1. Mechanical Properties Prof. Dr. Manal A. El-Ebiary
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Mechanical Properties Prof. Dr. Manal A. El-Ebiary

2. Prof. Dr. Manal A. El Ebiary
Dental Bio- Materials Department
Faculty of Dentistry
Tanta & MUST Universities

3. Elastic Impression Materials
Aqueous elastic impression materials (Hydrocolloids)
Non-aqueous elastic impression materials (rubber bases)

4. Elastic Impression Materials

5. Aqueous Hydrocolloid impression
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

6. ( change in temperature)
Hydrocolloid
Reversible
Agar
( change in temperature)
Irreversible
Alginate
(Chemical reaction)
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

7. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Suspension
Solution
Colloid
Hydro-
colloid
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

8. Hydrocolloids Solvent and Solute Colloids Solution
single phase, which means a homogenous mixture, where the solute exists as small molecules or ions in the solvent.
Emulsion
heterogeneous two-phase system, a dispersed phase of particles of at least sufficient size to be seen microscopically, dispersed in a medium.
Colloids

9. HYDROCOLLOIDS
Colloids between these two extremes. heterogeneous two-phase system, like suspension particle size of the dispersed phase is smaller.
hydrocolloids when the dispersion medium is water.
Colloids may exist in the sol and gel state.

10. sol = viscous liquid
sol → gel (agglomeration of the molecules of dispersed phase, to form fibrils or chains of molecule), in a network pattern, called brush heap structure.
Agglomeration of the molecules of the dispersed phase to form chains of molecules in a network pattern,

11. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Brush heap
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

12. Sol Gel 1- Reduction in temperature e.g. (reversible as in agar)
2- Chemical reaction e.g. (irreversible as in alginate)

13. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Sol Viscous liquid
Gel jelly like structure
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

14. General properties of hydrocolloids

15. 1. Gel strength: The strength or toughness of a gel depends on:
a. The concentration of the fibrils: The greater the concentration, the stronger the material.
b. The concentration of fillers: Which are inert powders added to a gel to render it less flexible.
c. In reversible gels: The lower the temperature, the stronger the gel and vice versa.

16. 2. Dimensional changes after setting:
The loss of water is termed synersis and occurs also by evaporation.
The uptake of water is called imbibition
synersis and imbibition of the gel should be avoided as the former causes shrinkage, and the latter results in swelling and expansion.

17. Storage media, such as: 2% potassium sulfate or
100% relative humidity, reduce the dimensional changes.
The best results are obtained with 100% relative humidity (storage in 100% relative humidity results in minimum amount of shrinkage).
Hydrocolloid impression must be poured within a short time after removal from the mouth

18. 3. Disinfection:
→ Disinfection should be relatively rapid to prevent dimensional changes.
Disinfectant is sprayed on the exposed surface.

19. The impression should not be soaked in the disinfectant
The impression should not be soaked in the disinfectant. Immediately wrap the impression in a disinfectant soaked paper towel and place it in a sealed plastic bag for 10 minutes.
Finally remove the wrapped impression from the bag, unwrap, rinse thoroughly, shake off the excess water and pour the model with stone.

20. 4. Compatibility with gypsum:
[Gypsum cast may be too soft]:
This may be due to the presence of the water on the surface of the hydrocolloid which affects the setting and surface properties of the gypsum cast
Or due to the chemical composition of some hydrocolloids which retard the setting of gypsum products.

21. This disadvantage can be overcome by two ways:
1- By immersing the impression in a solution containing an accelerator for the setting of gypsum products, before pouring the impression with the gypsum.
2- By incorporating a plaster hardener or accelerator in the hydrocolloid material by the manufacturer.
3- The cast should not be left too long in contact with the impression. The set stone absorbs water from the water-filled impression. The result is a chalky surface with poor details.

