Inelastic impression material

1. INELASTIC IMPRESSION
MATERIAL - II
ASWATI SOMAN
PG RESIDENT

2. IMPRESSION COMPOUND
 Non-elastic impression material
 Mucocompressive
 Thermoplastic
 Reversible

3. OTHER NAMES
 Dental compound
 Modelling compound
 Modelling plastic
 Setting action:Sets by physical change
ie. Softens by heating and hardened by cooling

4.  Supplied in the form of cakes(red) and sticks (green, gray or red)
 Various colour indicate different working and softening
temperature
 Red compound is a softer compound that softens at lower
temperature and not accurate
 Green compound has slightly higher melting temperature,
provides more accurate surface details and can be used for
border moulding
 Sheet form – making impression
 Stick form- border moulding
 Cone and cylinders –tube impression

5. TYPES
 Type I - LOW FUSING
 Type II - HIGH FUSING

6. TYPE - I
 Low fusing
 Used as an impression material
 Supplied either as sheets or sticks
 Sheet – recording impression of edentulous ridges
 Stick material – border moulding, recording impression of
single crown using copper ring technique
 Fusion temp approx. above 45degree celsius

7. TYPE II
 High fusing
 Tray compound
 Used for making trays to be used in oral cavity
 Fusion temp approx. above 70degree celsius

8. COMPOSTION
 THERMOPLASTIC RESINS OR WAXES
 FILLER
 LUBRICANT

9. COMPOSITION OF
IMPRESSION
COMPOUND
COMPONENT FUNCTION
Thermoplastic material
(47%)
Natural resin
 Shellac
 Dammar
 Rosin or sandrac
Synthetic Resin
 Coumerone indene
Waxes
 Beeswax
 Colophony
Characterizes the softening
temperature
Filler (50%) Talc
Calcium carbonate
Limestone
• Gives the body by
increasing the viscosity
• Reduces thermal
contraction
• Improves rigidity
Lubricant(3%) Stearic acid
(Or plasticizer like gutta
purcha)
Improves the flow properties

10.  FILLER : To overcome tackiness, control degree of flow and
minimize shrinkage due to thermal contraction
 Platicizer: waxes and resin tend to produce brittless and
tackiness which is overcome by addtion of plasticizers

11.  Thermoplastic material with glass transition
temperature of about 55-60º
(above which it becomes soft to take up a new form)
 On cooling---hardens—retaining an impression

12.  Coeff. of thermal expansion of resins and waxes is very
high—are highly non-linear within the temp range of dental
interest
 Shrinkage is in the order of 1.5% and is due to the thermal
contraction from mouth to room temp,.

13.  The material has poor dimensional stability -- model
must be poured as soon as possible after the
impression is taken; ie., within 1 hour.
 The thermal conductivity of impression compound is
very low,(on softening, the outside will always soften
first.) Thus, the material must be placed in the water
bath to allow sufficient time for it to achieve a
uniform temperature.

14. PROPERTIES OF IMPRESSION COMPOUNDS
 Flow
AT 37 DEGREE
CELSIUS(ON REMOVAL
OF IMPRESSION)
AT 45 DEGREE
CELSIUS
(INTRODUCTION OF
IMPRESSION)
I
[IMPRESSION
COMPOUND-LOW
FUSING]
</= 6% >/= 85%
II
TRAY COMPOUND[HIGH
FUSING]
</= 2% 70-85%

15.  Tray compound not distort at mouth temperature
 Flow is measured at the stated temperature by
applying a 2kg load to the flat end of a cylindrical
specimen 6mm high by 10mm diameter for 10 min

17. VISCOSITY
 Most viscous impression material
 4000 pas
 As impression compound is highly viscous, it limits
the degree of fine detail which can be recorded in
an impression.
 It characterizes compound as a mucocompressive
impression material.

18. Advantages of viscosity
 It records the full depth of the sulcus ,so that a
denture with adequate retention can be designed.
 Only a viscous material such as compound is able
displace the lingual and buccal soft tissues
sufficiently.

19. DIMENSIONAL STABILITY
 With an increase in temperature
 Relaxation of impression compound occurs in a short
period of time--”WARPAGE “ or “DISTORTION OF
THE IMPRESSION”
Minimized by
 Thorough cooling before removal from mouth
 Constructing cast/die within one hour

20. Factors that produce significant internal stresses are-
 High value of coefficient of thermal expansion
 Poor thermal conductivity
 Relatively large temperature drop from the
softening temperature to room temperature.

