Impression material final /dental courses

IMPRESSION
MATERIALS AND
IMPRESSION
TECHNIQUES IN
FIXED PARTIAL
DENTURE
INDIAN DENTAL ACADEMY
Leader in continuing Dental
Education
www.indiandentalacademy.com

CONTENTS
Introduction
Impression materials
•Classification of impression materials
•Properties of impression materials
- Hydrocolloids
- Synthetic elastomers.
•Principles of impression material manipulation
Impression techniques
•Individual arch impression technique
1) Reversible hydrocolloid (Agar-agar) technique
2) Irreversible hydrocolloid (Alginate) technique
3) Hydrocolloid laminate technique
4) Elastomeric impression techniques
- Putty wash impression techniques
- Multiple mix impression technique
- Monophase impression technique

Other impression techniques
•Copper band / tube impression techniques
•Intra oral coping impression system
•Matrix impression system
•Dual arch / double bite impression technique
Evaluation of impression
Flaws related to impression
•Visible flaws
•Invisible flaws
 Disinfection of impression
Conclusion
List of References

CLASSIFICATION OF IMPRESSION MATERIAL
Nonelastic Elastic
Synthetic elastomersHydrocolloids1922
Waxes, gums, resins
1927
Plaster of paris
1934
Zinc oxide eugenol
1935
Impression compound
1974
Eugenol-free paste
1925
Agar-Agar
1943
Alginate
1955
Polysulphides
1958
Condensation-silicones
(Type 1 silicone)
1966
Polyethers
1976
Addition silicone
(Type II silicone)www.indiandentalacademy.com

Hydrophilic group
Hydrocolloids
Polyether
Hydrophobic group
Polysuphide
C – silicone
A – silicone (PVS)
• Works in wet environment
(blood and saliva)
• Readily wettable by the gypsum
• Resistant to wetting (repelled by
hemorrhage or tissue fluids)
• Not readily wettable by the gypsumwww.indiandentalacademy.com

ELASTOMERIC IMPRESSION MATERIALS
Depending on viscosity
Light body
Medium body / regular body
Heavy body
Putty
Depending on elastic properties and dimensional change
ANSI / ADA specification No. 19
Type I elastomeric impression material
Type II elastomeric impression material
Type III elastomeric impression materialwww.indiandentalacademy.com

PROPERTIES OF IMPRESSION MATERIAL
(Hydrocolloid group)
Reversible hydrocolloid
(Agar-Agar)
Sol Gel
Irreversible hydrocolloid
(Alginate)
Sol Gel
Physical
change
Chemical
change
Soluble alginate react with calcium sulfate
to form insoluble calcium alginate
Liquenfaction temperature
700
-1000
C
Gelation temperature
370
– 500
C

Agar-Agar :
Introduced by Sears 1937
First elastic impression material
Longest continuous use
Ingredients :
Agar (Organic hydrophillic colloid ) → 8-15%
Water → > 80-85%
Borax
Potassium sulphate
Available as :
Tray material
Syringe material www.indiandentalacademy.com

Irreversible hydrocolloid (Alginate) :
During World War II
Salt of alginic acid (anhydro βd mannuronic acid)
Ingredient :
Sodium / potassium triethanolamine alginate
Calcium sulphate
Sodium triphospate
Diatomaceous earth
• Dust free alginate
• Chromatic indicator

PROPERTIES OF HYDROCOLOIDS
Accuracy
Reversible hydrocolloid is most accurate
Irreversible hydrocolloid  Incapable of reproducing fine details
- Roughness of impression surface
Dimensional stabilty
As a result of syneresis and imbibition
Storage media – 100% relative humidity
– 2% potassium sulphate
Thermal change
Chilled water cooled trays (150
C)  warmer room temperature
(230
C) www.indiandentalacademy.com

Tear strength
• Poor tear resistance
• Subgingival extensions are susceptible to tear
Compatibility with gypsum
• Borax  retards setting of gypsum
• Sodium salt used in alginate  sodium sulphate
Rough or soft cast / dies

