Final yr impression / dental implant courses by Indian dental academy

Concepts and techniques
of impression making
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

Contents:
Introduction
Selection of impression material:
Examination
Selection of impression technique
Selection of impression material
selection of impression tray
Prelimnary impression
Custom tray
Border molding
Secondary impression
impression for hypermobile ridges
composite compression impression
Impression for unemployed
mandibilar ridge
denture space determination
functional impressions
review of literature
conclusion
references
www.indiandentalacademy.com

The journey towards successful denture
fabrication begins with making accurate
impressions.
Therefore a good impression will help to insure
that complete denture is stable, retentive and
comfortable. So, the knowledge of different
impression techniques are very important for
us to achieve a good impression.

• Examination and conditioning of the
patient and the mouth.
• Complete case history
• Clinical examination
• Identifying and correcting adverse conditions
• Factors that complicate impression making
• Old denture wearer.

• Selection of impression technique:
1. Clinical findings.
2. Experience of the dentist.
3. Availability of materials.
4. Patient related factors.
Time
Undercuts
Old denture wearer

Selection of impression material:
• Prelimnary impression materials:
impression compound
alginate.
• Final impression materials:
Alginate
Elastomers
Zincoxide eugenol impression paste.
Impression plaster
Tissue conditioners
waxes

• Modelling compound:
• Easily correctable.
• Can be border molded.
• Not influenced by saliva
• Can be used as impression tray.
• Can be scraped easily to provide relief.
• Viscous.
• Cannot record fine details.
• Compound sticks used for border molding.
• Inelastic

• Alginate:
• Elastic
• Primary and final impression
• Records good details
• Not correctable but easily remade
• Not dimensionally stable.
• Donot adhere to tray.

• Elastomeric impression materials:
• Elastic
• Fine details
• Hydrophobic
• Adhesive required.
• Available in different viscosities
• Dimensionally stable.
• Cannot be adjusted after set.
• Prolonged setting time.

• Zinc oxide eugenol impression paste:
• Rigid and inelastic.
• Adheres to tray
• Flows readily and records fine details.
• Burning sensation and tissue irritation.
• Dimensionally stable.
• bulk of the impression is minimal.
• Flaking or breaking during trimming.

• Tissue conditioners:
• Functional impression.

• Impression plaster:
• Minimal pressure technique.
• Flows readily and records fine details.
• Rigid
• Wash impression
• Absorbs saliva.
• Dimensionally accurate with anti
expansion solution.

• Waxes:
• Flow at mouth temperature.
• Exert pressure
• Fine details not recorded.
• Corrections made.

Selection of impression trays:
• A device that is used to carry ,confine
and control impression material while
making an impression.
Stock trays.
Custom trays
Perforated
Non perforated.
Dentulous
edentulous

Stock trays
• Caulk’s edentulous rimlock trays.
• Mc Gowen’s winkler trays-useful for
flat lower ridge
• STOKtrays-designed by Arthur Krol
available in
Square,round,tapering shapes

• Usually stock trays though supplied
in different sizes ,donot fit the
edentulous mouth with desired
accuracy.
• To produce satisfactory impression
and avoid variations in transmitted
pressure, there must be a
reasonably even thickness of
impression material over the
entire fitting surface and flanges
of the tray almost reach the
functional position of the sulci and
frena and yet not displace them.
tray

• Custom trays:
• Close fitting or spaced trays
• Shellac
• Acylic resin
• Thermoformed polymer sheet

• Seating of the patient:
maxillary mandibular

• Prelimnary impression:
a negative likeliness made for the
purpose of diagnosis or the
fabrication of the impression tray.

using alginate
using impression compound.
For Primary impression high viscosity
material is preffered as it allows
to compensate better for the
shortcomings in the fit and extension
of the stock tray.

• Selection of stock tray:
• Tray extensions checked
• Defficiencies corrected.
• Lingual border of mandibular tray
• maxillary tray for Deep palate

Primary Impression in
alginate.
Tray should be adjusted by
bending .
Selection of stock tray. . Position borders at hamular notches.
Lift the tray anteriorly, 3-5
mm space for impression
material. www.indiandentalacademy.com

Border of ray should be
short of tissue reflection.
Adequate clearance in frenal
areas.
Tray should be
smoothened.

