Impressions in fpd

GPT - 8
• IMPRESSION:
• a negative likeness or copy in reverse of the
surface of an object;
• an imprint of the teeth and adjacent
structures for use in dentistry

Impression
Materials
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensaton
Addition
Agar (reversible)
Alginate (irreversible)

Impression technique in fpd
I. Putty-wash impression
II. Dual-phase impression
III. Mono-phase impression
IV. Hydrocolloid laminate technique
V. Copper-band impression technique
VI. Impression using vacuum-adapted splints
VII. Impression using preformed crown shells
VIII. Dual-arch impression technique
IX. Functional check bite impression
X. Matrix impression system
XI. Cast impression coping technique
XII. Digital impressions

Putty-Wash Impression:
This is a stock tray impression technique. There
are two methods to make a putty wash impression
1. One step/ Single mix putty-wash impression
2. Two step/double mix putty wash impression.

One step/ Single mix putty-wash
impression
• In this procedure both the materials
(light body and putty) are used
simultaneously.
• The putty material is loaded into the
stock tray.
• The Light body material is syringed
around the tooth preparation.
• A full mouth Impression is made
using the loaded stock tray

• Two step/double mix putty wash
impression
• In this procedure putty impression made
in suitable stock tray and then the light
body material is syringed over the putty
impression and also over the tooth
preparation.
• Space for the light body material is
created by placing the polyethylene sheet
as spacer before making putty
impression or by scraping the material
using BPblade or round bur

Advantages:
1. Eliminates the time and cost of fabricating custom
tray.
2. Metal stock trays are rigid and are less susceptible to
distortion.
Disadvantages:
1. More impression material is required.
2. Metal trays must be sterilized.
3. The thickness of impression material will be uneven,
and hence uneven polymerization shrinkage may occur.

Copper-Band Impression Technique
• The copper-band or tube is used to obtain
an impression of multiple preparations
when there are only vague margins on one
or two preparations that are not adequately
replicated in the impression.
• The patient's condition, the extent of the
aberration evaluated, and judgment
determines whether the copper band
technique saves time or a remake of the
original impression is more appropriate

The copper band or copper tube impression in made
with following Combinations of techniques:
1. The original copper tube and modeling compound
method
2. Avariety of copper tube and elastomer combinations
3. Resin copings and elastomer
4. Polycarbonate crowns and elastomers
5. Resin (provisional) crowns or fixed partial dentures
with
Elastomers

• All the techniques make use of a rigid
carrier for the impression
• material and the carrier typically
becomes the part of the impression.
• The registration of the finish line is
initially achieved in the carrier.
• The displacement of the gingiva is
usually accomplished as the modeling
Compound or elastomer is delivered to
the sulcus.

VIII. Dual-Arch Impression Technique:
The simultaneous recording of tooth
preparations , the opposing antagonistic
teeth, and the inter-occlusal relation of the
relative opposing dentition within a single
impression for the fabrication of one or two
indirect restorations was first introduced
by Wilson & Werrin in 1983.

Technique.
1. The syringe material is injected into the area to be recorded.
2. The high viscosity material is mixed and placed in excess on
both the arches.
3. The tray is placed in between the arches.
4. Patient is asked to occlude (bite) slowly
5. After making the impression, the patient is instructed to open his
mouth slowly.
6. As the patient opens his mouth, the tray will adhere to one arch.
7. Bilateral pressure (right and left) should be applied to remove
the tray as it helps to minimize distortion .

8. Die stone is poured into the
impression of the tooth
preparation.
9. The impressions are boxed and
casts of both arches are poured.
10. Articulation should be done on
a hinge articulator with an incisal
pin to maintain vertical dimension

Advantages
1.Less impression material is required as only one part of the
arch is
recorded.
2.Less time is taken as both the arches are recorded
simultaneously.
3.Maximum intercuspation position can be recorded more
accurately as it is recorded during function.
Disadvantages
1. Distortion is possible because the tray is not rigid
2. Cannot be used for more than one casting per quadrant.

X. Matrix Impression System
The matrix impression system uses three impression
materials:
1. Asuitable elastomeric semi-rigid material required to
form
the matrix
2. A high viscosity elastomeric impression material, which
will preferably bond to matrix-forming material, and
3. A stock tray with a medium viscosity elastomeric
Impression material to pickup the matrix impression and
the remaining
arch not covered by the matrix

XII. Digital impression
•
• With the techniques of computer-aided design
and computer-aided manufacturing (CAD/CAM)
being applied in the field of prosthodontics, a
concept of intraoral digital impressions was put
forward in the early 1980s.
• It has drawn comprehensive attention from
dentists and has been used for dental
prosthesis fabrication in a number of cases.
• This new digital impression technique is
expected to bring about absolute digitization to
the mode of prosthodontic

CAD/CAM systems are composed of three major
parts:
(1) a data acquisition unit, which collects the data
from the region of the preparation teeth and
neighboring structures and then converts them to
virtual impressions (an optical impression is
created at this moment directly or indirectly)
(2) software for designing virtual restorations
anchored in virtual impressions and setting up all
the milling parameters
(3) a computerized milling device for
manufacturing
the restoration with solid blocks of the chosen
restorative material

The main digital impression systems available
on the market
include
CEREC, Lava C.O.S. system, iTero, E4D, and
TRIOS.
They vary from each other in terms of various
features such as working principle, light source,
the necessity of powder coat spraying,
operative process, and output file format.

Conclusion
The accuracy as well as dimensional stability
of an impression may be depending on the
type of the material used, type of the tray
selected,
and the technique followed. With availability
of various techniques And advancements the
operator should select a material and
technique
Which suits best for the particular situation.

REFERENCES
1. Nooji D, Sajjan MC. Impression techniques for fixed partial denture.
2014, LAP LAMBeRT academic publications.
2. Malone William F P, David L Koth. Tyllman’s theory and practiceof fixed
prosthodontics. 8th Edn. Ishiyaku EuroAmerica, Inc.
3. Brian M. How to make a good impression (crown and bridge).Br Dent J
2001 vol.191: 402-405.
H.T.Shillingburg:fundamentals of fixed prosthodontics
3rd edn
Rosenstiel:cotemporary fixed prosthodontics 3rd edn Mosby 2002
A Clinical handbook of inlays, crown& bridges-geroge F Kantorwicz
D C N A: ceramics oct 1977 21;4

Impressions in fpd

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Impressions in fpd