Biomaterials Flashcards
What is alginate?
It is irreversible hydrocolloid (impression material).
What are the chief ingredients in soluble alginates?
Sodium alginate, Potassium alginate, and Triethanolamine alginate
What is imbibition?
Absorbing more water and swelling when immersed in water. e.g. 1 hr in water
What is Syneresis?
Contracting/exudating liquid on material’s surface. e.g. 1 hr left to dry
What do viscoelastic and thixotropic mean?
Viscoelastic: both viscous and elastic characteristics when undergoing deformation.
Thixotropic: to become liquefied (less viscous) when shaken, stirred, patted, or vibrated.
Impression materials must be 1) Viscous (isn’t runny and will stay inside the tray) and 2) Elastic (Doesn’t distort or tear during the removal from the mouth. Tends to stay or return to its original shape with applied stress).
Are hydrocolloids hydrophobic or hydrophilic?
Hydrophilic??
How can the setting time of a hydrocolloid be sped up or slowed down?
Inc temp of water, dec setting time. e.g. 10 deg C inc, 1 min dec in setting time
Dec temp of water, inc setting time.
What is hydrocolloid?
Substance that forms gel in the presence of water.
What general procedures are hydrocolloids used for?
Impression material:
reproduce form and relationship of oral tissues
negative recording of dental structure
Cast obtained or diagnosis and construction of prostheses
What is gypsum?
Calcium sulfate. Naturally occurs as calcium sulfate dihydrate and thermally processed (water removed) to calcium sulfate hemihydrate (packaged for use).
In lab, mixed with water to reform dihydrate form (reversible reaction).
What is gypsum used for in dentistry?
Plaster models, stone working models, and die stone for removable dies.
How is dehydrate converted to hemihydrate?
Heat removes water from gypsum and converts dihydrate to hemihydrate.
[Gypsum Powder]+[H2O] [Gypsum] +[Heat]
What is slurry water?
It’s the water with the stone particles that’s left after trimming your cast. The stone particles suspended in the water act as initiation spots for crystal formation of the gypsum. If you used all slurry water, it would set extremely quickly and not give you much working time. crystals are forming in the slurry water
How much expansion does each basic type of dental gypsum display in normal use? (0.05 – 0.20%)
Plaster: 0.020%
Stone: 0.10%
Die Stone: 0.05%
What are the differences between plaster (simplest type of dental gypsum) and die stone (highest
quality type of dental gypsum) in regards to water to powder mixing ratio, expansion, porosity, crushing strength, and setting time?
Plaster W/P ratio: 0.5 Expansion: 0.20% Porosity: 35% Crushing Strength: 1,600 psi Setting Time: 11 min
Die Stone W/P ratio: 0.24 Expansion: 0.05% Porosity: 10% Crushing Strength: 5,500 psi Setting Time: 6 min