Deficient borders corrected by
adding utility wax.
Tray extension in buccal space
and tissue side of posterior
border.

Location of hamular notches. Mark the vibrating line.
Some alginate to be placed
in vestibule.
Alginate to be placed in
deepest part of palate.www.indiandentalacademy.com

Tray to be rotated into the mouth
and seated first at the back of
the mouth.
Upper lip elevated.
Tray is held in the mouth. Labial and buccal borders
to be molded.www.indiandentalacademy.com

Completed maxillary Primary Impression with
rounded and molded peripheries.

Mandibular alginate impression.
Tray should cover retromolar
pad.
metal edentulous tray. Retromolar pad should be
identified

Bending and cutting the tray for
adjustment.
Adding utility
was to extend
lingual border.

Patient told to do tongue
movements.
Patient told to raise the tongue
and tray is rotated in the
mouth.
Gently mold the labial and buccal areas.www.indiandentalacademy.com

• Completed Mandibular Primary Impression.

Prelimnary impression with
impression compound.
Compound placed in
the tray.
Modelling compund. Softenend in water
bath and kneaded.

Should cover mylohyoid ridge
and external oblique ridge.
Molded with fingers to ridge
form.
Gently warmed over a flame. Before insertion, tempering in
warm water bath.www.indiandentalacademy.com

Patient instructed for
Tongue movements.
Tray should be gently
seated and border moulding
done.
Any short areas can be
remolded.
Impression should cover
all denture bearing area.

Common faults
Mandibular
• Insufficient depth in
posterior lingual pouch:
lingual,labial and buccal
sulci.
Edge of the tray showing
through the impression.
An asymmetrical
impression.
Maxillary:
• Defficiency in the
midline of palatal
vault.
• Excess material
extending beyond
posterior palatal border
of the tray.
one or more region of
sulci
• Tray flange exposure.

Alginate wash impression technique:
• Resorbed mandibular
ridges.
• Using impression
compound has the
benefit of pushing aside
the floor of the mouth
and cheeks which tend
to become trapped by
the edge of the tray.

Preperation for Secondary
Impression
• Denture
outline
marked on
the
primary
impression
.Completed
preliminary
casts.

Denture outline accentuated. Posterior border of tray marked.distal
to denture border.
Wax added for relief. Special tray.
custom tray
1mm from mucobuccal fold
2mm past the
estimated
border.
25mm from vestibule to the top of the
handle,3-4mm thick

Checking for tray extensions:
• Visual examination
• The diagnostic impression
• Correction of overextension
• Correction of underextension.
Impression material
tray

Borders should be beveled. Vibrating line marked.
Tray inserted in mouth. Overextensions trimmed.

Tray should be short of 2
mm from base of sulcus Borders should be adjusted.
Extra clearence in frenal
areas

External oblique ridge
marked.
Tray outline marked 2-3 mm
short of denture outline.
Custom tray fabricated.
Posterior border of tray should
cover anterior half of the pad.

Pencil mark
transferred to fitting
surface.
Anterior border of the tray adjusted .
Tray border should be resting
against the ridge.
Lingual border adjusted.

Tissue stops
• Prevent seating of the tray too superiorly or posteriorly.
• Stabilize the tray
• Uniform thickness of the material.
• Molar or cuspid areas.
• Palatal aspect of the ridge till mucobuccal fold.-maxillary
• Mucobuccal fold to the lingual floor –mandibular.
• Ways to produce-inlab during construction of special tray.
• Chair side in mouth
• Chair side on cast.

Finger rests:
• Keep fingers which stabilise the tray
and support the impression.
• Absence of these result in inaccuracies
resulting from fingers restricting
border molding movements of soft
tissue.

• Border molding:
The shaping of the border ares of
an impression material by functional
or manual manipulation of the size of
the vestibule.

Materials:
• Modelling compound sticks
• Autopolymerizing acrylic resin
• Metallic pastes
• Elastomeric materials
• Impression waxes

• Modelling compound sticks:
• Advantages:
• Soften easily but are quite hard at
mouth or room temperature so other
areas of periphery can be molded
with least possible distortion to the
previously completed section.
• Corrections easily accomplished.

