Silicone based impression materials

SILICONE BASED IMPRESSION
MATERIALS
CONDENSATION SILICONE
AAMIR GODIL
FIRST YEAR P.G.
DEPARTMENT OF PROSTHODONTICS
M.A.R.D.C.

OUTLINE
2
CONDENSATION SILICONE IMPRESSION
MATERIAL
• Introduction
• Chemistry of Condensation Silicone
Impression Material
• Review of Physical and Chemical Properties
• Advantages and Disadvantages
• Conclusion

INTRODUCTION
3
MATERIAL

Elastic impression materials were developed from
synthetic rubber by S.L. Pearson at the University
of Liverpool in 1955.
The introduction of rubber-based, polysulfide
impression materials was followed by silicone-
based materials, both of which are still in use.
Following these, elastic polyether impression
materials were introduced, followed in recent
times by polyvinylsiloxane impression materials.
Hoffman-Axthelm, W. History of Dentistry. Chicago,
Quintessence Put. CO., Inc., 1981. p. 284
4

• Condensation silicone was the first type of silicone
impression material.
• Also known as conventional silicones.
• Setting occurs at room temperature , and so are also
called RTV silicones.
MATERIAL
5

CHEMISTRY OF CONDENSATION
SILICONE IMPRESSION MATERIAL
(C- Silicone)
6
MATERIAL

7
MATERIAL

COMPOSITION
Supplied as two paste system:
• Base paste:
• Hydroxyterminated polysiloxane polymer
• Filler (cristobalite, talc, starch)
• Catalyst:
– Liquid catalyst:
• Cross-linking agent (e.g tetraethoxy silane) +
• Activator (dibutyl-tin dilaurate)
– Paste catalyst:
• Cross-linking agent, activator, inert oil
• Filler
8
MATERIAL

Institute of Medical Biochemistry, 1st Fac. Med., Charles University,
and Institute of Dental Research in Prague
9

• The instability of condensation-type silicone materials is
attributed to the production of an alcohol byproduct
during polymerization
• A two-step putty/wash technique was developed in
which the use of a thin layer of wash material minimizes
the amount of alcohol byproduct and thereby retains
the dimensional stability within acceptable limits.
(Craig RG. A review of properties of rubber impression
materials. J Mich Dent Assoc 1977;59:254-61.)
• To further overcome some of the problem associated
with condensation silicones, another silicone material
was introduced that polymerizes by an addition reaction
in which no byproduct is produced.
MATERIAL
10

REVIEW OF PHYSICAL AND
CHEMICAL PROPERTIES
11
MATERIAL

OVERVIEW
MATERIAL
12

• The proposed definition of the working time of an
elastomeric impression material suggested by ISO
(1988) is "the period of time between the start of
mixing and the commencement of the development
of elasticity and the loss of plasticity"
• This would seem to be a very sensible definition, but
most techniques used for the evaluation of working
time simply monitor a change in viscosity or rigidity
(Wilson, 1966; McCabe and Bowman, 1981; ISO,
1988)
MATERIAL
13
WORKING AND
SETTING TIME

At 230C
3.3 minutes
At 370C
2.5 minutes
At 230C
11.0 minutes
At 370C
8.9 minutes
MEAN WORKING TIME MEAN SETTING TIME
Usually, working time is measured at room temperature and setting
time at mouth temperature
14
MATERIAL

HOW ARE THE WORKING AND SETTING
TIME ASSESSED?
• Penetrometer tests are used
• End of working time: The time when a blunt needle of
specified dimension fails to penetrate the volume of given
material at a specified depth
• End of setting time: The time when a blunt needle of
specified dimension fails to permanently indent the set
material
• In British Standards Test, reciprocating rheometer is
used. The property recorded is more close to viscosity and
shear thinning properties compared to elasticity
15
MATERIAL

WHAT ARE THE FACTORS INFLUENCING
WORKING AND SETTING TIME?
Decrease in temperature
(Cooling of glass slab and storing materials at room
temperature can help in prolonging the working and
setting time)
Decrease in viscosity
Increase in temperature
( Rise in temperature accelerates the curing rate )
Increase in viscosity
(Changing the proportions of base/catalyst can alter
the setting reaction)
16
MATERIAL

DIMENSIONAL STABILITY
WHAT ARE THE FACTORS AFFECTING DIMENSIONAL
STABILITY?
Polymerisation Shrinkage
By-Product Release
Thermal Contraction
Imbibition
Incomplete Recovery | Viscoelsticity
17
MATERIAL

