This document discusses elastic impression materials called alginate. Alginate is derived from seaweed and sets via a chemical reaction between sodium alginate and calcium sulfate. It has a fast setting type and a normal setting type. Alginate is mixed by sprinkling powder into water and stirring vigorously. Its properties include flexibility, elasticity, and the ability to capture surface details. Alginate has advantages like ease of use and patient comfort, but disadvantages like poor dimensional stability and strength.

1. Elastic impression materials
irreversible hydrocolloids
alginate

2. CONTENTS
∞ Introduction
∞ Types
∞ Available as
∞ Application
∞ Composition
∞ Setting reaction
∞ Properties
∞ Manipulation
∞ Mixing time
∞ Working time
∞ Gelation time
∞ Impression disinfectant
∞ Advantages & Disadvantages

3. Introduction :
 Alginate is derived from alginic acid
which is a mucous extract by species of
brown seaweed.
 Alginic acid is a naturally occurring
hydrophilic colloidal polysaccharide .
Classification :
 Type I - Fast setting
 Type II - Normal setting

4. AVAILABLE AS :
 Dust free alginates.
 Chromatic alginates – alginates which
changes color on setting.
APPLICATIONS :
a. To make impression with undercuts & excess of saliva.
b. Preliminary impression for complete dentures.
c. To make study models and working casts.
d. For duplicating models.

5. COMPOSITION :
Sodium or potassium or triethanol alginate - 15
Calcium sulfate ( reactor ) - 16
Zinc oxide - 4
Potassium titanium fluoride - 3 %
Diatomceous earth - 60
Sodium phosphate ( retarder ) - 2
Coloring and flavoring agents - Trac

6. SETTING REACTION
By chemical reaction :
Alginate + Water Sol Gel
REACTION 1 :
REACTION 2 :
Sodium + Calcium + Water Calcium
Alginate Sulfate Alginate
(Powder) (Gel) +
Sodium sulfate
4224344 Na3)(CaCaSO3 SOPOPO 3Na2

7. Contd….
As this reaction occurs rapidly, a retarder is
add to prolong the working time.
The reactor Calcium sulfate reacts with the
retarder Sodium phosphate and then with
Sodium Alginate.
GEL STRUCTURE :
The gel structure consists of Brush heap
structure enclosing unreacted sodium alginate,
Water, fillers & by products.

8. PROPERTIES of ALGINATE :
1. Taste and Odor - Pleasant.
2. Flexibility - about 14% at 12.2 N stress.
3. Elasticity and Elastic recovery - Highly elastic & has 98.2%
elastic recovery.
4. Reproduction of Surface details - Low as compared to Agar.
5. Strength
 Compressive strength – Ranges from 0.5 to 0.9 MPa.
 Tear strength – Ranges from 0.4 to 0.7 kN/m.
6. Syneresis and Imbibition – distortion may occur.
7. Dimensional stability – Low dimensional stability.
8. Biological properties – No chemical or allergic reaction.
9. Adhesion - Tray adhesives are used or perforated trays.

9. MANIPULATION :
Equipment required :
# Flexible plastic bowl.
# Metal spatula.
≥ W/P ratio – 1 : 2 - Powder is sprinkled into the water.
≥ Stirring motion - to wet the powder with water.
≥ Then a rapid spatulation by Swiping or stropping
against wall is done.
≥ Vigorous 8 motion is also used.
≥ Mechanical device can be used.

10. Mixing time :
For fast setting Alginate – 45 secs
For normal setting Alginate – 60 secs
Working time :
Type I – 1¼ mins.
Type II – 2 mins.
Gelation time :
Type I – 1.5 to 2 mins.
Type II – 3 to 4.5 mins.

11. Tray selection :
 Mechanical tray.
Rim lock
Perforated tray
 Applying adhesive.
 Both.
Time of Removal :
The impression should be left in mouth for 2 to 3 mins
after initial set.
Impression Disinfectant :
Disinfectants include Phenol, Iodophor, Bleach or
glutaraldehyde.

12. Advantages :
∆ Easy to mix & manipulate.
∆ Flexibility of set material.
∆ Comfortable & hygiene.
∆ Good details even in presence of saliva.
∆ Low cost.
Disadvantages :
∆ Cannot be electroplated.
∆ Poor dimensional stability.
∆ Distortion may occur.
∆ Poor tear strength.
∆ Can’t be used for RPD, crowns & FPDs.

13. “ We just make impressions so
that others will get impressed on
YOU “