Reversible and Irreversible Hydrocolloid
The setting rate of an irreversible hydrocolloid may be slowed safely and effectively by:
a. using cold water
b. using hot water
c. using soda
a. using cold water
An example of irreversible hydrocolloid:
Alginate
An example of a rigid/inelastic impression material would be
-plaster, wax
-impression compound
-zinc oxide/eugenol
A replica of the teeth and surrounding teeth structures that is used for diagnosis and treatment planning called:
Diagnostic casts and/or Die
When converting from a sol to a gel, a reversible hydrocolloid undergoes what kind of reaction?
Physical change/Thermoplastic
A busy dental hygienist took alginate impressions of a patient and put them in the lab. Several hours later, the models were poured. Which process was MOST likely to have occurred in the dental impressions?
a. gelation
b. imbibition
c. syneresis
Answer: Syneresis
Name any Advantages of alginate impression material:
Hydrophillic – compatible with the oral environment (easier to take impression)
Inexpensive
Easy to use
Does not require special equipment
One impression was left exposed to air and another was stored in excess water. The uptake of water associated with hydrocolloid impressions is called:
a. Calcination
b. Syneresis
c. Imbibition
d. Hydration
C. Imbibition
Disadvantage of alginate impression material:
Water evaporates – meaning the impression shrinks.
-Syneresis - as the impression sets it contracts slightly and water is squeezed out
-Imbibition - the ability to absorb liquid
-If mixed to thin or if impression does not have enough thickness (2-4mm) it can tear of deform
-Needs to be poured immediately.
When evaluating a maxillary impression, all of the following structures should be captured except:
a. Frenula
b. Hard palate
c. Uvula
d. Maxillary tuberosity
c. Uvula