Linear contraction of four elastomeric impression
materials
SIGNIFICANCE
-To attain maximum accuracy,
polysulfide and C- silicone
casts should be poured
immediately.
Immediately is defined as the
period within the first 30
minutes, even for putty wash
technique. (Phillips’)
- Polyether and A-silicone will
yield accurate casts even after
24 hours to one week.
18
MATERIAL

DIMENSIONAL CHANGE
AFTER SETTING
• The unrestrained dimensional change after setting has been
reported by Craig (1986b), Mansfield and Wilson (1975), Eames
et al (1979), Ohsawa and Jorgensen (1983), and Bell et al (1976).
• The values show some variation from product to product of the
same type, but the decreasing order of dimensional stability is
ADDITION SILICONES
POLYETHERS
POLYSULFIDES
CONDENSATION SILICONES
(After 24 hr in air of 50% relative humidity)
MATERIAL
19

EFFECT OF HUMIDITY
ON DIMENSIONAL STABILITY
Bell et al (1976)
• The effect of low, medium, and high humidity on the dimensional
changes of stored rubber impressions of polysulfides, condensation
silicones, and polyethers
• The dimensional change of all three types was affected. The standard
polysulfide was affected the least, followed by the condensation
silicone and polyether
• The optimum storage condition for polysulfides was high humidity; for
condensation silicone, medium humidity; and for polyether, low
humidity
MATERIAL
20
BELL, J.W.; DAVIES, E.H.; and VON FRAUNHOFER, J.A. (1976): The Dimensional Changes of
Elastomeric Impression Materials under Various Conditions of Humidity, / Dent 4:73-82.

REPRODUCTION OF
ORAL DETAIL
ACCURACY OF STONE MODELS
• A variety of laboratory models has been used to evaluate
the accuracy of rubber impression materials.
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MATERIAL
(Reisbick and Matyas, 1975; Stackhouse, 1975; Stauffer et al., 1976; Marcinak et al., 1980;
Lacy et al., 1981a,b; Augsburger et al., 1981; Marcinak and Draughn, 1982; Finger and
Ohsawa, 1983; Johnson and Craig, 1985)
Polyether
Addition Silicone
Polysulfide
Condensation
Silicone

RECOVERY FROM UNDERCUTS
Johnson and Craig (1985)
• The addition and condensation silicones
demonstrated the best recovery as a result of
being removed from undercuts and the least
change between models from an initial and a
second pour
MATERIAL
22

Tjan et al. (1986) and Linke et al. (1985)
• Standard gold castings were used to evaluate the accuracy of dies
from the impressions of crowns, MOD's, and occlusal inlays.
• Agar was less accurate than were silicones and the polyether for
making impressions of occlusal or MOD inlays.
• A delay in pouring condensation silicone impressions of MOD's
and crowns resulted in a decrease in accuracy which was not
observed for occlusal inlays.
MATERIAL
23
TJAN, A.H.L.; WHANG, S.B.; TJAN, A.H.; and SARKISSIAN, R. (1986): Clinically Oriented Evaluation of
the Accuracy of Commonly Used Impression Materials, / Prosthet Dent 56:4-8.
LINKE, B.A.; NICHOLLS, J.I.; and FAUCHER, R.R. (1985): Distortion Analysis of Stone Casts Made from
Impression Materials,/ Prosthet Dent 54:794-802
ACCURACY

WETTING AND CONTACT ANGLE
MATERIAL
24

COMPATIBILITY WITH
DIE MATERIALS
• Lorren et al. (1976) measured the contact angles of mixes of
dental stone on elastic impression materials and found
values :
MATERIAL
25
Condensation Silicone 95°
Polysulfide 70°
Polyether 50°
Addition Silicone (Hydrophillic) 40°
• They also found a direct relationship between the contact
angle and the number of bubbles occurring on casts.
LORREN, R.A.; SALTER, D.J.; and FAIRHURST, C.W. (1976): The Contact Angles of Die
Stone on Impression Materials, / Prosthet Dent 36:176-180.

