Impressions in Fixed Partial Dentures

IMPRESSIONS
IN
FIXEDPARTIAL DENTURES
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION

 To obtain an impression is the first step necessary for
the indirect fabrication of a prosthesis.
 An impression is an imprint or negative likeness of
teeth and tissues.
 Fixed prosthodontics is practiced as indirect
restorations.

 Well-fitting indirect restorations can only be made if
there are accurate casts of the oral tissues available,
made from high quality impressions.
 A good quality impression is only obtained when we
have a thorough knowledge of materials, their
properties, and techniques for their best manipulation.

TERMINOLOGIES

IMPRESSION : A negative likeliness or copy
in reverse of the surface of an object; an
imprint of the teeth and adjacent structures for
use in dentistry – G.P.T-8
IMPRESSION TRAY : A receptacle into
which suitable impression material is placed to
make a negative likeliness (or) a device that is
used to carry, confine, and control impression
material while making impression– G.P.T-8

IMPRESSION MATERIAL: Any substance or
combination of substances used for making an
impression or negative reproduction. – G.P.T-
8
IMPRESSION TECHNIQUE : A method and
manner used in making a negative likeness. –
G.P.T-8

HistoryHistory
 Philip Pfaff-1756
 First described taking impression with softened
wax
 Christopher Francois Delabarre-1820
 Introduced the metal impression tray
 Chapin Haris-1853
 First used Plaster of Paris for making impressions
 Charles Stent-1857
 Introduced the first impression compound

 Sears-1937
 First used agar hydrocolloids for recording
crown impressions.
 United States-1945
 Introduced alginate during World War II.
 SL Pearson-1955
 Developed synthetic rubber base impression
materials
 Polysulfide- Late 1950’S
 First developed as an industrial sealant.

 Condensation Silicone- Early 1960’s
 Addition Silicone-1970’s
 Polyether- Late 1970’s
 Polyether Urethane Dimethacrylate - Late
1980’s

Properties Of An Ideal Impression
1)Complete plasticity before cure
2)Sufficient fluidity to record fine detail.
3)The ability to wet the oral tissues.
4) Dimensional accuracy.
5)Dimensional stability.
6)Complete elasticity after cure.
7)Optimal stiffness. www.indiandentalacademy.com

Impression Materials Used In F.P.D
1)Hydrocolloid impression material
a) Reversible hydrocolloid
b) Irreversible hydrocolloid
2)Elastomeric impression materials
a) Polysulfide
b)Addition silicone
c) Condensation silicone
d)Polyether Dimethacrylate

AGAR (reversible hydrocolloid)
History
 In 1925, Alphous Poller of Vienna was granted a
British patent for a totally different type of
impression material.
 Later Poller's 'Negacoll’ was modified and
introduced to the dental profession as 'Dentacol’
in 1928.

Example
 Slate Hydrocolloid (Van R)
 Cohere
 Superbody
 Super syringe

 Available as - syringe and tray material
Composition:
Component Function Composition
Agar Brush – heap structure 13 – 17%
Borax Strength 0.2 – 0.5%
Potassium Sulfate Gypsum hardener 1.0 – 2.0%
Water Reaction 80%
Alkyl Benzoate Prevent growth of mold in
impression material during
storage.
0.1%
Color and Flavors Taste & appearance Trace

 Setting reaction:
Agar hydrocolloid (hot) Agar hydrocolloid (cold)
(Sol) (Gel)
Cool to 43 C
Heat to 100 C
Manipulation:
Three chamber conditioning unit
(1) Liquefy at 100 0
C for 10 minutes converts
gel to sol
(2) Store at 65 – 68 0
C place in tray
(3) Temper at 46 0
C for 3 minutes
seat tray
(4) cool with water at 20 0
C for 3 minutes
converts sol to gel

Advantages
 Accurate reproduction of surface detail
 Hydrophilic
 displace moisture, blood, fluids
 Inexpensive
 No custom tray or adhesives
 Pleasant
 No mixing required

Disadvantages
 Initial expense
 special equipment
 Material prepared in advance
 Tears easily
 Dimensionally unstable
 immediate pour
 single cast
 Difficult to disinfect