KEY PROPERTIES FOR ELASTOMERIC IMPRESSION
MATERIALS
Accuracy / Detail capture :
ADA No. 19 →fine detail of 25µm
PVS impression material → best
Reversible hydrocolloid → least
Reproduction of fine detail of gypsum die materials → 50 µm
Lower the viscosity → Increased fine detail
Putty material → reported fine detail of 75µm
Clinical consideration
One stage putty wash impression

DIMENSIONAL
STABILITY
Polymerization
shrinkage
Loss of
Byproduct
Thermal contraction
(370
C to 230
C)
Imbibition
(water, disinfectants)
Incomplete recovery
(viscoelastic behavior)

ANSI / ADA specification No. 19.
At the end of 24 hours contraction should not exceed 0.5 % for
type I and III material or 1.0% for type II elastomers.
Polysulphide Condensation silicone
Water Ethylalcohol
Impression should be cast not more than 30mins after removal.
Polyether and PVS impression → NO byproduct
Polyether  absoption and swelling should be casted within
one hour and stored in dry environment.
PVS  stored for weeks
Byproduct

Tear strength:
Measures the resistant to fracture of an elastomeric material
subjected to tensile force acting perpendicular to a surface flaw.
Point of consideration → Interproximal, subgingival areas
→ Slot and groove
Polymerized material
in the gingival crevice
Torn material during
removalwww.indiandentalacademy.com

Lowest Highest
Hydrocolloids, silicones, polyether, polysulphide.
Hydrocolloid –Tear strength value – Polysulphide
1/10th
Increase in consistency → Increase in the tear strength value
Snap removal → Increase in tear strength value

ELASTIC RECOVERY
Elastic → withdrawn from undercuts
“Rebound back”
No impression material → 100% elasticity
PVS impression materials → > 99%
Condensation silicone 98% and polyether 99%
• Greater the depth of undercut → greater the permanent
distortion
• Higher the viscosity → less elastic recovery.
Clinical consideration
To maximize elastic recovery eliminate or block the undercuts.

Flexibility / stiffness :
The stiffness of the impression material
Lowest Highest
Polysulphide, Condensation silicones, addition silicones, polyether
Reversible hydrocolloid → least rigid
The conventional polyether 27 times as stiff as the light body
polysulphide impression material.
Clinical considerations :
Impression of multiple periodontally compromised teeth
Long and thin preparations → # of delicate gypsum die.
Difficult to remove from undercuts (Exceeds the tear strength
of material) - Tearingwww.indiandentalacademy.com

Difficult to remove the impression from patient mouth
• Hard tissue undercut / soft tissue undercut
Custom tray with an adequate bulk of material in the area 3 times
the depth of undercut.
Undercut due to tilted teeth
Use of rigid impression material
• Dual arch impression to compensate for the - tray flexibility
- To provide rigidity

RHEOLOGICAL PROPERTY
(flow and viscosity)
Adequate flow → Grooves
Pinholes
Cervical margin detail
Thixotropic behavior:
Material become less viscous and more fluid under repeated action
of pressure.
PVS and polyethers → thixotropic
Pseudoplastic behaviour :
Viscosity of unset material decreases with and increase shearing
speed “shear thinning property”.
Significance of the property monophase impression technique
Use of high viscosity material.www.indiandentalacademy.com

Surface wetting :
Hydrocolloids → Truly hydrophillic impression material
(water based)
Detailed impression in “wet field”.
Polyether impression materials → hydrophilic
Need dry field to capture the detail for an acceptable impression
Conventional silicones → hydrophobic
Contact angle > 950
Difficult to cast the impression → Bubble free cast
Use of extrinsic /topical surfactant
Dilute solution of soap.
“Spray on” surfactant (debubblizer spray)
To lower the surface tension (decreases contact angle)

Newer hydrophilic silicone
Formulations
Addition of intrinsic surfactant
Nonionic surfactant (nonyl phenoxy polyethanol)
Graft the surfactant to the silicone polymer
(Improves the wettability and reduces the contact angle)
Studies → quality of the impression obtained clinically is unrelated
to the surface activation of the material.
Panichuttra R (1991) Chai JY (1991)
Newer hydrophilic materials performs no better than original
formulation of PVS in wettability of pouring the dies.www.indiandentalacademy.com

