Impressions for fixed partial dentures /certified fixed orthodontic courses by Indian dental academy

IMPRESSIONS
IN
FIXEDPARTIAL DENTURES

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INDIAN DENTAL ACADEMY
Leader in continuing dental education



INTRODUCTION


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To obtain an impression is the first step necessary for
the indirect fabrication of a prosthesis. 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.T8

IMPRESSION TECHNIQUE : A method and
manner used in making a negative likeness. –
G.P.T-8

History
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Philip Ptaff-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

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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.

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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.


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

Impression Techniques
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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
- Laminate Technique
- Wet Field Technique
6. The matrix system

STOCK TRAY IMPRESSION
TECHNIQUE (Putty wash technique):
Mixing method: Double mix and single mix
Procedure :
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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.

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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.


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Cover putty with the manufacturer’s
spacer (a sheet of polyethylene)

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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.

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SINGLE MIX TECHNIQUE:
MAKING FINAL IMPRESSION:
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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.


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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.

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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
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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
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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 showthough in any areas of the
impression except at tissue
stops.

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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


Thermoplastic Tray

Thermoplastic custom tray
material

Material is softened in
hot water

Material being adapted to
spaced cast

2-3 mm thick hard splint material is softened and adapted using
vacuum adaptation machine.

Visible light – polymerized custom tray

Visible light-polymerized custom
tray material

Material adapted to the
spaced cast

The assembly is placed on the turntable of a special curing unit and exposed to intense light

Prepare syringe:
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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 must have a vertical dimension holding stop such
as an incisal pin or other metal-to-metal contact.
There should be sufficient space distal to the terminal tooth in
the arch to allow tray approximation.

Technique

Evaluate the fit of the tray in the
patients mouth.
Observe

the

complete

bilateral

closure and the patients comfort.


Making the final impression
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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.

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

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


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.


Laminate Technique (or) Agar
Alginate Combination Technique
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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
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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.


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The hydraulic pressure of the
viscous tray materials forces the
fluid syringe hydrocolloid down
into the areas to be recorded.

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This motion displaces the syringe
materials as well as blood and
debris throughout the sulcus


The matrix impression system
This system uses three impression materials

 Matrix impression material
 Tray impression material
 Matrix forming material


Matrix impression material :
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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 gingiva and to effectively flush
the debris out of the sulcus.
High viscosity polyether is preferable for this
procedure.


Tray impression material:
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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 ; a stock tray is used to incorporate the
matrix and the remaining teeth in the arch.

Matrix forming material :
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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.


Immediately after tooth preparation
and before any retraction procedures

Clear plastic carrier selected from
assortment of premade forms.

Matrix is made in carrier with polyvinyl siloxane material before soft tissue is retracted.


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Slender bur or knife edged rubber
wheel used to enlarge interproximal
embrasures.

Black Lines Indicate Sulcular extension

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Thick red line indicates crest of gingiva.
Two black marks point out proximal contacts
that must be relieved.

Matrix should extend one half to two thirds of tooth
beyond prepared teeth and close to gingival crest.


Impression 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
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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.


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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.


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Ciesco JN, Malone WF, Sandrik JL, Mazur B : Comparison of
elastomeric impression materials used in fixed prosthodontics; J
Prosthet Dent. 1981 Jan; 45(1):89-94: Five elastomeric impression
materials were evaluated: two polysulfides (one lead-cure and one nonlead cure), two silicones (one condensation polymerization and one
addition polymerization), and one polyether. These materials were
subjected to simulated clinical conditions. Two techniques were
evaluated. All materials were evaluated initially with use of a custom
tray and manufacturers' adhesive. A second evaluation was performed
without using the tray system. Both techniques were subjected to
statistical comparison. Conclusions of the research were as follows: 1.
All impression materials that were poured immediately and evaluated
using a custom tray and adhesive consistently demonstrated superior
results in comparison to those tested without the custom tray. 2.
Polyether material consistently yielded superior results with or without
a custom tray when compared to the other impression materials. The
additional polymerization silicone ranked second, followed by the leadcure polysulfide and the condensation polymerization silicone,
respectively.


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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 (intraabutment and interabutment) 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.

Thank you
Leader in continuing dental education


Impressions for fixed partial dentures /certified fixed orthodontic courses by Indian dental academy

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