ALGINATE (irreversible hydrocolloid)
 Alginate was developed as a substitute for agar when
the agar impression material became scarce because
of World war II (Japan was a prime source of agar).
Examples
 Jeltrate (Dentsply/Caulk)
 Coe Alginate (GC America)
 Integra
 Superjel
 Tropicalgin
 Xantalgin

Composition
Component Function Weight percentage
Na / Potassium
alginate
Soluble alginate 15
Calcium sulfate
dihydrate
Reactor 16
Potassium titanium
Fluoride
Accelerator 3
Zinc oxide Filler particles 4
Diatomaceous earth Filler particles 60
Sodium phosphate Retarder 2

Modified alginates
 Alginate in the form of sol - containing the water
but no source of calcium ions - a reactor of
Plaster of Paris
 Alginates modified by the incorporation of
silicone polymers (paste form)
 Dustless alginate - glycerin incorporated to
agglomerate the particles.
 Making the powder denser so that no dust is
formed when the lid is opened after tumbling.

Setting reaction: (gelation process)
2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4
Na alginate + CaSO4 Ca alginate + Na2SO4
(powder) (gel)
H2O

NEWER ALGINATES
 Kromopan 100.
manufactured by LASCOD
 MILLENIUM ALGIN is
considered an alginate of
new generation alginate.
 The impression can be
stored for many hours in a
Long Life Bag before
casting the model without
undergoing any change for
over 100 hours

AUTOMIX DISPENSING: (Alginate
from Kerr international)
 No hand mixing. Eliminates
mess and cleanup. Saves time and
material.
 Delivery options. Cartridge or
Volume™ auto mix dispensing.
 Impressions remain stable. You
can pour immediately or when
it’s convenient. Impressions
retain dimensional stability for
months.

Manipulation
 W/P ratio as specified by the
manufacturer.
 Mixing is done in a clean flexible
plastic bowl with a clean wide bladed,
reasonably stiff metal spatula.
 The mixing is started with a stirring
motion to wet the powder with water.
 Once the powder has been moistened,
rapid spatulation by swiping or
stropping against the side of the bowl is
done.
 A vigorous figure-eight motion can also
be used

Mechanical mixing devices

Advantages:
 Inexpensive
 Easy to use
 Hydrophilic
 displace moisture, blood, fluids
 Stock trays

Disadvantages:
 Tears easily
 Dimensionally unstable
 immediate pour
 single cast
 Lower detail reproduction
 unacceptable for working cast of fixed
prosthodontics
 High permanent deformation
 Difficult to disinfect

NON AQUEOUS ELASTOMERIC
IMPRESSION MATERIALS
 These are Synthetic rubbers.
 These mimic natural rubber (scarce during World
War II)
 Initially called rubber impression materials
 Currently referred as elastomers or elastomeric
impression materials.

Polysulfide
 The first elastomer used
for dental impressions
Examples
 Permlastic (Kerr)
 Omni-Flex (GC America)
– copper hydroxide
system.
 Coe-flex (GC-Amer)
 Neo-plex (Miles)

 Available in 3 viscosities,
 light body and medium body heavy body.

Setting reaction:

Manipulation
 With the proper lengths of the two pastes squeezed
onto a mixing pad or glass slab, the catalyst paste is
first collected on a stainless steel spatula and then
distributed over the base, and the mixture is spread
out over the mixing pad.
 The mass is then scraped up with the spatula blade
and again smoothed out.

 If sufficient force is applied and spatulation is
performed rapidly, the material will seem thinner
and easier to handle. This phenomenon is known
as pseudoplasticity.
 Most accurate impressions are made using custom
acrylic trays because of uniform thickness of the
material.

Advantages Disadvantages
 Long working time
 Proven accuracy
 High tear resistance
 Less hydrophobic
 inexpensive to use
 Long shelf life
Requires a custom tray
Must be poured in
stone immediately
Potential for
significant distortion
Odor offends patients
Messy and stains
clothes
Second pour is less
accurate

SILICONES

CONDENSATION SILICONE
 Condensation reaction – a polymerization reaction in which
the polymer chains all grow simultaneously and a reaction
byproduct is formed.
Available In Three Viscosities:
 Light body
 Medium body
 Putty body
Supplied as:
 Paste – two pastes in collapsible tubes
 Putty – jars