BIOCOMPATIBILITY
Probability of allergic or toxic reaction → small
Hypersensitivity potential → polyether catalyst
• Contact dermatitis
• No cytotoxic effects
Point of consideration :
Residual segment of impression material → severe gingival
inflammation.
Difficult to detect → radioopacity of polysulphide can help
Clinical consideration :
Examine the gingival sulcus immediately after impression removal.
- Evidence of tearing
- Tight interproximal contactwww.indiandentalacademy.com

CONTAMINATION
Inhibition of polymerization of PVS impression material.
Direct inhibition
• Direct contact with latex gloves
• Impression are made with rubber dam in place
Mechanism of inhibition → Element sulphur react with
chloroplatinic acid catalyst present in PVS impression material.
Element sulphur → Zinc diethyl dithiocarbamate (preservative/
vulcanizing accelerator)
Indirect inhibition
Indirect contact of tooth and periodontal tissues during tooth
preparation and gingival displacement procedure.
Limited to small isolated areaswww.indiandentalacademy.com

SIGN OF INHIBITED POLYMERIZATION
Rippled surface characteristics
Impression material
set against guaze
piece
Impression material
set against latex
sample
Rubber dam interfering with the
setting of an addition-curing
silicone
Unpolymerized rippled surface Polymerized surface

Unpolymerized material remain
adherent to prepare teeth surface
•Contaminated surface will be slippery and sticky to touch
Clinical consideration :
Use of non latex gloves – Vinyl gloves
– Polyethene gloves
Avoid touching the tooth preparation and gingival areas
Avoid handling retraction cord with gloved hands.
Baumann (1995) sulfur concentration 0.005%  total inhibition of
polymerization of PVS www.indiandentalacademy.com

Katsuhiko Kimoto et al 2005 → indirect latex gloves contamination →
“particulate sulphur / sulphur chloride may be easily transferred from
latex gloves to vinyl gloves and gingival retraction cord”
SEM
observation
EPMA
analysis
Sulphur particles
Contaminated vinyl gloves
Contaminated gingival
retraction cord
Elemental analysis

Effect of sulphur containing medicaments used with
gingival displacement cord
Duncan JD et al (1991) De Camargo et al (1993)
Inhibition of polymerization of PVS impression material is
attributed to indirect contamination
“Questioned the effect of retraction cord medicaments”
Aisling OM et al (2000)
Studied the effect of aluminium chloride, ferric sulfate and ferric
subsulfate on the dimensional accuracy and surface detail
reproduction of PVS impression material.
Aluminium chloride  Extremely rough, melted appearance of finish line.
Ferric sulfate  pooling of residual medicaments  destroying the marginal
integrity.
CLINICAL CONSIDERATION
Rinse the medicaments off tooth preparation
Browning et al (1994) simple rinsing with mouth wash, hydrogen
peroxide, air water syringe are in effective.

PRINCIPLES OF IMPRESSION MATERIAL
MANIPULATION
Uniform bulk of the material
Uniform amount of impression bulk → for uniform shrinkage
Cross sectional thickness requirement
Water based (hydroclloid) impression material - 4-6 mm thickness
provided by stock tray
Lower surface area / volume ratio → less dimensional change.
Elastomeric impression material – 2mm thickness
Provided by custom tray
Bomberg et al (1985) Difference in cross sectional thickness of
material in stock tray is about 1.5 to 2mm thicker than the custom
tray. www.indiandentalacademy.com

TRAY SELECTION AND PREPARATION OF THE TRAY
• Tray should be rigid.
• Dimensionally stable.
• Resist the deformation (loading heavy body material).
• Provides the space for optimal thickness.
Plastic vs metal stock trays

• Metal tray offers greatest rigidity compared to flexible plastic
stock trays.
• Stock trays mainly used in putty wash impression material.
Wassell and Ibbetson (1991) reported distortion when putty wash
was used in either flexible or rigid plastic tray either with or
without reinforcement.
Custom tray vs stock tray
• Controls thickness of impression material (approx. 2-3 mm)
• Gordon et al (1990) custom tray produces the die that were
more accurate compared to those produced by stock tray.
Selfcure tray acrylic material (should be made 24 hours before).
Light cure materials (can be used almost immediately).www.indiandentalacademy.com

