) were far from ideal
because they were hard, flowed too slowly, or were
• 1930 - According to Applegate a series of true
physiologic waxes was developed by the cooperative
effort of G.C.Bowles , S.G.Applegate and himself and
was made available in 1935.
• Early 1930’s
First real impetus in use of zinc oxide eugenol for
impression materials came From A.W.Ward and
Ward’s preparation was intended more so for a surgical
pack , but he also said that it could also be used as
lining for dentures as an impression material .
Kelly’s preparation was primarily intended as an
Harry.L.Page introduced the mucostatic concept.
The advocates of this concept such as Page, Albinson,
Dykin and Addison thought the universally accepted
concept involving compression of soft tissues and
relief of the hard areas was in error because
hydrostatics proved that human tissues was not
amenable to either of this condition.
They believed that the impression should be an
absolute accurate negative of the ridge tissues at
Dirksen reported the findings of his research in IOWA
which resulted in the development of still another
physiologic impression wax. Over the years
functional waxes have grown steadily in popularity
and many clinicians have suggested methods for
– Applegate for immediate dentures
– Mc. Cracken, borkin, and faber for mandibular
– Hardy , ostrem and schultz for complete denture
Trapozzano described one of the early techniques
using Zinc oxide eugenol paste. Compound
preliminary impressions were made in stock trays
and plaster of paris casts were poured. Vulcanite or
shellac bases were constructed, on which occlusion
rims of wax or compound were placed. After a
tentative vertical and centric relation was established
, the final corrective impression was made using
closed mouth technique.
• 1942- Pendleton suggested a fluid wax technique
using asiatic or indian paraffin fro the final
• Wright and Denen suggested using alginate in a
border molded perforated customized acrylic tray.
• Collett described an alginate technique for the
maxillary impression using the material as a wash in
a modeling paste preliminary impression .
Elastomeric impression materials were introduced.
They were of two chemical types.
– Silicone base
• Pierson in 1955 reported on a new elastic material of
a polysulfide base (thiokol).
Shortly there after silicone base materials were
elastomeric impression materials were intended
primarily for making impressions for
• And for fixed partial dentures
• Chase in 1961 first described the moldable acrylic
material used for tissue conditioning and for
functional(dynamic) impression for complete
According to Emmett Beckley in 1973 , the first
moldable acrylic material consisting of an ethyl
methacrylate and an ethinol liquid was developed by
Clark Smith and he (Beckley) performed the first
practical research with this material in complete
• The bones of the upper and lower edentulous jaws
are covered with soft tissue, and the oral cavity is
lined with soft tissue known as mucous membrane.
• The denture bases rest on the mucous membrane,
which serves as a cushion between the bases and the
• The mucous membrane is composed of two layers
The mucosa is formed by the stratified squamous
epithelium and a subjacent layer of connective
tissue known as the lamina propria.
• The submucosa is formed by connective tissue.
It may contain glandular , fat , or muscle cells and
transmits the blood and nerve supply to mucosa.
• The thickness and consistency of submucosa are
largely responsible for the support that the soft tissue
affords the denture, since in most instances the
submucosa makes up the bulk of the mucous
• In a healthy mouth the submucosa is firmly attached
to the periosteum of the underlying bone of the
residual ridge and will usually successfully withstand
the pressure of the denture.
• The oral mucosa is divided
in three catogories
depending on its location
in the mouth
• Masticatory mucosa-25%
• Lining mucosa-60%
• Specialized mucosa-15%
The Masticatory mucosa covers the crest of the ridge
The residual attached gingiva firmly adherent to the
• Hard palate
It is characterized by a well defined keratinized layer on its
outermost surface subject to changes in thickness
The specialized mucosa covers the dorsal surface of the
tongue. This mucosal covering is keratinized
The Lining mucosa - nonkeratinized layer
Ventral surface of the tongue
Unattached gingiva found on slopes of residual
the tray type
Depending on theories of impression making
• Also known as definite pressure impressions.
• Because denture retention is tested most during mastication,
many dentists formerly considered it essential for the tissues
to remain in contact with the denture during chewing.
• It was logical to them to make impressions that would press
the tissues in the same manner as chewing forces, thus
ensuring contact during chewing stroke.
• However, dentures made from such impressions did not fit
well at rest, because tissues so distorted tend to rebound.
• Furthermore, these abused tissues will not be able to long
maintain the shape that they assumed on the day of
• Many of the proponents of pressure impressions advocate the
use of closed mouth techniques.
• But closed mouth technique do not allow for adequate
muscle trimming of the periphery.