• Norling and Reisbick (1979) measured the contact angles of
saturated calcium sulfate dihydrate solutions to be:
– Polysulfide impressions = 80°
– Condensation silicone impressions = 97°
– polyether impressions = 15°
• When they incorporated non-ionic surfactants into polysulfide
and silicone impression materials, the wettability of gypsum mixes
increased and the number of surface bubbles decreased.
• The working time of the silicone was increased; however, the
working time of the polysulfide was unchanged, as was the
permanent deformation or dimensional change.
MATERIAL
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NORLING, B.K. and REISBICK, M.H. (1979): The Effect of Nonionic Surfactants on Bubble
Entrapment in Elastomeric Impression Materials, / Prosthet Dent 42:342-347

DISINFECTION
• Recommended material for elastomeric impression
materials:
– Glutaraldehydes
– Chlorine compounds
– Iodophores
– Phenolics
• Method: Immersion
• Disinfectant requiring more than 30 minutes exposure
time are not recommended.
27
MATERIAL

28
MATERIAL
COMMERCIALLY AVAILABLE DISINFECTANTS

• An evaluation of polysulfides, poly ethers, and condensation and addition
silicones with a variety of disinfectants was conducted.
• They found in some cases that some disinfectants adversely affected impression
materials, and therefore care should be used in selection of a satisfactory
combination.
• The smallest dimensional changes were observed for addition silicones with:
MATERIAL
29
BERGMAN, M.; OLSSON, S.; and BERGMAN, B. (1980): Elastomeric Impression Materials. Dimensional Stability
and Surface Detail Sharpness Following Treatment with Disinfection Solutions, Siued Dent J 4:161-167.
STORER, R. and McCABE, J.F. (1981): An Investigation of Methods Available for Sterilising Impressions, Br
Dent J 151:217-219.
Bergman et al (1980)
Storer and McCabe (1981)
Cidex 2.4% activated glutaraldehyde
Techno-sept Propanolol
Hibitane 8g/L chlorhexidine gluconate
K-644 Potassium bromide
Benzalkon Benzalkonium chloride

RHEOLOGICAL PROPERTIES
• The data for condensation silicones could be fitted to
kinetic equations, but the kinetics was not consistent
with the stoichiometry.
• However, the dependence of reaction rate on catalyst-
base ratio was qualitatively consistent with kinetic and
network considerations.
30
MATERIAL
COOK, W.D. (1982a): Rheological Studies of the Polymerization of Elastomeric Impression Materials. I. Network
Structure of the Set State, / Biomed Mater Res 16:315-330.
COOK, W.D. (1982b): Rheological Studies of the Polymerization of Elastomeric Impression Materials. II. Viscosity
Measurements, / Biomed Mater Res 16:331-344.
COOK, W.D. (1982c): Rheological Studies of the Polymerization of Elastomeric Impression Materials. III. Dynamic
Stress Relaxation Modulus, / Biomed Mater Res 16:345-357.

Polysulfide
C-Silicone
A- Silicone
Polyether
31
MATERIAL
Creep Compliance
The rate at which strain
increases for a constant applied
stress

ELASTICITY
• The material should be adequately elastic such that it does
not undergo permanent deformation on retrieval
• Setting time as mentioned by the manufacturer may not
be adequate to provide sufficient elasticity under clinical
conditions
A- Silicone
C-Silicone
Polyether
Polysulfide
Amount of permanent deformation following
strain in compression
32
MATERIAL

MATERIAL
33

• Refers to the resistance to fracture of an elastomeric
material subjected to a tensile force acting perpendicular
to surface flaw.
• Tear strength (N/m) (lb/m) =
Maximum force needed to pull the specimen apart (N)
Thickness of the specimen (m)
TEAR STRENGTH
34
MATERIAL

WHAT IS THE SIGNIFICANCE OF TEAR
STRENGTH?
• Material can tear while recording impression of subgingival or
interproximal areas
• If a material tears in such areas, a portion may remain
embedded in the gingival sulcus or the interproximal area,
which may be difficult to locate due to lack of radiopacity of
these materials (except polysulfides)
Poly-
sulfide
Polyether
Silicones
TearStrength
35
MATERIAL

BIOCOMPATIBILITY
Allergy Toxic Reactions Hypersensitivity
Cell Cytotoxicity Analysis:
Polysulfides Silicones Polyether
+++
Significance:
If evidence of tearing is detected during careful inspection of gingival
sulcus, immediate retrieval of the remnant should be done
36
MATERIAL

ADVANTAGES AND DISADVANTAGES
37
MATERIAL

ADVANTAGES
• Lower price
• Good elastic recovery
• Easily seen margins
• Sufficient working time
• Pleasant odor and taste
DISADVANTAGES
• Low tear strength
• Volatile by product
• Shrinking of impression over time
• Limited shelf life
• Dimensional stability is affected due to by product
• Hydrophobic
• Usually hand-mix version only
38
MATERIAL

CONCLUSION
39
MATERIAL

Thank You
40
MATERIAL

Silicone based impression materials

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