Tray should be of 2-3mm thick to ensure sufficient rigidity.
Incorporation of stops
 Guide the clinician for positive seating
 Three widely spaced stops
 Non functional cusp of unprepared teeth, edentulous areas
or the palate.
Buccal ridges to facilitate easy removal
Painting of tray adhesives
(7-15 min drying time)

Adhesion of the impression material to the tray
For accurate impression → proper adherance to the tray
Impression material shrinks towards the tray adhesive as it
polymerize.
Chemical paint on tray adhesives
Bond strength of adhesive
Proper dry time → wet adhesive act as a lubricant
Cho GC et al (1995) painting the adhesive on the tray atleast 7-
15 min before making the impression permits formation of
adequate bond strength of the material to the tray.
Perforation / holes → 50% bond strength
Roughening the inner surface of tray (Grit SC paper) → 140%
bond strength. www.indiandentalacademy.com

Tin foil or aluminium foil should be used over the wax spacer to
prevent decrease in adhesive bond
Bond strength to tray
Chai et al (1991) adhesive strength to acrylic resin custom tray was
significantly lower than polystyrene or metal stock tray
VLC tray (triad)  increase bond strength

Adequate mixing and loading :
Earlier materials → base and catalyst tubes
Present materials → cartridges with mixing tips
→ Gun like dispensor
Automixing system :
• Lesser inherent voids
• Extend the essential working time
• Reduced waste
• Uniformity in proportioning

ELECTRIC MACHINE DEVICE
(Dynamic Mechanical Mixer)
Provides uniform mix with touch of a button
Far fewer voids in the set elastomerswww.indiandentalacademy.com

TISSUE MANAGEMENT
Control of moisture
Adequate displacement of the gingiva → “open gingival cuff”
To record precise extent of finish line and immediate tooth
surface below the finish line.
Emergence profile.
To prevent overcontoured restoration
For accurate detailed reproduction
0.2-0.3mm crevice opening
Mechanical
displacement
Chemical
adjuncts
Surgical
wideningwww.indiandentalacademy.com

Merocel tissue displacement strips
MECHANICAL DISPLACEMENT METHODS
Temporary widening of gingival
crevice  natural elasticity of
gingiva
Laufer BZ et al (1997) once
the cord is removed gingiva
can close up with in 30 sec.
Retraction cord Placement time
8 – 10 min

Expasyl Kaolin with aluminium chloride
(putty like material)
CHEMICAL ADJUNCT
•Control the hemorrhage / tissue fluids
•Used with non impregnated cord.
•Chloride and sulphates of aluminium and iron

Electro surgery (troughing)
SURGICAL WIDENING
Lasers
Thin lining of the gingival crevice is removed
Rotary instrument (gingitage)
Rotary diamond / ceramic burs
DISPLACEMENT GEL MATERIAL
Gel cord Tissue goo

AGAR IMPRESSION TECHNIQUE
Armamentarium :
Water cooled trays Conditioning unit
Tray and syringe
material
Procedure :
Tray material Syringe material Loaded tray in
tempering bath

Dentate arch is
flooded with water
Water cooling tubes
connected to seated
tray
Completed
impression
Disadvantages –
• Dimensionally unstable / distortion during gelation
• Initial expenditure for instruments
• Multiple pouring is not possible

ALGINATE IMPRESSION TECHNIQUE
Clinical interest :
Recording the dentition opposing a planned prosthesis
(non working cast)
For the study cast / diagnostic cast – diagnostic wax up
– mock preparations
For matrix – interim restoration (temporization)
CLINICAL CONSIDERATIONS
TRAY SELECTION
Perforated metal / rigid plastic trayswww.indiandentalacademy.com

