Impressions for fpd / implant dentistry course

IMPRESSIONS
IN
FIXED PARTIAL
DENTURESINDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION

 .

 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

AGAR (reversible hydrocolloid)
History
 In 1925, Alphous Poller of Vienna was granted a
British patent for a totally different type of
impression material called as Negacol
 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
 No mixing required

Disadvantages
 Initial expense
 special equipment
 Material should be prepared in advance
 Tears easily
 Dimensionally unstable
 Pour immediately
 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
 Zelgan, jeltrate (Dentsply)
 Coe Alginate (GC America)
 Integra(kerr)

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

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

Modified alginates
 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.

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

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 America)

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

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
 High tear resistant
 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 grow simultaneously and a reaction
byproduct is ethanol
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)

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
 Good working and
setting time
Disadvantages:
Permanent deformation –
high – 1-3%
Poor dimensional stability
high shrinkage
 Hydrophobic

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 )
 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
 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 )

Advantages
 Highly accurate
 Good dimensional
stability
 hydrophilic
 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

Impression Techniques
 1. Stock tray technique/putty wash technique
- Double mix
- Single mix
 2. Custom tray technique
- Single mix
- Double 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.
 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.

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.

SINGLE MIX TECHNIQUE:
 For the stock tray Single mix insert the low viscosity
impression material into the prepared area
 Putty material is loaded into the stock tray
 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.
 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 low viscosity material 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
maximum intercuspation position 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 on 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 green 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.
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 for 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.

Final impression in reversible hydrocolloid

Laminate Technique (or) Agar
Alginate Combination Technique
 After injecting the syringe agar on to
the area to be recorded, an impression
tray containing a mix of chilled
alginate that will bond with the
syringe agar is positioned on it.
 The alginate gels by a chemical
reaction, whereas the agar gels by
means of contact with the cool
alginate rather than the water
circulating through the tray.

Advantages
1. Less air bubbles
2. Water cooled trays are not required
3. It sets faster than the regular agar technique.

Wet Field Technique
 This is relatively new technique
which has become popular.the areas
to be recorded are actually flooded
with warm water.
 Then the syringe material is
introduced quickly, liberally and in
bulk to cover the occlusal and/or
incisal areas only.
 while the syringe material is still
liquid, the tray material is seated.

 The hydraulic pressure of the
viscous tray materials forces the
fluid syringe hydrocolloid down
into the areas to be recorded.
 This motion displaces the syringe
materials as well as blood and
debris throughout the sulcus

The matrix impression system
Gus J. Livaditis jpd 1998, vol 79,issue 2
 The system uses a custom matrix to control the sulcular
environment and to deliver the impression material
subgingivally . It also incorporates the attributes of
traditional impression methods and overcomes partial the
deficiencies of impression making such as registration of
the subgingival Margins, gingival retraction and relapse,
hemostasis and sulcular cleaning, strengthening the
sulcular flange of impression and simplification for
making complex impressions.

The system uses three impression materials
 1.A suitable elastomeric semi rigid material to form the
matrix.
 2. 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
 3. 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.

Clear plastic carrier selected from
assortment of premade forms.
Matrix is made in carrier with polyvinyl siloxane material before soft tissue is retracted.
Immediately after tooth preparation
and before any retraction procedures


Black Lines Indicate Sulcular extension.
Thick red line indicates crest of gingiva.
Two black marks point out proximal contacts
that must be relieved.
Slender bur or knife edged rubber
wheel used to enlarge interproximal
embrasures.
Matrix should extend one half to two thirds of tooth
beyond prepared teeth and close to gingival crest.

syringe is used to fill matrix with high
viscosity impression material.
Matrix impression is seated with
light pressure.
Stock tray filled with medium viscosity impression material is seated over matrix
impression before matrix material polymerizes.

REVIEW OF LITERATURE
 Nachum Samet DMD, Michael Shohat DMD, Alon Livny
DMD and Ervin I. Weiss DMD: A clinical evaluation of fixed
partial denture impressions; J Prosthet Dent, volume 94,
issue 2, August 2005, pages 112 – 117: This study evaluated the
quality of impressions sent to commercial laboratories for the
fabrication of fixed partial dentures (FPD) by describing the
frequency of clinically detectable errors and by analyzing
correlations between the various factors involved. Within the
limitations of this study, impressions made with polyethers had
the most detectable errors, followed by condensation-type
silicones. The high frequency of detectable errors found in
impressions sent for FPD fabrication is of concern.

 Hung SH, Purk JH, Tira DE, Eick JD : Accuracy of one-step
versus two-step putty wash addition silicone impression technique;
J Prosthet Dent 1992 May; 67(5):583-9: This study compared the
accuracy of one-step putty wash with two-step putty wash impression
techniques. Five addition silicone impression materials-Mirror 3 (MR),
Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute (A)--
were tested. A stainless steel model containing two full-crown
abutment preparations was used as the positive control. Five
replications for one-step and two-step putty wash impressions of the
master model were made for each test material. Accuracy of the
materials was assessed by measuring six dimensions on stone dies
poured from impressions of the master model. Accuracy of addition
silicone impression material is affected more by material than
technique. Accuracy of the putty wash one-step impression technique
was not different from the putty wash two-step impression technique
except at one of the six dimensions where one-step was more accurate
than two-step. Mirror 3 putty wash two-step impression presented less
distortion than Mirror 3 Extrude putty wash one-step or two-step
impression.

 Nissan J, Laufer BZ, Brosh T, Assif D : Accuracy of three
polyvinyl siloxane putty-wash impression techniques; J
Prosthet Dent. 2000 Feb; 83(2):161-5; This study assessed
the accuracy of 3 putty-wash impression techniques (1) 1-step
(putty and wash impression materials used simultaneously);
(2) 2-step with 2-mm relief (putty first as a preliminary
impression to create 2-mm wash space with prefabricated
copings. In the second step, the wash stage was carried out);
and (3) 2-step technique with a polyethylene spacer (plastic
spacer used with the putty impression first and then the wash
stage). using the same impression material (polyvinyl
siloxane) in a laboratory model. For each technique, 15
impressions were made of a stainless steel master model that
contained 3 complete crown abutment preparations, which
were used as the positive control. Accuracy was assessed by
measuring 6 dimensions on stone dies poured from
impressions of the master model.
CONCLUSION: The polyvinyl siloxane 2-step, 2-mm, relief
putty-wash impression technique was the most accurate for
fabricating stone dies.

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.

REFERENCES
 1.Phillips science of dental materials – 11th
edition – Anusavice
 2.fundamentals of fixed prosthdontics- 3rd
edition Herbert T.Shillingburg
 3.Dental Materials – E. C. Coombe
 4.Applied Dental Materials – 8th Edition –
McCabe
 5.Contemporary Fixed Prosthodontics – 3rd
edition Stephen F.Rosenstiel

1.Nachum Samet DMD, Michal Shohat DMD, Alon
Livny DMD and Ervin I. Weiss DMD: A clinical
evaluation of fixed partial denture impressions; J
Prosthet Dent, volume 94, issue 2, August 2005, pages
112 – 117.
2.Hung SH, Purk JH, Tira DE, Eick JD : Accuracy of
one-step versus two-step putty wash addition silicone
impression technique; J Prosthet Dent. 1992 May;
67(5):583-9.
3. Laufer BZ, Brosh T, Assif D : Accuracy of three
polyvinyl siloxane putty-wash impression techniques; J
Prosthet Dent. 2000 Feb; 83(2):161

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