• Isofunctional impression plastic
sticks.
• Soften easily and have much longer
working time .
• Softer at room temperature compared
to compound sticks.

• Autopolymerizing acrylic resins:
• Rimseal
• Flexacryl.
• Disadvantages:
• Irritating
• Strong odor
• Heat produced polymerization.

• Premixed self curing soft resins:
• Added to the periphery of an existing denture.
• Material gradually polymerizes to a semisolid state in few
hours-functional border molding.
• Advantages:
• Less irritating
• Easy to use.
• Disadvantage:
• Consistency changes each time the container is opened.
• If denture border is grossly defficient the material will slump
as it cannot flow into the vestibule that is 6mm away from the
border.

• Elastomeric materials:
• Heavy body-border molding.
• Advantage-wide range of working and
setting time.
• Elastic recovery good.
• Disadvantage:
• Borders difficult to trim
• Addition requires time consuming mix of new
materials.

• Impregum-Smith etal.polyether based
material.
• Simultaneous border molding.
Advantages:
1.Can be trimmed
with knife or burr
2.Corrected with
modelling compound
or wax.
Disadvantages;
1.Skill and great care
required.
Good prelimnary
impressions are
important as
underextensions cannot
be detected.

Impression waxes-adaptol
Advantages
• Simultaneous border
molding.
• Donot irritate
• Additions easy
• Cannot injure oral
tissues if correct
temperature is applied
Disadvantages
• Distorts easily and must
be handled carefully
• Insertion not to be
delayed
• Chilled wax subjected
to flaking and breaking
while trimming
• Not strong enough to
correct
underextensions.

• Segment by segment
• One step:

• Simultaneous molding of all borders:
• Advantages:
• Time saving.
• Less discomfort to the patient.
• Less effort for the dentist.

• Requirements:
• Have sufficient body
• Allow some preshaping of the borders
• Setting time3-5minutes
• Retain adequate flow when seating in the mouth.
• Allow finger placement of the material in to
defficient parts after seating of tray.
• Not cause excessive displacement of tissues
• Readily trimmed and carved so that excess
material can be carved and borders shaped before
the final impression is made

The tray rotated in mouth
and cheek gently
massaged.
Compound molded with
fingers.
Softened again with alcohol
torch.
Tempered in warm water
bath. www.indiandentalacademy.com

Appropriate molding will have mat
surface.
Compound added in buccal frenum
area.

Recording the frenum.Molded buccal and labial
borders.
Excess compound on tissue
side trimmed.
Compound placed on
posterior border.

Junction of tray and
compound smoothened.
Tray seated in mouth with firm
pressure.
Border molded
maxillary custom
tray.

Compound placed on posterior
border
Compound added on buccal
border
The tray gently seated in
place.
The border should be
smooth,round and convex.

Border molding continued in labial borders.
Border molding the lingual areas.

Genial tubercles
should be
covered.
Border molded
mandibular tray

TEST FOR RETENTION
mandibular
• Protrude the tongue
• Move tongue in lateral
direction
• Roll tongue back to
touch palate.
• Open the mouth.
• Exerting vertical pull
on handle
• Forward pressure on
distal aspect of the
handle.
maxillary
• Upward and outward
pressure in the incisor
region.
• Upward and outward
pressure in the
premolar region.
• Pulling the upper lip
downward.

Preparing and instructing patient
• Preparing tray for impression:
removing the relief wax
Removing spacer wax
Escape holes
Reducing the borders
Applying adhesive
Protecting the mouth
Drying the mouth.

The final impression:
• Mixing
• Loading
• Seating
• Removing the impression
• Inspecting
• Correcting
• remaking

Master impression with impression
plaster.
• Custom tray with2.5mm spacer.
• Tissue stops
• Pheripheral tracing.
• Impression.

The border molded compound tray
technique:
• Advantage:
• Same appointment.
• Impression should be accurate with
proper border molding.
• Even thickness of compound in the tray
must be maintained.

• Seperating the compound
• Trimming the compound tray
• Attaching handles
• Border molding
• Scraping the compound.
• Making the final impression.