TRAY MODIFICATION
 With tracing compound
 Wax – non rigid
– distortion
TRAY ADHESIVE
Perforations – insufficient
To prevent detachment of
impression
(Distortion of the cast)
Extend 2-3 mm outer surface
Loading of the tray
Sectional placement Wet gloved finger
Detachment 1mm
occlusal error

MOUTH PREPARATION
Smearing / buttering
Rinsing with water
Pre packing palatal vault
Blocking – large interdental spaces under the contact points
– bridge pontic to prevent drag / tearing
(with wax)

TRIMMING AND HANDLING THE IMPRESSION
Removal of unsupported alginate Should not be placed firm surface
(anterio-posterior distortion)
“Holding tree” Rinsing with water
(saliva / blood / food debris)
Completely recorded
trimmed impressionwww.indiandentalacademy.com

HYDROCOLLOID LAMINATE TECHNIQUE
ALGINATE – AGAR METHOD
Suggested by Schwartz in (1951)
Prepared tooth
surfaces
Injection of reversible
hydrocolloid
Stock tray with chilled
alginate
Combined alginate –agar impression Master castwww.indiandentalacademy.com

Critical to success  bond between agar and alginate
Advantages :
• Satisfactory surface reproduction
• Good wettability (smooth, dense model)
• Simple conditioning (no tempering bath / water cooled trays)
• More economical
Disadvantages :
• The bond between agar and alginate is not sound
• Higher viscosity alginate displaces agar hydrocolloid
Lin et al (1988)
Accuracy of the combination hydrocolloid material was
comparable to that of polysulfide and better than either reversible
or irreversible hydrocolloid.

PUTTY WASH IMPRESSION TECHNIQUES
(Stock tray impression technique)
One stage or one step putty wash impression
(Simultaneous technique / sqash technique / twin mix technique)
In this technique putty and wash are recorded simultaneously
Disadvantage :
Difficult to control thickness of wash material
Higher viscosity material displaces the wash material
- Critical areas captured in putty rather than light body
Setting distortion of the putty add to over all distortion of
impression

 Horizontal ridges / creases
•Axial surfaces of the teeth
•Improper blending of
putty and wash phases

TWO STAGE OR TWO STEP PUTTY WASH
TECHNIQUE
Two steps unspaced impression technique
Preoperative putty impression is recorded
Preset putty impression is relined with thin layer of wash
Two step spaced impression technique
Preoperative putty impression is made
Space for the light body wash material is provided to reline
the putty

Putty impression with polyethene spacer sheet and
then wash
• Spacer prevents the penetration of the putty into the interproximal
areas
Gauging away the putty impression to provide space and
then wash
Scalpel to create space

PUTTY SCRAPER / SCOOP
Sluices / escape channels are cut  excess material to escape
PVS putty impression as custom tray with 2 mm space
Putty material is used to fabricate a custom tray
With a two layer of base plate wax over the
diagnostic cast as a 2 mm space

DISADVANTAGES
• Distortion during seating the putty.
Pressure while seating the putty Compression of impression
Shorter narrower dieElastic recovery

•Distortion – Outward flexion of the trays
- Recoil of flexible trays
-Resulting in dies undersized buccolingually
•Distortion – Unspaced putty wash
Build up of hydrostatic pressure.
Put the set putty and walls of the tray outside
Arbitrary spacing
Uneven thickness of wash uneven shrinkage
Locally relieved impression (sectional wash)
Incomplete seating of the set putty
Stepped occlusal surface www.indiandentalacademy.com

INJECTION MOULDED PUTTY WASH TECHNIQUE
Brian Millar (2001)
Preoperative full arch putty impression
Drilling the hole through the tray perforation
Cut away gingival margin region and buccal
escape channel
Putty is reinserted and light body
is injected through the hole

Injection moulded
impression
Advantage :
• Can be used with single arch or dual arch trays
• Suited for recording of multiple prepared teeth
• Economical
• Can be used to repair impressions

DUAL PHASE IMPRESSION TECHNIQUE
(Multiple mix technique,laminate single impression technique
custom tray impression technique)
Two consistencies
• Light body syringe material
(wash type)
Heavy body – tray material
• Tray material will force the light
body material into the gingival
sulci and preparation detail
Custom tray with 2 – 3 mm space

ADVANTAGES
Uniform thickness of impression material (2-3 mm)
Viscosities of 2 materials reduces drags and improves the blending of
2 phases.
Good marginal definition.
No distortion due to recoiling of plastic tray and putty.
Less impression material is required.
DISADVANTAGES
Construction of custom tray (time / cost)
Differential shrinkage

Monophase impression technique
(Single viscosity technique)
•Medium viscosity – polyether or addition silicone
•Used as both tray material and syringe material
•Custom tray with 3 mm spacer
Depends on pseudoplastic property
DISADVANTAGES
•Reduced ability to flow into intra coronal features and gingival
crevice
•Greater amount of polymerization shrinkage compared to heavy body
•Surface reproduction may not be as good as light body materialwww.indiandentalacademy.com

BAND / TUBE IMPRESSION TECHNIQUES
Impression techniques in this category
• The original copper band and modeling compound
• Variety of copper tube and elastomer combination
• Tube impression with acrylic resin and elastomer combination
Characteristics
• Rigid carrier for the impression material (buried/embedded in final impression)
• Registration of finish line is achieved in carrier
• Carrier is designed to extend slightly apical to finish line
Sulcular extension of tube  “Displacement of gingiva”
Retraction less impression or cordless procedureswww.indiandentalacademy.com

THE ORIGINAL COPPER BAND AND MODELING COMPOUND
2mm wider Extend 1 mm beyond the
finish line
Compound plug
Holes for retention
Internal surface coated
with tray adhesives
Copper Tube And Elastomers

TUBE IMPRESSION WITH ACRYLIC RESIN
AND ELASTOMER COMBINATION
MH Goldfogel et al (1989)
Prepared tooth with final
finish line
Aluminium tube trimming / adaptation
Tube with acrylic resin
Acrylic resin tube with recorded
finish line

Tube is relieved for
wash space
(0.5mm)
Relieved tube with
vent hole
Polysufide wash
impression
Over impression with
embedded tube
Cross section of impression tube
Gingival tissue
Prepared tooth
Relieves space with wash
Acrylic resin
Aluminium tube
Vent hole

Disadvantage :
Band adaptation and trimming  time consuming
trauma and haemorrhage
Copper band and impression compound
Distortion of the compound
Rigid nature – fracturing of dies
Replaced with band and elastomers techniques
Softer band / tubes – flexing distortion
Elastic deformation of elastomers which may reversed when
impression is removed
Advantage :
Mechanical displacement of gingiva  Clean and complete
impression

INTRA ORAL COPING IMPRESSION TECHNIQUES
Polycarbonate crown shell and elastomer
Resin coping and elastomers
Interim restoration (Resin crown) with elastomers
Cast impression coping technique
A
B
C
Preformed shell
Impression material
Tray material
Impression using preformed polycarbonate crown shell
By Dimashkish and Steven M Morgano (1995)
Crown shell with regular body is
placed over prepared tooth
Pick up impression with regular body

Trimmed individual copings
Custom tray field with heavy body
Over impression is
made
Final impression
Individual coping with
syringe material
RESIN COPING AND ELASTOMER
Kirk Gardner, Gerald H (1981)
Resin coping with elastomers (silicon, polyether)

INTERIM RESIN COPINGS AND ELASTOMERS
Impression using vacuum adapted temporary splint
Anthony La Forgia (1970)  for multiple prepared abutment
Temporary splint (interim
restoration) to create tray
former
Two impression
- Heavy body
- Equal parts of light and regular body
Over all impression is made using
regular body rubber base

CAST IMPRESSION COPING TECHNIQUE
George J Vasilakis and Maria D Vasilakis
Procedure steps Fabrication of metal copings
- Coping with 0.7 mm internal space
- Internal surface of coping
 Roughing with sand blasting
 Coarse diamond
 Adhesives
- Coping with nail shaped head and
retention beads, buccal marking
- The clean copies are tested for
proper fit and preparation coverage

