What is reversible hydrocolloids?
Among the oldest dental impression materials still in use, reversible hydrocolloid impression materials are formulated with agar and effectively solidify from their liquid state to a solid gel state in the mouth to capture a highly accurate impression.
Why agar agar is reversible?
Agar is a reversible hydrocolloid because it can pass repeatedly between highly viscous gel and low viscosity sol simply through heating and cooling. However, alginate once converted to the gel form cannot be converted back into the sol, and is therefore said to be irreversible hydrocolloid material (4).
What is a common irreversible hydrocolloid that we use?
2 Alginate. Alginate is an irreversible hydrocolloid largely used in dentistry [15].
Which irreversible material is hydrocolloid?
Alginate
Alginate is an elastic, irreversible hydrocolloid impression material. Irreversible hydrocolloid impressions form an inseparable part of indirect restorations. Alginate is one of the most frequently used dental materials; and alginate impression is a simple, cost-effective, and indispensable part of dental practice.
What are the reversible impression materials?
Agar hydrocolloid (reversible), alginate hydrocolloid (irreversible), and a variety of elastomeric impression materials (polyethers and polyvinyl siloxanes) are the most commonly used impression materials. Sears introduced reversible hydrocolloid in 1937.
How do you manipulate agar?
Manipulation of Agar Heat in water at 100 ° C (212 °F) for 8 – 10 minutes. Temper in 46 ° C (115 °F) water for 2 minutes before taking the impression to increase the viscosity and pressure applied to the syringe material, also making comfortable for the patient.
What are the two physical changes of a hydrocolloid impression material?
V. Two impression materials are considered to be hydrocolloid materials because their major component is water. Both materials change from a viscous liquid state, called the sol, to a semisolid, rubbery state, called the gel. The sol state is a solution of one material dissolved in another.
Which alginate impression is taken first?
mandibular arch
The mandibular arch is taken first. Many patients tend to gag on the maxillary impression because they experience the sensation that the alginate is flowing down their throats. Ifthe mixture is 100 fluid or the tray overfilled gagging may actually occur.