Examples:
 Speedex
(Coltene/Whaledent)
 Primasil (TISS Dental)
 Accoe (GC-Amer)
 Xantopren (Unitek)
 Elasticon (Kerr)
 Cuttersil (Miles)

Composition:
Composition Components Function
Base paste Hydroxyl terminated
polydimethyl siloxane
prepolymer
undergoes cross linking
to form rubber
Silica Filler
Reactor Orthoethyl Silicate Cross linking agent
Stannous octate Catalyst

Advantages:
 Better elastic properties
 Clean, pleasant
 Stock tray
 putty-reline
 Good working and
setting time
Disadvantages:
Permanent deformation –
high – 1-3%
Poor dimensional stability
high shrinkage
polymerization
Hydrophobic
poor wettability

ADDITION SILICONES
 Frequently called polyvinylsiloxane or vinyl
polysiloxane impression materials.
Supplied in 4 viscosities
 Light body
 Medium body
 Heavy body
 Putty

Examples:
 Extrude (Kerr)
 Express (3M/ESPE)
 Aquasil (Dentsply Caulk)
 Genie (Sultan Chemists)
 Virtual (Ivoclar Vivadent)

Composition:
Components Function
Base paste Hydroxyl terminated
polymethyl siloxane
prepolymer
Undergoes cross linking
to form rubber
Colloidal silica Filler
Reactor Polyvinyl silicone
prepolymer
Colloidal silica Filler
Chloroplatinic acid Catalyst

Advantages:
 Excellent reproduction of
surface details
 Highly accurate
 High dimensional stability
 pour up to one week
 Stock or custom trays
 Multiple casts
 Easy to mix
 Pleasant odor
Disadvantages:
 Expensive
 Short working time
 Lower tear strength
 Possible hydrogen gas
release

POLYETHER
 First material introduced for dental impressions.
 Introduced in Germany in late 1960s.
Available as
 Base and accelerator in collapsible tubes.
 The accelerator tube is usually smaller.
 Earlier supplied in single viscosity.
 A third tube containing a thinner was provided.
Available in 3 viscosities
 Light body
 Medium body
 Heavy body

Examples
 Impregum F (3M/ESPE)
 Permadyne (3M/ESPE)
 Pentamix (3M/ESPE)
 P2 (Heraeus Kulzer)
 Polygel (Dentsply Caulk)

SETTING REACTION:

Advantages
 Highly accurate
 Good dimensional
stability
 Least hydrophobic
 Good surface detail
 Pour within one week
 Multiple casts
 Good wettability
 Good shelf life
Disadvantages
Expensive
Short working time
Rigid
difficult to remove from
undercuts
Bitter taste
Low tear strength
Absorbs water
- changes dimension
- Leaches components

POLYETHER URETHANE
DIMETHACRYLATE
Composition:
 - polyether urethane
dimethacrylate resin.
 - diketone initiator
 - amine accelerator
 - 40 – 60% silica filler
(SILICON DIOXIDE)

 Clear tray (TRANSPARENT),
 photo initiated by 400 – 500 nm blue light
 Advantage - unlimited working time
(CONTROLLED BY OPERATOR),
 short setting time
 Disadvantage - surface polymerization is inhibited by
moisture.

Impression Techniques
 1. Stock tray technique
- Double mix
- Single mix
 2. Custom tray technique
- Single mix
 3. Closed bite double arch technique
 4. Copper band technique
 5. Reversible hydrocolloid technique

STOCK TRAY IMPRESSION
TECHNIQUE (Putty wash technique):
Mixing method: Double mix and single mix
Procedure :
 Place patient in supine position.
 Operator is positioned at nine o clock and
assistant is positioned at 3 o’clock position.
 Select tray type based on relative need for
retention and personal preference.
 Select tray shape and size based on patients arch
shape and size.

 Coat the tray with adhesive on
the inside and rim.
 Mix the high viscosity putty
impression material according to
manufacturer’s instructions.
 Roll putty into elongated
cylinder.
 Insert into the stock impression
tray.

 Cover putty with the manufacturer’s
spacer (a sheet of polyethylene)
 Insert and seat the tray with a rocking
motion.
 Hold and wait until initial set.
 Remove from the mouth with minimal
sideward movement.
 Wait and test for final set with the
clinical final set, which is when a finer
nail impression rebounds completely.
 Peel off the spacer.
 Remove excess impression material with
a sharp knife.

SINGLE MIX TECHNIQUE:
MAKING FINAL IMPRESSION:
 Choose a large mixing pad
approximately six by eight
inches.
 Choose a spatula that is long
enough to pick up the mixed
impression material, yet
sufficiently pliable to mix the
material against the pad.

 Mix the low-viscosity,
impression material according to
manufacturer’s instructions.
 First use a circular motion,
joining the two strands. Then a
figure eight motion to blend and
flatten the mixture onto the
mixing pad.
 While flattening the mixture,
limit the number of times of
lifting the spatula from the pad,
this reduces the number of voids
in the mixture.

 Load the low viscosity impression
material on to a syringe .
 Syringe in the inaccessible area
first eg disto lingual line angle.
 Seat the tray .
 Wait for the final set.
 Remove the tray parallel to the
preparation path of withdrawal.
 The impression is evaluated for the
finish lines and for any distortion
and tear.

DOUBLE MIX TECHNIQUE:
 For the stock tray double mix insert the low viscosity
impression material into the tray without overfilling it.
 Spread the cheeks one at a time, first with the tray and then
with an index finger.
 Position the tray over the arch.
 Seat from posterior to anterior, allowing the excess to
extrude anteriorly.
 Apply force in a vertical direction until further seating is
impossible.
 Evaluate final position and adjust tray quickly if necessary.

EVALUATING FINAL
IMPRESSION
 Elastomeric material should be
present 0.5 mm beyond visible
finish line.
 Note presence of bur marks, the
junction of smooth root surface,
and continuous finish line.
 There should be no shiny
smooth areas; if present, they
suggest moisture contamination.
 There should be no tray show-
though in any areas of the
impression except at tissue
stops.

 There must be no voids present,
they suggest mixing problems or
contamination.
 There should be no thin areas
leaving the finish line unsupported.
These areas distort under the weight
of the stone.

Custom Tray Fabrication For Elastomeric
Impression
1)Mark the border of the
tray on the diagnostic
cast with a pencil
approximately 5mm
apically to crest of the
free gingiva.

2)Adapt a wax spacer to the
diagnostic cast two layers
for 2.5mm thickness
approximately.

Tray Stops

3)Apply a layer of tinfoil over
the wax.
4)Mix autopolymerizing acrylic
resin according to manufacturers
recommendation
5)Adapt the resin to the cast
when in dough stage.

Tray handle is made
Borders are trimmed and the tray is polished

Lateral wings can be made which will help in easy
removal of the tray

Prepare syringe:
 Lubricate the syringe lightly.
 Trim tip. Open orifice to increase rate of flow or close
orifice to decrease rate of flow.
 Measure arch length of tray to guide in dispensing the
amount of elastomer. (Dispense one time the length
of the tray for the low viscosity elastomer).

Making the final impression.
Medium or high viscosity is used in
the tray and low viscosity in the syringe.
The syringe is loaded with the low
viscosity material and syringed in the
prepared site.
The high viscosity material is placed
in the custom tray and seated in the
mouth.

The impression is removed and
evaluated.

Close Bite Double Arch Method
synonyms :dual quad tray, double arch ,
triple arch , accu -bite ,closed mouth impression.
Requirements
The articulator should provide for a positive stop or there should
be sufficient teeth to maintain the vertical dimension.
There should be sufficient space distal to the terminal tooth in
the arch to allow tray approximation.

Advantages
The physical deformation of the mandible is minimal
The shifting of teeth occurring during maximum intercuspation
is captured.
Less impression material is needed.
Less gagging may occur.
Disadvantages
The tray is not rigid .
Limited to one casting per quadrant .
The distribution of impression material is not uniform

Technique
Evaluate the fit of the tray in the
patients mouth.
Observe the complete bilateral closure
and the patients comfort.
Practice till the patient is familiar with
the task.

Making the final impression
 Mix the low viscosity material and
load the syringe
 The high viscosity material is used in
the tray.
 After the low viscosity material is
syringed the tray is positioned on the
arch.
 Instruct the patient to close the mouth
and observe for the interdigitation on
the opposite arch.
 Wait for the material to set .

Instruct the patient to open the
mouth remove the tray by
applying equal pressure bilaterally.
Evaluate the impression.

Copper Band or Tube Method
The copper band is used to salvage an impression of multiple
preparation where there is only vague margins on one or two
preparation that are not adequately replicated in the impression.
Fitting of the copper band to preparation
A copper band is selected and annealed by heating on a flame
and quenching in alcohol.
Mark the finish line with the explorer and round off the edges.
evaluate the fit and cut orientation hole in top one fifth of the
facial surface .

Copper band with orientation holes

Copper band contoured

Evaluating the fit of the copper band
The circumference of the copper
band must be such that it will fit
over the preparation and still
project into the gingival crevice.
An oversize band should not be
used since it will impinge on the
gingival tissues.

Making the compound plug
The red stick compound is heated over the Bunsen flame .
Insert the warm compound mass to fill approximately the top
third of the copper band.
Seat and orient on to preparation and compress excess in to the
band.
The compound should just touch the occlusal surface .
Remove and evaluate the impression, only the occlusal surface
should be impressed.
Remove 0.2mm of the compound to create space for the heavy
body poly vinyl silicone.
Drill a hole through the centre of the compound plug.

Making the impression.
Make 4 to 5 holes evenly distributed above the bottom of the
copper tube for the retention of the impression material.
Coat the internal surface sparingly with adhesive .
Clean and isolate the preparation.
Mix heavy viscosity material and inject in to the band and
position it on the tooth.
Wait the material to set remove the band and inspect the
impression

Copper band with the final impression

Reversible hydrocolloid technique
This impression technique requires a special conditioning unit
which consists of 3 thermostatically controlled water baths.
1. A liquefaction bath .
2.A storage bath .
3.A tempering bath.

Rimlock trays with stops

Procedure
Select the correct size of water cooled impression trays.
Place small modeling compound or prefabricated stops in the
tray to prevent over seating .
Fill the impression tray with heavy bodied material from the
storage bath and place it in the tempering bath
Load the syringe material in the syringe and replace it in the
storage bath.
Carefully remove the retraction cord and flood the tooth with
water.

Inject the syringe material on the tooth cover the entire tooth.
Remove the impression tray from the bath wipe with the gauze
and place it in the mouth.
After seating cold water is circulated through the tray until the
impression material is set.
Remove the impression with a rapid motion, wash with cold
water ,evaluate for accuracy.

Removal of the retraction cord

Injecting hydrocolloide into the sulcus

Final impression in reversible hydrocolloid

The matrix impression system
 The system uses a custom matrix to control the sulcular
environment and to deliver the impression material to the
subgingival to be immersed, it also incorporates the
Attributes of traditional impression methods and
overcomes in partial the deficiencies in registration of the
subgingival Margins, gingival retraction and relapse,
homeostasis and sulcular cleaning strengthening the
sulcular flange of impression and simplification for
making complex impressions.

The system uses three impression materials
 A suitable elastomeric semi rigid material to form the
matrix.
 A high viscosity elastomeric impression material which
will preferably bond to the matrix forming material,
required to make an impression of the preparation of the
matrix
 A stock tray with medium viscosity elastomeric
impression material to pick up the matrix impression and
remaining arch not covered by the matrix.
 Carrier for matrix forming material, it may be either
custom made or stock available.

Matrix impression material :
 This material is used to fill the matrix and generate
the critical portion of the impression.
 It would be a high viscosity material to facilitate the
displacement of the gingival and to effectively flush
the debris out of the sulcus.
 High viscosity polyether is preferable for this
procedure.

Tray impression material:
 The impression material that is placed in the stock
tray should be compatible with and bond to the
matrix forming material and the impression material
lining the matrix.
 The viscosity of the tray material should be
considerably less than that of the matrix material to
facilitate impression removal because the matrix
manages the critical portion of the impression
removal because the matrix manages the critical
portion of the impression; a stock tray is used to
incorporate the matrix and the remaining teeth in the
arch.

Matrix forming material :
 On setting this impression material needs to provide
a semi rigid matrix .
 The matrix forming material should register details
equal to the best impression materials
 Matrix forming materials should be rapid setting
and compatible with matrix impression and tray
impression materials.

 Many paired material will bond at the time of contact
when their unpolymerized material comes into
contact with the polymerized component. Substantial
forces are generated .
 On removal delaminating may occur within the
matrix. Polyether adhesive is most effective for non-
bonding pair of materials.

Clinical procedures :
 Immediately after tooth preparation and before any
retraction procedures, select or create a carrier for the
matrix forming material.
 The carrier can be a manufactured product in various
shapes and sizes in the office with vacuum forming
equipment or may be made with wax directly in the
mouth.
 The carrier should provide 3-4 mm space between its
wall and the prepared teeth and 2-3mm between its
walls and adjacent unprepared teeth. It should extend to
one tooth beyond the prepared tooth on both sides when
the teeth are present.

 It should also extend 2-3mm on the ridge
beyond the margin of the gingiva. All the soft
tissue under the preplanned pontics and
precision attachments should be included in the
carrier.
 Fill the carrier with Ramitec or PUS occlusal
registration material and position it over the
prepared teeth. The carrier should be held to
create a 1-2mm thick occlusal wall over the
unprepared teeth.
 After the material polymerizes, remove the
impression from the mouth and separate the
matrix from the carrier. Trim it with a scalpel.

 Place the retraction cord around each prepared tooth
leaving one end of the cord protruding 2-3mm for easy
retrieval. A moist cord will prevent the chances of
gingival bleeding, when it is removed. Any blood in the
sulcus during retraction procedure should be cleaned.
No dried blood should be left on the prepared teeth,
since it cannot be removed from the tooth with the
impression material.
 Make high viscosity material and load in a conventional
impression syringe. dispense the material to fill in the
preparation depression of the matrix then apply the
material generously on all the soft tissue side .this must
be done in a manner as not to trap air in the occlusal
recesses . Unlike other procedures, vent holes in the
matrix should not be placed in an attempt to prevent air
entrapment.

 Remove all retraction cords optionally; additional
material from the syringe may be dispensed around the
preparation .it is not essential to direct this material into
the sulcus because this objective will be accomplished
by the matrix. Additional material is pushed ahead to
flush out debris from the sulcus . this step is considered
to be more valuable when the prepared teeth are small
in dimension and less material is available within the
matrix
 Seat the filled matrix on the prepared teeth (the adjacent
teeth and structures help for orientation. excessive force
should not be applied a vertically directed force should
be applied with light pressure

 Immediately make a mix of medium viscosity
impression material, load the stock tray seat the
stock tray over the seated matrix impression.
 After the impression materials are completely
set, remove the impression and examine it for
defects the matrix is often visible through the
matrix impression material. This is acceptable.
 When the impression is acceptable, form the
master cast according to the desired procedure.
 Keeping one half to two thirds of a tooth beyond
the prepared tooth or teeth will help index the
positioning of the matrix.

 Remove the excess material that extend to the facial and
lingual portions The final matrix should delineate the
occlusal surface on axial walls of the preparation and
the crest of the gingival tissue because gingival
retraction has not been implemented ,the crevice
between the prepared tooth surfaces and gingival tissue
should also be discernible.
 When their crevice has not been recorded or if large
voids have occurred in the matrix it should be remade.
Unlike tube /coping techniques, it is not important to
register the finish line at this stage .it is the crest of the
gingival tissue that has to be recorded in the matrix.
 If the impression of the preparation is made at a later
visit, label the matrix and set it aside for trimming,
when the impression is to be made during the
preparation visit proceed with refining the matrix.

Summary
A good impression is an exact replica of each prepared
tooth and should include adequate amount of the
unprepared surfaces adjacent to the margin.
Impression technique and material should be selected on the
basis of biologic factor dictated by the anatomy and the
physiology of the mouth dictated by the orofacial tissues.
Even though there are innumerable techniques and
procedure for impression making ,it is the responsibility of the
dentist to select the best possible procedure based on sound
knowledge , for achieving the best possible result for the
patient. www.indiandentalacademy.com

Thank you
For more details please visit

Impressions in Fixed Partial Dentures

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (10)

Similar to Impressions in Fixed Partial Dentures

Similar to Impressions in Fixed Partial Dentures (20)

More from Indian dental academy

More from Indian dental academy (20)

Impressions in Fixed Partial Dentures