short presentation about impression techniques and theories which are use in dentistry...it will help to understand which technique is useful for different patients.

1. Impression Theories
And Techniques
Ankita Gupta
Bds final year

2. 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 (gpt 8)

4. Classification Of impression Techniques
A.Based on the theories of impression
-Pressure theory
-Minimal pressure theory
-Selective pressure theory

5. B.Based on the position of the mouth while
making the impression
-Open mouth
-Closed mouth
C.Based on the method of manipulation for
border moulding
-Hand manipulation
-Functional manipulation

6. Pressure Theory
-Also known as mucocompressive theory or definite
pressure theory.
- This theory is proposed on the assumption that tissues
recorded during mastication or under functional
pressure provided better support and retention for the
denture.
-A heavy bodied material such as impression compound
is used.

7. Technique the pressure theory was introduced by
Greene is as follows:
-The preliminary impression with compound is made.
-A custom tray is fabricated with its periphery short by
1/8inch.
-A secondary impression is made in this tray using
compound
-Occlusal surfaces are then made.
-Areas to relieved(eg.median palatal raphe)are softened
and the impression is again inserted in the mouth &is
held under biting pressure for 1or2 minutes.

8. -The borders are molded by asking the patient to
perform functional movements like
whistling,smiling etc.
Advantages better retention and support during
occlusal functions like mastication.
Disadvantagesexcessive pressure could lead to
increased alveolar bone resorption eventually
resulting in loose dentures.
Pressure on sharp shiny ridges often results in pain.

9. Minimal pressure theory
Also known as mucostatic or non pressure
technique.
-According to the principal,interfacial surface
tension was the only significant way of retaining
complete denture. Thus,retention is achieved
through accurate tissue adaptation.
Accordingly,the impression should cover only those
areas of the denture foundation where the mucosa is
firmly attached.
-The dentures made with this technique have short
flanges.

10. PASCAL’S LAW
The pressure applied on the confined
liquid will be equally transmitted
undiminished throughout the liquid in all
directions.

11. Advantages:High regards for tissue health and
preservation.
Disadvantages:Shorter flanges prevent wider
distribution of masticatory stresses.
-With reduced coverage possibility of getting greater
retention is lost.
-Lack of border molding reduces effective peripheral
seal further reducing retention.
-Lack of border seal also permits food to slip beneath
the dentures.
-The short flanges may reduces support for the face
which can affect esthetics and short flanges would
means less lateral stability.

12. Selective Pressure Theory
This technique combines the principles of both
pressure theory and minimal pressure techniques.
-This theory is based on the understanding of both
anatomy and physiology of basal seat and
surrounding areas.
-The basal seat area divided into different zones
according to withstand masticatory loads without
undergoing resorption(primary stress bearing area)
-other were to be recorded at rest(secondary stress
bearing area).

13. -While other areas could be relieved(relief areas).
-Primary stress bearing area of maxilla:
hard palate
postero lateral slopes of residual alveolar ridge
-Secondary stress bearing area of maxilla:
rugae area
maxillary tuberosity
alveolar tubercle
-Relief Areas
incisive papilla
mid palatine raphe
torus palatinus

14. Stress bearing area of mandible
buccal shelf area
residual alveolar ridge
Relief areas
mental foramen
genial tubercle
mylohyoid ridge
mandibular tori

15. Advantages consider more physiological functions of
the tissue basal seat , therefore appears more sound
& appealing
Disadvantages some areas are still recorded under
functional load ,still there are chances of rebounding
and loosing of retention.
(still selective pressure theory is more popular)

16. Open Mouth Impression
● The open mouth impression is built in a tray which
carries the impression material of choice into the
desired contact with the supporting tissue and
into an approximate relation to peripheral tissue
when mouth is opened and without applying
pressure.
● The rationale behind this method is that denture
do not dislodge when subjected to biting forces.

17. It develops a contour of impression surface which is
in harmony with the relaxed supporting tissues,and
which may be out of perfect adaptation with these
tissues when the denture is subjected to occlusal
loading.

18. Closed mouth impression technique
-Requires wax occlusal rims to be fabricated on
primary cast.
-The patient made to close on those rims and a general
clearance is made for the various frenula so that the
patient can manipulate his tissues by
closing,swallowing and sucking to form peripheral
borders.

19. Making Impression For The Edentulous
Patient
1.Examination and conditioning of the patient and
the mouth.
2.Selection of impression material
3.Selection of impression tray
4.Seating of the patient
5.Selectionof impression technique
6.Making the preliminary impression
7.Constructing the primary cast
8.Fabrication of custom tray
9.Border molding
10.Making of the final impression

20. A. Examination and conditioning of the
patient and the mouth
-A complete case history and clinical examination
is done.
-It also includes the factors that complicate the
impression making like gagging ,poor
neuromuscular coordination ,excessive salivation
etc
old denture wearer: if the patient is old denture
wearer,patient is instructed to leave the old
denture out of the mouth for at least 48hours
prior to final impression.

21. B. Selection Of Impression Material
Material is selected according to the clinical findings
classification
based on the elasticity
1.Rigid-zinc oxide eugenol paste , impression compound
etc.
2.Elastic-alginate,elastomeric impression material.
Based on its use
1.Preliminary impression materials
2.Final impression materials

22. C. Selection Of Tray
● A tray is a device which is used to carry,confine
and control impression material while making an
impression.
● Classification of impression trays:
● Based on whether trays are prefabricated or individualized
● 1.stock trays 2.custom trays
● Based on presence or absence of retentive holes
● 1.perforated 2.non perforated
● Depending on whether they are meant for dentate or
edentate: 1.dentate trays 2.edentate trays
● 3.combination trays

23. Perforated and non perforated edentulous stock trays.

24. D. Seating Of The Patient:
For max. impression
upright position is ideal
sin
is
For mandibular operator stand facing the patient to the
front and right side of the patient
*for right handed operator

25. E. Making The Impression
● Border molded custom tray technique
● This technique is very accurate but requires
2separate sessions.
● the first appointment
Preliminary impression is made in a stock tray with
impression compound.(it is contraindicated for
hypermobile ridges)

26. Laboratory phase
impression is used to construct a study cast and cast is
used to make a custom tray
The Second Appointment
custom tray is border
molded and final impression is made in the border
molded tray loaded with zinc oxide eugenol

27. Impression techniques for hypermobile
ridges
A primary impression is made with alginate and a
special tray is constructed with relief wax placed
over the hypermobile tissues .
Border molding is carried out and final impression
is made after removing the wax spacer with the free
flowing material .
Escape holes are placed in the hypermobile area of
the tray .

28. Factors Which Complicate Impression
Making:
1.Uncooperative patients
2.Excessive salivation
3.Hyperactive gag reflex

29. Thank you