22. Reversible hydrocolloid
Agar
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

23. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Application
Full mouth impression
Quadrate impression
Duplicating material
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

24. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
It is supplied as a sealed container to prevent evaporation of water
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

25. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Composition
Agar 13% it is polysaccharides from seaweeds
Borax to increase gel strength and increase viscosity but it retards the setting reaction of gypsum products
Potassium sulfate to counteract the retarding effect of borax
Water 83% as a dispersion medium
filler to control strength , viscosity , rigidity
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

26. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Manipulation
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

27. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

28. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

29. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Cooling (43C)
Heating (100 C)
Agar
Sol
Agar
Gel
Hysteresis
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

30. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Hysteresis
The liquefaction temp. and gelation temp. are different
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

31. Sequence during manipulation
Heating in boiling water for 10 minutes to obtain fluid materials
Stored at 65 C
Conditioning or tempering at 46 C to cool the material to be compatible with oral tissue
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

32. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Removal of the impression by sharp snap removal to avoid inaccuracy to from viscoelastic nature of the material
Pouring the impression immediately .however possible storage in 100% humidity if needed
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

33. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Properties
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

34. Accuracy Flow :- sufficiently fluid to record fine details
Dimensional stability
( Evaporation - syneresis - imbibition )
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

35. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Elasticity :- it is a viscoelastic materials , elastic recovery 98.8%
Then rapidly removal is necessary to avoid deformation or distortion
Compatibility with gypsum product avoid soft surface of stone model
Retention with tray :- by using perforated tray
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

36. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Mechanical properties :- agar thickness = 4:6 mm to increase tear strength
Difficult technique and time consuming
Cannot electroplated due to imbibition
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

37. Irreversible hydrocolloid
Alginate
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

38. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Application
The most widely used materials
Full mouth impression
Quadrate impression
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

39. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Composition
Potassium alginate or sodium alginate, To react with Ca ion to give Ca alginate gel
Calcium sulfate ,to release Ca ion to react with alginate
Trisodium phosphate to delay gel formation ( retarder)
Filler e.g. Diatomaceous earth to strength the gel
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

40. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Setting reaction
Retardation step
Gelation step
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

41. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Manipulation
Shack well
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

42. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

43. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

44. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

45. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

46. Factors affecting setting time
Temperature
Ratio
Type
Mixing rate
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

47. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Slower or faster setting can be achieved, by using cooler or warmer water respectively.
Reduction of the powder ratio leads to increases the setting time, but it reduces the strength and accuracy of the alginate.
Type of alginate
Fast setting = l: 2 min.
Regular setting =2:4 min.
Increase mixing time leads to decrease setting time.
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

48. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Properties
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

49. Accuracy Flow :- high flow to record fine details
Dimensional stability
( Evaporation - syneresis - imbibition )
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

50. Compatibility with gypsum products
Impression Tray
Hydrocolloid
impression
Gypsum model
Gypsum products are generally cast into an impression that could contain bacterial or viral contaminants. Impressions are disinfected but the process is not sufficiently consistent to guarantee that there is not risk to laboratory technicians. Some gypsum products contain disinfectants. Lab technicians routinely wear gloves to protect themselves from persistent bacteria such as Hepatitis C.
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

51. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Impression Tray
VERY
FAST
(SNAP)
RAPID removal of an elastomeric impression material leads to the least chance for plastic deformation if the procedure involves rapid elastic deformation. Remove the impression with a SNAP. [CLICK] This creates a rapid loading rate. Remember that all polymers are very STRAIN RATE SENSITIVE. [CLICK] If the stress is applied quickly, then all the energy is stored elastically and the material will not undergo plastic deformation. This is particularly important in the region of the greatest deformations (e.g., the margins) [CLICK] Fast removal rates [CLICK] guaranteet that loads (see the blue dotted line) only generate elastic deformations. Slow removal rates [CLICK] would actually cause plastic deformation and distort the impression in critical areas.
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

52. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Elasticity :- it is a viscoelastic materials , elastic recovery 97.3%
Flexibility It is the most flexible of all elastic impression materials then easy removed from mouth
Retention with tray :-
by using perforated tray
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

53. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Mechanical properties :- thickness = 4:6 mm to increase tear strength and rapid removal increase tear strength and decrease deformation
Cannot electroplated due to imbibition
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary

54. Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary
Goodbye
Hydrocolloid impression materials Prof .Dr. Manal A. El-Ebiary