21. Thermal behaviour of impression
compound
80 -100ºC The material becomes sticky ,adheres
to the container and messy to handle
because volatile ingredients like low
molecular weight compounds and
plasticizer are leached out from the
material.
55-70ºC The material softens at this
temperature to form a plastic mass.
45ºC Temperature is safe to be placed in
the mouth

22. 43.5ºC Fusion temperature of impression
Compound The crystalline fatty
acids begin to solidify with
reduction in plasticity.
39ºC Glass transition temperature
37ºC. Material hardens in the mouth at
this temperature and can be
removed
23-25ºC Room temperature. Material can
be cooled under tap water.

23. FUSION TEMPERATURE (43.5ºC)
 It is the temperature below which a definite reduction
in plasticity occurs during the cooling of the
impression compound.
 Above this temperature, soften material remains
plastic while the impression is being made. it is the
temperature at which crystalline fatty acids solidify

24. GLASS TRANSITION TEMPERATURE 39ºC
 The reversible transition in amorphous materials
(or in amorphous regions within semi crystalline
materials) from a hard and relatively brittle state
into a molten or rubber like state.

25. THERMAL CONDUCTIVITY
 Is very low, when heated the external surface
heats up rapidly but the whole mass takes longer
time.
 If overheated while softened over flame, more
volatile components may get
vaporized/ignited(steric acid)
 Prolonged immersion in water cause leaching of
the soluble components
CRAIG

26. COOLING
 Impressions formed by placing the softened
compound into a suitable copper band for indirect
inlay are usually cooled in the mouth with water from
a syringe(16-18ºC).
 Rapid cooling results in the formation of internal
stresses.

27. Requirement of standard of type I material
 Capable of recording sharp grooves of 0.24 -
.4mm wide cut into the surface of a metal test
block

28. MANUPULATION
 It is softened in warm water bath (60-70 deg C)
 After the compound is removed from the water bath it
is usually kneaded with fingers in order to obtain
uniform plasticity throughout the mass
 Then placed in non perforated stock trays
 After the compound is moulded to the shape of the
impression tray, it is inserted into patients mouth and
held in place until the impression cools.

29. Effects Of Wet Kneading
 Kneading improves handling qualities
 Water when incorporated acts as a plasticizer.
 It increases the flow of softened compound and the
hardened impression.
 Flow can exceed the ADA standards and result in
increase in the risk of distortion.
 Kneading for 1-3 minutes –Flow may be more than
doubled.
 Once incorporated water remains for a long time and
subsequent reheating and kneading has a cumulative
effect.

30. DISINFECTION OF IMPRESSION COMPOUND
 Immersion in 2% alkaline glutaraldehyde
 Immersion in 1:10 dilution sodium hypochlorite or iodophor
for specified time period
Disinfection of Dental Impression- A Current Overview. /J. Pharm. Sci. & Res. Vol.
8(7), 2016, 661-664

31. APPLICATIONS 1. Primary impressions for edentulous
mouth.
2. Tube impressions for individual
tooth.
3. Peripheral Tracing for border
moulding.
4. Check undercuts for inlay
preparation.
5. Conveniently used to secure rubber
dam retainers so they remain stable

32. GREEN STICK COMPOUND
 Supplied in stick forms
 Fusion temperature – 43- 45 deg C
 Used for border moulding and copper tube technique

33. COPPER RING TECHNIQUE
McCabe

34.  Recording single crown preparation in stick compound
employing a hallow tube
 Surface of the compound is copper plated in an electroplating
bath and an epoxy resin metal die is made
 A separate locating impression is made
 Die is inserted to the impression
 Stone is poured into the impression and working model is
made

35. BORDER MOULDING TECHNIQUE
 Used for recording functional depth of sulcus
 2 methods
 Sectional border moulding
 Single step border moulding

36.  Green stick is heated uniformly over flame
 Applied over spl tray border
 Tempered in water bath and put inside patients mouth
 Different movements are done
 Remove after it hardens

38. ADVANTAGES
 Most widely used for preliminary impression making of
edentulous arch
 Non irritant
 Easy to use
 Reusable
 Economical
 Good shelf life
 Can be electroplated to form accurate and abrasion resistant
dies

39. DISADVANTAGES
 Technique sensitive – if not prepared properly, volatile materials
can be lost
 Difficult to record details because of its high viscosity.
Compress soft tissues while making impression.
 Distortion due to its poor dimensional stability
 Difficult to remove it if there are severe undercuts.
 There is always the possibility of overextension especially in the
peripheral portions.

