L3 hydrocolloids Flashcards
NEGATIVE imprint of the tissues in the mouth, from
which a POSITIVE replica/model can be formed
dental impressions
[rigid/flexible]
Zinc oxide eugenol
Impression plaster (Type 1 gypsum)
Dental compound
rigid
[rigid/flexible]
Agar hydrocolloid
Alginate hydrocolloid
Polysulfide rubber
Silicone rubber
Polyether rubber
flexible
[reversible/irreversible]
Dental compound
Agar hydrocolloid
→ no chemical change
→ dependent on temperature
→ can be used again
reversible
[reversible/irreversible]
Alginate hydrocolloid
Impression plaster
Zinc oxide eugenol
Polysulfide rubber
Silicone rubber
Polyether rubber
→ chemical reaction occurs
→ cannot be reverted back to its
pre-set state
irreversible
- Flexible, REVERSIBLE hydrocolloid impression material
- ADA Specification 11: Agar Impression Materials
AGAR HYDROCOLLOID
- Flexible, IRREVERSIBLE hydrocolloid impression material
- ADA Specification 18: Alginate Impression Materials
ALGINATE HYDROCOLLOID
[solution/suspension/colloid]
Has a dissolving agent (solvent) and a dissolved
substance (solute)
solution
solution/suspension/colloid]
Components can be mixed temporarily but will
eventually settle
suspension
- light scatters, unlike in solutions where light passes through the mixture
- Determines whether a mixture is a true solution or a colloid
tyndall effect (colloids)
Micelles on the dispersed phase interlock and produce
a jelly-like consistency
gelation
gel strength characteristics: (3)
- Brush-heap density or concentration
- Temperature: the lower the temperature, the stronger
the gel - Addition of fillers and chemicals
DIMENSIONAL EFFECTS
- Absorption of water as the gel swells when placed in water
Imbibition
DIMENSIONAL EFFECTS
- Fluid exudation or the expression of fluid to the surface of the gel structure
Syneresis
DIMENSIONAL EFFECTS
- Conversion of water from liquid to vapor
evaporation
DIMENSIONAL EFFECTS
- No adequate storage for any hydrocolloid impression material
poor dimensional stability
- Flexible, reversible hydrocolloids
- Gelatin-like substance like the one used in baking
- Not widely used anymore bc hard to manipulate
- Derived from a seaweed
- no chem rxn, just temp change
REVERSIBLE HYDROCOLLOIDS: AGAR
things needed when taking an agar impression:
- A hydroprocessor (summarized in the table below)
- 3 sextant trays used; 2 for the sides and 1 for the front part
alginate type i fast set
- mixing time:
- working time:
- setting time:
- mixing time: 30-45 sec
- working time: >75 sec
- setting time: 1-2 mins
alginate type 2 normal set:
- mixing time:
- working time:
- setting time:
- mixing time: 45-60sec
- working time: >120 sec
- setting time: 2-4.5mins
def of terms:
The whole process of setting for hydrocolloids
gelation
def of terms:
Art of the mix; when you start mixing your alginate up until
it sets
gelation time
def of terms:
- Length of time from the start of mixing until you reach a
semi-hard stage of alginate wherein you can manipulate
the product into the patient’s mouth
working time