First impression (wash step)
Stock tray with master / over impression
( polyether material)
Final impression with trapped cast coping
Negates need for gingival displacement
Can be used for full mouth reconstruction
Flexing distortion www.indiandentalacademy.com

ADVANTAGES OF INTRAORAL IMPRESSION COPING
SYSTEM
Recontouring of copings / provisional crown is easier and avoids
trauma to the gingival tissue.
Small bulk of impression material  minimizes the
polymerization shrinkage.
Intraoral copings hydraulically displaces air and fluids
For multiple preparations
- Difficulty in controlling saliva / fluids
- Short working time
Negates need for gingival displacement

Three impression procedures using three viscosities of impression materials
Matrix forming
material
Matrix impression
material
Heavy body material Medium body
Tray impression
material
Semi rigid material
(occlusal registration material)
MATRIX IMPRESSION SYSTEM (MIS)
Gus J Livaditis (1998)

CLINICAL STEPS FOR IMPRESSION MAKING
Completed tooth preparation Clear plastic carrier
(4 mm of
space)
PVS occlusal
registration material
Trimming of the matrix
(1/2 to 2/3
beyond the prepared
Marking for crest
of gingiva and
sulcular extension
Refining the matrix
Matrix formation
Trimming the inter
proximal embrasurrswww.indiandentalacademy.com

Relief for axial wall (0.25 – 0.75)
with intac incisal or occlusal aspect
Refined matrix in place
Completing the impression
Matrix loaded with high heavy body and
seated with light vertical pressurewww.indiandentalacademy.com

Stock tray with medium body
seated over matrix impression
Full completed impression
• Controlled dental gingival environment
• Improves the gingival displacement and sulcular cleansing phase
Features
• Registration of subgingival finish line
• Gingival retraction and relapse
• Haemostasis and sulcular cleansing
• Strengthened the sulcular flange of the impression
• Simplification for making complex impressionswww.indiandentalacademy.com

DUAL ARCH IMPRESSION TECHNIQUE
(Double bite, closed bite, triple tray technique)
Introduced by Wilson and Werrin (1983)
Captures the – prepared teeth
opposing arch
interocclusal articulation
Maximum
intercuspation position
(MIP)
Indications
One or two units bounded by intact and
opposed dentition
Patient cooperation – S/be able to close in MIP
Stable, reproducible MIP
Space for connector bar behind the last molars
(quadrant trays) www.indiandentalacademy.com

Contra indications :
Rapidly ascending ramus
Excesses soft tissue distal to molars
Advantages :
Eliminates mandibular flexure
Less chair side time / less effort / fewer steps  three separate
procedures in one step
Less impression material
More comfortable to patient
Disadvantages :
Not a functionally generated technique  limited to one unit
Non uniform distribution of impression material
Flexible plastic tray, depends on impression material for rigidity

DUAL ARCH IMPRESSION TRAYS
Complete arch impression tray
Metal trays
Plastic trays

DUAL ARCH IMPRESSION TECHNIQUES
One step technique
Low or medium viscosity impression material (for syringe
material)
Bite registration material or heavy body material (tray material)

1. Prepare tooth
2. Verify that patient can close with tray in mouth.
3. Check the patient can close repeatedly into MIP
4. Adhesive on side of tray-not on gauze
5. Mix heavy body & load tray
6. Mix light body & load syringe. Start timing
7. Inject light body and have patient close in ICP
8. Orient and seat the tray ask the patient to close in MIP (check
the reference teeth
9. Remove impression and inspect for completeness
Two step technique :
Preoperative impression (putty / bite registration material)
Second impression syringe ( light / monophase)
Limitation : Depends on patient ability to bite into same MIPwww.indiandentalacademy.com

TWO STAGE LAMINAR IMPRESSION TECHNIQUE
Developed by Dr. Gary Schoenrock (1989)
Laminar flow  the way of fluid under pressure flows with the
constricted space
Required preoperative double arch impression (bite registration
material)

Completed impression
To enlarge exit holeDitching around gingival margin
Seated
Pre liminary impression
Tip placed in
distal hole
Impression flows out
of mesial hole

Advantage :
Light body material engulfs the tooth without creating
compressive forces
Residue (blood, etc) flushed out of the exit hole
Used with double arch tray

