Impression Materials, Gypsum, Mouthguards, and Tray Materials Flashcards
What are 2 water based impression materials?
Alginates and agar-agar
What feature of water based impression materials allows them to wet tooth structure and gypsum?
They are hydrophilic
What is the actual name for alginate impression material?
Irreversible hydrocolloid impression material
Alginate impression material is used to make dental impressions for what?
Removable partial dentures, preliminary impressions for complete dentures, orthodontic study models and study models
What are alginate impressions not used for in the mouth?
Crown and bridge impressions (lack of accuracy)
Alginic acid is soluble in water and forms what when it is mixed with water?
Sol
What is sol?
Resembles a solution, but is made up of colloidal particles dispersed in a liquid
What are the reactants for irreversible hydrocolloid impression material?
Sodium or potassium alginate (12-15%), calcium sulfate dihydrate (8-12%)
What is a retarder for irreversible hydrocolloid impression material?
Sodium phosphate (2%)
What is the reinforcing filler for irreversible hydrocolloid impression material?
Diatomaceous earth (70%)
What are the two main chemical reactions of irreversible hydrocolloid impression material?
1st: provides adequate working time (retarder)
2nd: after the sodium phosphate has reacted, remaining calcium sulfate reacts with sodium alginate to form an insoluble calcium alginate, which forms a gel with the water
What is syneresis?
Loss of water to the surroundings
What is imbibition?
Pick up water from the surroundings
What is dimensional stability of alginate impressions?
Because it is a gel, it undergoes shrinkage or expansion upon loss or gain of water
What is the main advantage of hydrophobic impression materials?
They provide better stability
What is the main disadvantage of hydrophobic impression materials?
They do not wet tooth structure or gypsum well
What is type I gypsum?
Impression plaster or mounting plaster
What is type II gypsum?
Laboratory plaster or model plaster
What is type III gypsum?
Laboratory stone, dental stone, or quick stone
What is type IV gypsum?
Die stone
Laboratory stone and die stone are what kind of gypsum plaster?
High strength plaster
What is gypsum?
The dihydrate form of calcium sulfate CaSO4-2H2O, that is found in a compact mass in nature
What is calcination?
This is the process of driving off part of the water of calcium dihydrate to form calcium sulfate hemihydrate
If all of the different gypsum materials are chemically identical why do they have different properties?
They do because of changes in the way calcination was performed
Gypsum plaster is composed of what?
Beta form of calcium sulfate hemihydrate crystals
Gypsum stone is composed of what?
Alpha form of calcium sulfate hemihydrate crystals
What is type V gypsum?
High-strength, high-expansion dental stone
Why is dental plaster weaker than dental stone?
- porosity of the particles, requiring more water for a plaster mix
- irregular shapes of particles prevent them from fitting together tightly
About how much stronger is stone than plaster?
2.5X
What is a way to improve gypsum resistance to abrasion?
Add gypsum hardeners like colloidal silica or synthetic resin
What is the product triad used for?
Custom tray material that is visibly light cured
