Dr MEENU MERRY C PAUL Professor-Prosthodontics Malabar Dental College and Research Centre ,Edappal

1. ALGINATE
IMPRESSION
MATERIAL
Dr Meenu Merry C Paul
Professor-Prosthodontics
Malabar Dental College&Research Centre
Irreversible Hydrocolloid…

2. IRREVERSIBLE HYDROCOLLOID
Material that cannot return to a solution state after it becomes a gel.
Alginate is the irreversible hydrocolloid most widely used for preliminary
impressions.

3. HYDROCOLLOID IMPRESSION
MATERIALS
Hydro means water.
Colloid means gelatin substance.
Material used to obtain preliminary and final
impressions.

4. In hydrocolloids,the dispersion medium is water.
Agar or Algin,dissolved in water-Hydrocolloids
(dispersed phase)
Algin in water-Alginate hydrocolloid(irreversible)
Agar in water-Agar hydrocolloid(reversible)

5. Elastic
Aqueous
Hydrocolloids
Non-aqueous
Elastomers
Polysulfide
Silicones
Polyether
Condensation
Addition
Agar (reversible)
Alginate (irreversible)
O’Brien, Dental Materials & their Selection
1997

6.  Agar - secondary bonds (weak) hold the fibrils together- break at
slightly elevated temperatures and become re-established as it cools
to room temperature - reversible
 Alginate - the fibrils are formed by chemical action - irreversible

7. COMPOSITION
Diatomaceous earth
 A filler that adds bulk to the material.
Zinc oxide
 Adds bulk to the material.
Potassium titanium fluoride
 Added so as not to interfere with the setting and surface strength.

8. COMPOSITION
Potassium alginate
 Comes from seaweed; is also used in foods such as ice cream as a thickening
agent.
Calcium sulfate
 Reacts with the potassium alginate to form the gel.
Trisodium phosphate
 Retarder(Added to slow down the reaction time for mixing).

9. SETTING REACTION
OF
ALGINATE

10. Colloids with liquid as dispersion medium can exist in 2 forms
SOL
GEL
SOL is viscous liquid
GEL is semisolid elastic,jelly like
Here network of fibrils form a weak slightly elastic brush heap
structure.

11. SOL GEL
If the concentration of a dispersed phase in the hydrocolloid is sufficient the
sol may be converted to a semisolid state called as gel (gelation)

12. SOL-GEL TRANSFORMATION BY CHEMICAL
CHANGE….
Here the fibrils are held together by chemical forces.
It is irreversible and hence the name irreversible
hydrocolloid.
Eg : Alginate

13. Sol-Gel transformation …..
In the gel state,
Dispersed phase agglomerates forming chains / fibrils called micelles,
which branch and intermesh giving a characteristic brush heap structure.
The dispersion medium is held in the interstices between the fibrils by
capillary attraction / adhesion

14. PACKAGING AND STORING OF ALGINATE
Containers about the size of a coffee can are the most commonly used form of
packaging.
Premeasured packages are more expensive, but save time by eliminating the
need for measurement of the powder.
Shelf life of alginate is approximately 1 year.

15. ALGINATE SETTINGS
Normal set alginate
Working time of 2 minutes and a setting time of up to 41/2
minutes after mixing.
Fast set alginate
Working time of 11/4 minutes and a setting time of 1 to 2
minutes.
Working time
The time allowed for mixing the alginate, loading the tray,
and positioning the tray in the patient's mouth.
Setting time
The time required for the chemical action to be completed.

16. Control of setting time
•Altering temperature of the mixing
water
• Retarder

17. ALTERING THE SETTING TIMES OF
ALGINATE
Cooler water can increase the setting time if additional time is needed for the
procedure.
Warmer water can reduce or shorten the setting time of the procedure.

18. WATER-TO-POWDER RATIO
An adult mandibular impression generally requires two scoops of powder and
two measures of water.
An adult maxillary impression generally requires three scoops of powder and
three measures of water.

19. Figure of ‘8’ motion

20. TAKING AN ALGINATE IMPRESSION
Explain the procedure to the patient:
 The material will feel cold, there is no unpleasant taste, and the material will set
quickly.
 Breathe deeply through your nose to help you relax and be more comfortable.
 Use hand signals to communicate any discomfort.

21. •Making the impression
•Removal of impression
•Storage of impression

22. AN ACCEPTABLE ALGINATE IMPRESSION
The impression tray is centered over the central and
lateral incisors.
There is a complete "peripheral roll," which includes all
of the vestibular areas.
The tray is not "overseated," which would result in
exposure of areas of the impression tray.
The impression is free from tears or voids.
There is sharp anatomic detail of all teeth and soft
tissues.
The retromolar area, lingual frenum, tongue space, and
mylohyoid ridge are reproduced in the mandibular
impression.
The hard palate and tuberosities are recorded in the
maxillary impression.

23. PROPERTIES
Working Time → 1.25 - 4.5 min
Setting Time → 1.5 – 5.0 min
Recovery from deformation → 98.2%
Flexibility → 8 – 15%
Compressive strength → 5000 – 9000 g/cm2
Tear strength → 380 – 700 g/cm2

24. COMPATIBILITY WITH GYPSUM
Impression must be rinsed in cold water to remove any saliva and blood
If Impression is stored for >1/2hr, it should be rinsed in water to remove any
exudates that has been formed
Set gypsum cast should not remain in contact with alginate impression for
longer time

25. POOR COMPATIBILITY OVERCOME BY
Immersing impression in 2% K2SO4 prior to pouring the impression
Using products incorporating gypsum hardener

26. CAUSES FOR DISTORTION AND
DIMENSIONAL CHANGE OF ALGINATE
If an alginate impression is stored in water or in a very wet paper towel, the
alginate will absorb additional water and expand. This condition is called
imbibition.
If an alginate impression remains in the open air, moisture will evaporate from the
material, causing it to shrink and distort. This condition is called syneresis.

27. DIMENSIONAL STABILITY
Alginate has a tendency, after it sets to lose (syneresis) or absorb
(imbibition) water, depending on the atomosheric conditions
surrounding it.If conditions are dry it loses water & shrinks; if immersed
in water, it imbibes moisture or swells.

28. DISINFECTION OF IMPRESSIONS
1% sodium hypochlorite or 2% glutaraldehyde
To be immersed for 10 min, rinsed and poured immediately

29.  1) Alginate in the form of sol - containing the water but no source of
calcium ions - a reactor of Plaster of Paris
Two component system (paste form)
- alginate sol
- calcium reactor
 2) Alginates modified by the incorporation of silicone polymers (paste
form)
- fine detail reproduction
- tear resistance
- poor dimensions stability
Modified alginates

30. ADVANTAGES
Inexpensive impression material.
Easy to manipulate.
Pleasant taste and odor.
Sets quickly.
Very good biological tolerance
Requires little armamentarium
Good compatability with cast and die
materials