• Very often dentures made with closed mouth technique are
over-extended and must be arbitrarily trimmed.
• The materials used for this technique include
impression compound, waxes and soft liners.
Good retention during function.
• The type of the sub mucosa & the relation
of the supporting bone to the denture
bases show best to record the soft tissues.
• The oral mucosa with a tightly attached sub mucosa
covers the crest & slopes of the residual alveolar ridges &
anterior 2/3rd of the palate. When this type of mucosa is
displaced in an impression & a denture is constructed on a
cast made from this impression & the denture is seated,
the tissues will attempt to return to its undisplaced
• This effort of the tissues to return to its
undisplaced position creates objectionable
forces that produce pressure to the
supporting bone & dislodging pressure
against the denture.
It is not desirable to record this
type of tissue in a displaced position.
Disadvantages of Mucocompressive
• 1 : Dentures made from such impression
do not fit well at rest ‘coz tissues so
distorted tend to rebound to its former
contour. Dentures will fit well during
mastication, and will lift up at rest due to
tissue rebound. This results in premature
Disadvantages of Mucocompressive
• 2 : Pressure is sufficient to
interfere with the blood
supply to the tissues of
basal seat & eventually
cause resorption of the
Due to constant
pressure on the tissues,
mucosal tissue reaction is
Disadvantages of Mucocompressive
• 3 : Dentures are in occlusal contact for only
a relatively short period of time & the
constant pressure even at rest , even if
equal may overstress the tissues.
The total time
during 24 hours associated with directs
functional occlusal force application to
periodontal tissue is 17.5 minutes .
Disadvantages of Mucocompressive
• 4 : Closed mouth technique does not
allow for adequate muscle trimming of
the periphery. Dentures made are often
overextended & must be arbitrarily
• Also known as minimal pressure impressions.
• Addison in 1944 described this technique and attributed this
• The main point of the mucostatic principle concerned Pascal’s
law, which states that which states that pressure on a
confined liquid will be transmitted through the liquid in all
• The pressure
applied on the
will be equally
the liquid in all
• According to this concept, the mucosa being more than 80
percent water, will react like a liquid in a closed vessel and
thus cannot be compressed.
• According to the principle of mucostatics, the impression
material should record without distortion, every detail of the
mucosa so that the completed denture would fit all minute
elevations and depressions.
• Mucostatics further demanded that a metal base be used
rather than the dimensionally stable scrylics.
• Most important of all, the mucosal topography is not
static over a 24 hour period.
• There is a difference between the mucosal contours
just after rising in morning, and that which exist after
12 hours in the upright position.
• So it would appear that all the infinite details
achieved in the impression would be altered by the
time the denture was finished.
• The adherents of the mucostatic principle considered
interfacial surface tension as the only important
retentive mechanism in complete dentures.
• The mucostatic principle ignores the value of
dissipating masticatory forces over the large possible
basal seat area.
• If for eg, patient could develop the masticatory force of
30lb, it is evident that larger the basal seat area ,the
less force will be exerted on each sq millimeter of
is preserved and
Suitable to areas
where the residual
ridges are sharp,
thin & flat flabby
Disadvantages Of Mucostatic Technique
• 1: Inadequate support :
Ridge tissues are not uniformly displaceable & a
base made from a mucostatic impression will
result in the firmer areas bear greatest part of
pressure & the more displaceable areas giving
little (less) support. This condition is
undesirable from viewpoint of bone
preservation & comfort.
Disadvantages of Mucostatic Technique
• 2 : Lack of Peripheral Seal: The
impressions made by mucostatic technique
does not displaces even the soft tissues at
the borders. This theory would eliminate any
possibility of border seal & result in absence
of secondary retention which in many
instances is even greater than the primary
Disadvantages of Mucostatic Technique
• 3 : SHORT FLANGE LENGTH :
The impressions made with non-pressure
technique were significantly under extended.
The flanges of the dentures are shorter. Short
flanges do not support the lips and cheeks.
Selective pressure impressions
• It is an impression technique that combines pressure over
certain areas and little pressure over others.
• The technique utilizes a preliminary compound impression
that is generously relieved over the midline and incisive
• 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 presssure.
• Thus the papilla and midline 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.
• This principle of impression making is based on the belief that
the mucosa over the ridge is best able to withstand pressure
,whereas covering the midline is thin and contains very little
• Some feel that It is impossible to record areas with
• Some areas still recorded under functional load, the
dentures still faces the potential danger of
rebounding and loosing retention.
• 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.
Depending on the technique
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.
