1. Elastomeric Impression Materials
Irreversible; Non-aqueous

2. Impression materials – elastic impression materials
hydrocolloids (aqueous)
agar (reversible)
alginate (irreversible)
elastomers (nonaqueous)
polysulfide
polyether
silicone (condensation, addition)

3. Elastomeric polymers: elasticity
Undisturbed (unstretched) polymer molecules naturally curl up
covalent bonds along polymer back-bone are randomly directional, imparting a random curvature to the molecule. The curled configuration is the lowest energy state of the molecule.

4. Elastomeric polymers: elasticity
After stretching, the polymer molecules will return to the curled (lowest energy) configuration.
completely elastic (in principle)
not completely elastic because polymer molecules slide with respect to one another while the ensemble is stretched

5. Elastomeric polymers: elasticity
When stretched, polymer molecules line up parallel to one another. Sliding between polymer molecules is resisted by:
van der Waals forces; hydrogen bonding
tangling among polymer molecules
cross links between polymer molecules

6. Polysulfide
Elastomer Impression Materials

7. Polysulfide & other elastomeric
impression materials were
traditionally supplied in two
tubes, one containing a “base”
paste and the other containing
a “catalyst” paste.

8. Polysulfides - development
used in industry since 1929
liquid polysulfides developed by Thiokol labs in 1943
used in dentistry since early 1950s

9. Polysulfides – base polymer
low molecular weight polymer (2000 – 4000 amu)
terminal mercaptan groups – SH
condensation reaction

10. Base paste
Catalyst paste

11. Polysulfide – Base Paste
Polysulfide Polymer
Filler
74%
balance

12. Polysulfide – Catalyst Paste
Lead dioxide
Dibutyl phthalate
Sulfur
Other ingredients
78%
17% 3% 2%

13. Polysulfide – reactions scheme:
polysulfide base + lead dioxide
polysulfide rubber + water

14. polymerization of polysulfide oligomersC S R m H 3 n S H SH H S R n S H H S H C 3

15. Rm = - CH2 - CH2 - O - CH2 - CH2 -
Rn = - CH2 - CH2 - O - CH2 - S - S -

16. polymerization of polysulfide oligomersC S R m H 3 n
oxygen from PbO 2 O S H SH H S R n
mercaptan S H H S H C 3

17. forms sulfur – sulfur bonds C H H C H S S R S S C S S R S S R S S S S3 H C H S S R S S C S S R S S R n m n S S S S C S S
+ 3 H 2 O H C H
by-product
cross-link C H 3

18. The dimensional stability of polysulfide impressions along
the mesial and distal dimensions
of a crown die is poor. PS
impressions release water as a
by-product of the polymerization
reaction. Evaporation of the
water causes the dimensional
change.
After making a PS impression,
one must pour a stone model
within the 1st hour to minimize the loss of accuracy
due to evaporation of the by-product.
Lacy AM, Fukui H, Bellman T & Jendresen MD (1981)
Journal of Prosthetic Dentistry 45(3)

19. The dimensions of stone dies are being measured here.
Note that the die appears to
expand with time.
Lacy AM, Fukui H, Bellman T & Jendresen MD (1981)
Journal of Prosthetic Dentistry 45(3)

20. Dies are larger than the tooth when the impression material
is bonded to the tray with adhesive. Shrinkage is toward
the custom tray.
If the contraction of the impression material continues,
dies poured later will be larger than dies pour earlier.

21. Condensation Silicone
Elastomeric Impression Materials
Condensation silicones are no longer used in U.S. dental practices.

22. Condensation
Silicones
Wash
Putty

23. Elastomeric Impression Materials
Polyether
Elastomeric Impression Materials

25. Polyether Impression Pastes
Composition of
Polyether Impression Pastes
Base
Catalyst
polyether prepolymer
aromatic alkyl sulfonate
silica filler
glycoether phthalate
(plasticizer)
glycoether phthelate

26. polyether prepolymer Like addition silicones, the reaction occurs3 N 2 O x R n p
ethyleneimine
rings
rings open during polymerization – possibly less polymerization shrinkage.
polyether prepolymer
Like addition silicones, the reaction occurs
without a by-product.

27. S O R C l C l alkyl dichlorobenzene sulfonate 3
Catalyst for polyether polymerization reaction – difficult to handle – carcinogen when separate

28. Polyethers – setting time, stiffness
Polyether will set more quickly than polysulfide and is stiffer when set.
The setting of both impression materials is sensitive to temperature, but polysulfides are more sensitive to temperature.
Reciprocating rheometer

29. Dimensional change with time:
2 polysulfides
& 2 polyethers
condensation silicone
low humidity:
Storage at high humidity will expand a PE impression. Resulting stone will be smaller than actual tooth. A crown built from this stone die will be too small.
2 polyethers
condensation
silicone
high humidity:

30. Electrical mixer - dispensers: Pentamix 2 dispenser
photos: 3M Espe; 2005
Polyether is very viscous – difficult to stir. Electrical mixer makes sense.