40. Magic with Simple Materials-Admixture (Modified
Impression Compound the Golden Standard)
 KV Halini Kumari1 *, Abhishek Velekar2 , R Prakash3 and
Abhitha Seshadri4
 For making an ideal impression, material requires rigidity for
dimensional stability and adequate flow for accuracy with an
allowance for registering and finer adjustments.
 Incorporation of greenstick compound (one full length stick)
into impression compound (three-fourth of compound cake)
makes it almost the perfect material of choice, good and an
accurate impression is an art and science. Handling the
properties of material and their selection is very important.
KV Halini Kumari1 *, Abhishek Velekar2 , R Prakash3 and Abhitha Seshadri4
.Magic with Simple Materials-Admixture (Modified Impression Compound the Golden Standard. Indian Journal of Mednodent
and Allied Sciences Vol. 2, No. 3, November, 2014, pp- 267-270

41. Softening condition of impression compound for
border molding of removable denture
 Tomofumi et al.jp journal 10091-1152
 Study is to clarify the optimum softening condition of impression
compound for border molding foe which we measured the
pressure assumed to be loaded on the impression compound
during border molding
 Concluded that for border molding, muscle pressure of all
regions during the functional movements can be registered with
red and green softened by immersion in 60 deg water for 30 sec
and pink softened for20sec
Softening condition of impression compound for border molding of removable denture. Tomofumi et al.jp
journal 10091-1152

42. Comparison of The Surface Area Coverage of The
Impressions Made of Impression Compound And Alginate:
An in Vitro Evaluation.
 *Khajuria RR1 , Hajira N2 , Safaya R3 , Singh R4.IOSR Journal
of Dental and Medical Sciences.Volume 16, Issue 12(Dec.
2017), PP 06-10
 This study has been conducted to compare the surface area
coverage in the maxillary and mandibular primary impressions
using alginate and impression compound.
 The impression compound is a better material for fabricating
complete denture for edentulous patients as compared to
alginate in terms of surface area coverage. Maxillary arches
are found to have more surface area as compared to their
counterpart mandibular arches

43. Comparative evaluation of border molding using two
different techniques in maxillary edentulous arches:
A clinical study
 Anchal Qanungo et al
 The aim of this in vivo study was to compare the single-step
border molding technique using injectable heavy viscosity
addition silicone with sectional border molding technique using
low fusing impression compound by evaluating the retention of
heat cure trial denture bases
 Sectional border molding technique proved to be more
retentive as compared to single-step border molding although
clinically the retention appeared comparable
Anchal Qanungo, Meena Ajay Aras, Vidya Chitre, Ivy Coutinho, Praveen Rajagopal, Ashwin Mysore. Comparative evaluation of
border molding using two different techniques in maxillary edentulous arches: A clinical study. The Journal of Indian
Prosthodontic Society

44. IMPRESSION PLASTER
 Non-elastic
 Irreversible
 Mucostatic material
 Powder –water system

45.  Similar in composition with dental plaster
ß-calcium sulphate hemihydrate reacts with water to form calcium
sulphate dihydrate
 Used at a higher water powder ratio(0.60 approx.)
 Fluid mix –for finer details and mucostatic properties

46.  Products of dry calcination
 Type 1 and type 2 gypsum products
 The beta hemihydrate thus manufactured are slightly modified
to obtain suitable properties, by some addition for use as
impression materials or model plaster

47. ANTI-EXPANSION (AGENTS) SOLUTION: for
decreasing setting expansion
 Potassium sulphate– secondary effect of accelerating the setting
reaction
 Borax– retarder to control setting characteristics
 Alazarin red –pigment used for distinction between model
(plaster) and impression (plaster)

48.  Freshly mixed plaster is normally used in special
tray (with 1 to 1.5mm spacer)
 Plaster impression… ”as a wash” in primary
compound impression------ involves ‘puddling’ of
impression into place---unlike other materials, while
impression making with plaster the tray is gently
moved from side to side and antero-posterior for
handling characteristics of the material(fluidity)
McCabe
IMPRESSION PLASTER (ADA specification no. 25) is
Ca sulphate beta hemihydrate obtained by
modifying model plaster or P.O.P by adding small
amounts of:
Uncalcined
gypsum &
calcium
sulphate
anhydrite
to
decrease
S.T to
4(+or-)1
minute
Accelerato
rs &
retardors:
Control W.T
&S.T
Balancing
Chemicals(
Pot.Sulphat
e and
borax) to
reduce S.E
to
minimum
0-0.15%
Potato
starch/sug
ar- soluble
plaster for
dissolving
and
separation
of cast
from
impression
Coloring
pigments(a
lizarin) to
identify
margins

