3. INTRODUCTION
Impression compounds are thermoplastic
materials softened to their working
consistency by immersion in hot water or by
warming over the flame.
Rigid after setting and has poor elastic
properties
6. TYPE I
Available as sheets, sticks, cylinders and
cones
Should flow readily at just above mouth
temperature
Should be capable of recording sharp grooves
0.2-4 mm wide into the surface of metal test
block
Most viscous of impression material i.e 4000
(pas) thus characterized as mucocompressive
7. TYPE I
Low Fusing - Green stick compound- 54 C
Medium Fusing – Impression compound -
8. TYPE I – SHEETS
Recording Impression of edentulous ridge
Manipulation:
Compound softened in water bath kneaded
with finger to improve qualities
Temperature of water bath 55-60◦C is ideal
for 4-5 mins to ensure complete softening
9. Conti..
Gauze is placed at bottom of water bath to
prevent adherence
Soften by heat, inserted in an impression tray
and placed against tissue before it cools to a
rigid mass
10. TYPE I - STICKS
Soften with flame
Skill and experience is required
Material is tempered in a water bath before
placing in the patient’s mouth
Used to refine /modify peripheral extent of
special tray for CD or edentulous region of RPD
Used for securing rubberdam retainer and
occlusal registration plate
Recording single crown preparation
11. STICKS - COPPER RING
TECHNIQUE
Recording a single
tooth preparation
using stick
Hollow open ended
copper tube used as
a tray
12. Conti…
A separate locating impression is also
recorded of the prepared tooth
The die is inserted into this impression and a
stone working model is made by pouring a
stone
This technique is superseded by the use of
rubber base
Still used where moisture control is a problem
13. STICKS - MANIPULATION
For adequate border seal for retention of CD
Trimming special tray until it is short of lines
of movement of mucosa
Tray periphery is coated with soften
greenstick and tray replaced in mouth
Cheeks are manipulated to stimulate
functional movement to produce dynamically
generated shape
14. Conti..
Care should be taken not to burn patient
Used in distal extent of palatal coverage of
upper denture for border seal
15. TYPE II
Also k/a tray compound
Making impression tray
Not distorted at mouth temperature
Used for corrective wash impression by
adapting soften compound on study model and
border of denture area trimmed
Tray compound lacks dimensional stability and
strength
Thus replaced by acrylics and plastics
16. PROPERTIES
Glass transition temperature
Temperature at which material losses its
hardness i.e. 39◦C or brittleness
At this stage it is not plastic or soft enough for
making impression
Forms a rigid mass upon cooling
17. PROPERTIES
Fusion Temperature:
Indicates definite reduction in plasticity of
materials during cooling
Heating at approximately 43.5◦C material
soften to plastic mass that can be manipulated
Above this temperature soften material
remains plastic while impression being made
18. PROPERTIES
Fusion Temperature:
Once the impression tray is seated, it should
be held gently(passively) in position until the
impression cools below the fusion temperature
Impression should not be removed until it
reaches oral temperature
19. THERMAL PROPERTIES
Coefficient of thermal expansion 0.3% is
acceptable
conductivity is very low thus need extended
time to achieve thorough heating and cooling
The materials should be uniformly soft at the
time it is placed on the tray and thoroughly
cooled in the tray before the impression is
withdrawn from the mouth
20. THERMAL PROPERTIES
Cold water can be sprayed on the tray while it
is in the mouth until the compound is
thoroughly hardened prior to removal of
impression tray from mouth
Low thermal conductivity influences cooling
Outerside cools rapidly and innerside remains
soft thus adequate time is required for cooling
21. SOFTENING AND FLOW
Soften at point just above mouth temperature
and exhibit adequate flow to adapt closely to
tissue and register details
Hardens at mouth temperature and exhibit
minimum flow to reduce danger of distortion
on removal
23. VISCOSITY
Most viscous of impression material i.e.
4000(pas)
70 times greater than impression plaster
100 times greater than light body elastomers
24. VISCOSITY
Significance
1. Limits degree of fine detail which can be
recorded in impression
2. Characterizes compound as a mucocompressive
impression material
25. VISCOSITY
Advantage
1. Recording impression of some edentulous
patient for recording full depth of sulcus so
that a denture with adequate retention can be
designed
2. Able to displace the lingual and buccal soft
tissue sufficiently
26. DIMENSIONAL STABILITY
Relaxation can occur in short time period with
increased temperature
Relaxation causes warpage or distortion of
impression
27. DIMENSIONAL STABILITY
To reduce distortion one has to allow the
thorough cooling of impression before
removal from mouth
Construct cast or die as soon as possible
(within 1 hr)
28. PRECAUTIONS
Prolong heating /immersion in water bath
cause compound to be brittle and grainy due
to leaching out of low molecular weight
ingredients e.g. stearic acid
Compound should not be allowed to boil or
inginite so that the constituents are volatized
while using flame
29. PRECAUTIONS
Incorporation of water acts as plasticizer
Wet kneading causes incorporation of water in
compound causes increased flow at mouth
temperature causing distortion on removal
Reheating also causes increased flow
30. ADVANTAGES
Cheap and reusable
Does not produce irritation to patient
Can be remodify and resoften again till the
accurate impression is obtain
Compatible with die and model materials
Easily electroplated to form accurate and
abrasion resistant dies
31. DISADVANTAGES
Difficult to record details because of high
viscosity
Mucocompressive
Distortion due to poor dimensional stability
Difficult to remove from severe undercuts
Does not have pleasant taste
32. DISINFECTION
In 2% alkaline glutaraldehyde solution
impression is immersed for 10 minutes ,
rinsed and poured
33. ADA specification 3 for impression compound
1. Requires to be homogenous
2. Should be smooth and glossy in appearance after
passed through flame
3. Must be firm and smooth while trimming with
sharp knife at room temperature
4. Manufactures must indicate:
Method of softening
Working temperature
Data/curve showing shrinkage from 40-20◦C
34. REFERENCES
Applied Dental Materials - 9th edition-Jhon
F.McCabe and Angus W.G.Walls
Restorative Dental Material – Craige
Phillips’ Science of Dental Materials 11th
edition - Knneth J Anusavice
Dental Material Science, Mannippalli
Dental Materials and Their Selection, 3rd
edition, William J O’Brein