ALGINATE HYDROCOLLOID

BY: ISHU SINGLA

BDS II PROF.

The word Alginate comes from alginic acid i.e. anhydro beta d-mannuronic acid. Like agar, it is a natural Hydrophillic Colloidal Polysaccheride extracted from brown seaweed.

The present alginate hydrocolloid was developed as a substitute for agar when it becomes uncommon due to World War II.

Currently alginate is more popular than agar for dental impression, because it is simple to use.

WORLD WAR II

Alginate is supplied as:- bulk packing Preweighed packets for individual impression

A plastic scoop is supplied for taking the bulk powder.

A plastic cylinder is also supplied for measuring the water.

In general 16g of

powder ( 2 scoops ) is mixed with

38 ml of water.

COMPOSITION OF ALGINATE HYDROCOLLOID

Ingredients % by wt. FunctionsSoluble alginates ex.- Sodium or Potassium or Triethanolamine alginate

15% Dissolve in water and form a viscous sol being soluble in nature

Calcium sulphate ( Reactor )

16% Reacts with soluble alginates and form insoluble calcium alginate

Zinc Oxide 4% Act as a filler particle

Potassium Titanium Fluoride

3% Act as accelerator for the setting of a stone to be poured in impression to ensure hard, dense surface of a cast.

Diatomaceous Earth 60% Also act as a filler , provide strength and stiffness

Sodium Phosphate ( Retarder )

2% Reacts with calcium sulphate there by retard the setting of impression

Coloring and flavouring agent

traces For the comfort of patient

SETTING REACTION / GELATION PROCESS

When a alginate powder is mixed with water, a sol is formed which later sets to gel by a chemical reaction.

Insoluble calcium alginate is produced when soluble sodium alginate reacts with calcium sulphate.

However, this reaction is too fast, there is not enough working time, so a reaction is delayed by addition of a retarder i.e. sodium phosphate.

Calcium sulphate prefers to react with retarder first.

It reacts with sodium or potassium alginates only when the supply of retarder is over.

This will delays the reaction and increase the working time for us.

Thanks Sodium Phosphate

Retarder Reactor

ReactorSoluble Alginate Insoluble Alginate

CLASSIFICATION Type I – Fast Setting Type II – Normal Setting

MIXING TIME For fast set alginate = 45 sec. For normal set alginate = 60 sec.

Over mixing results in – - Reduction in final strength - Reduction in working time

Under mixing results in – - inadequate wetting, lack of homogeneity - poor recording of detail

WORKING TIME For fast set alginate – 1 min. 25 sec. For normal set alginate – 2 min.

GELATION TIME For fast setting alginate – 1.5 to 2.0 min. For normal setting alginate – 3 to 4.5 min.

Ideal gelation time is 3-4 min.

The dentist can control the setting time by altering the temperature of water for mixing alginate material.

- colder the water longer is the gelation time - warmer the water shorter is the gelation

time

Control of setting time by changing w/p ratio is not recommended in case of alginate.

PROPERTIES OF ALGINATE HYDROCOLLOID Taste and Odour – Alginate has a pleasant taste and smell for the comfort of a

patient. Flavors include strawberry, orange, mint, vanilla.

Strength – Alginate has a poor tear strength. Factors affecting strength are:- - w/p ratio too much or too little water reduces gel

strength - Mixing time over and under mixing both will reduces

strength - Time of removal of impression strength increases if the

time of removal is delayed for few minutes after setting

Syneresis and Imbibition – Like agar, it also exhibit the properties of synresis and

imbibition.

Dimensional stability – Set alginates have poor dimensional stability due to

evaporation, syneresis and imbibition. Therefore like in case of Agar, cast should be poured immediately.

Adhesion – Alginate does not adhere well to the tray. Good adhesion is

important for accuracy of impression. So, retention to the tray is achieved by mechanical locking features in the tray or by applying an adhesive.

1. It is easy to mix and manipulate.

2. Minimum requirement of equipments.

3. Low cost.

4. Comfortable to patient

5. Accuracy is there if properly handled.

6. Gives a good surface detail even in presence of saliva.

1. It cannot be corrected.

2. Poor dimensional stability – it cannot be store for a long time.

3. Poor tear strength.

4. It is not recommended where a high degree of accuracy is required, e.g., RPDs and FPDs etc.

ADVANTAGES DISADVANTAGES

USES OF ALGINATE HYDROCOLLOID It is used for impression making - when there are undercuts - in mouth with excessive flow of saliva - for partial dentures with clasp

For making a preliminary impression for complete dentures.

For duplicating models.

LAMINATE TECHNIQUE It is the combined agar-alginate technique.

In this technique - Tray material chilled alginate - syringe material hot agar

Advantages – 1. water cool tray is not required more convenient

2. syringe agar records the tissue more accurately 3. it sets faster than regular agar technique

Disadvantages – 1. Agar alginate bond failure.

METHOD OF LAMINATE TECHNIQUE After injecting a syringe agar on the area to be recorded, an

impression tray containing a mix of chilled alginate is positioned over it that will bond with the agar.

The alginate get solidify by means of chemical reaction whereas agar solidify through contact with cool alginate rather than the water circulating through the tray.

Since the agar, not the alginate is in contact with prepared teeth, maximum detail is reproduced.

Because only the syringe material needs to be heated, equipment cost is lowered and less preparation time is required.

MODIFIED ALGINATES

Traditional alginate material is used as a two component system of powder and water in which no reaction occur until powder is added to water to initiate the reaction.

But now we can purchase alginate in a sol form, containing the water but has no source of calcium ions. MODIFIED ALGINATE

Then a reactor of plaster of paris can then be added to a sol

THANK YOU