Outcome 1 - Impression Material Flashcards
What is Irreversible Hydrocolloid?
Impression material that cannot return to the sol state after it becomes a gel. Alginate is the irreversible hydrocolloid most widely used for preliminary impressions.
What is Sol?
A liquid colloid is referred to as sol
What is a Gel?
A colloid in its semi-hard or rubbery consisitency is referred to as gel
What is Synerisis?
The property of a material to lose water and shrink
What is Imbibition?
The property of a material to gain water and expand
What is a Hydrocolloid?
Hydro meaning water & colloid meaning a gelatinous substance
A large portion of hyrdocolloid material is water, therefore, making them very susceptible to dimensional changes
What is a colloid?
A colloid is a mixture of microscopic particles that are suspended in another medium
Irreversible hydrocolloid vs. Reversible Hydrocolloid
Irreversible Hydrocolloid or alginate is supplied as a poweder which is mixed to form a viscous sol. Once a gel has formed, it CANNOT be changed back to the sol consistency becuse a chemical reaction cannot be reversed.
A Reversible hydrocolloid or agar is supplied as a gel that is heated to change it to a sol - as it cools it gels again. It CAN change back and forth.
The treatement plan for an indirect restoration is determined using the following diagnostic tools:
-accurate patient medical and dental history
-radiographs
-intraoral examination
-diagnostic study models (mounted to an articulator)
-occlusal records such as “Face Bow” records
Preliminary impression materials are used in prepartion of:
-pre treatment and post treatment records
-study and diagnostic casts
-in the fabrication of mouth guards
-whitening trays
-provisional coverage (temp restorations)
-orthodontic appliances
-custom impression trays
What is the irreversible hydrocolloid (alginate) obtained from?
Sea Kelp
For irreversible hydrocolloid, the means of transforming the sol to gel is..
to add calcium sulphate; however, since the reaction must take place in the mouth, it must be delayed until the impression material gets through all stages of manipulation and is placed in the mouth. Therefore, a third soluble salt, trisodium phosphate is added to act as a retarder. The calcium phosphate will first react with the trisodium phosphate, before reacting with the soluble alginate.
Different types of irreversible hydrocolloid / alginate available?
Normal set or fast set - the mixing, working and setting times of the two types are very different
What is a problem with irreversible hydrocolloid / alginate?
A loss of accuracy with increased time of storage
How should alginate materials be stored?
At cool temperatures and never in an area in which the temperature may be high - most alginate materials deteriorate rapidly at elevated temperatures and in the presence of moisture (the material will usually become thin during mixing resulting in reduced strength and greater deformation when removed from the mouth)