FLAWS RELATED TO IMPRESSION TECHNIQUE
Visible flaws :
Finish line not visible  Inadequate gingival displacement
• Gingival inflammation and bleeding
 Delay impression for 10 days
 Papillary injection of LA
 Microbrush soaked in ferric / aluminium surface
• Crevicular fluid and heamorrhage
Use of two cord technique  better moisture controlwww.indiandentalacademy.com

Poor moisture
control
Dry field
Air bubbles / voids in critical areas
Mixing
Syringing
 Keep syringe tip in expressed
material
 Start syringing from distal
interproximal area (distoligual)
 Fill the base of grooves, boxes first
Tray loading and tray seating

Drags
Reason :
Poor flow of putty
Premature syringe of impression material
Poor bond between the tray and syringe material
Unset / unpolymerized impression material  contamination
INVISIBLE FLAWS
Tray and impression recoil
Permanent deformation
Detachment of impression from the trays

DISINFECTIONS OF IMPRESSIONS
• To prevent exposure and cross infection
• Disinfection before poring the cast.
Disinfection methods :
• Spray on disinfectants
• Immersion of impression in chemical dinifectant (Submerged /
soaking)
Types of chemical disinfectant used :
• Chlorine compounds
• Synthetic phenolic compounds
• Glutaraldehyde
• Idophores
• Combination of phenols and alcohols

Hydrophilic impression material → hydrocolloids, polyether
should be sprayed rather than immersion.
Idophore sprays, sodium hypochlorite sprays (1:10 ratio).
Agar (reversible hydrocolloid) → 10 min immersion in 2%
alakaline glutaraldehyde → more than 20 min affects the
dimensional stability and surface detail.
Alginate (irreversible hydrocolloid) → Westerholm et al (1992)
full strength (5.25%) sodium hypochlorite spray.
Polysulphide and condensation silicone immersion in sodium
hypochlorite, glutaraldehyde 10-30min.
Jennings K (1991) fewer microorganisms are retained on the
surface of PVS impression than on other material prior to
disinfection.

Holten et al 1991
Dimensional stability of PVS after sterilization procedure using
conventional autoclave system and ETO (ethylene oxide gas)
Sterilization with ethylene oxide gas resulted in gas inclusion in
the impression material which form bubbles in dyes.
Hesby RM et al (1997)
Radiofrequency glow discharge for disinfecting PVS impression
This procedure claimed to clean and improve the wettability of
the impression surface.

REFERENCES
• Phillips science of dental materials. 11th
edition, Anusavice Kenneth J.
• Contemporary fixed prosthodontics. 3rd
ed. Rosensteil
• Fundamental of fixed prosthodontics 3rd
edition, Quint Pub Shillinburg H.T
• Tyrman’stheory and practice of fixed prosthodontics 7th
edition. Malone
milliam FP.
• Dent update 2005; 32: 169-175.
• Dent update 2005; 32: 374-393
• JPD 2005; 93: 433-8.
• Dent Update 2004; 31: 40-45
• DCNA fixed prosthodontics 2004 48(2): 445-471
• Gen Dent 2003; 48-50.
• BDJ 2002; 192(7): 377-387
• BDJ 2002; 192(12): 679-689.
• Compendium 2002; 23(12): 1172-1182.

• Quint Int 2000; 31: 201-203.
• JPD 1992; 68: 728-32
• JADA 1983 (106) 194-195.
• JADA 1996; 127: 234-240.
• JADA 1997; 128: 1277-1281.
• JPD 1983; 49(2): 198-202.
• BDJ 2001; 191(7): 402-406.
• BDJ 2002; 192 (12): 679-690.
• JPD 1998;75: 208-16.
• JPD 1998; 79: 200-7.
• JPD 1970; 23(1): 44-50
• JPD 1995; 73: 95-6.
• Qun Dent 1989; 20(8): 555-560
• JPD 1971; 26(5): 491-496
• JPD 2000; 84: 237-40
• JPD 1975; 33(4): 417-421.www.indiandentalacademy.com

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