Impression Techniques

1. Impression Techniques
By Muhammad Rafay Imran
&
Yusra Mahar

2.  Impression : A negative likeness or copy in reverse
of the surface of an object ; an imprint of teeth
and adjacent structure for use in dentistry.

3.  Impression trays :
A receptacle in to which
suitable impression material is placed to make
negative replica.

4.  Impression trays can be classified broadly into stock trays and custom trays.
 Stock Trays :
Stock trays for partially edentulous patients may be perforated
to retain the impression material or they maybe constructed with a rim lock
for this purpose.
 Another type of stock stray designed for the reversible type of hydrocolloids is
water cooled trays. It contains tubes through which water can be circulated
for the purpose of cooling the tray.

6. Disadvantages of Stock Trays
 The peripheral borders may not be accurately
recorded
 Considerably more bulkier than a custom tray.

7. Custom Impression Trays
 Peripheral borders can be precisely recorded in the impression
 Thickness of impression material can be controlled
 Custom trays are sometime needed for mouth that are abnormally or unusual
configuration

8. Impression Techniques
 Physiologic impression technique
 McLean and Hindels method
 The Fluid wax method
 Selected Pressure technique

9. Physiologic impression technique
 This technique records the ridge position by placing an occlusal load on the
impression tray as the impression is being made
 These techniques produced a generalized displacement of the mucosa to a
greater or lesser degree
 This displacement was intended to record the tissue in the configuration it
would assume when occlusal loading was applied to a partial denture in
function.

10. McLean’s Impression Technique
 A Custom impression tray is constructed over a preliminary cast
 Functional impression of distal extension ridge is made. Patient applies some
biting force with occlusal rims
 Then an alginate impression is made with the 1st impression held in its
functional position with finger pressure.

11. Hindels modification of McLean’s
technique
 Main difference of this McLean’s technique is that impression of edentulous
ridge is not made under pressure but is an anatomic impression made at rest
with ZOE paste.
 As the hydrocolloid impression was being made finger pressure was through
holes In the tray to the anatomic impression.

12. The Fluid Wax Method
 Zinc Oxide eugenol and impression plaster are suitable impression materials
for this technique as fluid wax adheres well to them
 The anterior and posterior vibrating lines are marked as described in the
conventional technique. These lines are marked in the patient’s mouth
immediately after making the wash impression

13. Selected pressure impression technique
 The objective of this technique are :
 The equalization of support between the abutment teeth
and the soft tissue
 To direct more force to those portions of the ridge which
is able to absorb the stress without reverse response
 Protect the areas of the ridge which is least able to absorb
force.

14.  Areas where relief is provided will be least
displaced as the impression is recorded. In those
areas of the tray where relief is not provided
greater displacement of the underlying mucosa
will occur.
 Mandibular Arch posterior region
 Crest of Arch
 Buccal Shelf
 Lingual slope.

15.  The end result of this selected pressure
impression technique si that the denture base
made impression will be closely adapted to and in
firm contact with the tissue covering the buccal
shelf area of the edentulous ridge.
 The ridge crest on the other hand is lightly
adapted to the tissue and effects of occlusal
loading will be less in this area.