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
Preferred because the operator can see
whether muscle trimming is done properly
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
• Saving of time
• Appointment time may fatiguing the dentist
• Tendency for overextensions
• Problem of limited space between the
tuberosity and pear shaped pad
• No control over the amount of pressure
during the final impressions
• Soft tissues – displaced- rebound
• bone resoption
Depending on the tray type
Beginning of good impression starts
with the selection of the correct
Trays used for primary impression making
are called stock trays. These are factory
made and available in various sizes.
They are made of metal or plastic, can
be perforated or non perforated.
An appropriate stock tray should be
selected for each patient.
Points to be considered during Tray Selection
There should be at least 2 – 3 mm
clearance between the stock tray and the
ridge. It should have 5 – 6 mm clearance
for impression compound.
With the stock tray in position in the
mouth, the handle of the tray is tilted
downwards and the posterior border of
the tray is observed. The tray should
extend over the tuberosity and the
Points to be considered during Tray Selection
• The tray should be neither too large nor
too small. In both cases a distorted
impression will result.
• If the tray is too large, it will distort
the border tissues by pulling them
away from the bone.
• If the tray is too small, the border
tissues will collapse inwards towards
the residual ridge thus reducing
support for the denture.
Selection of Tray for Maxillary Arch
• After examining the alveolar
ridges & palate for shape & size,
suitable upper stock tray is chosen
& inserted in the mouth.
• The posterior border of the tray is
raised to make contact with the
anterior part of the soft palate. It
must cover the maxillary
• The tray is then slowly raised
anteriorly & lateral flanges
watched for clearance of the
PRIMARY ( PRELIMINARY ) IMPRESSION
The ideal relationship of a stock tray to the sulcus and the denture bearing mucosa
• They are of two types:
• In order to avoid permanent distortion of an
elastic impression material as it is withdrawn
from the undercut areas, an adequate
thickness of the material is required.
• The special tray should be constructed on the
preliminary cast after a spacer of appropriate
thickness for the planned impression material
has been adopted to it.
• Alginate is the most commonly used elastic
impression material for edentulous patients
and this requires the spacer of about 3mm.
• The elastomers have a better elastic recovery
than alginate and so require less spacing of
the special tray.
• Are used with impression materials that are
used in the section such as zinc oxide-eugenol
impression paste and light-bodied elastomers.
• It is an advantage if a lower acrylic close-fitting
tray has vertical pillars in the premolar regions
to act as finger rests.
• These rests keep the fingers, which stabilise
the tray and support the impression, well clear
of critical border areas of the impression
when it sets.
• If this is not done, inaccuracies will result from
fingers restricting the border molding
movements of the soft tissues.
• They can also displace excess material into the
• The anterior stub handle is for holding and
manipulating the tray.
• Its shape avoids interference with the lower
lip which otherwise can make placement of
the tray difficult and can hinder border
trimming of the impression in that area.
Depending on the purpose of the
The negative replica of the oral tissues used to prepare a
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.
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
Fabriction of custom tray.
Developing the posterior palatal seal.
Making the wash impression.
Depending on the material used
STEPS IN MAKING AN IMPRESSION
Preliminary examination of the patient
Seating the patient
Selection of the tray
Selection of the material
Preliminary examination of the patient
• A complete case history and thorough clinical
examination is done.
• Factors that can complicate impression making are
• Patient education.
Seating of the patient
Position of the operator for
Position of the operator for
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, conform or configure 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
• And in the lower the general form and size of basal
seat is studied.
• First technique:- border- molded special tray:
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.
The tissue surface and borders of the tray, including
the rim of wax, are painted with an adhesive
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.
Primary impression making
• With alginate (Maxillary)
A wax spacer is placed within the outlined border to
provide space in the tray for final impression
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.
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.
• 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.
• The requirements of such a material are that it
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
5. Allow finger placement of the material into
deficient parts after the tray is seated
• Not cause excessive displacement of the tissues of
• Be readily trimmed & shaped so excess material can
be carved & the borders shaped before the final
impression is made.
• 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.
4. Position the polyether material on the borders, making
certain that a minimum width of 6 mm exists on inner
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
9. Remove tray when impression material is set.
10. Examine border molding to determine that it is
• Preparing the tray to secure the final
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
5. Make the final impression in silicone, metallic oxide
paste, or rubber base.
• Most of the difficulties encountered when making
impressions can be traced to the operator’s lack of
attention to details of technique, and especially the
acceptance of a poor stock tray impression.
• It is of extreme importance that the preliminary
impression records the entire possible denture-
bearing surface but, at the same time, does not
encroach on movable muscular tissues.