• Closed mouth technique:

• Using old dentures as an impression
tray.

Patients wearing upper complete
denture opposed by lower natural
teeth.
Chronic complete denture wearers
Maxillary anterior ridge replaced by
fibrous tissue; reduced support for
dentures.
Patient complains of loose dentures
Impression techniques to avoid undue
tissue displacement.
Impression technique for hypermobile ridges

• Mucocompression without
displacement.
• Primary impression with alginate and
special tray with relief in that region.
• Hobrik technique
• mucostatic ,openwindow technique-
Zafrulla khan technique.

• Mucocompression without displacement:
• Two stage technique designed to compress the
flabby tissue so that the compression through
out the whole of the maxillary denture bearing
area is as uniform as possible.

mucostatic ,openwindow technique-
Zafrulla khan technique.
– Special tray with a window cut in the
region of the displaceable tissue.

– Wash impression
with ZOE paste.
Border molding with
low fusing compound.

– Tray re-inserted, impression plaster
syringed over displaceable tissue.

Completed impression.

• Composition compression technique:
• It is designed to take an impression of the
tissues underpressure so that ,under the
stresses of mastication ,the pressure
transmitted through the entire mucosa to
the underlying bone is approximately
equal over its whole surface.

• Impression technique for unemployed
mandibular ridge:
• Impression recorded mucostatic over the
crest of the ridge and mucocompressive on
the peripheral parts and prevents any load
being placed on unemployed part of the
ridge.
• Increased bulk and surface area of
denture.

• IndicatedIndicated
– Unemployed lower alveolar ridge unable
to provide acceptable support against
vertical loads and positive stability
against lateral forces.www.indiandentalacademy.com

• MethodMethod
– Primary impression made with alginate or
putty elastomer.
– Impression relieved over ridge crest area
and wash impression obtained with low
viscosity material.www.indiandentalacademy.com

• Customized special tray with 2mm spacer
constructed.
• Spacer removed ; tray perforated in
crestal region .www.indiandentalacademy.com

• Low fusing compound used to obtain
impression of primary cast with special
tray. www.indiandentalacademy.com

• Impression reduced in the region of
buccal & lingual sulci ; border
molding refined in patient’s mouth.
• Painful areas relieved.
• Tray re-insertion should not result
in pain.
• Impression completed with light –
bodied elastomer.

Denture spaceDenture space
The portion of the oral cavity that is or may be
occupied by the maxillary and / or mandibular
denture (s).www.indiandentalacademy.com

Neutral ZoneNeutral Zone
• That area in the mouth, where, duringThat area in the mouth, where, during
functions thefunctions the forcesforces of the tongueof the tongue
pressingpressing outwardoutward areare neutralizedneutralized by theby the
forcesforces of the cheeks and lips pressingof the cheeks and lips pressing
inwardinward..
• Hence a possible zone of
equilibriumwww.indiandentalacademy.com

• IndicationsIndications
– Past denture looseness
due to powerful lower lip
activity.
– Non-replacement of
missing teeth leading to
tongue / cheeks / lips
partially occupying the
usual denture space.
– Enlarged tongue,
E.g. Down’s Syndrome.
– Abnormal anatomy,
E.g. Hemimandiblectomy.
– Inability to wear a lower
denture

• Generally done for lower
• Materials used-Waxes,ZnOE,rubber
base putty, self-cure acrylic, impression
compound,tissue conditioners.

• On accurate master casts, stabilized
denture bases are constructed.
• Wire loops embedded over ridge
crest for retention.
Denture spaceDenture space
determinationdetermination

• Low fusing compound rims attached
to bases.
• Patient trained to perform a range of
functional movements such as
smiling, swallowing, speaking, etc.
• Compound rims softened and denture
bases inserted ; functional
movements carried out.

