PRD 132: Alginate/Gypsum

Gypsum

A naturally occurring material consisting of calcium sulfate and water molecules

Type 1 impression plaster

Mounting stone

Type 2 impression plaster

Model plaster

Type 3 dental stone

Study casts, micro stone, yellow color we use

Type 4

high strength low expansion Die stone

Type 5

high strength high expansion dental stone

Calcination

the process of driving a specific amount of water out of gypsum to create specific plasters, stones, or investment die stones

Increased water

Less strength, more porosity, less expansion, increased setting time

Less water

More strength, less porosity, more expansion, decreased setting time

Increasing spatulation

Shortens the setting time

Exothermic

Setting reaction of gypsum is

Room temperature increasing

Will increase the rate of reaction and shorten set time

Closed container/imbibition

All gypsum products should be in a ______ to avoid

Less Setting time

Hot water, less water, increased spatulation time, use of slurry water

More setting time

Cold water, more water, decreased spatulation time

Vibrator

Must be used w/ gypsum to overcome surface tension and bubbles (doesn't work w/ alginate sets too fast)

Vaccuum mixer

Mixes both gypsum and alginate

Alginate

Irreversible hydrocolloid material used for taking preliminary impressions

Hydrocolloid

A mixture within water

Colloid

Particles of one substance that are evenly dispersed throughout another substance

Mucous extract

Alginate has ______ from brown seaweed

Active ingredient

Potassium alginate is the active ingredient (water soluble salt) derived from seaweed

15%

Potassium alginate amount

Calcium sulfate

Reacts w/ potassium alginate to form the gel (insoluble calcium alginate)

16%

Calcium sulfate amount

Tri-Sodium Phosphate

Slows the reaction time for mixing (reacts preferentially w/ calcium sulfate as a retarder)

Diatomaceous earth

Filler for built of material (primary ingredient) in alginate

60%

Primary ingredient diatomaceous earth amount

Potassium titanium fluoride

Added for surface strength in alginate

3%

Amount of potassium titanium fluoride

Sol/Gel Phases

Phases of alginate setting

Replicate teeth and soft tissue (vestibule and palate) although INACCURATE

What is the purpose of diagnostic impression

Pleasant odor, biocompatible, cheap, elastic, adequate strength

Advantages of alginate

Cold water

Maximizes working time for alginate

Do not move

After seating the tray

30 seconds

Mix alginate/water

1 minute

Working time

1:30

Setting time

Imbibition

Absorption of water, causing an object to swell

Syneresis

Loss of water, causing something to shrink

Undercut

Can make impression harder to remove

Treatment planning, dental legal records, provisional restoration

Why do we make mounted study models

Treatment planning

Patient doesn't have to be present, identify teeth position/occlusion, treatment presentation to patient

Provisional restorations

You use study models to set the putty matrix fabrication for crowns

Once

Alginate impressions can only be poured

Alginate

Pink in color

Micro stone

Yellow in color

Mounting stone

Blue in color (not used in this impression lab)

Maxillary

Four scoops of alginate

mandibular

Three scoops of alginate

Alginate to water ratio

1:1

Room temp water

Recommended so it doesn't take too long or too quick to set

Fluffed

Alginate powder should be ____ not dense and level it off

Maxillary

Load the tray in one scoop

Mandibular

Load the tray in two-three scoop

Occlusal surfaces

Before placing the tray, smear alginate on ____ to prevent bubbles

12 o clock

Maxillary you want to stand

9 if right 3 if left

Mandibular you want to stand

2 minutes, fingernail

Gelatin process takes ____, you can test w/ ur ____ to make a clean cut

40 ml water

For the micro stone, you add first

60 degrees

Hold impression at ____ on vibration platform and flow the gypsum slowly into the tray

10-15 minutes

The stone sets in