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Agar – Agar in Dentistry Part One

In this post we will learn about Hydrocolloids, Sol-Gel Transformation, Uses of Agar – Agar in Dentistry, Composition, Commercial Brands, Supplied As, Preparation and Types of Agar


Agar is a hydrocolloid, which basically consists of gelatin particles suspended in water and water is the dispersion medium.

Solution – uniformly dispersed solute and solvent eg salt in water – exist as a single phase

Suspension – visible insoluble particles in solute e.g. dust in water.

Emulsion – visible insoluble liquid in liquid e.g. oil in water

Sol-Gel Transformation

Hydrocolloids can exists in 2 different forms – SOL and GEL.

Sol – has the appearance & characteristics of a viscous liquid.

Gel – a jelly like elastic semi-solid – produced from sol by a process called Gelation – by formation of fibrils or chains or micelles of the dispersed phase which become interlocked – brush heap structure.

Gelation – The conversion of sol to gel.

The conversion can occur in two ways.

  1. By temperature changes
  2. By chemical changes

By temperature changes

Gelation is brought about by a reversible process. Eg Agar. The fibrils are held together by secondary molecular forces. So that they break at slightly elevated temperature and become re-established as the hydrocolloid cools to room temperature.

The temperature at which these changes occurs is the Gelation temperature.

The Gel is converted to sol when it is heater to a higher temperature which is known as Liquifaction temperature.

The temperature lag is known as hysterisis.

By Chemical Changes

Conversion of sol to gel is brought about by chemical reaction, the fibrils thus formed are held together by primary bond and are unaffected by temperature. Hence they are called irreversible hydrocolloid. Eg. Alginate

Gel can be converted to sold by heating, cooling a sol caused it to become a gel.

Agar (hot)[Sol] ← heat to 100 C / cool to 43 → Agar (cold)[Gel]


1925 – Alphous Poller – Negacol.

Modified & introduced in dental profession as Dentalcol in 1928

Agar is an organic hydrophilic colloid (polysaccharide) extracted from certain types of seaweed (kelp plant).

It is sulphuric ester of a linear polymer of galactose.

Uses of Agar

Widely used at present for cast duplication

For full mouth impression without deep undercuts

As a tissue conditoner


Water – 84% – dispersion medium

Agar phase – 13-17% – gelling agent, dispersed

Borates retards – 0.2-0.5% – improves strength and setting of plaster or stone

Potassium sulphate – 1-2% – it counters the retarding effect of borates and provides good surfaces on gypsum models/dies

Alkyl benzoates – 0.1% – preservatives

Fillers like diatomaceous earth, clay, silica, wax, rubber and inert powder for control of strength, viscosity and rigidity.

Coloring and flavoring agents (traces)

Commercial Brands

Acculoid / Cartrilloid (Van R)

Sugident (Lactona)

Cohere / SuperBody / SuperSyringe (Ghingi-pak)

Indentic (Cadco)

Supplied As

Solid gel in collapsible tubes (for impression)

No. of cylinders in glass jar (Syringe matreial)

In bulk containers (for duplication)

Preparation of Agar

Cleanliness, maintenance and care of the conditioner and strict adherence to time and temperature are mandatory.

The water pots should be clean and free of any foreign material, eg, wax, calcium deposits and “scum” from the boiling water.

Keep Conditioners clean

Failure to keep pots clean will result in temperature variations

Clean cool distilled water is placed in the three pots

The conditioner is turned on.

Thirty minutes should be allowed for the water to reach the desired temperature before proceeding.

The boiling pot temperature should be maintained.

The water is brought to a boil, and boiling is continued for 10 minutes.

Tooth preparation – should be caries free, without undercuts (if present – should be filled with cements resins or composites)

The cervical margins should be distinct

Trays should be selected and tried in the patients mouth before the impression material is placed in them.

There should be 3 mm of impression material around the teeth occlusally and laterally.

Types of Agar

Heavy bodied – in poly tubes or flex skins

Medium bodied

Regular bodied

Light bodied – in syringes

In next post we will learn about Manipulation of Agar, Conditioning Unit and Properties of Agar https://dentalpockets.com/blog/manipulation-agar-agar-in-dentistry-part-2/

To buy premium agar visit https://dental.keystoneindustries.com/product/supergel-alginate-impression-material/

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