Recommended movementsRecommended movements
Smile
Swallow
‘ooh’
‘ah’

• Wash impression obtained with light –
bodied elastomer brushed on compound
rims.
• Functional movements repeated.www.indiandentalacademy.com

• Plaster matrices constructed around
records.
• Matrices guide in arranging & waxing teeth
& polished surfaces in optimum denture
space. www.indiandentalacademy.com

• PrecautionsPrecautions
– Stable record bases not interfering with muscle
activity.
– Patient to be trained in molding procedure prior to
insertion of loaded tray.
– Excessive volume of molded material to be avoided
– causes distortion of potential denture space.
– External impression may be totally unlike the shape
of a “normal” denture, hence laboratory staff must
be instructed about reproduction of the recorded
contours.

Functional impressionsFunctional impressions
• IndicationsIndications
– Reduced retentive forces ( Atrophic ridges )
– High displacing forces ( Uncontrolled muscle
activity)
• Peripheral form molded by peri–denture
musculature.
• Existing denture utilized for the procedure.

• MethodMethod
– Tissue conditioning materials usually
employed for the procedures.

• Impression surface & periphery of existing
denture reduced by 1.5-2mm to create
space.
• Fitting surface of denture cleaned & dried.
• Material mixed & spread over fitting surface.www.indiandentalacademy.com

• Denture seated in patients mouth;
patient instructed to close in centric
occlusion.
• Patient encourage to perform
functional movements such as
talking, swallowing, smiling, to obtain
a functionally generated impression.

• Denture removed after 5 – 6Denture removed after 5 – 6
minutes ; inspected and surplusminutes ; inspected and surplus
material trimmed.material trimmed.www.indiandentalacademy.com

• Patient returns after few hours;Patient returns after few hours;
impression inspected & cast poured.impression inspected & cast poured.

• Factors complicating impression
making:
• Uncooperative patients
• Excessive salivation.
• Hyperactive gag reflex.

• Hyperactive gag reflex:
• Causes:
• Iatrogenic-physical and visual stimuli.
• Systemic problems
• Psychological factors
• Problems in existing prosthesis.

• Management:
• Reduction of amount and duration of
stimuli.
• Distraction maneuvers
• Prosgressive desensitization:
• Pharmacologic management.

• John Osborne1964:Two impression
methods for mobile fibrous ridges.

• Tryde et al 1965 “Dynamic impression
methods :”
• This is an impression procedure for patients
with advanced mandibular residual ridge resorption.
• The advantages of dynamic impressions are
• Avoidance of the dislocating effect of the muscles
on improperly formed denture borders.
• Complete utilization of the possibilities of active
and passive tissue fixation of the denture

• John D Walter 1973 “Composite impression
procedures” :
• These procedures allow the use of more than
one impression material according to local
indications. Such techniques may also be employed
for large impressions which are difficult or
impossible to obtain with a single tray.
Techniques:
• The edentulous fibrous ridge :
• Impression technique for restricted access to the
oral cavity:

Shanath Shetty,P.Venkat 2007:the selective
pressure maxillary impression :a review of
techniques and presentation of alternate
custom tray design

• Conclusion:
Though there are many techniques and
procedures available for a dentist to make
an ideal impression, the procedures that
follows should be based on sound biological
principles, depending on patients oral and
systemic conditions, by understanding the
concept of function of oral tissues.

References:
• Prosthetic treatment of the edentulous patient –
Basker and Davenport.4th
edition.
• Boucher’s prosthodontic treatment for edentulous
patient -9th
edition.
• Impression for complete dentures-Bernard Levin
• Fenn Clinical dental prosthetics-3rd
edition.
• Complete denture prosthodontics-3rd
edition
John .J.Sharry.
• Syllabus of complete dentures-fourth edition –
Charles M Heartwell.
• Essentials of complete denture prosthodontics-
second edition-Sheldon Winkler.

• John Osborne-Two impression methods for mobile fibrous ridges :British
dental journal,november 3,1964,pg392-394
• Tryde et al “Dynamic impression methods :”journal of prosthetic
dentistry,1965,volume15,issue 6,pg1023.
• John D Walter “Composite impression procedures” journal of prosthetic
dentistry,1973,volume30,issue 4,pg385.
• Shanath Shetty,P.Venkat :the selective pressure maxillary impression :a
review of techniques and presentation of alternate custom tray design
.journal of indian prosthodontic society,march 2007,volume 7,issue
1.page8-12.
•

Final yr impression / dental implant courses by Indian dental academy

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