31. Polyethers – brands: varying viscosity
Impregum Penta Soft (3M Espe) *
Permadyne (3M Espe) *
Impregum (3M Espe)
P2 (Hereaus Kulzer)
* Not sold as monophase

32. Polyethers - advantages
less hydrophobic than others – inherently hydrophobic
not affected by latex gloves
dimensional stability good, except at high humidity

33. Polyethers - disadvantages
very stiff – can loosen periodontally compromised teeth
poor taste & smell
may distort during disinfection (keep immersion brief)

34. Elastomeric Impression Materials
Addition Silicone
Elastomeric Impression Materials

35. Composition of Addition Silicone Pastes Base Catalyst
poly(methyl siloxane)
vinyl groups are substituted for a small percentage of the methyl groups
poly (methyl siloxane)
hydrogens are substituted for a small percentage of the methyl groups
platinum and palladium powder
chloroplatinic acid
(or some other platinum-containing compound)
filler

37. H2PtCl6 increases the reaction rate 106 times
Addition Silicones - catalyst
Chloroplatinic Acid:
H2PtCl6 increases the reaction rate 106 times

38. Polymerization of addition silicone oligomersH H 3 H Si C H 3 O Si C C H + 2 O H C H 3 C H 3 H C Si H + H C C Si O 3 2 C H H O C H 3 3 O Si C C H + H Si C H 2 3 C H 3
Some products release hydrogen during and after setting.

39. Polymerization of addition silicone oligomers
siloxane backbone C H H H 3 O Si C C Si C H 3 C H H H O H H C H 3 3 H C Si C C Si O 3
chloroplatinic acid
catalyst C H H H O H H C H 3 3 O Si C C Si C H 3 C H H H 3
Notice that there is no by-product. The siloxane backbone is cross-linked in three dimensions.

40. Addition silicone elastomeric impression materials:
Current material:
Extrude TM
Kerr Corp.
dual paste
cartridge
mixing tip

41. Addition silicone elastomeric impression materials:

42. Addition silicone elastomeric impression materials:

43. Addition silicones – mixing
pseudoplastic – becomes less viscous as shear rate increases
automix syringes reduces voids by 25%

44. The dimensional stability of addition silicone impressions along
the mesial and distal dimensions
of a crown die is relatively good.
AS impressions do not release a
by-product during polymerization
and, consequently, are very stable.
Lacy AM, Fukui H, Bellman T & Jendresen MD (1981)
Journal of Prosthetic Dentistry 45(3)
When using addition silicone impression materials, one does
not have to pour the stone immediately. It is possible to
ship the impression to the lab and allow the lab to pour the
stone model.

45. Addition silicones – brands: varying viscosity
hydrophilic brands*:
Exafast NDS (GC America)
Affinis (Coltene / Whaledent)
Imprint II (3M Espe)
Aquasil (Dentsply / Caulk)
* All the above are sold in light, medium, heavy, and sometimes putty viscosity
* Not sold as monophase

46. Addition silicones – brands: varying viscosity
hydrophilic brands*:
Honigum (Zenith/DMG)
Standout (Kerr) *
Virtual (Ivoclar Vivadent)
Aqualsil Ultra (Dentsply / Caulk)
All the above are sold in light, medium, heavy, and sometimes putty viscosity
* Not sold as monophase

47. Addition silicones – disinfection
impressions can be immersed for 30 minutes in aqueous solution of either 1:10 hypochlorite or 2% glutaralde-hyde without ill effect

48. Addition silicones – setting retardation
setting of putties may be retarded by some latex gloves & rubber dams
sulfur in the latex is the problem – vinyl gloves do not retard setting

49. Addition silicones - advantages
tasteless; odorless
dimensional stability good
relatively easy removal from mouth
can be disinfected without dimensional changes (immerse briefly)

50. Addition silicones - disadvantages
set may be retarded by latex gloves
not inherently hydrophilic; moisture from saliva, blood etc. can interfere; surfactant-containing overcome this problem, but how well?

51. Elastomers
Comparing Properties

52. Properties of Elastomeric Impression Materials - Working Times
Good while learning, longer than desirable in practice.

53. Mechanical properties of Elastomeric Impression Materials - Permanent Deformation
Least elastic.

54. Reducing permanent deformation:
Mechanical properties of Elastomeric Impression Materials - Permanent Deformation
Reducing permanent deformation:
Reduced if deformation is brief: remove impressions quickly
Reduced if there is less deformation: larger undercuts will produce more permanent deformation

55. Mechanical properties of Elastomeric Impression Materials - Strain in Compression
Very flexible.
Some very stiff
Very stiff

56. Mechanical properties of Elastomeric Impression Materials - Tear Strength
an advantage for
polysulfides

57. Dimensional Accuracy of Stone Casts Poured One Hour after an Impression was Made
** All these are acceptable. **
Johnson & Craig. J Prosthet Dent 1985;53:
Custom trays were used to make the
PS, PE & AS impressions.

58. Dimensional Accuracy of Stone Casts Poured One Hour after an Impression was Made
This is a concern. The stone die is too small, so the casting made on the die will not seat.
Johnson & Craig. J Prosthet Dent 1985;53:
* Custom trays were used to make the
PS, PE & AS impressions.

59. Properties of Elastomeric Impression Materials - Dimensional Change at 24 hours
very stable; note that there is still polymerization shrinkage.

60. Properties of Elastomeric Impression Materials - Contact Angles / Stone Castability
Low contact angles are associated with more complete fill of elastomer molds by stone.

61. Properties of Elastomeric Impression Materials - Contact Angles / Stone Castability
Adding surfactants to addition silicones elastomers decreases the contact angle and increases fill of elastomer molds by liquid stone

62. End