49.  Separating agent has to be coated between plaster
impression and model
 Water absorbing property ---patient c/o dry sensation
after impression recording
 Disinfection of plaster
10 min soak in Sod. Hypochlorite solution

50.  The powder should be sprinkled into water---
30seconds allowed to wet the powder---then mixed
for the minimum time necessary to obtain a
homogenous mix
 Plaster must be stored in an airtight container
because it will absorb water from the air which may
adversely affect its setting time

51. After setting, plaster
impression becomes BRITTLE
Hence cannot undergo any
compressive/ tensile strain
without fracturing
Hence not suitable for
undercut situations
McCabe

52. Fragments RECONSTRUCTED to form a
complete impression
Then “to fracture”
Impression plaster was allowed “to SET”

53.  Rapid setting in order to avoid discomfort to patient and
dentist
 Smaller setting expansion – similar to type 4 die stone
 Lower strength for fracture to occur if undercuts engaged
 Amt. of pot. Sulphate is more ---- expansion must be kept to
minimum

54.  Impression plaster is very useful impression material to
record impressions of patients with flabby ridge-----which
is to be recorded at rest
 Here impression plaster is more useful because of the fact
that a more viscous material may capture an abnormal
pattern of tissue displacement.

55. Two stage
technique
commonly
used for
recording
flabby
ridges
1. Special tray with appropriate spacers for ZnOE paste (well supported) + a
window overlying the flabby area
2. Impression of the bulk is recorded with ZnOE
3. Excessive material removed from the window
4. Impression re-seated in the mouth
5. Shape of the flabby ridge at rest is then recorded by painting plaster into its
surface with a brush and keying this impression into the impression tray

56. 0
0

57. PROPERTIES OF IMPRESSION PLASTER
 Easy to mix-----avoid trapping air bubbles(which
can cause surface inaccuracies)
 Amt. of pot. Sulphate is more than that of model
plaster----as for impressions the expansion must be
kept to minimum
 Borax counteracts accelerating property of
pot.sulfate
 Working time= 2-3 min
Setting time=2-3min

58.  Mixed material has a very low viscosity------so is
MUCOSTATIC
 Hydrophilic- adapts readily to soft tissues recording
their surface details with great accuracy
 Material is best used in a special tray
(shellac/acrylic) to a thickness of 1-1.5mm
 Alternatively can be used as a wash impression with
compound special tray

59.  Good dimensional stability----so a time delaying
pouring the model is of no consequence.
 A separating medium (usually a solution of sodium
alginate) must be used between impression plaster
and model plaster

60. REFERENCES
 Phillips ‘Science of Dental materials.11th Ed by Anusavice
 Restorative Dental Materials .13th Ed by Robert G.Craig and
John M Powers
 Dental Materials and their selection-4th Ed-William J Obrien
 Clinical Aspects of dental materials;Marcia Gladwin and Michael
Bagby
 Introduction to dental mateials by Richard Van Noort
 Applied dental materials – 8th edition, MaCabe
 Materials used in dentistry- 2nd edition, Mahalaxmi

61.  S. Mir Mohammad Rezaei,1 A. Monzavi,1 A. Dehghan Naieri2
The Comparison Flow of Four Impression Compounds (Green
Stick) with ADA Standard . Journal of Dentistry, Tehran
University of Medical Sciences, Tehran, Iran (2004; Vol. 1, No. 3)
 KV Halini Kumari1 *, Abhishek Velekar2 , R Prakash3 and
Abhitha Seshadri4. Magic with Simple Materials-Admixture
(Modified Impression Compound the Golden Standard. Indian
Journal of Mednodent and Allied Sciences Vol. 2, No. 3,
November, 2014, pp- 267-270
 Softening condition of impression compound for border molding
of removable denture, Tomofumi et al.jp journal 10091-1152

62.  *Khajuria RR1 , Hajira N2 , Safaya R3 , Singh R4 .Comparison of
The Surface Area Coverage of The Impressions Made of
Impression Compound And Alginate: An in Vitro Evaluation.
IOSR Journal of Dental and Medical Sciences. 2279-
0861.Volume 16, Issue 12
 Hemalatha.R. Disinfection of Dental Impression- A Current
Overview. /J. Pharm. Sci. & Res. Vol. 8(7), 2016, 661-664