Discussion

1. IMPRESSION COMPOUND
Dr. Anjana Maharjan

2. CONTENT Introduction
 Composition
 Type
 Properties
 Dimensional Stability
 Precaution
 Advantage/Disadvantage

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

4. COMPOSITION
Ingredients Parts
Rosin 30
Copal resin 30
Carnauba wax 10
Stearic acid 5
Talc 25 (75)
Coloring agent Appropriate Amount

5. TYPE
1. Lower Fusing - Impression Compound
2. Higher Fusing – Tray Compound

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 This technique is superseded by the use of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

22. SOFTENING AND FLOW

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

35. Thank you