Hydrocolloids Impression Dental Material

Hydrocolloids In Dentistry

Factors Controlling Setting Time of ZOE Impression Paste

Factors affecting the setting time of zinc oxide eugenol impression paste are as follows:

Composition of Agar – Agar

The reversible hydrocolloid impression material is agar.

Composition :

Hydrocolloids Impression Dental Material

A reversible hydrocolloid is also known as agar. It is an elastic impression material. 

Classifiation of  reversible hydrocolloid

Based on the viscosity (ISO 21563:2013)

• Type 1: Heavy bodied (for use as tray material)
• Type 2: Medium-bodied (for use as tray or syringe material)
• Type 3: Light bodied (for syringe use only)
• Type 4: Light-bodied for agar-alginate combination technique.

The function of Ingredients:

• Agar: Basic constituent for tray material.
• Borate: Provide strength to gel.
• Potassium sulphate: Counteract retarding effect of borate and ensure proper setting of cast and die.
• Hard wax: Act as filer, and provides strength, viscosity, and rigidity.
• Thixotrophic material: Acts as a plasticizer.
• Alkyl Benzoate: Preservative
• Coloring and flavoring: For patient comfort and acceptance.
• Water: As dispersion medium.

Uses of  reversible hydrocolloid:

• • For cast duplication
  • For full mouth impressions without deep undercut.
  • For FPD impressions.
  • As tissue conditioner.

Advantages of  reversible hydrocolloid

• Preparation of accurate dies is possible.
• Good elastic properties reproduce most undercut areas.
• Good recovery from distortion.
• Saliva in the mouth creates no problem.
• Well-tolerated by the patient.
• It is economical.
• Can be reused.

Disadvantages of  reversible hydrocolloid

• The flow of material is not good
• Electroplating cannot be done
• During insertion, patient experienced thermal discomfort
• Only a single model is poured
• Special and expensive instruments are required
• The impression should be poured immediately.

Reversible And Irreversible Hydrocolloid Impression Materials

An impression is defined as “an imprint or negative likeness of the teeth and/or edentulous areas where the teeth have been removed, made in a plastic material which becomes relatively hard or set while in contact with these tissues. Impressions may be made of full complements of teeth, of areas where some teeth have been removed, or in mouth from which all teeth have been removed.

Difference between Reversible and Irreversible Hydrocolloid:

Disinfectants And Irreversible Hydrocolloid Impressions

As the impression is removed from the mouth, it is disinfected before pouring the cast to prevent cross-contamination. As per the protocol of Centers for disease control and Prevention, hydrocolloid impressions should be immersed in household bleach, iodophors, or synthetic phenols.

As impression is taken out from the mouth, it is thoroughly rinsed and then disinfectant is sprayed over the impression. Now the impression is wrapped in a disinfectant-soaked towel and is sealed for 10 minutes. As disinfection get a complete impression is thoroughly rinsed with water to remove remnants of disinfectant which can affect the surface of the cast when gypsum is poured.

Question 2. Write a short note on the composition of alginate.
Answer:

Composition of Alginate: